Background The Bundelkhand Craton is significant for preserving the multiphase granitoids magmatism from Paleoarchean to Neoarchean periods.It consists of a variety of granite rocks,including TTGs,sanukitoids,and high...Background The Bundelkhand Craton is significant for preserving the multiphase granitoids magmatism from Paleoarchean to Neoarchean periods.It consists of a variety of granite rocks,including TTGs,sanukitoids,and high-K granitoids.This study presents geochemical characteristics of high-silica(68.97 wt.%–73.99 wt.%),low-silica(58.73wt.%–69.94 wt.%),and high K_(2)O(2.77 wt.%–6.16 wt.%)contents of granitoids.Objective The data on Bundelkhand Craton’s granitic magmatism and geodynamics is not sufficiently robust.Geochemical data from this study will be used to further understand the origin,source,and petrogenesis of granitoid rocks and their implications for the evolution of geodynamics.Methodology Twenty-one samples were collected and analyzed for major,trace,and REE elements.Major elements were measured using X-ray fluorescence spectrometry(XRF),and trace and REE elements were analyzed by ICP-MS.Standard procedures from the Geological Survey of India were followed.Results The geochemical analysis presents high-silica(68.97-73.99 wt.%),low-silica(58.73-69.94 wt.%),and high K_(2)O(2.77-6.16 wt.%)contents in granitoids,classified as granite-granodiorite.The rocks are calcic to calcalkalic,magnesian,and range from peraluminous to metaluminous composition.REE patterns showed strong LREE enrichment relative to HREEs,with prominent negative Eu anomalies corresponding to earlier plagioclase fractionation.Multi-element patterns revealed negative anomalies in Nb,Sr,P,and Ti and positive anomalies in Pb.Conclusion The geochemical signatures attributed to the post-collisional magma generation and continental crustal contamination.The studied rocks show A-type and A2-type lineage,suggesting they originated from the melting of continental crust during transitional/post-collisional tectonic activity.The formation of hybrid granitoids in the Bundelkhand Craton is connected to the fractionation of hybrid magmas in shallow-seated magma chambers during these tectonic processes.展开更多
The lack of a comprehensive whole-rock geochemical and mineralogical dataset for the Archean granitoids of the Aravalli-Banded Gneissic Complex(BGC),northwest India,results in significant challenges for their correct ...The lack of a comprehensive whole-rock geochemical and mineralogical dataset for the Archean granitoids of the Aravalli-Banded Gneissic Complex(BGC),northwest India,results in significant challenges for their correct characterization and assessment of their antiquity.The new field,mineralogical and geochemical data classify the Jaisamand granitoids into sanukitoids,TTGs,and transitional TTGs,which are most likely coeval in nature.The obtained results,in conjuncture with the previously published geochemical and geochronological results of the Aravalli-BGC granitoids,unveil the Neoarchean affinity of the Jaisamand pluton.The TTGs were generated by the melting of a subducting slab(metabasite)at shallow(high-HREE-Y TTGs)to moderate depths(medium-HREE-Y TTGs)above the garnet-in line but still within the plagioclase stability field,with garnet-poor residue.The ascending TTG melts were transformed into sanukitoids through differential interaction with the overlying mantle wedge peridotite.The TTG melts,generated at different pressures,interacted with older TTGs at lower and middle crustal levels to form the transitional TTGs.The coexistence of high-HREE-Y and medium-HREE-Y TTGs and sanukitoids suggests a subduction-related setting for the Jaisamand granitoids.The heat required for simultaneous melting at shallow and deeper depths during the Neoarchean was provided by the upwelling asthenosphere due to slab break-off.The study also revealed the occurrence of altered granitoids in the Jaisamand pluton,showing evidence of albitization and silicification.These rocks do not represent the pristine mineralogy and should be carefully examined to avoid misleading interpretations,particularly for the Archean granitoids.展开更多
The Shuangjianzishan deposit is a typical magmatic-hydrothermal deposit located in the southern Great Xing'an Range.Recent investigations have identified significant copper and tin mineralization at depth within t...The Shuangjianzishan deposit is a typical magmatic-hydrothermal deposit located in the southern Great Xing'an Range.Recent investigations have identified significant copper and tin mineralization at depth within the Shuangjianzishan deposit;however,the coupling relationship between magmatic emplacement and mineralization processes remains debated.This study presents whole-rock geochemistry,zircon LA-ICP-MS U-Pb dating,and zircon Hf isotope analyses of granite from the northern Shuangjianzishan deposit.The analysis results indicate the granite crystallized between 252.3 and 257.9 Ma,corresponding to Late Permian magmatic activity.The granite displaysε_(Hf)(t)=5.95-14.87,and t_(DM2)=333-900 Ma.Geochemically,the granite is rich in Si and Al,with high K,classified as a calc-alkaline,weakly peraluminous rock.LREEs are enriched,while HREEs are depleted,and a slight negative Eu anomaly,all of which are consistent with A-type granite characteristics.The Hercynian granite in the Shuangjianzishan deposit formed during the latter or post-collisional stages of the collision orogeny following the closure of the Paleo-Asian Ocean in the late Paleozoic era.The material source indicates a mixed origin,involving both crust and mantle contributions.The granite is also enriched in Cu,Pb,and Zn,suggesting its potential role as an ore-forming material source for the Shuangjianzishan deposit.This study proposes a potential link between Hercynian magmatism and mineralization at the Shuangjianzishan deposit for the first time,suggesting that multistage metallogenesis may be a response to successive magmatic events from Hercynian to Yanshanian periods in the mining area.展开更多
Distinguishing high-grade mafic-ultramafic rocks originally crystallized from within-plate basaltic magmatism is challenging and crucial because the chemical composition of the igneous rocks has been modified during h...Distinguishing high-grade mafic-ultramafic rocks originally crystallized from within-plate basaltic magmatism is challenging and crucial because the chemical composition of the igneous rocks has been modified during high-grade metamorphism,causing misidentification of the characters of the parental magma.Proterozoic metamorphosed mafic dykes occur throughout the Chhotanagpur Gneissic Complex(CGC)of eastern Indian shield.The E-W trending mafic dykes from the Saltora area in the southeastern CGC underwent metamorphism in two episodes:M1(650 MPa;770℃)and M2(300 MPa;744℃).The metamafics are enriched in LILE,depleted in HFSE,and display strong fractionation of LREE,nearly flat HREE patterns in a chondrite-normalized REE diagram,and show tholeiitic differentiation trend.Their geochemical affinity is towards rift-related,continental within-plate basalts.About 7%–10%melting of the carbonated spinel-peridotite sub-continental lithospheric mantle(SCLM)produced the parental mafic magma.The pre-existing SCLM was metasomatized by slab-derived fluid during the previous subduction.The upwelling of the asthenosphere in a post-collisional tectonic setting caused E-W trending fractures,lithospheric thinning,and gravitational collapse.These dykes were emplaced during crustal extension around 1070 Ma.The remarkable geochemical similarity between the mafic dykes of Saltora and Dhanbad,the ca.1096 Ma Mahoba(Bundelkhand craton),and the ca.1070 Ma Alcurra mafic dykes in Australia supports a genetic link.展开更多
The Qinghai-Tibet Plateau possesses the thickest continental crust on Earth,yet the timing of its formation remains debated.In this study,we conducted zircon U-Pb isotopic dating,geochemical and Sr-Nd-Pb-Hf isotopic a...The Qinghai-Tibet Plateau possesses the thickest continental crust on Earth,yet the timing of its formation remains debated.In this study,we conducted zircon U-Pb isotopic dating,geochemical and Sr-Nd-Pb-Hf isotopic analyses on the Xuexiumaer biotite quartz monzonite porphyry(BQMP)sampled from the Lake Dajia area in southern Gangdese.This study aims to estimate the paleo-crustal thickness beneath this region during the early India-Asia collision stage using whole-rock Sr/Y and(La/Yb)N ratios as proxies.Results reveal that the Xuexiumaer BQMP was formed at~51 Ma in a collisional tectonic setting following Neo-Tethyan slab breakoff,and is an I-type granitoid derived primarily from partial melting of juvenile mafic lower crust with subordinate ancient crustal input.The estimated paleo-crustal thickness in the Lake Dajia area at~51 Ma is less than 40 km.This indicates that although the Qinghai-Tibet Plateau had already undergone significant crustal thickening and attained an exceptionally thick crust(>50 km)prior to the India-Asia collision as demonstrated by previous studies,some regions still maintained a crust only slightly thicker than the average continental crust(~35 km)at the initial collision stage.This limited crustal thickening likely resulted from underplating of subduction-related mafic magma at the mantle-crust boundary.展开更多
This study presents whole-rock major,trace elements and Sr-Nd-Hf isotopic compositions,as well as zircon UPb geochronological data,for the peraluminous and aluminous granitoids in northern Guangdong Province,South Chi...This study presents whole-rock major,trace elements and Sr-Nd-Hf isotopic compositions,as well as zircon UPb geochronological data,for the peraluminous and aluminous granitoids in northern Guangdong Province,South China,in order to investigate their petrogenesis and tectonic implications.The Qingzhou granodiorites(458.5-455.4 Ma)are peraluminous(A/CNK=1.05-1.96).They have relatively high initial^(87)Sr/^(86)Sr ratios(I_(Sr)=0.7087-0.7148),lowε_(Nd)(t)values(-11.2 to-10.1)and a variety of zirconε_(Hf)(t)values in the range-13.4 to+4.81.By contrast,the Damaoshan granodiorites(458.1 Ma)are metaluminous(A/CNK=0.79-0.94)in composition,with I_(Sr)values of 0.7083 to 0.7110,ε_(Nd)(t)values of-7.92 to-5.28 and zirconε_(Nf)(t)values of-8.69 to-2.06.The Gaoshou quartz diorites(449 Ma)are metaluminous-peraluminous.Their I_(Sr)values vary from 0.7104 to 0.7111 withε_(Nd)(t)values from-9.64 to-8.63.Geochemical data and Sr-Nd-Hf isotope compositions indicate that the Qingzhou,Damaoshan and Gaoshou intrusions are primarily derived from the partial melting of metagreywackes,tonalitic rocks and amphibolite,respectively.The crustal materials in northern Guangdong,from top to bottom consist of Paleozoic sequences,metasediments with a V_(p)of<6.0 km/s,metaigneous rocks with a V_(p)of 6.3-6.7 km/s and amphibolite with a V_(p)of~7.03 km/s.展开更多
The Tong’an-Baishuidong mining district(TBMD),located in the eastern section of the Jiangnan Orogen,is a newly discovered granite-type lithium mining district.Thisstudy presents new monazite U-Pb chronological,whole-...The Tong’an-Baishuidong mining district(TBMD),located in the eastern section of the Jiangnan Orogen,is a newly discovered granite-type lithium mining district.Thisstudy presents new monazite U-Pb chronological,whole-rock geochemical,and Nd-Pb isotopic data to reveal the petrogenesis and geodynamic setting of the Wutang granites in the TBMD.The monazite U-Pb age of 145.8±1.0 Ma indicates that the granites were emplaced at the end of the Late Jurassic.Whole-rock geochemical results demonstrate that the Wutang granites are enriched in SiO_(2)(72.80-73.40 wt%)but depleted in CaO(0.44-0.90 wt%)and MgO+TiO_(2)+TFeO(1.79-2.05 wt%).These granites exhibit negative Eu anomalies(δEu=0.3−0.4)and high aluminum saturation indexes(A/CNK=1.2−1.6),differentiation indexes(DI=90-92),and Rb/Sr ratios(4.7-8.1).They also have moderate Ba contents(239-278 ppm)and low Sr contents(52.7-82.0 ppm)as well as low Nb/Ta(2.2-5.3)and Zr/Hf(21.3-31.5)ratios.All these indicate that they are highly fractionated granites.Additionally,these granites contain 5-10 wt%muscovite but no hornblende,with calculated corundum contents of 2.3-5.5 wt%.They have low high-field strength element(HFSE)contents(Zr+Nb+Ce+Y=182-202 ppm)and zircon saturation temperatures(700-770℃),with Th and Y negatively linked with Rb.These petrographic and geochemi-cal features further reveal that the Wutang granites belong to highly fractionated S-type granites.TheεNd(t)values of these granites range from−9.03 to−8.23,corresponding to two-stage model ages(T DM2)of 1488-1553 Ma.The initial Pb isotope ratios are:(206 Pb/^(204)Pb)i=18.38-18.55,(^(207)Pb/^(204)Pb)i=15.67-15.68,and(^(208)Pb/^(204)Pb)i=38.62-38.67.These Nd-Pb isotopic results demonstrate that the parental magma originated from the partial melting of ancient crustal materials.In the meantime,the TBMD in the eastern section of the Jiangnan Orogen was in a compression-extension transitional setting associated with the episodic subduction of the Paleo-Pacific Plate.展开更多
The western margin of the Yangtze Block hosts diverse Neoproterozoic igneous rocks,with exposed S-type granites serving as key indicators for deciphering regional geological evolution.This study focuses on the Jiudaow...The western margin of the Yangtze Block hosts diverse Neoproterozoic igneous rocks,with exposed S-type granites serving as key indicators for deciphering regional geological evolution.This study focuses on the Jiudaowan granite pluton,located on the western margin of the Yangtze Block,through systematic petrographic,whole-rock geochemical,zircon and monazite U-Pb geochronology,and whole-rock Nd isotopic analyses aiming to elucidate its petrogenesis and tectonic significance.The Jiudaowan granite pluton is a composite body,consisting of the Luotaijiu,Jiudaowan,and Daheishan units,characterized by biotite monzogranites,muscovite-plagioclase granites,and two-mica monzogranites,respectively.LA-ICP-MS zircon and monazite U-Pb dating reveals crystallization ages between 832 and 798 Ma.The three units are peraluminous,containing minerals such as muscovite,garnet,and tourma-line,and exhibiting high SiO_(2)(72.99-77.83 wt%),Al_(2)O_(3)(12.36-15.02 wt%),and A/CNK values(1.06-1.43),con-firming their classification as peraluminous S-type granites.Compositional variations within the Jiudaowan granite pluton are primarily controlled by protolith composition and melting mechanisms.The pluton is distinguished by low CaO/Na_(2)O ratios(0.02-0.18),high Rb/Sr(0.83-113)and Rb/Ba(0.33-15.2)ratios,and negativeεNd(t)values(−13.6 to−9.1),indicating derivation from partial melting of het-erogeneous metasedimentary sources.MgO,TiO_(2),Rb/Sr,and whole-rock Zr saturation temperatures suggest that the Luotaijiu and Daheishan units formed via biotite dehydration melting,whereas the Jiudaowan unit resulted from muscovite dehydration melting.Additionally,the Jiudaowan granite pluton displays a clear negative correlation between Al_(2)O_(3),CaO,Fe_(2)O_(3)T,MgO,TiO_(2),and SiO_(2),along with pronounced Eu negative anomalies and depletions in Sr and Ti,suggesting fractional crystallization of feldspar,mica,and Fe-Ti oxides during magma emplacement.Similarly,variable incompatible element ratios of Nb/U(1.07-18.97)and Nb/La(0.24-26.88)further indicate minor crustal assimilation and contamination during magma evolution.Integrating regional geological data,we propose that the Jiudaowan pluton formed during crustal thickening associated with post-collisional extension,likely related to the breakup of the Rodinia supercontinent.展开更多
Ten rock samples consisting of one pyroclastic density current(PDC1)deposit,seven lava flows(LF1–7),and two summit lava domes(LD1,2)were studied to understand the petrogenesis and magma dynamics at Mt.Sumbing.The str...Ten rock samples consisting of one pyroclastic density current(PDC1)deposit,seven lava flows(LF1–7),and two summit lava domes(LD1,2)were studied to understand the petrogenesis and magma dynamics at Mt.Sumbing.The stratigraphy is arranged as LF1,PDC1,LF2,LF3,LF4,LF5,LF6,LF7,LD1,and LD2;furthermore,these rocks were divided into two types.TypeⅠ,observed in the oldest(LF1)sample,has poor MgO and high Ba/Nb,Th/Yb and Sr.The remaining samples(PDC1–LD2)represent typeⅡ,characterized by high MgO and low Ba/Nb,Th/Yb and Sr values.We suggest that type I is derived from AOC(altered oceanic crust)-rich melts that underwent significant crustal assimilation,while typeⅡoriginates from mantle-rich melts with less significant crustal assimilation.The early stage of typeⅡmagma(PDC1–LF3)was considered a closed system,evolving basaltic andesite into andesite(55.0–60.2 wt%SiO_(2))with a progressively increasing phenocryst(0.30–0.48φ_(PC))and decreasing crystal size distribution(CSD)slope(from-3.9 to-2.9).The evidence of fluctuating silica and phenocryst contents(between 55.9–59.7 wt%and 0.25–0.41φ_(PC),respectively),coupled with the kinked and steep(from-5.0 to-3.3)CSD curves imply the interchanging condition between open(i.e.,magma mixing)and closed magmatic systems during the middle stage(LF4–LF6).Finally,it underwent to closed system again during the final stage(LF7–LD2)because the magma reached dacitic composition(at most 68.9 wt%SiO_(2))with abundant phenocryst(0.38–0.45φ_(PC))and gentle CSD slope(from-4.1 to-1.2).展开更多
The tectonic evolution and crustal accretion process of the North Qilian Orogenic Belt(NQOB)are still under debate because of a lack of integrated constraints,especially the identifi cation of the tectonic transition ...The tectonic evolution and crustal accretion process of the North Qilian Orogenic Belt(NQOB)are still under debate because of a lack of integrated constraints,especially the identifi cation of the tectonic transition from arc to initial collision.Here we present results from zircon U-Pb geochronology,whole-rock geochemistry,and Sr-Nd-Pb isotope geochemistry of the Beidaban granites to provide crucial information for geodynamic evolution of NQOB.Zircon U-Pb dating yields an age of 468±10 Ma for the Beidaban granites and most of the Beidaban samples contain amphibole,are potassium-rich,and have A/CNK values ranging from 0.7 to 0.9,illustrating that the Middle Ordovician Beidaban granites are K-rich,metaluminous,calc-alkaline granitoid.The geochemical characteristics indicate that the Beidaban granites are transitional I/S-type granitoids that formed in an arc setting.The isotopic compositions of initial(87 Sr/86 Sr)i values ranging from 0.70545 to 0.71082(0.70842 on average)andεNd(t)values ranging from−10.9 to−6.7(−8.8 on average)with two-stage Nd model ages(T DM2)of 1.74-2.08 Ga suggest that the Beidaban granites originated from Paleoproterozoic crustal materials.In addition,the initial Pb isotopic compositions(^(206)Pb/^(204)Pb=19.14-20.26;^(207)Pb/^(204)Pb=15.71-15.77;^(208)Pb/^(204)Pb=37.70-38.26)and geochemical features,such as high Th/Ta(17.43-30.12)and Rb/Nb(6.01-15.49)values,suggest that the Beidaban granite magma source involved recycled crustal components with igneous rocks.Based on these results in combination with previously published geochronological and geochemical data from other early Paleozoic igneous rocks,we suggest that the timing of the tectonic transition from arc to the initial collision to the fi nal closure of the North Qilian Ocean can be constrained to the Middle-Late Ordovician(ca.468–450 Ma).展开更多
Geodynamic mechanism responsible for the generation of Silurian granitoids and the tectonic evolution of the Qilian orogenic belt remains controversial. In this study, we report the results of zircon U–Pb age, and sy...Geodynamic mechanism responsible for the generation of Silurian granitoids and the tectonic evolution of the Qilian orogenic belt remains controversial. In this study, we report the results of zircon U–Pb age, and systematic whole-rock geochemical data for the Haoquangou and Liujiaxia granitoids within the North Qilian orogenic belt and the Qilian Block, respectively, to constrain their petrogenesis, and the Silurian tectonic evolution of the Qilian orogenic belt. Zircon U–Pb ages indicate that the Haoquangou and Liujiaxia intrusions were emplaced at423 ± 3 Ma and 432 ± 4 Ma, respectively. The Haoquangou granodiorites are calc-alkaline, while the Liujiaxia granites belong to the high-K calc-alkaline series.Both are peraluminous in composition and have relatively depleted Nd isotopic [ε_(Nd)(t) =(-3.9 – + 0.6)] characteristics compared with regional basement rocks, implying their derivation from a juvenile lower crust. They show adakitic geochemical characteristics and were generated by partial melting of thickened lower continental crust. Postcollisional extensional regime related to lithospheric delamination was the most likely geodynamic mechanism for the generation of the Haoquangou granodiorite, while the Liujiaxia granites were generated in a compressive setting during continental collision between the Qaidam and Qilian blocks.展开更多
The Daerlong granitic complex in Linkou area is located at the convergence position of the Jiamusi and Songliao blocks.A systematic study of field geology,petrography,zircon U-Pb dating and wholerock major and trace e...The Daerlong granitic complex in Linkou area is located at the convergence position of the Jiamusi and Songliao blocks.A systematic study of field geology,petrography,zircon U-Pb dating and wholerock major and trace elements has been conducted for the Daerlong granitic complex,aiming to determine its formation age,petrogenesis and tectonic setting,and further constrain the nature and evolution of the Mudanjiang Ocean.Field and petrographic observations show that the Daerlong granitic complex mainly consists of three rock types from old to young,i.e.,biotite granodiorite,syenogranite and monzogranite.Geochemical data suggest that all the types of granitoids are high in silicon,rich in potassium,moderate in aluminum(A/CNK=0.94-1.10),poor in iron and magnesium,rich in LILEs and depleted in HFSEs,belonging to the weakly peraluminous high-K calc-alkaline series.Combined with mineral assemblages and geochemical discrimination diagrams,it can be determined that the studied granitoids are of igneous crustderived I-type origin,which underwent strong fractional crystallization and crystal accumulation during magmatic evolution.Zircon LA-ICP-MS U-Pb dating results show that the different types of granitoids were emplaced in a wide age range from 301 to 240 Ma,indicating a long-lived Late Carboniferous to Middle Triassic granitic magmatism occurred in the western Jiamusi Block.The Daerlong granitoids have similar geochemical characteristics of subduction-related igneous rocks.Considering the spatial and temporal distribution of Late Paleozoic to Early Mesozoic igneous rocks within eastern Heilongjiang Province,it is concluded that the Daerlong granitic complex was formed in an active continental margin setting rather than a continental rift environment.The results suggest that the Mudanjiang Ocean might not be a limited ocean evolved from the rifting of the unified Jiamusi-Songnen microcontinent.展开更多
Early Palaeozoic Cambrian A-type Kathalguri Granites in the Mikir Hills of northeastern (NE) India were studied to better understand the geodynamic settings in this region. This research presents new whole-rock geoche...Early Palaeozoic Cambrian A-type Kathalguri Granites in the Mikir Hills of northeastern (NE) India were studied to better understand the geodynamic settings in this region. This research presents new whole-rock geochemical and Sr, Nd, Pb isotopic data for the Cambrian granites in the Kathalguri Granite in Mikir Hills. The Kathalguri Granite shows geochemical characteristics of high SiO2, K2O and low FeOT, MgO, CaO, and P2O5 compositions. They belong to a high K Shoshonite to ultra-potassic series and display a weak metaluminous to peraluminous feature with A/CNK values of 0.83 to 1.02 with corundum and anorthite normative. FeOT/MgO varies from 2.93 - 7.49, is moderately oxidized and belongs to magnetite series. The rocks have a high ΣREE composition of 370.80 - 1353.23 ppm (average 568.55) and are enriched in LREE with flat HREE and (La/Yb)N values of 8.10 - 18.99, and display obvious strong negative Eu anomalies. Trace elements of the studied granites are characterized by enrichment in Rb, Th, U, Pb, Hf, and Sm, and depletion of Ba, Nb, Ta, and Sr. They display geochemical features of high Zr + Y + Nb + Ce values (241 - 934 ppm) and Ga/Al ratios 2.49 - 3.01 consistent with A-Type granites. Based on particular geochemical features, such as high Rb/Nb (3.10 - 19.53) and Low Y/Nb (0.09 - 2.28), Kathalguri Granite can be further classified as an A1-type subgroup. Granites display relatively low Sr (N ratio varying between 0.53 - 0.89 suggesting that the melts generated at greater depths (18 - 40 km), and fractionation at low pressures (−3 and total HGU 98.96 to 214.20. Kathalguri Granite dated by Rb-Sr isotopic isochrone as 489 ± 19 Ma with an initial 87Sr/86Sr 0.7199 ± 0.0017 and MSWD of 4.1, εSr(I) varied between 161.62 - 332.08 suggests that the Kathalguri Granite have originated from partial melting of ancient, evolved continental crustal material. The Sm-Nd Systematics has given a depleted mantle model (TDM) age ranging from 1733 - 2063 Ma with high negative εNd(t) values (−10.39 to −15.18) also hint at some heterogeneity or multiple source contributions in the melting process of the protolith. Xenoliths of older mafic rocks and Barapani arenites are seen within the Kathalguri Granite and are also supported by geochemical signatures of recycled crustal materials both mafic and sedimentary. It formed during the Cambrian reorganization of lithospheric plate motion related to the Pan-African-Braziliano event.展开更多
The major element, trace element and rare earth element（REE） of the intrusion rock from the Dachang ore field in Guangxi, China, were analyzed. The results show that the phenocryst（about 15%） and matrix（about 85%...The major element, trace element and rare earth element（REE） of the intrusion rock from the Dachang ore field in Guangxi, China, were analyzed. The results show that the phenocryst（about 15%） and matrix（about 85%） mainly consist of quartz, K-feldspar and plagioclase. The rock is composed of low content of Si and high content of Al2O3, low contents of Ca, Fe2O3, Na, TiO2, etc. The intrusion rock has the medium alkali content, attributing to K-rich type rock; and contains medium to low REE contents, of which light rare earth elements（LREEs） and heavy rare earth elements（HREEs） are highly fractionated, showing a weak negative Ce anomaly and a negative Eu anomaly. These rocks are enriched in LREE, and the large ion lithophytes elements（LILE） are rich in Rb, Sr, and U; the high-field-strength elements（Nb, Th, etc） are relatively depleted. The REE chondrite-normalized patterns are consistent with the overall, roughly indicating their similar characteristics, sources and evolution. The intrusion rock mainly formed during the collisional and within-plate periods.展开更多
Skarn is the main altered rock type and is of great importance to mineralization and ore-prospecting in the Shizhuyuan area of Hunan province, China. Its features of petrography, mineralogy and geochemistry were st...Skarn is the main altered rock type and is of great importance to mineralization and ore-prospecting in the Shizhuyuan area of Hunan province, China. Its features of petrography, mineralogy and geochemistry were studied systematically. The results show that the skarn mainly consists of garnet skarn, secondary wollastonite-garnet skarn, tremolite-clinozoisite skarn, and few wolframine garnet skarn, idocrase-garnet skarn and wollastonite skarn with granoblastic texture, granular sheet crystalloblastic texture, and massive structure, disseminated structure, mesh-vein structure, comb structure, and banded structure. And, it is mainly composed of garnet, fluorite, chlorite, hornblende, epidote, tremolite, plagioclase, biotite, muscovite, plagioclase, quartz, idocrase, and calcite and so on. The chemical components mainly include SiO2, Al2O3, Fe2O3, MgO and CaO, and the trace elements and REEs consist of Li, Be, V, Co, Zn, Ga, Rb, Sr, Y, Ce, Nd, Pb and Bi, etc. And, the obvious fractionation exists between LREE and HREE, and it shows typical features of Nanling ore-forming granite for W？Sn polymetallic deposit. Skarn is derived from the sedimentary rock, such as limestone, mudstone, argillaceous rock, and few pelitic strips. It is affected by both Shetianqiao formation strata and Qianlishan granite during the diagenesis, indicating a strong reduction environment. The occurrence of skarn, whose mutation site is favorable to the mineralization enrichment, is closely related to the mineralization and prospecting.展开更多
The Indosinian post-collisional Wulong pluton intruded into the Mesoproterozoic Fuping Group, South Qinling, central China. In the southern part of the pluton, some mafic enclaves have sharp or gradational contact rel...The Indosinian post-collisional Wulong pluton intruded into the Mesoproterozoic Fuping Group, South Qinling, central China. In the southern part of the pluton, some mafic enclaves have sharp or gradational contact relationships with the host biotite granodiorite. Geochemistry, zircon LA-ICP MS （laser ablation inductively-coupled plasma mass spectrometry） U-Pb chronology and Sr- Nd-Pb isotope geochemistry of the pluton are reported in this paper. The biotite granodiorite shows close compositional similarities to high-silica adakite. Its chondrite-normalized REE patterns are characterized by strong HREE depletion （Yb = 0.33--0.96 10-6 and Y = 4.77-11.19 ×10^-6）, enrichment of Ba （775-1386 x 10-6） and Sr （643-1115 × 10^-6） and high Sr/Y （57.83-159.99） and Y/Yb （10.99-14.32） ratios, as well as insignificant Eu anomalies （6Eu = 0.70-0.83）, suggesting a feldspar-poor, garnet±amphibole-rich residual mineral assemblage. The mafic enclaves have higher MgO （4.15- 8.13%）, Cr （14.79-371.31 × 10-6）, Ni （20.00-224.24× 10^-6） and Nb/Ta （15.42-21.91） than the host granodiorite, implying that they are mantle-derived and might represent underplated mafic magma. Zircon LA-ICP MS dating of the granodiorite yields a ^206pb/^238U weighted mean age of 208±2 Ma （MSWD=0.50, 1σ）, which is the age of emplacement of the host biotite granodiorite. This age indicates that the Wulong pluton formed during the late-orogenic or post-collisional stage （〈242±21 Ma） of the South Qinling belt. The host biotite granodiorite displays ^87Sr/^86Sr = 0.7059-0.7062, Isr = 0.7044-- 0.7050,^143Nd/^144Nd = 0.51236-0.51238, εNd（t）= -2.26 to -2.66 to ^206Pb/^204pb = 18.099-18.209, ^207pb/^204pb = 15.873-15.979 and ^208pb/^204pb = 38.973-39.430. Those ratios are similar to those of the Mesoproterozoic Yaolinghe Group in the South Qinling. Furthermore, its Nd isotopic model age （-1.02 Ga） is consistent with the age （-1.1 Ga） of the Yaolinghe Group. Based on the integrated geological and geochemical studies, coupled with previous studies, the authors suggest that the Wulong adakitic biotite granodiorite was probably generated by dehydration melting of the Yaolinghe Group-like thickened mafic crust, triggered by underplating of mafic magma at the boundary of the thickened mafic crust and hot lithospheric mantle, and that the Wulong adakitic biotite granodiorite may have resulted from thinning and delamination of the lower crust or breakoff of the subducting slab of the Mianlue ocean during the Indosinian post-collisional orogenic stage of the Qinling orogenic belt.展开更多
South Qinling Tectonic Belt（SQTB）is located between the Shangzhou-Danfeng and Mianxian-Lueyang sutures.There are a lot of early Mesozoic granitoid plutons in its middle segment, comprising the Dongjiangkou-Zhashui g...South Qinling Tectonic Belt（SQTB）is located between the Shangzhou-Danfeng and Mianxian-Lueyang sutures.There are a lot of early Mesozoic granitoid plutons in its middle segment, comprising the Dongjiangkou-Zhashui granitoid plutons at the northeast,Huayang-Wulong-Laocheng granitoid plutons at the central part,Xiba granitoid pluton at the northwest and Guangtoushan-Liuba granitoid plutons at the southwest.These Indonisian granitoids contain a mass of various scale mafic enclaves,which show sometimes clear boundaries and sometimes transitional boundaries with their host granitoids.These granitoids also exhibit metaluminous to peraluminous series,commonly higher Mg# and a wide range of petrochemistry from low-K tholeiite series,through mid-K and high-K calc-alkaline series to shoshonite series and predominated samples are attributed to mid-K and high-K calc-alkaline series.Detailed analyses in Sr-Nd isotopic systematics and petrochemistry reveal that there may be regionally initial granitoid magma of the Indonisian granitoid plutons,comprising Dongjiangkou-Zhashui,Huayang-Wulong-Laocheng,Xiba,and Guangtoushan-Liuba granitoid plutons,which were produced by hybrids of magmas in various degrees,and the initial magmas were derived from both the mantle and the lower continental crust（LCC）sources in the SQTB.The initial granitoid magma further did the magma hybrid with the magmas from the LCC,crystallization fractionation,and assimilation with upper crustal materials during their emplacement to produce these granitoid plutons in the SQTB.These magmatism processes are most likely to occur under continent marginal arc and syn-collision to post-collision tectonic backgrounds.展开更多
The Xuhe mafic rocks, located in Ziyang county of Shaanxi Province, are dominated by diabase-porphyrite, gabbro-diabase, diabase, and pyroxene diorite. Primitive mantle-normalized multi-element patterns show that, the...The Xuhe mafic rocks, located in Ziyang county of Shaanxi Province, are dominated by diabase-porphyrite, gabbro-diabase, diabase, and pyroxene diorite. Primitive mantle-normalized multi-element patterns show that, the Xuhe marie rocks are enriched in large ion lithophile elements （LITE）, such as Ba and Pb, depleted in K and Sr for basic rocks, and are depleted in Sr, P and Ti for pyroxene diorite. Chondrite-normalized REE patterns display LREE enrichment （LaN/YbN = 9.34- 13.99） and have normalized patterns for trace element and REE similar to that of typical OIB. Detailed SIMS zircon U-Pb dating yields emplacement ages of 438.4 ± 3.1 Ma for Xuhe mafic rocks. The relatively low MgO （basic rock： 3.11-7.21 wt%; pyroxene diorite： 0.89-1.21 wt% ） and Mg# （0.20- 0.49） for Xuhe mafic rocks suggest that they were possibly originated from an extremely evolved magma. The rising parental mafic magmas underwent pyroxene and plagioclase fractionation. Crustal contamination of pyroxene diorite before emplacement occurred at a higher crustal level compared to other lithology in Xuhe mafic rocks. The degree of partial melt was low （5%-10%） and in garnetspinel transition facies. Sr-Nd isotope of pyroxene diorite and enrichment mantle characteristics for Xuhe mafic rocks suggest that mafic rocks in the North Daba Mountains were derived from a mixture of HIMU, EMII and small amount of EMI components. Furthermore, this study discusses mantle geodynamic significance of Xuhe mafic rocks in the Silurian, which indicates subduction and uplift of magma caused back-arc extension.展开更多
Mesozoic granitic intrusions are widely distributed in the Nanling region, South China. Yanshanian granites are closely connected with the formation of tungsten deposits. The Xihuashan granite is a typical representat...Mesozoic granitic intrusions are widely distributed in the Nanling region, South China. Yanshanian granites are closely connected with the formation of tungsten deposits. The Xihuashan granite is a typical representative of tungsten-bearing granite. The Xihuashan granite consists mainly of medium-grained porphyritic biotite granite, medium-grained biotite granite and fine-grained twomica granite, which correspond to LA-ICP-MS zircon U-Pb ages of 555.5±0.4 Ma, 553.0±0.6 Ma and 552.8±0.9 Ma, respectively. Rocks from the Xihuashan mining area displays high SlOe （73.85% to 76.49%） and NaeO＋K20 contents （8.09% to 9.43%）, belonging to high-K calc-alkaline series. They are metaluminous to weakly peraluminous with A/CNK values ranging from 0.96 to 5.06. All granites in this study area are rich in Rb, Th, U and Pb, and depleted in Ba, Sr, P, Ti, Nb and Eu, especially depleted in medium-grained biotite granite and fine-grained two-mica granite. The medium-grained porphyritic biotite granites usually have high LREE concentrations, whereas medium-grained biotite granite and fine-grained two-mica granite displays high HREE contents. Our geochemical data reveal that the studied rocks are highly fractionated I-type granite. The magma underwent strong magma differentiation with decreasing temperature and increasing oxygen fugacity, which may explain the formation of three types of distinct granites. Variations of Rb, Sr and Ba concentrations in different type granites were controlled by fractional crystallization of biotite and feldspar. Fractional crystallization of monazite, allanite and apatite resulted in LREE changes in granite, and formation of garnet mainly caused HREE changes. Granites from the Xihuashan mining area have relatively high εd（t） values （-9.77 to -55.46）, indicating that they were probably generated by partial melting of underlying Proterozoic metasedimentary rocks with minor addition of juvenile crust or mantlederived magmas.展开更多
The Paleoproterozoic Liiliang Metamorphic Complex （PLMC） is situated in the middle segment of the western margin of the Trans-North China Orogen （TNCO）, North China Craton （NCC）. As the most important lithologic...The Paleoproterozoic Liiliang Metamorphic Complex （PLMC） is situated in the middle segment of the western margin of the Trans-North China Orogen （TNCO）, North China Craton （NCC）. As the most important lithological assemblages in the southern part of the PLMC, Guandishan granitoids consist of early gneissic tonalities, granodiorites and gneissic monzogranites, and younger gneissic to massive monzogranites. Petrochemical features reveal that the early gneissic tonalities and granodiorites belong to the medium-K calc-alkaline series; the early gneissic monzogranites are transitional from high-K calc-alkaline to the shoshonite series; the younger gneissic to massive monzogranites belong to the high-k calc-alkaline series, and all rocks are characterized by right- declined REE patterns and negative Nb, Ta, Sr, P, and Ti anomalies in the primitive mantle normalized spidergrams. SHRIMP zircon U-Pb isotopic dating reveals that the early gneissic tonalities and granodiorites formed at -2.17 Ga, the early gneissic monzogranites at -2.06 Ga, and the younger gneissic to massive monzogranites at -1.84 Ga. Sm-Nd isotopic data show that the early gneissic tonalities and granodiorites have eNd（t） values of ＋0.48 to -3.19 with Nd-depleted mantle model ages （TDM） of 2.76--2.47 Ga, and early gneissic monzogranites have eNd（t） values of -0.53 to -2.51 with TDM of 2.61--2.43 Ga, and the younger gneissic monzogranites have eNd（t） values of -6.41 to -2.78 with a TDM of 2.69--2.52 Ga.These geochemical and isotopic data indicate that the early gneissic tonalities, granodiorites, and monzogranites were derived from the partial melting of metamorphosed basaltic and pelitic rocks, respectively, in a continental arc setting. The younger gneissic to massive monzogranites were derived by partial melting of metamorphosed greywackes within the continental crust. Combined with previously regional data, we suggest that the Paleoproterozoic granitoid magmatism in the Guandishan granitoids of the PLMC may provide the best geological signature for the complete spectrum of Paleoproterozoic geodynamic processes in the Trans-North China Orogen from oceanic subduction, through collisional orogenesis, to post-orogenic extension and uplift.展开更多
基金Geological Survey of India,Northern Region have provided the financial funding for the study.
文摘Background The Bundelkhand Craton is significant for preserving the multiphase granitoids magmatism from Paleoarchean to Neoarchean periods.It consists of a variety of granite rocks,including TTGs,sanukitoids,and high-K granitoids.This study presents geochemical characteristics of high-silica(68.97 wt.%–73.99 wt.%),low-silica(58.73wt.%–69.94 wt.%),and high K_(2)O(2.77 wt.%–6.16 wt.%)contents of granitoids.Objective The data on Bundelkhand Craton’s granitic magmatism and geodynamics is not sufficiently robust.Geochemical data from this study will be used to further understand the origin,source,and petrogenesis of granitoid rocks and their implications for the evolution of geodynamics.Methodology Twenty-one samples were collected and analyzed for major,trace,and REE elements.Major elements were measured using X-ray fluorescence spectrometry(XRF),and trace and REE elements were analyzed by ICP-MS.Standard procedures from the Geological Survey of India were followed.Results The geochemical analysis presents high-silica(68.97-73.99 wt.%),low-silica(58.73-69.94 wt.%),and high K_(2)O(2.77-6.16 wt.%)contents in granitoids,classified as granite-granodiorite.The rocks are calcic to calcalkalic,magnesian,and range from peraluminous to metaluminous composition.REE patterns showed strong LREE enrichment relative to HREEs,with prominent negative Eu anomalies corresponding to earlier plagioclase fractionation.Multi-element patterns revealed negative anomalies in Nb,Sr,P,and Ti and positive anomalies in Pb.Conclusion The geochemical signatures attributed to the post-collisional magma generation and continental crustal contamination.The studied rocks show A-type and A2-type lineage,suggesting they originated from the melting of continental crust during transitional/post-collisional tectonic activity.The formation of hybrid granitoids in the Bundelkhand Craton is connected to the fractionation of hybrid magmas in shallow-seated magma chambers during these tectonic processes.
基金the Ministry of Earth Sciences,New Delhi(MoES/P.O/(Geo)/100(2)/2017).
文摘The lack of a comprehensive whole-rock geochemical and mineralogical dataset for the Archean granitoids of the Aravalli-Banded Gneissic Complex(BGC),northwest India,results in significant challenges for their correct characterization and assessment of their antiquity.The new field,mineralogical and geochemical data classify the Jaisamand granitoids into sanukitoids,TTGs,and transitional TTGs,which are most likely coeval in nature.The obtained results,in conjuncture with the previously published geochemical and geochronological results of the Aravalli-BGC granitoids,unveil the Neoarchean affinity of the Jaisamand pluton.The TTGs were generated by the melting of a subducting slab(metabasite)at shallow(high-HREE-Y TTGs)to moderate depths(medium-HREE-Y TTGs)above the garnet-in line but still within the plagioclase stability field,with garnet-poor residue.The ascending TTG melts were transformed into sanukitoids through differential interaction with the overlying mantle wedge peridotite.The TTG melts,generated at different pressures,interacted with older TTGs at lower and middle crustal levels to form the transitional TTGs.The coexistence of high-HREE-Y and medium-HREE-Y TTGs and sanukitoids suggests a subduction-related setting for the Jaisamand granitoids.The heat required for simultaneous melting at shallow and deeper depths during the Neoarchean was provided by the upwelling asthenosphere due to slab break-off.The study also revealed the occurrence of altered granitoids in the Jaisamand pluton,showing evidence of albitization and silicification.These rocks do not represent the pristine mineralogy and should be carefully examined to avoid misleading interpretations,particularly for the Archean granitoids.
基金financed by the Inner Mongolia Geological Exploration Fund Project (Grant No. 2020YS03)the project of “Geology of Mineral Resources in China” from China Geological Survey (Grant Nos. DD20221695, DD20190379, DD20160346)+1 种基金the Project of Transformation in Scientific and Technological Achievements (Grant Nos. 2023CX10, HE2121)the Fundamental Research Funds of the Central Public Welfare Scientific Research Institutes (Grant No. JKYZD202313)
文摘The Shuangjianzishan deposit is a typical magmatic-hydrothermal deposit located in the southern Great Xing'an Range.Recent investigations have identified significant copper and tin mineralization at depth within the Shuangjianzishan deposit;however,the coupling relationship between magmatic emplacement and mineralization processes remains debated.This study presents whole-rock geochemistry,zircon LA-ICP-MS U-Pb dating,and zircon Hf isotope analyses of granite from the northern Shuangjianzishan deposit.The analysis results indicate the granite crystallized between 252.3 and 257.9 Ma,corresponding to Late Permian magmatic activity.The granite displaysε_(Hf)(t)=5.95-14.87,and t_(DM2)=333-900 Ma.Geochemically,the granite is rich in Si and Al,with high K,classified as a calc-alkaline,weakly peraluminous rock.LREEs are enriched,while HREEs are depleted,and a slight negative Eu anomaly,all of which are consistent with A-type granite characteristics.The Hercynian granite in the Shuangjianzishan deposit formed during the latter or post-collisional stages of the collision orogeny following the closure of the Paleo-Asian Ocean in the late Paleozoic era.The material source indicates a mixed origin,involving both crust and mantle contributions.The granite is also enriched in Cu,Pb,and Zn,suggesting its potential role as an ore-forming material source for the Shuangjianzishan deposit.This study proposes a potential link between Hercynian magmatism and mineralization at the Shuangjianzishan deposit for the first time,suggesting that multistage metallogenesis may be a response to successive magmatic events from Hercynian to Yanshanian periods in the mining area.
基金funded by a major research project grant from the UGC (F.-43-367/2014(SR)) and teachers’ research grant from the University of Calcutta awarded to Dr Bapi GoswamiDST-sponsored Women Scientist scheme-A (SR/WOS-A/EA-47/2018 (G) dated 06.05.2019) awarded to Ms. Poulami Roy is highly acknowledged for their financial help
文摘Distinguishing high-grade mafic-ultramafic rocks originally crystallized from within-plate basaltic magmatism is challenging and crucial because the chemical composition of the igneous rocks has been modified during high-grade metamorphism,causing misidentification of the characters of the parental magma.Proterozoic metamorphosed mafic dykes occur throughout the Chhotanagpur Gneissic Complex(CGC)of eastern Indian shield.The E-W trending mafic dykes from the Saltora area in the southeastern CGC underwent metamorphism in two episodes:M1(650 MPa;770℃)and M2(300 MPa;744℃).The metamafics are enriched in LILE,depleted in HFSE,and display strong fractionation of LREE,nearly flat HREE patterns in a chondrite-normalized REE diagram,and show tholeiitic differentiation trend.Their geochemical affinity is towards rift-related,continental within-plate basalts.About 7%–10%melting of the carbonated spinel-peridotite sub-continental lithospheric mantle(SCLM)produced the parental mafic magma.The pre-existing SCLM was metasomatized by slab-derived fluid during the previous subduction.The upwelling of the asthenosphere in a post-collisional tectonic setting caused E-W trending fractures,lithospheric thinning,and gravitational collapse.These dykes were emplaced during crustal extension around 1070 Ma.The remarkable geochemical similarity between the mafic dykes of Saltora and Dhanbad,the ca.1096 Ma Mahoba(Bundelkhand craton),and the ca.1070 Ma Alcurra mafic dykes in Australia supports a genetic link.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.92155305 and 42103066)the National Key Research and Development Plan(Grant No.2023YFC2908400 and 2024YFC2910102)the Fundamental Research Funds for the Central Universities(Grant No.FRF-TP-24-046A).
文摘The Qinghai-Tibet Plateau possesses the thickest continental crust on Earth,yet the timing of its formation remains debated.In this study,we conducted zircon U-Pb isotopic dating,geochemical and Sr-Nd-Pb-Hf isotopic analyses on the Xuexiumaer biotite quartz monzonite porphyry(BQMP)sampled from the Lake Dajia area in southern Gangdese.This study aims to estimate the paleo-crustal thickness beneath this region during the early India-Asia collision stage using whole-rock Sr/Y and(La/Yb)N ratios as proxies.Results reveal that the Xuexiumaer BQMP was formed at~51 Ma in a collisional tectonic setting following Neo-Tethyan slab breakoff,and is an I-type granitoid derived primarily from partial melting of juvenile mafic lower crust with subordinate ancient crustal input.The estimated paleo-crustal thickness in the Lake Dajia area at~51 Ma is less than 40 km.This indicates that although the Qinghai-Tibet Plateau had already undergone significant crustal thickening and attained an exceptionally thick crust(>50 km)prior to the India-Asia collision as demonstrated by previous studies,some regions still maintained a crust only slightly thicker than the average continental crust(~35 km)at the initial collision stage.This limited crustal thickening likely resulted from underplating of subduction-related mafic magma at the mantle-crust boundary.
基金supported by the China Geological Survey Project(No.DD20243455)the National Natural Science Foundation of China(NSFC Project 41302046)。
文摘This study presents whole-rock major,trace elements and Sr-Nd-Hf isotopic compositions,as well as zircon UPb geochronological data,for the peraluminous and aluminous granitoids in northern Guangdong Province,South China,in order to investigate their petrogenesis and tectonic implications.The Qingzhou granodiorites(458.5-455.4 Ma)are peraluminous(A/CNK=1.05-1.96).They have relatively high initial^(87)Sr/^(86)Sr ratios(I_(Sr)=0.7087-0.7148),lowε_(Nd)(t)values(-11.2 to-10.1)and a variety of zirconε_(Hf)(t)values in the range-13.4 to+4.81.By contrast,the Damaoshan granodiorites(458.1 Ma)are metaluminous(A/CNK=0.79-0.94)in composition,with I_(Sr)values of 0.7083 to 0.7110,ε_(Nd)(t)values of-7.92 to-5.28 and zirconε_(Nf)(t)values of-8.69 to-2.06.The Gaoshou quartz diorites(449 Ma)are metaluminous-peraluminous.Their I_(Sr)values vary from 0.7104 to 0.7111 withε_(Nd)(t)values from-9.64 to-8.63.Geochemical data and Sr-Nd-Hf isotope compositions indicate that the Qingzhou,Damaoshan and Gaoshou intrusions are primarily derived from the partial melting of metagreywackes,tonalitic rocks and amphibolite,respectively.The crustal materials in northern Guangdong,from top to bottom consist of Paleozoic sequences,metasediments with a V_(p)of<6.0 km/s,metaigneous rocks with a V_(p)of 6.3-6.7 km/s and amphibolite with a V_(p)of~7.03 km/s.
基金funded by the Program of Science and Technology Department of Jiangxi Province(2023KDG01002 and 2023KDG01003)the National Natural Science Foundation of China(42062006 and 41962007)+1 种基金the Key Research and Development Program of Jiangxi Province(20223BBG71015)the Personnel Training Project of Jiangxi Bureau of Geology(2023JXDZKJRC02,2022JXDZKJRC04,and 2024JXDZKJRC05).
文摘The Tong’an-Baishuidong mining district(TBMD),located in the eastern section of the Jiangnan Orogen,is a newly discovered granite-type lithium mining district.Thisstudy presents new monazite U-Pb chronological,whole-rock geochemical,and Nd-Pb isotopic data to reveal the petrogenesis and geodynamic setting of the Wutang granites in the TBMD.The monazite U-Pb age of 145.8±1.0 Ma indicates that the granites were emplaced at the end of the Late Jurassic.Whole-rock geochemical results demonstrate that the Wutang granites are enriched in SiO_(2)(72.80-73.40 wt%)but depleted in CaO(0.44-0.90 wt%)and MgO+TiO_(2)+TFeO(1.79-2.05 wt%).These granites exhibit negative Eu anomalies(δEu=0.3−0.4)and high aluminum saturation indexes(A/CNK=1.2−1.6),differentiation indexes(DI=90-92),and Rb/Sr ratios(4.7-8.1).They also have moderate Ba contents(239-278 ppm)and low Sr contents(52.7-82.0 ppm)as well as low Nb/Ta(2.2-5.3)and Zr/Hf(21.3-31.5)ratios.All these indicate that they are highly fractionated granites.Additionally,these granites contain 5-10 wt%muscovite but no hornblende,with calculated corundum contents of 2.3-5.5 wt%.They have low high-field strength element(HFSE)contents(Zr+Nb+Ce+Y=182-202 ppm)and zircon saturation temperatures(700-770℃),with Th and Y negatively linked with Rb.These petrographic and geochemi-cal features further reveal that the Wutang granites belong to highly fractionated S-type granites.TheεNd(t)values of these granites range from−9.03 to−8.23,corresponding to two-stage model ages(T DM2)of 1488-1553 Ma.The initial Pb isotope ratios are:(206 Pb/^(204)Pb)i=18.38-18.55,(^(207)Pb/^(204)Pb)i=15.67-15.68,and(^(208)Pb/^(204)Pb)i=38.62-38.67.These Nd-Pb isotopic results demonstrate that the parental magma originated from the partial melting of ancient crustal materials.In the meantime,the TBMD in the eastern section of the Jiangnan Orogen was in a compression-extension transitional setting associated with the episodic subduction of the Paleo-Pacific Plate.
基金supported by the Deep Earth Probe and Mineral Resources Exploration-National Science and Technology Major Project(Grant No.2024ZD1001600)National Natural Science Foundation of China(Grants Nos.42302223,42162012 and 42402069)Yunnan Fundamental Research Projects(Grants No.202401CF070093).
文摘The western margin of the Yangtze Block hosts diverse Neoproterozoic igneous rocks,with exposed S-type granites serving as key indicators for deciphering regional geological evolution.This study focuses on the Jiudaowan granite pluton,located on the western margin of the Yangtze Block,through systematic petrographic,whole-rock geochemical,zircon and monazite U-Pb geochronology,and whole-rock Nd isotopic analyses aiming to elucidate its petrogenesis and tectonic significance.The Jiudaowan granite pluton is a composite body,consisting of the Luotaijiu,Jiudaowan,and Daheishan units,characterized by biotite monzogranites,muscovite-plagioclase granites,and two-mica monzogranites,respectively.LA-ICP-MS zircon and monazite U-Pb dating reveals crystallization ages between 832 and 798 Ma.The three units are peraluminous,containing minerals such as muscovite,garnet,and tourma-line,and exhibiting high SiO_(2)(72.99-77.83 wt%),Al_(2)O_(3)(12.36-15.02 wt%),and A/CNK values(1.06-1.43),con-firming their classification as peraluminous S-type granites.Compositional variations within the Jiudaowan granite pluton are primarily controlled by protolith composition and melting mechanisms.The pluton is distinguished by low CaO/Na_(2)O ratios(0.02-0.18),high Rb/Sr(0.83-113)and Rb/Ba(0.33-15.2)ratios,and negativeεNd(t)values(−13.6 to−9.1),indicating derivation from partial melting of het-erogeneous metasedimentary sources.MgO,TiO_(2),Rb/Sr,and whole-rock Zr saturation temperatures suggest that the Luotaijiu and Daheishan units formed via biotite dehydration melting,whereas the Jiudaowan unit resulted from muscovite dehydration melting.Additionally,the Jiudaowan granite pluton displays a clear negative correlation between Al_(2)O_(3),CaO,Fe_(2)O_(3)T,MgO,TiO_(2),and SiO_(2),along with pronounced Eu negative anomalies and depletions in Sr and Ti,suggesting fractional crystallization of feldspar,mica,and Fe-Ti oxides during magma emplacement.Similarly,variable incompatible element ratios of Nb/U(1.07-18.97)and Nb/La(0.24-26.88)further indicate minor crustal assimilation and contamination during magma evolution.Integrating regional geological data,we propose that the Jiudaowan pluton formed during crustal thickening associated with post-collisional extension,likely related to the breakup of the Rodinia supercontinent.
基金funded by the Faculty of Geography under the scheme of“Dana Hibah Penelitian Mandiri Dosen Tahun 2023 Tahap 1”。
文摘Ten rock samples consisting of one pyroclastic density current(PDC1)deposit,seven lava flows(LF1–7),and two summit lava domes(LD1,2)were studied to understand the petrogenesis and magma dynamics at Mt.Sumbing.The stratigraphy is arranged as LF1,PDC1,LF2,LF3,LF4,LF5,LF6,LF7,LD1,and LD2;furthermore,these rocks were divided into two types.TypeⅠ,observed in the oldest(LF1)sample,has poor MgO and high Ba/Nb,Th/Yb and Sr.The remaining samples(PDC1–LD2)represent typeⅡ,characterized by high MgO and low Ba/Nb,Th/Yb and Sr values.We suggest that type I is derived from AOC(altered oceanic crust)-rich melts that underwent significant crustal assimilation,while typeⅡoriginates from mantle-rich melts with less significant crustal assimilation.The early stage of typeⅡmagma(PDC1–LF3)was considered a closed system,evolving basaltic andesite into andesite(55.0–60.2 wt%SiO_(2))with a progressively increasing phenocryst(0.30–0.48φ_(PC))and decreasing crystal size distribution(CSD)slope(from-3.9 to-2.9).The evidence of fluctuating silica and phenocryst contents(between 55.9–59.7 wt%and 0.25–0.41φ_(PC),respectively),coupled with the kinked and steep(from-5.0 to-3.3)CSD curves imply the interchanging condition between open(i.e.,magma mixing)and closed magmatic systems during the middle stage(LF4–LF6).Finally,it underwent to closed system again during the final stage(LF7–LD2)because the magma reached dacitic composition(at most 68.9 wt%SiO_(2))with abundant phenocryst(0.38–0.45φ_(PC))and gentle CSD slope(from-4.1 to-1.2).
基金This study was fi nancially supported by the Youth Science and Technology Talent Recruitment Project of Gansu Province(2022-19)Technological Innovation Project of Gansu Provincial Department of Natural Resources(2022-3,2022-4,2022-28)+2 种基金National Natural Science Foundation of China(Nos.42073059 and 42303034)Outstanding Youth Fund of Anhui Provincial Department of Education(No.2022AH020084)Doctoral Startup Foundation of Suzhou University(2021BSK038)。
文摘The tectonic evolution and crustal accretion process of the North Qilian Orogenic Belt(NQOB)are still under debate because of a lack of integrated constraints,especially the identifi cation of the tectonic transition from arc to initial collision.Here we present results from zircon U-Pb geochronology,whole-rock geochemistry,and Sr-Nd-Pb isotope geochemistry of the Beidaban granites to provide crucial information for geodynamic evolution of NQOB.Zircon U-Pb dating yields an age of 468±10 Ma for the Beidaban granites and most of the Beidaban samples contain amphibole,are potassium-rich,and have A/CNK values ranging from 0.7 to 0.9,illustrating that the Middle Ordovician Beidaban granites are K-rich,metaluminous,calc-alkaline granitoid.The geochemical characteristics indicate that the Beidaban granites are transitional I/S-type granitoids that formed in an arc setting.The isotopic compositions of initial(87 Sr/86 Sr)i values ranging from 0.70545 to 0.71082(0.70842 on average)andεNd(t)values ranging from−10.9 to−6.7(−8.8 on average)with two-stage Nd model ages(T DM2)of 1.74-2.08 Ga suggest that the Beidaban granites originated from Paleoproterozoic crustal materials.In addition,the initial Pb isotopic compositions(^(206)Pb/^(204)Pb=19.14-20.26;^(207)Pb/^(204)Pb=15.71-15.77;^(208)Pb/^(204)Pb=37.70-38.26)and geochemical features,such as high Th/Ta(17.43-30.12)and Rb/Nb(6.01-15.49)values,suggest that the Beidaban granite magma source involved recycled crustal components with igneous rocks.Based on these results in combination with previously published geochronological and geochemical data from other early Paleozoic igneous rocks,we suggest that the timing of the tectonic transition from arc to the initial collision to the fi nal closure of the North Qilian Ocean can be constrained to the Middle-Late Ordovician(ca.468–450 Ma).
基金funded by Gansu Provincial Natural Science Foundation (Grant Numbers 21JR7RA503 and22JR5RA819)the Fundamental Research Funds for the Central Universities (Grant lzujbky-2021-ct07)+1 种基金the Key Talent Project of Gansu Province (2022-Yangzhenxi)the National Second Expedition to the Tibetan Plateau (2019QZKK0704)。
文摘Geodynamic mechanism responsible for the generation of Silurian granitoids and the tectonic evolution of the Qilian orogenic belt remains controversial. In this study, we report the results of zircon U–Pb age, and systematic whole-rock geochemical data for the Haoquangou and Liujiaxia granitoids within the North Qilian orogenic belt and the Qilian Block, respectively, to constrain their petrogenesis, and the Silurian tectonic evolution of the Qilian orogenic belt. Zircon U–Pb ages indicate that the Haoquangou and Liujiaxia intrusions were emplaced at423 ± 3 Ma and 432 ± 4 Ma, respectively. The Haoquangou granodiorites are calc-alkaline, while the Liujiaxia granites belong to the high-K calc-alkaline series.Both are peraluminous in composition and have relatively depleted Nd isotopic [ε_(Nd)(t) =(-3.9 – + 0.6)] characteristics compared with regional basement rocks, implying their derivation from a juvenile lower crust. They show adakitic geochemical characteristics and were generated by partial melting of thickened lower continental crust. Postcollisional extensional regime related to lithospheric delamination was the most likely geodynamic mechanism for the generation of the Haoquangou granodiorite, while the Liujiaxia granites were generated in a compressive setting during continental collision between the Qaidam and Qilian blocks.
基金Supported by the National Key R&D Program of China(No.2016YFC0666108-02).
文摘The Daerlong granitic complex in Linkou area is located at the convergence position of the Jiamusi and Songliao blocks.A systematic study of field geology,petrography,zircon U-Pb dating and wholerock major and trace elements has been conducted for the Daerlong granitic complex,aiming to determine its formation age,petrogenesis and tectonic setting,and further constrain the nature and evolution of the Mudanjiang Ocean.Field and petrographic observations show that the Daerlong granitic complex mainly consists of three rock types from old to young,i.e.,biotite granodiorite,syenogranite and monzogranite.Geochemical data suggest that all the types of granitoids are high in silicon,rich in potassium,moderate in aluminum(A/CNK=0.94-1.10),poor in iron and magnesium,rich in LILEs and depleted in HFSEs,belonging to the weakly peraluminous high-K calc-alkaline series.Combined with mineral assemblages and geochemical discrimination diagrams,it can be determined that the studied granitoids are of igneous crustderived I-type origin,which underwent strong fractional crystallization and crystal accumulation during magmatic evolution.Zircon LA-ICP-MS U-Pb dating results show that the different types of granitoids were emplaced in a wide age range from 301 to 240 Ma,indicating a long-lived Late Carboniferous to Middle Triassic granitic magmatism occurred in the western Jiamusi Block.The Daerlong granitoids have similar geochemical characteristics of subduction-related igneous rocks.Considering the spatial and temporal distribution of Late Paleozoic to Early Mesozoic igneous rocks within eastern Heilongjiang Province,it is concluded that the Daerlong granitic complex was formed in an active continental margin setting rather than a continental rift environment.The results suggest that the Mudanjiang Ocean might not be a limited ocean evolved from the rifting of the unified Jiamusi-Songnen microcontinent.
文摘Early Palaeozoic Cambrian A-type Kathalguri Granites in the Mikir Hills of northeastern (NE) India were studied to better understand the geodynamic settings in this region. This research presents new whole-rock geochemical and Sr, Nd, Pb isotopic data for the Cambrian granites in the Kathalguri Granite in Mikir Hills. The Kathalguri Granite shows geochemical characteristics of high SiO2, K2O and low FeOT, MgO, CaO, and P2O5 compositions. They belong to a high K Shoshonite to ultra-potassic series and display a weak metaluminous to peraluminous feature with A/CNK values of 0.83 to 1.02 with corundum and anorthite normative. FeOT/MgO varies from 2.93 - 7.49, is moderately oxidized and belongs to magnetite series. The rocks have a high ΣREE composition of 370.80 - 1353.23 ppm (average 568.55) and are enriched in LREE with flat HREE and (La/Yb)N values of 8.10 - 18.99, and display obvious strong negative Eu anomalies. Trace elements of the studied granites are characterized by enrichment in Rb, Th, U, Pb, Hf, and Sm, and depletion of Ba, Nb, Ta, and Sr. They display geochemical features of high Zr + Y + Nb + Ce values (241 - 934 ppm) and Ga/Al ratios 2.49 - 3.01 consistent with A-Type granites. Based on particular geochemical features, such as high Rb/Nb (3.10 - 19.53) and Low Y/Nb (0.09 - 2.28), Kathalguri Granite can be further classified as an A1-type subgroup. Granites display relatively low Sr (N ratio varying between 0.53 - 0.89 suggesting that the melts generated at greater depths (18 - 40 km), and fractionation at low pressures (−3 and total HGU 98.96 to 214.20. Kathalguri Granite dated by Rb-Sr isotopic isochrone as 489 ± 19 Ma with an initial 87Sr/86Sr 0.7199 ± 0.0017 and MSWD of 4.1, εSr(I) varied between 161.62 - 332.08 suggests that the Kathalguri Granite have originated from partial melting of ancient, evolved continental crustal material. The Sm-Nd Systematics has given a depleted mantle model (TDM) age ranging from 1733 - 2063 Ma with high negative εNd(t) values (−10.39 to −15.18) also hint at some heterogeneity or multiple source contributions in the melting process of the protolith. Xenoliths of older mafic rocks and Barapani arenites are seen within the Kathalguri Granite and are also supported by geochemical signatures of recycled crustal materials both mafic and sedimentary. It formed during the Cambrian reorganization of lithospheric plate motion related to the Pan-African-Braziliano event.
基金Project(41202051)supported by the National Natural Science Foundation of ChinaProject([2014]76)supported by the Platform of Scientific and Technological Innovation for Hunan Youth,China+1 种基金Project(2014T70886)supported by the Special Program of the Postdoctoral Science Foundation of ChinaProject(2012M521721)supported by China Postdoctoral Science Foundation
文摘The major element, trace element and rare earth element（REE） of the intrusion rock from the Dachang ore field in Guangxi, China, were analyzed. The results show that the phenocryst（about 15%） and matrix（about 85%） mainly consist of quartz, K-feldspar and plagioclase. The rock is composed of low content of Si and high content of Al2O3, low contents of Ca, Fe2O3, Na, TiO2, etc. The intrusion rock has the medium alkali content, attributing to K-rich type rock; and contains medium to low REE contents, of which light rare earth elements（LREEs） and heavy rare earth elements（HREEs） are highly fractionated, showing a weak negative Ce anomaly and a negative Eu anomaly. These rocks are enriched in LREE, and the large ion lithophytes elements（LILE） are rich in Rb, Sr, and U; the high-field-strength elements（Nb, Th, etc） are relatively depleted. The REE chondrite-normalized patterns are consistent with the overall, roughly indicating their similar characteristics, sources and evolution. The intrusion rock mainly formed during the collisional and within-plate periods.
基金Project(41202051)supported by the National Natural Science Foundation of ChinaProject(2015CX008)supported by the Innovation-driven Plan in Central South University,China+4 种基金Project(2016JJ1022)supported by Hunan Provincial Natural Science Outstanding Youth Foundation of ChinaProject(CSUZC201601)supported by the Open-end Fund for the Valuable and Precision Instruments of Central South University,ChinaProject(2014T70886)supported by the Special Program of the Postdoctoral Science Foundation of ChinaProject(2012M521721)supported by China Postdoctoral Science FoundationProject(XKRZ[2014]76)supported by the Platform of Scientific and Technological Innovation for Hunan Youth,China
文摘Skarn is the main altered rock type and is of great importance to mineralization and ore-prospecting in the Shizhuyuan area of Hunan province, China. Its features of petrography, mineralogy and geochemistry were studied systematically. The results show that the skarn mainly consists of garnet skarn, secondary wollastonite-garnet skarn, tremolite-clinozoisite skarn, and few wolframine garnet skarn, idocrase-garnet skarn and wollastonite skarn with granoblastic texture, granular sheet crystalloblastic texture, and massive structure, disseminated structure, mesh-vein structure, comb structure, and banded structure. And, it is mainly composed of garnet, fluorite, chlorite, hornblende, epidote, tremolite, plagioclase, biotite, muscovite, plagioclase, quartz, idocrase, and calcite and so on. The chemical components mainly include SiO2, Al2O3, Fe2O3, MgO and CaO, and the trace elements and REEs consist of Li, Be, V, Co, Zn, Ga, Rb, Sr, Y, Ce, Nd, Pb and Bi, etc. And, the obvious fractionation exists between LREE and HREE, and it shows typical features of Nanling ore-forming granite for W？Sn polymetallic deposit. Skarn is derived from the sedimentary rock, such as limestone, mudstone, argillaceous rock, and few pelitic strips. It is affected by both Shetianqiao formation strata and Qianlishan granite during the diagenesis, indicating a strong reduction environment. The occurrence of skarn, whose mutation site is favorable to the mineralization enrichment, is closely related to the mineralization and prospecting.
文摘The Indosinian post-collisional Wulong pluton intruded into the Mesoproterozoic Fuping Group, South Qinling, central China. In the southern part of the pluton, some mafic enclaves have sharp or gradational contact relationships with the host biotite granodiorite. Geochemistry, zircon LA-ICP MS （laser ablation inductively-coupled plasma mass spectrometry） U-Pb chronology and Sr- Nd-Pb isotope geochemistry of the pluton are reported in this paper. The biotite granodiorite shows close compositional similarities to high-silica adakite. Its chondrite-normalized REE patterns are characterized by strong HREE depletion （Yb = 0.33--0.96 10-6 and Y = 4.77-11.19 ×10^-6）, enrichment of Ba （775-1386 x 10-6） and Sr （643-1115 × 10^-6） and high Sr/Y （57.83-159.99） and Y/Yb （10.99-14.32） ratios, as well as insignificant Eu anomalies （6Eu = 0.70-0.83）, suggesting a feldspar-poor, garnet±amphibole-rich residual mineral assemblage. The mafic enclaves have higher MgO （4.15- 8.13%）, Cr （14.79-371.31 × 10-6）, Ni （20.00-224.24× 10^-6） and Nb/Ta （15.42-21.91） than the host granodiorite, implying that they are mantle-derived and might represent underplated mafic magma. Zircon LA-ICP MS dating of the granodiorite yields a ^206pb/^238U weighted mean age of 208±2 Ma （MSWD=0.50, 1σ）, which is the age of emplacement of the host biotite granodiorite. This age indicates that the Wulong pluton formed during the late-orogenic or post-collisional stage （〈242±21 Ma） of the South Qinling belt. The host biotite granodiorite displays ^87Sr/^86Sr = 0.7059-0.7062, Isr = 0.7044-- 0.7050,^143Nd/^144Nd = 0.51236-0.51238, εNd（t）= -2.26 to -2.66 to ^206Pb/^204pb = 18.099-18.209, ^207pb/^204pb = 15.873-15.979 and ^208pb/^204pb = 38.973-39.430. Those ratios are similar to those of the Mesoproterozoic Yaolinghe Group in the South Qinling. Furthermore, its Nd isotopic model age （-1.02 Ga） is consistent with the age （-1.1 Ga） of the Yaolinghe Group. Based on the integrated geological and geochemical studies, coupled with previous studies, the authors suggest that the Wulong adakitic biotite granodiorite was probably generated by dehydration melting of the Yaolinghe Group-like thickened mafic crust, triggered by underplating of mafic magma at the boundary of the thickened mafic crust and hot lithospheric mantle, and that the Wulong adakitic biotite granodiorite may have resulted from thinning and delamination of the lower crust or breakoff of the subducting slab of the Mianlue ocean during the Indosinian post-collisional orogenic stage of the Qinling orogenic belt.
基金provided by the National Scientific and Tecnological Support Program of China(Grant No:2006BAB01A11)
文摘South Qinling Tectonic Belt（SQTB）is located between the Shangzhou-Danfeng and Mianxian-Lueyang sutures.There are a lot of early Mesozoic granitoid plutons in its middle segment, comprising the Dongjiangkou-Zhashui granitoid plutons at the northeast,Huayang-Wulong-Laocheng granitoid plutons at the central part,Xiba granitoid pluton at the northwest and Guangtoushan-Liuba granitoid plutons at the southwest.These Indonisian granitoids contain a mass of various scale mafic enclaves,which show sometimes clear boundaries and sometimes transitional boundaries with their host granitoids.These granitoids also exhibit metaluminous to peraluminous series,commonly higher Mg# and a wide range of petrochemistry from low-K tholeiite series,through mid-K and high-K calc-alkaline series to shoshonite series and predominated samples are attributed to mid-K and high-K calc-alkaline series.Detailed analyses in Sr-Nd isotopic systematics and petrochemistry reveal that there may be regionally initial granitoid magma of the Indonisian granitoid plutons,comprising Dongjiangkou-Zhashui,Huayang-Wulong-Laocheng,Xiba,and Guangtoushan-Liuba granitoid plutons,which were produced by hybrids of magmas in various degrees,and the initial magmas were derived from both the mantle and the lower continental crust（LCC）sources in the SQTB.The initial granitoid magma further did the magma hybrid with the magmas from the LCC,crystallization fractionation,and assimilation with upper crustal materials during their emplacement to produce these granitoid plutons in the SQTB.These magmatism processes are most likely to occur under continent marginal arc and syn-collision to post-collision tectonic backgrounds.
基金granted by the foundamental research funds for central public welfare research institutes(Grant No.K1313)the Natural Sciences Foundation of China(Grant No.41302080)China State Geological Investigation Program(Grant No.1212011121091,12120114009401)
文摘The Xuhe mafic rocks, located in Ziyang county of Shaanxi Province, are dominated by diabase-porphyrite, gabbro-diabase, diabase, and pyroxene diorite. Primitive mantle-normalized multi-element patterns show that, the Xuhe marie rocks are enriched in large ion lithophile elements （LITE）, such as Ba and Pb, depleted in K and Sr for basic rocks, and are depleted in Sr, P and Ti for pyroxene diorite. Chondrite-normalized REE patterns display LREE enrichment （LaN/YbN = 9.34- 13.99） and have normalized patterns for trace element and REE similar to that of typical OIB. Detailed SIMS zircon U-Pb dating yields emplacement ages of 438.4 ± 3.1 Ma for Xuhe mafic rocks. The relatively low MgO （basic rock： 3.11-7.21 wt%; pyroxene diorite： 0.89-1.21 wt% ） and Mg# （0.20- 0.49） for Xuhe mafic rocks suggest that they were possibly originated from an extremely evolved magma. The rising parental mafic magmas underwent pyroxene and plagioclase fractionation. Crustal contamination of pyroxene diorite before emplacement occurred at a higher crustal level compared to other lithology in Xuhe mafic rocks. The degree of partial melt was low （5%-10%） and in garnetspinel transition facies. Sr-Nd isotope of pyroxene diorite and enrichment mantle characteristics for Xuhe mafic rocks suggest that mafic rocks in the North Daba Mountains were derived from a mixture of HIMU, EMII and small amount of EMI components. Furthermore, this study discusses mantle geodynamic significance of Xuhe mafic rocks in the Silurian, which indicates subduction and uplift of magma caused back-arc extension.
基金supported by the National Key Basic Research Program(2012CB416700,2007CB411408),a special fund managed by the State Key Laboratory of Ore Deposit Geochemistry,Institute of Geochemistry,Chinese Academy of Sciences,and the State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences in Wuhan
文摘Mesozoic granitic intrusions are widely distributed in the Nanling region, South China. Yanshanian granites are closely connected with the formation of tungsten deposits. The Xihuashan granite is a typical representative of tungsten-bearing granite. The Xihuashan granite consists mainly of medium-grained porphyritic biotite granite, medium-grained biotite granite and fine-grained twomica granite, which correspond to LA-ICP-MS zircon U-Pb ages of 555.5±0.4 Ma, 553.0±0.6 Ma and 552.8±0.9 Ma, respectively. Rocks from the Xihuashan mining area displays high SlOe （73.85% to 76.49%） and NaeO＋K20 contents （8.09% to 9.43%）, belonging to high-K calc-alkaline series. They are metaluminous to weakly peraluminous with A/CNK values ranging from 0.96 to 5.06. All granites in this study area are rich in Rb, Th, U and Pb, and depleted in Ba, Sr, P, Ti, Nb and Eu, especially depleted in medium-grained biotite granite and fine-grained two-mica granite. The medium-grained porphyritic biotite granites usually have high LREE concentrations, whereas medium-grained biotite granite and fine-grained two-mica granite displays high HREE contents. Our geochemical data reveal that the studied rocks are highly fractionated I-type granite. The magma underwent strong magma differentiation with decreasing temperature and increasing oxygen fugacity, which may explain the formation of three types of distinct granites. Variations of Rb, Sr and Ba concentrations in different type granites were controlled by fractional crystallization of biotite and feldspar. Fractional crystallization of monazite, allanite and apatite resulted in LREE changes in granite, and formation of garnet mainly caused HREE changes. Granites from the Xihuashan mining area have relatively high εd（t） values （-9.77 to -55.46）, indicating that they were probably generated by partial melting of underlying Proterozoic metasedimentary rocks with minor addition of juvenile crust or mantlederived magmas.
基金support forthis study was provided by the National Natural ScienceFoundation of China(No.:40821002,40872120,40420120135,40472096,and 40472118)
文摘The Paleoproterozoic Liiliang Metamorphic Complex （PLMC） is situated in the middle segment of the western margin of the Trans-North China Orogen （TNCO）, North China Craton （NCC）. As the most important lithological assemblages in the southern part of the PLMC, Guandishan granitoids consist of early gneissic tonalities, granodiorites and gneissic monzogranites, and younger gneissic to massive monzogranites. Petrochemical features reveal that the early gneissic tonalities and granodiorites belong to the medium-K calc-alkaline series; the early gneissic monzogranites are transitional from high-K calc-alkaline to the shoshonite series; the younger gneissic to massive monzogranites belong to the high-k calc-alkaline series, and all rocks are characterized by right- declined REE patterns and negative Nb, Ta, Sr, P, and Ti anomalies in the primitive mantle normalized spidergrams. SHRIMP zircon U-Pb isotopic dating reveals that the early gneissic tonalities and granodiorites formed at -2.17 Ga, the early gneissic monzogranites at -2.06 Ga, and the younger gneissic to massive monzogranites at -1.84 Ga. Sm-Nd isotopic data show that the early gneissic tonalities and granodiorites have eNd（t） values of ＋0.48 to -3.19 with Nd-depleted mantle model ages （TDM） of 2.76--2.47 Ga, and early gneissic monzogranites have eNd（t） values of -0.53 to -2.51 with TDM of 2.61--2.43 Ga, and the younger gneissic monzogranites have eNd（t） values of -6.41 to -2.78 with a TDM of 2.69--2.52 Ga.These geochemical and isotopic data indicate that the early gneissic tonalities, granodiorites, and monzogranites were derived from the partial melting of metamorphosed basaltic and pelitic rocks, respectively, in a continental arc setting. The younger gneissic to massive monzogranites were derived by partial melting of metamorphosed greywackes within the continental crust. Combined with previously regional data, we suggest that the Paleoproterozoic granitoid magmatism in the Guandishan granitoids of the PLMC may provide the best geological signature for the complete spectrum of Paleoproterozoic geodynamic processes in the Trans-North China Orogen from oceanic subduction, through collisional orogenesis, to post-orogenic extension and uplift.
