Basalts from the Late Carboniferous to Early Permian are extensively developed in the central Lhasa subterrane,southern Xizang.Studying the petrogenesis of these rocks may have implications for the late Paleozoic arc ...Basalts from the Late Carboniferous to Early Permian are extensively developed in the central Lhasa subterrane,southern Xizang.Studying the petrogenesis of these rocks may have implications for the late Paleozoic arc magmatism along the central Lhasa subterrane uncovering more of the evolution of the Sumdo Paleo-Tethys Ocean and its dynamic mechanism.Basalt samples from the Luobadui Formation in the Leqingla area,NW of Linzhou City in the central Lhasa subterrane,southern Xizang exhibit arc-like geochemical signatures in a subduction-zone tectonic setting characterized by high Al_(2)O_(3)and low TiO_(2)contents,fractionated REE patterns with low Nb/La ratios and high LREE concentrations,and negative HFSE anomalies.Based on their higher Th/Ce,Nb/Zr,and lower Ba/Th,Pb/Nd ratios,slightly negative to positiveε_(Nd)(t)values,and the relatively high Sr-Pb isotopic compositions,these samples were probably derived from partial melting of a depleted mantle source of garnet+spinel lherzolite,metasomatized by subducted sediments around 297 Ma.Modeling of the trace elements indicates that these basalts experienced fractional crystallization of olivine,clinopyroxene and minor plagioclase during magma ascent and eruption.It is proposed that these Late Carboniferous–Early Permian basalts are associated with the northward subduction of the Sumdo Paleo-Tethys Ocean seafloor along the southern margin of the central Lhasa subterrane.展开更多
Feldspar Pb isotopes have been widely used to trace magmatic formation and evolution processes.However,it remains unclear whether post-magmatic thermal events can affect feldspar Pb isotopic ratios.Here,the in situ Pb...Feldspar Pb isotopes have been widely used to trace magmatic formation and evolution processes.However,it remains unclear whether post-magmatic thermal events can affect feldspar Pb isotopic ratios.Here,the in situ Pb isotopic composition of feldspar hosted in granitic rocks(thirteen Archean and one Paleoproterozoic)from the northern Kongling terrane,Yangtze Craton,South China,is analyzed.The samples reveal a substantial variation in their Pb isotopic composition,spanning the gap between the 1.9 Ga and present-day geochrons,which indicates extensive resetting by later tectonothermal events.This resetting was interpreted to have likely resulted from Paleoproterozoic and Neoproterozoic tectonothermal events related to the assembly and breakup of the Columbia and Rodinia supercontinents.These results suggest that Pb isotopes should be used cautiously when tracing magma sources and petrogenesis in magmatic rocks that have experienced post-magmatic reworking.However,the in situ Pb isotopic composition of feldspar in ancient granitoids may also potentially be used to reveal later tectonothermal events.The extensive resetting of the Pb isotopic composition in feldspar by regional thermal events may also provide new insights into our understanding of the Pb isotope paradox.展开更多
The Southern Granulite Terrane(SGT),the wedgeshaped southern termination of Peninsular India,is a mosaic of several crustal blocks and intervening collisional sutures/shears which developed through multiple orogenic c...The Southern Granulite Terrane(SGT),the wedgeshaped southern termination of Peninsular India,is a mosaic of several crustal blocks and intervening collisional sutures/shears which developed through multiple orogenic cycles during Mesoarchean to late Neoproterozoic-Cambrian.The SGT has been the focus of global geoscience world for more than four decades mainly with regard to deep crustal processes,crustmantle architecture,polyphase structural evolution,extreme crustal metamorphism,growth and recycling of continental crust,and the assembly-evolution-disruption of supercontinents through time,among other aspects.展开更多
Based on geological, chronological, geochemical and Nd isotopic studies of the high-grade basement of the Qilian terrane, the authors have drawn the following main conclusions: (1) the high-grade basement of the Qilia...Based on geological, chronological, geochemical and Nd isotopic studies of the high-grade basement of the Qilian terrane, the authors have drawn the following main conclusions: (1) the high-grade basement of the Qilian terrane consists mainly of meta-argillo-arenaceous rocks and granites and its bulk part was formed in the period of 0.8–1.0 Ga (the Jinningian period); (2) most of the meta-argillo-arenaceous rocks and granitic rocks have strong negative Eu and Ba anomalies (Eu/Eu*= 0.47–0.71 and Ba/Ba*=0.16–0.64), with fDM and ENd (1.0 Ga) ranging from 1.87 to 2.26 Ga and from ?8.54 to ?4.06 respectively, showing relatively high maturity; and (3) the Jinningian granitic rocks are a typical product of continent-continent collision, being probably related to the formation of the supercontinent Rodinia. These studies, combined with the study of high-grade basement rocks near the Qilian terrane, suggest that before the Jinningian period, the Qilian-Qaidam northern-margin terrane and Dunhuang-Alxa terrane were separated from each other, belonging to different plate systems of the North China craton and Yangtze platform respectively. The Qilian orogenic belt was the same as or similar to the Qiling orogenic belt in terms of the geological evolution history at least before the Jinningian period.展开更多
The Bikou volcanic terrane is predominated by subalkaline tholeiitic lavas. Rock samples display lower initial ratios of Sr and Nd, 0.701248-0.704413 and 0.511080-0.512341 respectively. 207Pb and 208Pb are significant...The Bikou volcanic terrane is predominated by subalkaline tholeiitic lavas. Rock samples display lower initial ratios of Sr and Nd, 0.701248-0.704413 and 0.511080-0.512341 respectively. 207Pb and 208Pb are significantly enriched in the lavas. Most samples have positive εNd, which indicates that the magma was derived from EM-type mantle source, while a few samples with negative εNd indicate that there was contamination in the magma evolution. Magma differentiation is demonstrated by variations of LREE and LILE from depletion to enrichment. Additionally, normalized REE patterns and trace elements showed that lavas from the Bikou volcanic terrane have similar characteristics to those of basalts in arc settings caused by subduction and collision. Analyses showed that the Bikou volcanic terrane is a volcanic arc. New evidence proved that the Hengdan Group, north of the Bikou arc, is a turbidite terrane filling a forearc basin. Consequently, the Bikou volcanic terrane and the Hengdan turbidite terrane construct an arc-basin system. New SHRIMP ages showed that this arc-basin system developed on the northern margin of the Yangtze craton in the Neoproterozoic (846-776 Ma), and this arc-basin system is in agreement with the tectonic processes of Rodinia in the Neoproterzoic.展开更多
The paper presents an overview of the relationships between the interior structures of tectonic terranes and the distribution of tectonic-metallogenic zones in Southeast Asia. Episodic tectonic activities occurred in ...The paper presents an overview of the relationships between the interior structures of tectonic terranes and the distribution of tectonic-metallogenic zones in Southeast Asia. Episodic tectonic activities occurred in this archipelagic area, generating metallogenic belts in multi-terranes. Since the Late Paleozoic, opening and closure of the Paleotethys and Neotethys led to multiple suture zones between different blocks, mainly between the Indochina terrane, the Nambung terrane, the Sibumasu terrane and the West Myanmar terrane. During the Mesozoic to Cenozoic, the formation of accreted terranes and their related islands was caused by subduction and collision processes between the Pacific and Australian plates toward the Eurasian Continent, forming Sundaland and its affiliated islands, the Philippines and its subsidiary islands, the Papua New Guinea terrane and its related islands and the Sunda epicontinental arc system. Within the margin of terranes resulted in the structural transfer zones, their secondary tectonic units can be divided into island arc belts, back-arc basins, suture zones, marginal fold belts and orogenic belts. The metallogenic assemblages are mainly distributed within these structural zones of the terranes. According to the relationship between these tectonic units and the distribution of mineral resources, the tectonic-metallogenic belts can be divided into 24 metallogenic belts in Southeast Asia. They are characterized by a diversity and frequency of metallogenic material combination which is likely to reflect the complexity of the material distribution during mineralization processes, mostly by the structural transformation during the dissociation-convergence process between multiple terranes. Therefore, the formation of ore deposits was not only restricted by the evolution(opening and closure) of Paleo-and Neotethys, but may also be controlled by the interaction of the terranes with different tectonic attributes which provided multiple sources of metallogenic material.展开更多
Petrological analysis and LA-ICP-MS zircon U-Pb dating were conducted on high- pressure marie granulites, which occured as xenolith within TTG gneisses, from the Nanshankou Village of the Jiaobei terrane, Shandong Pen...Petrological analysis and LA-ICP-MS zircon U-Pb dating were conducted on high- pressure marie granulites, which occured as xenolith within TTG gneisses, from the Nanshankou Village of the Jiaobei terrane, Shandong Peninsula in the north-eastern part of the North China Craton （NCC）. The mafic HP grannlite is composed of garnet, clinopyroxene, orthopyroxene, amphibole and symplectitic clinopyroxene, orthopyroxene, plagioclase, ilmente and magnetite which were formed after the decomposition of porphyroblastic garnet and clinopyroxene. Four stages of metamorphic mineral assemblages for the mafic HP granulites were constrained by detail petrological and mineralogical in- vestigations. The early prograde assemblage is represented by the mineral inclusions within garnet and clinopyroxene porphyroblasts （Opx1＋Pl1＋Qtz1）, recording the metamorphic conditions at -754-757 ℃, 0.63-0.71 GPa; peak metamorphic conditions were determined at -874-891 ℃, 1.32-1.35 GPa with the mineral assemblage of Grt2＋Cpx2＋Amp2＋Pl2＋Qtz2. Retrograde minerals derived from symplectitic assemblage Opx3＋Cpx3＋Amp3＋Pl3＋Qtz3＋Ilm3±Mag3 were formed at 693-796℃, 0.60-0.84 GPa. A final greensehist to sub-greenschist facies event was recorded by the exsolution of actinolite and albite within a retrograded clinopyroxene, as well as the occurrence of prehnite, chlorite and calcite minerals. Accordingly, a clockwise P-T path was concluded on the basis of the different stages of mineral asseblage. Cathodoluminescence imaging, trace element and U-Pb dating of zircons from the mafic HP granulites recorded similar charactistics for three episodes of Paleo-Meso Proterozoic metamorphic events. These are the metamorphic events preserved in mafic and pelitic granulites in the Jiao-Liao-Ji belt （JLJB） with 207 pb/206pb ages of 2.0-1.9 Ga for peak metamorphism and of 1.86-1.84 Ga for decomposing process, followed by a retrograde amphibolite facies metamorphic event related to the post-orogenic extension at the age of 1.76-1.74 Ga, resulting the exhumation of the granulite to the upper crust level.展开更多
The plate affiliation of the North Dabie terrane （NDT） has been controversial. To address this fundamental question, an integrated study of internal structure, in-situ U-Pb dating and trace element analysis in zirco...The plate affiliation of the North Dabie terrane （NDT） has been controversial. To address this fundamental question, an integrated study of internal structure, in-situ U-Pb dating and trace element analysis in zircons and field investigation for migmatite in the NDT was carried out, which reveals par- ticipation of crustal rocks of the North China Craton （NCC） in the protolith in addition to the more common crustal rocks of the Yangtze Craton （YC）. The evidence of an NCC affinity for protolith of migmatite in the NDT is the -2.5 Ga （2 486±14 and 2 406±26 Ma） magamtic age and -1.8 Ga （1 717±79 Ma） metamorphic age in the relict zircon domains because these two age groups are characteristic for the evolution of the NCC. The evidence of a YC affinity for protolith of migmatite in the NDT is the more common 0.7-0.8 Ga （e.g., 787±12 Ma） magamtic zircon age. Mid-Neoproterozoic magmatic age （0.7-0.8 Ga） is a symbol of YC basement rocks. In view of the widely exposed YC crustal components in the NDT, we suggest that the protolith of the NDT is mainly crustal rocks from the YC with minor crustal components from the NCC. The zircon rim domains and new growth grains from all the migmatite sam- ples are characterized by anatectic zircons and have a widely concordant ages ranging from 112.2±2.8 to 159.6±4.3 Ma with several peak values, suggesting a long lasting multistage anatexis. In conclusion, the NDT has a mixed protolith origin of both the YC and the NCC crustal rocks were strongly remoulded by anatexis during orogenic collapse.展开更多
: The 3He/4He ratios of most eclogites from the Dabie-Sulu terrane range from 0.056 to 0.67 Ra; the data points fall into the mixing part of the crust and the mantle in the 3He-4He diagram. The 3He/4He ratios of eclog...: The 3He/4He ratios of most eclogites from the Dabie-Sulu terrane range from 0.056 to 0.67 Ra; the data points fall into the mixing part of the crust and the mantle in the 3He-4He diagram. The 3He/4He ratios of eclogites are obviously correlated with the types of their surrounding rocks. The helium isotope composition of the eclogites from the Bixiling complex possesses characters of mantle-derived rocks with the 3He/4He ratio being 5.6 Ra. The 4He concentration of the eclogites exhibits visible inverse correlation with the δ18O value of the quartz in the eclogites from the Sulu area. The δ18O values of the eclogites change synchronously with those of the country rocks. Those results suggest that protoliths of the eclogites were basic-ultrabasic rock bodies or veins intruding into the continental crust in the early stage; strong exchange and hybridization between the basic-ultrabasic rocks and continental rocks and the atmospheric water during the intrusion led to abrupt increase of the 3He/4He ratios, δ18O values and Nd(0) values of the intrusive bodies or veins, which show characters of continental rocks. This indicates that the eclogites are autochthonous.展开更多
The southern Lhasa Terrane is famous for its huge magmatic belt which records the magmatism during Mesozoic and Cenozoic. Although the Mesozoic continental-margin setting in the southern Lhasa Terrane has been identif...The southern Lhasa Terrane is famous for its huge magmatic belt which records the magmatism during Mesozoic and Cenozoic. Although the Mesozoic continental-margin setting in the southern Lhasa Terrane has been identified, details of this tectonic setting and the evolution history during the Late Cretaceous remain unclear. To further constrain these issues, we present zircon LA-ICP-MS U-Pb, Hf isotopic and geochemical data of the Gongbari dacites （of the Sangri Group） which intruded by Paleocene granodiorites from the eastern part of the southern Lhasa Terrane, Tibet. New age data indicate that the dacites were generated at -95.4 Ma, which suggests the Sangri Group volcanism may last to Late Cretaceous. The Gongbari dacites are characterized by high Sr （428-758 ppm） contents, low concentration of heavy rare earth elements and Y （e.g. Yb=0.78-1.14 ppm; Y=8.85-11.4 ppm） with high Sr/Y （41.91-67.59） and La/Yb （22.64-30.64） ratios, similar to those of adakite. The rocks are calc-alkaline, metaluminous, enriched in LILEs, depleted in HFSEs, and have positive tar（t） values （＋7.7 to ＋11.6）. The Gongbari dacites were probably produced by partial melting of young and hot subducted Neo- Tethyan oceanic crust under amphibolite to garnet amphibolite-facies conditions. Though the Gangdese Mountains may have formed before Indo-Asian collision, the southern margin of Lhasa Terrane might not go through obviously crustal thickening during the northward subduction of Neo-Tethyan oceanic lithosphere.展开更多
Muscovite 40 Ar-39 Ar dating of muscovite-quartz schist, eclogite and retrograde eclogite indicates an Indosinian orogenesis occurred at 220-240 Ma in the Lhasa terrane, which is caused by the closure of Paleo-Tethyan...Muscovite 40 Ar-39 Ar dating of muscovite-quartz schist, eclogite and retrograde eclogite indicates an Indosinian orogenesis occurred at 220-240 Ma in the Lhasa terrane, which is caused by the closure of Paleo-Tethyan ocean basin and the following collision of the northern Lhasa terrane and southern Gondwana land. This Indosinian orogenesis is further confirmed by the regional sedimentary characteristics, magmatic activity and ophiolite mélange. This evidence suggests that the Indosinian orogenic belt in the Lhasa terrane is widely distributed from the Coqen county in the west, and then extends eastward through the Ningzhong and Sumdo area, finally turning around the eastern Himalayan syntaxis into the Bomi county. Based on the evolutionary process, the geological development of Lhasa terrane from early Paleozoic to early Mesozoic can be divided into seven stages. All of the seven stages make up a whole Wilson circle and reveal a perfect evolutionary process of the Paleo-Tethys ocean between the northern Lhasa terrane and southern Gondwana land. The Indosinian orogenisis is a significant event for the evolution of the Lhasa terrane as well as the Tibetan Plateau.展开更多
Several Cretaceous Carlin-like or hydrothermal gold deposits along the Garze-Litang suture zone and Early Cretaceous hydrothermal copper mineralization along the southeastern margin of the Songpan-Garze fold belt were...Several Cretaceous Carlin-like or hydrothermal gold deposits along the Garze-Litang suture zone and Early Cretaceous hydrothermal copper mineralization along the southeastern margin of the Songpan-Garze fold belt were presumed to have a magmatic heat source. However, no actual coeval mag- matic events nearby were discovered. Here, we report zircon SIMS U-Pb age, whole-rock geochemical and Sr-Nd isotopic data of the Xiqiu basalts in the southern end of the Yidun terrane, eastern Tibetan Plateau. New zircon U-Pb ages yield weighted mean ^206pb/^238U age of 117.7±1.6 Ma. The basalts are classified as calc-alkaline to alkaline and have relatively high MgO （4.77 wt.%-10.84 wt.%） and Mg number values （Mg^#=（100×Mg/（Mg＋Fe^2＋））; 45.35-67.28） and positive εNd（t） （t=118 Ma） values （＋1.86 to ＋3.2）, suggesting a OIB-like mantle source that is consistent with the normalized patterns of trace elements and rare earth elements （REEs）. Geochemical data suggest that the primary basaltic magma was generated by low degree partial melting of a heterogeneous source of peridotite-dominated with a minor component of garnet- eclogite or pyroxenite and experienced olivine＋clinopyroxene dominated fractional crystallization. The primary melt compositions calculated from the high MgO samples, in turn, suggest that the Xiqiu basalts were generated at 1.6-2.9 GPa with abnormally hot mantle potential temperatures from 1 465 to 1 540℃. The melting temperatures are similar to the abnormally hot mantle underneath the Colorado Plateau and hotter than the mid-ocean range basalt （MORB） mantle and normal intra-continental mantle. Combined with previous studies, the Cretaceous Xiqiu basalts allow us to reconstruct a tectonic and geodynamic evolution- ary model responsible for the Late Jurassic to Late Cretaceous geological records （magmatism, ore deposits and enhanced exhumation） in the Yidun terrane and southern Songpan-Garze fold belt.展开更多
The nature and evolution of the Proto-Tethys Ocean originated from the breakup of the supercontinent Rodinia remain controversial. Early Paleozoic magmatism and metamorphism can pro- vide important constraints on the ...The nature and evolution of the Proto-Tethys Ocean originated from the breakup of the supercontinent Rodinia remain controversial. Early Paleozoic magmatism and metamorphism can pro- vide important constraints on the closure of the Proto-Tethys Ocean. This paper reports on a set of geological, petrographical, geochronological, mineralogical and geochemical data for Early Paleozoic granite, gabbro, granulite and granitic leucosome in the northern Wulan terrane of the Quanji Massif. Zircon LA-ICP-MS U-Pb dating reveals two episodes of magmatism, with the emplacement of a gran- itic pluton at 476.7±2.8 Ma and a gabbroic dike at 423±2 Ma. Whole-rock geochemistry suggests an arc affinity for the magma of the granitic pluton but a post-collisional extension setting for the gabbroic dike. Zircon LA-ICP-MS U-Pb dating also shows that the peak granulite-facies metamorphism and anatexis occurred at --475 Ma, coeval with the formation of the granitic pluton in the Quanji Massif as well as the early lawsonite-bearing eclogites in the North Qaidam high-pressure and ultrahigh-pressure (HP-UHP) metamorphic belt to the south. The granulite-facies metamorphism with peak P-T condi- tions at 718-729 ℃ and 0.46-0.53 GPa is characterized by an anticlockwise P-T path. Our data provide compelling evidence for Early Paleozoic paired metamorphic belts with HP-UHP metamorphism in the North Qaidam to the south and low PIT metamorphism in the Quanji Massif as a continental arc to the north, hence suggesting a northward subduction polarity for the Proto-Tethys oceanic plate. The intrusion of the post-collisional gabbroic dike supports for the closure of the Proto-Tethys Ocean in north- western China before 423 Ma.展开更多
The granulitized eclogites from the Luliangshan terrane of the North Qaidam UHP metamorphic belt occur as lenses within pelitic gneisses and orthogneisses. Combined petrologic data and phase equilibrium modeling indic...The granulitized eclogites from the Luliangshan terrane of the North Qaidam UHP metamorphic belt occur as lenses within pelitic gneisses and orthogneisses. Combined petrologic data and phase equilibrium modeling indicate a multi-stage metamorphic history of the granulitized eclogites:(1) an earlier eclogite facies metamorphism(P>18.5 kbar, T> 830℃) is deduced from omphacite relics in the matrix and rare omphacite inclusions within garnet. The possible assemblage is garnet+omphacite+rutile+ quartz;(2) the early stage of high pressure granulite facies assemblages(garnet+clinopyroxene+ plagioclase+rutile+quartz+liquid) developed in the early decompression process has a P-T regime of 17.5 kbar and 852–858 ℃, constrained by plagioclase and clinopyroxene inclusions in garnet. The late stage of high pressure granulite assemblages(garnet+clinopyroxene+amphibole+plagioclase+rutile+quartz+liquid) records an isothermal decompression process with the pressure successively declining from 17.5 to 14.7 kbar and to 11.3 kbar at 858 ℃;(3) the later medium pressure granulite facies assemblage(garnet+ orthopyroxene+clinopyroxene+amphibole+plagioclase+ilmenite+liquid+quartz) indicates a drop in pressure and rise in temperature at P-T conditions of 7.6–7.7 kbar and 878–883 ℃;(4) retrogressive amphibolite facies stage, which is represented by amphibole+plagioclase kelyphitic rims around garnet, formed under conditions of <5 kbar and <650 ℃. The preservation of medium pressure granulite facies assemblage and the garnet composition feature constrain a following isobaric cooling path during late exhumation. This process suggests a clockwise P-T path and indicates that the granulitized eclogites record a high grade "Barrovian" metamorphic overprint at the middle-lower crust during exhumation. The present data show that the Luliangshan terrane is a "hot" HP-UHP terrane.展开更多
The late Neoarchean metamorphosed volcanic rocks in the southern Liaoning Terrane(SLT) of the eastern North China Craton(NCC) are mainly composed of amphibolites and felsic gneisses and can be chemically classified as...The late Neoarchean metamorphosed volcanic rocks in the southern Liaoning Terrane(SLT) of the eastern North China Craton(NCC) are mainly composed of amphibolites and felsic gneisses and can be chemically classified as basalt(Group#1),basaltic andesite(Group#2),dacite(Group#3) and rhyodacite(Group#4).LA-ICP-MS zircon U-Th-Pb dating reveals that they formed at ~2.53-2.51 Ga.Group#1 samples are characterized by approximately flat chondrite-normalized rare earth element(REE) patterns with low(La/Yb)_N ratios and a narrow range of(Hf/Sm)N ratios,and their magmatic precursors were generated by partial melting of a depleted mantle wedge weakly metasomatized by subducted slab fluids.Compared to Group#1 samples,Group#2 samples display strongly fractionated REE patterns with higher(La/Yb)_N ratios and more scattered(Hf/Sm)N ratios,indicative of a depleted mantle wedge that had been intensely metasomatized by slab-derived melts and fluids.Group#3 samples are characterized by high MgO and transition trace element concentrations and fractionated REE patterns,which resemble typical high-Si adakites,and the magmatic precursors were derived from partial melting of a subducted oceanic slab.Group#4 samples have the highest SiO_2 and the lowest MgO and transition trace element contents,and were derived from partial melting of basaltic rocks at lower crust levels.Integrating these tholeiitic to calcalkaline volcanic rocks with the mass of contemporaneous dioritic-tonalitic-trondhjemitic-granodioritic gneisses,the late Neoarchean volcanic rocks in the SLT were most likely produced in an active continental margin.Furthermore,the affinities in lithological assemblages,metamorphism and tectonic regime among SLT,eastern Hebei to western Liaoning Terrane(EH-WLT),northern Liaoning to southern Jilin Terrane(NL-SJT),AnshanBenxi continental nucleus(ABN) and Yishui complex(YSC) collectively indicate that an integral and much larger continental block had been formed in the late Neoarchean and the craton-scale lateral accretion was a dominantly geodynamic mechanism in the eastern NCC.展开更多
The link between the crustal deformation and mantle kinematics in the Tibetan Plateau has been well known thanks to dense GPS measurements and the relatively detailed anisotropy structure of the lithospheric mantle.Ho...The link between the crustal deformation and mantle kinematics in the Tibetan Plateau has been well known thanks to dense GPS measurements and the relatively detailed anisotropy structure of the lithospheric mantle.However, whether the crust deforms coherently with the upper mantle in the Shan-Thai terrane(also known as the Shan-Thai block) remains unclear.In this study, we investigate the deformation patterns through strain rate tensors in the southeastern Tibetan Plateau derived from the latest GPS measurements and find that in the Shan-Thai terrane the upper crust may be coupled with the lower crust and the upper mantle.The GPS-derived strain rate tensors are in agreement with the slipping patterns and rates of major strike-slip faults in the region.The most prominent shear zone, whose shear strain rates are larger than 100×10^(–9) a^(–1), is about 1000-km-long in the west, trending northward along Sagaing fault to the Eastern Himalayan Syntaxis in the north, with maximum rate of compressive strain up to –240×10^(–9) a^(–1).A secondary shear zone along the Anninghe-Xiaojiang Fault in the east shows segmented shear zones near several conjunctions.While the strain rate along RRF is relatively low due to the low slip rate and low seismicity there, in Lijiang and Tengchong several local shear zones are present under an extensional dominated stress regime that is related to normal faulting earthquakes and volcanism, respectively.Furthermore, by comparing GPS-derived strain rate tensors with earthquake focal mechanisms, we find that 75.8%(100 out of 132) of the earthquake T-axes are consistent with the GPS-derived strain rates.Moreover, we find that the Fast Velocity Direction(FVDs) at three depths beneath the Shan-Thai terrane are consistent with extensional strain rate with gradually increasing angular differences, which are likely resulting from the basal shear forces induced by asthenospheric flow associated with the oblique subduction of the India plate beneath the Shan-Thai terrane.Therefore, in this region the upper crust deformation may be coherent with that of the lower crust and the lithospheric mantle.展开更多
The newly-discovered Donglufang Moe Cu porphyry-skarn deposit is located in the southern Yidun Terrane, southeast Tibet, with more than 80 million tonnes(Mt) of reserves(grading 0.15 wt.% Mo and0.48 wt.% Cu) hosted in...The newly-discovered Donglufang Moe Cu porphyry-skarn deposit is located in the southern Yidun Terrane, southeast Tibet, with more than 80 million tonnes(Mt) of reserves(grading 0.15 wt.% Mo and0.48 wt.% Cu) hosted in Triassic strata and Late Cretaceous granodiorite porphyry. Ree Os dating of molybdenum ore yielded a weighted mean age of 84.9 ± 1.0 Ma and an isochron age of 85.2 ± 0.6 Ma.LA-ICP-MS Ue Pb dating of zircons from the granodiorite porphyry yielded206 Pb/238 U ages ranging from 87.4 Ma to 84.2 Ma with a weighted mean206 Pb/238 U age of 85.1 ±0.5 Ma, indicating a temporal linkage between granitic magmatism and Moe Cu mineralization. Geochemical analyses show that the granodiorite porphyries are I-type granites with Si O_2 contents of 64.3 -66.7 wt.%. These rocks are typically metaluminous with high K_2 O/Na_2 O ratios, low Mg O(1.32 -1.56 wt.%), Cr(5.6 -12.9 ppm), Ni(3.79 -10.81 ppm), Mg#(43 -52) values, and high Sr(304 -844 ppm), Sr/Y(21.2 -50.8) and La/Yb ratios(37.0 -60.1). They are enriched in light rare-earth elements(LREE) relative to heavy rare-earth elements(HREE), with slightly negative Eu anomalies, and are enriched in Th, U and large ion lithophile elements(LILE, e.g., K and Rb), and depleted in high field strength elements(HFSE, e.g., Nb, Ta, P and Ti). They also show negative zircon εHf(t) values(-6.7 to -2.3) and negative whole rock εNd(t) values(à5.2 to-4.3), as well as old Hfe Nd model ages, indicating the magmas were derived from a thickened ancient lower crust within the garneteamphibolite facies. Considering the tectonic evolution of the Yidun Terrane, geochemical characteristics of granodiorite porphyry, and the ages of mineralization obtained in this study. We suggest that the Donglufang deposit was formed in a post-collisional setting, which has a genetic relationship with the emplacement of the granodiorite porphyry. The present study provide key information for the exploration of the Late Cretaceous metallogeny in the Yidun Terrane.展开更多
Abstract: Through a study of the geotransect from Golmud to Ejin Qi published recently, the tectonics of the crust beneath the area from the northern Qinghai-Tibet plateau (Qaidam and the Qilian Mountains) to the bord...Abstract: Through a study of the geotransect from Golmud to Ejin Qi published recently, the tectonics of the crust beneath the area from the northern Qinghai-Tibet plateau (Qaidam and the Qilian Mountains) to the border between China and Mongolia and its structure, composition and tectonic evolution have been revealed, and abundant information about the deep structures has been provided. Based on the research into the geotransect, it is suggested that the crust in this area was formed by the assembly of the terranes in different geological stages. Following the formation of the Palaeo-Asian continent, the north part of the corridor of the transect became a part of the huge unifying continent by the end of the Early Permian. In the Mesozoic and Cenozoic, as a result of the compression mainly by the push of the Qinghai-Tibet plateau on the south, the unique crustal structure and geomorphologic features on the northern Qinghai-Tibet plateau were formed. This geotransect together with the Yadong-Golmud geotransect constitutes a long geotransect which runs across the western Chinese continent.展开更多
In order to constrain temperature during subduction and subsequent exhumation of fel- sic continental crust, we carried out a Ti-in-zircon thermometer coupled with zircon internal structure and U-Pb age on migmatitic ...In order to constrain temperature during subduction and subsequent exhumation of fel- sic continental crust, we carried out a Ti-in-zircon thermometer coupled with zircon internal structure and U-Pb age on migmatitic gneisses from the Weihai region in the Sulu ultra-high pres- sure （UHP） metamorphic terrane, eastern China. The Weihai migmatitic gneisses are composed of in- tercalated compositional layers of melanosome and plagioclase （Pl）-rich lencosome and K-feldspar （Kfs）-rich pegmatite veins. Four stages of zircon growth were recognized in the Weihai migmatitic gneisses. They successively recorded informations of protolith, prograde metamorphism, decompres- sional partial melting during early stage exhumation and subsequent fractional crystallization of pri- mary melt during later stage cooling exhumation. The inherited cores in zircon from the melanosome and the Pl-rich leucosome suggest that the pro- tolith of the migmatitic gneiss is Mid- Neoproterozoic （-780 Ma） magmatic rock. Metamorphic zircons with concordant ages ranging from 243 to 256 Ma occur as over- growth mantles on the protolith magmatic zir- con cores. The estimated growth temperatures （625-717 ＂C） of the metamorphic zircons have a negative correlation with their ages, indicating a progressive metamorphism in HP eciogite-facies condition during subduction. Zircon recrystal- lized rims （228-2 Ma） in the PI-rich ieucosome layers provide the lower limit of the decompress-sional partial melting time during exhumation. The ages from 228^-2 to 219~2 Ma recorded in the Pl-rich leucosome and the Kfs-rich pegmatite vein, respectively, suggest the duration of the fractional crystallization of primary melt during exhumation. The calculated growth temperatures of the zircon rims from the Pl-rich leucosome range from 858 to 739 , and the temperatures of new growth zircon grains （219±2 Ma） in Kfs-rich vein are between 769 and 529 . The estimated temperatures have a positive correlation with ages from the Pl-rich leucosome to the Kfs-rich pegmatite vein, strongly indi- cating that a process of fractional crystallization of the partial melt during exhumation.展开更多
Bangong-Nujiang collisional zone(BNCZ)is an older one in Qinghai-Tibet Plateau and resulted in the famous Bangong-Nujiang metallogenic belt,which plays an important role in evaluating the formation and uplift mechanis...Bangong-Nujiang collisional zone(BNCZ)is an older one in Qinghai-Tibet Plateau and resulted in the famous Bangong-Nujiang metallogenic belt,which plays an important role in evaluating the formation and uplift mechanism of plateau.The northern and central Lhasa Terrane composed the southern part of the BNCZ.Since ore deposits can be used as markers of geodynamic evolution,the authors carried 1∶50000 stream sedimental geochemical exploration in the Xiongmei area in the Northern Lhasa Terrane to manifest the mineralization,and based on this mineralization with geochemical and chronological characteristics of related magmatic rocks to constrain their geodynamics and connection with the evolution of the Lhasa Terrane.The authors find Early Cretaceous magma mainly resulted in Cu,Mo mineralization,Late Cretaceous magma mainly resulted in Cu,Mo,and W mineralization in the studying area.The results suggest a southward subduction,slab rolling back and break-off,and thickened lithosphere delamination successively occurred within the Northern Lhasa Terrane.展开更多
基金the National Key Research and Development Program of China(Grant No.2022YFF0800903)the National Natural Science Foundation of China(Grant Nos.42302107,92162322,42261144669,41922022,42003036)+4 种基金the China Geological Survey(Grant Nos.DD20243512,DD20230008)the National Postdoctoral Research Program of China(Grant No.GZC20232489)the Second Tibetan Plateau Scientific Expedition and Research(Grant No.2021QZKK0304)Xing Dian Youth Talent Plan of Yunnan Province(Grant No.XDYC-QNRC-2022-0136)the UNESCO:IUGS IGCP-662 Program。
文摘Basalts from the Late Carboniferous to Early Permian are extensively developed in the central Lhasa subterrane,southern Xizang.Studying the petrogenesis of these rocks may have implications for the late Paleozoic arc magmatism along the central Lhasa subterrane uncovering more of the evolution of the Sumdo Paleo-Tethys Ocean and its dynamic mechanism.Basalt samples from the Luobadui Formation in the Leqingla area,NW of Linzhou City in the central Lhasa subterrane,southern Xizang exhibit arc-like geochemical signatures in a subduction-zone tectonic setting characterized by high Al_(2)O_(3)and low TiO_(2)contents,fractionated REE patterns with low Nb/La ratios and high LREE concentrations,and negative HFSE anomalies.Based on their higher Th/Ce,Nb/Zr,and lower Ba/Th,Pb/Nd ratios,slightly negative to positiveε_(Nd)(t)values,and the relatively high Sr-Pb isotopic compositions,these samples were probably derived from partial melting of a depleted mantle source of garnet+spinel lherzolite,metasomatized by subducted sediments around 297 Ma.Modeling of the trace elements indicates that these basalts experienced fractional crystallization of olivine,clinopyroxene and minor plagioclase during magma ascent and eruption.It is proposed that these Late Carboniferous–Early Permian basalts are associated with the northward subduction of the Sumdo Paleo-Tethys Ocean seafloor along the southern margin of the central Lhasa subterrane.
基金supported by the Key Laboratory of Gold Mineralization Processes and Resource Utilization,MNRShandong Provincial Key Laboratory of Metallogenic Geological Process and Resource Utilization(Grant No.KFKT202103)National Natural Science Foundation of China(Grant No.41876037)。
文摘Feldspar Pb isotopes have been widely used to trace magmatic formation and evolution processes.However,it remains unclear whether post-magmatic thermal events can affect feldspar Pb isotopic ratios.Here,the in situ Pb isotopic composition of feldspar hosted in granitic rocks(thirteen Archean and one Paleoproterozoic)from the northern Kongling terrane,Yangtze Craton,South China,is analyzed.The samples reveal a substantial variation in their Pb isotopic composition,spanning the gap between the 1.9 Ga and present-day geochrons,which indicates extensive resetting by later tectonothermal events.This resetting was interpreted to have likely resulted from Paleoproterozoic and Neoproterozoic tectonothermal events related to the assembly and breakup of the Columbia and Rodinia supercontinents.These results suggest that Pb isotopes should be used cautiously when tracing magma sources and petrogenesis in magmatic rocks that have experienced post-magmatic reworking.However,the in situ Pb isotopic composition of feldspar in ancient granitoids may also potentially be used to reveal later tectonothermal events.The extensive resetting of the Pb isotopic composition in feldspar by regional thermal events may also provide new insights into our understanding of the Pb isotope paradox.
文摘The Southern Granulite Terrane(SGT),the wedgeshaped southern termination of Peninsular India,is a mosaic of several crustal blocks and intervening collisional sutures/shears which developed through multiple orogenic cycles during Mesoarchean to late Neoproterozoic-Cambrian.The SGT has been the focus of global geoscience world for more than four decades mainly with regard to deep crustal processes,crustmantle architecture,polyphase structural evolution,extreme crustal metamorphism,growth and recycling of continental crust,and the assembly-evolution-disruption of supercontinents through time,among other aspects.
基金supported by China National Natural Science Foundation Grant 49732070.
文摘Based on geological, chronological, geochemical and Nd isotopic studies of the high-grade basement of the Qilian terrane, the authors have drawn the following main conclusions: (1) the high-grade basement of the Qilian terrane consists mainly of meta-argillo-arenaceous rocks and granites and its bulk part was formed in the period of 0.8–1.0 Ga (the Jinningian period); (2) most of the meta-argillo-arenaceous rocks and granitic rocks have strong negative Eu and Ba anomalies (Eu/Eu*= 0.47–0.71 and Ba/Ba*=0.16–0.64), with fDM and ENd (1.0 Ga) ranging from 1.87 to 2.26 Ga and from ?8.54 to ?4.06 respectively, showing relatively high maturity; and (3) the Jinningian granitic rocks are a typical product of continent-continent collision, being probably related to the formation of the supercontinent Rodinia. These studies, combined with the study of high-grade basement rocks near the Qilian terrane, suggest that before the Jinningian period, the Qilian-Qaidam northern-margin terrane and Dunhuang-Alxa terrane were separated from each other, belonging to different plate systems of the North China craton and Yangtze platform respectively. The Qilian orogenic belt was the same as or similar to the Qiling orogenic belt in terms of the geological evolution history at least before the Jinningian period.
基金supports from the National Natural Science Foundation of China(grants 40172071 and 40211120151 to Yan Quanren)the Ministry of Science and Technology of the People’s Republic of China(grant 2202CB412608 to Wang Zongqi)+2 种基金the China Geological Survey(grant DKD2001002 to Wang Zongqi)the University of Nevada Las Vegas(to Hanson)and the Geological Society of America(to Druschke)are gratefully appreciated.
文摘The Bikou volcanic terrane is predominated by subalkaline tholeiitic lavas. Rock samples display lower initial ratios of Sr and Nd, 0.701248-0.704413 and 0.511080-0.512341 respectively. 207Pb and 208Pb are significantly enriched in the lavas. Most samples have positive εNd, which indicates that the magma was derived from EM-type mantle source, while a few samples with negative εNd indicate that there was contamination in the magma evolution. Magma differentiation is demonstrated by variations of LREE and LILE from depletion to enrichment. Additionally, normalized REE patterns and trace elements showed that lavas from the Bikou volcanic terrane have similar characteristics to those of basalts in arc settings caused by subduction and collision. Analyses showed that the Bikou volcanic terrane is a volcanic arc. New evidence proved that the Hengdan Group, north of the Bikou arc, is a turbidite terrane filling a forearc basin. Consequently, the Bikou volcanic terrane and the Hengdan turbidite terrane construct an arc-basin system. New SHRIMP ages showed that this arc-basin system developed on the northern margin of the Yangtze craton in the Neoproterozoic (846-776 Ma), and this arc-basin system is in agreement with the tectonic processes of Rodinia in the Neoproterzoic.
基金financially supported by the Natural Science Foundation of China (Nos. 41573039 41673040 U1603245)
文摘The paper presents an overview of the relationships between the interior structures of tectonic terranes and the distribution of tectonic-metallogenic zones in Southeast Asia. Episodic tectonic activities occurred in this archipelagic area, generating metallogenic belts in multi-terranes. Since the Late Paleozoic, opening and closure of the Paleotethys and Neotethys led to multiple suture zones between different blocks, mainly between the Indochina terrane, the Nambung terrane, the Sibumasu terrane and the West Myanmar terrane. During the Mesozoic to Cenozoic, the formation of accreted terranes and their related islands was caused by subduction and collision processes between the Pacific and Australian plates toward the Eurasian Continent, forming Sundaland and its affiliated islands, the Philippines and its subsidiary islands, the Papua New Guinea terrane and its related islands and the Sunda epicontinental arc system. Within the margin of terranes resulted in the structural transfer zones, their secondary tectonic units can be divided into island arc belts, back-arc basins, suture zones, marginal fold belts and orogenic belts. The metallogenic assemblages are mainly distributed within these structural zones of the terranes. According to the relationship between these tectonic units and the distribution of mineral resources, the tectonic-metallogenic belts can be divided into 24 metallogenic belts in Southeast Asia. They are characterized by a diversity and frequency of metallogenic material combination which is likely to reflect the complexity of the material distribution during mineralization processes, mostly by the structural transformation during the dissociation-convergence process between multiple terranes. Therefore, the formation of ore deposits was not only restricted by the evolution(opening and closure) of Paleo-and Neotethys, but may also be controlled by the interaction of the terranes with different tectonic attributes which provided multiple sources of metallogenic material.
基金supported by the National Natural Science Foundation of China (No. 41272072)the NSFC/NRF Research Cooperation Programm (No. 41761144061)the SDUST Research Fund (No. 2015TDJH101)
文摘Petrological analysis and LA-ICP-MS zircon U-Pb dating were conducted on high- pressure marie granulites, which occured as xenolith within TTG gneisses, from the Nanshankou Village of the Jiaobei terrane, Shandong Peninsula in the north-eastern part of the North China Craton （NCC）. The mafic HP grannlite is composed of garnet, clinopyroxene, orthopyroxene, amphibole and symplectitic clinopyroxene, orthopyroxene, plagioclase, ilmente and magnetite which were formed after the decomposition of porphyroblastic garnet and clinopyroxene. Four stages of metamorphic mineral assemblages for the mafic HP granulites were constrained by detail petrological and mineralogical in- vestigations. The early prograde assemblage is represented by the mineral inclusions within garnet and clinopyroxene porphyroblasts （Opx1＋Pl1＋Qtz1）, recording the metamorphic conditions at -754-757 ℃, 0.63-0.71 GPa; peak metamorphic conditions were determined at -874-891 ℃, 1.32-1.35 GPa with the mineral assemblage of Grt2＋Cpx2＋Amp2＋Pl2＋Qtz2. Retrograde minerals derived from symplectitic assemblage Opx3＋Cpx3＋Amp3＋Pl3＋Qtz3＋Ilm3±Mag3 were formed at 693-796℃, 0.60-0.84 GPa. A final greensehist to sub-greenschist facies event was recorded by the exsolution of actinolite and albite within a retrograded clinopyroxene, as well as the occurrence of prehnite, chlorite and calcite minerals. Accordingly, a clockwise P-T path was concluded on the basis of the different stages of mineral asseblage. Cathodoluminescence imaging, trace element and U-Pb dating of zircons from the mafic HP granulites recorded similar charactistics for three episodes of Paleo-Meso Proterozoic metamorphic events. These are the metamorphic events preserved in mafic and pelitic granulites in the Jiao-Liao-Ji belt （JLJB） with 207 pb/206pb ages of 2.0-1.9 Ga for peak metamorphism and of 1.86-1.84 Ga for decomposing process, followed by a retrograde amphibolite facies metamorphic event related to the post-orogenic extension at the age of 1.76-1.74 Ga, resulting the exhumation of the granulite to the upper crust level.
基金supported by the National Basic Research Program of China (No. 2015CB856101)the National Natural Science Foundation of China (Nos. 41372076 and 41572039)the Natural Science Foundation of Hubei Province (No. 2015CFB190)
文摘The plate affiliation of the North Dabie terrane （NDT） has been controversial. To address this fundamental question, an integrated study of internal structure, in-situ U-Pb dating and trace element analysis in zircons and field investigation for migmatite in the NDT was carried out, which reveals par- ticipation of crustal rocks of the North China Craton （NCC） in the protolith in addition to the more common crustal rocks of the Yangtze Craton （YC）. The evidence of an NCC affinity for protolith of migmatite in the NDT is the -2.5 Ga （2 486±14 and 2 406±26 Ma） magamtic age and -1.8 Ga （1 717±79 Ma） metamorphic age in the relict zircon domains because these two age groups are characteristic for the evolution of the NCC. The evidence of a YC affinity for protolith of migmatite in the NDT is the more common 0.7-0.8 Ga （e.g., 787±12 Ma） magamtic zircon age. Mid-Neoproterozoic magmatic age （0.7-0.8 Ga） is a symbol of YC basement rocks. In view of the widely exposed YC crustal components in the NDT, we suggest that the protolith of the NDT is mainly crustal rocks from the YC with minor crustal components from the NCC. The zircon rim domains and new growth grains from all the migmatite sam- ples are characterized by anatectic zircons and have a widely concordant ages ranging from 112.2±2.8 to 159.6±4.3 Ma with several peak values, suggesting a long lasting multistage anatexis. In conclusion, the NDT has a mixed protolith origin of both the YC and the NCC crustal rocks were strongly remoulded by anatexis during orogenic collapse.
文摘: The 3He/4He ratios of most eclogites from the Dabie-Sulu terrane range from 0.056 to 0.67 Ra; the data points fall into the mixing part of the crust and the mantle in the 3He-4He diagram. The 3He/4He ratios of eclogites are obviously correlated with the types of their surrounding rocks. The helium isotope composition of the eclogites from the Bixiling complex possesses characters of mantle-derived rocks with the 3He/4He ratio being 5.6 Ra. The 4He concentration of the eclogites exhibits visible inverse correlation with the δ18O value of the quartz in the eclogites from the Sulu area. The δ18O values of the eclogites change synchronously with those of the country rocks. Those results suggest that protoliths of the eclogites were basic-ultrabasic rock bodies or veins intruding into the continental crust in the early stage; strong exchange and hybridization between the basic-ultrabasic rocks and continental rocks and the atmospheric water during the intrusion led to abrupt increase of the 3He/4He ratios, δ18O values and Nd(0) values of the intrusive bodies or veins, which show characters of continental rocks. This indicates that the eclogites are autochthonous.
基金funded by grants from the National Natural Science Foundation of China (No.40930313)the China Geological Survey (No.12120114057701,No.12120114061801 and No.12120114061501)
文摘The southern Lhasa Terrane is famous for its huge magmatic belt which records the magmatism during Mesozoic and Cenozoic. Although the Mesozoic continental-margin setting in the southern Lhasa Terrane has been identified, details of this tectonic setting and the evolution history during the Late Cretaceous remain unclear. To further constrain these issues, we present zircon LA-ICP-MS U-Pb, Hf isotopic and geochemical data of the Gongbari dacites （of the Sangri Group） which intruded by Paleocene granodiorites from the eastern part of the southern Lhasa Terrane, Tibet. New age data indicate that the dacites were generated at -95.4 Ma, which suggests the Sangri Group volcanism may last to Late Cretaceous. The Gongbari dacites are characterized by high Sr （428-758 ppm） contents, low concentration of heavy rare earth elements and Y （e.g. Yb=0.78-1.14 ppm; Y=8.85-11.4 ppm） with high Sr/Y （41.91-67.59） and La/Yb （22.64-30.64） ratios, similar to those of adakite. The rocks are calc-alkaline, metaluminous, enriched in LILEs, depleted in HFSEs, and have positive tar（t） values （＋7.7 to ＋11.6）. The Gongbari dacites were probably produced by partial melting of young and hot subducted Neo- Tethyan oceanic crust under amphibolite to garnet amphibolite-facies conditions. Though the Gangdese Mountains may have formed before Indo-Asian collision, the southern margin of Lhasa Terrane might not go through obviously crustal thickening during the northward subduction of Neo-Tethyan oceanic lithosphere.
基金Financial support was provided by Geological Survey Program of China Geological Survey (Grant No. 1212010610105)the Basic Foundation of Institute of Geology, Chinese Academy of Geological Sciences (Grant No. J0918)
文摘Muscovite 40 Ar-39 Ar dating of muscovite-quartz schist, eclogite and retrograde eclogite indicates an Indosinian orogenesis occurred at 220-240 Ma in the Lhasa terrane, which is caused by the closure of Paleo-Tethyan ocean basin and the following collision of the northern Lhasa terrane and southern Gondwana land. This Indosinian orogenesis is further confirmed by the regional sedimentary characteristics, magmatic activity and ophiolite mélange. This evidence suggests that the Indosinian orogenic belt in the Lhasa terrane is widely distributed from the Coqen county in the west, and then extends eastward through the Ningzhong and Sumdo area, finally turning around the eastern Himalayan syntaxis into the Bomi county. Based on the evolutionary process, the geological development of Lhasa terrane from early Paleozoic to early Mesozoic can be divided into seven stages. All of the seven stages make up a whole Wilson circle and reveal a perfect evolutionary process of the Paleo-Tethys ocean between the northern Lhasa terrane and southern Gondwana land. The Indosinian orogenisis is a significant event for the evolution of the Lhasa terrane as well as the Tibetan Plateau.
基金supported by the National Natural Science Foundation of China (Nos. 41372212, 41672216, and 41702207)
文摘Several Cretaceous Carlin-like or hydrothermal gold deposits along the Garze-Litang suture zone and Early Cretaceous hydrothermal copper mineralization along the southeastern margin of the Songpan-Garze fold belt were presumed to have a magmatic heat source. However, no actual coeval mag- matic events nearby were discovered. Here, we report zircon SIMS U-Pb age, whole-rock geochemical and Sr-Nd isotopic data of the Xiqiu basalts in the southern end of the Yidun terrane, eastern Tibetan Plateau. New zircon U-Pb ages yield weighted mean ^206pb/^238U age of 117.7±1.6 Ma. The basalts are classified as calc-alkaline to alkaline and have relatively high MgO （4.77 wt.%-10.84 wt.%） and Mg number values （Mg^#=（100×Mg/（Mg＋Fe^2＋））; 45.35-67.28） and positive εNd（t） （t=118 Ma） values （＋1.86 to ＋3.2）, suggesting a OIB-like mantle source that is consistent with the normalized patterns of trace elements and rare earth elements （REEs）. Geochemical data suggest that the primary basaltic magma was generated by low degree partial melting of a heterogeneous source of peridotite-dominated with a minor component of garnet- eclogite or pyroxenite and experienced olivine＋clinopyroxene dominated fractional crystallization. The primary melt compositions calculated from the high MgO samples, in turn, suggest that the Xiqiu basalts were generated at 1.6-2.9 GPa with abnormally hot mantle potential temperatures from 1 465 to 1 540℃. The melting temperatures are similar to the abnormally hot mantle underneath the Colorado Plateau and hotter than the mid-ocean range basalt （MORB） mantle and normal intra-continental mantle. Combined with previous studies, the Cretaceous Xiqiu basalts allow us to reconstruct a tectonic and geodynamic evolution- ary model responsible for the Late Jurassic to Late Cretaceous geological records （magmatism, ore deposits and enhanced exhumation） in the Yidun terrane and southern Songpan-Garze fold belt.
基金supported by the National Natural Science Foundation of China(Nos.41072044,41130315 and 41530319)
文摘The nature and evolution of the Proto-Tethys Ocean originated from the breakup of the supercontinent Rodinia remain controversial. Early Paleozoic magmatism and metamorphism can pro- vide important constraints on the closure of the Proto-Tethys Ocean. This paper reports on a set of geological, petrographical, geochronological, mineralogical and geochemical data for Early Paleozoic granite, gabbro, granulite and granitic leucosome in the northern Wulan terrane of the Quanji Massif. Zircon LA-ICP-MS U-Pb dating reveals two episodes of magmatism, with the emplacement of a gran- itic pluton at 476.7±2.8 Ma and a gabbroic dike at 423±2 Ma. Whole-rock geochemistry suggests an arc affinity for the magma of the granitic pluton but a post-collisional extension setting for the gabbroic dike. Zircon LA-ICP-MS U-Pb dating also shows that the peak granulite-facies metamorphism and anatexis occurred at --475 Ma, coeval with the formation of the granitic pluton in the Quanji Massif as well as the early lawsonite-bearing eclogites in the North Qaidam high-pressure and ultrahigh-pressure (HP-UHP) metamorphic belt to the south. The granulite-facies metamorphism with peak P-T condi- tions at 718-729 ℃ and 0.46-0.53 GPa is characterized by an anticlockwise P-T path. Our data provide compelling evidence for Early Paleozoic paired metamorphic belts with HP-UHP metamorphism in the North Qaidam to the south and low PIT metamorphism in the Quanji Massif as a continental arc to the north, hence suggesting a northward subduction polarity for the Proto-Tethys oceanic plate. The intrusion of the post-collisional gabbroic dike supports for the closure of the Proto-Tethys Ocean in north- western China before 423 Ma.
基金financially supported by the National Natural Science Foundation of China (Nos. 41630207, 41572180)the China Geological Survey (No. DD20160022)
文摘The granulitized eclogites from the Luliangshan terrane of the North Qaidam UHP metamorphic belt occur as lenses within pelitic gneisses and orthogneisses. Combined petrologic data and phase equilibrium modeling indicate a multi-stage metamorphic history of the granulitized eclogites:(1) an earlier eclogite facies metamorphism(P>18.5 kbar, T> 830℃) is deduced from omphacite relics in the matrix and rare omphacite inclusions within garnet. The possible assemblage is garnet+omphacite+rutile+ quartz;(2) the early stage of high pressure granulite facies assemblages(garnet+clinopyroxene+ plagioclase+rutile+quartz+liquid) developed in the early decompression process has a P-T regime of 17.5 kbar and 852–858 ℃, constrained by plagioclase and clinopyroxene inclusions in garnet. The late stage of high pressure granulite assemblages(garnet+clinopyroxene+amphibole+plagioclase+rutile+quartz+liquid) records an isothermal decompression process with the pressure successively declining from 17.5 to 14.7 kbar and to 11.3 kbar at 858 ℃;(3) the later medium pressure granulite facies assemblage(garnet+ orthopyroxene+clinopyroxene+amphibole+plagioclase+ilmenite+liquid+quartz) indicates a drop in pressure and rise in temperature at P-T conditions of 7.6–7.7 kbar and 878–883 ℃;(4) retrogressive amphibolite facies stage, which is represented by amphibole+plagioclase kelyphitic rims around garnet, formed under conditions of <5 kbar and <650 ℃. The preservation of medium pressure granulite facies assemblage and the garnet composition feature constrain a following isobaric cooling path during late exhumation. This process suggests a clockwise P-T path and indicates that the granulitized eclogites record a high grade "Barrovian" metamorphic overprint at the middle-lower crust during exhumation. The present data show that the Luliangshan terrane is a "hot" HP-UHP terrane.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.41530207 and 41772188)。
文摘The late Neoarchean metamorphosed volcanic rocks in the southern Liaoning Terrane(SLT) of the eastern North China Craton(NCC) are mainly composed of amphibolites and felsic gneisses and can be chemically classified as basalt(Group#1),basaltic andesite(Group#2),dacite(Group#3) and rhyodacite(Group#4).LA-ICP-MS zircon U-Th-Pb dating reveals that they formed at ~2.53-2.51 Ga.Group#1 samples are characterized by approximately flat chondrite-normalized rare earth element(REE) patterns with low(La/Yb)_N ratios and a narrow range of(Hf/Sm)N ratios,and their magmatic precursors were generated by partial melting of a depleted mantle wedge weakly metasomatized by subducted slab fluids.Compared to Group#1 samples,Group#2 samples display strongly fractionated REE patterns with higher(La/Yb)_N ratios and more scattered(Hf/Sm)N ratios,indicative of a depleted mantle wedge that had been intensely metasomatized by slab-derived melts and fluids.Group#3 samples are characterized by high MgO and transition trace element concentrations and fractionated REE patterns,which resemble typical high-Si adakites,and the magmatic precursors were derived from partial melting of a subducted oceanic slab.Group#4 samples have the highest SiO_2 and the lowest MgO and transition trace element contents,and were derived from partial melting of basaltic rocks at lower crust levels.Integrating these tholeiitic to calcalkaline volcanic rocks with the mass of contemporaneous dioritic-tonalitic-trondhjemitic-granodioritic gneisses,the late Neoarchean volcanic rocks in the SLT were most likely produced in an active continental margin.Furthermore,the affinities in lithological assemblages,metamorphism and tectonic regime among SLT,eastern Hebei to western Liaoning Terrane(EH-WLT),northern Liaoning to southern Jilin Terrane(NL-SJT),AnshanBenxi continental nucleus(ABN) and Yishui complex(YSC) collectively indicate that an integral and much larger continental block had been formed in the late Neoarchean and the craton-scale lateral accretion was a dominantly geodynamic mechanism in the eastern NCC.
基金partially supported by National Natural Science Foundation of China (grants 41474090 and 41490610)the financial support by the China Scholarship Councilthe Basic Research Project of Institute of Geology, CEA (IGCEA1314)
文摘The link between the crustal deformation and mantle kinematics in the Tibetan Plateau has been well known thanks to dense GPS measurements and the relatively detailed anisotropy structure of the lithospheric mantle.However, whether the crust deforms coherently with the upper mantle in the Shan-Thai terrane(also known as the Shan-Thai block) remains unclear.In this study, we investigate the deformation patterns through strain rate tensors in the southeastern Tibetan Plateau derived from the latest GPS measurements and find that in the Shan-Thai terrane the upper crust may be coupled with the lower crust and the upper mantle.The GPS-derived strain rate tensors are in agreement with the slipping patterns and rates of major strike-slip faults in the region.The most prominent shear zone, whose shear strain rates are larger than 100×10^(–9) a^(–1), is about 1000-km-long in the west, trending northward along Sagaing fault to the Eastern Himalayan Syntaxis in the north, with maximum rate of compressive strain up to –240×10^(–9) a^(–1).A secondary shear zone along the Anninghe-Xiaojiang Fault in the east shows segmented shear zones near several conjunctions.While the strain rate along RRF is relatively low due to the low slip rate and low seismicity there, in Lijiang and Tengchong several local shear zones are present under an extensional dominated stress regime that is related to normal faulting earthquakes and volcanism, respectively.Furthermore, by comparing GPS-derived strain rate tensors with earthquake focal mechanisms, we find that 75.8%(100 out of 132) of the earthquake T-axes are consistent with the GPS-derived strain rates.Moreover, we find that the Fast Velocity Direction(FVDs) at three depths beneath the Shan-Thai terrane are consistent with extensional strain rate with gradually increasing angular differences, which are likely resulting from the basal shear forces induced by asthenospheric flow associated with the oblique subduction of the India plate beneath the Shan-Thai terrane.Therefore, in this region the upper crust deformation may be coherent with that of the lower crust and the lithospheric mantle.
基金financially supported by the National Basic Research Program of China (No. 2015CB452605)the Natural Science Foundation of China (No. 41602089)Fundamental Research Funds for the Central Universities (No. 20170713174019)
文摘The newly-discovered Donglufang Moe Cu porphyry-skarn deposit is located in the southern Yidun Terrane, southeast Tibet, with more than 80 million tonnes(Mt) of reserves(grading 0.15 wt.% Mo and0.48 wt.% Cu) hosted in Triassic strata and Late Cretaceous granodiorite porphyry. Ree Os dating of molybdenum ore yielded a weighted mean age of 84.9 ± 1.0 Ma and an isochron age of 85.2 ± 0.6 Ma.LA-ICP-MS Ue Pb dating of zircons from the granodiorite porphyry yielded206 Pb/238 U ages ranging from 87.4 Ma to 84.2 Ma with a weighted mean206 Pb/238 U age of 85.1 ±0.5 Ma, indicating a temporal linkage between granitic magmatism and Moe Cu mineralization. Geochemical analyses show that the granodiorite porphyries are I-type granites with Si O_2 contents of 64.3 -66.7 wt.%. These rocks are typically metaluminous with high K_2 O/Na_2 O ratios, low Mg O(1.32 -1.56 wt.%), Cr(5.6 -12.9 ppm), Ni(3.79 -10.81 ppm), Mg#(43 -52) values, and high Sr(304 -844 ppm), Sr/Y(21.2 -50.8) and La/Yb ratios(37.0 -60.1). They are enriched in light rare-earth elements(LREE) relative to heavy rare-earth elements(HREE), with slightly negative Eu anomalies, and are enriched in Th, U and large ion lithophile elements(LILE, e.g., K and Rb), and depleted in high field strength elements(HFSE, e.g., Nb, Ta, P and Ti). They also show negative zircon εHf(t) values(-6.7 to -2.3) and negative whole rock εNd(t) values(à5.2 to-4.3), as well as old Hfe Nd model ages, indicating the magmas were derived from a thickened ancient lower crust within the garneteamphibolite facies. Considering the tectonic evolution of the Yidun Terrane, geochemical characteristics of granodiorite porphyry, and the ages of mineralization obtained in this study. We suggest that the Donglufang deposit was formed in a post-collisional setting, which has a genetic relationship with the emplacement of the granodiorite porphyry. The present study provide key information for the exploration of the Late Cretaceous metallogeny in the Yidun Terrane.
基金This paper is one of the results of the project"The Golmud-Ejin Geoscience Transect Interdisciplinary Research".The project was supported by the former Ministry of Geology and Mineral Resources(MGMR)and the National Natural Science Foundation of China(NNSFC).The leaders of the Project are Profs.Wang Zeju,Wu Gongjian and Xiao Xuchang.
文摘Abstract: Through a study of the geotransect from Golmud to Ejin Qi published recently, the tectonics of the crust beneath the area from the northern Qinghai-Tibet plateau (Qaidam and the Qilian Mountains) to the border between China and Mongolia and its structure, composition and tectonic evolution have been revealed, and abundant information about the deep structures has been provided. Based on the research into the geotransect, it is suggested that the crust in this area was formed by the assembly of the terranes in different geological stages. Following the formation of the Palaeo-Asian continent, the north part of the corridor of the transect became a part of the huge unifying continent by the end of the Early Permian. In the Mesozoic and Cenozoic, as a result of the compression mainly by the push of the Qinghai-Tibet plateau on the south, the unique crustal structure and geomorphologic features on the northern Qinghai-Tibet plateau were formed. This geotransect together with the Yadong-Golmud geotransect constitutes a long geotransect which runs across the western Chinese continent.
基金supported by the National Key Basic Research Program of China (No.2009CB825001)the National Natural Science Foundation of China (Nos.40603002,41072046,and 41090371)the Fundamental Research Funds for the Central Universities,China University of Geosciences,Wuhan (No.CUG120121)
文摘In order to constrain temperature during subduction and subsequent exhumation of fel- sic continental crust, we carried out a Ti-in-zircon thermometer coupled with zircon internal structure and U-Pb age on migmatitic gneisses from the Weihai region in the Sulu ultra-high pres- sure （UHP） metamorphic terrane, eastern China. The Weihai migmatitic gneisses are composed of in- tercalated compositional layers of melanosome and plagioclase （Pl）-rich lencosome and K-feldspar （Kfs）-rich pegmatite veins. Four stages of zircon growth were recognized in the Weihai migmatitic gneisses. They successively recorded informations of protolith, prograde metamorphism, decompres- sional partial melting during early stage exhumation and subsequent fractional crystallization of pri- mary melt during later stage cooling exhumation. The inherited cores in zircon from the melanosome and the Pl-rich leucosome suggest that the pro- tolith of the migmatitic gneiss is Mid- Neoproterozoic （-780 Ma） magmatic rock. Metamorphic zircons with concordant ages ranging from 243 to 256 Ma occur as over- growth mantles on the protolith magmatic zir- con cores. The estimated growth temperatures （625-717 ＂C） of the metamorphic zircons have a negative correlation with their ages, indicating a progressive metamorphism in HP eciogite-facies condition during subduction. Zircon recrystal- lized rims （228-2 Ma） in the PI-rich ieucosome layers provide the lower limit of the decompress-sional partial melting time during exhumation. The ages from 228^-2 to 219~2 Ma recorded in the Pl-rich leucosome and the Kfs-rich pegmatite vein, respectively, suggest the duration of the fractional crystallization of primary melt during exhumation. The calculated growth temperatures of the zircon rims from the Pl-rich leucosome range from 858 to 739 , and the temperatures of new growth zircon grains （219±2 Ma） in Kfs-rich vein are between 769 and 529 . The estimated temperatures have a positive correlation with ages from the Pl-rich leucosome to the Kfs-rich pegmatite vein, strongly indi- cating that a process of fractional crystallization of the partial melt during exhumation.
基金Financial support was provided by the program of China Geological Survey(DD20190167)National Natural Science Foundation of China(41902099)。
文摘Bangong-Nujiang collisional zone(BNCZ)is an older one in Qinghai-Tibet Plateau and resulted in the famous Bangong-Nujiang metallogenic belt,which plays an important role in evaluating the formation and uplift mechanism of plateau.The northern and central Lhasa Terrane composed the southern part of the BNCZ.Since ore deposits can be used as markers of geodynamic evolution,the authors carried 1∶50000 stream sedimental geochemical exploration in the Xiongmei area in the Northern Lhasa Terrane to manifest the mineralization,and based on this mineralization with geochemical and chronological characteristics of related magmatic rocks to constrain their geodynamics and connection with the evolution of the Lhasa Terrane.The authors find Early Cretaceous magma mainly resulted in Cu,Mo mineralization,Late Cretaceous magma mainly resulted in Cu,Mo,and W mineralization in the studying area.The results suggest a southward subduction,slab rolling back and break-off,and thickened lithosphere delamination successively occurred within the Northern Lhasa Terrane.
