The North China Craton(NCC)experienced significant lithospheric thinning of over 100 km during the Mesozoic,accompanied by extensive magmatic activity and extensional tectonics.However,the timing and mechanism of this...The North China Craton(NCC)experienced significant lithospheric thinning of over 100 km during the Mesozoic,accompanied by extensive magmatic activity and extensional tectonics.However,the timing and mechanism of this thinning remain the subjects of debate.This study presents zircon U-Pb ages,Hf isotopic data and whole-rock elemental and Sr-Nd isotopic compositions of the Guanshui monzonites and diorites in the eastern NCC.Zircon U-Pb dating reveals that both rock types formed at ca.130 Ma.The monzonites,characterized by high Mg^(#)(50.9-57.9),low Nb/U ratios(2.53-3.89)and depleted isotopic compositions,suggest derivation from asthenospheric mantle modified by slab-derived fluids.The diorites,distinguished by low SiO_(2)(49.5-50.8),high Mg^(#)(66.7-68.5)and an EM2-type enriched mantle isotopic signature,point to a lithospheric mantle source modified by subducted sediment melts.The coexistence of monzonites and diorites suggests a transition in magma source from lithospheric to asthenospheric mantle,implying that lithospheric thinning may have commenced around 130 Ma.The destruction of the NCC was likely driven by localized,small-scale drip-style detachment processes,rather than wholesale lithospheric removal.展开更多
The stratum lithology and geological structure of the highway tunnel in the mountainous areas of western China are complex,and the engineering geological conditions are complicated.When the highway tunnel passes throu...The stratum lithology and geological structure of the highway tunnel in the mountainous areas of western China are complex,and the engineering geological conditions are complicated.When the highway tunnel passes through different lithological strata,its structural design and construction technology are completely diff erent.Therefore,in order to support the tunnel design and construction,the tunnel survey Among them,the identification of the contact boundary between magmatic rock and metamorphic rock and the grade of surrounding rock is very important.Through magnetotelluric survey of the Mupi tunnel of Jiuzhaigou-Mianyang highway on G8513 line,2D forward numerical simulation,1D,2D,3D inversion,and engineering geological analysis,it is revealed that the electrical characteristics of each layer,focusing on the identification of the contact boundary between magmatic rock and metamorphic rock.This study provides the electrical characteristics of the magmatic rock and metamorphic rock contact boundary of the Mupi Tunnel.It is speculated that the boundary is revealed by the tunnel construction excavation,which verifies the correctness of the geophysical inversion model and provides a more detailed design basis for the tunnel design.I believe that taking the Mupi Tunnel survey as an example,through this research,it can provide detailed geophysical evidence for highway tunnels to distinguish between magmatic rock and metamorphic rock.展开更多
The geochemical characteristics of rare earth elements of magmatic rocks of Yanshanian stage were studied in the south of Anhui Province and northeast of Jiangxi Province, Jiangnan Uplift. The result shows that the ma...The geochemical characteristics of rare earth elements of magmatic rocks of Yanshanian stage were studied in the south of Anhui Province and northeast of Jiangxi Province, Jiangnan Uplift. The result shows that the magmatic rocks of Yanshanian stage in the south of Anhui Province are the typical crust source type and those in the northeast of Jiangxi Province have the characteristics of mantle source type. So the polymetal deposits having relation to the magmatic rocks of Yanshanian stage in the northeast of Jiangxi Province were developed better than those in the south of Anhui Province. The research results of the rare earth elements are confirmed by the studies of geophysics,tectonic setting and stable isotope at the same time. It also indicates that the rare earth elements are the effective approach to tracing the material sources of magmatic rocks.展开更多
REE geochemical characteristics of the magmatic rocks and gold deposits in Shizishan ore-field of Tongling were studied. Three types of the magmatic rocks have almost the same chondrite-normalized REE patterns, Eu and...REE geochemical characteristics of the magmatic rocks and gold deposits in Shizishan ore-field of Tongling were studied. Three types of the magmatic rocks have almost the same chondrite-normalized REE patterns, Eu and Ce anomalous values, and ∑REE, ∑LREE/∑HREE regular changes, which indicates that their magmas come from the same source and their digenetic mechanism is fractional crystallization. In three gold deposits, the mineral ores and related altered rocks have similar chondrite-normalized REE patterns and sharp Eu positive anomalous values. The REE contents reduced from the magmatic rocks to skamization or alteration magmatic rocks, skam type ores, sulphide type ores, wall-rocks limestone or marble. The REE geochemical characteristics of the ores and related rocks show that primary fluids originated from magmatic differentiation in lower pressure of shallow crust, ore-forming hydrothermal solutions gained REE and mineralization elements further from leaching the magmatic rocks, then superimposed and reformed the limestones or marbles and deposited ore-forming material.展开更多
In this study,we report systematically field observations,geochronology,whole-rock geochemistry and Sr-Nd-Hf isotopic dataset on the various types of magmatic rocks collected from the Zedang area.Chemically,the diabas...In this study,we report systematically field observations,geochronology,whole-rock geochemistry and Sr-Nd-Hf isotopic dataset on the various types of magmatic rocks collected from the Zedang area.Chemically,the diabase and gabbro have a low-K calc-alkaline affinity,whereas the basalt and plagiogranite have medium to high-K calc-alkaline characteristics.In addition,the basalts are highly enriched in light rare earth elements(LREE)and large ion lithophile elements(LILE),but strongly depleted in high strength field elements(HFSE),indicating that their magma source probably was derived from a subduction-or arc-related setting.In contrast,both the gabbro and diabase mainly demonstrate an N-MORB-like affinity consistent with normal mid-oceanic ridge basalt(N-MORB)origin.The zircon U-Pb dating results suggest that the basalts were crystallized earlier at ca.158–161 Ma(Oxfordian stage),but the gabbro was crystallized at ca.131 Ma(Hauterivian stage of Early Cretaceous).The zircon U-Pb dating results correspond with the field observations that the veins of gabbro intruded basalt.Furthermore,the plagiogranite has a weighted mean age of ca.160 Ma(MSWD=2.1)consistent with the basalt within the uncertainty.The basalt and the plagiogranite have significantly positiveεHf(t)values(+5.8 to+15.6 and+8.6 to+16.1,respectively),suggesting that they were originated from partial melting of a depleted source.However,basalt and plagiogranite are characterized by the wide variations ofεHf(t)values indicating minor amounts of exotic crustal material input during the later magma evolution.Additionally,the basalt shows duplex geochemical features of island-arc and mid-oceanic ridge basalt,corresponding to the supra-subduction zone-(SSZ)type affinity.To sum up,two distinct magmatic events identified in this study probably suggest an intra-oceanic arc system existing in the Zedang area during the Late Jurassic,but the intra-oceanic arc subduction extinguished in the Early Cretaceous as suggested by the N-MORB-like gabbro and diabase.Integrated with regional background and different rock types,as well as geochemical features,we conclude that intra-oceanic arc subduction setting developed during the Late Jurassic in the Zedang area,southern Tibet.展开更多
The Early Jurassic bimodal volcanic rocks in the Yeba Formation, situated between Lhasa, Dagze and Maizhokunggar, composed of metabasalt, basaltic ignimbrite, dacite, silicic tuff and volcanic breccia, are an importan...The Early Jurassic bimodal volcanic rocks in the Yeba Formation, situated between Lhasa, Dagze and Maizhokunggar, composed of metabasalt, basaltic ignimbrite, dacite, silicic tuff and volcanic breccia, are an important volcanic suite for the study of the tectonic evolution of the Gangdise magmatic arc and the Mesozoic Tethys. Based on systematic field investigations, we carried out geochemical studies on representative rock samples. Major and trace element compositions were analyzed for these rock samples by XRF and ICP-MS respectively, and an isotope analysis of Rb-Sr and Sm-Nd was carried out by a MAT 262 mass spectrograph. The results show that the SiO2 contents in lava rocks are 41 %-50.4% and 64 % -69 %, belonging to calc-alkaline basalt and dacite. One notable feature of the basalt is its low TiO2 content, 0.66%-1.01%, much lower than those of continental tholeiite. The ∑REE contents of basalt and dacite are 60.3-135 μg/g and 126, 4--167.9μg/ g respectively. Both rocks have similar REE and other trace element characteristics, with enriched LREE and LILE relative to HREE and HFS, similar REE patterns without Eu anomaly. The basalts have depleted Ti, Ta and Nb and slightly negative Nb and Ta anomalies, with Nb = 0.54--1.17 averaging 0. 84. The dacites have depleted P and Ti and also slightly negative Nb and Ta anomalies, with Nb= 0. 74 -1. 06 averaging 0. 86. Major and trace elemental and isotopic studies suggest that both basalt and dacite originated from the partial melting of the mantle wedge at different degrees above the subduction zone. The spinal Iherzolite in the upper mantle is likely to be their source rocks, which might have been affected by the selective metasomatism of fluids with crustal geochemistry. The LILE contents of both rocks were affected by metamorphism at later stages. The Yeba bimodal volcanic rocks formed in a temporal extensional situation in a mature island arc resulting from the Indosinian Gangdise magmatic arc.展开更多
In order to explore the control effect of backfill mining on dynamic disasters under special geological mining conditions of overlying thick magmatic rock(TMR),a three-dimensional numerical model of a panel of one sid...In order to explore the control effect of backfill mining on dynamic disasters under special geological mining conditions of overlying thick magmatic rock(TMR),a three-dimensional numerical model of a panel of one side goaf in Yangliu coal mine with double-yield backfill material constitutive model was developed.The simulation results were then compared with field monitoring data.The dynamic disaster control effect of both caving and backfill mining was analyzed in three different aspects,i.e.,displacement field,stress field and energy field.The results show that in comparison to the full caving mining method,the bearing capacity of the goaf after backfilling was enhanced,the backfill mining can effectively reduce the stress and energy accumulated in the coal/rock body,and the backfill mining eliminates the further moving space of TMR and prevents its sudden rupture.Before TMR fracture,the subsidence displacement of TMR was reduced by 65.3%,the front abutment stress of panel decreased by 9.4%on average and the high energy concentration zone around panel was also significantly reduced.Overall,the results of this study provide deeper insights into the control of dynamic disasters by backfill mining in mines.展开更多
Morphological and chemical studies on zircon grains from gabbro and granite of the Pingtan magmatic complex, Fujian Province, eastern China, show that there are three stages of zircon growth. The early stage of zircon...Morphological and chemical studies on zircon grains from gabbro and granite of the Pingtan magmatic complex, Fujian Province, eastern China, show that there are three stages of zircon growth. The early stage of zircon growth is characterized by colorlessness, high transparence and birefringence, low and dispersive Ipr and Ipy, weak and homogeneous BSE brightness, lower Hf content and depletion of U, Th and Y; the middle stage is characterized by abruptly increasing lpy, progressively strong and sectoral-zoning BSE brightness, higher Hf content and enrichment of U, Th and Y with Th/U 〉 1; the late stage of growth is characterized by brownish color, poor transparence, low birefringence, highest Ipr and Ipy, middle and oscillatorily-zoning BSE brightness, highest contents of Hf, U and Y with Th/U 〈 1. The stages are considered to be formed in a deep magma chamber, ascent passage and emplacement site, respectively. Due to the more or less long residual time of the magma chamber, the difference in age between the early and late stages of zircon might be great enough to be distinguished, which can be attributed to tectonic constraint for the magnlatism.展开更多
A new method for determining the partial melting depth of mantle-derived magma and lithospheric thickness in continental regions is derived from REE geochemistry. This effective technique uses variations in the Ce/Yb ...A new method for determining the partial melting depth of mantle-derived magma and lithospheric thickness in continental regions is derived from REE geochemistry. This effective technique uses variations in the Ce/Yb and Sm/Yb ratios found in mainly volcanic rocks in continental China. The ratios change with the depth of origin consistent with the correlation between lithospheric thickness and the Ce/Yb and Sm/Yb ratios found in oceanic basalt. These ratios increase exponentially with the depth of origin, the lithospheric thickness, of a wide variety of Cenozoic volcanic basalt and Paleozoic kimberlite in the North China Craton, northeastern China continent and vicinity. This functional relationship with depth is shown in a plot of the ratios that forms a concordia curve, which is closely expressed by formulas using 8–degree polynomials. These provide a more accurate gage in measuring the lithospheric thickness than the traditional geophysical methods. When applied to volcanic rock of different ages it also reveals how the thickness has changed over time and thus, greatly aids the understanding of the tectonic history. Relations between the COcontent, mineral reactions and pressure in the upper asthenosphere beneath the base of the lithosphere appears to affect the proportions of REE in partial melts and brings about a close correlation between lithospheric thickness and the Ce/Yb and Sm/Yb ratios in mantle–derived magmatic rock. This thickness gauge, for both continental and oceanic lithosphere, provides a new approach in analyzing the lithospheric thickness in different tectonic settings and geologic times.展开更多
Objective Petrogenesis of the Paleoproterozoic mafic dikes and their tectonic implications are of great significance to the tectonic evolution of the Yangtze craton as well as the paleoposition of the Yangtze craton r...Objective Petrogenesis of the Paleoproterozoic mafic dikes and their tectonic implications are of great significance to the tectonic evolution of the Yangtze craton as well as the paleoposition of the Yangtze craton relative to the Columbia supercontinent.Till now,展开更多
Abstract: Types of polymerized molecular network structure and degree of bond breakdown for glass phases of magmatic inclusions and glassy matrix in volcanic rocks from the Shengli oilfield have been defined by the la...Abstract: Types of polymerized molecular network structure and degree of bond breakdown for glass phases of magmatic inclusions and glassy matrix in volcanic rocks from the Shengli oilfield have been defined by the laser Raman spectroscopic investigation. There are significant differences in types of polymerized molecular network structure and degree of bond breakdown of the magmatic glass phases between the non-CO2 and CO2 gas pools: magmatic glass phases of fluid inclusions and matrix in volcanic rocks from the CO2 gas pool contain more sheet network molecules and have a greater degree of bond beakdown than those from the non-CO2 gas pool; and when gas bubbles occur in evolving magma, magma saturated with volatile components has more sheet network molecules. The results suggest the magmadegassing mechanism of the formation of CO2 gas pools in the Shengli oilfield.展开更多
Objective The Sachakou Pb-Zn polymetallic deposit is located in Hetian County, Xinjiang （geographical coordinates of E78° 57＇ 54.30＂-78°59＇ 53.63＂, N34° 39＇ 27.50＂-34° 40＇ 57.21＂）. It be...Objective The Sachakou Pb-Zn polymetallic deposit is located in Hetian County, Xinjiang （geographical coordinates of E78° 57＇ 54.30＂-78°59＇ 53.63＂, N34° 39＇ 27.50＂-34° 40＇ 57.21＂）. It belongs to the West Kunlun orogenic belt on the northwest edge of the Qinghai-Tibet Plateau and is connected to the Sanjiang orogenic belt to the south （Spurlin et al., 2005）. In recent years, a series of Pb-Zn mineralized spots and deposits have been discovered in this area one after another, which is called the Huoshaoyun ore concentration area. Among them, the Sachakou Pb-Zn deposit has reserves up to140 Mt, which has reached a large scale. However, the study on the genesis of deposits in this area has only just begun. This work studied the genesis ofthis Pb-Zn deposit in order to provide new ideas for the genesis of regional deposits and regional prospecting.展开更多
The Mazhuangshan area lies in northeast to Aqikekuduke, where are distributed intermediate\|acid rocks, which were formed in the Middle\|Late Carboniferous epoch. The magmatic rocks are peraluminous and belong to calc...The Mazhuangshan area lies in northeast to Aqikekuduke, where are distributed intermediate\|acid rocks, which were formed in the Middle\|Late Carboniferous epoch. The magmatic rocks are peraluminous and belong to calcareous series. All values of ACNK(1.03-\{2.12\}), ANK(1.67-2.93), SI(4.1-33), δ(0.71-4.82), La/ΣREE(0.09-0.26) ΣLREE/ΣHREE(1.76-11.01), (La/Sm)\-N(1.60-6.35), (Sm/Nd)\-N(0.33-0.58), (La/Yb)\-N(4.7-12.1), La\-N/Lu\-X(5.9-11.8), (Ce/Yb)\-N(3.14-6.64), δEu(0.38-\{1.06\}), Rb\-N/Sr\-N(42-120) and Sr\+*(0.02-0.2) demonstrate they vary with DI(\{45-90\}). S\|B diagram also shows that the lithophile elements are abundant in acidic magmatic rocks. Moreover, it is concluded that the primitive magma originated from a subduction zone at the continental edge, and underwent fractional crystallization and contamination, then generated the magmatic rocks. The multi\|cation index (R1: 3055-3993, R2: 286-438) shows that the primitive magma originated from the mantle. All these conclusions are beneficial for exploring gold deposits in the area.展开更多
The Yarlung Zangbo suture zone extends more than2000 km along southern Tibet and marks the boundary between the Indian subcontinent and Eurasia.The Zedong terrane has been not suggested to represent the vestige of suc...The Yarlung Zangbo suture zone extends more than2000 km along southern Tibet and marks the boundary between the Indian subcontinent and Eurasia.The Zedong terrane has been not suggested to represent the vestige of such an intra-oceanic arc developed within the Neo-Tethys Ocean,as a result of the northward subduction of the Neo-Tethys Ocean during the Late Jurassic.In this study,we present detailed geochemical and geochronological data of various types of magmatic rocks widely exposed in the Zedong terrane to constrain the formation age and tectonic setting of the Zedong terrane.We found that the Zedong volcanic rocks belong to high K2O calc-alkaline series,whereas the diabase and gabbro plotted in the low-K calcalkline.The basalt rocks are highly enriched in LREE and LILE,but strongly depleted in HFSE,indicating they were derived from a metasomatized mantle.Both gabbros and diabase have similar N-MORB geochemistry indicates that the cumulates were produced from MOR setting.Zircons from four samples,including the basalt rocks(158-161Ma)are older than the gabbro(131 Ma),certificate the gabbro are as the vein intrude into the basalt rocks.This suggests that the volcanic eruption and plutonic emplacement were coevally developed in the Zedonghave similar positiveεHf(t)values(+2.0 to+15.6)and(+8.6 to+18.4),indicating they were stemmed from similarly depleted mantle sources,same with the gabbro and granitic rocks from the Gangdese arc.Therefore,we proposed that the basalt rocks in the Zedong terrane were formed through partial melting of the mantle wedge metasomatized by slab-released fluids/melts.A part of hydrous basalts were underplated in the thickened lower crust beneath the Zedong terrane,which gave rise to the cumulate and granitic rocks.This suggests that the Zedong terrane represents a slice of the active continental margin developed on the southern margin of the Lhasa terrane as a result of the northward subduction of the Neo-Tethys Ocean during the Late Jurassic,although a possible intra-oceanic arc setting cannot be excluded.展开更多
Within southern Mali, the Syama belt constitutes a linear major structure-oriented N-S, which host several gold deposits (e.g., Syama and Tabakoroni) and prospect areas (e.g. Tellem). The Syama Belt is formed by magma...Within southern Mali, the Syama belt constitutes a linear major structure-oriented N-S, which host several gold deposits (e.g., Syama and Tabakoroni) and prospect areas (e.g. Tellem). The Syama Belt is formed by magmatic rocks (basalts, lamprophyres, andesites, dacites and microgranites);sedimentary rocks (shales) and volcano-sedimentary rocks (pyroclastics). The magmatic rocks are divided into two main volcanic series: tholeiitic affinity rocks (basalts and lamprophyres) and calc-alkaline affinity (andesites) that are the most evolved. The field relationships between rocks of these two series suggest that the calc-alkaline series are younger the tholeiitic series. These tholeiitic series present the Mid-Ocean Ridge Basalt (MORB) affinity whereas the calc-alkaline series would be linked to an island arc-type. This coexistence is not an isolated case within the West African Craton (WAC). Otherwise, the Syama belt has all the characteristics of other belts, within which a number of gold deposits are developed, in the WAC.展开更多
The Niangzhong diabase dikes,dated at 138.1±0.4 Ma,are located within the outcrop area of the Comei large igneous province(LIP).These diabase samples can be divided into two groups:samples in Group 1 show varying...The Niangzhong diabase dikes,dated at 138.1±0.4 Ma,are located within the outcrop area of the Comei large igneous province(LIP).These diabase samples can be divided into two groups:samples in Group 1 show varying MgO(1.50 wt.%-10.25 wt.%)and TiO_(2)(0.85 wt.%-4.63 wt.%)contents,and enriched initial isotope compositions(^(87)Sr/^(86)Sr(t)=0.7056-0.7112,ε_(Nd)(t)=-0.3-+3.8),with OIB-like REEs and trace elements patterns,resulting from low degree melting of garnet-bearing lherzolite mantle sources;in contrast,samples in Group 2 show limited MgO(4.14 wt.%-7.75 wt.%)and TiO_(2)(0.98 wt.%-1.69 wt.%)contents,and depleted initial isotope compositions(^(87)Sr/^(86)Sr(t)=0.7075-0.7112,ε_(Nd)(t)=+5.5-+6.2),with N-MORB-like REEs and trace elements patterns,resulting from relatively high degree melting of spinel-bearing lherzolite mantle source.Combined with the published representative data about Comei LIP,we summarize that the source components for Comei LIP products include OIB end-member,enriched OIB end-member,and N-MORB end-member,respectively.Melts modeling suggests that magmas in the Comei LIP evolve in a relatively high oxygen fugacity condition,which influenced their fractionation sequences and led to systematic changes of TiO_(2)contents,Ti/Y and Ti/Ti*ratios.From the spatial and temporal distribution of above three end-member samples,deep process of Kerguelen plume during the Comei LIP formation can be interpreted as the interaction among the Kerguelen plume,the overlying lithospheric mantle,and the upwelling asthenosphere.The magmatism of Comei LIP began at~140 Ma and then lasted and peaked at~132 Ma with the progressively lithospheric thinning of eastern Gondwana upon the impact of Kerguelen plume.展开更多
Geochemical data and Sr-Nd isotopes of the host rocks and magmatic microgranular enclaves(MMEs)collected from the Oligocene Nodoushan Plutonic Complex(NPC) in the central part of the Urumieh-Dokhtar Magmatic Belt(UDMB...Geochemical data and Sr-Nd isotopes of the host rocks and magmatic microgranular enclaves(MMEs)collected from the Oligocene Nodoushan Plutonic Complex(NPC) in the central part of the Urumieh-Dokhtar Magmatic Belt(UDMB) were studied in order to better understand the magmatic and geodynamic evolution of the UDMB. New U-Pb zircon ages reveal that the NPC was assembled incrementally over ca. 5 m.y., during two main episodes at 30.52 ± 0.11 Ma and 30.06 ± 0.10 Ma in the early Oligocene(middle Rupelian) for dioritic and granite intrusives, and at 24.994 ± 0.037 Ma and 24.13 ± 0.19 Ma in the late Oligocene(latest Chattian) for granodioritic and diorite porphyry units,respectively. The spherical to ellipsoidal enclaves are composed of diorite to monzodiorite and minor gabbroic diorite(SiO_2 = 47.73-57.36 wt.%; Mg# = 42.15-53.04); the host intrusions are mainly granite,granodiorite and diorite porphyry(SiO_2 = 56.51-72.35 wt.%; Mg# = 26.29-50.86). All the samples used in this study have similar geochemical features, including enrichment in large ion lithophile elements(LILEs, e.g. Rb, Ba, Sr) and light rare earth elements(LREEs) relative to high field strength elements(HFSEs) and heavy rare earth elements(HREEs). These features, combined with a relative depletion in Nb,Ta, Ti and P, are characteristic of subduction-related magmas. Isotopic data for the host rocks display ISr = 0.705045-0.707959, εNd(t) =-3.23 to +3.80, and the Nd model ages(TDM) vary from 0.58 Ga to 1.37 Ga. Compared with the host rocks, the MMEs are relatively homogeneous in isotopic composition,with Isr ranging from 0.705513 to 0.707275 and εNd(t) from -1.46 to 4.62. The MMEs have TDM ranging from 0.49 Ga to 1.39 Ga. Geochemical and isotopic similarities between the MMEs and their host rocks demonstrate that the enclaves have mixed origins and were most probably formed by interactions between the lower crust-and mantle-derived magmas. Geochemical data, in combination with geodynamic evidence, suggest that a basic magma was derived from an enriched subcontinental lithospheric mantle(SCLM), presumably triggered by the influx of the hot asthenosphere. This magma then interacted with a crustal melt that originated from the dehydration melting of the mafic lower crust at deep crustal levels. Modeling based on Sr-Nd isotope data indicate that ～50% to 90% of the lower crust-derived melt and ～10% to 50% of the mantle-derived mafic magma were involved in the genesis of the early Oligocene magmas. In contrast,～45%-65% of the mantle-derived mafic magma were incorporated into the lower crust-derived magma(～35%-55%) that generated the late Oligocene hybrid granitoid rocks. Early Oligocene granitoid rocks contain a higher proportion of crustal material compared to those that formed in the late Oligocene. It is reasonable to assume that lower crust and mantle interaction processes played a significant role in the genesis of these hybridgranitoid bodies, where melts undergoing fractional crystallization along with minor amounts of crustal assimilation could ascend to shallower crustal levels and generate a variety of rock types ranging from diorite to granite.展开更多
Carboniferous—Lower Permian volcanic rocks and small\|scale basic and ultrabasic intrusions occur in Chabu\|Chasang region of central Qiangtang plateau in northern Tibet Detailed studies of petrology and geochemistry...Carboniferous—Lower Permian volcanic rocks and small\|scale basic and ultrabasic intrusions occur in Chabu\|Chasang region of central Qiangtang plateau in northern Tibet Detailed studies of petrology and geochemistry of magmatic rocks further indicate that there were really a Late Paleozoic rift valley in Chabu\|Chasang area, and no so\|called Paleo\|Tethys suture zone existed there. The rift initially split in early Carboniferous, access the peak in Lower Permian, is closed and folded during Late Permian. The volcanic rocks composed of mainly basalts, a small amount of basaltic andesites and andesites, are zonally distributed, and occur alternately with flysch or flyschoid sandstones, slates, pebbled slates, radiolarian cherts and carbonate rocks. The sedimentary facies change rapidly toward both sides and show rapid deposits of proximal gravity flow.展开更多
Fractional crystallization of parental magmas of shoshonitic or silica-saturated,ultrapotassic affinity,with variable amount of concurrent crustal assimilation,may result in granitic and syenitic rocks.Typical plutoni...Fractional crystallization of parental magmas of shoshonitic or silica-saturated,ultrapotassic affinity,with variable amount of concurrent crustal assimilation,may result in granitic and syenitic rocks.Typical plutonic members of the shoshonitic series are monzonites and quartz monzonites,whilst syenites and quartz syenites are the dominant plutonic products of the ultrapotassic series.Lamprophyric magmas are commonly found in association with both series and are frequently part of coeval mingling/mixing systems.Ultrapotassic and shoshonitic primary magmas,including lamprophyric ones,are derived from amphibole-phlogopite-bearing mantle sources produced by previous,subduction-related metasomatism.Acidic and intermediate rocks can be derived from such parental magmas,generally through AFC processes.Shoshonitic-like granitoids,which have not clear relation with intermediate or basic shoshonitic rocks,or are produced dominantly by crustal melting,should be named high-Ba-Sr granitoids.This study focuses mainly on Neoproterozoic shoshonitic and silica-saturated ultrapotassic rock associations formed in post-collisional settings from southern Brazil and Uruguay.The source of magmas,their evolution,the role played by crustal contamination in modifying pristine geochemical signatures and their tectonic control are discussed based on elemental and Sr-Nd isotope geochemistry.The main features of plutonic rocks related to the shoshonitic series are their potassic,silica-saturated alkaline character,predominance of monzonitic to syenitic compositions,high Sr and Ba contents,monotonous,light REE-enriched patterns,and moderate HFSE contents.Syntectonic shoshonitic and high Ba-Sr granitoids within shear zones show lower alkali,LREE,HFSE,and Sr contents than those formed away from the main deformation sites.Plutonic rocks related to the extended silica-saturated ultrapotassic series are mostly syenites,alkalifeldspar granites and lamprophyres with K_(2)O/Na_(2)O ratios above 2.The typical values of^(87)Sr/^(86)Sri for shoshonitic plutonic rocks are 0.706–0.708,ranging from 0.704 to 0.710.Theε_(Nd)(t)values are negative and vary from 0 to-24.Crustal contribution tends to increase^(87)Sr/^(86)Sri and decreaseε_(Nd)(t)values,depending on protolith isotope signature,melting conditions and volume of assimilated material.Ultrapotassic rocks,on the other hand,show higher^(87)Sr/^(86)Sri ratios,from 0.709–0.711 up to 0.720.Geochemical evidence,including Sr-Nd isotope data,indicates that the shoshonitic and ultrapotassic rocks discussed in this study were formed from OIB-like sources with strong influence of previous subduction,probably a phlogopite,K-amphibole bearing veined mantle.Lithological variability in ultrapotassic-shoshonitic associations is interpreted to result from(i)variation of source composition,(ii)different melt fractions from similar sources,(iii)mixing-mingling,fractional crystallization,and assimilation processes.展开更多
The tectonic setting of the Himalaya during the Early Paleozoic has been a subject of enduring debate within the scientific community.Newly discovered bimodal intrusive rocks from comprehensive field geological invest...The tectonic setting of the Himalaya during the Early Paleozoic has been a subject of enduring debate within the scientific community.Newly discovered bimodal intrusive rocks from comprehensive field geological investigation in the central mountain range were subjected to petrology,zircon U-Pb geochronology,zircon Hf isotopes and whole-rock geochemistry analyses.The Palie bimodal intrusive rocks,comprising amphibolite and granitic gneiss,were formed at~489 Ma.The amphibolite exhibits geochemical characteristics consistent with N-MORB,while the granitic gneiss is classified as high potassium calc-alkaline peraluminous S-type granite.Both igneous rocks exhibit negative zirconε_(Hf)(t)values and display ancient T_(DM)^(C)ages.In conjunction with regional geological survey findings,it can be inferred that the formation of the Palie bimodal intrusive rocks occurred within a post-collision extensional tectonic setting.The amphibolite genesis involved partial melting of an enriched lithospheric mantle with some crustal assimilation,whereas the origin of the granitic gneiss can be attributed to partial melting of pre-existing felsic crust.Our data indicate that during the Early Paleozoic,the Himalaya underwent a transition from a pan-African collisional setting to post-collisional extensional tectonics.展开更多
基金supported by the Jiangsu Innovation and Entrepreneurship Project(JSSCBS20211225).
文摘The North China Craton(NCC)experienced significant lithospheric thinning of over 100 km during the Mesozoic,accompanied by extensive magmatic activity and extensional tectonics.However,the timing and mechanism of this thinning remain the subjects of debate.This study presents zircon U-Pb ages,Hf isotopic data and whole-rock elemental and Sr-Nd isotopic compositions of the Guanshui monzonites and diorites in the eastern NCC.Zircon U-Pb dating reveals that both rock types formed at ca.130 Ma.The monzonites,characterized by high Mg^(#)(50.9-57.9),low Nb/U ratios(2.53-3.89)and depleted isotopic compositions,suggest derivation from asthenospheric mantle modified by slab-derived fluids.The diorites,distinguished by low SiO_(2)(49.5-50.8),high Mg^(#)(66.7-68.5)and an EM2-type enriched mantle isotopic signature,point to a lithospheric mantle source modified by subducted sediment melts.The coexistence of monzonites and diorites suggests a transition in magma source from lithospheric to asthenospheric mantle,implying that lithospheric thinning may have commenced around 130 Ma.The destruction of the NCC was likely driven by localized,small-scale drip-style detachment processes,rather than wholesale lithospheric removal.
基金National Natural Science Foundation of China(41630640)National Science Foundation of Innovation Research Group(41521002)+1 种基金National Natural Science Foundation of China(41790445)Construction S&T Project of Department of Transportation of Sichuan Province(Grant No.2020A01).
文摘The stratum lithology and geological structure of the highway tunnel in the mountainous areas of western China are complex,and the engineering geological conditions are complicated.When the highway tunnel passes through different lithological strata,its structural design and construction technology are completely diff erent.Therefore,in order to support the tunnel design and construction,the tunnel survey Among them,the identification of the contact boundary between magmatic rock and metamorphic rock and the grade of surrounding rock is very important.Through magnetotelluric survey of the Mupi tunnel of Jiuzhaigou-Mianyang highway on G8513 line,2D forward numerical simulation,1D,2D,3D inversion,and engineering geological analysis,it is revealed that the electrical characteristics of each layer,focusing on the identification of the contact boundary between magmatic rock and metamorphic rock.This study provides the electrical characteristics of the magmatic rock and metamorphic rock contact boundary of the Mupi Tunnel.It is speculated that the boundary is revealed by the tunnel construction excavation,which verifies the correctness of the geophysical inversion model and provides a more detailed design basis for the tunnel design.I believe that taking the Mupi Tunnel survey as an example,through this research,it can provide detailed geophysical evidence for highway tunnels to distinguish between magmatic rock and metamorphic rock.
文摘The geochemical characteristics of rare earth elements of magmatic rocks of Yanshanian stage were studied in the south of Anhui Province and northeast of Jiangxi Province, Jiangnan Uplift. The result shows that the magmatic rocks of Yanshanian stage in the south of Anhui Province are the typical crust source type and those in the northeast of Jiangxi Province have the characteristics of mantle source type. So the polymetal deposits having relation to the magmatic rocks of Yanshanian stage in the northeast of Jiangxi Province were developed better than those in the south of Anhui Province. The research results of the rare earth elements are confirmed by the studies of geophysics,tectonic setting and stable isotope at the same time. It also indicates that the rare earth elements are the effective approach to tracing the material sources of magmatic rocks.
基金Project supported bythe National Natural Science Foundation of China (40472052)
文摘REE geochemical characteristics of the magmatic rocks and gold deposits in Shizishan ore-field of Tongling were studied. Three types of the magmatic rocks have almost the same chondrite-normalized REE patterns, Eu and Ce anomalous values, and ∑REE, ∑LREE/∑HREE regular changes, which indicates that their magmas come from the same source and their digenetic mechanism is fractional crystallization. In three gold deposits, the mineral ores and related altered rocks have similar chondrite-normalized REE patterns and sharp Eu positive anomalous values. The REE contents reduced from the magmatic rocks to skamization or alteration magmatic rocks, skam type ores, sulphide type ores, wall-rocks limestone or marble. The REE geochemical characteristics of the ores and related rocks show that primary fluids originated from magmatic differentiation in lower pressure of shallow crust, ore-forming hydrothermal solutions gained REE and mineralization elements further from leaching the magmatic rocks, then superimposed and reformed the limestones or marbles and deposited ore-forming material.
基金financially co-supported by the Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources (Nos. J1901-7,J1901-16)the State Scholarship Fund (No. 201904180031)+4 种基金the National Key Research and Development Project of China (No. 2016YFC0600310)the 2nd Tibetan Plateau Scientific Expedition (No. 2019QZKK0802)the National Natural Science Foundation of China (Nos. 41672046,41641015,41762005,41720104009,41703036)the China Geological Survey (No. DD201190060)the International Geological Correlation Project (No. IGCP-649)
文摘In this study,we report systematically field observations,geochronology,whole-rock geochemistry and Sr-Nd-Hf isotopic dataset on the various types of magmatic rocks collected from the Zedang area.Chemically,the diabase and gabbro have a low-K calc-alkaline affinity,whereas the basalt and plagiogranite have medium to high-K calc-alkaline characteristics.In addition,the basalts are highly enriched in light rare earth elements(LREE)and large ion lithophile elements(LILE),but strongly depleted in high strength field elements(HFSE),indicating that their magma source probably was derived from a subduction-or arc-related setting.In contrast,both the gabbro and diabase mainly demonstrate an N-MORB-like affinity consistent with normal mid-oceanic ridge basalt(N-MORB)origin.The zircon U-Pb dating results suggest that the basalts were crystallized earlier at ca.158–161 Ma(Oxfordian stage),but the gabbro was crystallized at ca.131 Ma(Hauterivian stage of Early Cretaceous).The zircon U-Pb dating results correspond with the field observations that the veins of gabbro intruded basalt.Furthermore,the plagiogranite has a weighted mean age of ca.160 Ma(MSWD=2.1)consistent with the basalt within the uncertainty.The basalt and the plagiogranite have significantly positiveεHf(t)values(+5.8 to+15.6 and+8.6 to+16.1,respectively),suggesting that they were originated from partial melting of a depleted source.However,basalt and plagiogranite are characterized by the wide variations ofεHf(t)values indicating minor amounts of exotic crustal material input during the later magma evolution.Additionally,the basalt shows duplex geochemical features of island-arc and mid-oceanic ridge basalt,corresponding to the supra-subduction zone-(SSZ)type affinity.To sum up,two distinct magmatic events identified in this study probably suggest an intra-oceanic arc system existing in the Zedang area during the Late Jurassic,but the intra-oceanic arc subduction extinguished in the Early Cretaceous as suggested by the N-MORB-like gabbro and diabase.Integrated with regional background and different rock types,as well as geochemical features,we conclude that intra-oceanic arc subduction setting developed during the Late Jurassic in the Zedang area,southern Tibet.
文摘The Early Jurassic bimodal volcanic rocks in the Yeba Formation, situated between Lhasa, Dagze and Maizhokunggar, composed of metabasalt, basaltic ignimbrite, dacite, silicic tuff and volcanic breccia, are an important volcanic suite for the study of the tectonic evolution of the Gangdise magmatic arc and the Mesozoic Tethys. Based on systematic field investigations, we carried out geochemical studies on representative rock samples. Major and trace element compositions were analyzed for these rock samples by XRF and ICP-MS respectively, and an isotope analysis of Rb-Sr and Sm-Nd was carried out by a MAT 262 mass spectrograph. The results show that the SiO2 contents in lava rocks are 41 %-50.4% and 64 % -69 %, belonging to calc-alkaline basalt and dacite. One notable feature of the basalt is its low TiO2 content, 0.66%-1.01%, much lower than those of continental tholeiite. The ∑REE contents of basalt and dacite are 60.3-135 μg/g and 126, 4--167.9μg/ g respectively. Both rocks have similar REE and other trace element characteristics, with enriched LREE and LILE relative to HREE and HFS, similar REE patterns without Eu anomaly. The basalts have depleted Ti, Ta and Nb and slightly negative Nb and Ta anomalies, with Nb = 0.54--1.17 averaging 0. 84. The dacites have depleted P and Ti and also slightly negative Nb and Ta anomalies, with Nb= 0. 74 -1. 06 averaging 0. 86. Major and trace elemental and isotopic studies suggest that both basalt and dacite originated from the partial melting of the mantle wedge at different degrees above the subduction zone. The spinal Iherzolite in the upper mantle is likely to be their source rocks, which might have been affected by the selective metasomatism of fluids with crustal geochemistry. The LILE contents of both rocks were affected by metamorphism at later stages. The Yeba bimodal volcanic rocks formed in a temporal extensional situation in a mature island arc resulting from the Indosinian Gangdise magmatic arc.
基金Project(2017YFC1503100)supported by the National Key Research and Development Program of ChinaProjects(51974062,41672301,51811530312)supported by the National Natural Science Foundation of ChinaProject(N180101028)supported by the Fundamental Research Funds for the Central Universities,China。
文摘In order to explore the control effect of backfill mining on dynamic disasters under special geological mining conditions of overlying thick magmatic rock(TMR),a three-dimensional numerical model of a panel of one side goaf in Yangliu coal mine with double-yield backfill material constitutive model was developed.The simulation results were then compared with field monitoring data.The dynamic disaster control effect of both caving and backfill mining was analyzed in three different aspects,i.e.,displacement field,stress field and energy field.The results show that in comparison to the full caving mining method,the bearing capacity of the goaf after backfilling was enhanced,the backfill mining can effectively reduce the stress and energy accumulated in the coal/rock body,and the backfill mining eliminates the further moving space of TMR and prevents its sudden rupture.Before TMR fracture,the subsidence displacement of TMR was reduced by 65.3%,the front abutment stress of panel decreased by 9.4%on average and the high energy concentration zone around panel was also significantly reduced.Overall,the results of this study provide deeper insights into the control of dynamic disasters by backfill mining in mines.
基金This work is supported by the National Natural Science Foundation of China （No. 40572038）.
文摘Morphological and chemical studies on zircon grains from gabbro and granite of the Pingtan magmatic complex, Fujian Province, eastern China, show that there are three stages of zircon growth. The early stage of zircon growth is characterized by colorlessness, high transparence and birefringence, low and dispersive Ipr and Ipy, weak and homogeneous BSE brightness, lower Hf content and depletion of U, Th and Y; the middle stage is characterized by abruptly increasing lpy, progressively strong and sectoral-zoning BSE brightness, higher Hf content and enrichment of U, Th and Y with Th/U 〉 1; the late stage of growth is characterized by brownish color, poor transparence, low birefringence, highest Ipr and Ipy, middle and oscillatorily-zoning BSE brightness, highest contents of Hf, U and Y with Th/U 〈 1. The stages are considered to be formed in a deep magma chamber, ascent passage and emplacement site, respectively. Due to the more or less long residual time of the magma chamber, the difference in age between the early and late stages of zircon might be great enough to be distinguished, which can be attributed to tectonic constraint for the magnlatism.
基金supported by the Ministry of Land and Resources of China under grant No.201211095
文摘A new method for determining the partial melting depth of mantle-derived magma and lithospheric thickness in continental regions is derived from REE geochemistry. This effective technique uses variations in the Ce/Yb and Sm/Yb ratios found in mainly volcanic rocks in continental China. The ratios change with the depth of origin consistent with the correlation between lithospheric thickness and the Ce/Yb and Sm/Yb ratios found in oceanic basalt. These ratios increase exponentially with the depth of origin, the lithospheric thickness, of a wide variety of Cenozoic volcanic basalt and Paleozoic kimberlite in the North China Craton, northeastern China continent and vicinity. This functional relationship with depth is shown in a plot of the ratios that forms a concordia curve, which is closely expressed by formulas using 8–degree polynomials. These provide a more accurate gage in measuring the lithospheric thickness than the traditional geophysical methods. When applied to volcanic rock of different ages it also reveals how the thickness has changed over time and thus, greatly aids the understanding of the tectonic history. Relations between the COcontent, mineral reactions and pressure in the upper asthenosphere beneath the base of the lithosphere appears to affect the proportions of REE in partial melts and brings about a close correlation between lithospheric thickness and the Ce/Yb and Sm/Yb ratios in mantle–derived magmatic rock. This thickness gauge, for both continental and oceanic lithosphere, provides a new approach in analyzing the lithospheric thickness in different tectonic settings and geologic times.
基金financially supported by National Science Foundation of China(grant No.41303026)the funded project of the China Geological Survey(grants No.DD20160030,DD20160351 and DD20160029)
文摘Objective Petrogenesis of the Paleoproterozoic mafic dikes and their tectonic implications are of great significance to the tectonic evolution of the Yangtze craton as well as the paleoposition of the Yangtze craton relative to the Columbia supercontinent.Till now,
基金This research was supported by the National Natural Science Foundation of China grant 49573186.
文摘Abstract: Types of polymerized molecular network structure and degree of bond breakdown for glass phases of magmatic inclusions and glassy matrix in volcanic rocks from the Shengli oilfield have been defined by the laser Raman spectroscopic investigation. There are significant differences in types of polymerized molecular network structure and degree of bond breakdown of the magmatic glass phases between the non-CO2 and CO2 gas pools: magmatic glass phases of fluid inclusions and matrix in volcanic rocks from the CO2 gas pool contain more sheet network molecules and have a greater degree of bond beakdown than those from the non-CO2 gas pool; and when gas bubbles occur in evolving magma, magma saturated with volatile components has more sheet network molecules. The results suggest the magmadegassing mechanism of the formation of CO2 gas pools in the Shengli oilfield.
基金the 8th Geological Brigade of Aksu,Xinjiang, the Institute of Geology of the Chinese Academy of Geological Sciencesthe Beijing Research Institute of Uranium Geology,CNNC
文摘Objective The Sachakou Pb-Zn polymetallic deposit is located in Hetian County, Xinjiang （geographical coordinates of E78° 57＇ 54.30＂-78°59＇ 53.63＂, N34° 39＇ 27.50＂-34° 40＇ 57.21＂）. It belongs to the West Kunlun orogenic belt on the northwest edge of the Qinghai-Tibet Plateau and is connected to the Sanjiang orogenic belt to the south （Spurlin et al., 2005）. In recent years, a series of Pb-Zn mineralized spots and deposits have been discovered in this area one after another, which is called the Huoshaoyun ore concentration area. Among them, the Sachakou Pb-Zn deposit has reserves up to140 Mt, which has reached a large scale. However, the study on the genesis of deposits in this area has only just begun. This work studied the genesis ofthis Pb-Zn deposit in order to provide new ideas for the genesis of regional deposits and regional prospecting.
文摘The Mazhuangshan area lies in northeast to Aqikekuduke, where are distributed intermediate\|acid rocks, which were formed in the Middle\|Late Carboniferous epoch. The magmatic rocks are peraluminous and belong to calcareous series. All values of ACNK(1.03-\{2.12\}), ANK(1.67-2.93), SI(4.1-33), δ(0.71-4.82), La/ΣREE(0.09-0.26) ΣLREE/ΣHREE(1.76-11.01), (La/Sm)\-N(1.60-6.35), (Sm/Nd)\-N(0.33-0.58), (La/Yb)\-N(4.7-12.1), La\-N/Lu\-X(5.9-11.8), (Ce/Yb)\-N(3.14-6.64), δEu(0.38-\{1.06\}), Rb\-N/Sr\-N(42-120) and Sr\+*(0.02-0.2) demonstrate they vary with DI(\{45-90\}). S\|B diagram also shows that the lithophile elements are abundant in acidic magmatic rocks. Moreover, it is concluded that the primitive magma originated from a subduction zone at the continental edge, and underwent fractional crystallization and contamination, then generated the magmatic rocks. The multi\|cation index (R1: 3055-3993, R2: 286-438) shows that the primitive magma originated from the mantle. All these conclusions are beneficial for exploring gold deposits in the area.
基金funded by grants from the Ministry of Science and Technology of China (Sinoprobe-05-02)the NSF China (Nos. 41502062, 41672046, 41202036)+2 种基金the China Geological Survey (Nos. DD20160023)grants from the Institute of Geology, Chinese Academy of Geological Sciences (J1526)IGCP-649
文摘The Yarlung Zangbo suture zone extends more than2000 km along southern Tibet and marks the boundary between the Indian subcontinent and Eurasia.The Zedong terrane has been not suggested to represent the vestige of such an intra-oceanic arc developed within the Neo-Tethys Ocean,as a result of the northward subduction of the Neo-Tethys Ocean during the Late Jurassic.In this study,we present detailed geochemical and geochronological data of various types of magmatic rocks widely exposed in the Zedong terrane to constrain the formation age and tectonic setting of the Zedong terrane.We found that the Zedong volcanic rocks belong to high K2O calc-alkaline series,whereas the diabase and gabbro plotted in the low-K calcalkline.The basalt rocks are highly enriched in LREE and LILE,but strongly depleted in HFSE,indicating they were derived from a metasomatized mantle.Both gabbros and diabase have similar N-MORB geochemistry indicates that the cumulates were produced from MOR setting.Zircons from four samples,including the basalt rocks(158-161Ma)are older than the gabbro(131 Ma),certificate the gabbro are as the vein intrude into the basalt rocks.This suggests that the volcanic eruption and plutonic emplacement were coevally developed in the Zedonghave similar positiveεHf(t)values(+2.0 to+15.6)and(+8.6 to+18.4),indicating they were stemmed from similarly depleted mantle sources,same with the gabbro and granitic rocks from the Gangdese arc.Therefore,we proposed that the basalt rocks in the Zedong terrane were formed through partial melting of the mantle wedge metasomatized by slab-released fluids/melts.A part of hydrous basalts were underplated in the thickened lower crust beneath the Zedong terrane,which gave rise to the cumulate and granitic rocks.This suggests that the Zedong terrane represents a slice of the active continental margin developed on the southern margin of the Lhasa terrane as a result of the northward subduction of the Neo-Tethys Ocean during the Late Jurassic,although a possible intra-oceanic arc setting cannot be excluded.
文摘Within southern Mali, the Syama belt constitutes a linear major structure-oriented N-S, which host several gold deposits (e.g., Syama and Tabakoroni) and prospect areas (e.g. Tellem). The Syama Belt is formed by magmatic rocks (basalts, lamprophyres, andesites, dacites and microgranites);sedimentary rocks (shales) and volcano-sedimentary rocks (pyroclastics). The magmatic rocks are divided into two main volcanic series: tholeiitic affinity rocks (basalts and lamprophyres) and calc-alkaline affinity (andesites) that are the most evolved. The field relationships between rocks of these two series suggest that the calc-alkaline series are younger the tholeiitic series. These tholeiitic series present the Mid-Ocean Ridge Basalt (MORB) affinity whereas the calc-alkaline series would be linked to an island arc-type. This coexistence is not an isolated case within the West African Craton (WAC). Otherwise, the Syama belt has all the characteristics of other belts, within which a number of gold deposits are developed, in the WAC.
基金supported by the Second Tibetan Plateau Scientific Expedition and Research(No.2019QZKK0702)the National Natural Science Foundation of China(Nos.92055202,41873023,42102059)+3 种基金the China Geological Survey(No.DD20190057)the National Key Research and Development Project of China(No.2016YFC0600304)the Basic Scientific Research Fund of Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources(Nos.J1901-1,J190110)the National Foundation from China Scholarship Council。
文摘The Niangzhong diabase dikes,dated at 138.1±0.4 Ma,are located within the outcrop area of the Comei large igneous province(LIP).These diabase samples can be divided into two groups:samples in Group 1 show varying MgO(1.50 wt.%-10.25 wt.%)and TiO_(2)(0.85 wt.%-4.63 wt.%)contents,and enriched initial isotope compositions(^(87)Sr/^(86)Sr(t)=0.7056-0.7112,ε_(Nd)(t)=-0.3-+3.8),with OIB-like REEs and trace elements patterns,resulting from low degree melting of garnet-bearing lherzolite mantle sources;in contrast,samples in Group 2 show limited MgO(4.14 wt.%-7.75 wt.%)and TiO_(2)(0.98 wt.%-1.69 wt.%)contents,and depleted initial isotope compositions(^(87)Sr/^(86)Sr(t)=0.7075-0.7112,ε_(Nd)(t)=+5.5-+6.2),with N-MORB-like REEs and trace elements patterns,resulting from relatively high degree melting of spinel-bearing lherzolite mantle source.Combined with the published representative data about Comei LIP,we summarize that the source components for Comei LIP products include OIB end-member,enriched OIB end-member,and N-MORB end-member,respectively.Melts modeling suggests that magmas in the Comei LIP evolve in a relatively high oxygen fugacity condition,which influenced their fractionation sequences and led to systematic changes of TiO_(2)contents,Ti/Y and Ti/Ti*ratios.From the spatial and temporal distribution of above three end-member samples,deep process of Kerguelen plume during the Comei LIP formation can be interpreted as the interaction among the Kerguelen plume,the overlying lithospheric mantle,and the upwelling asthenosphere.The magmatism of Comei LIP began at~140 Ma and then lasted and peaked at~132 Ma with the progressively lithospheric thinning of eastern Gondwana upon the impact of Kerguelen plume.
文摘Geochemical data and Sr-Nd isotopes of the host rocks and magmatic microgranular enclaves(MMEs)collected from the Oligocene Nodoushan Plutonic Complex(NPC) in the central part of the Urumieh-Dokhtar Magmatic Belt(UDMB) were studied in order to better understand the magmatic and geodynamic evolution of the UDMB. New U-Pb zircon ages reveal that the NPC was assembled incrementally over ca. 5 m.y., during two main episodes at 30.52 ± 0.11 Ma and 30.06 ± 0.10 Ma in the early Oligocene(middle Rupelian) for dioritic and granite intrusives, and at 24.994 ± 0.037 Ma and 24.13 ± 0.19 Ma in the late Oligocene(latest Chattian) for granodioritic and diorite porphyry units,respectively. The spherical to ellipsoidal enclaves are composed of diorite to monzodiorite and minor gabbroic diorite(SiO_2 = 47.73-57.36 wt.%; Mg# = 42.15-53.04); the host intrusions are mainly granite,granodiorite and diorite porphyry(SiO_2 = 56.51-72.35 wt.%; Mg# = 26.29-50.86). All the samples used in this study have similar geochemical features, including enrichment in large ion lithophile elements(LILEs, e.g. Rb, Ba, Sr) and light rare earth elements(LREEs) relative to high field strength elements(HFSEs) and heavy rare earth elements(HREEs). These features, combined with a relative depletion in Nb,Ta, Ti and P, are characteristic of subduction-related magmas. Isotopic data for the host rocks display ISr = 0.705045-0.707959, εNd(t) =-3.23 to +3.80, and the Nd model ages(TDM) vary from 0.58 Ga to 1.37 Ga. Compared with the host rocks, the MMEs are relatively homogeneous in isotopic composition,with Isr ranging from 0.705513 to 0.707275 and εNd(t) from -1.46 to 4.62. The MMEs have TDM ranging from 0.49 Ga to 1.39 Ga. Geochemical and isotopic similarities between the MMEs and their host rocks demonstrate that the enclaves have mixed origins and were most probably formed by interactions between the lower crust-and mantle-derived magmas. Geochemical data, in combination with geodynamic evidence, suggest that a basic magma was derived from an enriched subcontinental lithospheric mantle(SCLM), presumably triggered by the influx of the hot asthenosphere. This magma then interacted with a crustal melt that originated from the dehydration melting of the mafic lower crust at deep crustal levels. Modeling based on Sr-Nd isotope data indicate that ～50% to 90% of the lower crust-derived melt and ～10% to 50% of the mantle-derived mafic magma were involved in the genesis of the early Oligocene magmas. In contrast,～45%-65% of the mantle-derived mafic magma were incorporated into the lower crust-derived magma(～35%-55%) that generated the late Oligocene hybrid granitoid rocks. Early Oligocene granitoid rocks contain a higher proportion of crustal material compared to those that formed in the late Oligocene. It is reasonable to assume that lower crust and mantle interaction processes played a significant role in the genesis of these hybridgranitoid bodies, where melts undergoing fractional crystallization along with minor amounts of crustal assimilation could ascend to shallower crustal levels and generate a variety of rock types ranging from diorite to granite.
文摘Carboniferous—Lower Permian volcanic rocks and small\|scale basic and ultrabasic intrusions occur in Chabu\|Chasang region of central Qiangtang plateau in northern Tibet Detailed studies of petrology and geochemistry of magmatic rocks further indicate that there were really a Late Paleozoic rift valley in Chabu\|Chasang area, and no so\|called Paleo\|Tethys suture zone existed there. The rift initially split in early Carboniferous, access the peak in Lower Permian, is closed and folded during Late Permian. The volcanic rocks composed of mainly basalts, a small amount of basaltic andesites and andesites, are zonally distributed, and occur alternately with flysch or flyschoid sandstones, slates, pebbled slates, radiolarian cherts and carbonate rocks. The sedimentary facies change rapidly toward both sides and show rapid deposits of proximal gravity flow.
基金Brazilian Research Council(CNPq)for the productivity grants to Lauro Valentim Stoll Nardi(No.306605/2018-0)and Maria de Fátima Bitencourt(No.311486/2015-0)funding through Universal Project(No.481841/2012-1)。
文摘Fractional crystallization of parental magmas of shoshonitic or silica-saturated,ultrapotassic affinity,with variable amount of concurrent crustal assimilation,may result in granitic and syenitic rocks.Typical plutonic members of the shoshonitic series are monzonites and quartz monzonites,whilst syenites and quartz syenites are the dominant plutonic products of the ultrapotassic series.Lamprophyric magmas are commonly found in association with both series and are frequently part of coeval mingling/mixing systems.Ultrapotassic and shoshonitic primary magmas,including lamprophyric ones,are derived from amphibole-phlogopite-bearing mantle sources produced by previous,subduction-related metasomatism.Acidic and intermediate rocks can be derived from such parental magmas,generally through AFC processes.Shoshonitic-like granitoids,which have not clear relation with intermediate or basic shoshonitic rocks,or are produced dominantly by crustal melting,should be named high-Ba-Sr granitoids.This study focuses mainly on Neoproterozoic shoshonitic and silica-saturated ultrapotassic rock associations formed in post-collisional settings from southern Brazil and Uruguay.The source of magmas,their evolution,the role played by crustal contamination in modifying pristine geochemical signatures and their tectonic control are discussed based on elemental and Sr-Nd isotope geochemistry.The main features of plutonic rocks related to the shoshonitic series are their potassic,silica-saturated alkaline character,predominance of monzonitic to syenitic compositions,high Sr and Ba contents,monotonous,light REE-enriched patterns,and moderate HFSE contents.Syntectonic shoshonitic and high Ba-Sr granitoids within shear zones show lower alkali,LREE,HFSE,and Sr contents than those formed away from the main deformation sites.Plutonic rocks related to the extended silica-saturated ultrapotassic series are mostly syenites,alkalifeldspar granites and lamprophyres with K_(2)O/Na_(2)O ratios above 2.The typical values of^(87)Sr/^(86)Sri for shoshonitic plutonic rocks are 0.706–0.708,ranging from 0.704 to 0.710.Theε_(Nd)(t)values are negative and vary from 0 to-24.Crustal contribution tends to increase^(87)Sr/^(86)Sri and decreaseε_(Nd)(t)values,depending on protolith isotope signature,melting conditions and volume of assimilated material.Ultrapotassic rocks,on the other hand,show higher^(87)Sr/^(86)Sri ratios,from 0.709–0.711 up to 0.720.Geochemical evidence,including Sr-Nd isotope data,indicates that the shoshonitic and ultrapotassic rocks discussed in this study were formed from OIB-like sources with strong influence of previous subduction,probably a phlogopite,K-amphibole bearing veined mantle.Lithological variability in ultrapotassic-shoshonitic associations is interpreted to result from(i)variation of source composition,(ii)different melt fractions from similar sources,(iii)mixing-mingling,fractional crystallization,and assimilation processes.
基金supported by the China Geological Survey Program(Grant No.DD20220989)the National Natural Science Foundation of China(Grant No.41972118)。
文摘The tectonic setting of the Himalaya during the Early Paleozoic has been a subject of enduring debate within the scientific community.Newly discovered bimodal intrusive rocks from comprehensive field geological investigation in the central mountain range were subjected to petrology,zircon U-Pb geochronology,zircon Hf isotopes and whole-rock geochemistry analyses.The Palie bimodal intrusive rocks,comprising amphibolite and granitic gneiss,were formed at~489 Ma.The amphibolite exhibits geochemical characteristics consistent with N-MORB,while the granitic gneiss is classified as high potassium calc-alkaline peraluminous S-type granite.Both igneous rocks exhibit negative zirconε_(Hf)(t)values and display ancient T_(DM)^(C)ages.In conjunction with regional geological survey findings,it can be inferred that the formation of the Palie bimodal intrusive rocks occurred within a post-collision extensional tectonic setting.The amphibolite genesis involved partial melting of an enriched lithospheric mantle with some crustal assimilation,whereas the origin of the granitic gneiss can be attributed to partial melting of pre-existing felsic crust.Our data indicate that during the Early Paleozoic,the Himalaya underwent a transition from a pan-African collisional setting to post-collisional extensional tectonics.
