Petrology,geochemistry and metamorphic evolution of Lancang Group in the Changning-Menglian complex belt and its implications on the tectonic evolution of the Paleo-TethysEI北大核心CSCD

Lancang Group within the Changning-Menglian complex belt in the Sanjiang area, Yunnan Province involves many kinds of meta-sediments, including staurolite-kyanite-bearing garnet-mica schist, garnet-mica schist, chloritoid-white mica schist and chlorite-glaucophane-albite schist. Detailed petrographic observation, mineral chemistry analysis and phase equilibrium modelling have shown that these meta-sediments preserve distinctly metamorphic evolutions. The staurolite-kyanite-bearing garnet-mica schist records the decompression and cooling histories related to retrograded metamorphic processes from middle-temperature eclogite facies to amphibolite facies with a peak mineral assemblage of garnet + kyanite + phengite + jadeite formed at the P-T condition of about 19 similar to 30kbar and 600 similar to 750 degrees C. For the garnet-mica schist, the peak metamorphic mineral association constrained by X-Prp and X-Grs in garnet, and Si content in phengite includes garnet + phengite + omphacite + lawsonite + paragonite and the related P-T condition is around 17 similar to 19. 5kbar and 430 similar to 475 degrees C . The chloritoid-white mica schist is characterized by the mineral assemblage of chloritoid + phengite + paragonite + chlorite whereas the peak mineral assemblage includes phengite + paragonite + carpholite. The peak P-T condition defined by Si content in phengite is limited in the range of 17 similar to 19kbar and 300 similar to 330 degrees C. Both garnet-mica schist and chloritoid-white mica schist consistently record heating and decompression processes from lawsonite-blueschist facies to epidote-blueschist facies. Metamorphic reactions and mineralogy of chlorite-glaucophane-albite schist roughly give the P-T condition of 9 similar to 11kbar and 430 similar to 520 degrees C. Studies on the geochemistry of Lancang Group reveal that these meta-sediments show the geochemistry affinity to the continental arc, active continental margin and upper crust sediments. The protoliths are mainly mud rock and sandstone with low maturity and a little of mafic-intermediate volcanic rock. The sediment sources are predominantly intermediate-acid magmatic rocks with old sedimentary contamination to different degree. Tectonic discrimination diagrams show that meta-sediments in the Lancang Group are mainly derived from the continental island arc or active continental margin tectonic setting. Combined with the metamorphism and geochemistry characteristics of these rocks in the Changning-Menglian complex belt, it is therefore inferred that the meta-sediments of Lancang Group display various metamorphic evolutions. Lancang Group are considered to have experienced multi-phase/stage and complex tectonic evolution histories.     

Geochemistry,petrogenesis and tectonic setting of the peraluminous granites in the nacheng gold deposit,Yongning, Guangdong北大核心

The Nacheng granite locates in the Yong ning area, Guangdong Province. This paper studied petrographical and chronological characteristics of this granite as well as its petrogenesis and geological significance. The Nacheng granite mainly consists of quartz (40%-50%), orthoclase (25%-30%), palgioxlase (15%-20%) with minor accessory minerals of quartz apatite and magnetite. Geochemical analyses show that the manziying granite has high content of SiO2 (75. 56%) , K2O (4.72%), Al2O3 (13. 34%) and total alkali (Na2O+K2O=7. 49%), but relatively low MgO (0. 04%-1. 29%) and CaO (0. 39%-2. 21%). The ratios of K2O/Na 2O are generally higher than 1. The Rittmann indexes are between 1-2. 43, belonging to the high-K calc-alkaline series. The values of A/CNK vary from 1. 12 to 1. 32 with an average of 1. 10, showing the characteristics of peraluminous S type granites. Trace element analyses show that the Nacheng granite has relatively high REE content of 82. 6 × 10-6 225. 68 × 10-1, and displays right-inclined V-shape REE patterns with relatively high fractionations of LREE and HREE[(La/Yb)N = 1. 51-9. 66] and pronounced negative Eu anomalies (δEu = 0. 31-0. 74) in the chondrite-normalized REE diagrams, suggesting a typical crust-derived grandite. The magmas may be divided into two types: "low-temperature" type from mudstones and "high-temperature" type from sandstones. The Nacheng granites were formed from the post-orogenic tectonic setting.     

Morphotectonics and tectonic processes of the Southwest Indian OceanEI北大核心CSCD

The Southwest Indian mid-ocean ridge (SWIR) is an ultraslow spreading ridge. Based on the submarine bathymetric data, we develop a new division principle on submarine morphotectonics and subdivide the SWIR into the seven-order tectonic geomorphologic units. Taking its submarine morphotectonics in the middle segment and adjacent seafloors of the mid-ocean ridge between Discovery II and Gallieni transform faults as a sample, this paper systematically analyzes its tectonic evolution, segmentation, segmentation and propagation mechanism, the formation of the central rift valley, the ridge-plume interactions, and the ocean ridge jumping. The results showed that the mid-ocean ridges can be divided into four three-order morphotectonics units (i.e., one-order segments of mid-ocean ridge), from west to east, which are separated by the Andrew Bain, the Prince Edwards, the Discovery II, and the Gallieni transform faults, respectively, corresponding to ridge landforms associated with a strongly hotspot-affected ridge, a weakly hotspot-affected ridge, and a normal ultraslow spreading ridge. Each segment can be further subdivided into three or four secondary segments. This paper focuses only on the segmentation and division from fourth-order to seventh-order morphotectonics units between the Discovery II and the Gallieni transform faults (i.e., the fourth-order morphotectonics unit of mid-ocean ridges can be subdivided into other three secondary units). Here the seventh-order morphotectonics unit consists of segments of laterally-aligned rifts (shear zone), en echelon rifts, and other transverse-faulting structures. The mid-ocean ridge segment experienced three oceanic ridge jumping at about 80 Ma, 60 Ma and 40 Ma, respectively, which were affected by the Marion and Crozet hotspots, or the Madagascar Plateau, etc. The oceanic processes of the SWIR are related to the Gondwana breakup, and its tectonic processes has been analyzed in detail as the periodic pull-apart extension, domino-style half-graben, graben subsidence, oceanic core complex, etc. in axial mid-oceanic ridge since 20 Ma. ©, 2015, Science Press. All right reserved.     

Geochemistry of the ore-bearing porphyry of lurige mo (Cu) deposit,Qinghai: Implications for tectonic setting and lithogenesis北大核心

Lurige molybdenite-copper deposit is a newly discovered deposit in the northern Sanjiang polymetallic ore belt, southern Qinghai, China. This paper presents data of major elements, trace elements, Sr-Nr-Pb isotopes and petrological analyses and studies, the geochcmical characteristics of the Lurige porphyries to reveals the origin, source area and tectonic background of formation of the porphyries. The geochcmical data indicate that (1) the porphyries belong to the cal-alkaline series, (2) 87Sr/86 Sr= (0. 705 351 -0. 706 830), 206Pb/204 Pb= ( 19. 2032 -19.3650), 207PV204Pb= (15.6850-15.6583), 202Pb/204Pb = (39.2616-39.5228), (3) LREE and LILE are enriched in the porphyries, (4) the biotite granitic porphyries show weak Eu-deficit anomaly and the leucogranitic porphyries have strong Eu-deficit anomaly. These findings suggest that the source was probably located in the mantlecrust transition area, which was contaminated by the fluid carried in the subducted slab. The enriched magma was probably directed by the strike-slip fault system formed during the Indo-Asia collision in the Eocene, and then emplaced in the study area.     

Geochronology,Geochemistry and Petrogenesis of the Pungco Ophiolite,TibetEI北大核心CSCD

Although the middle section of the Bangong-Nujiang suture zone has been intensively investigated, its tectonic framework and evolution is still controversy. The Pungco ophiolite has a relative complete ophiolitic complex, which is an ideal specimen for studying this tricky problem. LA-ICP-MS U-Pb dating of zircons from the diabasic rock yielded an age of 159.0±2.1 Ma. This age suggests that the Pungco ophiolite was formed in the Late Jurassic, indicating the development of the Late Jurassic ophiolite in the third ophiolitic subzone. The whole-rock major and trace element compositions of diabasic and basaltic rocks exhibit mixed arc and N-MORB geochemical characteristics. Two diabasic samples have (87Sr/86Sr)i values of 0.7055 and 0.7063 and εNd(t) values of 11.28 and 11.84, respectively. The geochemical signatures and formation age of the Pungco ophiolite suggest that this ophiolite was probably produced in an active continental fore-arc setting. It originated from a N-MORB-like depleted mantle source with the involvement of subducted-slab fluids. Considering the regional geological background, the Pungco ophiolite was likely generated during the southward subduction of the Bangong-Nujiang Tethyan oceanic lithosphere beneath the Lhasa terrane, and belongs to a regional archipelagic arc-basin system together with the other Early Jurassic-Early Cretaceous ophiolites from the northern Tibet Lake district. © 2018, Science Press. All right reserved.     

Provenance and tectonic setting of the Gudongjing Group in Beishan OrogenSCIEI北大核心CSCD

增生造山带中陆源碎屑岩物源区特征的研究可为解剖造山带结构甚至大陆地壳的形成和演化提供关键证据。北山造山带中部的古硐井群被认为是前寒武纪稳定沉积盖层,是北山造山带存在微陆块的重要依据。本文围绕古硐井群的物源区特征,进行了碎屑颗粒和重矿物统计、全岩主微量元素地球化学分析、碎屑锆石U-Pb年代学和Hf同位素测试。古硐井群碎屑岩的碎屑颗粒多呈棱角状,主要为石英、长石,同时含大量硅质岩碎屑和一定数量的火山岩碎屑;重矿物组成以褐铁矿、锆石、白钛石、尖晶石为主,角闪石、电气石、辉石次之,暗示物源区可能存在蛇绿岩、增生杂岩。全岩主量元素以高硅、高铝、富碱、低锰为特征,结合REE、Cr、Co、Sc和Th等惰性元素含量特征共同指示了长英质的物源区。最年轻的碎屑锆石年龄为443.9±13Ma,表明古硐井群最大沉积时限为晚奥陶世。碎屑锆石的年龄高度集中于470Ma附近,且该区间锆石ε_Hf(t)值多为正值,指示物源区存在大量新生地壳物质。本文推测古硐井群可能形成于增生楔楔顶盆地;研究结果支持北山造山带是古生代持续增生造山的产物这一认识。     

Pre-Cenozoic tectonic attribute and setting of the Song Da zone,VietnamEI北大核心CSCD

Rock association and regional unconformity are identified based on field survey and mapping for the stratigraphy, tectonics, metamorphic rock and igneous rocks in the Song Da zone, the northwestern Vietnam. Pre-Cenozoic in the Song Da zone is divided into three structural layers: (1) the Presinian crystalline basement, (2) the Cambrian-lower part of Upper Triassic, and (3) the upper part of Upper Triassic-Cretaceous. The Pre-Cenozoic structural successions of the Song Da zone show similar features with those of the Yangtze-South China plate: (1) In the Presinian, both of them have TTG complex and Khondalite series of similar ages and experienced similar tectonic evolution; (2) In the Cambrian-early Upper Triassic, the phosphorite and thick-layered limestone are comparable, and the Permian-Triassic basalt in the Song Da zone has genetic mechanism similar to that of the Emeishan basalt; (3) In the late Upper Triassic-Cretaceous, the volcanic-sedimentary faulted basins and thick continental red beds are comparable to those in East China. It can be concluded that the Song Da zone should have been part of the southwestern Yangtze-South China plate, and the boundary between the Yangtze-South China plate and Indochina plate is the Song Ma suture zone which contains ophiolite remnants. Tectonic settings of different structural layers indicate that the Song Da Zone experienced geological events such as the Columbia and Rodinia Supercontinent, sedimentation of the stable platform cover, closure of the Paleo-Tethys, and NW subduction of the Paleo-Pacific plate to the Eurasian plate. The Pre-Cenozoic basement of the Yinggehai Basin is the seaward extension of the Song Da zone, which shows similar tectonic features.     

Reprint of “Depositional environment and tectonic implications of the Paleoproterozoic BIF in Changyi area,eastern North China Craton: Evidence from geochronology and geochemistry of the metamorphic wallrocks”

The Changyi banded iron formation (BIF) in the eastern North China Craton (NCC) occurs within the Paleoproterozoic Fenzishan Group. Three types of metamorphic wallrocks interbedded with the BIF bands are identified, including plagioclase gneisses and leptynites, garnet-bearing gneisses and amphibolites. Protolith reconstruction suggests that the protoliths of the plagioclase gneisses and leptynites are mainly graywackes with minor contribution of pelitic materials, the garnet-bearing gneisses are Fe-rich pelites contaminated by clastics, and the amphibolites are tholeiitic rocks. Trace elements of La, Th, Sc and Zr of the plagioclase gneisses and leptynites and the garnet-bearing gneisses support that these meta-sedimentary rocks were probably derived from recycling of Archean rocks with felsic and mafic materials differentiated into different rock types. ²⁰⁷Pb/²⁰⁶Pb ages of detrital zircons from the meta-sedimentary rocks concentrate at 2.7–3.0 Ga, confirming their derivation from the Archean rocks. The presence of several Paleoproterozoic detrital zircons (2240 to 2246 Ma), however, also suggests minor involvement of Paleoproterozoic materials. The Archean detrital zircons have ε_Hf(t) values varying from − 0.7 to 7.6, which mainly fall between the 3.0 Ga and 3.3 Ga average crustal evolution lines on the age vs. ε_Hf(t) diagram, further illustrating that the rocks providing materials for the meta-sedimentary rocks mainly originated from partial melting of a Mesoarchean crust. This is strongly supported by their crust-like trace element distribution patterns (such as Nb, Ta, P and Ti depletion) and ancient Nd depleted mantle model ages (T_DM = 2.9–3.4 Ga). In addition, the remarkably high ε_Hf(t) values (7.5 to 9.3) of the Paleoproterozoic detrital zircons constrain the Paleoproterozoic materials to originate from a depleted mantle. The amphibolites show low SiO₂ (46.5 to 52.8 wt.%) and high MgO (5.68 to 10.9 wt.%) contents, crust-like trace element features and low ε_Nd(t) values (− 4.5 to − 0.3), suggesting that these ortho-metamorphic rocks were mainly derived from subcontinental lithospheric mantle with some contamination by Archean crustal materials. Since an intra-continental environment was required for the formation of the above metamorphic rocks, these rocks not only confine the depositional environment of the Changyi BIF to be an intra-continental rift, but also support the rifting processes of the eastern NCC during Paleoproterozoic.     

Determination of Early Paleozoic metamorphic event in the Longshan Complex and its geological implicationSCIEI北大核心CSCD

长期以来,陇山杂岩的归属问题一直存在争议。本文对出露于秦岭-祁连山结合部位的陇山杂岩中石榴黑云斜长片麻岩和石榴斜长角闪岩进行了详细的岩石学、P-T温压计算、独居石和榍石U-Pb年代学研究。通过详细的岩相学观察,石榴黑云斜长片麻岩的变质峰期矿物组合为石榴子石+黑云母+斜长石+石英;石榴斜长角闪岩中则识别出了以石榴子石+单斜辉石+角闪石+斜长石+石英为峰期的变质矿物组合。通过传统温压计计算,石榴黑云斜长片麻岩(样品21LS40)和石榴斜长角闪岩样品(样品21LS42-1)的峰期变质P-T条件分别为700℃、0.72GPa和710℃、0.74GPa。激光剥蚀电感耦合等离子体质谱(LA-ICP-MS) U-Pb数据表明,石榴黑云斜长片麻岩中独居石的206Pb/238U的加权平均年龄为407~435Ma。石榴斜长角闪岩中榍石的下交点年龄分别为410±7Ma、409±5Ma和426±10Ma,榍石中Zr含量温度计的计算结果分别为750℃、751℃和748℃(假定压力为0.7GPa)。本文从变质作用的角度出发,将陇山杂岩与秦岭杂岩进行温压条件和变质时代对比研究,认为陇山杂岩与东秦岭杂岩高压-超高压岩石的最后一期退变质作用和西秦岭天水地区的秦岭杂岩麻粒岩相变质作用类似,可能为北秦岭造山带的西延。     

Geospatial technology and structural analysis for geological mapping and tectonic evolution of Feiran–Solaf metamorphic complex,South Sinai,Egypt

The Sinai Peninsula constitutes an important district of the Egyptian lands where it forms a triangular portion in northeastern Egypt. The southern Sinai metamorphic complexes are the northern uppermost part of the Arabian–Nubian Shield revealing the upper and middle crust from the East African Orogeny, in which they tectonically evolved. The Feiran–Solaf metamorphic complex (FSMC) of Sinai, Egypt is one of the highest grades metamorphic complexes of a series of basement domes that trends NW and crops out throughout the Arabian–Nubian Shield. The main aim of the present study is to apply the geospatial technology and to represent the capability of the geospatial technology to estimate the combined influence of lithology and structure studies, and to construct the lithological and structural maps of FSMC. Furthermore, detailed structural analysis is carried out to reveal the different ductile and brittle deformational events and proposed the tectonic evolutionary model for the study area. Mainly geospatial technology and structural analysis software have been used to go well with the aim of the present study. Developing specific image processing of satellite images and structural analysis were succeeded to discriminate the various lithological rock units, and the geological structural features of the FSMC, using geographic information system tools to construct the different thematic maps, were extracted. The present detailed investigations of the enhanced satellite images, structural analysis, and field verification reveal that the FSMC reached its present tectonic setting through more than four deformational phases concluding that the Pan-African Najd Fault System continued in Sinai and was reactivated during Red Sea tectonics as indicated by the dextral shear zone (Rihba) bordering the northern side of the FSMC.     

Late Paleozoic tectonic -magmatic evolution history of the northeastern ChinaSCIEI北大核心CSCD

Northeastern China is suited in the eastern part of the Central Asian Orogenic Belt, and it is mainly composed of Erguna Massif, Xing'an Massif, Songnen-Zhangguangcai Range Massif, Jiamusi Massif, and Nadanhada Terrane. The Late Paleozoic magmatism was relatively intense accompanied with multiple stages of amalgamation in several microcontinents, therefore these magmatic products are an important media in recording the Late Paleozoic tectonic evolution history of the northeastern China. According to the petrological, geochronological, and geochemical characteristics of Late Paleozoic igneous rocks in the northeastern China, we found that the Late Paleozoic magmatism was based on Carboniferous -Permian igneous rocks. The Early Carboniferous magmatic products are gabbro, diorite and granite, the Late Carboniferous magmatic products are mainly composed of granitoids with minor gabbro, and the Permian magmatic products are mainly granitoids. Meanwhile, these Late Paleozoic igneous rocks mostly exhibit typical arc characteristics. In addition, the Late Paleozoic igneous rocks in eastern Jilin and Heilongjiang provinces are mainly Permian granitoids with minor gabbro, and these Permian igneous rocks show typical arc characteristics. Combined with petrological, geochronological, geochemical and isotopic characteristics, we suggest that the Late Paleozoic igneous rocks in the Great Xing'an Range and eastern Jilin and Heilongjiang provinces underwent different magmatic evolution history, and the microcontinents in NE China had different crustal growth history.     

Zircon U-Pb gcochronology and geochemical characteristics of the reshui monzogranite in the eastern kunlun and their tectonic significances北大核心CSCD

In order to probe the genesis and tectonic significance of the granite in the Reshui area, geoehronologicai and geochemical studies of the Reshui monzogranite have been carried out in this paper. The results show that the Reshui monzogranite has LA-1CP-MS zircon U-Pb age of 231 ±1 Ma, indicating that it was formed in late Triassic. It has high contents of Si()2(68. 74%-7l.69%) , Al,(),( 14. 78%-15. 18%). and k,()( 3. 78%-4. 32% ) , with k,()/Na,() ratios ranging from 1. 05 to 1. 32 ,r Rttmann indexes ranging from 1. 87 to 2. 21 . and A/CNk values varying from 1. 03 to 1. 07, respectively. Thus, the Reshui monzogranite belongs to the high k calc-Alkaline weak peraluminous granite. In addition, it has total REE contents(ΣREE) of I 18. 28x 10-6 - 148. 1 x 10-6, with right declined REE distribution patterns showing strong enrichment of LREE and relative depletion of HREE. Its large ion lithophile elements( L1LE) , including Rb. Ra, Th, and l.REE are enriched, while its high field strength elements( HESE) , including Nh, Ta, P. and Ti, are relatively depleted. It has characteristics of the 1-Type granite. It could be mainly sourced from the partial melting of the subducted slab or basic rocks of the lower crust, mixed partly with mantle materials. Combining with regional geological background, it is believed that the Reshui monzogranite was formed by the interaction of the crust and mantle under the tectonic environment of collision-post collision.     

Effects of aspects on soil environment and plant growth on the Qinghai-Tibet Plateau北大核心CSCD

The different aspects lead to great differences in the processes of water,heat,and energy balance,which further affect the soil environment and the growth of alpine plants. Based on an experimental study with eight aspects（abbreviated as octagonal platform）of Huashixia frozen soil observation base on the Qinghai-Tibet Plateau,the influence of aspects on soil environments and alpine vegetation growth was studied. The results showed that：（1）After 6 years,the soil temperature of each slope near the surface（10 cm and 30 cm depth）from high to low was as follows：south > southeast > southwest > west > east > northwest > northeast > north,that is,the relatively sunny slope（east,southeast,south and southwest）was higher than the relatively shady slope（west,northwest,north and northeast）. However,there was no significant difference in soil water con⁃ tent between the sunny slope and the shady slope at the depth of 0~30 cm. （2）The growth trend of aboveground vegetation（including plant height,coverage and aboveground biomass）on sunny slope was better than that on shady slope. The growth trend of underground vegetation（including root depth and underground biomass）on sunny slope was worse than that on shady slope. （3）In the depth of 0~10 cm,the content of soil organic carbon and total nitrogen on sunny slope was higher than that on shady slope. However,the content of total phosphorus on sunny slope was lower than that on shady slope. There was no significant difference in total potassium and available nutrients among different slopes（P>0. 05）. In general,the effect of temperature on vegetation growth and nutrient distribution is significant in alpine regions,and these findings provides an important reference for vegetation restoration and energy balance research in different aspects. © 2023 The Author(s).     

Geochemistry and geochronology of migmatites of the Kurul’ta-Nyukzha segment and the problem of correlation between metamorphic events in the Dzhugdzhur-Stanovoi folded area,Eastern Siberia

Crystalline schists of the El’gakan unit (Nyukzha River) were affected by penetrative (volume) replacement by plagiogneisses and granite-gneisses (Lc₁) and were then transformed into a polymigmatite complex with successively developing leucosomes Lc₂, Lc₃, and Lc₄. After a thrust-nappe structure was formed in response to collision processes, a new generation of granite veins was produced (Lc₅), and then tonalite gneisses Lc ₆ ^avt and branching migmatites with leucosomes Lc ₆ ^all were formed along strike-slip fault zones. Zircons from granite-gneisses Lc₁ were classified into four types (populations) based on SHRIMP II data. Type I (rhythmically zonal cores) were dated at 2960 and 3010 Ma, which is correlated with the age of the magmatic (predominantly volcanic) protolith. Types II and III were dated at 2703 Ma, which corresponds to granitization under amphibolite-facies conditions and the origin of the Stanoi granite-gneiss. This event is correlated with granulite metamorphism and ultrametamorphism over the whole territory of the Dzhugdzhur-Stanovoi folded area. The most widely spread type IV of the zircons has an age of 1915 Ma, which corresponds to the metamorphism coeval with overthrusting and, hence, with the collision of the Stanovoi plate and a margin of the Siberian Platform. Concentrations of REE, U, and Th and the Th/U ratio were determined to systematically decrease from type I to IV of the zircons (except their type III, whose Th/U ratio increases to >1). Zircons from Lc₅ have a concordant age of 139 Ma, which is comparable with the age of the Late Stanovoi granites. The compositional changes from the older cores to younger rims of zircons from Lc₅ are analogous to those mentioned above for zircon from Lc₁. The concordant age of zircons from Lc ₆ ^avt is 127–130 Ma. Their Th/U ratio increases from cores (<1) to rims (>1), which suggests that melt may have appeared when Lc ₆ ^avt was formed. ICP-MS analyses of 53 rock samples reveal differences in the character of the trend (increase/decrease) and magnitude of the changes in the concentrations of trace elements in the distinguished granitization and migmatization series; correlations were revealed between the concentrations of elements and composition of the rock groups. For example, the development of Lc₁ was associated with enrichment in Rb, Sr, Ba, LREE, Th, Zr, and Hf at depletion in Nb, Ta, U, and HREE relative to the original rocks. The leucosomes of the Lc₂, Lc₃, and Lc₄ migmatites are depleted in all of these elements except LILE, which is thought to be explained by infiltration-controlled granitization with volume replacement and partial melting at the development of vein leucosome and the subsequent mobilization of the melts together with residues. The different signs of the changes in the LREE and LILE concentrations is unusual for anatectic processes and can be modeled by equilibrium or disequilibrium melting.     

Relationships between lower and upper crust tectonic during doming: the mylonitic southern edge of the Velay metamorphic core complex (Cévennes-French Massif Central)

Petrological, structural, and thermochronological analyses have been focused on the Mylonitic Metamorphic Vellave Zone (MMVZ), which wraps around the southern edge of the Velay metamorphic core complex dome. Mineral-stretching lineations in the Sil-Bt zone are everywhere perpendicular to the dome edge, the strong mylonitic foliation displays top-to-the south normal shearing, and preferential quartz orientations show high-temperature prismatic <a> deformation interpreted as pure shear patterns. The Sil-Bt zone reflects the dome dynamics during its forced emplacement and uplift. From the contact aureole of the Borne monzogranite, through greenschist facies, and until the And-Crd-Bt zone of the MMVZ, the series are affected by constant syn-metamorphic top-to-the-northeast shearing, acting since at least 320 Ma and reflecting upper crust tectonics during doming: the detachment system. A constriction-dominated deformation regime characterizes the And-Crd-Bt zone, together with the fact that thermochronometers (micas Ar/Ar, U-Th/Pb monazite) are set at 310 Ma, reflecting fast cooling and uplift high in the crust, consequently, the MMVZ is a mylonite that represents the interaction of dome dynamics and the tectonic environment of the upper crust. The Velay dome was forcibly emplaced in the country rocks, and has intruded its own detachment, showing the relationship between the detachment and the dynamic of the dome on its southern edge.     

Geochemistry and tectonic significance of peridotites from the South Sandwich arc–basin system, South Atlantic

Petrographic and geochemical studies of peridotites from the South Sandwich forearc region provide new evidence for the evolution of the South Sandwich arc–basin system and for the nature of interactions between arc magma and oceanic lithosphere. Peridotites from the inner trench wall in the north-east corner of the forearc vary from clinopyroxene-bearing harzburgites, through samples transitional between harzburgites and dunites or wehrlites, to dunites. The harzburgites are LREE depleted with low incompatible element abundances and have chromites with intermediate Cr# (ca. 0.40). Modelling shows that they represent the residues from 15–20% melting at oxygen fugacities close to the QFM buffer. The dunites have U-shaped REE patterns, low incompatible element abundances and high Cr# (0.66–0.77). Petrography and geochemistry indicate that the latter are the product of intense interaction between peridotite and melt saturated with olivine under conditions of high oxygen fugacity (QFM + 2). The transitional samples are the product of lesser interaction between peridotite and melt saturated with olivine ± clinopyroxene. The data demonstrate that the harzburgites originated as the residue from melting at a ridge (probably the early East Scotia Sea spreading centre), and were subsequently modified to transitional peridotites and dunites by interaction with South Sandwich arc magmas. The second dredge locality, near the South Sandwich Trench–Fracture Zone intersection, yielded rocks ranging from lherzolite to harzburgite that could similarly have resulted from a two-stage melting and enrichment process, but involving a more fertile mantle residue and a reacting melt that is transitional between MORB and island arc tholeiite. The South Sandwich peridotites have a similar petrogenetic history to those from Conical Seamount in the Mariana forearc in the sense that both involved interaction between arc magma and pre-existing mantle lithosphere of different provenance. However, the precise compositions of the magma and mantle components vary from location to location according to the precise tectonic setting and tectonic history. Overall, therefore, data from the South Sandwich and Izu–Bonin–Mariana systems emphasise the potential significance of peridotite geochemistry in unravelling the complex tectonic histories of forearcs past and present. Received: 31 August 1999 / Accepted: 3 December 1999     

The Permian mafic intrusive events in the northwestern margin of the Tarim Basin and their tectonic significanceSCIEI北大核心CSCD

塔里木大火成岩省是我国境内发现的两个重要的二叠纪大火成省之一,不仅有大规模的溢流相玄武岩喷发,还有复杂多样的侵入岩及其组合。以往的研究主要集中在二叠系等显生宙地层发育区,对于前寒武系等古老层系中是否存在二叠纪岩浆侵入未引起重视。本文通过野外地质调查,在阿克苏地区前寒武系中识别出数条侵入南华系的基性岩墙和较大规模侵入震旦系的基性岩床。岩墙、岩床与围岩之间均显示出典型的侵入接触关系,包括岩体内部结晶粗、边部结晶细的淬冷边结构、岩床顶底面显著的切层现象以及包裹围岩团块等;显微镜下观察表明,辉绿岩具有典型的辉绿结构和嵌晶含长结构。锆石U-Pb年代学结果表明,侵入下震旦统的辉绿岩岩床和侵入南华系的辉绿岩岩墙的侵位时代在误差范围内基本一致,约为290Ma。岩石地球化学特征表明,辉绿岩岩床具有与洋岛玄武岩(OIB)相似的稀土及微量元素配分模式,结合Sr-Nb-Pb同位素测试结果,认为它们来源于碳酸盐化的富集型岩石圈地幔部分熔融,而辉绿岩岩墙具有Nb、Ta、Zr、Hf等负异常的地球化学特征,可能来自曾被俯冲相关流体/熔体交代的岩石圈地幔源区。本文的早二叠世辉绿岩岩床和岩墙的形成时代、岩浆源区和岩浆演化...     

Geochemistry and zircon U–Pb geochronology of the Pulang complex,Yunnan province,China

The Pulang complex is located tectonically at the southern margin of the Yidun–Zhongdian island arc belt in Yunnan province, China, and is closely related to formation of the Pulang copper deposit, which is the largest copper deposit in Asia. The Pulang complex can be divided into three intrusion stages based on contact relationships and petrological characteristics: (1) a first stage of quartz dioritic porphyry; (2) a second stage of quartz monzonitic porphyry; and (3) a third stage of granodioritic porphyry. The crystallization ages of these intrusion stages were determined by single-zircon U–Pb dating, yielding ages of 221.0 ± 1.0, 211.8 ± 0.5, and 206.3 ± 0.7 Ma for the first, second, and third stages, respectively. These dates, integrated with previous geochronological data and field investigations, indicate that the second-stage quartz monzonitic porphyry has a close spatial and temporal relationship with the large Pulang porphyry copper deposit. These age data, geochemical and Sr–Nd isotopic results suggest that the Pulang complex formed in the Indo-Chinese epoch (257 ～ 205 Ma) by multiphase intrusion of a mixture of mantle- and crust-derived magmas.     

The feature and tectonic setting of Dongqiao podiform chromitite in the central segment of the Bangong Lake-Nujiang suture zone in TibetSCIEI北大核心CSCD

早侏罗世东巧蛇绿岩位于班公湖-怒江缝合带(班怒带)东段,蕴含较为丰富的豆荚状铬铁矿资源。东巧地幔橄榄岩主体由方辉橄榄岩组成,铬铁矿赋存在其内部的纯橄岩脉中。方辉橄榄岩和纯橄岩均显示出弧前橄榄岩的特征。方辉橄榄岩中橄榄石的Fo值为89.8~92.2,斜方辉石的和单斜辉石的Mg^(#)值分别变化于89.7~92.0和92.7~95.1,铬尖晶石的Cr^(#)值(Cr^(#)=100×Cr/(Cr+Al))为60.8~75.9;纯橄岩中橄榄石的Fo值为91.7~92.5,斜方辉石Mg^(#)值变化于91.7~92.1,单斜辉石的Mg^(#)值变化于94.0~94.6,铬尖晶石的Cr^(#)值为69.0~83.1。铬铁矿主要呈致密块状和浸染状构造,其中铬尖晶石的矿物包裹体有橄榄石、斜方辉石、单斜辉石、角闪石和铂族矿物等。矿石中的铬尖晶石与橄榄岩中的铬尖晶石相比,具有较高的Cr^(#)值(72.5~86.9)和Mg^(#)值(52.8~70.5),较低的Al_(2)O_(3)(6.25%~13.6%)、TiO_(2)(0.06%~0.16%)和Zn(518×10^(-6)~714×10^(-6)),属于高铬型铬铁矿,平衡熔体与玻安质熔体有亲缘性。方辉橄榄岩中铂族元素(PGE)总含量(14.01×10^(-9)~32.81×10^(-9))近似于原始地幔,IPGE(Os、Ir和Ru)/PPGE(Rh、Pt和Pd)的比值均大于1;纯橄岩的PGE总量(13.36×10^(-9)~16.08×10^(-9))略低于原始地幔,IPGE和PPGE富集程度近似;铬铁矿的铂族元素总量(108.4×10^(-9)~645.7×10^(-9))远远高于原始地幔和地幔橄榄岩中PGE的含量,且IPGE以及Rh相对原始地幔富集,而Pt和Pd相对亏损,具明显右倾特征的配分模式,指示东巧地幔橄榄岩和铬铁矿形成过程经历了熔体抽取和交代作用。通过与全球典型豆荚状铬铁矿矿床的特征对比,认为班怒带的蛇绿岩应该有良好的铬铁矿成矿背景。     

Structure and tectonic evolution of the Late Jurassic–Early Cretaceous Wandashan accretionary complex,NE China

The Late Jurassic–Early Cretaceous Wandashan accretionary complex (AC) in NE China is a key region for constraining the subduction and accretion of the Palaeo-Pacific Ocean; however, the protoliths and structure of the region remain poorly understood, resulting in debates regarding crustal growth mechanisms and subduction-related accretionary processes in Northeast China. In this contribution, we integrate detailed field observations, ocean plate stratigraphy (OPS) reconstruction, and associated geological data to determine the structure and tectonic evolution of the Wandashan AC. The Wandashan AC formed through the progressive incorporation of OPS units along an oceanic trench. The observed OPS comprises, in ascending order, Permian basalt and limestone, Middle Triassic–Early Jurassic chert, Middle Jurassic siliceous shale and mudstone, and Late Jurassic–Early Cretaceous turbidite. Numerous NNE–SSW-striking thrust faults have segmented the OPS into a series of bedding-parallel tectonic slices that were successively thrust over the Jiamusi massif along a basal thrust (the Yuejinshan Fault), producing a large-scale imbricate thrust system. The Wandashan AC underwent oceanward accretion via multiple deformational processes. The OPS units were detached and rearranged along or within a decollement through offscraping, underplating, thrusting, and duplexing. The units were then emplaced over the Jiamusi massif along the basal thrust. The timing of accretion and thrusting is constrained to the latest Middle Jurassic to earliest Early Cretaceous (ca. 167–131 Ma). Reconstructed accretion-related structural lines within the Wandashan AC trend dominantly NE–SW, close to the direction of Jurassic extension at the eastern Asian continental margin. Large-scale left-lateral strike-slip movement on the Dunmi Fault during the late Early Cretaceous resulted in the folding of structural lines within the Wandashan AC, producing their present-day westward-convex orientation.