Geochronology, Geochemistry and Sr-Nd-Pb-Hf Isotopes of No. I Complex from the Shitoukengde Ni–Cu Sulfide Deposit in the Eastern Kunlun Orogen, Western China: Implications for the Magmatic Source, Geodynamic Setting and Genesis

The Shitoukengde Ni-Cu deposit, located in the Eastern Kunlun Orogen, comprises three mafic-ultramafic complexes, with the No. I complex hosting six Ni-Cu orebodies found recently. The deposit is hosted in the small ultramafic bodies intruding Proterozoic metamorphic rocks. Complexes at Shitoukengde contain all kinds of mafic-ultramafic rocks, and olivine websterite and pyroxene peridotite are the most important Ni-Cu-hosted rocks. Zircon U-Pb dating suggests that the Shitoukengde Ni-Cu deposit formed in late Silurian （426-422 Ma）, and their zircons have ~Hf（t） values of-9.4 to 5.9 with the older TDMm ages （0.80-1.42 Ga）. Mafic-ultramafic rocks from the No. I complex show the similar rare earth and trace element patterns, which are enriched in light rare earth elements and large ion iithophile elements （e.g., K, Rb, Th） and depleted in heavy rare earth elements and high field strength elements （e.g., Ta, Nb, Zr, Ti）. Sulfides from the deposit have the slightly higher ~34S values of 1.9-4.3%o than the mantle （0 ~ 2%o）. The major and trace element characteristics, and Sr-Nd-Pb and Hf, S isotopes indicate that their parental magmas originated from a metasomatised, asthenospheric mantle source which had previously been modified by subduction-related fluids, and experienced significant crustal contamination both in the magma chamber and during ascent triggering S oversaturation by addition of S and Si, that resulted in the deposition and enrichment of sulfides. Combined with the tectonic evolution, we suggest that the Shitoukengde Ni-Cu deposit formed in the post-collisional, extensional regime related to the subducted oceanic slab break-off after the Wanbaogou oceanic basalt plateau collaged northward to the Qaidam Block in late Silurian.

Revisiting Late Quaternary Slip-rate along the Maqu Segment of the Eastern Kunlun Fault, Northeast Tibet

The Late Quaternary slip rate along the Maqu segment of the eastern Kunlun Fault was estimated using a combination of high-resolution remote sensing imagery interpretation, field observations and differential Global Positioning System（GPS） measurements of offset river terraces, and 14 C dating of snail shells collected from offset risers. The results show that the left-slip rate along the segment is 3–5 mm/a, and that the vertical slip rate is 0.3–0.5 mm/a. Both the horizontal and vertical slips on the segment remain consistent over a distance of ~100 km. It means that no slip gradient as previously suggested occurred along the Maqu segment, and which thus might behave as an independent seismogenic fault. Judging from multiple relationships among young terrace offsets, we infer that co-seismic surface rupture produced by a characteristic earthquake with a magnitude of Ms7.0–7.5 on the Maqu fault could generate a horizontal slip of 4.5–5 m and a vertical slip of 0.45–0.5 m, with a corresponding ratio（Dh/Dv） of about 9. Two surface rupture events must have occurred over the past 3300 years, the latest one possibly between 1485 cal BP and 1730 cal BP.

Fission Track Geochronology of Xiaonanchuan Pluton and the Morphotectonic Evolution of Eastern Kunlun since Late Miocene

Apatite fission track （AFT） thermochronology of seven samples from the Xiaonanchuan （小南川） pluton in the Kunlun （昆仑） pass area was carried out, for the purpose of determining the timing of cooling and the relation between the exhumation and the morphotectonic processes. The AFT ages yield low denudation rates of 0. 020--0. 035 mm/a during the late Miocene, which correspond to a stable geomorphic and weak tectonic uplifting environment. The low denudation rates can be considered as the approximate tectonic uplifting rates. The AFT geochronology shows puroxysmully rapid cooling since the Pliocene and an apparent material unroofing of more than 3 km in the Xiaonanchuan area. This was not the result of simple denudation. The rapid cooling was coupled with the intensive orogeny since the Pliocene, which was driven by tectonic uplifting. The accelerated relief building was accompanied by a series of faulting, which caused the basin and the valley formation and sinking. The space pattern of the AFT ages also shows differential uplifting, which decreases northwardly. This trend is supported by the regional AFT data, which indicate that the exhumation decreases northwardly in eastern Kunlun. This trend also exists in cast-west orientation from the western Kunlun range to the eastern. The uplif- ting trend is also supported by gcomorphic characteristics including the elevation and the relief differences well as the distribution of the Late Cenozoic volcanism.

Discovery of the Jiawengmen Stromatolite Assemblage in the Southern Belt of Eastern Kunlun, NW China and Its Significance

This paper reports a newly discovered Late Mesoproterozoic-Early Neoproterozoic stromatolite assemblage, named here the ＂Jiawengmen stromatolite assemblage＂, represented by a Conophyton-Baicalia association in the Jiawenmen area in the southern belt of the Eastern Kunlun. This stromatolite assemblage is dominated by large-scale conical stromatolites and related elements, i.e., Conophyton garganicus var. inkeni, C. cf. ressoti Menchikov, Jacutophyton cf., Conicodomenia f., which commonly co-exist with elements of the group of Baicalia. This assemblage can be correlated with that of the middle Jixian-middle Qingbaikou System in North and Northwest China, but is different from that in South China. Correlation can also be made with that in the upper horizon of the Middle Riphean-lower horizon of the Upper Riphean in the South Ural Mountains and Siberia of Russia, in North Africa, and in the Alaskan Peninsula of North America. These facts suggest that the Jiawengmen stromatolite assemblage probably colonized during 1300-850 Ma ago. Accordingly, the stromatolite-bearing carbonate rocks are then proposed to correspond to the middle Jixian System-middle Qingbaikou System or the upper Middle Riphean-lower Upper Riphean. Our stromatolite data further suggest that a Precambrian microblock, named the Xialawen microblock here, occurred in the southern belt of Eastern Kunlun, the western part of the Maqên microblock. Similar stromatolite assemblages in the Maqên microblock and those blocks that occurred in North China, Siberia and North Africa point to similar paleogeographic and paleoenvironmental conditions. These microblock and blocks were probably located at low latitudes and on the continental margins of the Rodinian supercontinent, where warm epicontinental seas were favorable to widespread colonization of stromatolites during the Late Mesoproterozoic-Eady Neoproterozoic. However, these stromatolite assemblages are quite different from those of the South China block, which is suggestive of different paleogeographic contexts, and probably also of a different tectonic affinity.

Early-Middle Permian Reef Frameworks and Reef-building Models in the Eastern Kunlun Mountains

Reef frameworks and building models of the Early-Middle Permian in the eastern Kunlun Mountains have been verified through studies of reef-building communities, palaeoecology and carbonate facies. The eastern Kunlun reefs are built mainly by 6 reef-building communities, which include 11 major categories of frame-building organisms and 6 categories of reef-associated organisms. Eight types of reef-frames have been distinguished and eleven kinds of rocks identified to belong to 6 reef facies. Three sorts of reefs classified by previous researchers, namely mudmounds, knoll reefs and walled reefs, are well developed in the study area. Such reef-facies association and reef distribution show that there are 4 models of reef growth and development, i.e. the tidal-bank knoll-reef model, the plateau-margin wall-reef model, the composite wall-reef model and the deep-water mudmound model. The reefs are mainly constructed by calcareous sponge and calcareous algae, which are similar to all Permian reefs in other area

Discovery of Jinning Cycle Magmatism in Eastern Part of Eastern Kunlun Orogenic Belt and Its Significance

From the isotopic dating study of gneissic granodiorite, the authors discovered magmatism of the Jinning cycle. Intrusive rocks were formed in the Neoproterozoic, whose Pb Pb ages range from (913±4) Ma to (1 011±4) Ma and U Pb concordia age is (703±15) Ma. The tectonic settings of the rocks are volcanic arc or syn collision. After the formation of the intrusive rocks, these rocks also experienced reconstruction of Caledonian metamorphism. Based on the Ar Ar dating of metamorphic mineral of muscovite, the metamorphic time is determined to range from (386.8±0.8) Ma to (389.44±3.70) Ma.

Distribution of Rare Earth Elements in Early Permian Reef-Island Ocean Sediments in Eastern Kunlun

Abstract: Based on the study of stratigraphy and fossils, the Early Permian ocean in eastern Kunlun is recognized as a kind of reef-island ocean, in which there exist many different kinds of sediment, including patch carbonate platform, reef facies, transitional facies and deep basin sediments. It has been found that the total contents of REEs increase gradually from carbonate platform facies to deep basin facies. Meanwhile, sediments of different facies have different REE distribution patterns and different Ce anomalies. Most of the sediments of patch carbonate platform facies or reef facies are characterized by extremely negative Ce anomalies or moderately negative Ce anomalies (Ce/Ce*=0.33 to 0.55), and medium or thin-bedded limestones of transitional facies by moderately negative Ce anomalies (Ce/Ce*=0.49 to 0.60). However, sediments of deep basin facies show weak or no negative Ce anomalies (Ce/Ce*=0.69 to 1.47), among which the value of Ce/Ce* in the radiolarian chert is 1.47.

Gold Resources Potential Assessment in Eastern Kunlun Mountains of China Combining Weights-of-evidence Model with GIS Spatial Analysis Technique

Resources potential assessment is one of the fields in geosciences,which is able to take great advantage of GIS technology as a substitution of traditional working methods.The gold resources potential in the eastern Kunlun Mountains,Qinghai Province,China was assessed by combining weights-of-evidence model with GIS spatial analysis technique.All the data sets used in this paper were derived from an established multi-source geological spatial database,which contains geological,geophysical,geochemical and remote sensing data.Three multi-class variables,i.e.,structural intersection,Indosinian k-feldspar granite and regional fault,were used in proximity analysis to examine their spatial association with known gold deposits.A prospectivity map was produced by weights-of-evidence model based on seven binary evidential maps,all of which had passed a conditional independence test.The study area was divided into three target zones of high potential,moderate potential and low potential areas,among which high potential areas and moderate potential areas accounted for 20% of the total area and contained 32 of the 43 gold deposits.The results show that the gold resources potential assessment in the eastern Kunlun Mountains has a higher precision.

Geological characteristics and metallogenic prospect of marine volcanic rock-type copper deposits in eastern Kunlun Mountains area, Xinjiang

The Katelixi Cu-Zn deposit is a marine volcanic rock-type copper deposit discovered for the first time in the Tokuzidaban Group in eastern Kunlun Mountains area. It is hosted in the Lower Carboniferous Tokuzidaban Group volcanic strata. The orebodies are obviously controlled by the strata and their ore-bearing rocks are a suite of greyish-green mafic tuffs, generally parallel-stratiform, stratoid and lenticular in form, occurring in limestone as well as in the contact between limestone and carbon-bearing siltstone. This ore deposit possesses distinct characteristics of marine volcanic rock sedimentaion. The geological, petrochemical and REE characteristics of its occurrence pro-vide strong evidence suggesting that this deposit is of marine volcanic rock sedimention origin, basically identical to those of some typical marine volcanic rock-type copper deposits in Xinjiang and other parts of China. Marine vol-canic rocks are well developed in the Lower Carboniferous Tokuzidaban strata in eastern Kunlun Mountains area. In addition to this deposit, we have also found a number of copper polymetallic ore deposits or occurrences in associa-tion with marine volcanc activities in many places where there is a good metallogenic prospect. A breakthrough in the understanding of ore prospecting and genesis has not only filled up the gap in prospecting this type of ore depos-its in this area, but also is of great significance in directing exploration of this type of ore deposits in this area.

Lower Permian formations of different geodynamic environments in A'nyemaqen ophiolitic zone (Buqingshan Mts., eastern Kunlun, Qinghai Province, China)

Lower Permian formations within the Buqingshan Mountains (A'nyemaqen ophiolitic zone, eastern sector of the eastern Kunlun) were formed in the following paleogeodynamic environments (from north to south): ( 1 ) shelf and slope of a passive continental margin in a marginal sea; (2) partially Permian metamorphic rocks of subduction-accretion complexes and volcanogenic rocks of an ensimatic island arc, of the age limited from above by the Asselian - Sakmarian;and (3) an island arc slope and oceanic trench. Subduction-accretion complexes and the island arc volcanites are overlain with a sharp angular unconformity by a carbonate-conglomerate sequence, which presents as local molasse of the Early Permian age. Based on fusulinids from the basal limestone, the age of the local molasse is first defined as the Yakhtashian-Bolorian, i.e. Artinskian-Kungurian (?). The thorough investigations revealed that the initial closure of the eastern Paleotethys within the eastern Kunlun corresponded to the Sakmarian-Yakhtashian (Artinskian) boundary, whereas in the western Paleotethys sector (Northern Pamirs) the closure occurred considerably earlier, prior to the Late Bashkirian.Thus, the idea that the Paleotethys in the eastern Kunlun reached its maximum width in the Permian, is highly questionable.During the Early Permian the A'nyemaqen branch of the Paleotethys intensely decreased. Beginning from the Bolorian (Kungurian) and up to the end of the Permian this branch represented its relict in the form ora marginal sea depression. It may be suggested that the Paleotethys closure in the A'nyemaqen took place gradually from the west to the east and covered a long period from the Late Carboniferous to the terminal Early Permian.

Zircon U-Pb geochronology and Hf isotopic constraints on petrogenesis of Carnian Huanglonggou granodiorites in Wulonggou area of Eastern Kunlun Orogen,NW China

The Wulonggou area located in the Eastern Kunlun Orogen in NW China is characterized by extensive granitoid magmatism,ductile faulting and orogenic gold mineralization.The Huanglonggou granodiorite is cut by an orogenic gold-bearing fault.This study investigated the major and trace-element compositions,zircon U-Pb dates and zircon Hf isotopic compositions of the Huanglonggou granodiorite.One Huanglonggou granodiorite sample yielded a weighted mean U-Pb zircon age of^221 Ma(Carnian).The Carnian granodiorite is metaluminous,with high alkalis contents of 6.37%--8.86%,high Al_2O_3contents of 15.41%--16.19%,high Sr contents of(426--475)×10^(-6),relatively high Sr/Y ratios,high(La/Yb)_Nvalues and low HREE,suggesting an adakite type high-Si O_2granite.The Huanglonggou granodiorite sample has zirconε_(Hf)(t)values ranging from-4.4 to+1.1.These Hf isotopic data suggest that the Carnian granodiorite was likely derived from the partial melting of subducted Paleo-Tethys oceanic slab.It is suggested that the Late Triassic granodiorite was emplaced during the northward subduction of Paleo-Tethys oceanic slab.Orogenic gold mineralization in the Wulonggou area formed after the emplacement of the Late Triassic intrusive rocks.

Crustal architecture and metallogeny associated with the Paleo-Tethys evolution in the Eastern Kunlun Orogenic Belt,Northern Tibetan Plateau

The Eastern Kunlun Orogenic Belt(EKOB)in the Northern Tibet Plateau hosts a wide variety of metal deposits related to the Late Paleozoic to Mesozoic magmatism.In this study,we investigate the spatiotemporal distribution of the Late Paleozoic to Mesozoic granitic rocks and associated metal deposits in the EKOB and provide a comprehensive compilation of the geochronological,geochemical and isotopic data on these rocks.We compute regional zircon Hf isotope and crustal thickness maps from the data,based on which a comprehensive model is proposed involving subduction(ca.270–240 Ma),continental collision(ca.240–224 Ma),and post-collisional extension(ca.224–200 Ma)for the Late Paleozoic to Mesozoic Paleo-Tethys evolution in the EKOB.Zircon Hf isotopic and crustal thickness mapping of Late Paleozoic to Mesozoic magmatic rocks was carried out to evaluate their spatio-temporal and genetic links with the regional metallogeny.The polymetallic Fe-skarn and porphyry Cu(Mo)deposits in the EKOB are located above the Moho uplift region,featuring a comparatively thin crust.Granites associated with porphyry Cu(Mo)and polymetallic Fe skarn mineralization are commonly characterized by highε_(Hf)(t)and younger T_(DM)cvalues,whereas granite related to Cu-Mo-Sn skarn deposits exhibit more variableε_(Hf)(t)values,T_(DM)c ages,and the crust thickness,which suggest that more crustal materials contributed to the formation of Cu-Mo-Sn skarn deposits than those for porphyry Cu(Mo)and polymetallic Fe skarn mineralization.In contrast,vein-type Au deposits are located primarily where the Moho surface displays a depression,i.e.,where the continental crust is relatively thick.The magmatic rocks associated with Au mineralization are characterized by lowε_(Hf)(t)and high T_(DM)cvalues,representing reworked ancient crustal components,similar to those associated with porphyry Mo and epithermal Ag-Pb-Zn-(Au)deposits.Our study indicates that the emplacement of magmatic-hydrothermal deposits was controlled by the crustal structure and magma sources.

Fission Track Thermochronology Evidence for Multiple Periods of Mineralization in the Wulonggou Gold Deposits, Eastern Kunlun Mountains, Qinghai Province

It is a puzzle to determine metallogenetic ages in the world. This article uses zircon fission track （FT） dating to probe the mineralizing epochs of Wulonggou （五龙沟） gold ore deposits in eastern Kunlun （昆仑） Mountains. Total of six zircon FT ages have been obtained and can be divided into groups of 235-216 and 197-181 Ma, as well as 162 and 124 Ma, revealing multiple epochs of metalloge- netic processes took place in Wulonggou area, mainly first two age groups. The mineralizing ages be- come lower from northeast Yanjingou （岩金沟） to southwest Hongqigon （红旗沟）. The second epoch of 197-181 Ma is first achieved by this work. It is shown that the FT ages consist with other isotopic data and reflect different regional thermotectonic events.

Sulfur-and Lead-Isotope Geochemistry of the Balugou Cu-Pb-Zn Skarn Deposit in the Wulonggou Area in the Eastern Kunlun Orogen, NW China

The small-scale Balugou Cu-Pb-Zn skarn deposit（45 298 tonnages of ore at 0.1% to 3.99% Cu, 0.20% to 0.43% Pb and 0.76% to 10.92% Zn） is located in the Wulonggou area in the eastern Kunlun orogen, NW China. Ore deposition is spatially and temporally related with the pre-collisional Anisian Balugou granites（~244 Ma）. The mineralization hosted by the contact between marble beds within the Paleo-Proterozoic Jinshuikou Group and Balugou granites, was structurally and lithologically controlled. The mineralogy of the Balugou deposit includes an early simple skarn mineral gangue（epidote with little diopside） and a late complicated quartz sulfide assemblage（pyrite, pyrrhotite, chalcopyrite, sphalerite, galena, bornite, quartz, carbonate and chlorite）. The δ34S values of eighteen sulfides range from-2.1‰ to ＋2.8 ‰, with an average of ＋0.07‰, and the calculated δ34SH2S values for H2 S in hydrothermal fluids range from-3.2‰ to ＋2.4‰, with an average of ＋0.03‰, suggesting a relatively homogeneous magmatic（±mantle） source, with sulfur produced directly by the Balugou granites. The sixteen sulfides have 206Pb/204 Pb ratios from 18.367 4 to 18.384 1, 207Pb/204 Pb ratios from 15.634 6 to 15.641 5, and 208Pb/204 Pb ratios from 38.455 5 to 38.485 0, which are close to those of K-feldspars from the Balugou granites, but are far away from age-corrected lead isotopic ratios of six wall-rock samples. So it was considered that the Pb sources of sulfides must be almost derived from the Balugou granites rather than the older wall-rocks. Collectively, it＇s suggested that the Balugou Cu-Pb-Zn deposit belongs to skarn deposit, and the sulfur and lead deposited in it were leached from the Anisian Balugou granites.

A Comparison about Metamorphism among the Oldest-Rock Units from Orogenic Belts of Dabie,Eastern Qinling and Eastern Kunlun of Central Mountain Ranges,China

The Dabie orogen, Eastern Qinling orogen and Eastern Kunlun orogen are the major components of the Central Mountain Ranges of China and each has distinctively metamorphic processes in their oldest rock units. The Dabie orogen oldest rock units had experienced an intermediate-higher pressure, upper amphibolite to lower granulite facies metamorphism in the Indosinian intracontinental subduction collision event. The clockwise pt path, synchronous attainment of t max and p max and a segment of high slope retrograde path suggest a tectono driven rapid exhumation of the oldest rock units to upper middle crustal level following the end of the subduction collision process. The oldest rock units, also called Qinling Group, of Eastern Qinling Mountains suffered intensively collisional metamorphism at an immature plate tectonic framework during Jinningian movement about 1 000 Ma ago. The clockwise pt path with reach of t max following several hundreds of MPa decreasing from p max suggests that the denudation of the deeply burial rock units was due essentially to isostatic relaxation. During the Caledonian stage, the highly metamorphosed oldest rock units suffered from a high t thermal event in arc environment and superimposed by contact metamorphism. After thermal peaks, the rock units were exhumed in a short distance and cooled down isobarically. No regional metamorphism higher than upper greenschist facies condition since 300 Ma has been traced within exposed rocks in the eastern portion of Northern Qinling orogen. The oldest rock units in the Eastern Kunlun orogen were metamorphosed to upper amphibolite facies to lower granulite facies rocks early or during the Luliang movement (some 1 800 Ma ago). The high grade metamorphic rock units had a long resident time at the deep crustal level, and were exhumed to middle upper crustal level during the Caledonian to Hercynian tectonometamorphic events. Shallow erosion of the orogenic belt led to good preservation of the low pressure metamorphic belt.

Late Neogene Mountain Building of Eastern Kunlun Orogen: Constrained by DEM Analysis

Topography, as a net result of the dynamic interaction between endogenesis and exogenesis, holds immense information on tectonic uplift, surface erosion and thus mountain building. The eastern Kunlun （昆仑） orogen, which experienced significant Late Neogene tectonic uplift and is located in an arid environment, is advantageous for morphotectonic analysis based on well-preserved tectonic landforms. The digital elevation model （DEM） analysis was carried out for the central segment of the eastern Kunlun orogen based on shuttle radar topography mission （SRTM） data. River longitudinal profile analysis indicates that major rivers across the orogen are characterized by high river gradient indexes and intensive tectonic uplift. Differential uplift was also identified in swath-topography analysis in the studied area, which can be divided into three major tectonic-geomorphie units by orogenicstrike-parallel faults. It is indicated that the most active region is located to the south of the Xidatan （西大滩） fault with significant differential uplift. Another identified fault with differential uplift is the Middle Kunlun fault; however, the timing of which is suggested to be much older than that of the Xidatan fault. These analyses are concordantly supported by both field survey and studies of thermochronology, which in turn indicates that the DEM analysis bears great potential in morphotectonic analysis.

Mixing events between the crust- and mantle-derived magmas in Eastern Kunlun: Evidence from zircon SHRIMP Ⅱ chronology

Various shaped mafic microgranular enclaves (MMEs) together with several mafic massifs are developed within the Yuegelu granitoid pluton in the eastern part of the Eastern Kunlun. On the basis of detailed field geological surveying and of the results of the petrological and geo-chemical studies it is suggested that there must be some ge-netic relationship among the granodiorite host, the MMEs and the hornblende (Hb)-gabbro massifs. Magmatic zircon grains are extracted from samples of granodiorite host rock, Hb-gabbro and the MMEs for U-Pb dating. The U-Pb ages are determined by using SHRIMP Ⅱ technique, which yields the ages of 242±6 Ma, 239±6 Ma and 241±5 Ma, respectively. The overall correspondence in the U-Pb dating results of them excludes the possibility that the MMEs in the granitoids are solid refractory relics from the source region or that they are xenoliths from the wall rocks. It can also rule out the possibility of a later emplacement of basic magma after the solidification of the granitoids. This dating result indicates that they are the products of magma mixing in early-mid Triassic epoch. Among them the granitoid host is chemically akin to the acidic end member during the magma mixing process, the Hb-gabbro is akin to the basic ones while the MMEs are the incompletely mixed basic magma clots trapped in the acidic magma. Combined with the results from other researches on this pluton it is reasonable to con-sider that in the mid-Triassic the Eastern Kunlun granitoid belt had undergone a process of magma mixing between the mantle-derived basic magma and the crustal acidic magma which indicates that the injection of mantle materials and energy into the crust and the reactions between them played an important role in the formation of the granitoid rocks.

New paleontological evidence on time determination of the east part of the Eastern Kunlun Mélange and its tectonic significance

New paleontological evidence suggests that the composition of the matrix and slices from the middle and the south of the Eastern Kunlun Mélange Belt is very complex, ranging from Proterozoic to Mesozoic in geological time. A Cambrian acritarch assemblage has been discovered from the middle part of the Eastern Kunlun Mélange, a Neoproterozoic to the early Paleozoic acritarch assemblage has been discovered from the south of the Eastern Kunlun Mé lange, and so has been an Early Permian radiolarian from the A’nyemaqen Mélange in Buqing- shan. In addition, some sporopollen has been obtained from the Mesozoic tectonic slices. The above-mentioned paleontological evidence indicates that the Eastern Kunlun Orogenic Belt experienced two episodes from ocean to continent from the Neoproterozoic to the Early Paleo- zoic and in the Late Paleozoic respectively. In the process of intracontinent development in Mesozoic, because of heavy thrust-nappe, strike-slip sheer and crust shortening, the Mesozoic formation was intercalated in mélange by slices and the Eastern Kunlun Orogenic Belt became more complex.

EMP chemical ages of monazites from Central Zone of the eastern Kunlun Orogen:Records of multi-tectonometamorphic events

Two generations of monazite were identified in one mica schist sample from the central zone of the eastern Kunlun Orogen at the northern margin of the Qinghai-Tibet Plateau. The first generation was found in the cores of garnet porphyroblasts with relatively high Y2O3 contents (averaging 1.012±0.088 wt%). The second generation occurs either as inclusions in the rims of garnet porphyroblasts,matrix kyanite,plagioclase and quartz,or as separate crystals associated with matrix biotite and muscovite mostly having a relatively low Y2O3 content (averaging 0.479±0.100 wt%). Electron microprobe (EMP) Th-U-Pbtotal chemical dating for two grains of the first generation monazite yields average ages of 455 ± 18 Ma and 420 ± 20 Ma,respectively; six grains of the second generation gave an average age of 246.1 ± 3.8 Ma. These ages suggest that the core and rim of the garnet porphyroblasts and their associated assemblages record two events of significant tectonometamorphism. The formation of the Ordovician monazite is related to the tectonometamorphic event responsible for continuous amalgamation of the Gondwanaland in the Late Pan-African period or for consumption of the Proto-Tethys,whereas the development of the Triassic monazite is related to the tectonometamorphic event for consumption of the Paleo-Tethys.

Discovery of Paleogene palynological assemblages from the Wanbaogou Group-complex in western part of the Eastern Kunlun orogenic belt and its geological significance

The Wanbaogou Group-complex is a suit of mélange aggregation of the Eastern Kunlun orogenic belt, which is divided into two parts, i.e. the exotic blocks and the matrix strata. Based on stromatolite fossils yielded in the exotic blocks, the age of this group-complex was once defined to the Precambrian. Recently, two Paleogene palynological assemblages have been found in samples from the matrix strata of the Upper Part in this group-complex by the authors: in ascending order, the Al- nipollenites-Quercoidites assemblage of Late Eocene and the Caryapollenites-Pinuspollenites as- semblage of Early Oligocene. Those results show that the matrix strata of this mélange were mainly formed in Paleogene, and the event causing mixture should be a Himalayan Movement Phase. This paper is designed to provide some detailed evidence for determining the age of the matrix strata in this group-complex based upon study at the Kunlunqiao Section, which would be of important geo- logical significance for further understanding this group-complex as a suit of mélange aggregation and establishing or improving the stratigraphic framework of the studied region. The new finding will cer- tainly benefit from now on the investigation on geotectonic and sedimentary evolution of Eastern Kunlun.