Polymetamorphism of the ultrahigh-temperature granulites in the Rauer Group,East Antarctica:new evidence from zircon SHRIMP U-Pb ages

The Rauer Group is located on the eastern margin of the early Paleozoic Prydz Belt in East Antarctica,and the typical ultrahigh-temperature(UHT,>900℃)granulites outcrop on Mather Peninsula.However,the timing of UHT metamorphism and P–T path of the UHT granulites have long been debated,which is critical to understanding the tectonic nature and evolution history of the Prydz Belt.Thus,both a sapphirine-bearing UHT metapelitic granulite and a garnet-bearing UHT mafic granulite are selected for zircon SHRIMP U-Pb age dating.The results show that metamorphic zircon mantles yield weighted mean^(206)Pb/^(238)U ages of 918±29 Ma and 901±29 Ma for the metapelitic and mafic granulites,respectively,while zircon rims and newly grown zircons yield weighted mean^(206)Pb/^(238)U ages of 523±9 Ma and 532±11 Ma,respectively.These new zircon age data suggest that the UHT granulites may have experienced polymetamorphism,in which pre-peak prograde stage occurred in the early Neoproterozoic Grenvillian orogenesis(1000–900 Ma),whereas the UHT metamorphism occurred in the late Neoproterozoic to early Paleozoic Pan-African orogenesis(580–460 Ma).This implies that P–T path of the UHT granulites should consist of two separate high-grade metamorphic events including the Grenvillian and Pan-African events,which are supposed to be related to assembly of Rodinia and Gondwana supercontinents respectively,and hence the overprinting UHT metamorphic event may actually reflect an important intracontinental reworking.

Geochemistry and SHRIMP Zircon U-Pb Age of Post-Collisional Granites in the Southwest Tianshan Orogenic Belt of China:Examples from the Heiyingshan and Laohutai Plutons

The Heiyingshan granite and the Laohutai granite plutons exposed in the Southwest Tianshan resemble A-type granites geochemically. Analysis shows that the both are ferron calc-alkalic peraluminous or ferron alkali-calcic peraluminous with a relatively high concentration of SiO2 （〉70%）, high alkali contents （Na20 ＋ K20 = 7.14%-8.56%; K20〉N20; A/CNK = 0.99-1.20）, and pronounced negative anomales in Eu, Ba, St, P and Ti. A SHRIMP zircon U-Pb age of 285±4 Ma was obtained for the Heiyingshan hornblende biotite granite intrusion. The geochemical and age dating data reported in this paper indicate that these granites were formed during the post-collisional crustal extension of the Southwest Tianshan orogenic belt, in agreement with the published data for the granites in the South Tianshan.

U-Pb Age and Hf Isotope Study of Detrital Zircons from the Wanzi Supracrustals:Constraints on the Tectonic Setting and Evolution of the Fuping Complex,Trans-North China Orogen

Located in the middle segment of the Trans-North China Orogen, the Fuping Complex is considered as a critical area in understanding the evolution history of the North China Craton （NCC）. The complex is composed of various high-grade and multiply deformed rocks, including gray gneiss, basic granulite, amphibolite, fine-grained gneiss and marble, metamorphosed to upper amphibolite or granulite facies. It can be divided into four rock units： the Fuping TTG gneisses, Longquanguan augen gneisses, Wanzi supracrustals, and Nanying granitic gneisses. U-Pb age and Hf isotope compositions of about 200 detrital zircons from the Wanzi supracrustals of the Fuping Complex have been analyzed. The data on metamorphic zircon rims give ages of 1.82-1.84 Ga, corresponding to the final amalgamation event of the NCC, whereas the data for igneous zircon cores yield two age populations at -2.10 and -2.51 Ga, with some inherited ages scattering between 2.5 and 2.9 Ga. These results suggest that the Wanzi supracrustals were derived from the Fuping TTG gneisses （-2.5 Ga） and the Nanying granitic gneisses （2.0-2.1 Ga） and deposited between 2.10 and 1.84 Ga. All zircons with -2.51 Ga age have positive initial εHf values from ＋1.4 to ＋10.9, suggesting an important crustal growth event at -2.5 Ga through the addition of juvenile materials from the mantle. The Hf isotope data for the detrital zircons further imply that the 2.8 Ga rocks are important components in the lower crust, which is consistent with a suggestion from Nd isotope data for the Eastern Block. The zircons of 2.10 Ga population have initial εHf values of-4.9 to ＋6.1, interpreted as mixing of crustal re-melt with minor juvenile material contribution at 2.1 Ga. These results are distinct from that for the Western Block, supporting that the Fuping Complex was emplaced in a tectonic active environment at the western margin of the Eastern Block.

Zircon U-Pb Age and Geochemistry of the Ore-hosting Ultramafic Complex of Zhou'an PGE-Cu-Ni Deposit,Henan Province,Central China

The Zhou＇an PGE-Cu-Ni deposit was recently discovered in the Qinling orogenic belt bound by the Yangtze and the North China Cratons. It is a blind deposit thoroughly covered by the Cenozoic alluvial sediments in the Nanyang Basin. As the first large PGE-Cu-Ni deposit discovered in the Qinling-Dabie-Sulu orogenic belt, its geological and geochemical characteristic, isotope age, genesis and tectonic setting are of wide concern in both scientific studies and ore exploration. In this contribution, we report the results obtained from a pioneering study. The Zhou＇an ultramafic complex is ferruginous, with m/f = 4.79-5.08, and shows the nature of tholeiite series. It is rich in light rare earth elements, Rb, Th, U, La, Sm, Zr and Hf, and poor in heavy rare earth elements, Nd and Ta, suggesting an intraplate setting. It has high S7Sr/S6Sr and low 143Nd/144Nd ratios. The ratios of Zr/Nb, La/Nb, Ba/ Nb, Rb/Nb, Th/Nb, Th/La and Ba/La, suggest the magma originated from lithosphere mantle. The Fo values of olivine and Pd/Ir-Ni/Cu diagram suggest primary magma was High Mg basalt. The laser ablation inductively coupled plasma atomic emission spectroscopy zircon U-Pb age is 641.5 ± 3.7 Ma.

New Insights into the Late Triassic Nadigangri Formation of Northern Qiangtang, Tibet, China： Constraints from U-Pb Ages and Hf Isotopes of Detrital and Magmatic Zircons

We report here U-Pb age and in situ Hf isotopic results for detrital and magmatic zircons from one conglomerate and four tuffite samples from the Late Triassic Nadigangri Formation across the North Qiangtang depression, Tibet. Coupled with previously published data in the region, this paper proposes new insights into the geochronological framework for the Nadigangri Formation. The deposition ages of tuffite from top to bottom in the Woruo Mountain, Quem Co and Dongqu River, are 203 Ma, 226 Ma, 221.5 Ma and 221.1 Ma, respectively. The detrital zircons yield a younger cluster of ages of 201.5-225 Ma from the conglomerate of the Quem Co Formation. The Late Triassic Nadigangri Formation defines a temporal range approximately between 201 and 225 Ma （Norian-Rhaetian）, including three predominant groups of 220-225 Ma, 210-217 Ma and 201-205 Ma, which correspond with the three main rifting episodes of initial rifting, further rifting and final rifting. Positive ~Hf（t） value and low model ages in younger detrital zircons suggests a juvenile character. However, the Hf isotopes of magmatic zircons display the presence of reworked ancient crust with 1.1-1.8 Ga. These results provide strong constraints not only on the temporal range of the Late Triassic Nadigangri Formation, but also on the onset of the Qiangtang Mesozoic rift basin.

Zircon LA-ICP-MS U-Pb Age and Island-Arc Origin of the Bayanhua Gabbro in the Hegenshan Suture Zone, Inner Mongolia

Objective The Bayanhua Nb-enriched gabbro is newly discovered in the Diyanmiao-Meilaotewula SSZ-type ophiolitic m61ange belt of the Hegenshan suture zone, Inner Mongolia. Nb-enriched arc gabbros are usually believed to result from partial melting of the mantle wedge peridotites metasomatized by slab melts derived from the subducting oceanic slab, which represent arc magmatic markers of the oceanic subduction zone. However, whether the Hegenshan ocean basin of the Paleo-Asian Ocean was in its subduction stage in the Early Permian requires further study for a final conclusion, and what is the evolution process of the oceanic subduction and lithospheric mantle of the Hegenshan suture zone remains speculative for the lack of further definitely petrological and chronological evidence and constraints. Therefore, this study carried out zircon LA-ICP-MS U-Pb geochronology and geochemistry on the Bayanhua Nb-enriched gabbro to discuss its origin, in order to provide new evidence for the tectonic evolution of the Hegenshan suture zone of the eastern Central Asian Orogenic Belt.

Discovery of the Dagele Eclogite in East Kunlun,Western China and Its Zircon SHRIMP U-Pb Ages:New Constrains on the Central Kunlun Suture Zone

Objective Eclogites are important indicators of ancient plate boundaries or paleosuture zones. Despite their great geological significance, very few investigations have been carried out in the Kunlun region. The Central East Kunlun fault zone was believed to be an Early Paleozoic suture zone, but there has been no reliable evidence for this, though studies on ophiolite, granite, and basic granulite indicate that the Early Paleozoic orogeny occurred in the East Kunlun. This work focused on the Dagele eclogites in Central East Kunlun to provide new constraints for the Central East Kunlun suture zone.

New Zircon U-Pb Age of Granodiorite in Chifeng at the Northern Margin of North China Craton and Constraints on Plate Tectonic Evolution

Objective The North China Craton （NCC） is one of the oldest cratons in the world. The accretionary belt at its northern margin has been the focus of scholars both at home and abroad （Zhu Junbing and Ren Jishun, 2017）. In recent years, a series of Late Paleozoic-Mesozoic intrusions trending E-W have been discovered within the northern margin of the NCC, forming a magmatic belt. The study on the origin and tectonic setting of this magmatic belt not only has important significance for understanding the Late Paleozoic-Mesozoic tectonic evolution history of the northern margin of the NCC, but also can provide key constraints on the evolution of its surrounding Xing＇an- Mongolia orogenic belt and the Paleo-Asian Ocean. At present, no Devonian to early stage of Early Carboniferous intrusion has been reported within the northern margin of the NCC.

New Zircon U-Pb Age of the Babu Ophiolites in Southeast Yunnan,China and Constrains of Plate Subduction Time

Objective The Babu ophiolite in Malipo County of southeastern Yunnan is interpreted as remanant ocean crust and represents a possible branch of Paleo-Tethyan Ocean in South China. It consists mainly of mafic and ultramafic rocks. These rocks are very important to understand the evolution of the Paleo-Tethyan Ocean. However, the Babu ophiolite is still disputed and the mafic and ultramafic rocks have been inferred to be part of the Emeishan large igneous province （LIP） by some researchers. In this paper, we present zircon U-Pb data on the metabasalts in Malipo to reveal the formation time of mafic and ultramafic rocks and their tectonic nature.

New Zircon U-Pb Age of the Super-Large Lijiagou Spodumene Deposit in Songpan Garze Fold Belt, Eastern Tibet： Implications for Early Jurassic Rare-Metal Polymetallic Event

Objective The Songpan-Garze Fold Belt(SGFB),located in the eastern part of the Tibet Plateau and west of the Sichuan Basin,is an important pegmatite province in China.Some famous pegmatite type deposits occur in the SGFB,including the Xuebaoding,Jiajika,Keeryin rare metal deposits and Danba muscovite deposit(Li Jiankang et al.,2015).The newly discovered super-large Lijiagou

Discovery of rhyolitic tuffaceous slate in the southwestern margin of Yangtze Craton:Zircon U-Pb ages(2491 Ma)and tectonic-thermal events

The Mesoproterozoic Dongchuan Group that is widely exposed in Yimen area,central Yunnan Province is a series of sedimentary sort of low-grade metamorphic rocks interbedded with volcanic rocks,which are closely related to the early tectonic evolution of the Earth.However,its formation era,sedimentary filling sequence,and geotectonic characteristics have always been in dispute.In this study,several rhyolitic tuffaceous slate interlayers with a centimeter-level thickness were found in the previously determined Heishan Formation of the Dongchuan Group located to the western part of Yimen-Luoci fault zone.This paper focuses on the study of the rhyolitic tuffaceous slate in Qifulangqing Village,Tongchang Township,Yimen County.LA-ICP-MS zircon dating was conducted,achieving the crystallization age of magma of 2491±15 Ma and the metamorphic ages of about 2.3 Ga,2.0 Ga,and 1.8 Ga for the first time.Meanwhile,according to in-situ Hf isotope analysis,the zirconεHf(t)values were determined to range from−3.0 to 7.6,with an average of 2.7.Furthermore,the first-stage Hf model age(TDM1)was determined to be 2513−2916 Ma,indicating that the provenance of the rhyolitic tuffaceous slate is the depleted mantle or juvenile crust between the Middle Mesoarchean and the Late Neoarchean.Therefore,it is believed that the strata of the slate were deposited in the Late Neoarchean,instead of the Mesoproterozoic as determined by previous researchers.Accordingly,it is not appropriate to group the strata into the Mesoproterozoic Dongchuan Group.Instead,they should be classified as the Maolu Formation of the Neoarchean Puduhe Group given the lithologic association and regional information.Furthermore,the magma ages of 2491±15 Ma are highly consistent with the eras of the large-scale Late Neoarchean orogenic magmatic activities on the northern margin of the Yangtze Craton,and thus reflect the orogenic process consisting of subduction and collision from Late Neoarchean to Early Paleoproterozoic.The magmatic activities during this period were possibly caused by the convergence of the supercontinent Kenorland.Meanwhile,the metamorphic ages of 2.3 Ga,2.0 Ga,and 1.8 Ga are highly consistent with three metamorphic ages of 2.36 Ga,1.95 Ga,and 1.85 Ga of the northern margin of the Yangtze Craton,indicating that the strata experienced Paleoproterozoic tectonic-thermal events.The study area is located on the eastern margin of Qinghai-Tibet Plateau,and thus was possibly re-transformed by magmatism subjected to the subduction of the Meso-Tethys Ocean during the Early Cretaceous.The discoveries made in this study will provide strong petrological and chronological evidence for analyzing the early crustal evolution of the Yangtze block.

Zircon U-Pb ages and Hf isotopic characteristics of the Dehe biotite monzonitic gneiss pluton in the North Qinling orogen and their geological significance

The Dehe granitic pluton intruded the Xiahe Group which is in the core complex of the North Qinling Orogenic Belt(NQOB).It shows gneissic bedding and possesses typical S-type granite minerals such as muscovite and garnet.LA-ICP-MS U-Pb isotopic dating of the Dehe granite yielded a weighted average age of 925±23 Ma which represents the emplacement age of the pluton.Most of the εHf(t) values are negative,and the two-stage model ages are consistent with the age of the Qinling Group.The isotope data show that the Dehe granite was formed in the following geological setting:in the syn-collision setting of the NQOB in the Neoproterozoic,crustal thickening induced partial melting of materials derived from the Qinling complex,and then the maga upwelled and intruded into the Xiahe Group.The formation of the Dehe S-type granite implied the occurrence of a convergent event in the QOB during the Neoproterozoic.

LA-ICPMS U-Pb Ages of Zircon from Metaleucosomes, Olongbuluke Microcontinent, North Qaidam, and Implications on the Response to the Global Rodinia Supercontinent Assembly Event in NW China

U-Pb dating was conducted on different domains of zircons from metamorphosed leucosomes in Delingha （ 德令哈） complex, the lower basement rocks of the Olongbuluke （欧龙布鲁克 ） microcontinent, North Qaidam, in order to review its complex tectonothermal history. The zircon core is comprised of highly-modified magmatic zircon relicts, the zircon mantle was produced in response to anatexis of a Late Protoproterozoic thermal event; age and isotopic composition of both the zircon core and the zircon mantle have been seriously disturbed due to the thermal event related with growth of the zircon overgrowth rim. The 207 PIV 206 Pb apparent age of the overgrowth rim was estimated to be - 1 030 Ma. This Late Mesoproterozoic thermal event has been interpreted as a response to the global Rodinia supercontinent assembly event in the Olongbuluke microcontinent, Northwest China.

New Zircon U-Pb Age of Granodiorite from the Shayikenbulake Be Deposit in Altay, Xinjiang and its Significance

Objective Intrusive rocks are widely distributed in Altay, Xinjiang, and appear in every structural belt. The rocks are mainly granite （Song Peng et al., 2017）, which formed from 523 Ma to 202 Ma and can be divided into five periods： 479-421 Ma, 410-370 Ma, 368-313 Ma, 300- 252 Ma and 247-202 Ma. However, intrusive rocks earlier than the Ordovician are rarely found. The small- scale low-grade metamorphic granite intruded in the Kanasi Group is the oldest intrusion reported up to now, which is the only one formed in the Early Cambrian （5234-19 Ma, Liu Yuan et al., 2013）. Few Cambrian intrusions limit the study of early magmatic-tectonic evolution in Altay. Medium-free-grained granodiorite is exposed widely in the Shayikenbulake deposit of Central Altay, and occurs as batholith. It formed in the Early Cambrian indicated by U-Pb dating, and is an ideal intrusion for studying Cambrian magmatic-tectonic events in Altay.

Zircon U-Pb Ages of Bottom and Top Parts of the Zhangjiakou Formation in Lingyuan Area(West Liaoning Province) and Luanping Area (North Hebei Province) and Their Significance

In Lingyuan region of West Liaoning Province, the Zhangjiakou Formation (J_3z) and the Yixian Formation (K_1y) display an angular unconformity. That is, the Lower Mesozoic strata of the Zhangjiakou Formation are ENE (near E-W) oriented, while the overlying strata of the Yixian Formation exhibit an NNE orientation. The results of LA-ICP-MS zircon U-Pb ages show the Zhangjiakou Formation formed from about 130 Ma to 132 Ma in Lingyuan and 135 Ma to 136 Ma in Luanping (North Hebei Province), respectively. Three conclusions can be drawn: (1) The Zhangjiakou Formation in Lingyuan is comparable to that in Luanping, with the volcanic rocks of the Zhangjiakou Formation from Lingyuan being younger than those from Luanping. (2) 5-6 Ma difference between the top of the Zhangjiakou Formation and the bottom of the Yixian Formation in Lingyuan proves the angular unconformity between the two formations; and it reflects that the 5-6 Ma interval period is the main period of the transition of tectonic framework in Mesozoic in North Hebei and West Liaoning. In the interval period, the magmatic action went up to high tide in Mesozoic in the northeast of China. Moreover, after the interval period, the “Rehe fauna” developed into “erupted” period. This reflects that the interval period is also an important biological interface in Northern Hebei and Western Liaoning. (3) The Dabeigou Formation in Luanping should correspond to the upper part of the Zhangjiakou Formation, but not to the lower part of the Yixian Formation.

First Report of Zircon U-Pb Ages from Lubei Cu-Ni Sulfide Deposit in East Tianshan of Central Asian Orogenic Belt, NW China

Objective The East Tianshan mafic-ultramafic rocks belt mainly produced in the eastern Jueluotage belt is an important part of the Central Asia Orogenic Belt （CAOB）. The well- known deposits including Huangshan, Huangshandong, Tulaergen, Hulu, Xiangshan were have been consecutively discovered in this belt （Duan Xingxing et al., 2016）. The new discovery of the Lubei Cu-Ni sulfide deposit in recent years, which locates in the west of Jueluotage belt, has great significance to the westward extension of the East Tianshan Cu-Ni metallogenic belt. To determine whether the mineralization age of the Lubei Cu-Ni sulfide deposit is consistent with other typical deposits, this study conducted zircon U-Pb geochronology on the diorite from the Lubei Cu-Ni sulfide deposit in order to provide new information for further exploring direction of Cu-Ni prospecting in East Tianshan.

Geochemistry and zircon U-Pb ages of the Oligocene sediments in the Baiyun Sag, Zhujiang River Mouth Basin

In this study,element geochemistry and zircon chronology are used to analyze the Oligocene sediments in the Baiyun Sag,Zhujiang River Mouth Basin.The experimental results are discussed with respect to weathering conditions,parent rock lithologies,and provenances.The chemical index of alteration and the chemical index of weathering values of mudstone samples from the lower Oligocene Enping Formation indicate that clastic particles in the study area underwent moderate weathering.Mudstone samples exhibit relatively enriched light rare earth elements and depleted heavy rare earth elements,"V"-shaped negative Eu anomalies,and negligible Ce anomalies.The rare earth element distribution curves are obviously right-inclined,with shapes and contents similar to those of post-Archean Australian shale and upper continental crust,indicating that the samples originated from acid rocks in the upper crust.The Hf-La/Th and La/Sc-Co/Th diagrams show this same origin for the sediments in the study area.For the samples from the upper Enping deltas,the overall age spectrum shows four major age peaks ca.59–68 Ma,98–136 Ma,153–168 Ma and 239–260 Ma.For the Zhuhai Formation samples,the overall age spectrum shows three major age peaks ca.149 Ma,252 Ma and 380 Ma.The detrital zircon shapes and U-Pb ages reveal that during Oligocene sedimentation,the sediments on the northwestern margin of the Baiyun Sag were supplied jointly from two provenances:Precambrian-Paleozoic metamorphic rocks in the extrabasinal South China fold zone and Mesozoic volcanic rocks in the intrabasinal Panyu Low Uplift,and the former supply became stronger through time.Thus,the provenance of the Oligocene deltas experienced a transition from an early proximal intrabasinal source to a late distal extrabasinal source.

New Zircon U-Pb Age of the Ore-bearing Porphyry from the Kuga Copper Deposit in the Eastern Bangongco–Nujiang Matallogenic Belt, Tibet

Objective As the third most important copper polymetallic metallogenic belt in Tibet, the Bangongco-Nujiang metallogenic belt （BNMB） has attracted much attention among geoscientists all over the world （Lin Bin et al., 2017a）. There are two ore clusters in the westem of BNMB, the Duolong giant porphyry-epitherrnal Cu （Au, Ag） ore cluster and the Ga＇erqiong-Galalelarge porphyry- skarn Cu （Au） ore cluster （Lin Bin et al., 2017a; 2017b）. Now, the latest exploration advances show that the Kuga project is the first economic porphyry-skam copper deposit in the eastern of BNMB, with over 0.4 Mt melt copper （333＋334） @ 0.9%. However, the Kuga deposit is poorly studied about its diagenetic age. In this study, we present a zircon U-Pb LA-ICP-MS dating of ore-bearing biotite granite, in order to identify the time of the ore- related magmatism and reveal the relationship with the westem of BNMB.

Zircon SIMS U-Pb Age of the Shaxinan Melagabbro, Eastern Tianshan and Constraints on Fe-Ti-V Oxide Mineralization

Objective The late Paleozoic Fe-Ti-V oxide deposit of the eastern Tianshan is an important orthomagmatic deposit type in the Central Asia Orogenic Belt （CAOB）. A series of Fe-Ti -V oxide deposits and mineralized mafic-ultramafic intrusions have been recognized recently, such as those in Hongliangzi, Weiya, Yaxi, Shaxinan and Shaxi on the Central Tianshan massif, and Niumaoquan on the southern margin of the Harlik belt （Shi et al., 2018a）. Only a few Fe -Ti-V oxide deposits in the eastern Tianshan （e.g., Weiya and Niumaoquan） have been studied, and their chronology need to be further constrained for study of regional Fe-Ti- V oxide metallogenic mechanism and variation of mantlederived magmas during the orogenic process.

Discovery of Ophiolitic Mélange in the North Region of Geji County, Northwest Tibet and Its Zircon U-Pb Age

Objective The Bangong Co–Nujiang River suture zone is the great boundary between the Lhasa and Qiangtang terranes in the Tibetan Plateau.A series of major scientific issues are still controversial at present such as the subduction polarity and evolutionary process of this suture（Wei Shaogang et al.,2017）.