The research on highly fractionated granite has significant implications for both the evolution and compositional maturation of the continental crust and metallogenic exploration. As a means of further understanding crustal evolution and promoting ore exploration in the Bangong–Nujiang metallogenic belt (BNMB), we present the petrography, zircon LA–ICP–MS U–Pb age, and Hf isotopic data, along with the whole-rock geochemical and Sr–Nd isotopic composition on Kese highly fractionated granite in the Baingoin area within the BNMB, central Tibet. The results show that Kese granite possesses a zircon U–Pb age of 127.8 ± 1.7 Ma and a relative enrichment in zircon Hf isotopic composition (−12.8~+0.3) with a two-stage Hf model age of 1.2~2.0 Ga. This granite belongs to the high-K calc-alkaline series, characterized by a strongly peraluminous feature, and is enriched in large-ion lithophile elements (LILEs) and Nd isotopes (−7.86~−7.74). The granite was likely to have been derived from the mixed melts derived from 40%~45% juvenile basaltic lower crust, 15%~20% ancient lower, and 40% middle–upper, following intense fractional crystallization processes involving amphibole, biotite, plagioclase, and some accessory minerals during the magma’s evolution. We infer that Kese highly fractionated granite can be formed from the continental collision of the Lhasa–Qiangtang terranes initiated before 128 Ma. The reworking of pre-existing juvenile and ancient crustal materials drove the composition of the northern Lhasa terrane to that of a mature continental crust. Moreover, the distinctive geochemical features have shown that the high degree of differentiation led to intense magmatic–hydrothermal interaction during the formation of Kese granite. A comparison of the geochemical characteristics of mineralized and barren granites suggests that the highly fractionated granites in Baingoin from the BNMB have a high economic potential and are suitable for preliminary exploration of Sn–W-(U) deposits.

共和盆地处于西秦岭、南祁连、东昆仑造山带结合部,其中发现了高温干热岩及多套烃源岩,但地热藏和油气藏的成因、资源潜力与分布规律尚不清楚,难以对其开展准确评价和有效勘探开发.本文在系统研究共和盆地及周缘地层发育、沉积充填、构造变形与盆地深部结构的基础上,深入探讨了盆地演化的动力学机制,分析了盆地地热藏和油气藏的成藏主控因素,预测了有利分布区带和勘探方向.多期活动的哇洪山-温泉、多禾茂、瓦里贡、塘格木右行走滑逆冲断裂与青海南山左行走滑逆冲断裂异向、同向相交(切),叠加地幔上涌作用,导致在中新生代共和盆地长期处于走滑-伸展的独特环境,并控制了盆地7个隆起、断陷构造单元的展布及属性.它经历了6期演化阶段:早中三叠世处于昆北弧前盆地及陆缘火山弧带,共和盆地基底主要岩石发育;晚三叠世阿尼玛卿洋闭合并发生碰撞造山,共和盆地褶皱基底形成;晚三叠纪末期发生碰撞后伸展,发育初始小型陆内裂谷盆地;在侏罗纪-白垩纪区域性伸展环境下形成局部断陷盆地;古近纪晚期-中新世发育拉分-断陷盆地;中新世末至今发育陆内前陆盆地.形成了3个大构造-沉积层序和8个亚层序,发育了深海陆棚相-碳酸盐岩台地相-火成岩相以及多旋回的冲积扇-河流相-滨浅湖相-半深湖相等陆相沉积层序,它们记录了共和盆地的叠合发育演化及多期改造过程,与古特斯阿尼玛卿洋俯冲、后撤式俯冲、碰撞后伸展的近程效应响应,与班公-怒江、雅鲁藏布江新特提斯洋打开、俯冲、闭合以及印度/欧亚大陆碰撞过程的远程效应响应.共和盆地构造-沉积演化特色造就了盆地较好的油气和地热的能源资源条件.盆地发育有中下侏罗统羊曲组、下白垩统万秀组、新近系咸水河组和临夏组等三套烃源岩,可形成上-中-下三套潜力油气勘探层系,需进一步开展地层精细对比、区带评价和圈闭落实工作.共和盆地深部5层结构构造特征及盆地形成动力学过程揭示了其具有丰富的地热能资源潜力.幔源上涌驱动导致地壳内各层向上扰动,叠加走滑伸展的盆地发育环境,形成短路径-多源增热模式.地幔上涌、中下地壳局部熔融体提供了区域热源、局部热源;陆缘弧和碰撞相关花岗岩类叠加多期次断裂、裂缝及热液活动起到"控热储及热传导"作用;上覆巨厚细粒沉积岩阻热扩散而形成"控热盖",是中高温干热岩型地热藏主控因素,也为浅层水热型地热的生成奠基.研究成果可为存在局部高大地热流的陆内中小型盆地地热藏研究提供借鉴.

The thermal history process and heat source experienced by the hot dry rock in the Gonghe basin of Qinghai is an urgent problem to be solved in understanding the formation of the hot dry rock geothermal reservoir. Different periods and different types of veins can provide evidence for the thermal process and heat source experienced by the hot dry rock. After investigation, it was found that the tourmaline veins in the Dangjiasi pluton in the northeast of the basin and the underground hot dry rock are similar to the later fault occurrence in the area. Whether it represents a later thermal event needs to be determined. This study selected the tourmaline from the cores in Well GR1 and Well DR3 and in Dangjiasi plutons are used as the key research objects to carry out petrographic, zircon U-Pb, electron probe analysis, LA-MC-ICPMS in -situ trace element and B isotope analysis to constrain the origin and source of tourmaline veins. The results show that the tourmaline -bearing cores in Wells GR1 and DR3 and the Dangjiasi granite are alkali feldspar granite, high -magnesium diorite and monzonite granite respectively; the tourmaline veins in the granite body in the outcrop area are about 20cm wide, and their occurrence is upright, the formation age of its surrounding rocks is 239 similar to 241Ma. Backscattering and microscopic image features reveal that the tourmaline in the hot dry rock Wells GR1 and DR3 and the Dangjiasi pluton are alkali group schorl and magnesium tourmaline, with multiple fluid sources at different distances. The in -situ tourmaline 8"B is distributed in the range of 11. 50% similar to -11. 93%c, which is similar to the average 8"B value of continental crust ( -10%o +/- 3%o); Combined with regional geological data, it is believed that in the Late Triassic, the region as a whole was in the collision period or post-collision period, and the continental crust was thickened and partially melted to form S -type granites ( similar to 220Ma). Meanwhile, the boron containing fluids in the magma emplaced in the early I -type granites ( similar to 240Ma) with a subduction setting to form the tourmaline veins.

青海共和盆地干热岩经历的热历史过程、热源是了解干热岩地热藏形成亟待解决的难题,不同时期、不同类型的脉体可为其经历的热过程、热源提供证据.经调查发现,盆地东北当家寺岩体及井下干热岩中电气石脉体与该区后期断裂产状相近,是否代表后期热事件需要确定.本研究选择对GR1井、DR3井中酸性侵入岩岩芯和当家寺露头岩体中发现的电气石脉体开展了岩相学、锆石年代学、电子探针、LA-MC-ICPMS原位微量元素及B同位素分析,以约束电气石脉体的成因和源区.结果表明,GR1、DR3井岩芯及当家寺岩体含有电气石脉体的岩性分别是碱长花岗岩、高镁闪长岩及二长花岗岩;其中露头区花岗岩体中电气石脉的宽度约20cm,产状直立,其围岩的形成时代为239～241 Ma.背散射及显微图像特征揭示,GR1井和DR3井下中酸性侵入岩及当家寺岩体中电气石为碱族的黑电气石和镁电气石,具有远近不同的多个流体来源.δ11 B分布在-11.50‰～-11.93‰,与大陆地壳平均的同位素组成δ11 B值(-10‰±3‰)相近.结合区域地质资料,认为在晚三叠世时期,该区域整体处于碰撞期或后碰撞期,陆壳加厚发生部分熔融形成S型花岗岩(～220Ma),其中含硼的热液流体侵位于早期具有俯冲背景的I型花岗岩(～240Ma)中形成电气石脉.

Gonghe basin, located at the junction of Qinling, Qilian and Kunlun orogenic belts, records complex tectonic, magmatic, metamorphic and sedimentary events, and is a key area to study the tectonic and magmatic evolution of the northern Tibetan Plateau. In recent years, the discovery of high-temperature Hot Dry Rock (HDR) in Gonghe basin makes this area a strategic base of new geothermal resources. However, the composition, emplacement age, temperature, pressure, depth and spatiotemporal distribution of HDR are not clear, which restricts the exploration and exploitation of geothermal energy and the understanding of tectonic-thermal evolution history in this area. In combination with the regional geological survey data, we carried out systematic petrology, zircon U-Pb geochronology and mineral thermobarometer on three drilling cores and field outcrop samples of Qiabuqia area in the northeastern Gonghe basin. It is found that the hot dry rocks in this area are mainly composed of granodiorite, tonalite, monzonitic granite and syenite granite, with diorite enclave occasionally. The results of electron microprobe analysis show that most of the hornblendes in the samples are iron hornblende. The hornblende-plagioclase thermobarometer results show that the formation pressure of hornblende in the HDRs of the Gonghe basin belongs to medium low pressure (1. 91 similar to 3. 52kbar) , with medium to low temperature (681 similar to 693 degrees C ) , and the crystallization depth of magma is about 7. 2 similar to 13. 2km. The results reveal that the crystallization temperature of magma in Qiabuqia area of Gonghe basin is 643 similar to 804 degrees C , while the Gouhou complex in the northern Qiabuqia has higher crystallization temperature than the drilling cores in the south. Zircon U-Pb geochronology analysis shows that the protoliths of Qiabuqia area in the northeastern Gonghe basin were mainly formed in 243 similar to 236Ma and 225 similar to 210Ma. There were different periods and different origins of intrusion, which was related to the subduction and closure of the Paleo-Tethys ocean basin in the northern Qinghai-Tibet Plateau during Indosinian. After that, at least 4. 2km of crust rock was exposed above HDR in the Gonghe basin. Combined the previous multiple geophysical data, the deep four-layer architectural structure profile is constructed. The heat source of HDR may be related to the upwelling of mantle and the existence of melting body in the middle and lower crust. And influenced by several hidden faults, the geothermal reservoirs of the HDR under the basement in the Gonghe basin have been partition.

AbstractThe South Altyn Orogenic Belt (SAOB) is one of the most important orogenic belts in NW China, consisting of the South Altyn Continental Block and the Apa–Mangya Ophiolitic Mélange Belt. However, its Palaeozoic tectonic evolution is still controversial. Here, we present petrological, geochemical, zircon U–Pb and Lu–Hf isotopic data for the Mangya plutons with the aim of establishing the Palaeozoic tectonic evolution. We divide the Early Palaeozoic magmatism in the Apa–Mangya Ophiolitic Mélange Belt into four episodes and propose a plate tectonic model for the formation of these rocks. During 511–494 Ma, the South Altyn Ocean (SAO) was in a spreading stage, and some shoshonite series, I-type granitic rocks were generated. From 484 to 458 Ma, the oceanic crust of the SAO subducted northward, accompanied by large-scale magmatic events resulting in the generation of vast high-K calc-alkaline series, I-type granitic rocks. During 450–433 Ma, the SAO closed, and break-off of the subducted oceanic slab occurred, with the generation of some high-K calc-alkaline series, I–S transitional type granites. The SAOB was in post-orogenic extensional environment from 419 to 404 Ma, and many A-type granites were generated.

The Gonghe basin is located on the northeastern margin of the Qinghai-Tibet Plateau. The petrogenesis of Early-Middle Triassic magmatic rocks in the Gonghe basin and its adjacent areas was still controversial since past studies mainly focused on the outcropped rocks. This paper reports petrology, electron microprobe analysis ( EMPA ) on feldspar, the major and trace element geochemistry , zircon U-Pb chronology and Lu-Hf isotopic compositions of the granitoid core samples of 2450 similar to 3000m GR1 Well, which is for the geothermal resources of the hot dry rock ( HDR) in the Gonghe basin, Qinghai. The petrography and EMPA results reveal that the granitic pluton is mainly composed of trondhjemite, tonalite and granodiorite ; and the U-Pb dating results show that the magmatic crystallization ages of the trondhjemite and tonalite are 236. 5Ma and 241. 6 Ma, respectively. The major and trace element geochemical characteristics show these granites are mainly metaluminous and belong to the high-K calc-alkaline series. Incompatible elements ( Ta, Nb, Hf) of the Middle Triassic granites (236. 5 similar to 241. 6 Ma) and the Hf isotopic characteristics of the zircons in them indicate that the granite association has the volcanic arc affinity and syn-collision affinity, which means the subduction-collision transition occurred in the Middle Triassic in the Gonghe area. Based on the data in this paper and regional backgrounds, we suggest that the formation of the Early-Middle Triassic granite association in the Gonghe basin is closely related to the southward subduction of the Zongwulong Ocean during the Indosinian period. There is a unified continental marginal arc environment along the Zongwulong-Qinghai Nanshan-northem margin of West Qinling belt before Middle Triassic; and after the subduction-collision transition occurred at 236 similar to 241Ma, the belt was in the collision and post-collision period in the Late Triassic.

通过锆石LA-MC-ICP-MS Lu-Hf同位素分析,结合前人地球化学资料对舒家店地区中酸性侵入岩进行了研究.主量、微量元素地球化学特征表明区内侵入岩为准铝质,具有岛弧岩浆岩的特征,区内岩浆的演化可能经历了同化混染与分离结晶(AFC)过程.通过分析,我们认为舒家店地区的早白垩世岩浆活动可能与早白垩世初太平洋板块的斜向俯冲相关,侵入岩的形成演化受到了区域构造应力场的制约.Hf同位素分析及计算结果表明,除两个继承性锆石核外,本区侵入岩锆石的εHf(t)均为负值,橄榄安粗岩系列侵入岩的εHf(t)值为-8.6～-4.1,高钾钙碱性系列εHf(t)值为-13.4～-4.7.与高钾钙碱性系列相比,橄榄安粗岩系列侵入岩的εHf(t)更接近球粒陨石演化线.从εHf(t)值的变化特征来看,两个系列侵入岩均为来源于富集地幔,且在演化过程中混染了地壳物质,而高钾钙碱性系列在这个过程中混入了更多的地壳物质.

安徽铜陵矿集区出露的侵入岩可划分为高钾钙碱性和橄榄安粗岩系列,作为铜陵7大矿田之一的焦冲地区是否也存在两个系列侵入岩?它们的时代及成因与整个铜陵地区的侵入岩是否相同?这些问题目前仍不清楚.本文选择铜陵焦冲矿田的侵入岩开展了岩相学、岩石地球化学、LA-ICPMS锆石U-Pb定年及原位Hf同位素地球化学研究.结果表明,焦冲矿田也存在高钾钙碱性系列和橄榄安粗岩系列侵入岩,前者的主要岩石类型为石英二长闪长岩、花岗闪长岩,后者为辉石二长闪长岩.LA-ICPMS锆石U-Pb定年结果显示,高钾钙碱性系列侵入岩年代与铜陵地区其他矿区同类岩石年代相同,约为142 Ma;而橄榄安粗岩系列侵入岩年代比铜陵地区其他矿区同类岩石年轻,约为136 Ma.总体上看,铜陵地区两个系列侵入岩具有多期次侵位的特征.焦冲高钾钙碱性系列侵入岩含有较多的老的继承性锆石,说明本区古老地壳卷入了岩浆形成过程.结合铜陵地区侵入岩的特征和焦冲矿田侵入岩岩石地球化学研究结果,笔者认为,焦冲矿田两个系列侵入岩成因与铜陵地区侵入岩相似,即橄榄安粗岩系列侵入岩是来自莫霍面附近深部位岩浆房富碱基性岩浆结晶分异后的产物,而高钾钙碱性系列侵入岩是深位岩浆房分异后的岩浆与浅位岩浆房长英质岩浆混合后的产物.

Objective The Dunhuang Block is located in the conjunction area of the Tarim Craton, Central Asian Orogenic Belt, North China Craton, and Tethyan tectonic domain, and is traditionally regarded as a Precambrian crystalline basement block. However, recent research concluded that

The Altun orogenic belt in northwest China is part of the northern margin of the Tibetan Plateau. The North Altun ophiolitic melange belt is an important tectonic unit within the Altun orogenic belt that contains voluminous early Paleozoic granitoids. In this study, we report the petrological features, geochemical compositions, and zircon U-Pb and Hf isotope data of three granitic plutons from the western segment of the North Altun ophiolitic melange belt. Zircon U-Pb dating yields magmatic crystallization ages of 499, 493 and 496 Ma for samples of granodiorite, quartz diorite and syenogranite, respectively. The granitoids have metaluminous to weakly peraluminous and medium-K to high-K calc-alkaline characteristics and display relative enrichments in large ion lithophile elements (Rb, Th, U, K) and light rare earth elements (LREE) and relative depletions in Nb, Ta, Sr, P and Ti, suggesting an arc-related origin. The granodiorites (499 Ma) have positive zircon epsilon(Hf)(t) values ranging from +1.87 to +6.59 with two-stage Hf model ages (T-DMC) of 1.05 to 1.35 Ga, implying that the granodiorites were derived from juvenile crust. The quartz diorites (493 Ma) have similar Hf isotopic characteristics to the granodiorites (epsilon(Hf)(t) = +2.59 to +6.04, T-DMC = 1.08 to 1.30 Ga), indicating derivation from juvenile crust. The syenogranites (496 Ma) have high total REE and K2O contents, and low zircon epsilon(Hf)(t) values (-1.69 to +1.54), suggesting that they were derived mainly from juvenile crust mixed with ancient crustal materials. Combined with data from previous studies, we conclude that magmatism in the North Altun ophiolitic melange belt can be subdivided into three episodes: Episode 1 (520-470 Ma) granitoids are related to subduction; Episode 2 (460-425 Ma) granitoids formed in a continent-continent collisional setting; and Episode 3 (<420 Ma) granitoids are post-collisional granites. Our results are consistent with south-directed subduction of the North Altun oceanic lithosphere beneath the Central Altun Block during the early Paleozoic (520-460 Ma), which was followed by collision with the Dunhuang Block. (C) 2019 Elsevier B.V. All rights reserved.

Numerous granitic intrusions crop out in the eastern segment of the North Qaidam block (NQ), NW China. To evaluate their ages, petrogenesis and genetic relationships to other granitoids in the NQ we present geochemical and geochronologic data for six intrusive bodies and review regional data. Zircon U-Pb (SHRIMP) dating yielded ages of 413 +/- 3 Ma for the Hadesengou granite; 254 +/- 3 Ma for the Xugeigou granite; 251 +/- 1 Ma for the Qiluoshan granite; 249 +/- 1 and 248 +/- 2 Ma for the Chahannuo hornblende diorite and granite, respectively; 240 +/- 2 Ma for the Chahanhe granite; and 250 +/- 1 and 244 +/- 3 Ma for the Shailekegoulei granodiorite and granite, respectively. Consequently, the Wulan plutons call be divided into two petrologic groups: Early Devonian (D-1) quartz monzonite and syenogranite, and Late Permian to Early Triassic (P-3-T-1) hornblende diorite, granodiorite, and granite. The D-1 granitic intrusions have geochemical affinities with A-type granites (A(2)-type) characterized by low Ca, Sr, Ba and Nb, and high Fe, Ca, Y and Rb, consistent with derivation by partial melting of metapelitic source rocks containing a small amount of metagraywacke. The P-3-T-1 l-type granitic intrusions are geochemically typical of active continental margin rocks, consistent with derivation by partial melting of metabasalt and clay-poor metagraywacke. Combined with previous studies, we recognize five periods of granitic magmatism in the NQ: (1) 465-473 Ma: (2) 423-446 Ma; (3) 391-413 Ma; (4) 372-383 Ma; and (5) 240-271 Ma. Based on the temporal-spatial distribution of granitic intrusions in the NQ and the regional tectonic evolution, we interpret the first and second periods of granitic magmatism as related to normal plate subduction, and the third period to slab break-off and exhumation of the subducted plate. The fourth stage of granitic magmatism is attributed to large-scale lithospheric mantle delamination, involving the differential movement of orogenic blocks. The fifth period of granitic plutonism probably reflects northward subduction of the East Kunlun Paleotethys oceanic crust and southward subduction of Zongwulong oceanic crust beneath the Oulongbuluke continental block. (C) 2018 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

The South Altyn continental block is an important geological unit of the Altyn Tagh orogenic belt, in which numerous Neoproterozoic granitoids crop out. Granitoids are mainly located in the Paxialayidang–Yaganbuyang area and can provide indispensable information on the dynamics of Rodinia supercontinent aggregation during the Neoproterozoic. Therefore, the study of granitoids can help us understand the formation and evolutionary history of the Altyn Tagh orogenic belt. In this work, we investigated the Yaganbuyang granitic pluton through petrography, geochemistry, zircon U–Pb chronology, and Hf isotope approaches. We obtained the following conclusions: (1) Yaganbuyang granitoids mainly consist of two‐mica granite and granodiorite. Geochemical data suggested that these granitoids are peraluminous calc–alkaline or high‐K calc–alkaline granite types. Zircon U–Pb data yielded ages of 939±7.1 Ma for granodiorite and ∼954 Ma for granitoids, respectively. (2) The ε Hf ( t ) values of two–mica granite and granodiorite are in the range of –3.93 to +5.30 and –8.64 to +5.19, respectively. The Hf model ages ( T DM2 ) of two‐mica granite and granodiorite range from 1.59–.05 Ga and 1.62–2.35 Ga, respectively, indicating that the parental magma of these materials is derived from ancient crust with a portion of juvenile crust. (3) Granitoids formed in a collisional orogen setting, which may be a response to Rodinia supercontinent convergence during the Neoproterozoic.

The Beila ophiolite is located in the middle part of the Bangong-Nujiang suture zone on the northern Tibetan plateau, and rodingites are widespread within serpentinized peridotites in the ophiolite. According to the mineral assemblages, the Beila rodingite can be divided into three types: Type I rodingites have a mineral assemblage of prehnite, chlorite, and minor diaspore; Type II rodingites comprise diopside, prehnite, chlorite, epidote, and minor hydrogrossular; and Type III rodingites underwent further rodingitization and contain more hydrogrossular and vesuvianite than the Type II rodingites. Zircon grains from two rodingite samples yielded SHRIMPU-Pb ages of 172-164 Ma with positive values of epsilon(Hf)(t)( +9.0 to +16.3) and mantle-like delta O-18 values (+4.31 to +6.82%), indicating the Beila ophiolite formed during the Middle Jurassic. The rodingitization of the Beila ophiolite took place in two stages. The early stage involved the production of the Type I and II rodingites during metasomatism by Ca-rich fluids with high CO2/H2O ratios, and this stage is characterized by the formation of Ca-silicates (diopside, prehnite, and hydrogrossular). The second stage involved the production of Type III rodingites at the shallower depths in exhumed mantle under the influence of fluids with lower CO2/H2O ratios. Estimates of the migration of elements during rodingitization (e.g. Ca, alkalis, Fe, Cr,Ni, Nb, Ti, rare earth elements, and large ion lithophile elements), combined with Sr-Nd isotopic compositions, indicate that the formation of the Beila rodingite involved an extensive exchange of materials among the protoliths, serpentinized peridotite, and subduction-related materials. The results indicate that analyses of rodingites in ophiolites can contribute to our understanding of material exchange during oceanic-plate subduction. (C) 2018 Elsevier B.V. All rights reserved.

The North Qilian orogenic belt underwent a complete Wilson Cycle through opening and closing of an ocean basin. Deepening the research of granite within can provide pivotal clues to reconstruct the subduction-accretion/collision orogenic framework.On the basis of systematic petrological and petrographical research,this paper conducts electron microprobe analy-sis on the main rock-forming minerals,aiming to determine the physicochemical conditions during rock formation and provide further constraints on the petrogenesis and tectonic setting.Results show that Qingshan monzogranite is mainly composed of K-feldspar(orthoclase),plagioclase(andesine-oligoclase),biotite(magnesian biotite),amphibole(magnesiohornblende)and quartz.Zircon saturation thermometer shows that the average temperature of initial magma is 750 ℃.Meanwhile,mineral chemistry analysis reveals that the average crystallization temperature for biotite is 647 ℃ and the oxygen fugacity during the rock formation is —15,corresponding to solidification depth of 6.73 km and solidification pressure of 1.85×108Pa.The data in this paper indicates that Qingshan monzogranite is I-type subsolvus granite,with the features of crust-mantle mixed source. Thus,it is proposed that Qingshan monzogranite belongs to calc-alkaline granite and produced under water-bearing condition.

The South Altyn continental block is an important geological unit of the Altyn Tagh orogenic belt.Numerous Neo-proterozoic granites outcrops in the South Altyn continental block,and are mainly located in Paxialayidang-Yaganbuyang-Kekesayi area.These granites provide indispensable dynamics information of the Rodinia supercontinent aggregation in Neo-proterozoic.Therefore,the study of granites can help us to understand the formation and evolution history of the Altyn Tagh o-rogenic belt.In this paper,Kekesayi granitic pluton was studied by means of petrography,geochemistry,zircon U-Pb chronol-ogy and Hf isotopic analyses.The results are as follows.(1)Main minerals of Kekesayi monzonitic granite are:quartz+K-feldspar+plagioclase+biotite+muscovite.Zircon U-Pb dating shows that the granite was emplaced in 947—945 Ma.(2) Geochemistry characteristics show high SiO2(71.54%—74.69%),K2O+Na2O(6.33%—7.40%)contents and low CaO(1.59%—2.00%),MgO(0.43%—0.61%)and TiO2(0.25%—0.37%)contents,with K2O/Na2O ratios of 1.02—1.71 and A/CNK ratios of 1.10—1.14,showing a typical high-K calc-alkaline series with peraluminous features.Meanwhile,the granite is also enriched in Rb,K,Th and La,and depleted in Nb,Ta,Sr and Ba,with negative Eu anormalies and relative enrichment in LREE.(3)εHf(t)values range from —4.09 to +3.87 while two-stage model ages(tDM2)vary in 1.6—2.0 Ga.It is argued that the Kekesayi monzonitic granites were derived from partial melting of the meta-grey wackes of Late Paleoproterozoic to Early Mesoproterozoic ancient crustal materials.In combination with other Neoproterozoic granite features,the petrogenesis and isotopic geochronology indicate that the Kekesayi monzonitic granite was formed in collisional orogeny setting and may have been triggered by the assemblage of Rodinia supercontinent in Neoproterozoic.

阿克腾龙山二长花岗岩位于南阿尔金茫崖地区北侧,讨论其成因类型、成岩年代以及构造环境,进而探讨南阿尔金造山带早古生代岩浆活动及壳幔相互关系.利用岩石地球化学、LA-ICP-MS锆石U-Pb年代学和Lu-Hf同位素分析研究了岩体的成因类型、成岩时代、物质来源和成岩环境.研究表明,该岩体属于弱过铝质、高钾钙碱性I型花岗岩.富集轻稀土元素,而相对亏损重稀土元素;岩浆演化过程中可能发生了以角闪石、磷灰石和金红石为主的分离结晶.岩体的成岩年龄为435～449 Ma.锆石的εHf（t）正、负值各半,说明岩体可能来源于古老地壳和新生地壳的混合物质,可能是新生地壳部分熔融并混合部分古老地壳物质形成,或者是新生地壳和古老地壳的混合物质部分熔融,经历分离结晶而成.成岩环境可能是俯冲洋壳板片断离后,由碰撞挤压转向伸展抬升的构造环境.

Early Paleozoic granitic magmatism in the North Qilian orogenic belt records a complete Wilson cycle and provides critical geological clues for unraveling the regional tectonic history. In this study, we report the results of zircon U-Pb ages, Hf isotopic analysis and systematic whole-rock geochemical data for the Late Ordovician Hongliuhe granite and Early Silurian Qingshan monzogranite in the western segment of the North Qilian orogenic belt to constrain their emplacement ages, petrogenesis, and regional evolution history. U-Pb dating reveals that the Hongliuhe granite was emplaced around 453-452 Ma, and the Qingshan monzogranite was emplaced about 440-438 Ma. A geochemical study shows that the two granites belong to the calc-alkaline to high-K calc-alkaline series. The Hongliuhe granite shows adakitic and peraluminous features, while the Qingshan monzogranite belongs to metaluminous to weak peraluminous granites. Zircons in the Hongliuhe granite show epsilon(Hf)(t) values ranging from -15.1 to +11.7 with two-stage Hf model ages (t(DM2)) of 687-2398 Ma, whereas zircons in the Qingshan monzogranite show epsilon(Hf)(t) values ranging from +5.7 to +11.0 with two-stage Hf model ages from 814 to 1057 Ma. The geochemical characteristics indicate that the Hongliuhe granite was a transitional I/S-type granite and was generated from a thickened lower crust with the addition of minor Paleo- to Mesoproterozoic crustal materials, which left a rutile + garnet + pyroxene +/- plagioclase residue. The Qingshan monzogranite formed from the partial melting of mafic crust with minor mantle-derived materials, and the fractionation of Ti-bearing phases, apatite and pyroxene occurred during the magma's evolution, which left an amphibole and plagioclase residue. We infer that the Hongliuhe granite formed during the northward subduction of the North Qilian Ocean, while the Qingshan monzogranite was generated during the post-collision stage between the Qilian and Alxa blocks. This observation indicates that syn-collision stage of the North Qilian orogenic belt began before 453 Ma, and that the extension regime began prior to 444 Ma. (C) 2018 Elsevier B.V. All rights reserved.

Objectives:A large number of granite bodies are exposed in the Wuland area adiacennt to the Dulan UHP terrain.In addition to a few studies,the geochemical characteristics and genesis of these granites and their tectonic significance are almost not much studied.Especially,the genetic relationship between the granites from Wulan and others in the North Qaidam UHP belt remains unclear.Therefore,our research focuses on the petrogenesis of the granite and its regional tectonic significance.Methods:Based on the field work,through the microscope observation,the whole rock chemical analysis and the Sr—Nd isotopic analysis of the granites,we determine the the granite affinity and petrogenesis.Combined with regional tectonic characteristics and other research achievements of granite in North Qaidam,we discuss the tectonic significance of granite from Wulan.Results:Gechemically,most of the granites from Wulan area,northern Qaidam belong to magnesian calc-alkaline series,a few to iron alkali-calc and alkaline series.The early granite is not only enriched in large ion lithophile elements (LILE),but also enriched in part of high field strength elements (HFSE) (such as Zr,Y,Nb),which belongs to A-type granite.The late granitoids are enriched in LILE and light rare earth elements (LREE),depleted in HFSE,and had LREE differentiation to be obvious but heavy rare earth element (HREE),with a weak negative Eu anomalies in REE patterns,which belongs to the I-type granite.The isotopic geochemistry shows that the 87Sr/86Sr ratio of the early granitoids is 0.7108 and Nd model age (T2DM) 2.10Ga,higher than those of late granites (87Sr/86Sr =0.7076 ～ 0.7107,T2DM =1.41Ga ～ 1.58Ga),but εNd(t) value of late granites (-11.6) are lower than that of the early granite (-4.8 to-6.8),indicating that early granite may originate from the Paleoproterozoic continental crust and the late granite from the Middle Proterozoic basaltic crust.Conclusions:This study shows that the early granitoid in Wulan area are related to the Qilian lithospheric delamination,which causes the thinning and stretching of Oulongbuluke continent block,also marks the beginning of Zongwulong rift;and the lategranitoids in the area are related to the oceanic crust subduction of Zongwulong under the Oulongbuluke continent block.

The Paleozoic granites in the North Qilian area are important for understanding the tectonic evolution of the orogenic belt. The granite in Shibaocheng area is studied by petrography, geochemistry, zircon U-Pb chronology and Hf isotopic analyses. The results show that:(1) The granite in Shibaocheng area has an emplacement age of 465 similar to 463Ma and belongs to calc-alkaline series with strongly peraluminous features. (2) The granite has low average temperatures of T-Zr (760 degrees C) and T-REE (732 degrees C), respectively. Meanwhile, the granite is characterized by positive epsilon(Hf)(t) values (+7.6 similar to +13.5) and two-stage Hf model ages of 581 similar to 957Ma. (3) Geochemical and isotopic data exhibits that the granite is better considered as transitional between I-and S-type granites, and is most likely derived from the juvenile basic crustal materials by the dehydration from amphiboles with minor addition of Mesoproterozoic-Neoproterozoic sedimentary components. The magma was without apparent fractional crystallization process while the residual rocks may be the granulite mainly composed by garnet, amphibole and plagioclase. (4) The granite in Shibaocheng area may be formed under the active continental margin setting triggered by the north dipping subduction of the North Qilian Ocean, and underwent a crustal contamination during magma emplacement into sedimentary cover.