青藏高原羌塘中部蜈蚣山印支期花岗岩的地球化学特征和黑云母^（40）Ar-^（39）Ar年龄     

胡培远  李才  苏犁  张红雨 《中国区域地质》2012,(6):843-851

本松错岩基是羌塘中部规模最大的花岗岩复合岩基,面积超过1800km2,由石炭纪、三叠纪和侏罗纪3个不同时代的花岗岩岩体组成,记录了羌塘中部不同时期的岩浆活动,是研究羌塘盆地构造演化的重要窗口。蜈蚣山花岗岩位于本松错复合岩基北部,前人认为其时代为侏罗纪,但是近期在蜈蚣山地区侏罗纪花岗岩中发现有少量印支期花岗岩出露,岩性主要为花岗片麻岩和二长花岗岩,可能为侏罗纪花岗岩的捕虏体。地球化学研究表明,二长花岗岩属高钾钙碱性过铝质花岗岩,形成于同碰撞环境,与区域内其它印支期中酸性岩浆岩类似,共同构成龙木错-双湖-澜沧江板块缝合带同碰撞—后碰撞岩浆弧。此外还对花岗片麻岩片麻理中的黑云母做了40Ar-39Ar测年,获得了175.8Ma±1.1Ma的定年结果,与其围岩侏罗纪花岗岩年龄相近,推测花岗片麻岩是印支期花岗岩受后期侵入的侏罗纪岩浆改造后的产物,本松错复合岩基应当是中酸性岩浆岩多期侵入的产物。  相似文献   

新疆东准噶尔老鸦泉岩体的锆石U-Pb年龄和地球化学组成   总被引：5，自引：0，他引：5  

韩宇捷  唐红峰  甘林 《矿物学报》2012,32(2):193-199

老鸦泉岩体是贝勒库都克锡矿带内最大的花岗岩体,它主要由黑云母钾长花岗岩组成。通过对2件样品的锆石LA-ICP-MS U-Pb同位素年龄测定,获得其206Pb/238U年龄值分别为301±2 Ma和300±5 Ma,指示该岩体侵位时代为晚石炭世。岩石地球化学组成表明,老鸦泉碱长花岗岩具有富硅、富碱,相对富集Rb、K、Th、U、Nd、Hf等元素,而贫Ba、Sr、P、Ti等元素,具强负Eu异常,总体显示A型花岗岩的地球化学特征。锆石U-Pb年龄及岩石地球化学特征都表明老鸦泉岩体的形成与晚石炭世北疆强烈的后碰撞岩浆活动有着密切关系。  相似文献   

西藏南部岗巴—定日地区花岗岩地球化学特征及其构造环境   总被引：1，自引：0，他引：1  

毛琼  邹光富  顾雪梅  陈岚 《矿物岩石》2012,32(1):67-73

通过对出露于西藏南部岗巴—定日地区花岗岩体的地球化学研究表明,岩石中SiO2,Al2O3,Na2O和FeO,MgO等的含量均高,贫CaO和Fe2O3;w(SiO2)介于71.40%～73.06%,A/CNK在1.17～1.34之间,为铝和硅过饱和类型的强过铝质花岗岩。岩石的稀土元素总量(ΣREE)为56.80×10-6～89.12×10-6,(La/Yb)N=6.30～18.26,(La/Sm)N=2.62～3.40,ΣLREE/ΣHREE=2.41～4.66;稀土元素配分曲线呈右倾型,具有弱的负铕异常。Nb,Ti等高场强元素具有明显的亏损,而Rb,U,La,Nd,Hf,Eu,Y等大离子亲石元素具有明显的正异常。岩石的87Sr/86Sr初始比值较高,87Sr/86Sr为(0.738 71～0.751 12)。综合研究认为,本区花岗岩的成因为陆壳部分熔融作用形成的,属陆壳改造型强过铝质花岗岩。本区花岗岩岩浆源区岩石成分主要为砂屑岩,其次为泥质岩,是上地壳部分熔融作用的结果。岩石的微量元素标准化曲线图、岩石地R1-R2图解、Rb-(Yb+Ta)和Rb-(Nb+Yb)图解均显示本区岩体形成于同碰撞构造环境的花岗岩,具有同碰撞岩浆活动的特征,是喜马拉雅早期印度板块与冈底斯板块的俯冲碰撞导致的地壳增厚,上地壳部分熔融的产物;为形成于同碰撞构造环境的花岗岩。  相似文献   

Early Cretaceous A-type granites and Mo mineralization,Aershan area,eastern Inner Mongolia,Northeast China: geochemical and isotopic constraints     

《International Geology Review》2012,54(11):1357-1376

The Jiazishan porphyry-type molybdenum deposit is located in the eastern Inner Mongolia Autonomous Region in China. Mineralization occurs mainly as veins, lenses, and layers within the host porphyry. To better understand the link between mineralization and host igneous rocks, we studied samples from underground workings and report new SHRIMP II zircon U–Pb and Re–Os molybdenite ages, and geochemical data from both the molybdenites and the porphyry granites. Seven molybdenite samples yield a Re–Os isochron weighted mean age of 135.4 ± 2.1 Ma, whereas the porphyry granite samples yield crystallization ages of 139 ± 1.5 Ma (Jiazishan deposit) and 133 ± 1 Ma (Taolaituo deposit). The U–Pb and Re–Os ages are similar, suggesting that the mineralization is genetically related to Early Cretaceous porphyry emplacement. Re contents of the molybdenite range from 21.74 ppm to 52.08 ppm, with an average of 35.92 ppm, whereas δ³⁴ S values of the sulphide vary from 1.3‰ to 4.2‰. The ores have ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb ratios of 18.178–18.385, 15.503–15.613, and 37.979–38.382, respectively. We also obtained a weighted mean U–Pb zircon age of 294.2 ± 2.1 Ma for the oldest granite in Jiazishan area. All granites are A-type granites. These observations indicate that the molybdenites and the porphyry granites were derived from a mixed source involving young accretionary materials and enriched subcontinental lithospheric mantle. A synthesis of geochronological and geological data reveals that porphyry emplacement and Mo mineralization in the Jiazishan deposit occurred contemporaneously with Early Cretaceous tectonothermal events associated with lithospheric thinning, which was caused by delamination and subsequent upwelling of the asthenosphere associated with intra-continental extension in Northeast China.  相似文献   

The 401–409 Ma Xiaodonggou granitic intrusion: implications for understanding the Devonian Tectonics of the Northwest China Altai orogen     

《International Geology Review》2012,54(5):540-555

Abstract

Palaeozoic granitoids in the Chinese Altai are important for understanding the evolution of the Central Asian Orogenic Belt (CAOB). The Xiaodonggou granitic intrusion, situated in the Chinese Altai (southern CAOB), is composed of two intrusive phases, medium-grained granite intruded by porphyritic granite. Zircon LA-ICP-MS U–Pb analyses of medium-grained granite and porphyritic granite yield ages of 409 ± 2 Ma and 400 ± 1 Ma, respectively, indicating that these formed in Early Devonian time. Medium-grained granite and porphyritic granite have similar geochemical features and Nd–Hf isotopic compositions. Arc-like geochemical characteristics (e.g. enrichment of LILEs and negative anomalies of Nb, Ta, Ti, and P) show that both phases are volcanic arc granites (VAGs). Geochemical and isotopic characteristics suggest that these magmas originated from melting older crust. Based on their near-zero or negative ε_Nd(t) values (?1.4to 0) and positive ε_Hf(t) values (+1.4 to +7.8), together with Nd model ages of 1.15–1.26 Ga and zircon Hf model ages of 0.90–1.30 Ga, we suggest that the Xiaodonggou granites were derived from a mixture of juvenile and old crustal components. Some other Devonian granitic intrusions were recently identi?ed in the Chinese Altai with ages between 416 and 375 Ma. These Devonian granites have similar geochemical characteristics and petrogenesis as Xiaodonggou granites. The formation of these Devonian granites was in response to subduction processes, suggesting that Chinese Altai was an active continental margin in Early Devonian time.  相似文献   

黑龙江东部晚三叠世A 型花岗岩的厘定及其构造环境的地球化学制约     

郑全波  汪岩  张广宇  金哲岩 《世界地质》2012,31(3):471-478

岩石学及元素地球化学研究结果表明,黑龙江省东部五营-汤旺河一带存在晚三叠世过铝质A 型花岗岩。A 型花岗岩由正长--碱长花岗岩类和碱性花岗岩组成,相当于Liegeois 提出的后碰撞作用阶段的产物,标志着造山事件趋于结束,新的板内环境开始。Rb --Sr 同位素测年显示其形成于晚三叠世,代表了佳木斯板块和松嫩-张广才岭板块在晚三叠世末期沿着嘉荫-牡丹江缝合带碰撞拼合后的伸展作用,标志着古亚洲洋构造域演化结束,黑龙江东部此时已经开始进入了滨太平洋构造域的板内演化阶段。  相似文献   

Neoproterozoic bimodal volcanic rocks and granites in the western Dabie area,northern margin of Yangtze block,China: implications for extension during the break-up of Rodinia     

《International Geology Review》2012,54(11):1370-1390

ABSTRACT

To better understand the Neoproterozoic tectonic evolution along the northern margin of Yangtze Block, we have determined the geochronological and geochemical compositions of newly recognized bimodal volcanic suite and coeval granites from the western Dabie terrain. LA-ICP-MS zircon U-Pb dating reveals that the felsic and mafic volcanics from the Hong’an unit have crystallization ages of 730 ± 4Ma and 735 ± 5Ma, respectively, indicating that the bimodal suite was erupted during the Neoproterozoic. The Xuantan, Xiaoluoshan, and Wuchenhe granites yield U-Pb ages of 742 ± 4 Ma, 738 ± 4 Ma, and 736 ± 4 Ma, respectively. The felsic volcanic rocks show peraluminous characteristics, and have a close affinity to S-type granite. The mafic volcanic rocks are basalt in compositions, and are likely generated from a depleted mantle source. The granites belong to high-K calc-alkaline and calc-alkaline series, display metaluminous to peraluminous, and are mainly highly fractionated I-type and A-type granite. The granites and felsic volcanics have zircon εHf(t) values of ?16.4 to + 5.6 and two-stage Hf model ages (T_DM2) of 1.28 to 2.40 Ga, suggesting that they were partial melting of varying Mesoproterozoic–early-Neoproterozoic crust. The granites have εNd_(t) of -14.7 to -1.5, and the two-stage Nd model ages (T_DM2) values of 1.54 to 2.61 Ga, also implying the Yangtze crustal contribution. These Neoproterozoic bimodal suite and coeval granites were most likely generated in a rifting extensional setting, triggered by the mantle upwelling, associated with crust–mantle interaction. Intensive magmatic rocks are widespread throughout the South Qingling, Suizhao, western Dabie and eastern Dabie areas during 810–720 Ma, and show peak ages at ~ 740 Ma. Combining regional geology, we support a continental rifting extensional setting for the north margin of the Yangtze Block during the break-up of the supercontinent Rodinia.  相似文献   

Two different magma series imply a Palaeogene tectonic transition from contraction to extension in the SE Korean Peninsula     

《International Geology Review》2012,54(11):1284-1295

Late Cretaceous–early Tertiary granites in the Gyeongsang Basin have distinctly different bulk-rock compositions. Calc-alkaline I-type metaluminous granites display petrographic features implying magma mixing, whereas A-type granites are hypersolvus and peralkaline. I-type plutons mainly consist of enclave-rich granodiorites and enclave-poor porphyritic granites typified by abundant plagioclase phenocrysts; these granitoids contain various mafic clots and magmatic/microgranular enclaves (MMEs). A-type bodies are perthitic alkali-feldspar granites characterized by interstitial annite + riebeckite-arfvedsonite. New SHRIMP-RG zircon U–Pb age dating of an I-type enclave-poor porphyritic granite and an A-type alkali-feldspar granite yielded ages of 65.7 ± 0.7 and 53.9 ± 0.3 million years, respectively. Based on prior geochronologic data and these contrasting ages of granitic magma genesis, SE Korea may have evolved tectonically from latest Cretaceous compression to late Palaeocene extension (i.e. orogenic collapse). The later part of the 66–54 Ma magmatic gap apparently includes the time of tectonic inversion in the SE Korean Peninsula, a far-field effect of the collision of the Indian subcontinent with Eurasia. This process is also reflected in the 69–52 Ma NNE-trending Eurasian apparent polar wandering path.  相似文献   

Petrogenesis of I-type granitoids from the Melrose Stock,east-central Nevada     

《International Geology Review》2012,54(13):1522-1558

The Melrose Stock in the Dolly Varden Mountains of east-central Nevada is one of the many Mesozoic intrusion s in the Basin and Range Province. It consists of monzonites, quartz monzonites, granodiorites, and granites sharply intruding Mississippian to Triassic units. Phenocrysts of plagioclase (An₃₈–An₂₄) with oscillatory zoning and albitic rims, hornblende ± diopside, and biotite are common. Coexisting phases include orthoclase, quartz and accessory magnetite, apatite, titanite, ilmenite, and allanite. Mineral compositions suggest that the intrusion was emplaced at ～720 ± 40°C and 1.8–2.3 kbar.

All rocks are metaluminous to slightly peraluminous, defining a calcalkalic trend in which the monzonites and syenites are shoshonitic. Rare earth element patterns indicate that all studied rock types are comagmatic. Harker plots show curvilinear trends with some kinks consistent with fractionation, and mixing/assimilation. Major-element modelling and petrographic evidence suggest three stages of fractionation/mixing: Stage 1 marked by the fractionation of diopside and plagioclase; Stage 2 by fractionation of plagioclase, hornblende ± orthoclase ± biotite, accompanied by mixing through convection; and Stage 3 by fractionation of biotite, hornblende, plagioclase, and orthoclase.

Mineralogic, petrographic, and major- and trace-element data demonstrate that all rocks are I-type granitoids, suggesting a significant mantle contribution. Spider diagrams show troughs for Ti, P, and Nb, indicating magma genesis in a subduction-zone setting. Discrimination diagrams classify all rocks as late orogenic. Magma was therefore generated from mantle metasomatized by subduction, differentiated to a monzonitic magma, and emplaced in the thinned continental crust during a period of extension late in the cycle of Elko orogeny.  相似文献   

The Late Triassic Dengfuxian A-type granite,Hunan Province: age,petrogenesis, and implications for understanding the late Indosinian tectonic transition in South China     

《International Geology Review》2012,54(4):428-445

The Triassic (Indosinian) granites in the South China Block (SCB) have important tectonic significance for understanding the evolution of Eastern Asia. The Dengfuxian biotite granite in eastern Hunan Province, China, reported in this article, was recognized as Late Triassic (late Indosinian) weakly peraluminous A-type granite with a zircon laser ablation inductively coupled plasma mass spectrometry U–Pb age of 225.7 ± 1.6 Ma. It is enriched in F, Cs, Rb, Th, high field strength elements, and rare earth elements (REEs) and depleted in Ba, Sr, P, Ti, Nb, and Ta, with high Ga/Al ratios and zircon saturation temperatures. The Dengfuxian biotite granite shows high initial Sr isotope values (0.715932 to 0.716499) and negative ?_Nd(t) (?10.46 to ?9.67) and ?_Hf(t) (?9.92 to ?6.29) values, corresponding to the Nd model ages of 1.79 to 1.85 Ga and the Hf model ages of 1.65 to 1.88 Ga. It is proposed that the Dengfuxian biotite granite was derived from high-temperature partial melting of the Palaeoproterozoic lower crust undergoing granulitization. Some Late Triassic A-type granites were recently identified in the SCB with the ages between 202 and 232 Ma. These A-type granites have the same geochemical characteristics and petrogenesis as Dengfuxian A-type granite, and show A₂-subtype granite affinity. The Late Triassic A-type granite formed a NE-trending granite belt, which is consistent with the main NE-trending faults in the SCB. The formation of these A-type granites was in response to the subduction of the palaeo-Pacific plate underneath the SCB, and indicates an extensional tectonic environment in the SCB. Combined with previous studies on tectonic evolution, we suggest that there may be a tectonic transition inside the SCB from compression to extension at least from 225 to 230 Ma.  相似文献