拉萨地块南缘日多地区叶巴组火山岩地球化学、年代学、锆石Lu-Hf同位素特征及其地质意义   总被引：2，自引：1，他引：1  

韩奎  周斌  王辉  乔新星  潘亮  罗金海  赵焕强  王峰 《地质通报》2018,37(8):1554-1570

拉萨地块南缘日多地区叶巴组火山岩以中酸性熔岩及火山碎屑岩占绝对优势为特征。以墨竹工卡县以东日多地区叶巴组火山岩代表性岩石组合为对象进行了地球化学、LA-ICP-MS锆石U-Pb年龄及锆石Lu-Hf同位素研究。研究结果表明,叶巴组火山岩具有轻稀土元素富集,富集大离子亲石元素Rb、Th、K,亏损高场强元素Nb、Ta、Ti(P、Hf)的地球化学特征。其中,基性火山岩具低钾、低钛和富钠、富铝的特征,Nb、Zr含量和Th/Y、Th/Yb、Ta/Yb值较高,而La/Nb值较低,呈现出大陆地壳组分增加的趋势。中酸性火山岩属中钾-高钾钙碱性系列,具有低钛、低镁和高铝的特征,微量元素含量及比值与大陆岛弧安山岩接近。叶巴组火山岩总体地球化学特征与陆缘弧火山岩相似。LA-ICP-MS锆石U-Pb测年获得英安岩和流纹质晶屑凝灰岩~(206)Pb/~(238)U年龄加权平均值分别为176.9±2.3Ma和162.2±3.3Ma,表明研究区叶巴组酸性火山岩形成于中侏罗世。锆石Hf同位素测试结果显示,εHf(t)值为2.43~11.42,二阶段模式年龄(t_(DM)~C)为482~1065Ma,暗示叶巴组酸性火山岩源区除新生地壳物质的部分熔融外,还明显受到古老结晶基底的影响。结合前人研究成果,认为叶巴组形成于早中侏罗世雅鲁藏布江洋北向俯冲于拉萨地块南缘之下的陆缘弧环境。  相似文献   

Origin of the serpentinites in the Lichi mélange,eastern Taiwan,China: implication from petrology and geochronology     

《China Geology》2018,1(4):477-484

Lichi mélange, located in the southern coastal range, eastern Taiwan, China, is a typical tectonic mélange of the plate’s boundary zone between the Eurasian Plate and the Philippine Sea Plate. It formed during the collision of the Luzon arc with the Eurasian Continent (arc-continent collision). It is composed of sandstone and/or mudstone matrix and many kinds and sizes of rock fragments, including some sedimentary rocks, volcanic rocks and a few metamorphic rocks. The serpentinite is one of the common fragments in the Lichi mélange. By the petrographic characteristics and the zircon U-Pb chronology analyses, protolith of the serpentinite is peridotite, the age is 17.7 ± 0.5 Ma. Taking the tectonic background into account, it is inferred that the serpentinite (serpentinised peridotite) come from the forearc basin (the North Luzon Trough) and was taken into the mélange by a second thrust westwards. The origin of the serpentinite in Lichi mélange is helpful to understand the formation of the Lichi mélange and can provide reliable detailed information for the study of the arc-continent collision orogenic activity in and offshore Taiwan.  相似文献   

贵州五指山特大型铅锌矿床闪锌矿的Rb-Sr定年及其地质意义          下载免费PDF全文

王生伟  金灿海  张玙  孙晓明  周清  廖震文  郭阳  蒋小芳  王子正 《沉积与特提斯地质》2018,38(3):77-87

贵州五指山铅锌矿床为近年新勘探出的特大型铅锌矿床,其成矿时代不明,成因类型及控矿因素争议较大。本文测定的该矿床那雍枝矿段闪锌矿的Rb-Sr等时线年龄,为458. 2±2. 9Ma (MSWD=1. 07,n=5),初始~(87)Sr/~(86)Sr=0. 713823±0. 000010,表明矿床的成矿时代为中奥陶世晚期至晚奥陶世早期,晚于赋矿地层沉积时代。结合矿床地球化学及矿床地质特征,认为五指山铅锌矿床为典型的后生矿床,成因类型属密西西比河谷型(MVT)铅锌矿床。五指山铅锌矿床的形成与加里东构造运动紧密相关,与黔中隆起构造事件对应。基底断层构造及破碎带是成矿作用的内在控制因素,而加里东期华夏地块与扬子陆块之间的碰撞造山运动,即都匀运动及广西运动是五指山特大型铅锌矿床成矿作用的外因。  相似文献   

Jurassic sediments in the Irkut basin and southwestern Transbaikalia: correlations based on paleobotanical and geochronological data     

A.V. Arzhannikova  A.O. Frolov  S.G. Arzhannikov  E.I. Demonterova  A.V. Ivanov  M. Jolivet  M.N. Rubtsova  A.L. Dorozhko 《Russian Geology and Geophysics》2018,59(6):620-634

The Jurassic growth of mountain ranges along the southern edge of the Siberian platform occurred in an active tectonic setting related to the closure of the Mongol-Okhotsk Ocean. The oceanic subduction and subsequent continent collision events induced compressive deformations at the platform boundary. Understanding the paleogeography related to the Mesozoic closure of the Mongol-Okhotsk Ocean requires dating and correlation of the Jurassic Prisayan Formation in the Irkut basin and Tugnuyskaya Formation in southwestern Transbaikalia. This work presents structural and paleobotanic results within both formations. ⁴⁰Ar/³⁹Ar dating of underlying volcanics from the upper member of the Ichetuyskaya Formation is used to refine the age of the sediment series and provide probable correlation. The results show that the Tugnuyskaya Formation initiated at the end of the Middle Jurassic-beginning of the Late Jurassic and was not coeval with the Prisayan Formation, whose upper fine-grained members were deposited in the early Middle Jurassic. ⁴⁰Ar/³⁹Ar dating of volcanics from the upper member of the Ichetuyskaya Formation yielded a Middle Jurassic age of 167.7 ± 1.2 Ma (Bajocian to Bathonian). The paleogeographic data analysis based on facies and mineralogical composition of sediments and on a study of source areas from Sm-Nd data and the U-Pb ages of detrital zircons from the deposits in the southern Irkut basin indicates that the deposition of the Prisayan Formation was followed by the intensification of relief building along the southern edge of the Siberian Platform. Our geochronological data show that active tectonic deformations in southwestern Transbaikalia evidenced in the volcanoclastic Ichetuyskaya Formation in the Tugnuy basin also occurred during the Middle Jurassic. The uppermost sediments of the Tugnuy basin were deposited at the end of the Middle Jurassic-Late Jurassic in a quiet tectonic setting with low relief and lacustrine-boggy depositional environments.  相似文献   

Provenance of detrital zircon from siliciclastic rocks of the Sebkha Gezmayet unit of the Adrar Souttouf Massif (Moroccan Sahara) – Palaeogeographic implications     

《Comptes Rendus Geoscience》2018,350(6):255-266

The Oued Togba and Sebkha Gezmayet units of the Adrar Souttouf Massif in the southern Moroccan Sahara are thought to represent tectonic fragments that may have an affinity to the Avalonian and Meguma terranes of eastern North America. Here we study siliciclastic rocks of the Sebkha Gezmayet unit with respect to their detrital zircon spectra. Beside the commonly used U–Th–Pb ages, several aspects of zircon morphology (length, width, roundness, surficial indicators of sedimentary transport, morphotype) are described. The detrital zircon age spectrum of the Sebkha Gezmayet unit resembles that of the already dated underlying igneous rocks. Occurrences of Early Devonian zircon ages are at odds with the magmatic history of the West African Craton but are common in the Avalonian and Meguma terranes, which were affected by the Appalachian orogenies. The scarcity of Mesoproterozoic detrital zircon grains corroborates the previously suggested Meguma terrane affinity of this part of the Adrar Souttouf Massif. Combining zircon morphology and isotopic data, we propose first assumptions on the sedimentary environments of the Sebkha Gezmayet unit during different periods of the Palaeozoic.  相似文献   

The Diamantina Monazite: A New Low‐Th Reference Material for Microanalysis          下载免费PDF全文

Guilherme O. Gonçalves  Cristiano Lana  Ricardo Scholz  Ian S. Buick  Axel Gerdes  Sandra L. Kamo  Fernando Corfu  Daniela Rubatto  Michael Wiedenbeck  Hermínio A. Nalini Jr.  Luiz Carlos A. Oliveira 《Geostandards and Geoanalytical Research》2018,42(1):25-47

Most monazite reference materials (RMs) for in situ U‐Pb geochronology are rich in Th; however, many hydrothermal ore deposits contain monazite that is low in trace element contents, including Th, U and Pb. Because of potential problems with matrix effects and the lack of appropriate matrix‐matched RMs, such variations can bias dating of hydrothermal deposits. In this paper, we describe a polycrystalline low‐U and low‐Th Diamantina monazite from the Espinhaço Range, SE Brazil. It has a U‐Pb ID‐TIMS weighted mean ²⁰⁷Pb^*/²³⁵U ratio of 0.62913 ± 0.00079, ²⁰⁶Pb^*/²³⁸U of 0.079861 ± 0.000088 and ²⁰⁷Pb^*/²⁰⁶Pb^* of 0.057130 ± 0.000031, yielding a weighted mean ²⁰⁶Pb^*/²³⁸U date of 495.26 ± 0.54 Ma (95% c.l.). In situ dates acquired with different methods (LA‐(Q, SF, MC)‐ICP‐MS and SIMS) are within uncertainty of the ID‐TIMS data. U‐Pb LA‐(Q, MC)‐ICP‐MS runs, using Diamantina as a primary RM, reproduced the ages of other established RMs within < 1% deviation. The LA‐MC‐ICP‐MS analyses yielded homogeneous Sm‐Nd isotopic compositions (¹⁴³Nd/¹⁴⁴Nd = 0.511427 ± 23, 2s; ¹⁴⁷Sm/¹⁴⁴Nd = 0.1177 ± 13, 2s) and εNd_(495 Ma) of ?18.7 ± 0.5 (2s). SIMS oxygen isotope determinations showed measurement reproducibility better than ± 0.3‰ (2s), confirming Diamantina's relative homogeneity at test portion masses below 1 ng.  相似文献   

内蒙古西乌旗格尔楚鲁晚三叠世流纹岩年代学、地球化学特征及其地质意义   总被引：1，自引：0，他引：1  

李红英  周志广  张达  李鹏举  柳长峰  陈利贞  陈诚  谷丛楠 《矿物岩石地球化学通报》2015,(3)

为确定西乌旗格尔楚鲁地区的一套浅色流纹岩的形成时代及其成岩构造环境,进而为探讨古亚洲洋闭合时间提供新的证据,本文对其开展了锆石U-Pb年代学、岩石学和地球化学研究。结果表明,流纹岩形成于221±1Ma;岩石富硅碱、贫钙镁、高Ga/Al值,A/CNK1;轻、重稀土元素分馏不明显,具有显著的Eu负异常;强烈亏损Sr、P、Ti,富集Zr,具有A2型花岗岩的特征,其成因可能是造山后伸展环境下幔源岩浆的底侵和地壳减薄,暗示研究区在三叠纪已经处于伸展背景,古亚洲洋在三叠纪之前已经闭合。研究区三叠纪伸展背景之下的岩浆活动始于早三叠世并一直持续到晚三叠世。  相似文献   

Zircon U–Pb,Molybdenite Re–Os and K‐feldspar 40Ar/39Ar Dating of the Bolong Porphyry Cu–Au Deposit,Tibet, China          下载免费PDF全文

Xiangping Zhu  Guangming Li  Huaan Chen  Dongfang Ma  Hanxiao Huang 《Resource Geology》2015,65(2):122-135

The Bolong porphyry Cu–Au deposit is a newly discovered deposit in the central Tibetan Plateau, and is ranked as the second largest copper deposit discovered to date in the Bangong‐Nujiang metallogenic belt in China. Three granodiorite porphyry phases occur within the Bolong porphyry Cu–Au deposit. Phyllic alteration is widespread on the surface of the deposit, and potassic alteration occurs at depth, associated with granodiorite porphyries. The copper and gold mineralization is clearly related to the potassic and phyllic alteration. Multiple chronometers were applied to constrain the timing of magmatic–hydrothermal activity at the Bolong deposit. Zircon U–Pb geochronology reveals that the granodiorite porphyry phases were emplaced at ca. 120 Ma. Re–Os data of four molybdenite samples from quartz–molybednite veinlets yielded an isochron age of 119.4 ± 1.3 Ma. The plateau age of hydrothermal K‐feldspar from the potassic alteration zone, analyzed by ⁴⁰Ar/³⁹Ar dating, is 118.3 ± 0.6 Ma, with a similar reverse isochron age of 118.5 ± 0.7 Ma. Therefore, the magmatic–hydrothermal activity occurred at ca. 120–118 Ma, which is similar in age to the neighboring Duobuza porphyry copper deposit. The period of 120–118 Ma is therefore important for the development of porphyry Cu–Au mineralization in the central Tibetan Plateau, and these porphyry deposits were formed during the final stages of the northward subduction of the Neo‐Tethys Ocean.  相似文献   

Stable Isotopic Geochemical and Geochronological Constraints on the Formation of the Shihu Gold Deposit: The Intracontinental Metallogeny of the Taihang Tectonic Belt,Eastern China          下载免费PDF全文

Shuzhi Wang  Jianzhong Hu  Yang Song  Xiao Cai  Tao Wang 《Resource Geology》2015,65(3):249-265

The Early Cretaceous Shihu gold deposit is located in the northern segment of the Taihang Tectonic belt, which extends across the central part of the North China Craton. The deposit is hosted predominantly by the Archean metamorphic crystalline units, and is spatially and temporally related to quartz diorite porphyry present extensively throughout the gold deposit. We studied the geology, geochronology and stable isotopic geochemistry. Zircon U–Pb LA–ICP–MS ages of the quartz diorite porphyry at deposit range from 134 ± 1 to 131 ± 2 Ma, which are coeval and probably genetically related to the mineralization. The majority of the sulfides of the gold deposit have δ³⁴S values ranging from ?1 to 2‰, which suggest an homogeneous magmatic source. In addition, the isotopic compositions of δ¹⁸O_fluid and δ¹⁸D_fluid vary from 2.1 to 7.0‰ and ?93 to ?65‰, respectively, suggesting that the magmatic fluids mingled with meteoric water. The Pb isotopic analyses reveal that both the ore‐forming materials and the quartz diorite porphyry originated from the lower crust and may have been mixed with mantle material. The ⁸⁷Sr/⁸⁶Sr_i and ¹⁴³Nd/¹⁴⁴Nd (¹⁴³Nd/¹⁴⁴Nd)_i ratios for the quartz diorite porphyry demonstrate that there was mixing of two end‐member (crust and the mantle) isotopic compositions. These results suggest that the ore‐forming fluids and materials were derived from lower‐crustal melting induced by mantle processes. Processes associated with the formation of the Shihu gold deposit differ significantly from those that characterize orogenic gold deposits, and instead are representative of formation in an intracontinental tectonic environment.  相似文献   

大兴安岭北段小柯勒河花岗斑岩脉成因及地质意义:锆石U-Pb年龄、岩石地球化学及Hf同位素制约     

宫昀迪  李碧乐  李治华  于润涛  孙永刚  张森 《吉林大学学报(地球科学版)》2021,51(6):1753-1769

为了探讨大兴安岭北段小柯勒河花岗斑岩脉的岩石成因、构造背景及地质意义,本文对其进行了锆石U-Pb年代学、岩石地球化学与Hf同位素的研究。岩石地球化学结果显示：花岗斑岩富硅（w（SiO₂）为69.85%~70.48%）、富碱（w（Na₂O+K₂O）为9.74%~9.89%）,贫镁（w（MgO）为0.34%~0.40%）、贫钙（w（CaO）为1.04%~1.20%）,A/CNK为0.98~1.02,属于准铝质-弱过铝质系列岩石;具有轻稀土元素富集和重稀土元素亏损的特征,中等Eu负异常,富集大离子亲石元素Rb、K和高场强元素Th、U、Hf、Zr,亏损大离子亲石元素Sr、Ba和高场强元素Nb、Ta、Ti、P。花岗斑岩中的10⁴Ga/Al值为2.32~3.68,分异指数I_D为87.63~89.01。综合分析认为小柯勒河花岗斑岩属于分异的I型花岗岩。花岗斑岩锆石U-Pb加权平均年龄为（124.0±0.6）Ma,属于早白垩世晚期。锆石ε_Hf（t）值为0.5~3.3,二阶段Hf同位素模式年龄T_DM2为1 150~970 Ma。结合岩石地球化学特征分析认为花岗斑岩源岩为由亏损地幔衍生的中-新元古代新增生地壳部分熔融的产物,并有少量古老地壳物质的加入。该花岗斑岩形成于早白垩世晚期蒙古-鄂霍茨克洋闭合背景下的伸展环境,此时太平洋板块持续向欧亚大陆俯冲,但对本区影响有限。  相似文献