Late Quaternary glaciations in the Cogarbu valley,Bhutanese Himalaya   总被引：1，自引：0，他引：1  

Xu Peng  Yixin Chen  Gengnian Liu  Beibei Liu  Yingkui Li  Qing Liu  Yesong Han  Weilin Yang  Zhijiu Cui 《第四纪科学杂志》2019,34(1):40-50

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吉林延边红太平铜多金属矿床脉型矿化的成矿时代与构造背景     

侯鹤楠  任云生  陆思宇  郝宇杰  杨群 《岩石学报》2020,36(3):820-836

吉林延边红太平铜多金属矿床位于兴蒙造山带东段,区内发育产于晚古生代火山沉积岩系中的层状铜多金属矿体和受岩体及构造控制的脉状铅锌矿体。为了确定脉型铅锌矿化的成矿时代与构造背景,本文对与脉状铅锌矿体相关的英安岩开展了LA-ICP-MS锆石U-Pb定年及岩石地球化学研究,并对脉状铅锌矿体中金属硫化物开展了Rb-Sr同位素定年。结果表明,英安岩中28个锆石测点的~(206)Pb/~(238)U加权平均年龄为204.1±2.0Ma(MSWD=0.24),脉状铅锌矿石中4件金属硫化物的Rb-Sr等时线年龄为206.8±9.0Ma(MSWD=2.0),二者在误差范围内基本一致,表明红太平矿床脉型铅锌矿化的成矿时代为晚三叠世末期。英安岩的稀土元素配分模式呈明显的轻稀土元素(LREEs)富集,轻重稀土分馏明显[(La/Yb)N=7.59～8.28],存在弱的Eu异常(δEu=0.65～0.68);微量元素以富集大离子亲石元素(LILEs:Rb、Ba和K)和不相容元素(U、Th),亏损高场强元素(HFSEs:Nb、Ta、P和Ti)为特征,表明原始岩浆应为壳-幔混源;脉状铅锌矿体中4件金属硫化物初始Sr同位素比值(87Sr/86Sr)i为0.705954～0.707101(均值0.706390),表明脉型铅锌矿化与壳-幔混源的岩浆作用密切相关。根据Rb-(Yb+Ta)及La/Yb-Th/Yb图解判别结果,结合区域构造演化分析,认为红太平矿区英安岩及相关的脉型铅锌矿化形成于活动大陆边缘的构造环境,与晚三叠世-早侏罗世(T_3-J_1)古太平洋板块向欧亚板块的俯冲作用密切相关。  相似文献   

西准噶尔红山地区晚古生代赞岐岩锆石U Pb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  

马飞宙  陈宣华  徐盛林  马芬  韩乐乐  丁伟翠  王叶 《地质学报》2020,94(5):1462-1481

中亚造山带西部西准噶尔地区红山花岗岩体内部发育多期似岩墙状安山质暗色条带,LA-ICP-MS锆石U-Pb同位素定年和岩石化学与同位素分析表明,它们具有不同的形成年龄、相同的源区和相似的形成过程。其中,具有不规则状或环状形态的暗色条带,其锆石U-Pb年龄为319.1±2.9 Ma和313.3±2.4 Ma,远大于红山岩体花岗岩锆石结晶年龄(305～301Ma),可能是红山岩体侵位过程中所捕掳的围岩;具有线性展布特征的安山质暗色条带,其锆石U-Pb年龄为295±2Ma,形成于红山岩体侵位之后,构成伸展岩墙群。红山岩体中的安山质暗色条带和线状岩墙群具有相似的岩石化学组成,富SiO_2(56.48%～63.09%)、MgO(3.56%～6.31%),具有高的Mg#值(51.74～62.40)及Na_2O/K_2O值(1.34～3.43);球粒陨石标准化稀土元素(REE)配分模式呈明显的右倾型,富集轻稀土元素(LREE)和大离子亲石元素(LILE)Rb、K、Ba、U、Sr,亏损高场强元素(HFSE)Th、Nb、Ce、P和重稀土元素,具较弱的负铕异常;其同位素组成特征为(~(87 )Sr/~(86 )Sr)i=0.703295～0.703620,(~(143) Nd/~(144) Nd)i=0.512612～0.512618,εNd(t)=6.91～7.62,(~(206) Pb/~(204) Pb)t为17.6883～17.9876,(~(207) Pb/~(204) Pb)t为15.5313～15.5686,(~(208)Pb/~(204)Pb)t为37.4460～38.0581。它们具有与赞岐岩类似的地球化学特征,总体表现出与弧岩浆作用相关的地球化学特征,可能具有共同的物质来源,为准噶尔洋板片俯冲消减后同一地幔源区在不同阶段的产物。其中,形成于弧岩浆作用时期的赞岐岩(319～313 Ma),构成与岛弧花岗岩类伴生的环状似岩墙状安山质暗色条带;形成于后造山伸展岩浆作用晚期的赞岐岩(～295Ma),构成与达拉布特左行走滑作用相关的陆内伸展岩墙群。安山质暗色条带(岛弧火山作用)、红山岩体(后造山伸展)和线状岩墙群(陆内伸展)记录了西准噶尔红山地区洋陆转换的全过程。  相似文献   

冈底斯中段厅宫地区比马组碎屑锆石U-Pb年龄     

周鹏  荣峰  多吉卫色  李强  唐华  范源 《沉积与特提斯地质》2020,40(2):141-150

桑日群广泛分布于冈底斯火山岩浆弧的中东段，是新特提斯洋俯冲作用的代表性记录。本文对冈底斯中段厅宫地区桑日群比马组开展了碎屑锆石U-Pb同位素测年和地球化学特征研究，结果表明：比马组所含的碎屑锆石具有85.7~143.5Ma、160.2~191.2Ma、334.4~364.1Ma和904Ma四个年龄段，其中最年轻的碎屑锆石年龄为85.7±1.9Ma，结合古生物资料，认为比马组形成于早—晚白垩世，其物源主要来自于拉萨地块，尤其是冈底斯岩基剥蚀源区；岩石地球化学特征显示，比马组沉积主要来源于长英质岩石，是上地壳源区物质经风化剥蚀后搬运沉积形成。  相似文献   

晚第四纪MIS6以来柴达木盆地成盐作用对冰期气候的响应   总被引：2，自引：0，他引：2  

陈安东  郑绵平  宋高  王学锋  李洪普  韩光  袁文虎 《地质论评》2020,66(3):611-624

气候是控制柴达木盆地盐类沉积的主要因素之一,但是其作用机制尚待明确。作者以柴达木盆地察汗斯拉图盐湖的3个含盐剖面为研究对象,采用多接收电感耦合等离子质谱(MC-ICP-MS)铀系测年测定其沉积时代,并通过X射线粉晶衍射(XRD)分析测定其盐类矿物种类。铀系测年显示D18剖面石盐和芒硝层的沉积时代为13.1±2.0 ka BP～15.9±2.5 ka BP,其中芒硝沉积年代属于末次冰期MIS2晚期;MXK2剖面芒硝层的沉积时代分别为131.7±39.5 ka BP和158.3±10.8 ka BP,D12剖面芒硝层的沉积时代分别为166.6±20.2 ka BP和198.0±20.6 ka BP,可以对应于倒数第二次冰期MIS6。XRD分析确定了3个剖面的盐类矿物主要为芒硝、石盐和石膏。综合多个盐湖晚第四纪成盐数据,本文认为倒数第二次冰期MIS6和末次冰期MIS2是柴达木盆地晚第四纪重要的成盐期,冰期的冷干气候有利于石盐和芒硝等盐类沉积。柴达木盆地"冰期成盐"的根本原因,是由于冰期环境下盆地周边山体冰川规模的扩张以及干冷的冰期气候,共同造成了盐湖补给水量的减少。此外,晚第四纪MIS6和MIS2的冰期降温也是导致盆地中冷相盐类沉积的直接原因。  相似文献   

Fluvial dynamics and 14C-10Be disequilibrium on the Bolivian Altiplano     

Kristina Hippe  Tiemen Gordijn  Vincenzo Picotti  Irka Hajdas  John D. Jansen  Marcus Christl  Christof Vockenhuber  Colin Maden  Naki Akçar  Susan Ivy-Ochs 《地球表面变化过程与地形》2019,44(3):766-780

Determining sediment transfer times is key to understanding source-to-sink dynamics and the transmission of environmental signals through the fluvial system. Previous work on the Bolivian Altiplano applied the in situ cosmogenic ¹⁴C-¹⁰Be-chronometer to river sands and proposed sediment storage times of ~10–20 kyr in four catchments southeast of Lake Titicaca. However, the fidelity of those results hinges upon isotopic steady-state within sediment supplied from the source area. With the aim of independently quantifying sediment storage times and testing the ¹⁴C-¹⁰Be steady-state assumption, we dated sediment storage units within one of the previously investigated catchments using radiocarbon dating, cosmogenic ¹⁰Be-²⁶Al isochron burial dating, and ¹⁰Be-²⁶Al depth-profile dating. Palaeosurfaces appear to preserve remnants of a former fluvial system, which has undergone drainage reversal, reduction in catchment area, and local isostatic uplift since ~2.8 Ma. From alluvium mantling the palaeosurfaces we gained a deposition age of ~580 ka, while lower down fluvial terraces yielded ≤34 ka, and floodplains ~3–1 ka. Owing to restricted channel connectivity with the terraces and palaeosurfaces, the main source of channel sediment is via reworking of the late Holocene floodplain. Yet modelling a set of feasible scenarios reveals that floodplain storage and burial depth are incompatible with the ¹⁴C-¹⁰Be disequilibrium measured in the channel. Instead we propose that the ¹⁴C-¹⁰Be offset results from: (i) non-uniform erosion whereby deep gullies supply hillslope-derived debris; and/or (ii) holocene landscape transience associated with climate or human impact. The reliability of the ¹⁴C-¹⁰Be chronometer vitally depends upon careful evaluation of sources of isotopic disequilibrium in a wide range of depositional and erosional landforms in the landscape. © 2018 John Wiley & Sons, Ltd.  相似文献   

大兴安岭北段索图罕地区碱长花岗岩成因及形成构造背景     

杨小鹏  王长兵  李文庆 《吉林大学学报(地球科学版)》2019,49(5):1338-1349

本文对大兴安岭北段索图罕地区碱长花岗岩进行了系统的全岩地球化学、锆石U-Pb同位素年代学的研究，并探讨了其成因和构造意义。LA-ICP-MS锆石U-Pb定年结果表明，花岗岩形成于早白垩世，年龄为（139.50±0.56）Ma。岩石地球化学结果显示，索图罕林场碱长花岗岩属于高钾钙碱性的A型花岗岩，岩石具有富硅和碱、贫CaO和MgO的特征，岩石稀土元素质量分数较高，相对富集轻稀土元素，具有明显的负Eu异常，富集Rb、Th、U、K等大离子亲石元素，亏损Nb、P、Ti等高场强元素，稀土元素配分图解具有右斜"V"字形的特征。索图罕林场碱长花岗岩为弱过铝质A型花岗岩，来源于地壳物质的部分熔融。样品微量元素构造判别图解落入后碰撞区域，代表伸展环境。结合区域地质特征，认为该碱长花岗岩的形成与蒙古-鄂霍茨克洋闭合后的岩石圈伸展相关。  相似文献   

内蒙古东乌旗葛根敖包石英闪长岩岩体年代学、地球化学及其地质意义     

向安平  陈毓川  佘宏全  李光明  李应栩 《地质通报》2019,38(9):1469-1483

内蒙古东乌旗地区新近发现的葛根敖包铅锌矿,成矿与赋矿岩体石英闪长岩关系密切,对石英闪长岩进行系统的LAICP-MS锆石U-Pb定年及锆石Hf同位素分析,并对石英闪长岩进行主量、微量和稀土元素分析。锆石U-Pb定年结果显示,石英闪长岩2个样品的锆石U-Pb年龄分别为299±1Ma和301±1Ma,均为晚石炭世。岩石主量、微量及稀土元素分析显示,石英闪长岩具有典型的富硅、富碱特征,Na_2O/K_2O值为1.14～1.93,平均1.39,明显富钠高钾,属高钾钙碱性系列;铝饱和指数A/CNK值为0.79～0.95,为准铝质或铝不饱和花岗岩类;轻、重稀土元素分馏显著,球粒陨石标准化稀土元素配分模式表现为明显的右倾,显示岩浆源区可能有石榴子石残留;并有微弱负Eu异常,δEu=0.80～0.91,δCe=0.89～0.96,均靠近1,指示源区无斜长石残留;同时具低Sr、高Yb特征;并指示高场强元素U、La、Nd、Zr相对富集,而Th、Nb、Sr、P、Ti相对亏损,且大离子亲石元素Rb、Ba、K相对富集,Nb/Ta值低,指示岩浆源区可能为幔源为主。锆石Hf同位素分析显示,εHf(t)值全部为正值,+10.8～+13.6(全部大于10,较高),TDM2介于440～629Ma之间,相对集中,明显大于其锆石U-Pb年龄,其年轻的TDM2年龄和较高的εHf(t)值表明,岩浆中有相当大的幔源物质的贡献。结合区域构造演化,认为葛根敖包石英闪长岩岩浆源区可能为亏损地幔物质部分熔融并在上升过程中受到少量壳源物质的混染,为活动陆缘弧环境的产物。  相似文献   

大兴安岭中部乌兰浩特地区林西组碎屑岩锆石U-Pb年龄、地球化学特征及其构造意义     

张海华  张健  黄欣  邱亮  苏飞  郑月娟  张德军 《地质通报》2019,38(9):1484-1500

内蒙古乌兰浩特地区出露一套缺少化石、遭受接触变质作用的厚层碎屑岩。在该套地层采集碎屑锆石样品,进行碎屑锆石U-Pb测年研究。80个锆石分析点的年龄可分为3个主要年龄区间:242～294Ma,年龄加权平均值为263.6±3.3Ma(n=50,MSWD=4.9),峰值年龄为261Ma;301～381Ma,峰值年龄为348Ma;454～530Ma,峰值年龄为487Ma。另有7个锆石分析点的年龄分别为824Ma、836Ma、859Ma、867Ma、1279Ma、1556Ma、2447Ma。261Ma的峰值年龄限定了该地层的沉积下限,即属晚二叠世林西组。主量元素SiO2含量为67.81%,Al_2O_3为18.22%,MgO为1.44%,CaO为0.41%,Na_2O为1.54%,K_2O为3.90%,K_2O/Na_2O为1.15～10.21;A_(12)O_3/(CaO+Na_2O)为4.87～26.38;稀土元素总量介于162.39×10-6～223.46×10-6之间,平均值为200.88×10-6,负Eu异常,Ce为1.00～1.05,轻稀土元素富集,重稀土元素亏损,微量元素以亏损Nb、Ta、Sr,富集Rb、Ba、La、Ce、Pb、Nd、Sm为特征。以上分析表明,林西组形成于活动大陆边缘构造背景。依据碎屑锆石年龄谱值信息,林西组沉积物源具多样性和复杂性,除东北各地块,同时存在华北板块和西伯利亚板块的物源信息,说明林西组沉积时期华北板块与西伯利亚板块可能已经开始俯冲碰撞过程。  相似文献   

Mesozoic to Cenozoic retroarc basin evolution during changes in tectonic regime,southern Central Andes (31–33°S): Insights from zircon U-Pb geochronology     

《Journal of South American Earth Sciences》2019

The southern Central Andes of Argentina and Chile (27–40°S) are the product of deformation, arc magmatism, and basin evolution above a long-lived subduction system. With sufficient timing and provenance constraints, Andean stratigraphic and structural records enable delineation of Mesozoic-Cenozoic variations in subsidence and tectonic regime. For the La Ramada Basin in the High Andes at ∼31–33°S, new assessments of provenance and depositional age provided by detrital zircon U-Pb geochronology help resolve deformational patterns and subsidence mechanisms over the past ∼200 Myr. Marine and nonmarine clastic deposits recorded the unroofing of basin margins and sediment contributions from the Andean magmatic arc during Late Triassic to Early Cretaceous extension, thermal subsidence, and possible slab rollback. Subsequent sediment delivery from the Coastal Cordillera corresponded with initial flexural accommodation in the La Ramada Basin during Andean shortening of late Early Cretaceous to Late Cretaceous age. The architecture of the foreland basin was influenced by the distribution of precursor extensional depocenters, suggesting that inherited basin geometries provided important controls on later flexural subsidence and basin evolution. Following latest Cretaceous to early Paleogene tectonic quiescence and a depositional hiatus, newly dated deposits in the western La Ramada Basin provide evidence for a late Paleogene episode of intra-arc and proximal retroarc extension (development of the Abanico Basin, principally in Chile, at ∼28–44°S). Inversion of this late Paleogene extensional basin system during Neogene compression indicates the southern Central Andes were produced by at least two punctuated episodes of shortening and uplift of Late Cretaceous and Neogene age.  相似文献