柴达木地块北缘全吉地块钾长石浅粒岩碎屑 锆石LA-ICP-MS U-Pb定年 ——对达肯大坂岩群时代的约束   总被引：3，自引：1，他引：2  

黄婉  张璐  巴金  廖梵汐  陈能松 《地质通报》2011,30(9):1353-1359

为查明全吉地块基底中达肯大坂岩群的最大沉积年龄,用LA-ICP-MS技术测定了钾长石浅粒岩中的锆石U-Pb年龄。CL图像和Th/U比值指示这些锆石均为岩浆成因的锆石。36个测点207Pb/206Pb年龄变化范围为2094~2280Ma,其中年龄谐和度高于90%的30个测点的207Pb/206Pb年龄相对概率密度曲线呈单峰分布特征,峰值年龄为2190Ma左右。结合全吉地块最早一期变质事件的年龄,钾长石浅粒岩原岩碎屑和所在的达肯大坂岩群的沉积年龄范围被约束在1.95~2.19Ga之间。本研究表明,前人在侵入于达肯大坂岩群的伟晶岩脉中获得的约2.42Ga年龄的锆石应捕获于围岩,属于继承性岩浆碎屑成因,该类锆石年龄不能用来约束达肯大坂岩群原岩的最小沉积年龄。  相似文献   

中亚造山带东段铀、钼矿床分布与中间地块的关系     

邵济安  张履桥  牟保磊 《吉林大学学报(地球科学版)》2011,41(6):1667-1675

在近年来中亚造山带东段多金属矿床研究取得新进展的基础上,选择铀、钼两类矿床,结合铀、钼元素的地球化学行为探讨成矿物质来源的多样性和成矿的多阶段演化。此外,从构造研究角度,结合中亚造山带东段中大量中间地块存在的构造现象,讨论中间地块与成矿作用的关系:中间地块经历了从大陆边缘的裂解、漂移和板块碰撞造山作用,在漫长而复杂的地质过程中遭受的多次改造,有利成矿物质的反复被萃取和聚集。最后提出印支期华北克拉通北缘和北部造山带的成矿作用与底侵背景下的伸展作用密切相关。  相似文献   

Late Variscan “Basin and Range” magmatism and tectonics in the Central Alps: evidence from U-Pb geochronology     

Urs Schaltegger  Fernando Corfu 《Geodinamica Acta》2013,26(2):82-98

Abstract

Towards the end of the Variscan orogeny, volcano-sedimentary basins were formed within the mountain hell. U-Pb age determinations on zircons of volcanic and plutonic rocks from intramontane basins of the Central Alps allows us to define the age of two volcano-sedimentary units: The former one was dated older than 333 Ma (probably Visean), the younger one was deposited in a short time span between 303 and 298 Ma (Stephanien). The latter contains tuffs (303 ± 4 Ma), ignimbrites and microgranites (299 ± 2 Ma) and intrusive rhyolites (300 ± 2 Ma) that are all coeval within analytical precision. Granitoid rocks intruded into the volcano-sedimentary rocks at 333 ± 2 Ma, 310 ± 3 Ma and 298 ± 2 Ma. An angular unconformity between the older and the younger units in the Tö di area (Aar massif) indicates uplift and erosion between 310 and 303 Ma.

Our results suggest the existence of two periods of late Variscan extension (or transtension) in the Alpine realm, both combined with magmatic activity. The extensional event of Stephaniun age is characterized by a short duration of only a few million years, between 303 and 298 Ma, comprising tectonic activity, volcanism and plutonism. The plutonic rocks are characterized by a dominant lithospheric mantle component, which was contaminated by different amounts of crostai material and might have been increasingly influenced by aslhcnos-pherie mantle melts in the course of crostai thinning. The ealc-alkaline geochemical characteristics of the granites may be explained as an inherited source feature.

The overall tectonic style and the mode of magmatism resembles the situation of the Basin-and-Kange Province (eastern USA). Consequently there is no need to invoke a late-Variscan Andean-type subduction to explain the geochemical composition of the magmatic rocks. We conclude that late-orogenic extension is an important tectonic stage of the Variscan orogeny, which lasted for some 50 million years. The extension led to thinning of the crust and upwelling of hot mantle, causing high heat flow, intrusion of mantle melts and formation of huge volumes of acid melts.  相似文献   

两广交界地区壶垌片麻状复式岩体的年代学和地球化学：对云开地块北缘早古生代构造-岩浆作用的启示   总被引：5，自引：2，他引：3  

覃小锋  王宗起  胡贵昂  曹洁  冯佐海 《岩石学报》2013,29(9):3115-3130

本文对两广交界地区发育的壶垌片麻状复式岩体进行了LA-ICP-MS锆石U-Pb定年和岩石学、地球化学、Sr-Nd-Pb同位素的分析研究。该复式岩体主要由片麻状英云闪长岩、片麻状花岗闪长岩和片麻状二长花岗岩组成,获得片麻状花岗闪长岩LA-ICP-MS锆石U-Pb谐和年龄为443.1±2.0Ma。其中片麻状英云闪长岩和片麻状花岗闪长岩总体具有较低硅(SiO2=62.92%~67.54%)、较低碱(K2O+Na2O=3.98%~5.17%)、准铝质(A/CNK=0.83~0.93)的化学组成特征,属于中钾含角闪石钙碱性花岗岩类(ACG);而片麻状二长花岗岩具有高硅(SiO2=71.55%~72.78%)、高碱(K2O+Na2O=6.65%~7.57%)、准铝-弱过铝质(A/CNK=0.92~1.05)的化学组成特征,属于高钾钙碱性花岗岩类(KCG)。岩石表现出富集大离子亲石元素(如U、Ba、Rb和Th)和轻稀土元素,而Nb、Ta和Ti等高场强元素和重稀土元素明显亏损,并具有较高的锶同位素初始比值((87Sr/86Sr)i=0.71268~0.71482)和较低的εNd(t)值(-9.4~-2.6),反映其具有俯冲消减作用形成的岛弧岩浆岩地球化学特征。结合区域地质特征分析认为,壶垌片麻状复式岩体很可能是在扬子板块和华夏板块之间的洋壳岩石圈向南俯冲的地球动力学背景下,引发软流圈地幔上涌,其所带来的热能诱发了岩石圈地幔和上覆云开地块的古老地壳物质重熔,形成以壳源为主的壳幔混源母岩浆,再经历不同程度分离结晶作用,从而形成了本区大陆边缘弧型岩浆岩。因此,壶垌片麻状复式岩体是云开地块北缘早古生代洋陆俯冲-碰撞的地质记录。  相似文献   

Origin of the Dongbo Peridotite Massif from the Western Part of the Yarlung Zangbo Suture Zone, Tibet: Evidence from Petrological and Os Isotopic Geochemical Data     

NIU Xiaolu  YANG Jingsui  XU Jifeng  LI Jie  CHEN Songyong  FENG Guangying  LIU Fei  XIONG Fahui  LIU Zhao 《《地质学报》英文版》2013,87(Z1):192-193

  相似文献   

东北亚跃进山拼贴带及邻域岩石圈结构特征的地电学证据   总被引：7，自引：5，他引：2       下载免费PDF全文

刘财  张兴洲  刘洋  杨宝俊  冯晅  王典  刘殿秘 《地球物理学报》2009,52(4):958-965

为进一步查清东北亚完达山地体与两侧的佳木斯地块、兴凯地块间接触关系以及对跃进山拼贴带域沉积盆地油气条件的控制作用,布设5条MT剖面,计长1104 km.结果显示:(1)研究区地电学结构主要特征为佳木斯地块从中部向南北两方向,这一稳定地块的“高阻核”减薄,兴凯地块的高阻块体自东而西逐渐加深增厚,完达山地体在南部具有较多的高阻块体,向北渐少.(2)完达山地体西南端呈一“牛角”形状范围把佳木斯地块和兴凯地块分开;与原认识的完达山地体、佳木斯地块在同江-宝清-当壁一带贴合的位置相比,从宝清开始向南移至麻山-桦林一带.(3)完达山地体构造成因包括两部分,一是俯冲引起的拼贴,二是软流圈物质的热上涌;佳木斯地块内所存在的“高阻核”边界可能是该地块东界.(4)4个沉积盆地除勃利盆地外,另外3个盆地的基底间或存在规模不大的高阻块,大多范围分布着高导带,对盆地的成烃环境是有利的.  相似文献   

Microstructural evolution and geologic significance of garnet pyriclasites in the Hoher-Bogen shear zone (Bohemian Massif, Germany)     

C. Bues  G. Zulauf 《International Journal of Earth Sciences》2000,88(4):803-813

Ductile extensional movements along the steeply inclined Hoher-Bogen shear zone caused the juxtaposition of Teplá-Barrandian amphibolites, granulites, and metaperidotites against Moldanubian mica schists and paragneisses. Garnet pyriclasites are well preserved within low-strain domains of this shear zone. Their degree of metamorphism is significantly higher than that of the surrounding rocks. Microstructural and mineral chemical data suggest in situ formation of the garnet pyriclasite by dehydration of pyroxene amphibolite at T>750–840°C and P<10–13 kbar including recrystallization-accommodated grain-size reduction of plagioclase and clinopyroxene, nucleation of garnet, and breakdown of amphibole into garnet+clinopyroxene+rutile. Subsequent decompression and retrograde extensional shearing led to the formation of mylonitic epidote amphibolite. The presence of lower crustal and mantle-derived slices within the Hoher-Bogen shear zone supports the view that (a) in Upper Devonian times the Teplá-Barrandian unit was thrust over Moldanubian rocks as a complete crustal unit, and (b) that during the subsequent Lower Carboniferous orogenic collapse, the garnet pyriclasite and metaperidotite were scraped off from the basal parts of the Teplá-Barrandian unit being dragged into the Hoher-Bogen shear zone due to dramatic and large-scale elevator-style movements. Received: 23 March 1999 / Accepted: 25 August 1999  相似文献   

扬子地块西南缘大面积低温成矿时代   总被引：41，自引：5，他引：36  

胡瑞忠  彭建堂  马东升  苏文超  施春华  毕献武  涂光炽 《矿床地质》2007,26(6):583-596

中国西南地区(川、滇、黔、桂、湘)发育有世界上很典型的低温成矿域,其面积之大(约90万km2)、包含的矿种之多(Au、Hg、Sb、As、P、Pb-Zn、U、Ni-Mo-PGE、重晶石、冰州石和分散元素等)、矿床组成和组合之复杂,在全球十分鲜见。扬子地块西南缘是中国西南大面积低温成矿域的重要组成部分。近年来,作者采用Rb-Sr、Sm-Nd、Ar-Ar等多种同位素定年方法,对扬子地块西南缘产出的磷矿、金矿、锑矿等低温矿床的成矿时代进行了较系统的研究。文章总结了这些研究成果,并结合前人的资料,初步拟定出该区存在三期大规模低温成矿作用,它们分别相当于晚元古代—早古生代(晚震旦世—早寒武世)、晚加里东期(晚志留世—早泥盆地)和燕山期(晚侏罗世—中白垩世)。该区的磷矿、重晶石矿和黑色页岩中的镍钼铂矿主要形成于晚元古代—早古生代,同位素年龄主要为585～540Ma;赋存于前寒武纪浅变质碎屑岩中的金-锑-钨矿床主要形成于晚加里东期,同位素年龄主要为435～380Ma;产于寒武系以后地层中的锑矿床主要是在中燕山期成矿,同位素年龄主要为160～140Ma;而该区的卡林型金矿和汞矿主要在燕山中晚期大规模成矿,同位素年龄主要为170～80Ma。  相似文献   

Phase equilibria modelling of retrograde amphibole and clinozoisite in mafic eclogite from the Tso Morari massif,northwest India: constraining the P–T–M(H2O) conditions of exhumation     

R. M. Palin  M. R. St‐Onge  D. J. Waters  M. P. Searle  B. Dyck 《Journal of Metamorphic Geology》2014,32(7):675-693

Phase equilibria modelling of post‐peak metamorphic mineral assemblages in (ultra)high‐P mafic eclogite from the Tso Morari massif, Ladakh Himalaya, northwest India, has provided new insights into the potential behaviour and source of metamorphic fluid during exhumation, and constrained the P–T conditions of hydration. A series of P–M(H₂O) pseudosections constructed in the Na₂O–CaO–K₂O–FeO–MgO–Al₂O₃–SiO₂–H₂O–TiO₂–O (NCKFMASHTO) system show that a number of petrographically distinct hydration episodes occurred during exhumation from peak P–T conditions (~640 °C, 27–28 kbar), resulting in the formation of abundant compositionally zoned amphibole and minor clinozoisite poikiloblasts at the expense of a peak assemblage dominated by garnet and omphacite. Initial hydration is interpreted to have occurred as a result of the destabilization of talc following isothermal decompression to ~23 kbar, which led to the formation of barroisite–winchite amphibole core domains. An episode of fluid infiltration from an external source at ~19 kbar, with or without syn‐decompressional cooling to ~560 °C, resulted in further barroisitic–winchitic amphibole growth, followed by the formation of clinozoisite poikiloblasts. Continued buoyancy‐driven exhumation to the base of the lower crust is constrained to have taken place with no additional fluid input. A final hydration event is characterized by the formation of magnesiohornblende rims on the barroisite–winchite cores, with the former interpreted to have formed during later prograde overprinting in the middle crust associated with the final stages of exhumation. Notably, the vast majority of externally sourced H₂O, comprising just over half of the current bulk rock fluid content, was added during this later hydration event. In a middle crustal setting, this is interpreted as the result of devolatilization reactions occurring in migmatitic host orthogneiss and/or metasedimentary units, or following the crystallization of partial melt.  相似文献   

The late-and post-Variscan tectonic evolution of the Western Border fault zone of the Bohemian massif (WBZ)     

A. Peterek  H. Rauche  B. Schröder  H.-J. Franzke  P. Bankwitz  E. Bankwitz 《International Journal of Earth Sciences》1997,86(1):191-202

 Paleostress analysis and evaluation of the stratigraphic unconformities reveal an extremely polyphase development of one of the most prominent fault zones of Central Europe, usually known as the Franconian Line (FL). Because the FL is just one fault zone, although it is the most important fault zone within a complex fault system, a more appropriate term is used herein: Western Border fault zone of the Bohemian massif (WBZ). The reconstruction of the paleostress history was carried out by analysing sequences of individual strain increments that belong to the same stratigraphic “units” (e.g., late-Variscan granites, Tertiary basalts). A succession of at least 15 paleostress directions and tectonic regimes have been determined since late-Variscan time. Received: 7 July 1996 / Accepted: 24 October 1996  相似文献