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   

闽中南平—宁化构造带南华纪陆缘弧岩浆活动：对武夷造山带构造演化的新启示     

姜杨  赵希林  李龙明  潘桂棠  徐敏成  黄文成  刘欢 《中国地质》2020,47(4):1010-1024

南平—宁化构造带沿线出露着以万全岩群和楼前组、西溪组等为代表的一系列新元古代火山-沉积岩系。系统的岩石学、年代学和地球化学研究表明,福建明溪和江西瑞金地区的楼前组浅变质英安岩和晶屑凝灰岩分别形成于(729±4)Ma和(735±6.7)Ma(LA-ICP-MS锆石U-Pb法),SiO2含量变化在65.22%～74.54%,相对富Al2O3(11.05%～16.80%)富碱(Na2O+K2O=4.88%～10.19%)而贫CaO、MgO和FeOT,ANK值和A/CNK值分别为1.23～1.78和0.98～1.57,Nb/Ta=12.44～17.28,Nd/Th=2.07～3.51,Ti/Zr=6.08～10.37,Ti/Y=68.51～154.71,属过铝质S型火山岩;明显富集大离子亲石元素(Ba、Rb等)而亏损高场强元素(Nb、Ta、Ti、P等),Zr/Nb=16.65～24.07,Th/Ta=12.94～16.93,δEu呈现明显负异常(0.33～0.62),显示岛弧岩浆岩的地球化学特征。综合区域地质资料及前人研究结果提出,南平—宁化一线在713 Ma前为活动大陆边缘环境,洋壳俯冲引发的岩浆活动形成了沿南平—宁化—瑞金一线展布的陆缘弧中酸性火山岩带,暗示此时南、北武夷之间尚未拼合形成统一的武夷地块,因而华夏地块不存在统一的前南华纪结晶基底。  相似文献   

内蒙古狼山地区早二叠世花岗闪长岩的年代学、地球化学特征及其构造背景     

田健  滕学建  刘洋  滕飞  郭硕  何鹏  王文龙 《中国地质》2020,47(3):767-781

内蒙古狼山山脉西侧分布有大面积的晚古生代岩浆岩,其时代集中在早石炭世—晚二叠世,不同时代岩浆岩岩石组合对于认识狼山地区晚古生代构造背景具有重要的意义。文章通过岩石学、岩相学、地球化学及Hf同位素等方法,对狼山地区查干乃呼都格一带花岗闪长岩体进行了研究。该岩体岩性为花岗闪长岩,LA-ICP-MS锆石U-Pb年龄显示,其206Pb/238U加权平均年龄为(299±1)～(293±2) Ma。岩石暗色矿物为角闪石及黑云母,富含闪长质包体,P_2O_5含量与SiO_2含量之间显示良好的负相关性,富钠(Na_2O含量为3.45%～4.96%),高钠钾比值(Na_2O/K_2O比值为1.33～2.52),岩石地球化学特征显示花岗岩成因类型为Ⅰ型花岗岩。岩石具有负的ε_(Hf)(t)值(-6.3～-2.0)及T_(DM2)为1437～1704 Ma(平均值为1606 Ma),显示了古—中元古代古老地壳熔融的特点,ε_(Hf)(t)-t及角闪石成因图解显示源区有幔源岩浆参与。花岗岩富集大离子亲石元素Rb、K、Pb,不同程度的亏损高场强元素Nb、Ta、P、Ti,轻稀土富集,重稀土亏损,弱的负Eu异常,显示了岩浆弧的地球化学特征。结合晚石炭世—早二叠世狼山地区侵入岩岩石组合为闪长岩+石英闪长岩+花岗闪长岩(英云闪长岩),早—中二叠世大石寨组火山岩岩石组合为玄武岩+玄武安山岩+安山岩+英安岩,总体反映了陆缘弧的岩石组合;狼山地区早二叠世处于大陆边缘弧的构造背景,与华北地块北缘中东部可以对比。  相似文献   

Granulites record the tectonic evolution from collisional thickening to extensional thinning of the Tongbai orogen in central China     

Qiang-Qiang Zhang  Xiao-Ying Gao  Ren-Xu Chen  Yong-Fei Zheng 《Journal of Metamorphic Geology》2020,38(3):265-295

A combined study of petrology and geochemistry was carried out for granulites from the Tongbai orogen in central China. The results reveal the tectonic evolution from collisional thickening to extensional thinning of the lithosphere at the convergent plate boundary. Petrographic observations, zircon U–Pb dating, and pseudosection calculations indicate that the granulites underwent four metamorphic stages, which are categorized into two cycles. The first cycle occurred at 490–450 Ma and involves high-P (HP) metamorphism (M1) at 785–815°C and 10–14 kbar followed by decompressional heating to 840–880°C and 8–9 kbar for medium-pressure granulite facies metamorphism (M2), defining a clockwise P–T path. The high pressure is indicated by the occurrence of inclusions of rutile+kyanite+K-feldspar in the garnet mantle. The second cycle occurred at c. 440 Ma and shows an anticlockwise P–T path with continuous heating to ultrahigh-temperature (UHT) metamorphism (M3) at 890–980°C and 9–11 kbar, followed by decompressional cooling to 740–880°C and 7–9 kbar (M4) till 405 Ma. The HP metamorphism is synchronous with the ultrahigh-pressure eclogite facies metamorphism in the Qinling orogen, indicating its relevance to the continental collision in the Cambrian. The UHT metamorphism took place at reduced pressures, indicating thinning of the collision-thickened orogenic lithosphere. Therefore, the Tongbai orogen was initially thickened by the collisional orogeny and then thinned, possibly as a result of foundering of the orogenic root. Such tectonic evolution may be common in collisional orogens where compression during continental collision switched to extension during continental rifting.  相似文献   

小兴安岭-张广才岭铁力地区侏罗纪辉绿岩年代学、地球化学、锆石Hf同位素特征及其构造意义   总被引：1，自引：0，他引：1  

葛茂卉  张进江  刘恺 《岩石学报》2020,36(3):726-740

小兴安岭-张广才岭地区中生代岩浆活动的成因及动力学背景对于揭示古太平洋的构造演化具有重要意义。本文选取小兴安岭-张广才岭铁力地区出露的辉绿岩墙为研究对象,进行锆石LA-ICP-MS U-Pb年代学、全岩地球化学和锆石Hf同位素等分析,对该基性岩的形成时代、岩石成因、岩浆源区以及形成的大地构造背景进行讨论。研究表明:辉绿岩锆石具有高Th/U比值( 0.3),CL图像显示微弱的振荡环带结构,具有岩浆锆石特征,~(206)Pb/~(238)U加权平均年龄为187±2Ma,即形成于早侏罗世;该岩体主要经历了橄榄石和单斜辉石的分离结晶作用,未遭受明显的地壳混染作用,并且具有Rb、Ba、U、Pb、K和Sr等流体活动元素相对富集,Th、Nb和Ta等非流体活动性元素相对亏损的地球化学特征,暗示其形成于被俯冲流体富集交代的亏损地幔部分熔融,源区可能为尖晶石-石榴石二辉橄榄岩,部分熔融程度约为6%～20%。结合该地区同时代的岩浆岩、变形构造、矿床特征和黑龙江蓝片岩的相关报道,本文认为小兴安岭-张广才岭地区在中生代期间处于活动大陆边缘环境,其岩浆岩的形成主要是由于存在于佳木斯地块和松嫩-小兴安岭地块间的牡丹江洋西向俯冲造成的。  相似文献   

Seafloor Geomorphology and Processes on the Western Continental Margin of India based on Multibeam Acoustic Backscatter Data Analysis     

Sumanta Dandapath  Andrew Menezes  Bishwajit Chakraborty  John Kurian  Koppella N. Prudhvi Raju 《Marine Geodesy》2018,41(2):177-200

An assessment of the multibeam sonar data of the central Western Continental Margins of India has been carried out to evaluate the seafloor geomorphology and processes by examining the geomorphological attributes e.g., slope, sediments, structures, etc. associated with geomorphic features. The variation in relief and the features located in the region have been mapped and interpreted collectively by utilizing several geospatial mapping tools. The backscatter strength across the area, apparently congruent with the local relief, has helped to examine the sediment movement on the seafloor. The prominent features found in the region include faults, pockmarks, mounds, submarine terraces, and submerged fossil reefs. Several areas with varying topography engender comparable fractal dimension at short scale breaks, and the probability density functions (PDFs) utilizing backscatter data depicting overlapping classes. The present study highlights how fractals and scale break parameters can be utilized to determine the seafloor processes and associated sedimentological dynamics in a complex geographical environment with strong bottom currents, seasonal upwelling, and faulted structure. The role and impact of the various geomorphic processes on the reworking of sediment movement and the overall progression of the seafloor morphology has been revealed for the first time in this part of the ocean bottom.  相似文献   

Tectonometamorphic evolution of the Atbashi high‐P units (Kyrgyz CAOB,Tien Shan): Implications for the closure of the Turkestan Ocean and continental subduction–exhumation of the South Kazakh continental margin          下载免费PDF全文

Chloé Loury  Yann Rolland  Stéphane Guillot  Pierre Lanari  Clément Ganino  Raphael Melis  Anthony Jourdon  Carole Petit  Olivier Beyssac  Sylvain Gallet  Patrick Monié 《Journal of Metamorphic Geology》2018,36(8):959-985

The South Tien Shan (STS) belt results from the last collision event in the western Central Asian Orogenic Belt (CAOB). Understanding its formation is of prime importance in the general framework of the CAOB. The Atbashi Range preserves high‐P (HP) rocks along the STS suture, but still, its global metamorphic evolution remains poorly constrained. Several HP units have been identified: (a) a HP tectonic mélange including boudins of mafic eclogites in a sedimentary matrix, (b) a large (>100 km long) high‐P metasedimentary unit (HPMU) and (c) a lower blueschist facies accretionary prism. Raman Spectroscopy on carbonaceous material combined with phengite and chlorite multiequilibria and isochemical phase diagram modelling indicates that the HPMU recorded homogeneous P–T conditions of 23–25 kbar and 560–570°C along the whole unit. ⁴⁰Ar/³⁹Ar dating on phengite from the HPMU ranges between 328 and 319 Ma at regional scale. These ages are interpreted as (re‐) crystallization ages of phengite during T_max conditions at a pressure range of 20–25 kbar. Thermobarometry on samples from the HP tectonic mélange provides similar metamorphic peak conditions. Thermobarometry on the blueschist to lower greenschist facies accretionary prism indicates that it underwent P–T conditions of 5–6 kbar and 290–340°C, highlighting a 17–20 kbar pressure gap between the HPMU‐tectonic mélange units and the accretionary prism. Comparison with available geochronological data suggests a very short time span between the prograde path (340 Ma), HP metamorphic peak (330 Ma), the T_max (328–319 Ma) and the final exhumation of the HPMU (303–295 Ma). Extrusion of the HPMU, accommodated by a basal thrust and an upper detachment, was driven by buoyant forces from 70–75 km up to 60 km depth, which directly followed continental subduction and detachment of the HPMU. At crustal depths, extrusion was controlled by collisional tectonics up to shallow levels. Lithological homogeneity of the HPMU and its continental‐derived character from the North Tien Shan suggest this unit corresponds to the hyper‐extended continental margin of the Kazakh continent, subducted southward below the north continental active margin of the Tarim craton. Integration of the available geological data allows us to propose a general geodynamic scenario for Tien Shan during the Carboniferous with a combination of (a) N‐dipping subduction below the Kazakh margin of Middle Tien Shan until 390–340 Ma and (b) S‐dipping subduction of remaining Turkestan marginal basins between 340 and 320 Ma.  相似文献   

南海北部陆坡深水区浅层天然气藏特征     

钟广见  张如伟  易海  冯常茂  赵忠泉 《热带海洋学报》2018,37(3):80-85

南海北部陆坡深水区的浅层天然气藏是一种伴随天然气水合物的新型油气藏, 具有埋藏浅、规模大的特点, 其埋藏深度一般小于300m。浅层天然气藏由深部裂解气沿断裂上升被天然气水合物封盖而形成, 识别似海底反射(BSR)是寻找浅层天然气藏有效方法。浅层天然气藏的气源主要有热解气、生物气和混合气, 陆坡张性断裂是气体运移的主要通道, 水合物下部的砂层是浅层天然气藏的主要储集层, 水合物层则是封盖层。从南海发现的天然气水合物分布特征看, 浅层天然气藏在陆坡深水区广泛分布且气藏厚度大, 潜在资源量非常可观, 是一种新型的开采成本相对低廉的油气藏。  相似文献   

Quantitative elemental mapping of granulite-facies monazite: Textural insights and implications for petrochronology     

Owen M. Weller  Simon Jackson  William G. R. Miller  Marc R. St-Onge  Nicole Rayner 《Journal of Metamorphic Geology》2020,38(8):853-880

Texturally complex monazite grains contained in two granulite-facies pelitic migmatites from southern Baffin Island, Arctic Canada, were mapped by laser ablation-inductively coupled plasma-mass spectrometry (using spot sizes ≤5 µm) to quantitatively determine the spatial variation in trace element chemistry (with up to 1,883 analyses per grain). The maps highlight the chemical complexity of monazite grains that have experienced multiple episodes of growth, resorption and chemical modification by dissolution–precipitation during high-grade metamorphism. Following detailed chemical characterization of monazite compositional zones, a related U–Pb data set is re-interpreted, allowing petrologically significant ages to be extracted from a continuum of concordant data. Synthesis of these data with pseudosection modelling of prograde and peak conditions allows for the temporal evolution of monazite trace element chemistry to be placed in the context of the evolving P–T conditions and major phase assemblage. This approach enables a critical evaluation of three commonly used petrochronological indicators: linking Y to garnet abundance, the Eu anomaly to feldspar content and Th/U to anatectic processes. Europium anomalies and Th/U behave in a relatively systematic fashion, suggesting that they are reliable petrochronological witnesses. However, Y systematics are variable, both within domains interpreted to have grown in a single event, between grains interpreted to be part of the same age population, and between samples that experienced similar metamorphic conditions and mineral assemblages. These observations caution against generalized petrological interpretations on the basis of Y content, as it suggests Y concentrations in monazite are controlled by domainal equilibria. The results reveal a c. 45 Myr interval between prograde metamorphism and retrograde melt crystallization in the study area, emphasizing the long-lived nature of heat flow in high-grade metamorphic terranes. Such long timescales of metamorphism would be assisted by the growth, retention and dominance of high-Th suprasolidus monazite, as observed in this study, contributing to the radiogenic heating budget of mid- to lower-crustal environments. Careful characterization of monazite grains suggests that continuum-style U–Pb data sets can be decoded to provide insights into the duration of metamorphic processes.  相似文献   

准噶尔盆地西北缘及玛湖凹陷沉积储集层研究进展^*          下载免费PDF全文

张昌民  尹太举  唐勇  郭旭光  赵康  潘进  陈美玲 《古地理学报》2020,22(1):129-146

准噶尔盆地西北缘玛湖凹陷中心区10×10⁸ t级砾岩大油区的发现,带动了该区沉积储集层研究的不断深入。作者梳理了准噶尔盆地西北缘及玛湖凹陷的沉积储集层研究现状和进展,认为准噶尔盆地西北缘及玛湖凹陷的沉积储集层研究的进展主要表现为: (1)提出了新的砂砾岩储集层岩石相和岩石学分析方法;(2)探索形成了新的沉积储集层地球物理测井和地震描述技术;(3)针对不同层系,在沉积物源、沉积相、沉积环境、沉积体系和沉积模式等方面取得大量新认识,建立了大型退覆式浅水缓坡扇三角洲沉积模式,指导油气勘探不断获得新突破;(4)在成岩作用理论指导下,所发现的储集层埋藏深度不断增加。研究表明,玛湖凹陷的沉积体系具有继承性: 从二叠纪到新近纪,发育了火山—碎屑岩沉积体系、细粒—蒸发盐沉积体系以及粗粒冲积扇、扇三角洲、辫状河三角洲等沉积体系,气候、构造和湖平面变化控制了沉积体系的形成和演化。沉积储集层研究为玛湖砾岩大油田的发现提供了有力的理论支持。未来应当加强针对古老层系和深部地层的沉积储集层研究工作,重视新理论新技术在西北缘和玛湖沉积储集层研究中的应用,已经形成的理论技术需要在勘探实践中接受进一步检验和完善。  相似文献