如何判定俯冲增生杂岩中的高度肢解的洋底高原-海山系统          下载免费PDF全文

肖庆辉  刘勇  程杨  邱瑞照  范玉须  裴斐  杨斌 《沉积与特提斯地质》2021,41(2):152-162

巨型洋底高原或海山系统到达俯冲带发生俯冲以后会在俯冲过程中发生肢解,在增生杂岩带中形成面目全非的小型洋底高原-海山系统的断块或碎片,使得在增生杂岩带中识别古老洋底高原-海山系统变得十分困难。为此,本文提出了基于洋板块地层、岩石学和地球化学联合研究的新方法及其识别标志,重新审定增生杂岩中洋底高原或海山的成因。  相似文献   

东昆仑山中段布尔汗布达山地区断裂特征及昆中断裂带南界讨论     

周琳雄  尹建华  王勇  郑科  张国忠  邓志龙 《中国地质调查》2021,8(5):74-83

布尔汗布达山西南缘属东昆仑造山带腹地,新太古代以来区域构造作用强烈。中二叠世,随着东昆仑地区多岛洋盆依次关闭,研究区形成数条近于平行的EW向深大断裂组合,构成昆中断裂带主体格架。通过研究分析与断裂相关的地形地貌、遥感影像、地球物理、岩石地层、变形变质、断裂结构组成、显微构造等,总结出主要断裂特征,并梳理了区内构造格架,针对尚未统一认识的昆中断裂带南界问题进行探讨,最终认为温冷恩断裂属昆中断裂带南界断裂。研究成果为进一步开展相关地质问题分析提供了依据。  相似文献   

A new understanding of Demala Group complex in Chayu Area,southeastern Qinghai-Tibet Plateau: Evidence from zircon U-Pb and mica 40Ar/39Ar dating     

《China Geology》2021,4(1):77-94

The Chayu area is located at the southeastern margin of the Qinghai-Tibet Plateau. This region was considered to be in the southeastward extension of the Lhasa Block, bounded by Nujiang suture zone in the north and Yarlung Zangbo suture zone in the south. The Demala Group complex, a set of high-grade metamorphic gneisses widely distributed in the Chayu area, is known as the Precambrian metamorphic basement of the Lhasa Block in the area. According to field-based investigations and microstructure analysis, the Demala Group complex is considered to mainly consist of banded biotite plagiogneisses, biotite quartzofeldspathic gneiss, granitic gneiss, amphibolite, mica schist, and quartz schist, with many leucogranite veins. The zircon U-Pb ages of two granitic gneiss samples are 205 ± 1 Ma and 218 ± 1 Ma, respectively, representing the ages of their protoliths. The zircons from two biotite plagiogneisses samples show core-rim structures. The U-Pb ages of the cores are mainly 644 –446 Ma, 1213 –865 Ma, and 1780 –1400 Ma, reflecting the age characteristics of clastic zircons during sedimentation of the original rocks. The U-Pb ages of the rims are from 203 ± 2 Ma to 190 ± 1 Ma, which represent the age of metamorphism. The zircon U-Pb ages of one sample taken from the leucogranite veins that cut through granitic gneiss foliation range from 24 Ma to 22 Ma, interpreted as the age of the anatexis in the Demala Group complex. Biotite and muscovite separates were selected from the granitic gneiss, banded gneiss, and leucogranite veins for ⁴⁰Ar/³⁹Ar dating. The plateau ages of three muscovite samples are 16.56 ± 0.21 Ma, 16.90 ± 0.21 Ma, and 23.40 ± 0.31 Ma, and the plateau ages of four biotite samples are 16.70 ± 0.24 Ma, 16.14 ± 0.19 Ma, 15.88 ± 0.20 Ma, and 14.39 ± 0.20 Ma. The mica Ar-Ar ages can reveal the exhumation and cooling history of the Demala Group complex. Combined with the previous research results of the Demala Group complex, the authors refer that the Demala Group complex should be a set of metamorphic complex. The complex includes not only Precambrian basement metamorphic rock series, but also Paleozoic sedimentary rock and Mesozoic granitic rock. Based on the deformation characteristics, the authors concluded that two stages of the metamorphism and deformation can be revealed in the Demala Group complex since the Mesozoic, namely Late Triassic-Early Jurassic (203 –190 Ma) and Oligocene –Miocene (24 –14 Ma). The early stage of metamorphism (ranging from 203 –190 Ma) was related to the Late Triassic tectono-magmatism in the area. The anatexis and uplifting-exhumation of the later stage (24 –14 Ma) were related to the shearing of the Jiali strike-slip fault zone. The Miocene structures are response to the large-scale southeastward escape of crustal materials and block rotation in Southeast Tibet after India-Eurasia collision.©2021 China Geology Editorial Office.  相似文献   

Research achievements of the Qinghai-Tibet Plateau based on 60 years of aeromagnetic surveys     

《China Geology》2021,4(1):147-177

The Qinghai-Tibet Plateau (also referred to as the Plateau) has long received much attention from the community of geoscience due to its unique geographical location and rich mineral resources. This paper reviews the aeromagnetic surveys in the Plateau in the past 60 years and summarizes relevant research achievements, which mainly include the followings. (1) The boundaries between the Plateau and its surrounding regions have been clarified. In detail, its western boundary is restricted by West Kunlun-Altyn Tagh arc-shaped magnetic anomaly zone forming due to the arc-shaped connection of the Altyn Tagh and Kangxiwa faults and its eastern boundary consists of the boundaries among different magnetic fields along the Longnan (Wudu)-Kangding Fault. Meanwhile, the fault on the northern margin of the Northern Qilian Mountains serves as its northern boundary. (2) The Plateau is mainly composed of four orogens that were stitched together, namely East Kunlun-Qilian, Hoh-Xil-Songpan, Chamdo-Southwestern Sanjiang (Nujiang, Lancang, and Jinsha rivers in southeastern China), and Gangdese-Himalaya orogens. (3) The basement of the Plateau is dominated by weakly magnetic Proterozoic metamorphic rocks and lacks strongly magnetic Archean crystalline basement of stable continents such as the Tarim and Sichuan blocks. Therefore, it exhibits the characteristics of unstable orogenic basement. (4) The Yarlung-Zangbo suture zone forming due to continent-continent collisions since the Cenozoic shows double aeromagnetic anomaly zones. Therefore, it can be inferred that the Yarlung-Zangbo suture zone formed from the Indian Plate subducting towards and colliding with the Eurasian Plate twice. (5) A huge negative aeromagnetic anomaly in nearly SN trending has been discovered in the middle part of the Plateau, indicating a giant deep thermal-tectonic zone. (6) A dual-layer magnetic structure has been revealed in the Plateau. It consists of shallow magnetic anomaly zones in nearly EW and NW trending and deep magnetic anomaly zones in nearly SN trending. They overlap vertically and cross horizontally, showing the flyover-type geological structure of the Plateau. (7) A group of NW-trending faults occur in eastern Tibet, which is intersected rather than connected by the nearly EW trending that develop in middle-west Tibet. (8) As for the central uplift zone that occurs through the Qiangtang Basin, its metamorphic basement tends to gradually descend from west to east, showing the form of steps. The Qiangtang Basin is divided into the northern and southern part by the central uplift zone in it. The basement in the Qiangtang Basin is deep in the north and west and shallow in the south and west. The basement in the northern Qiangtang Basin is deep and relatively stable and thus is more favorable for the generation and preservation of oil and gas. Up to now, 19 favorable tectonic regions of oil and gas have been determined in the Qiangtang Basin. (9) A total of 21 prospecting areas of mineral resources have been delineated and thousands of ore-bearing (or mineralization) anomalies have been discovered. Additionally, the formation and uplift mechanism of the Plateau are briefly discussed in this paper.©2021 China Geology Editorial Office.  相似文献   

由非季风区向季风区过渡过程中大气边界层结构的变化分析   总被引：2，自引：0，他引：2  

乔梁  张强  岳平  金红梅 《大气科学》2019,43(2):251-265

利用中国西北中部具有代表性的非季风区、夏季风影响过渡区和季风区的7个高空站的2013年夏季晴天07时、13时、19时（北京时）的大气边界层资料,通过分析大气边界层位温、比湿、风速的垂直结构,发现大气边界层结构及厚度在不同区域的分布特征:稳定边界层厚度、残余层顶高度和对流边界层厚度从非季风区、夏季风影响过渡区至季风区出现阶梯性大幅降低,从非季风区至夏季风影响过渡区,以及从夏季风影响过渡区至季风区,对流边界层厚度降幅依次为25.6%和81.8%,稳定边界层厚度降幅依次为58.3%和41.8%;在稳定边界层条件下,可观察到低空急流的存在,非季风区低空急流出现高度明显高于夏季风影响过渡区和季风区,且非季风区的低空急流风速也明显大于夏季风影响过渡区和季风区。通过分析与大气边界层发展最为密切的陆面热力因素在不同气候区的分布,净辐射值、日地-气温差最大值以及感热通量值在非季风区大于夏季风影响过渡区和季风区,从陆面热力过程为非季风区大气边界层厚度大于夏季风影响过渡区和季风区提供了理论依据。  相似文献   

新特提斯缝合带中段豆荚状铬铁矿成矿规律对比研究     

洪俊  姚文光  张晶  张辉善  吕鹏瑞  杨博 《地质学报》2015,89(9):1618-1628

新特提斯缝合带中的铬铁矿带是全球最重要的豆荚状铬铁矿成矿带之一,尤其是新特提斯缝合带中段,即穆斯林巴赫-科希斯坦-雅鲁藏布江一带,自东向西发育罗布莎、马拉坎德、穆斯林巴赫等若干大型铬铁矿床。本文系统总结和梳理新特提斯缝合带中段蛇绿岩的时空分布特征以及典型豆荚状铬铁矿的矿床特征、赋存规律和控矿因素。研究表明,蛇绿岩形成时代主体为中侏罗世—晚白垩世,自东向西大致呈逐渐变新的趋势,构造侵位的时代相近,为古新世—始新世;马拉坎德、瓦济里斯坦、穆斯林巴赫及贝拉铬铁矿,与罗布莎矿床相似,均属于富铬型铬铁矿,产于SSZ相关构造背景下,显示良好的岩相分带,具有良好的成矿条件;提出下一步找矿方向是针对成矿条件优越的蛇绿岩,解析层序剖面,识别纯橄岩与方辉橄榄岩的岩相分带,确定有利赋矿岩相。  相似文献   

Evidence of multi-stage faulting by clay mineral analysis: Example in a normal fault zone affecting arkosic sandstones (Annot sandstones)     

《Journal of Structural Geology》2015

Fault affecting silicoclastic sediments are commonly enriched in clay minerals. Clays are sensitive to fluid–rock interactions and deformation mechanisms; in this paper, they are used as proxy for fault activity and behavior. The present study focuses on clay mineral assemblages from the Point Vert normal fault zone located in the Annot sandstones, a Priabonian-Rupelian turbidite succession of the Alpine foredeep in SE France. In this area, the Annot sandstones were buried around 6–8 km below the front of Alpine nappes soon after their deposition and exhumed during the middle-late Miocene. The fault affects arkosic sandstone beds alternating with pelitic layers, and displays throw of about thirty meters. The fault core zone comprises intensely foliated sandstones bounding a corridor of gouge about 20 cm thick. The foliated sandstones display clay concentration along S–C structures characterized by dissolution of K-feldspar and their replacement by mica, associated with quartz pressure solution, intense microfracturation and quartz vein precipitation. The gouge is formed by a clayey matrix containing fragments of foliated sandstones and pelites. However, a detailed petrographical investigation suggests complex polyphase deformation processes. Optical and SEM observations show that the clay minerals fraction of all studied rocks (pelites and sandstones from the damage and core zones of the fault) is dominated by white micas and chlorite. These minerals have two different origins: detrital and newly-formed. Detrital micas are identified by their larger shape and their chemical composition with a lower Fe–Mg content than the newly-formed white micas. In the foliated sandstones, newly-formed white micas are concentrated along S–C structures or replace K-feldspar. Both types of newly formed micas display the same chemical composition confirmed microstructural observations suggesting that they formed in the same conditions. They have the following structural formulas: Na_0.05 K_0.86 (Al _1.77 Fe_0.08 Mg_0.15) (Si_3.22 Al_0.78) O₁₀ (OH)_2. They are enriched in Fe and Mg compared to the detrital micas. Newly-formed chlorites are associated with micas along the shear planes. According to microprobe analyses, they present the following structural formula: (Al_1,48 Fe_2,50 Mg_1,84) (Si_2,82 Al_1,18) O₁₀ (OH)₈. All these data suggest that these clay minerals are synkinematic and registered the fault activity. In the gouge samples, illite and chlorite are the major clay minerals; smectite is locally present in some samples.In the foliated sandstones, Kubler Index (KI) ((001) XRD peak width at half height) data and thermodynamic calculations from synkinematic chlorite chemistry suggest that the main fault deformation occurred under temperatures around 220 °C (diagenesis to anchizone boundary). KI measured on pelites and sandstones from the hanging and footwall, display similar values coherent with the maximal burial temperature of the Annot sandstones in this area. The gouge samples have a higher KI index, which could be explained by a reactivation of the fault at lower temperatures during the exhumation of the Annot sandstones formation.  相似文献   

西藏改则洞错地区白垩纪火山岩锆石U-Pb年代学、Hf同位素组成及对班公-怒江洋俯冲闭合的制约   总被引：1，自引：0，他引：1       下载免费PDF全文

付佳俊  丁林  许强  蔡福龙  岳雅慧  郭钰 《地质科学》2015,50(1):182-202

班公湖—怒江缝合带是青藏高原内一条重要的缝合带,其俯冲极性和闭合时限一直存在着争议,这无疑限制了我们对青藏高原演化历史的认识。本文对仲岗安山玄武岩和一套新发现的晚白垩世安山岩进行研究,获得了其锆石U-Pb年龄分别为123.75±0.92 Ma和74.23±0.76 Ma。仲岗安山玄武岩锆石的ε_(Hf)(t)值为-7.3~+4.4,具有岛弧玄武岩特征,指示班公湖—怒江洋盆在该地区仍然继续向北俯冲;晚白垩世安山岩锆石的ε_(Hf)(t)值为+3.1~+11.1,其可能是亏损地幔混熔了部分的陆壳物质而形成的,且不整合在蛇绿岩之上。结合区域资料本文认为班公湖—怒江洋盆在改则地区的闭合时限在100~75 Ma之间。  相似文献   

Polygonal deformation bands     

《Journal of Structural Geology》2015

We report for the first time the occurrence of polygonal faults in sandstone, which is compelling given that layer-bound polygonal fault systems have been observed so far only in fine-grained sediments such as clay and chalk. The polygonal faults are shear deformation bands that developed under shallow burial conditions via strain hardening in dm-wide zones. The edges of the polygons are 1–5 m long. The shear deformation bands are organized as conjugate faults along each edge of the polygon and form characteristic horst-like structures. The individual deformation bands have slip magnitudes ranging from a few mm to 1.5 cm; the cumulative average slip magnitude in a zone is up to 10 cm. The deformation bands heaves, in aggregate form, accommodate a small isotropic horizontal extension (strain <0.005). The individual shear deformation bands show abutting T-junctions, veering, curving, and merging where they mechanically interact. Crosscutting relationships are rare. The interactions of the deformation bands are similar to those of mode I opening fractures. The documented fault networks have important implications for evaluating the geometry of km-scale polygonal fault systems in the subsurface, top seal integrity, as well as constraining paleo-tectonic stress regimes.  相似文献   

Structural style in a young flexure-induced oblique extensional system,north-western Bonaparte Basin,Australia     

《Journal of Structural Geology》2015

In the north-western Bonaparte Basin (North West Shelf of Australia) Neogene to Recent flexure-induced extension superimposed obliquely over the Mesozoic rift structures. Thus, the area offers a good opportunity to investigate the dynamics and architecture of oblique extension fault systems. Analysis of basin-scale 2D and 3D seismic data along the Vulcan sub-basin shows that Neogene deformation produced a new set of extensional, en échelon faults, at places accompanied by the reactivation of the Mesozoic faults. The pre-existing Mesozoic structures strongly control the distribution of the Neogene-Recent deformation, both at regional and local scales. Main controls on the Neogene-Recent fault style, density and segmentation/linkage include: (1) the orientation of the underlying Mesozoic structures, (2) the obliqueness of the younger extension relative to the rift-inherited faults, and (3) the proximity to the Timor Trough. Three types of vertical relationships have been observed between Mesozoic and Neogene-Recent faults. Hard linkages seems to develop when both fault systems trend parallel, therefore increasing risks for trap integrity. It is suggested that the orientation of maximum horizontal stress (S_Hmax) relative to the Mesozoic faults, forming hydrocarbon traps, is critical for their potential seal/leak behaviour. Stratigraphic growth across the faults indicates that main fault activity occurred during the Plio-Pleistocene, which corresponds to the timing of tectonic loading on Timor Island and the development of lithospheric flexure. Synchronism of normal faulting with flexural bending suggests that extensional deformation on the descending Australian margin accompanied the formation of the Timor Trough.  相似文献