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181.
Ultra-high pressure metamorphic rocks in the Dabie-Su-Lu region, China: Their formation and exhumation 总被引:17,自引:0,他引:17
Cong Bolin Wang Qingchen Zhai Mingguo Zhang Ruyuan Zhao Zhongyan Ye Kai 《Island Arc》1994,3(3):135-150
Abstract Based on petrological, structural, geological and geochronological research, the authors summarize the progress of ultra-high pressure (UHP) metamorphic rock study since 1989 by Chinese geoscientists and foreign geoscientists in the Dabie-Su-Lu region. The authors introduce and discuss a two-stage exhumation process for the UHP metamorphic rocks that have various lithologies; eclogite, ultramafics, jadeitic quartzite, gneiss, schist and marble. The metamorphic history of UHP metamorphic rocks is divided into three stages, that is, the pre-eclogite stage, coesite eclogite stage, and retrograde stage. Prior to UHP metamorphism, the ultramafics had a high temperature environment assemblage of mantle and others had blueschist facies assemblages. The granulite facies assemblages, which have recorded a temperature increase event with decompression, have developed locally in the Weihai basaltic rocks. Isotopic ages show a long range from > 700 Ma to 200 Ma. The diversity in protoliths of UHP metamorphic rocks may be related to the variation of isotopic ages older than 400 Ma. The Sm-Nd dating of ~ 220 Ma could reflect the initial exhumation stage after the peak UHP metamorphism in relation to the collision between the Sino-Korean and Yangtze blocks and subsequent events. Petrological and structural evidence imply a two-stage exhumation process. During the initial exhumation, the UHP metamorphic rocks were sheared and squeezed up in a high P/T regime. In the second exhumation stage the UHP metamorphic rocks were uplifted and eventually exposed with middle crustal rocks. 相似文献
182.
Tectonic evolution of lower crustal rocks in an exposed magmatic arc section in the Hidaka metamorphic belt, Hokkaido, northern Japan 总被引:3,自引:0,他引:3
Abstract : The Hidaka metamorphic belt consists of an island-arc assembly of lower to upper crustal rocks formed during early to middle Paleogene time and exhumed during middle Paleogene to Miocene time. The tectonic evolution of the belt is divided into four stages, D0rs, D1, D2rs, and D3, based on their characteristic deformation, metamorphism, and igneous activity. The premetamorphic and igneous stage (D0) involves tectonic thickening of an uppermost Cretaceous and earliest Tertiary accretionary complex, including oceanic materials in the lower part of the complex. D1 is the stage of prograde metamorphism with increasing temperatures at a constant pressure during an early phase, and with a slight decrease of pressure at the peak metamorphic phase, accompanying flattening of metamorphic rocks and intrusions of mafic to intermediate igneous rocks. At the peak, incipient partial melting of pelitic and psammitic gneisses took place in the amphibolite–granulite facies transition zone, the melt and residuals cutting the foliations formed by flattening. In the deep crust, large amounts of S-type tonalite magma formed by crustal anatexis, intruded into the granulite facies gneiss zone and also into the upper levels of the metamorphic sequence during the subsequent stage. During D1 stage, mafic and intermediate magmas supplied and transported heat to form the arc-type crust and at the same time, the magmatic underplating caused extensional doming of the crust, giving rise to flattening and vertical uplifting of the crustal rocks. D2 stage is characterized by subhorizontal top-to-the-south displacement and thrusting of lower to upper crustal rocks, forming a basal detachment surface (décollement) and duplex structures associated with intrusions of S-type tonalite. Deformation structures and textures of high-temperature mylonites formed along the décollement, as well as the duplex structures, show that the D2 stage movement occurred under a N-S trending compressional tectonic regime. The depth of intra-crustal décollement in the Hidaka belt was defined by the effect of multiplication of two factors, the fraction of partial melt which increases downward, and the fluid flux which decreases downward. The crustal décollement, however, might have extended to the crust-mantle boundary and/or to the lithosphere and asthenosphere boundary. The subhorizontal movement was transitional to a dextral-reverse-slip (dextral transpression) movement accompanied by low-temperature mylonitization with retrograde metamorphism, the stage defined as D3. The crustal rocks from the basal décollement to the upper were tilted eastward on the N–S axis and exhumed during the D3 stage. During D2 and D3 stages, the intrusion of crustal acidic magmas enhanced the crustal deformation and exhumation in the compressional and subsequent transpressional tectonic regime. 相似文献
183.
地幔平衡部分熔融和岩浆分离结晶成因岩浆岩的判别 总被引:1,自引:1,他引:1
本文在讨论Ⅰ型(地幔平衡部分熔融成因)和Ⅱ型(岩浆分离结晶成因)岩浆岩元素丰度关系公式的基础上,建立了Ⅰ型和Ⅱ型岩浆岩系成因判别公式及判别法则。 相似文献
184.
Thermo-mechanical behaviour of rocks shows phenomenological similarities to that of clays. A visible decrease of strength and an increase in ductility at elevated temperatures are observed in drained conditions. In undrained conditions the strength decrease is even more dramatic and the ductile behaviour may turn into the brittle one, if a sufficient amount of water is present in the pores at the start of the process, or it is being released during heating by the decomposition of hydrous minerals. Applying a thermo-plasticity theory, major macroscopical characteristics of behaviour may be modelled. According to this theory, the elastic domain is postulated as temperature dependent, shrinking with temperature; heating may result in expansive or compactive volumetric irreversible strain depending on the confining stress. This theory is applied to the modelling of heat effects on local changes of permeability around a cylindrical nuclear waste container disposed off in deep clays, and in the numerical simulation of a mechanism initiating deep earthquakes. 相似文献
185.
浅成脉状金矿是指在近地在至1.5km深度,以充填方式形成,总体形状呈脉状金矿床。其赋矿围岩是多种多样的,以火山岩、次火山岩、浅侵入体最为常见,此外还有变质岩等。热液矿床的形成深度对矿体形状、产状、规模、物质组成和结构构造有重要影响。浅成脉状金矿是我国仅次于中深脉状金矿的第二个重要类型。介绍了浅成脉状金矿的地质特征及进一步分类的方案。 相似文献
186.
金川超镁铁质岩体矿物化学特征及矿物地质温度计、压力计研究 总被引:4,自引:0,他引:4
根据金川超镁铁质岩体主要造岩矿物和副矿物的共生组合关系及各种矿物的化学成分特点;选用5种较成熟、使用较方便的矿物地质温度计、压力计(主要是辉石温压计和角闪石压力计),对岩体形成的温、压条件进行了估算,其结果为:成岩温度为1000~1300℃(上限可到1400~1500℃),成岩压力约为5×10 ̄8~11×10 ̄8pa。金川超镁铁质岩体的主要岩石类型为尖晶石二辉橄榄岩,这一岩石类型在复杂体系相关系图中的稳定区域大致处于5×l0 ̄8~15×10 ̄8pa的范围,这与矿物温压计估算的成岩温压条件是一致的。 相似文献
187.
Influence of fluid chemistry on shear-wave attenuation and velocity in sedimentary rocks 总被引:2,自引:0,他引:2
Dung Vo-Thanh 《Geophysical Journal International》1995,121(3):737-749
188.
出露在利文斯顿岛中部的白垩纪火山岩为玄武岩-玄武安山岩-安山岩-英安岩组合,基本属于钙碱性系列,但具有低钾拉斑玄武岩的某些特点。岩石富集Rb、Th、Ba,轻度亏损Zr、Ti、Hf、Nb,较强亏损Cr和Ni,而且随着岩浆从基性向酸性成分的演化,富集(或亏损)程度加大。岩石的轻稀土元素中度富集,岩石的(Ce/Yb)CN比值较低。白垩纪火山岩形成在一个造山环境,是南设得兰岩浆弧的一部分。然而,在利文斯顿岛不同地区出露的岩石其化学性质有所区别,因此认为它们可能源于不同的岩浆体系。在晚古生代至早中生代,利文斯顿岛中部处于一个独特的浊积扇的构造环境。主要产在利文斯顿岛中部和汉那角的鲍勒斯山组火山岩与其它地点的中生代火山岩相比,无论岩相学特征还是岩石化学性质均有所不同。因此认为它们的产生同时受到太平洋板块的俯冲作用和该地构造位置所控制。史莱夫角的橄榄玄武岩成分中碱高硅低,并且通常表现出高铝的特点,这些性质与百耳斯半岛的玄武岩极为相似。区域上火山活动不断发展,活动中心逐渐向北东迁移,导致粗玄岩岩颈和岩席生成,最后是英云闪长岩的侵入。更新世至现代的依诺特角组橄榄玄武岩以化学成分中的低硅高碱含量区别于中生代火山岩。岩石的高M值 相似文献
189.
本文旨在研究多孔岩石声衰减机制及衰减和频率的关系,用共振法测量了人工多孔材料10~5Hz以下的弯曲振动能量损耗,发展了前人测量弹性模量的方法.实验结果表明:干燥试样的内耗基本上与频率无关:水饱和试样的内耗比干燥试样的大得多,并在24.0kHz有显著的弛豫峰;饱和试样的内耗主要产生于固体骨架与孔隙流体之间的相对运动.实验结果与Riot理论和局部流体流动机制一致,但未看到Dunn预言的“边界效应”. 相似文献
190.
Dhruba Mukhopadhyay Tapas Bhattacharya Tapan Chakraborty Arun Kanti Dey 《Journal of Earth System Science》1990,99(2):249-268
In the western part of the North Singhbhum fold belt near Lotapahar and Sonua the remobilized basement block of Chakradharpur
Gneiss is overlain by a metasedimentary assemblage consisting of quartz arenite, conglomerate, slate-phyllite, greywacke with
volcanogenic material, volcaniclastic rocks and chert. The rock assemblage suggests an association of volcanism, turbidite
deposition and debris flow in the basin. The grade of metamorphism is very low, the common metamorphic minerals being muscovite,
chlorite, biotite and stilpnomelane. Three phases of deformation have affected the rocks. The principal D1 structure is a
penetrative planar fabric, parallel to or at low angle to bedding. No D1 major fold is observed and the regional importance
of this deformation is uncertain. The D2 deformation has given rise to a number of northerly plunging major folds on E-W axial
planes. These have nearly reclined geometry and theL
2lineation is mostly downdip on theS
2surface, though some variation in pitch is observed. The morphology of D2 planar fabric varies from slaty cleavage/schistosity
to crenulation cleavage and solution cleavage. D3 deformation is weak and has given rise to puckers and broad warps on schistosity
and bedding. The D2 major folds south of Lotapahar are second order folds in the core of the Ongarbira syncline whose easterly
closure is exposed east of the mapped area. Photogeological study suggests that the easterly and westerly closing folds together
form a large synclinal sheath fold. There is a continuity of structures from north to south and no mylonite belt is present,
though there is attenuation and disruption along the fold limbs. Therefore, the Singhbhum shear zone cannot be extended westwards
in the present area. There is no evidence that in this area a discontinuity surface separates two orogenic belts of Archaean
and Proterozoic age. 相似文献