中祁连山东段史纳村一带湟源岩群表壳岩的变质作用及地化特征     

白云来  邓亚萍  程建生 《甘肃地质》1998,7(2):54-62

甘、青交界处民和县史纳村一带早元古宙湟源岩群表壳岩属一套“有层无序”地层,岩石组合为石英岩、绢云（二云）石英片岩、黑云斜长石英片岩、含榴（十字）二云石英片岩、角闪片岩等。晋宁旋回主要发生了区域动力热流变质作用,出现了从低绿片岩相—低角闪岩相的递增变质带,高峰期变质条件Ｐ＝３．８×１０８～４．８×１０８Ｐａ,Ｔ＝５５８～６４５℃。该套岩层具“褶叠层”性质,新测得Ｓｍ－Ｎａ全岩等时线年龄为１９００Ｍａ,为古元古代地质事件。变质作用Ｐ－Ｔ－ｔ轨迹具逆时针特征,表明此时为活动大陆边缘或是大陆岛弧环境。地质、地球化学资料表明湟源岩群表壳岩形成于大陆边缘裂谷环境,碎屑岩Ｎａ２Ｏ＋Ｋ２Ｏ＝５．２８×１０－２,Ｖ／Ｎｉ＝７,Ｓｃ／Ｎｉ＝１,Ｓｃ／Ｓｒ＝０．１。  相似文献   

New seismic data support Cenozoic rifting in George VI Sound, Antarctic Peninsula   总被引：1，自引：0，他引：1  

A. C. Bell  & E. C. King 《Geophysical Journal International》1998,134(3):889-902

New multifold seismic-reflection and wide-angle reflection/refraction data across George VI Sound, Antarctic Peninsula, show the presence of graben and horst structures indicating an extensional origin. The data suggest that rocks of an accretionary complex and fore-arc basin underlie the Sound and are in faulted contact along its eastern boundary with volcanic and plutonic rocks of the associated Mesozoic arc of western Palmer Land. A cover of possible syn- and postglacial Cenozoic deposits drapes the structures. The combination of new seismic, synthetic-aperture radar and previously acquired data suggests subduction-related rifting in the Sound was segmented, with opening in the south predominately by normal extension whilst in the north, dextral transtension predominated.  相似文献   

Three-dimensional seismic structure of the upper mantle beneath the central part of the Eurasian continent     

Ivan Koulakov 《Geophysical Journal International》1998,133(2):467-489

This work is a study of the upper-mantle seismic structure beneath the central part of the Eurasian continent, including the northern Mongolia, Altai and Sayan orogenic areas and the Baikal rift zone. Seismic velocity models are reconstructed using the inverse teleseismic scheme. This scheme uses information from earthquakes located within the study area recorded by the Worldwide Network. The seismic anomaly structure is obtained for different volumes in the study area that partially overlap one another. Special attention has been paid to the reliability of the results: several noise and resolution comparisons are made.
The main results are as follows. (1) A cell structure of anomalies is observed beneath the Altai–Sayan region: positive, cold anomalies correspond to regions of recent orogenesis, negative anomalies are located beneath the depression of the Great Lakes in Mongolia and Hubsugul Lake. (2) A large negative anomaly is observed beneath the Hangai dome in Mongolia. (3) Strong velocity variations are obtained in a zone around Baikal Lake. A large negative anomaly is traced beneath the southern margin of the Siberian craton down to a depth of 700 km. Contrasting positive anomalies (4–5 per cent) are observed at a depth of 100–300 km beneath the Baikal rift. Our geodynamical interpretation of the velocity structure obtained beneath central Asia involves the existence of two processes in the mantle: thermal convection with regular cells, and a narrow plume beneath the southern border of the Siberian plate.  相似文献   

赣东北-浙西北登山群和松木坞群中火山岩的地球化学   总被引：1，自引：0，他引：1  

赵风清  金文山  甘晓春  孙大中 《华北地质》1997,(2)

赣东北－浙西北新元古代登山群和松木坞群主要由板岩、砂岩、流纹岩、流纹质英安岩、玄武岩和玄武质安山岩组成，火山岩的Ｒｂ－Ｓｒ和Ｓｍ－Ｎｄ等时线年龄以及流纹岩中单颗粒锆石Ｕ－Ｐｂ年龄显示其成岩时代为８００－９００Ｍａ。登山群和松木坞群火山岩呈双峰式产出，其中镁铁质火山岩在化学成分上呈现出演化程度较高的特点（ｅｖｏｌｖｅｄｎａｔｕｒｅ），高强场元素（Ｔｉ、Ｎｂ、Ｔａ等）相对于碱土元素未发生明显亏损，反映其形成于大陆裂谷环境。镁铁质火山岩具低的Ｎｄ值，表明其来源于弱亏损的地幔源，也可能遭受一定程度的地壳混染作用改造。酸性火山岩在化学成分上表现出Ｓ型火山岩特点，但其变化于－１．９～＋２８，指示其为先存的长英质基底分熔作用的产物，但存在强烈的地慢物质添加作用。  相似文献   

东川裂谷因民期火山——岩浆活动特征   总被引：3，自引：1，他引：3  

何国朝  张祖圻 《矿产与地质》1997,11(4):236-242

东川裂谷因民期火山—岩浆活动强烈，也是重要的铁铜成矿期。火山活动旋回均经历爆发—喷发—喷溢—（喷流）阶段。主要发育在裂谷中心落因火山链和蓑衣坡火山盆地中。落因火山链早期形成火山—沉积角砾岩段，火山活动以喷溢的火山熔岩为主，主要有钠质基性熔岩、玄武岩、安山岩，均已蚀变，并有钠长斑岩的侵入活动。中期火山喷发形成凝灰岩类、火山碎屑岩类，发育了铁铜矿化。在蓑衣坡火山盆地中因民期火山—岩浆活动发育两次火山—沉积旋回，即两次爆发（角砾岩）—喷发（凝灰岩）—喷溢（熔岩）—喷流（硅质岩），在喷流相发育赤铁矿层和含铜硅质岩层。  相似文献   

Seismic stratigraphy and structural characteristics of back-arc rifts on the Izu-Ogasawara Arc     

Fumitoshi  Murakami 《Island Arc》1996,5(1):25-42

Abstract Seven back-arc rifts are recognized in the Izu-Ogasawara Arc, namely, the Hachijo, the Aogashima, the Myojin, the Sumisu, the Torishima, the Sofu and the Nishinoshima Rifts from north to south. The acoustic stratigraphy is divided into three units (Units A, B and C) based on the seismic reflection profiles crossing the rifts. The structure of the rifts systematically changes from a half-graben type to a full graben type in the back-arc rifts from the Hachijo Rift to the Torishima Rift. The Hachijo and the Aogashima Rifts have a structure of half-graben, and the Myojin Rift has both structural characteristics of a half-graben and a full graben. The Sumisu and the Torishima Rifts are an asymmetric full graben. The Sofu and the Nishinoshima Rifts have different structural characteristics from the remaining rifts, from the Hachijo Rift to the Torishima Rift. The boundary faults in the back-arc rifts from the Hachijo to the Torishima Rifts cut to Unit B. Unit B correlates with volcaniclastic sediments during pre-rift volcanism between 4 and 2 Ma. The pre-rift volcanism was probably widespread on the northern Izu-Ogasawara Arc as is the present arc volcanism. These factors suggest that the beginning of rifting is dated at some time after 2 Ma. The developing process of the rift consists of three stages; (i) a sag stage in the crust at the location of the large offset boundary fault; (ii) a stage of half-graben formation; (iii) a stage of full graben formation. The offset of the boundary faults becomes larger from the Hachijo Rift to the Torishima Rift and the east-west width of the rifts also widens to the south. This is presumably because the Hachijo Rift is an earlier rifting stage than the Sumisu and the Torishima Rifts. The more primitive structure in the rifting stage from the Torishima Rift to the Hachijo Rift is probably caused by the propagation of rifting from south to north. The structural difference between the rifts in the northern part and the Sofu and the Nishinoshima Rifts seems to be due to structural differences in the crust between the northern and the southern parts from the tectonic gap.  相似文献   

广东梅县嵩溪早侏罗世火山活动及其地质构造与成矿意义   总被引：2，自引：0，他引：2  

郑庆年 《矿产与地质》1996,(2)

从熔岩——玄武岩的岩石学、岩石化学、微量元素、稀土元素和锶同位素组成，以及火山旋回中玻璃碎屑岩诸方面特征，详细地研究了下侏罗统含矿层位内海底基性火山活动，阐述矿区玄武岩形成环境为夭折的大陆裂谷前期地壳槽形裂陷地堑系——裂陷槽。并讨论该裂陷槽环境中基性火山活动的银锑成矿意义  相似文献   

中条山区前寒武纪铜矿床地质历史演化及成矿年代   总被引：1，自引：0，他引：1  

李树屏  陈文明 《华北地质矿产杂志》1996,(3)

中条山区铜矿床是在中条古裂谷地质构造环境中演化形成的。本文从涑水杂岩期－绛县期－中条期－西阳河期等不同时代地质历史演化，分别探讨了中条山区不同类型铜矿床时空分布和成因上的内在联系。它们早期形成的矿源层受不同时代的层位和岩性控制，但在后期的２０００～２１００Ｍａ和１８００～１９００Ｍａ较大规模的构造－热事件，对不同类型铜矿床进行了叠加和改造，使铜质进一步富集，最终形成工业矿床  相似文献   

郯庐古岛弧构造系与金矿成矿的关系     

王学佑 《铀矿地质》1996,12(3):149-155

本文从郯庐断裂带整体地质构造特征出发，应用板块构造理论和遥感技术、地质调查、物化探等综合研究方法，初步提出郯庐断裂带应归属于东亚大陆古岛孤－新裂谷式巨型构造系统，它与现代西太平洋岛弧具有“相对应性”及“等结性”控制金矿成矿集中区的新认识，并据此探索和总结了金矿（含其他矿产）的成矿规律，为寻找“招掖”式金矿进行成矿前景预测。  相似文献   

Tectonic and geochemical characteristics and reserved conditions of a mantle source gas accumulation zone in eastern China   总被引：8，自引：0，他引：8  

Mingxin Tao  Yongchang Xu  Ping Shen  Wenhui Liu 《中国科学D辑(英文版)》1997,40(1):73-80

Along both sides of the Tancheng-Lujiang Fracture Zone in eastern China, a series of mantle source gas pools constitute a massive-scale tectonic accumulation zone in NNE direction, with the mantle geochemical characteristics of high concentrations of C0₂ and He, high³He/⁴He-⁴⁰Ar/³⁶Ar ratio system and high δ¹³Coo₂ ratios (the main frequency, -3.4%— 4.6%), showing no difference from the tectonic framework of the area. In the area, the tectonic environment is a rift formed as a result of diapiric mantle injection and crust thinning to form graben-type basins and lithospheric fractures. The mantle-derived volcanic rocks and inclusions are well-developed and a high geothermal zone (mantlesource) exists in the area. The characteristics of the three components (solid, liquid and gas) of mantle, concentrated all over the same tectonic space zone, show that the rift system is of a good tectonic environment or passage for mantle degassing and gas migration. The main types of the gas pools are volcano, fault-block, anticline, buried hill and so on, but most of them are combination traps closely related with fracture. For the mantle source gas pools, rift is an optimum tectonic region, and nearby lithospheric fracture, mantle source volcanic rocks or basement uplifts are a favourable structural location when reservoir-caprock association develops.  相似文献