青海团宝山花岗岩年代学、地球化学特征及其地质意义

青海省团宝山花岗岩位于南祁连东段,侵位于古元古代化隆群中.为了解其侵位时代、岩体成因和产出构造环境,利用LA-ICP-MS锆石U-Pb定年和地球化学测试方法对团宝山花岗岩岩体样品进行分析.获得其锆石U-Pb年龄为(776±8)Ma;该岩体SiO2、Al2O3和K2O含量较高,而FeOT、MgO和CaO含量较低,K2O/...     

苏皖北部地区晚元古代地层的马尔柯夫链分析

本文运用数学地质理论中的马尔柯夫链分析方法,对苏皖北部地区及鲁西南地区晚元古代地层进行了初步研究。文中选择6条比较典型的剖面,分别对它们进行了转移概率、极限概率、差值阵、置换分析和熵分析等方面的计算,并对所得结果做了相应的地质解释。分析结果,从定量方面揭示出了晚元古代时期苏皖海盆基底的“波动”史及其上覆地层的主要沉积韵律类型,以及盆地内不同部位、不同时代岩性变化的主要趋势及其阶段性;并认为,在晚元古代早期苏皖海盆中很可能同时存在有南、北两个沉积中心,而并非像以往所认为的那样,只有一个沉积中心。     

Evolution of the Australian lithosphere

The evolution of the Australian plate can be interpreted in a plate‐tectonic paradigm in which lithospheric growth occurred via vertical and horizontal accretion. The lithospheric roots of Archaean lithosphere developed contemporaneously with the overlying crust. Vertical accretion of the Archaean lithosphere is probably related to the arrival of large plumes, although horizontal lithospheric accretion was also important to crustal growth. The Proterozoic was an era of major crustal growth in which the components of the North Australian, West Australian and South Australian cratons were formed and amalgamated during a series of accretionary events and continent‐continent collisions, interspersed with periods of lithospheric extension. During Phanerozoic accretionary tectonism, approximately 30% of the Australian crust was added to the eastern margin of the continent in a predominantly supra‐subduction environment. Widespread plume‐driven rifting during the breakup of Gondwana may have contributed to the destruction of Archaean lithospheric roots (as a result of lithospheric stretching). However, lithospheric growth occurred at the same time due to mafic underplating along the eastern margin of the plate. Northward drift of Australia during the Tertiary led to the development of a complex accretionary margin at the leading edge of the plate (Papua New Guinea).     

Low-pressure granulite facies metamorphism in the Larsemann Hills area, East Antarctica; petrology and tectonic implications for the evolution of the Prydz Bay area

ABSTRACT Thermobarometric studies on various granulite facies areas along the Prydz Bay coast, East Antarctica (73°-79°E, 68°-70°S), show that, at around 1100 Ma, during a late Proterozoic orogeny, the rocks of the Larsemann Hills suffered a lower pressure metamorphic peak than the surrounding areas. Along the Prydz Bay coast, the rocks affected by this event include parts of the Vestfold Hills block plus all of the Rauer Group, the Larsemann Hills and the Munro Kerr Mountains. The dykes in the south-west corner of the Vestfold Hills were recrystallized during this event with little deformation at temperatures not quite as high as in the areas further south-west (650°C, 6.5 kbar) (Collerson et al., 1983), the Rauer Group was metamorphosed at 800°C and 7.5 kbar (Harley, 1987a), the Larsemann Hills at 750°C and 4.5 kbar, and the Munro Kerr Mountains probably at around 850°C and 5 kbar. Retrograde equilibration in the different areas occurred during decompression to about 10 km depth in all areas, followed by isobaric cooling at this depth. This paper shows that the peak metamorphism in the Larsemann Hills occurred at a pressure which is too low to have been the consequence of thermal relaxation of overthickened crust with normal mantle heat flow. Although other areas in Prydz Bay were metamorphosed at sufficiently high pressures so that their decompression paths are not inconsistent with a continental collision model, the inferred pre-metamorphic peak histories and the requirement of consistency with the Larsemann Hills, make it unlikely that collision followed by erosion-driven decompression is an appropriate model. We suggest that the thermal regime of the crust in the Larsemann Hills region was controlled by a perturbation in the asthenosphere, with magma invasion of the crust. We suggest that the 500 Ma event, represented in Prydz Bay by granitic outcrops at Landing Bluff and by several K/Ar ages from the Larsemann Hills area, was responsible for the final excavation of the terrane.     

中国中元古代裂谷作用及其对层控铜矿床的控制

本文以中国几个重要的层控铜矿为例,并以东川式铜矿及其成矿构造背景——昆阳拗拉谷为重点,分析了它们的大地构造背景和其它地质特征,指出它们均受裂谷—拗拉谷或类似的拉张-裂陷构造所控制,并归纳了这类矿床的主要特征。     

一个晚元古代水下冰足刻蚀作用的记录——水下冰推垄

在现代高纬陆棚冰海区的海底底床上,有大量由海冰形成的水下冰足机械刻蚀迹,但在古代冰期地层中却极少报道。笔者在湖南省石门县中岭乡杨家坪的震旦系剖面上发现一丘状构造,经分析,推断为一水下冰足刻蚀记录(图1)。该构造出露于南华大冰期的下冰期地层东山峰组底界以下约60m,在渫水河组上部。     

A structural synthesis of the Proterozoic Arabian-Nubian Shield in Egypt

Detailed structural geological and related studies were carried out in a number of critical areas in the Proterozoic basement of eastern Egypt to resolve the structural pattern at a regional scale and to assess the general characteristics of tectonic evolution, orogeny and terrane boundaries. Following a brief account of the tectonostratigraphy and timing of the orogenic evolution, the major structural characteristics of the critical areas are presented. Collisional deformation of the terranes ended about 615-600 Ma ago. Subsequent extensional collapse probably occurred within a relatively narrow time span of about 20 Ma (575 – 595 Ma ago) over the Eastern Desert and was followed by a further period of about 50 Ma of late to post-tectonic activity. The regional structures originated mainly during post-collisional events, starting with those related to extensional collapse (molasse basin formation, normal faulting, generation of metamorphic core complexes). Subsequent NNW-SSE shortening is documented by large-scale thrusting (towards the NNW) and folding, distributed over the Eastern Desert, although with variable intensity. Thrusts are overprinted by transpression, which was localized to particular shear zones. Early transpression produced, for example, the Allaqi shear zone and final transpression is documented in the Najd and Wadi Kharit-Wadi Hodein zones. Two terrane boundaries can be defined, the Allaqi and South Hafafit Sutures, which are apparently linked by the high angle sinistral strike-slip Wadi Kharit-Wadi Hodein shear zone with a tectonic transport of about 300 km towards the W/NW. In general, the tectonic evolution shows that extensional collapse is not necessarily the final stage of orogeny, but may be followed by further compressional and transpressional tectonism. The late Pan-African high angle faults were reactivated during Red Sea tectonics both as Riedel shears and normal faults, where they were oriented favourably with respect to the actual stress regime.     

皖南和赣东北蛇绿岩成因及其构造意义：元素和Sm－Nd同位素制约

本文对扬子块体南缘构造侵位于板溪群（及相应地层）的皖南和赣东北晚元古代蛇绿岩进行了系统的元素和Ｓｍ－Ｎｄ同位素地球化学研究，结果表明两套蛇绿岩具有类似的元素地球化学特征，即二者的火山岩元素地球化学特征均类似于形成于弧后盆地构造环境的拉斑玄武岩。但是，两套蛇绿岩的Ｎｄ同位素组成明显不同。赣东北蛇绿岩具有相当均一的高εＮｄ（Ｔ）值（＋５．５±１．２），表明来源于一较亏损的上地幔源区，并且没有受到明显的较成熟地壳物质的混染。相反，皖南蛇绿岩的εＮｄ（Ｔ）值低，并有较大的变化范围（＋４．５──１．０），并和Ｓｍ／Ｎｄ、Ｎｄ、ＭｇＯ、ＳｉＯ２呈明显的二元混合相关关系，表明蛇绿岩是由亏损幔源岩浆（初始εＮｄ（Ｔ）≈＋５．５）在结晶分异过程中与地壳组分（初始εＮｄ（Ｔ）≈－１）混合形成的。皖南和赣东北蛇绿岩的Ｎｄ同位素和元素地球化学特征以及该地区的同时代花岗岩和火山岩的时空分布特征，可以用华南和扬子元古宙陆－弧－陆碰撞模式来解释。大约在１．０Ｇａ前，扬子和华南块体之间存在一多岛弧洋盆。大陆边缘岛弧和大洋岛弧在扬子块体南缘发育演化。皖南和赣东北蛇绿岩就是在大陆边缘盆地和弧间盆地演化过程中形成的洋壳构造侵位的碎片。该地区Ｉ型     

Principal stages in evolution of Precambrian organic world: Communication 1. Archean and Early Proterozoic

Expounded in this work are the results of critical consideration of published and original data on biologic nature and appearance chronology of different groups of Archean and Lower Proterozoic (3.5–1.65 Ga) paleontological remains known from geological record. Conclusions are substantiated by morphological analysis of structurally preserved microfossils, their facies distribution, and by inferable genesis and principal evolutionary trends of Archean stromatolites. A special attention is paid to variations of organic and carbonate carbon isotope composition in sedimentary successions with paleontological remains and to recent information about discovered, most ancient biomarkers of large groups of organic world. As a result of this approach, a detailed model of Precambrian organic world evolution is suggested.