东南极拉斯曼丘陵镁铁质麻粒岩的地球化学特征及其中压变质作用          下载免费PDF全文

王彦斌  赵越  任留东  陈廷愚  刘小汉  仝来喜 《极地研究》1994,6(3):4-14

在东南极普里兹湾拉斯曼丘陵地区变泥质岩和长英质片麻岩中，定向分布着透镜状、扁豆状和香肠状镁铁质、超镁铁质麻粒岩。这些岩石主量元素、微量元素和稀土元素地球化学特征显示其原岩化学成分具镁铁质堆晶岩特征，并可能代表岩墙的构造作用残留体。在米洛半岛发现石榴子石周围有斜方辉石和斜长石的反应边，斜方辉石和斜长石由下述反应形成：石榴子石＋石英→斜方辉石＋斜长石。这个反应为减压反应，应用地质温压计确定其温度和压力分别为７４７±４８°Ｃ和６．３±０．５ｋｂａｒ，本文首次应用石榴子石－斜方辉石－斜长石－石英组合确立本区早期中压麻粒岩相事件的存在。本文还对镁铁质麻粒岩的原岩成因及矿物中的减压结构所代表的构造意义进行了探讨  相似文献   

A thousand years of environmental change and human impact in the alpine zone at Mt Kosciusko,New South Wales     

T. de Salis  C. A. Myers   《The Australian geographer》1994,25(1):77-87

This study reconstructs erosion, productivity, fire and vegetation records at Club Lake, in the alpine zone of Kosciusko National Park (the highest mountain region in Australia), and uses them to compare the prehistoric and historic periods. While disturbance in the prehistoric period was found to be minimal and mainly activated by fire, the impact of land uses after European arrival initiated a change in the erosion and fire regime and brought new grazing animals and exotic plant species. These triggered temporal changes in eutrophication and the nature of erosion, and significant vegetation changes. There was a reduction in the stability and persistence of species representation, especially in herbfield vegetation, and little recovery is evident despite the cessation of summer grazing. It is apparent that the area is very sensitive to disturbance by human impact and large fires.  相似文献   

福建马坑铁矿辉石的成因矿物学研究   总被引：2，自引：0，他引：2  

刘劲鸿 《福建地质》1993,12(4):248-257

本文研究了福建马坑铁矿床中辉石族矿物的时空分布、产状、种属及其晶体形态标型、物理标型、化学成分标型。通过不同成因的辉石(308个不同成因辉石)化学成分标型对比、图解等综合判别方法确定马坑铁矿中辉石有火山岩变质、沉积变质、接触交代和岩浆四种成因。矿体底部成矿建造为富Fe、K、Mn火山岩建造,中下部为富F、Mn硅铁质沉积建造,上部为富Ca、Mg、Mn、Fe、Si碳酸盐沉积建造。马坑矿床主矿体为海底火山沉积变质型铁矿。提出利用辉石的种属、含铁系数、化学标型判断有无矿体及其贫富的矿物学标志。  相似文献   

热变煤的光学结构及其地质意义     

方家虎  唐修义 《煤田地质与勘探》1993,21(5):21-25,33

不同岩性的岩体侵入不同初始煤级的煤，形成不同宽度的接触变质带，带中煤的光学结构发生大小不同的变化，这种变化具有一定的地质意义，本文强调了热变煤的特征标志是孔隙的存在，并着重探讨了热变煤中新生有机组分－热解碳与小球体光性与成因，指出热解碳具有指热意义，表示近处岩体存在，而小球体分其生成的各向异生体并非表明一定有岩体存在。  相似文献   

内华达山脉西部变质带的变质变形史及与秦岭造山带的对比     

钟增球  游振东 《地质科技情报》1993,12(4):8-16

美国内华达山脉(Sierra Nevada)西部变质带是古生代以来的活动大陆边缘和显生宙大陆增生的典范,通过对其变质变形史的研究及其与秦岭造山带的对比,认为其对中国造山带的研究,尤其是对大陆增生、增厚及演化历史等方面的研究有着重要的借鉴意义。  相似文献   

Orthopyroxene-bearing, mafic migmatites at Cone Peak, California: evidence for the formation of migmatitic granulites by anatexis in an open system   总被引：3，自引：0，他引：3  

E. HANSEN  M. STUK 《Journal of Metamorphic Geology》1993,11(2):291-307

Abstract Orthopyroxene-bearing migmatites, exposed at the summit of Cone Peak in the Santa Lucia Range, California, offer an opportunity to explore potential links between granulite facies metamorphism and migmatite formation. Geothermobarometry indicates that the metamorphic temperatures and pressures were in the approximate ranges of 700–750° C and 7.0–7.5 kbar. The rocks at the summit comprise three domains: relatively coarse-grained, leucocratic veins; relatively fine-grained, biotite-enriched zones at the margins of the veins; and a biotite–hornblende-bearing host rock. Orthopyroxene is concentrated in the veins, which have also the highest ratio of anhydrous to hydrous minerals of the three rock types. The composition of the veins, together with their textures and modes, suggest that they formed through anatexis involving a dehydration-melting reaction which consumed hornblende and produced orthopyroxene. Variability in mineralogy and composition indicates that there was some local migration of magma along the veins before their final solidification. The biotite-enriched zones formed either by the concentration of residual biotite at the margins of the vein, or through the metasomatic conversion of hornblende (and/or pyroxene) to biotite, or by a combination of the two processes. Significant differences in the chemistry of the neosome (vein + biotite-enriched zone) and the host rock rule out simple dehydration melting in a local closed system. The model that explains best the mineralogical and chemical patterns involves triggering of melting by an influx of a low- a _H2O mixed fluid which added K and Si to and removed Ca from the neosome.  相似文献   

胶北蓬莱群的变形与变质及其区域大地构造意义   总被引：6，自引：0，他引：6  

朱光 《大地构造与成矿学》1993,17(3):259-270

本文通过构造与变质研究及伊利石结晶度和同位素年龄测定。分析胶北蓬莱群的变形,变质及其区域大地构造意义。作为胶北唯一盖层的蓬莱群,在晚石炭世(299±4Ma)北北东—南南西区域挤压下首次遭受了强烈的蓬莱事件变形及低绿片岩相变质。其后的后蓬莱事件在胶北地区仅造成了局部的北北东—南南西向变形构造。作为华北板块南缘的胶北带,其上的蓬莱事件是华北与扬子板块沿胶南带碰撞的结果。这表明郯庐断裂带以东这两扳块碰撞发生在晚石炭世。在秦岭—大别山碰撞带以北的华北扳块南缘,由于碰撞也出现了类似胶北带的挤压变形。  相似文献   

Hydrologic and sediment modelling studies in the environmental impact assessment of a major tropical dam project     

G. Pickup 《地球表面变化过程与地形》1980,5(1):61-75

A computer-based study of the impact of the proposed Wabo hydroelectric scheme on the Purari River, Papua New Guinea was carried out. The HEC-6 model, Scour and Deposition in Rivers and Reservoirs developed by the Hydrologic Engineering Centre was used to simulate the effect of the dam on sediment transport and erosion in the lower Purari. Two runs with the model were carried out. The first one was used to establish baseline conditions and the second modelled dam impact. Before the study was carried out, data had to be collected on channel geometry, sediment input, river bed material size composition and hydraulic conditions in the river. Supplementary models also had to be developed to fill in gaps in runoff records and to describe flow in the river during power generation. Results of the investigation indicate that limited erosion will occur because of bed-armouring and the river will adjust towards a new equilibrium condition quite rapidly. The sediment output of the river into the Purari delta will change, load in the clay, silt and sand/gravel fractions decreasing by 22, 53 and 78 per cent respectively.  相似文献   

Coeval basin formation,plutonism and metamorphism in the Northern Tasmanides: extensional Cambro-Ordovician tectonism of the Charters Towers Province     

R. A. Henderson  C. L. Fergusson  I. W. Withnall 《Australian Journal of Earth Sciences》2020,67(5):663-680

Abstract

The Charters Towers Province, of the northern Thomson Orogen, records conversion from a Neoproterozoic passive margin to a Cambrian active margin, as characteristic of the Tasmanides. The passive margin succession includes a thick metasedimentary unit derived from Mesoproterozoic rocks. The Cambrian active margin is represented by upper Cambrian–Lower Ordovician (500–460?Ma) basinal development (Seventy Mile Range Group), plutonism and metamorphism resulting from an enduring episode of arc–backarc crustal extension. Detrital zircon age spectra indicate that parts of the metamorphic basement of the Charters Towers Province (elements of the Argentine Metamorphics and Charters Towers Metamorphics) overlap in protolith age with the basal part of the Seventy Mile Range Group and thus were associated with extensional basin development. Detrital zircon age data from the extensional basin succession indicate it was derived from a far-field (Pacific-Gondwana) primary source. However, a young cluster (<510?Ma) is interpreted as reflecting a local igneous source related to active margin tectonism. Relict zircon in a tonalite phase of the Fat Hen Creek Complex suggests that active margin plutonism may have extended back to ca 530?Ma. Syntectonic plutonism in the western Charters Towers Province is dated at ca 485–480?Ma, close to timing of metamorphism (477–467?Ma) and plutonism more generally (508–455?Ma). The dominant structures in the metamorphic basement formed with gentle to subhorizontal dips and are inferred to have formed by extensional ductile deformation, while normal faulting developed at shallower depths, associated with heat advection by plutonism. Lower Silurian (Benambran) shortening, which affected metamorphic basement and extensional basin units, resulted in the dominant east–west-structural trends of the province. We consider that these trends reflect localised north–south shortening rather than rotation of the province as is consistent with the north–south paleogeographic alignment of extensional basin successions.

1. KEY POINTS

2. Northern Tasmanide transition from passive to active margin tectonic mode had occurred by ca 510?Ma, perhaps as early as ca 530?Ma.

3. Cambro-Ordovician active margin tectonism of the Charters Towers Province (northern Thomson Orogen) was characterised by crustal extension.

4. Crustal extension resulted in the development of coeval (500–460?Ma) basin fill, granitic plutonism and metamorphism with rock assemblages as exposed across the Charters Towers Province developed at a wide range of crustal levels and expressing heterogeneous exhumation.

5. Protoliths of metasedimentary assemblages of the Charters Towers Province include both Proterozoic passive margin successions and those emplaced as Cambrian extensional basin fill.

  相似文献   

Environmental impact of the MV CITA on the foreshore of Porth Hellick, Isles of Scilly     

Smith NA 《Marine pollution bulletin》2004,49(11-12):1105-1108

The grounding of the container feeder vessel MV CITA on Newfoundland Rocks, Isles of Scilly, had an effect on the surrounding biota and benthic environment. Included in the CITA's cargo were five 40 ft containers holding pallets of polyester film used in the production of audio and visual recording tapes. The wreckage presented a minor but potentially chronic source of pollution through the delayed release of polythene film, which was left on the seabed as it was considered insufficiently valuable to warrant salvage. The polythene disintegrated and was washed upon the foreshore of Porth Hellick in minute shreds. The adjacent foreshore and two control sites within the islands were analysed using a 5-strand line and vegetation survey with 10 random quadrats within each line to determine the environmental impact of the polythene.  相似文献