Fluid-rock history of granulite facies humite-marbles from Ambasamudram, southern India.   总被引：1，自引：0，他引：1  

M. Satish-Kumar  H. Wada  M. Santosh  M. Yoshida 《Journal of Metamorphic Geology》2001,19(4):395-410

An extensive humite‐bearing marble horizon within a supracrustal sequence at Ambasamudram, southern India, was studied using petrological and stable isotopic techniques to define its metamorphic history and fluid characteristics. At peak metamorphic temperatures of 775±73°C, based on calcite‐graphite carbon isotope thermometry, the mineral assemblages suggest layer‐by‐layer control of fluid compositions. Clinohumite + calcite‐bearing assemblages suggest X_CO2 < 0.4 (at 700°C and 5 kbar), calcite + forsterite + K‐feldspar‐bearing assemblages suggest X_CO2>0.9 (at 790°C); and local wollastonite + scapolite + grossular‐bearing zones formed at X_CO2 of c. 0.3. Retrograde reaction textures such as scapolite + quartz symplectites after feldspar and calcite and replacement of dolomite + diopside or tremolite+dolomite after calcite+forsterite or calcite+clinohumite are indicative of retrogression under high X_CO2 conditions. Calcite preserves late Proterozoic carbon and oxygen isotopic signatures and the marble lacks evidence for extensive retrograde fluid infiltration, while during prograde metamorphism the possible infiltration of aqueous fluids did not produce significant isotopic resetting. Isotopic zonation of calcite and graphite grains was likely produced by localized CO₂ fluid infiltration during retrogression. Contrary to the widespread occurrence of humite‐marbles related to retrograde aqueous fluid infiltration, the Ambasamudram humite‐marbles record a prograde‐to‐peak metamorphic humite formation and retrogression under conditions of low X_H2O.  相似文献   

Skarns and Genesis of the Huanggang Fe-Sn Deposit, Inner Mongolia, China   总被引：2，自引：0，他引：2  

Li Juan WANG  Hidehiko SHIMAZAKI  Yoshihide SHIGA 《Resource Geology》2001,51(4):359-376

Abstract: The skarns and genesis were studied of the Huanggang Fe‐Sn deposit and the nearby Sumugou Zn‐Pb deposit in Inner Mongolia, China. In the Huanggang mine, Nos. 1 to 4 Fe ore bodies are arranged along a calcareous horizon from proximal to distal in this order to a granite intrusion named Luotuochangliang, while Sn ore body is situated near another granite intrusion named 204. According to the distance from the granitic intrusions, mineral assemblages in skarns are systematically changed. Garnet is the most predominant skarn mineral throughout the deposit. Hastingsitic amphiboles, however, predominate in the proximal skarns. Fluorite is common in the proximal skarns, while instead calcite is common in the distal skarns. Chlorite is characteristically present only in No. 3 ore body, and chlorite geothermometry gives near 300C for the mineralization of later stage. When garnet crystal shows zonal structure, isotropic andraditic garnet occupies the core, and is surrounded with anisotropic less‐andraditic garnet. The presence of white skarn along the boundary between main skarns and host sedimentary rocks confirms relatively reducing environment prevailing as a whole in the studied area. However, the compositional relation between coexisting garnet and clinopyroxene demonstrates that relatively oxidizing condition was achieved for garnet skarn and magnetite ore in the distal, Nos. 2 to 4 Fe ore bodies and Sumugou deposit, compared to that for garnet skarn in the proximal, No. 1 and Sn ore bodies. Preliminary study on the tin content of garnets in the studied area revealed a certain degree of contribution brought from granitic intrusives since the early stage of skarn formation, irrespective of proximal or distal. Oxygen isotope study on garnet, magnetite, quartz and skarn calcite, as well as hydrogen isotope study on hastingsitic amphibole, demonstrates mainly meteoric water origin for the skarn– and ore‐forming solutions. The occurrence of Sn, W, Mo and F minerals indicates that those elements were mainly supplied to the deposit later than the formation of skarns and iron ores, overlapping to them. These constraints allow to delineate the formation model of the deposit as follows (Fig. 10): At the time of late Jurassic to early Cretaceous, felsic activity occurred in this region as a part of Yanshanian magmatism, and formed granitic intrusions as well as thick volcanic piles on the surface. The circulation of meteoric water was provoked by the heat brought by the intrusions. By this circulation, much amount of iron was extracted from andesites of the Dashizhai Formation, and precipitated as skarns and magnetite ores along calcareous horizons near the bottom of the Huanggangliang Formation. Subsequently, volatile‐rich fluids with Sn, W and Mo were expelled from the solidifying granitic magmas, and precipitated these metals in the pre‐existing skarns and ores.  相似文献   

潜在震源区内部空间非均匀分布地震区划方法在攀西地区和晋中南地区的应用   总被引：2，自引：1，他引：2  

高孟潭  胥广银 《中国地震》1996,(Z1)

本文依据潜在震源区内部地震非均匀分布模型研究了攀西地区和晋中南地区地震区划问题。研究结果表明，一般使用的均匀分布模型会低估地震危险性结果，导致高烈度分区的面积缩小。本文讨论了不同的确定非均匀分布概率的方法对地震区划结果的影响。  相似文献   

Research　on　seismic　intensity　zonation　by　use　of　the　response　intensity　of　historical　earth－quakes───with　the　central　part　of　Shanxi　Province　as　an　example     

贾素娟  鄢家全 《地震学报(英文版)》1996,(4)

Ｒｅｓｅａｒｃｈｏｎｓｅｉｓｍｉｃｉｎｔｅｎｓｉｔｙｚｏｎａｔｉｏｎｂｙｕｓｅｏｆｔｈｅｒｅｓｐｏｎｓｅｉｎｔｅｎｓｉｔｙｏｆｈｉｓｔｏｒｉｃａｌｅａｒｔｈ┐ｑｕａｋｅｓｗｉｔｈｔｈｅｃｅｎｔｒａｌｐａｒｔｏｆＳｈａｎｘｉＰｒｏｖｉｎｃｅａｓａｎｅｘ...  相似文献   

白垩纪红层冰筏沉积的古气候及古地理意义   总被引：3，自引：1，他引：3       下载免费PDF全文

王东坡  刘立  L. A. Frakes 《沉积与特提斯地质》1996,16(4):6-11

冰筏沉积是负载沉积物的冰块进入海洋或湖泊中，冰块融化沉积物附落所形成的，它们可形成于高海拔具有明显气候垂直分带的低纬度地区或者是高纬度地区。我们在研究松辽盆地白垩纪古气候时，首次在泉头组层中发现冰筏沉积。根据泉头组孢粉组合的研究透明，它们除了具有热带－亚热植物的孢粉以外，还有少量喜冷分子混生现象。  相似文献   

上海金山张堰铜矿床地质特征     

张宏良  张洁 《上海国土资源》1996,(4):9-15

通过详查评价，提高了对矿床地质特征的研究程度。在继续肯定矿床的成矿严格受张堰花浆长岩体与金群的接触带控制的同时，对矿床的主要赋矿地层即外接带金山群的分层，构造其各类岩性组成在矿过程中的作用进行了详尽的厘定。  相似文献   

在确定潜在震源区中地震和地质资料的应用   总被引：3，自引：4，他引：3       下载免费PDF全文

张裕明 《地震地质》1992,14(3):275-278

在确定潜在震源区中如何应用地震和地质资料是编制中国地震烈度区划图(1990)的关键问题,包括如何利用地震和地质资料来勾划地震带和潜在震源区的范围和方向,以及确定本底地震和潜在震源区的震级上限  相似文献   

矿物学填图揭示金矿脉的隐蔽分带性：以玲珑金矿52号脉为例   总被引：1，自引：0，他引：1  

刘星 《矿物学报》1992,12(3):227-234

胶东许多金矿脉的矿物组合很简单,几乎全是石英、黄铁矿,难于进行分带性研究。通过对玲珑金矿52号脉的矿物学填图研究,发现该矿脉从上向下,黄铁矿的晶体形态{111}减少而{210}增加,+α值减小,P导型减少而N导型增加;石英的热发光强度增大。这些物性参数在矿脉空间的规律性变化,揭示了外观很单一的矿脉内部隐蔽着的空间分带性,并发现与金矿化强度有密切关系。研究结果还表明,52号脉在海拔+170m以上主要为上部矿体特征,受剥蚀程度不大,深部远景还大;成矿热液近于直立运移并具有水平方向的等距波动性;预测三个区段深部应保持良好矿化。以后的钻探工程证实了预测。  相似文献   

矽卡岩浆型铜矿床特征——以安徽铜陵东狮子山铜矿床为例   总被引：9，自引：0，他引：9       下载免费PDF全文

张叔贞  凌其聪 《地球科学》1993,2(6)

东狮子山铜矿床具有下列独特的特征:(1)矽卡岩是高温、高密度、粘稠的岩浆熔融体;(2)矽卡岩体与辉石二长岩体具有同源性;(3)矿体与矽岩体具有同源性;(4)成矿物质来自岩浆源,硫同位素测定的绝对值小于5‰;(5)矽卡岩矿物开始结晶温度为920C,可见熔融包裹体,成矿温度为620C;(6)成矿压力相当于1～2km深度条件;(7)矿石、矽卡岩具有典型的岩浆矿床的结构构造。  相似文献   

广东兴宁铁山嶂铁矿床地质特征及成因探讨     

黄云皇 《地质论评》1993,39(1):23-30

本文讨论了矿区夕卡岩和铁矿成因。夕卡岩主要受围岩岩性控制,有固定的层位,属层控夕卡岩。铁矿赋存于有火山岩、含泥镁质灰岩夹层的碎屑岩中,受地层、岩性控制。它是在沉积或火山—沉积作用的基础上,经过改造而成的矿床。矿床具多层性,矿体呈层状、顺层整合产出。它们不论沿走向还是向深部延伸都受一定地层层位和岩性控制。属沉积或火山—沉积热变质改造的层控矿床。  相似文献