Breccia-cored columnar rosettes in a rubbly pahoehoe lava flow,Elephanta Island,Deccan Traps,and a model for their origin     

Hetu Sheth  Ishita Pal  Vanit Patel  Hrishikesh Samant  Joseph D&#x;Souza 《地学前缘(英文版)》2017,8(6):1299-1309

Rubbly pahoehoe lava flows are abundant in many continental flood basalts including the Deccan Traps. However, structures with radial joint columns surrounding cores of flow-top breccia (FTB), reported from some Deccan rubbly pahoehoe flows, are yet unknown from other basaltic provinces. A previous study of these Deccan “breccia-cored columnar rosettes” ruled out explanations such as volcanic vents and lava tubes, and showed that the radial joint columns had grown outwards from cold FTB inclusions incorporated into the hot molten interiors. How the highly vesicular (thus low-density) FTB blocks might have sunk into the flow interiors has remained a puzzle. Here we describe a new example of a Deccan rubbly pahoehoe flow with FTB-cored rosettes, from Elephanta Island in the Mumbai harbor. Noting that (1) thick rubbly pahoehoe flows probably form by rapid inflation (involving many lava injections into a largely molten advancing flow), and (2) such flows are transitional to ‘a’ā flows (which continuously shed their top clinker in front of them as they advance), we propose a model for the FTB-cored rosettes. We suggest that the Deccan flows under study were shedding some of their FTB in front of them as they advanced and, with high-eruption rate lava injection and inflation, frontal breakouts would incorporate this FTB rubble, with thickening of the flow carrying the rubble into the flow interior. This implies that, far from sinking into the molten interior, the FTB blocks may have been rising, until lava supply and inflation stopped, the flow began solidifying, and joint columns developed outward from each cold FTB inclusion as already inferred, forming the FTB-cored rosettes. Those rubbly pahoehoe flows which began recycling most of their FTB became the ‘a’ā flows of the Deccan.  相似文献   

~(40)Ar-~(39)Ar Dating of Albite and Phlogopite from Porphyry Iron Deposits in the Ningwu Basin in East-Central China and Its Significance   总被引：2，自引：1，他引：1  

YU Jinjie  MAO Jingwen Institute of Mineral Resources  Chinese Academy of Geological Sciences  Beijing 《《地质学报》英文版》2004,78(2):435-442

40Ar-39Ar dating of albite from the Meishan and Taocun iron deposits yields plateau ages of 122.90±0.16 Ma and 124.89±0.30 Ma, and isochron ages of 122.60±0.16 Ma and 124.90±0.29 Ma, respectively. Phlogopite from the Zhongshan-Gushan ore field has a plateau age of 126.7±0.17 Ma and an isochron age of 127.21±1.63 Ma. Analysis of regional geodynamic evolution of the middle-lower Yangtze River region suggests that the porphyry iron deposits were formed as a result of large-scale lithosphere delamination and strong sinistral strike-slip movement of the Tancheng Lujiang fault zone. The copper, molybdenum and gold deposit system in the middle-lower Yangtze River region was formed during the stress transition period of the eastern China continent.  相似文献   

Morphology of rubbly pahoehoe (simple) flows from the Deccan Volcanic Province: Implications for style of emplacement     

Raymond A. Duraiswami  Ninad R. Bondre  Shreyas Managave 《Journal of Volcanology and Geothermal Research》2008

Lava flows with preserved bases and brecciated upper crusts constitute a morphological type that differs in character from typical pahoehoe and a'a: such flows have been reported from many provinces around the world. Previous studies had referred to these flows informally as ‘pahoehoe flows with rubbly tops’, ‘broken-top pahoehoe’ and ‘rubbly pahoehoe’. Recent studies have formally applied the latter term to describe parts of the well-studied Laki flow in Iceland as well as flows from the Columbia River Basalt province. Rubbly pahoehoe flows are abundant in the upper stratigraphic formations of the Deccan Volcanic Province (DVP), and are more commonly known as simple flows. This study presents detailed observations of such flows from various parts of the DVP and discusses their implications for understanding flow emplacement. These flows, which appear to be single units at the outcrop-scale, are generally much thicker and significantly more extensive than individual pahoehoe lobes that dominate the lower formations of the Deccan stratigraphy. They are characterised by preserved, gently undulating tachylitic bases but variably disrupted crustal zones that grade into flow-top breccias. The breccias are constituted of highly vesicular and oxidised fragments of varying sizes that appear to have been derived from previously formed pahoehoe crusts. Previous work has indicated that the morphology of these flows might be related to initial inflation, accompanied by rapid volatile exsolution and an increase in effusion rate and/or viscosity with time. This agrees reasonably well with the qualitative and quantitative models of emplacement developed for the Laki flow. The abundance of such flows in the upper formations of the Deccan stratigraphy clearly hints at a significant shift in the nature of the Deccan eruptions; this could be indicative of higher eruption rates during this period. This, in turn, raises the possibility of hazardous impact on the climate during the eruption of these flows, which is also discussed in the paper.  相似文献   

角砾岩型金矿床——种值得重视的金矿床类型   总被引：7，自引：3，他引：4       下载免费PDF全文

罗镇宽  苗来成  关康 《地质找矿论丛》1999,14(4):15-23

角砾岩型金矿床量种重要的金矿床类型。中国角砾岩型金矿床分为四种主要类型：与小侵入岩体有关的角砾岩型金矿床,与斑岩系统有关的角砾岩型金矿床;与火山一次火山岩有关的角砾岩型金矿床;产在不整合面或沉积间断面上的角砾岩型金矿床,文章在对第类矿床实例进行矿床地质特征描述后,分析了战国角砾岩金矿床的找矿前景并指出寻找角砾岩型金矿床最有希望的地区。  相似文献   

新疆伊宁县伊尔曼德热泉型金矿床地质特征及成因   总被引：22，自引：3，他引：19  

翟伟  杨荣勇  漆树基 《矿床地质》1999,18(1):47-54

伊尔曼德金矿床赋存于下石炭统大哈拉军山组第二岩性段硅化热液喷发角砾岩及其下伏上泥盆统吐呼拉苏组毒砂黄铁矿化凝灰质碎屑岩中,成矿作用可分为热液喷发沉积期和热液交代蚀变成矿期。由热液喷发作用形成的热液喷发角砾岩等热水沉积物,使金发生初步富集,循环的地下水热液与热液喷发角砾岩发生强烈的交代硅化蚀变作用,使金进一步富集而形成矿热泉型金矿床。含矿岩石富含Ａｕ、Ａｇ、Ａｓ、Ｓｂ、Ｈｇ、Ｂｉ,贫Ｃｕ、Ｐｂ、Ｚｎ  相似文献   

东准噶尔成矿带岩浆隐蔽爆破作用与成矿     

喻亨祥  夏斌  林锦富  刘家远  胡承琦 《地质论评》1999,45(6)

新疆东准噶尔地区乌伦布拉克铜矿、老山口铜—铁—金矿两地皆存在花岗质岩浆隐蔽爆破作用。前者形成了与潜火山英安玢岩侵入体密切伴生的英安玢岩质隐爆角砾岩,后者形成了与潜火山闪长玢岩侵入体相伴生的闪长玢岩质隐爆角砾岩和闪斜煌斑岩质隐爆角砾岩。岩浆隐蔽爆破作用是伴随该区华力西中晚期—晚期地槽褶皱造山运动而发生的一种超浅成岩浆作用,其与铜、金等金属成矿的关系密切;与其有关形成了隐爆角砾岩筒型铜(金)矿和破碎带蚀变岩型金矿。两种类型的矿床都显示出广阔的找矿前景。  相似文献   

钠长花岗岩—H2O—HF体系相关系及含黄玉花岗质岩石的成因   总被引：3，自引：0，他引：3  

熊小林  朱金初 《地质论评》1999,45(3):313-313

在Ｐ＝１００ＭＰａ,ｔ＝８４０－４５０℃条件下,通过钠长花岗岩Ｈ２Ｏ－ＨＦ体系相关系实验获得;（１）随体系Ｆ含量的增加,固相线温度显著下降。（２）石英和黄玉的温度稳定域上限升高,碱性长石的稳定域上限降低;在Ｆ≤４％时,体系能在固线性之上结晶出典型的黄玉花岗岩矿物组合;在Ｆ＝６％时,体系能在固相线之上结晶出典型的黄玉云英矿物组合;（２）含氟浅色花岗质熔体具有能分异出极端富Ｆ残余熔体的趋势。  相似文献   

豫西杜关锰银矿田火山隐爆角砾岩特征及其形成机制     

魏俊浩  袁艳宾  刘晓峰 《地质论评》1999,45(7):631-635

豫西杜关锰银矿田火山隐爆角砾岩的形成主要与气液挥发分和超浅成的燕山期闪长岩及闪长玢岩有关,并受该地区近东西向深断裂的控制,而火山隐爆角砾筒又控制着杜关地区锰银矿床（点）的分布,豫西杜关锰银矿田由若干个矿床（点）构成,矿田内已发现多处隐爆角砾岩筒,这些火山机构均与成矿有密切的关系。本文介绍了两个主要火山隐爆角砾岩筒的地质特征,并论述了两类隐爆角砾岩的形成机制。原地棱角状火山角砾岩是由火山爆发震碎作用造成的,异地溶蚀状角砾岩是由流化作用造成的。  相似文献   

山东五莲七宝山地区长老庄隐爆角砾岩带特征及意义          下载免费PDF全文

李双飞  陈建  黄鹂  朱伟  商祥鸿  高远  唐名鹰  管翔  邹占春  华磊 《山东国土资源》2023,39(3)

七宝山金铜矿位于胶莱盆地西南缘的七宝山地区,在金铜矿外围新发现长老庄含矿隐爆角砾岩带一条, 物探解译工作初步查明了该隐爆角砾岩带地质及地球物理特征：位于激电中梯高阻和低阻接触带上,深部呈低阻、中高激化异常。经钻探验证,在深部发现高品位的银铜铅矿体,矿石中粗粒方铅矿、黄铜矿结晶体肉眼可见,呈团块状富集,铜品位0.493%～5.125%,铅品位0.245%～6.606%,银品位55.2～547.1g/t。表明在金铜矿外围及深部仍具有寻找隐爆角砾岩型高品位银铜铅矿体的潜力。  相似文献   

吉林香炉碗子金矿床成矿地质特征及成因   总被引：1，自引：0，他引：1  

冯建忠  雒利平 《黄金地质》2000,6(3):8-12

吉林香炉碗子金矿位于华北地台北缘柳河地堑西侧太古宇鞍山群斜长角闪片麻岩,斜长角闪岩,变粒岩中,为一典型的隐爆角砾岩筒型中型金矿床。在空间和成因上受控于爱林东山,爱林西山隐爆角砾岩体。矿体呈脉状产于角砾岩内的蚀变破碎带中,流体包裹体以液相为主,盐度５．７％￣１３．５％,成矿温度１７３￣３５５℃,包裹体成分表明为Ｈ２Ｏ－ＣＯ２－ＮａＣｌ体系。矿床成因属次火山岩隐爆期后成矿的蚀变岩型金矿。  相似文献