The Deccan Traps in Space and Time: Geochemical Studies of the Eastern Deccan, Lower Western Ghats, and Madagascar

这是一个由三部分组成的分析程序，旨在利用现有记录良好的样本研究与德干有关的火山活动的基本方面；目标是从深入研究的西南部地区向外扩展知识，开始了解板块构造框架中巨大的德干事件以及与其他大型大陆溢流玄武岩的关系。1)现有的化学证据表明，德干西部的下六个组并不是简单地重复后来的五个较高级别的组的地球化学，现在已经很好地了解了这五个组。建议对下部组的熔岩进行Nd值、Pb值和Sr值的同位素研究。组合的化学和同位素数据将被用来评估其地幔来源的性质和演化(S)，在德干演替早期的混染作用和机制，以及与上复建造的关系。特别是古老的岩石圈地幔源区被软流圈源区取代；而AFC流程是否在早期占据主导地位，正如预测的那样？2)来自马达加斯加南部和东部的一套更早的溢流玄武岩代表了印度本土火山活动的一个阶段(70-80英里)。为了追踪火山活动的开始阶段，将对一套马达加斯加熔岩进行测量，结合岩相学、主量元素和微量元素，以及Frency Collegues的地质年代学工作，测量Ndsr和Pb值。3)尽管最近发现了一个包含德干西部组的巨大背斜构造，但该省东西向的地球化学地层学仍然完全未知。一种极端的观点认为，德干中部和东北部的熔岩只是西部建造的远端边缘(最远可达1000公里或更远)；另一种观点认为，前者的大部分或全部是从纳尔马达-孙线沿线的岩脉中更局部地喷发出来的，因此应该反映了它们独特的岩石成因。奥兰加巴德、奇卡尔达拉和那格浦尔地区W-I剖面的同位素、化学和岩石学数据将直接证实这两个相互冲突但关键的假设。

This is a thre-part analytical program to investigate fundammental aspects of Deccan-related volcanism using existing well-documented smaples; the goal is to expand knowledge outward from the intensively studied southwestern region, to begin to understand the huge Deccan episode ina plate-tectonic framework and with respect to other large continental flood basalts. 1) Existing chemical evidence shows that the lower six formations of the western Deccan do not simply repeat the geochemistry of the Five later, upper level formations, now quite well understood. A Nd, Pb, and Sr isotopic study of otherwise thoroughly characterized lavas from the lower formations is proposed. The combined chemical and isotopic data will be used to evaluate the nature and evolution of their mantle source(s), the roles and mechanisms of contamination early in the Deccan succession, and relationships to the overlying formations. In particular, were ancient lithospheric mantle sources supplanted by asthenospheric sources; and did AFC processes dominate early on, as has been predicted? 2) An even earlier suite of flood basalts from southern and eastern Madagascar represents a stage of volcanism (70-80 Myr) in India proper. Nd, Sr, and Pb isotopic ratios will be measured on a set of Madagascar lavas, in conjunction with petrographic, major and trace element, and geochronological work by Frency collegues, in order to trace the beginning phases of volcanic activity. 3) Though a huge anticlinal structure incorporating the western Deccan formations has been indentified recently, the geochemical stratigraphy of the province in a W-E direction remains completely unknown. On extreme view holds that lavas in the central and northeastern Deccan are simply distal fringes of the western formations (up to 1000 km or more away); another that most or all of the former were erupted more locally from dikes along the Narmada-Son Lineament and thus should reflect their own unique petrogenesis. Isotopic, chemical, and petrographic data on sections running W-I from Aurangabad, Chikaldara, and Nagpur areas will directly text these two conflicting but critical hypotheses.