Petrogenesis and mineral characteristics of the oldest volcanogenic breccia unit from the Himalayan foreland basin, India

GeoResJ Pub Date : 2017-06-01 DOI:10.1016/j.grj.2017.01.001
M.K. Shukla, Anupam Sharma
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引用次数: 3

Abstract

Jangalgali breccia unit (JBU), the oldest volcanogenic rock unit in the Himalayan foreland basin, has been studied from five different, however, stratigraphically equivalent localities of Jammu region in NW India. The field and thin section slides of JBU reveal that quartz and plagioclase are the two most common minerals and sanidine, magmatic zircon, rutile, hornblende and biotite are present as accessory phases. Petrographic signatures show that quartz and K-feldspar are set in a fine-grained cryptocrystalline glassy matrix and do not represent any preferred orientation. The euhedral hexagonal dipyramidal quartz phenocrysts, irregularly shaped inclusions having high volatile contents and no signatures of transport/reworking in phenocrysts prior to deposition are the prominent petrographic features of JBU. The mineral grains arrangement varies between tight-fitted fabric geometry to more open-chaotic packing. Overall, the field relationship, texture, mineralogy along with mineral chemistry, and presence of high gas and silica content in the host magma, support the volcanic origin of the JBU litho unit, which has wider implications towards understanding the timing of India-Asia collision as well as geodynamic evolution of the Himalayas.

印度喜马拉雅前陆盆地最古老火山角砾岩单元的岩石成因及矿物特征
Jangalgali角砾岩单元(JBU)是喜马拉雅前陆盆地最古老的火山成因岩石单元,在印度西北部查谟地区的五个不同的地层等效位置进行了研究。金红石、角闪石和黑云母为副相,石英和斜长石是最常见的矿物。岩石学特征表明,石英和钾长石嵌套在细粒隐晶玻璃状基质中,不代表任何优先取向。自面体六方双锥体石英斑晶、高挥发性的不规则包裹体和沉积前无输运/改造特征是JBU的突出岩相特征。矿物颗粒的排列在紧密配合的织物几何形状和更开放的混沌填料之间变化。总的来说,矿场关系、结构、矿物学和矿物化学以及寄主岩浆中高气体和二氧化硅含量的存在,支持JBU岩性单元的火山成因,这对理解印度-亚洲碰撞的时间以及喜马拉雅地区的地球动力学演化具有更广泛的意义。
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