权益分类	功能权益	普通用户	{{item.name}}会员
{{category.name}}	{{benefitItem.name}}

Reconstruction of geologic history of Indus suture zone of Ladakh, Indian Himalayas, by high resolution fossil and radiometric ages

通过高分辨率化石和辐射年龄重建印度喜马拉雅山拉达克印度河缝合带的地质历史

基本信息

批准号：
16403008
负责人：
KOJIMA Satoru
金额：
$ 5.89万
依托单位：
Gifu University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2004
资助国家：
日本
起止时间：
2004 至 2006
项目状态：
已结题

项目摘要

Main results of this project are summarized as follows.1. Late Triassic to Early Cretaceous radiolarians are found from chert clasts in the Hemis Conglomerate (syn-collisional Molasse sequence) along the Indus suture zone. Since the chert is considered to have been part of the ocean-plate cover sediments, these fossil evidence shows the pre-Late Triassic opening of the Ceno-Tethys (pre-Late Triassic rifting of Karakoram block from the northern margin of Gondwana) in Ladakh Himalayas.2. Shelf-facies marine formations along the Shyok suture zone are subdivided into the Middle Jurassic (Callovian) ammonoids-bearing Soltak Formation and Middle Cretaceous Shyok Formation with Albian Orbitolina. These fossils strongly indicate that the ocean along the Shyok suture was closed in the post-Middle Cretaceous time.3. Plutonic rocks of the Ladakh arc which were formed by the subduction of oceanic plate of Ceno-Tethys are calc-alkaline on the basis of their mineralogy and geochemistry, and have K-Ar ages of 50-51 Ma. Granite and diorite with calc-alkaline signature and 64-66 K-Ar ages are also distributed on the northern margin of the arc. These lines of evidence clearly show that the arc magmatism had continued at least for sixteen million years during 50-66 Ma before the collision between Eurasia and India.4. Mylonites along the Karakoram fault have vertical lineation and extensional deformation structures together with the right-lateral strike-slip shear indicators designating same sense as the present-day activity. These structures show a long and complicated deformation history more than fifteen million years until now. Aspect ratios of dynamically recrystallized quartz grains suggest that the width of shear zone has narrowed with the decreasing temperature of the fault zone.

本项目的主要成果总结如下：晚三叠世至早白垩世放射虫产于沿印度河缝合带的Hemis砾岩（同碰撞Molasse层序）中的燧石碎屑中。由于硅质岩被认为是海洋板块覆盖沉积物的一部分，这些化石证据表明，喜马拉雅拉达克地区的Ceno-Tethys（冈瓦纳北缘喀喇昆仑地块的晚三叠世前裂陷）在晚三叠世之前开放。沿Shyok缝合带的陆棚相海相地层可划分为中侏罗统（Callovian）含氨石的Soltak组和中白垩统含Albian Orbitolina的Shyok组。这些化石有力地表明，在中白垩纪后期，Shyok缝合线沿线的海洋是封闭的。拉达克弧深部岩体是由新生代-特提斯洋板块俯冲形成的，其矿物学和地球化学特征显示其钙碱性，K-Ar年龄为50 ~ 51 Ma。弧北缘还分布有钙碱性特征的花岗岩和闪长岩，K-Ar年龄为64 ~ 66岁。这些证据清楚地表明，在欧亚大陆和印度碰撞之前的50-66 Ma期间，弧岩浆活动至少持续了1600万年。喀喇昆仑断裂带糜棱岩具有垂直线理和伸展变形构造，其右侧走滑剪切标志与现今活动意义相同。这些结构显示了一个漫长而复杂的变形历史，到现在已经超过1500万年。动态再结晶石英晶粒长径比表明，随着断裂带温度的降低，剪切带的宽度逐渐变窄。