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Himalayan uplift by means of mineral dating and petrological study.

通过矿物测年和岩石学研究进行喜马拉雅隆起。

基本信息

批准号：
61540550
负责人：
ARITA Kazunori
金额：
$ 1.09万
依托单位：
Hokkaido University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1986
资助国家：
日本
起止时间：
1986 至 1987
项目状态：
已结题

项目摘要

The Himalayas heve been uplifted since Neogene. The uplift process of the Himalayas, as well as the relationship between the uplift and the movement of the Main Central Thrust zone, was investigated on the basis of metamorphic and tectonic studies in central Nepal and mineral datings by K-Ar and fission track methods. The following conclusions are reached:1. The Himalayas have undergone the polymetamorphism of barrovian-type metamorphism in Paleogene and shear-heating metamorphism in Neogene apart from some episodes of metamorphism in older ages.2. The meso- to micro- structural analyses on rocks of the Lesser and Higher Himalayas show that four stage of deformation are recognized in central Nepal and that activity of the second stage, which is due to thrusting of the Main Central Thrust zone, is most intense and extensive.3. The K-Ar ages of 61.5<plus-minus>3.1 Ma (hornblende) and 56.7<plus-minus>2.8 Ma(biotite) of the Himalayan gneisses are considered to show the cooling stage of the Paleogene metamorphd st4. Fission track datings on apatite and garnet from the Himalayan gneisses were unsuccessful owing to deficiency of their uranium content.5. Fission track ages of 14 zircons from 4 areas in the Himalayan gneiss zone have been dated to be 2.2-0.6 Ma with errors of 0.2-0.1 Ma. These ages are considered to show the cooling stage of the Neogene metamorphism.6. The relationsphi of these fission track ages to the elevation where the rock samples were collected indicates that the uplift rates of the Himalayan gneiss zone during 2.2-0.6 Ma are 3.24mm/y and 2.39mm/y for the ridge areas and 0.83mm/y and 0.47mm/y for the valley areas.7. Under the assumption that the anealing temperature of zircon is 200゜C and the geothermal gradient is 30゜C/km, the uplift rates during Quaternary are estimated to be 3.5-6.1mm/y. Therfore, the uplift rate of the Himalayas was accelerated in Quaternary.

自新近纪以来，喜马拉雅山脉一直在抬升。在尼泊尔中部变质和构造研究以及K-Ar和裂变径迹法矿物测年的基础上，研究了喜马拉雅山的隆升过程以及隆升与主中央冲断带运动的关系。得出以下结论： 1．喜马拉雅山除发生过一些晚时期的变质作用外，还经历了古近纪巴罗夫型变质作用和新近纪剪切加热变质作用。2．对小喜马拉雅山和高喜马拉雅山岩石的细观和微观结构分析表明，尼泊尔中部存在四期变形，其中第二期的变形活动最为强烈和广泛，这是由于主中央逆冲带的逆冲作用所致。3．喜马拉雅片麻岩的K-Ar年龄为61.5±3.1 Ma（角闪石）和56.7±2.8 Ma（黑云母），被认为显示了古近纪变质st4的冷却阶段。由于铀含量不足，对喜马拉雅片麻岩中的磷灰石和石榴石进行裂变径迹测年未能成功。5．喜马拉雅片麻岩带4个地区的14颗锆石裂变径迹年龄为2.2-0.6 Ma，误差为0.2-0.1 Ma。这些年龄被认为显示了新近纪变质作用的冷却阶段。6．这些裂变径迹年龄与岩石样品采集海拔的关系表明，喜马拉雅片麻岩带2.2-0.6 Ma期间的隆升速率，山脊地区为3.24mm/y和2.39mm/y，山谷地区为0.83mm/y和0.47mm/y。7．假设锆石退火温度为200゜C，地温梯度为30゜C/km，则第四纪抬升速率预计为3.5～6.1mm/y。因此，第四纪喜马拉雅山的隆升速度加快。