~(40)Ar/~(39)Ar geochronology studies of rocks in eastern Himalaya syntaxis
~(40)Ar/~(39)Ar geochronology studies of rocks in eastern Himalaya syntaxis
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发表时间：
2008
影响因子：
1.8
通讯作者：
Gong Jun;Chen Jian
中科院分区：
文献类型：
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作者：
Gong Jun;Chen Jian
对采自喜马拉雅构造结东部雅鲁藏布江峡谷的13个样品中的20种矿物进行了常规~（40）Ar/~（39）Ar年代学研究，结果表明：（1）所测矿物的~（40）Ar/~（36）Ar值接近295.5;（2）大部分高原年龄与其逆等时线年龄在误差范围内雅阁，年龄统计表明，大部分~（40）Ar/~（39）Ar年龄集中在1.3Ma和2.5Ma左右，表明南迦巴瓦地区分别在上新世中期和早更新世经历了两次快速冷却隆升事件，样品采集自峡谷的北方至南部，来自不同的海拔高度，分属不同的构造单元，其原岩的岩石成因和岩性各不相同，但大多数矿物（包括角闪石、黑云母、白云母和钾长石等）的~（40）Ar/~（39）Ar年龄值均低于正常值。不同样品中不同矿物的年龄具有相似性，同一样品中不同矿物的年龄并不按氩同位素体系封闭温度的大小分布，因此，南迦巴瓦地区岩石自上新世以来冷却速度非常快，因而该区矿物氩同位素体系的冷却过程明显不同于缓慢冷却环境，南迦巴瓦地区近3 Ma以来的温度为120~240℃/Ma，隆升速率为3.4~ 6.9mm/a。
Conventional ~(40)Ar/~(39)Ar geochronology studies have been done on 20 separate minerals in 13 samples which are from the Yarlung-Tsangpo River gorge,eastern Himalaya syntaxis.The ~(40)Ar/~(39)Ar geochronology data show that:(1) the values of (~(40)Ar/~(36)Ar); of all the minerals tested are close to 295.5;(2) most plateau ages are accord with their respective inverse isochron ages within error range.Age statistics indicate that most ~(40)Ar/~(39)Ar ages are focused on 1.3Ma and 2.5Ma approximately,indicating that Namjagbarwa region has undergone two fast cooling-uplift events in middle Pliocene and early Pleistocene respectively.The samples are collected from the northern to the southern parts of the gorge,they are from various altitude and belong to different tectonic units,and the petrogenesis and lithology of their protolith are different,but the ~(40)Ar/~(39)Ar ages of most minerals (including hornblende,biotite, muscovite and K-feldspar etc.) from various samples are similar,and the age of different minerals from a single sample are not distributed according to the value of the closure temperature to argon isotopic system.Therefore,it seems that the cooling rate of the rocks in Namjagbarwa region has being so fast since Pliocene that the cooling process to argon isotopic system of minerals from this area are apparently different from ones from slow cooling environment.The cooling rate of Namjagbarwa region has being 120～240℃/Ma and so an uplift rate of 3.4～6.9 mm/a since the latest 3Ma according to the data published in this paper.