Rapid early Miocene acceleration of uplift in the Gangdese Belt, Xizang (southern Tibet), and its bearing on accommodation mechanisms of the India-Asia collision
Rapid early Miocene acceleration of uplift in the Gangdese Belt, Xizang (southern Tibet), and its bearing on accommodation mechanisms of the India-Asia collision
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DOI：
10.1016/0012-821x(87)90224-x
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发表时间：
1987-12
影响因子：
5.3
通讯作者：
P. Copeland;T. Harrison;W. Kidd;Xu Ronghua;Zhang Yuquan
中科院分区：
文献类型：
--
作者：
P. Copeland;T. Harrison;W. Kidd;Xu Ronghua;Zhang Yuquan
在藏南冈底斯岩基的曲水岩体中，以250 m的垂直间隔采集了5个黑云母-角闪石花岗闪长岩相的样品。黑云母的~（40）Ar/~（39）Ar等时线年龄随海拔升高而单调递减，分别为26.8 ± 0.2，23.3 ± 0.5，19.7 ± 0.3，18.4 ± 0.4，17.8 ± 0.1Ma（Tc= 335°C）。共存的钾长石具有几乎相同的最小表观40 Ar/39 Ar年龄，为17.0 ± 0.4Ma（Tc= 285°C）。这些数据表明，藏南部分地区在中新世早期经历了一次脉冲式的隆升，在20 ~ 17 Ma的时间里，隆升速率从0.07 ~ 0.44mm/a。磷灰石裂变径迹年龄为9.9 ± 0.9Ma，表明本区17 ~ 9.9Ma的平均隆升速率为0.81mm/a，9.9Ma至今的平均隆升速率为0.30mm/a。拉萨以东30 km的达孜花岗岩中的钾长石测得的最小~（40）Ar/~（39）Ar年龄为35.9 ± 0.9Ma（Tc= 227°C），表明该地区自那时以来的平均隆升速率为0.21mm/a。曲水花岗闪长岩明显的脉冲式隆升和达孜岩体与曲水岩体隆升历史的差异表明，藏南经历了时间和空间上不连续的脉冲式隆升。这些数据与模型不一致，该模型要求青藏高原的大部分隆起发生在过去的2 Ma。这些数据支持的建议，印度和亚洲之间的会聚主要是由构造逃逸过程中的开放的南中国海32至17 Ma前，并允许分布缩短作为一种机制，地壳增厚和隆起的这一部分的青藏高原后20 Ma。
Five samples from a biotite-hornblende granodiorite phase of the 42.5 Ma Quxu pluton, Gangdese batholith, southern Tibet, have been collected at 250 m vertical intervals. Biotite from these rocks yields monotonically decreasing40Ar/39Ar isochron ages with decreasing elevation of 26.8 ± 0.2, 23.3 ± 0.5, 19.7 ± 0.3, 18.4 ± 0.4,and17.8 ± 0.1Ma (Tc= 335°C). Coexisting K-feldspars have virtually identical minimum apparent40Ar/39Ar ages of 17.0 ± 0.4Ma (Tc= 285°C). These data indicate parts of southern Tibet experienced a pulse of uplift in the early Miocene with the rate of uplift rising from 0.07 to ∼ 4.4 mm/year in the interval 20 to 17 Ma. An apatite fission track age of 9.9 ± 0.9Ma from this locality constrains the average uplift rate at this site to about 0.81 mm/year between 17 and 9.9 Ma and 0.30 mm/year from 9.9 Ma to present. K-feldspar from the Dagze granite, 30 km to the east, near Lhasa, yields a minimum apparent40Ar/39Ar age of 35.9 ± 0.9Ma (Tc= 227°C) which indicates an average uplift rate there of 0.21 mm/year since then. The marked pulse of uplift of the Quxu granodiorite and the difference in uplift history between the Dagze and Quxu plutons suggests southern Tibet has experienced discrete pulses of uplift variable in both space and time. These data are not consistent with models which require a large proportion of uplift of the Tibetan plateau to have occurred in the last 2 Ma. The data support the suggestion that convergence between India and Asia was largely accommodated by tectonic escape during the opening of the South China Sea 32 to 17 Ma ago and permit distributed shortening as a mechanism for crustal thickening and uplift of this part of the Tibetan plateau subsequent to 20 Ma.