Record of Crustal Thickening and Synconvergent Extension from the Dajiamang Tso Rift, Southern Tibet
Record of Crustal Thickening and Synconvergent Extension from the Dajiamang Tso Rift, Southern Tibet
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DOI：
10.3390/geosciences11050209
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发表时间：
2021-05-01
期刊：
影响因子：
2.7
通讯作者：
Ding, Lin
中科院分区：
文献类型：
--
作者：
Burke, William B.;Laskowski, Andrew K.;Ding, Lin
整个西藏中南部的北向裂谷为研究收缩造山带的同向伸展动力学提供了机会。在这项研究中，我们提供了来自大家莽裂谷的新数据，包括根据痕量/稀土元素锆石数据计算的定量地壳厚度，U-Pb年代学，以及锆石-He热年代学。这些资料制约了大家莽裂谷的折返时间和速率，并为评价同向会聚伸展的动力学模式提供了依据。我们的结果还提供了沿印度-亚洲缝合带的喜马拉雅-藏山造山带中白垩世至中新世演化的半连续记录。本文报道了日喀则弧前盆地和冈底斯岩基/林子宗组的火成岩锆石U-Pb年龄分别为103 Ma和70-42 Ma。大逆冲上盘弧前岩石的锆石-氦冷却年龄接近28 Ma，而大家莽左岸裂谷下盘冈底斯弧样的冷却年龄为16~8 Ma。这些数据揭示了沿印度-亚洲缝合带从收缩转换为伸展的大致时间(最小16 Ma)。来自锆石地球化学的地壳厚度趋势显示，在印度-欧亚碰撞开始(58 Ma)之前，地壳可能减薄(接近40公里)。初步碰撞后，在西藏岩浆活动数据库区域资料的支持下，地壳厚度在40 Ma前增加到50公里，并持续增厚到中新世早期。目前基于地球物理观测的地壳厚度估计表明，在东西向伸展(类似于16 Ma)开始后，没有证据表明地壳减薄，这表明现代地壳厚度可能是由上板块伸展平衡的俯冲印度岩石圈促进的。
North-trending rifts throughout south-central Tibet provide an opportunity to study the dynamics of synconvergent extension in contractional orogenic belts. In this study, we present new data from the Dajiamang Tso rift, including quantitative crustal thickness estimates calculated from trace/rare earth element zircon data, U-Pb geochronology, and zircon-He thermochronology. These data constrain the timing and rates of exhumation in the Dajiamang Tso rift and provide a basis for evaluating dynamic models of synconvergent extension. Our results also provide a semi-continuous record of Mid-Cretaceous to Miocene evolution of the Himalayan-Tibetan orogenic belt along the India-Asia suture zone. We report igneous zircon U-Pb ages of similar to 103 Ma and 70-42 Ma for samples collected from the Xigaze forearc basin and Gangdese Batholith/Linzizong Formation, respectively. Zircon-He cooling ages of forearc rocks in the hanging wall of the Great Counter thrust are similar to 28 Ma, while Gangdese arc samples in the footwalls of the Dajiamang Tso rift are 16-8 Ma. These data reveal the approximate timing of the switch from contraction to extension along the India-Asia suture zone (minimum 16 Ma). Crustal-thickness trends from zircon geochemistry reveal possible crustal thinning (to similar to 40 km) immediately prior to India-Eurasia collision onset (58 Ma). Following initial collision, crustal thickness increases to 50 km by 40 Ma with continued thickening until the early Miocene supported by regional data from the Tibetan Magmatism Database. Current crustal thickness estimates based on geophysical observations show no evidence for crustal thinning following the onset of E-W extension (similar to 16 Ma), suggesting that modern crustal thickness is likely facilitated by an underthrusting Indian lithosphere balanced by upper plate extension.