The South Tibet detachment shear zone in the Dinggye area: Time constraints on extrusion models of the Himalayas
The South Tibet detachment shear zone in the Dinggye area: Time constraints on extrusion models of the Himalayas
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DOI：
10.1016/j.epsl.2009.12.035
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发表时间：
2010-03
影响因子：
5.3
通讯作者：
P. Leloup;G. Mahéo;N. Arnaud;E. Kali;E. Boutonnet;Dunyi Liu;Xiaohan Liu;Haibing Li
中科院分区：
文献类型：
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作者：
P. Leloup;G. Mahéo;N. Arnaud;E. Kali;E. Boutonnet;Dunyi Liu;Xiaohan Liu;Haibing Li
我们调查了藏南拆离系（STDS）运动结束的时间，这是一个与喜马拉雅山脉平行超过1500公里的主要正断层系统。在定结附近（北纬28°10′，东经87°40′），STD向北倾斜10±5°，将古生代特提斯系与上喜马拉雅结晶系（UHCS）分开。在STD之下，UHCS在STD剪切带中变形强烈，线理走向NNE，剪切方向为NE的顶部。在云母片岩中，P-T轨迹受假剖面和石榴石化学的制约，显示出连续的变质条件：0.6GPa和0.5GPa，分别为0.550 °C和625°C。变形和未变形浅色花岗岩中独居石和锆石的U/Pb定年表明，在拆离体以下约100 m的STD剪切带中，韧性变形至少持续到1016 Ma，但在1015 Ma之前结束。下盘云母的Ar/Ar年龄介于14.6 ~ 13.6Ma之间，表明当时正断层活动持续存在，并迅速冷却至1320 °C。11 Ma前形成的南北向定界活动正断层切割并错断了STDS，从而为STDS运动的结束提供了最小边界。这些数据被解释为反映了0.3GPa（11 km）至0.6GPa（22 km）的折返沿着STDS开始之前，13.6和11 Ma之间结束。13 ~ 11 Ma前，长约1000 km的STDS在Gurla Mandata以东几乎同步停止，同时在增生棱柱体顶部由NNE-SSW向E-W向伸展突然转换，主冲断由下主中央冲断（MCT 1）向主边界冲断（MBT）跳跃，印度和亚洲会聚方向发生变化。这种同步性在逆冲楔或逆冲系统模型的框架中可能比在较低的通道流模型中得到更好的解释。在古尔拉曼达塔以西，STDS似乎提前了5到3 Ma停止，这可能与喀喇昆仑断层的局部相互作用有关，这一点需要理解。
We investigate the timing of end of motion along the South Tibet Detachment System (STDS), a major normal fault system that runs parallel to the Himalayan range for more than 1500km. Near Dinggye (∼28°10′N, 87°40′E), the STD dips ∼10±5° to the North and separates Paleozoic Tethyan series from Upper Himalayan Crystalline Series (UHCS). Immediately below the STD, the UHCS is highly deformed in the STD shear zone, lineations trend NNE and the shear senses are top to the NE. In micaschist, the P–T path constrained by pseudosection and garnet chemistry, shows successive metamorphic conditions of ∼0.6GPa and ∼550°C and 0.5GPa and 625°C. U/Pb dating of monazites and zircons in deformed and undeformed leucogranites suggests that ductile deformation lasted until at least ∼16Ma but ended prior to ∼15Ma in the STD shear zone ∼100m below the detachment. Ar/Ar micas ages in the footwall span between ∼14.6 and 13.6Ma, indicating rapid cooling down to ∼320°C, and suggesting persistence of normal faulting, at that time. The STDS is cut and offset by the N–S trending Dinggye active normal fault which initiated prior to 11Ma thus providing a minimum bound for the end of STDS motion. These data are interpreted as reflecting 0.3GPa (11km) to 0.6GPa (22km) of exhumation along the STDS starting prior to ∼16Ma, ending between 13.6 and 11Ma. The 1000km long stretch of the STDS east of the Gurla Mandata probably stopped almost synchronously between 13 and 11Ma ago, coevally with a sudden switch from NNE–SSW to E–W extension at the top of the accretionary prism, with a jump of the major thrust from the lower Main Central Thrust (MCTl) to the Main Boundary Thrust (MBT), and with a change in the India and Asia convergence direction. This synchronism is probably better explained in the frame of a thrust wedge or thrust system model than a lower channel flow model. West of the Gurla Mandata the STDS appears to stop 5 to 3Ma earlier, possibly related to local interactions with the Karakorum fault in a way that needs to be understood.