Magnetotelluric Evidence for Distributed Lithospheric Modification Beneath the Yinchuan‐Jilantai Rift System and Its Implications for Late Cenozoic Rifting in Western North China
Magnetotelluric Evidence for Distributed Lithospheric Modification Beneath the Yinchuan‐Jilantai Rift System and Its Implications for Late Cenozoic Rifting in Western North China
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DOI：
10.1029/2021jb022585
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发表时间：
2022-02
期刊：
影响因子：
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通讯作者：
Xin Li;Yuxiang Chen;Xiaobo Tian;Shaozhuo Liu
中科院分区：
文献类型：
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作者：
Xin Li;Yuxiang Chen;Xiaobo Tian;Shaozhuo Liu
银川—吉兰台裂谷系（YJRS）是位于华北西部鄂尔多斯地块西北缘的一条重要的新生代陆内裂谷带。尽管火山活动的缺失表明了被动起源，但构造驱动力和与裂谷相关的深层过程仍然知之甚少。在这里，我们使用新获得的宽带大地电磁 (MT) 数据对 YJRS 沿约 500 公里长的剖面的岩石圈电结构进行成像。在中下地壳层面，所得模型揭示了几个近垂直的地壳尺度导体，它们在空间上与裂谷平行的高角度正断层相关。我们将这些特征归因于盐分流体和由于最近从下方向地壳供应热量和挥发物而导致的部分融化的综合作用。在伸展过程中重新激活的穿地壳正断层充当了深层流体运移的渗透通道。在最上地幔中，存在约 400 公里宽的导电性增强区域，并且需要存在部分熔融。我们将此特征解释为通过富含挥发分的地幔的上升流和减压熔融而改变岩石圈的证据。与沿鄂尔多斯地块东缘山西裂谷系成像的狭窄（<100公里宽）地幔导体相比，这一特征表明YJRS经历了更大程度的岩石圈改造。结合额外的地质和地球物理观测，我们将这种本质差异归因于继承的岩石圈非均质性和印度-欧亚大陆碰撞造成的向东递减的远场影响。
The Yinchuan‐Jilantai rift system (YJRS) is a prominent Cenozoic intracontinental rift zone located along the northwestern margin of the Ordos Block in western North China. Although the absence of volcanism indicates a passive origin, the tectonic driving forces and rift‐related deep processes remain poorly understood. Here we use newly obtained broadband magnetotelluric (MT) data to image the lithospheric electrical structure along a ∼500‐km‐long profile across the YJRS. At middle–lower crustal levels, the resulting model reveals several subvertical, crustal‐scale conductors that spatially correlate with the rift‐parallel, high‐angle normal faults. We attribute these features to a combined effect of saline fluids and partial melt due to recent supply of heat and volatiles into the crust from below. The crustal‐penetrating normal faults that were reactivated during extension serve as permeable pathways for deep fluid migration. In the uppermost mantle, a ∼400‐km‐wide zone of enhanced conductivity is present and requires the presence of partial melt. We interpret this feature as evidence for lithospheric modification through upwelling and decompressional melting of the volatile‐enriched mantle. When compared with the narrow (<100‐km‐wide) mantle conductors imaged beneath the Shanxi rift system along the eastern margin of the Ordos Block, such a feature indicates the YJRS has experienced a larger extent of lithospheric modification. Combined with additional geologic and geophysical observations, we attribute this essential difference to the inherited lithospheric heterogeneity and the eastward decreasing far‐field impacts from the India‐Eurasia collision.