中间裂谷边缘同裂谷岩浆作用与构造伸展之间的相互作用
Interactions between syn-rift magmatism and tectonic extension at intermediate rifted margins
AI总结：
本研究通过二维数值模型揭示，南海中间裂谷边缘中，继承的高地温梯度使同裂谷岩浆侵入促进拆离断层与核杂岩形成，最终生成正常洋壳，凸显继承性对边缘结构的关键作用。
摘要：
中间裂谷边缘在陆洋转换带（COT）既不表现出向海倾斜反射体，也不表现出地幔剥露。相反，它们转变为正常厚度的、岩浆型彭罗斯型洋壳，因此不同于经典的富岩浆和贫岩浆端元模型。然而，几个中间边缘，如南海（SCS），显示出类似于贫岩浆边缘的拆离断层作用以及典型富岩浆边缘的岩浆底侵作用。在这些中间环境中，构造与岩浆作用如何相互作用尚不清楚。这里我们使用二维数值模型来证明，南海继承自先前板块俯冲的高初始地温梯度解释了几个关键观测：早期宽裂谷阶段，随后定位于具有大量下盘岩浆侵入的核杂岩，以及最终在破裂时形成正常火成洋壳。同裂谷下盘岩浆侵入引起的热弱化促进了下地壳韧性流动，推动了滚动铰链型拆离断层的发展和核杂岩的剥露。这些结构与加速的构造沉降相关，之后被与拆离相关的穹隆作用所缓和，正如在南海所观测到的。即使在我们的模拟中使用的超慢伸展速率下，破裂后也会出现正常厚度的洋壳，这强调了继承性在决定边缘结构、同裂谷岩浆作用的时空分布以及陆洋转换带性质方面的重要性。这种行为与贫岩浆边缘形成鲜明对比，在贫岩浆边缘，较冷的岩石圈和类似的超慢伸展不产生同裂谷岩浆作用，反而导致地壳脆化、地幔蛇纹石化和在陆洋转换带的剥露。
英文摘要：
Intermediate rifted margins exhibit neither seaward dipping reflectors nor exhumed mantle at the continent-ocean transition (COT). Instead, they transition into normal-thickness, magmatic Penrose-type oceanic crust, and thus diverge from the classic magma-rich and magma-poor end-member models. However, several intermediate margins, such as the South China Sea (SCS), display detachment faulting similar to magma-poor margins and magmatic underplating typical of magma-rich ones. How tectonics and magmatism interact in these intermediate environments is poorly understood. Here we use 2D numerical models to demonstrate that the elevated initial geotherm inherited from prior plate subduction in the SCS explains several key observations: an early phase of wide rifting, subsequent localization onto core complexes with substantial footwall magmatic intrusions, and eventual formation of normal igneous oceanic crust at break-up. Thermal weakening caused by syn-rift footwall magmatic intrusions facilitates lower crustal ductile flow, promoting the development of rolling-hinge type detachment faults and exhumation of core complexes. These structures are associated with accelerated tectonic subsidence, which is later moderated by detachment-related doming, as observed in the SCS. Normal-thickness oceanic crust occurs after break-up, even under ultra-slow extension rates used in our simulations, highlighting the importance of inheritance in determining margin architecture, the spatio-temporal distribution of syn-rift magmatism, and the nature of the COT. This behavior contrasts sharply with magma-poor margins, where a cooler lithosphere and similar ultra-slow extension produce no syn-rift magmatism, leading instead to crustal embrittlement, mantle serpentinization and exhumation at the COT.
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