The region of northern Borneo in South East Asia sits within a post-subduction setting formed by the recent termination of two sequential but opposed subduction systems. In this study we use seismic data from a recent temporary array deployment to image the crustal velocity structure beneath northern Borneo using a two-stage Bayesian trans-dimensional tomography scheme, in which period dependent phase velocity maps are first generated, and then used to build a 3-D shear wave model through a series of 1-D inversions. In the second stage, we also apply an Artificial Neural Network to solve the 1D inverse problem, which results in a smoother 3-D model compared to the TransD approach without sacrificing data fit. Our shear wave velocity model reveals a complex crustal structure. Under the Crocker Range, a heterogeneous velocity structure likely represents remnants of early Miocene subduction, including underthrust continental crust from subsequent continent-continent collision. In the east we observe high velocities that are interpreted to be igneous rocks in the crust generated by melting due to mid Miocene Celebes Sea subduction and later decompression melting as well as a low velocity zone that could represent underthrust sediment or duplexes from Celebes Sea subduction. A low velocity zone in the lower crust is present in a region of apparent crustal thinning. Our preferred explanation for this anomaly is remnant thermal upwelling within a failed rift that represents the on-shore continuation of the extension of the Sulu Sea, most likely caused by rollback of the Celebes Sea slab.

中文翻译：

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北婆罗洲的环境噪声层析成像揭示了俯冲和俯冲后过程的证据


东南亚婆罗洲北部地区位于俯冲后环境中，该区域由最近两个连续但相反的俯冲系统终止而形成。在这项研究中，我们使用来自最近临时阵列部署的地震数据，使用两阶段贝叶斯跨维断层扫描方案对婆罗洲北部下方的地壳速度结构进行成像，其中首先生成与周期相关的相位速度图，然后用于通过一系列 1-D 反演构建 3-D 剪切波模型。在第二阶段，我们还应用人工神经网络来解决一维逆问题，与 TransD 方法相比，这会产生更平滑的三维模型，而不会牺牲数据拟合。我们的横波速度模型揭示了复杂的地壳结构。在克罗克山脉下，非均质速度结构可能代表了早期中新世俯冲的残余物，包括随后大陆-大陆碰撞产生的逆冲大陆地壳。在东部，我们观察到高速，这些高速被解释为由于中新世中期西里伯斯海俯冲和后来的减压熔融而产生的地壳中的火成岩，以及一个低速区，这可能代表下冲沉积物或西里伯斯海俯冲的双工岩。下地壳中的低速区存在于明显的地壳变薄的区域。我们对这种异常现象的首选解释是失败裂谷内的残余热上升流，这代表了苏禄海在岸上延伸的延续，很可能是由西里伯斯海板块的回滚引起的。