Extensional magmatism caused by strain partitioning: insights from the mafic dikes hosted in Biesituobie batholith in West Junggar, CAOB
Extensional magmatism caused by strain partitioning: insights from the mafic dikes hosted in Biesituobie batholith in West Junggar, CAOB
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应变分配引起的伸展岩浆作用：来自中亚盆地西准噶尔别斯托别基岩基性岩脉的见解
DOI：
10.1007/s00531-022-02234-w
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发表时间：
2022-08
影响因子：
2.3
通讯作者：
Chunming Wu
中科院分区：
文献类型：
--
作者：
Yichao Chen;Jiahui Liu;Renjie Zhou;Wenjiao Xiao;Ji’en Zhang;Zhiyong Zhang;Qian W. L. Zhang;Zhen M. G. Li;Chunming Wu
岩浆作用与构造环境之间的联系是至关重要的，但也存在很大争议。CAOB的西准噶尔露出了一群寄生在Biesitoobie岩基中的闪长岩-辉长岩堤坝。这些岩脉是一族镁铁质岩浆，由褐铁矿、诺长岩-辉长岩和辉长岩组成，具有等粒、斑状和堆积结构。基性岩脉代表了不同的化学成分，这是由于不同的岩性结构所暗示的岩浆演化所致，特别是对镁、钙、锶和Eu来说，可能是由晶体分馏引起的。但普遍表现为Nb、Ta、Zr、Hf、Ti亏损，而Ba、U、U等元素呈亏损状态。LA-ICPMS测年结果表明，基性岩脉的锆石U-Pb年龄分别为265±4 Ma、269±1 Ma、270±2 Ma。基性岩脉与E-MORB型熔岩具有相似的地球化学特征，但具有较小的俯冲相似性。LREE/HREE比值较低，表明它们来自相对较浅的低压地幔。玄武岩-辉长岩岩脉和容矿岩基暗示了一种区域伸展作用，应变分配导致地壳变薄，地幔上涌。在区域上，二叠纪伸展岩浆活动主要分布在垂直于达尔伯特断裂的“裕民-庙尔沟轴”上。达尔伯特断裂的活动可能导致区域扭压应变分裂为沿走滑的达尔伯特断裂的简单剪切和垂直于该断裂的纯剪切。与纯剪切最大主应力平行的T形断裂导致地壳减薄和地幔上涌，形成“裕民-庙儿沟地轴”的伸展岩浆作用。这种构造背景可能是伸展岩浆活动的基本地球动力学背景，表明局部伸展可能与区域扭压作用相协调，这种模式不需要统一的区域伸展。
The connection between magmatism and the tectonic environment is essential yet highly debatable. The West Junggar, CAOB, outcropped a swarm of norite-gabbro dikes hosted in the Biesituobie batholith. The dikes are a family of mafic magma consisting of nortite, norite-gabbro, and gabbro with equigranular, porphyritic, and cumulate textures. The mafic dikes represent various chemical compositions due to the magma evolution suggested by the different lithological textures, especially for MgO, CaO, Sr, and Eu, possibly caused by the crystal fractionation. But commonly, they show depleted Nb, Ta, Zr, Hf, Ti, and enriched Ba, U. Geochronology study by LA-ICP-MS gives zircon U–Pb age of 265 ± 4 Ma, 269 ± 1 Ma, 270 ± 2 Ma for the mafic dikes, respectively. The mafic dikes show geochemical similarities with E-MORB type lava with minor subduction affinity. The low fraction on the LREE/HREE indicates that they were generated from a relatively shallow mantle with low pressure. The norite-gabbro dikes and the host batholith suggest a regional extension with crust thining upwelling of the mantle caused by strain partitioning. Regionally, the Permian extensional magmatism is distributed mainly in the “Yumin–Miaoergou axis, ” perpendicular to the Darburt fault. The activation of the Darburt fault might cause the partition of regional transpression strain into simple shear along the strike-slip Darburt fault and pure shear perpendicular to the fault. The T-fracture parallel with the maximum principal stress of the pure shear causes crustal thinning and mantle upwelling, generating the extensional magmatism in the “Yumin–Miaoergou axis.” This tectonic scenario might be the essential geodynamic background for extensional magmatism, which suggest that local extension might be coordinated with regional transpression, and a unified regional extension is not needed in such a model.
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