Mid-Cretaceous intra-oceanic arc-continent collision recorded by the igneous complex in central Myanmar
Mid-Cretaceous intra-oceanic arc-continent collision recorded by the igneous complex in central Myanmar
复制标题
DOI：
10.1016/j.lithos.2022.106637
复制
发表时间：
2022-02
期刊：
影响因子：
3.5
通讯作者：
Zong-Yong Yang;X. Bi;Jing-Jing Zhu-Jing;R. Hu;H. Zhong;K. Sein;Than Zaw;Dian-Zhong Wang
中科院分区：
文献类型：
--
作者：
Zong-Yong Yang;X. Bi;Jing-Jing Zhu-Jing;R. Hu;H. Zhong;K. Sein;Than Zaw;Dian-Zhong Wang
来自洋内弧的岩浆岩对于了解大陆地壳的形成和构造演化至关重要。印度-亚洲最终碰撞之前新特提斯洋的早期构造演化仍然是个谜，引发缅甸中部白垩纪岩浆作用的地球动力学过程仍然存在争议。缅甸西部地体 (WMT) Banmauk-Kawlin 地区 (BKC) 的白垩纪岩浆杂岩由 Kanza Chaung 花岗岩岩基、Mawgyi 火山岩和 Pinhinga 深成杂岩组成。 Kanza Chaung 基岩中各种岩石的锆石 U-Pb 定年结果表明，岩浆作用持续了大约 10 年。 110 至 约。 94 Ma，与 Mawgyi 火山的新地质年代学数据大致重叠。镁铁质岩石，包括来自 Mawgyi 火山的玄武岩和来自 Kanza Chaung 岩基的辉长岩，具有类似于洋内弧岩浆的地球化学特征，其特征是高大离子亲石元素 (LILE) 和低高场强元素 (HFSE) 以及平坦的微量元素模式。它们贫化了 Sr（初始 87Sr/86Sr = 0.7035–0.7054）和 Nd（εNd(t) = 0.39–6.71）同位素成分，锆石 εHf(t) 值范围为 +5.8 至 +16.1，可能源自地幔楔的部分熔融。玄武质岩浆分异作用形成的闪长岩具有相似的微量元素模式和Sr-Nd同位素。花岗岩很可能起源于新生岛弧下地壳的部分熔融，其高 SiO2（>65.0 wt%）、低 MgO（<2.50 wt%）以及贫 Nd 和锆石 Hf 同位素表明。 BKC 的 εNd(t) 值从 105 Ma 显着变化（从 ~ + 7 到 0），这与 Th/Nb、La/Ta 和 La/Sm 的时间增加相关。考虑到 WMT 地壳的年轻特征，这可以通过俯冲到地幔源中的外来同位素富集地壳成分来解释，而不是稳态沉积物俯冲和地壳污染。考虑到 WMT 中的阿尔比安不整合面和最近的古地磁数据，这些大陆地壳成分很可能是由碰撞引入的，随后是源自大印度的大陆条俯冲到 WMT 之下。因此，与印度大陆有亲和力的地壳可能在白垩纪中期增生成洋内弧（WMT）。
Magmatic rocks from intra-oceanic arcs are critical for understanding the formation of continental crust and tectonic evolution. The early tectonic evolution of the Neo-Tethyan Ocean before the final Indo-Asia collision remains mysterious, and the geodynamic processes that triggered the Cretaceous magmatism in central Myanmar is still debated. The Cretaceous magmatic complex in the Banmauk-Kawlin area (BKC), west Myanmar terrane (WMT) is composed of the Kanza Chaung granitoid batholith, the Mawgyi Volcanic rocks, and the Pinhinga plutonic complex. Zircon U-Pb dating results of various rocks from the Kanza Chaung batholith suggest magmatism lasted from ca. 110 to ca. 94 Ma, roughly overlapping with new geochronological data for the Mawgyi Volcanics. Mafic rocks, including basalts from the Mawgyi Volcanics and gabbros from the Kanza Chaung Batholith, have geochemical features resembling intra-oceanic arc magmas, characterized by high large-ion-lithophile elements (LILEs) and low high-field-strength elements (HFSEs) and flat trace element patterns. They have depleted Sr (initial87Sr/86Sr = 0.7035–0.7054) and Nd (εNd(t) = 0.39–6.71) isotopic compositions, with zircon εHf(t) values ranging from +5.8 to +16.1, probably derived from partial melting of the mantle wedge. Diorites formed by differentiation of basaltic magma have similar trace element patterns and Sr-Nd isotopes. The granitic rocks were likely originated from partial melting of juvenile arc lower-crust, indicated by their high SiO2(>65.0 wt%), low MgO (<2.50 wt%) and depleted Nd and zircon Hf isotopes. The εNd(t) values of the BKC shift markedly (from ~ + 7 to 0) from 105 to 94 Ma, which correlates with a temporal increase of Th/Nb, La/Ta, and La/Sm. Given the juvenile characteristics of the WMT crust, this can be explained by exotic isotopically enriched crustal components subducted into the mantle source, rather than steady-state sediment subduction and crustal contamination. Given the Albian unconformity in the WMT and recent paleomagnetic data, such continent crustal components were likely introduced by collision followed by subduction of Greater India-derived continental sliver beneath the WMT. Thus crust with an Indian continent affinity was possibly accreted to an intra-oceanic arc (WMT) during the mid-Cretaceous.