Abstract The Main Range and Eastern Provinces are two major granite belts in Southeast Asia. These granite belts extend southward from the southeastern Tibetan Plateau to Myanmar, and through Thailand into Peninsular Malaysia. They are interpreted to represent the magmatic expression of the closure of the Paleo-Tethys from the Permian to the Triassic. Myanmar lies in the heart of these granite belts. The Kyaing Tong and Tachileik granites in the far east of Myanmar are important components of the granite belts of Southeast Asia; however, due to the lack of reliable geochronology within eastern Myanmar, delineation of the Main Range and Eastern Province belts in this region is very poorly constrained. Here we present new zircon U Pb age, whole-rock composition, and Sr Nd isotope data from the Kyaing Tong and Tachileik granites from eastern Myanmar to address this geological problem. Measured ages of 207–216 Ma from the Kyaing Tong granites imply that they are a northern extension of the Main Range Province, whereas the Tachileik granites yield ages of 246–250 Ma, which suggests that they are the northern extension of the Eastern Province granite belt. Both belts in eastern Myanmar comprise biotite monzogranites and granodiorites and show similar geochemical features, such as having a high aluminum saturation index and an unfractionated composition. The granites from both provinces show enrichment in light rare earth elements (REE) and negative Eu anomalies. All samples demonstrate characteristic negative Ba, Nb, Ta, Sr and Ti anomalies, and a positive Pb anomaly, when plotted on spidergrams. The Kyaing Tong granites have high and variable initial 87Sr/86Sr ratios (0.717735–0.731271), negative eNd (t = 215 Ma) values (−14.2 to −10.4), and old TDM2 ages. Similarly, the Tachileik granites have high and variable initial 87Sr/86Sr ratios (0.715336–0.722712), negative eNd (t = 250 Ma) values (−12.4 to −11.3), and old TDM2 ages. Sr Nd isotope values show that these granites may be generated by mixing of two end-member lithologies: amphibolite and schist of the Lancang Group, which represents the lower crust of the Indochina block. We consider that both the Kyaing Tong and Tachileik granites are of I-type affinity. They were derived from partial melting of the amphibolite and underwent assimilation of schist. Our petrogenetic and zircon U Pb age data support models that relate the Eastern Province granites to continental arc during the Permian and syn-collisional magmatism in the Early Triassic, and the Main Range Province granites to post-collisional magmatism during the Middle to Late Triassic.

中文翻译：

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缅甸东部主要山脉和东部省花岗岩的岩石成因：锆石 U Pb 年龄和 Sr Nd 同位素的新见解

摘要 主山脉和东部省份是东南亚两大花岗岩带。这些花岗岩带从青藏高原东南部向南延伸至缅甸，再穿过泰国进入马来西亚半岛。它们被解释为代表古特提斯纪从二叠纪到三叠纪闭合的岩浆表现。缅甸位于这些花岗岩带的中心。缅甸远东的Kyaing Tong和Tachileik花岗岩是东南亚花岗岩带的重要组成部分；然而，由于缅甸东部缺乏可靠的地质年代学，该地区的主要山脉和东部省份带的划分非常有限。在这里，我们展示了新的锆石 U Pb 年龄、全岩成分、来自缅甸东部 Kyaing Tong 和 Tachileik 花岗岩的 Sr Nd 同位素数据，以解决这一地质问题。来自 Kyaing Tong 花岗岩的测量年龄为 207-216 Ma 意味着它们是 Main Range 省的北部延伸，而 Tachileik 花岗岩的年龄为 246-250 Ma，这表明它们是东部省花岗岩的北部延伸腰带。缅甸东部的两条带都包含黑云母二长花岗岩和花岗闪长岩，并显示出相似的地球化学特征，例如具有高铝饱和指数和未分馏成分。这两个省的花岗岩都显示出富含轻稀土元素（REE）和负 Eu 异常。当绘制在蛛网图上时，所有样品都显示出特征性的负 Ba、Nb、Ta、Sr 和 Ti 异常以及正 Pb 异常。Kyaing Tong 花岗岩具有高且可变的初始 87Sr/86Sr 比率 (0.717735–0.731271)、负 eNd (t = 215 Ma) 值 (-14.2 到 -10.4) 和旧的 TDM2 年龄。类似地，Tachileik 花岗岩具有高且可变的初始 87Sr/86Sr 比值 (0.715336–0.722712)、负 eNd (t = 250 Ma) 值（-12.4 至 -11.3）和旧的 TDM2 年龄。Sr Nd 同位素值表明这些花岗岩可能是由两种端元岩性混合生成的：代表印度支那地块下地壳的澜沧群角闪岩和片岩。我们认为 Kyaing Tong 和 Tachileik 花岗岩都具有 I 型亲和性。它们来自角闪岩的部分熔化并经历了片岩的同化作用。