Lithos ( IF 3.5 ) Pub Date : 2020-12-24 , DOI: 10.1016/j.lithos.2020.105955 Hai Jiang , Wen-Qian Li , Kui-Dong Zhao , Di Zhang , Shao-Yong Jiang
Two Early-Middle Triassic magmatic arc belts occur in the Indochina Block within Thailand, namely the Lampang Volcanic Belt and the Loei-Phetchabun Volcanic Belt, which are about 150 km apart and run parallel to each other. The Lampang Volcanic Belt has been extensively studied and suggested to be induced by eastward Paleotethyan subduction, whereas the Loei-Phetchabun Volcanic Belt has not been well constrained due to the scarcity of geochronological and geochemical data. Here we report a detailed study on zircon UPb dating, elemental geochemistry and SrNd isotopes for the Phu Rai diorites recently identified in Loei Province, NE Thailand. The Phu Rai diorites yield Middle Triassic (ca. 239 Ma) emplacement ages. They are calc-alkaline rocks characterized by arc-like trace element patterns and depleted SrNd isotopic compositions ((87Sr/86Sr)i = 0.70371–0.70392; εNd(t) = +1.65 to +2.54). These geochemical and isotopic signatures reveal that the Phu Rai diorites were most likely derived from a depleted mantle wedge metasomatized by subducted sediment-derived melts and slab-derived fluids, and modified by limited degree of fractional crystallization involving clinopyroxene, amphibole and FeTi oxides combined with weak plagioclase accumulation. Based on our results and others from the literature, we suggest the existence of an Early-Middle Triassic (ca. 250–239 Ma) magmatic arc belt in NE Thailand, which is not directly linked to eastward Paleotethyan subduction, but is possibly associated with eastward subduction of the Nan back-arc basin. Specifically, the ca. 239 Ma Phu Rai diorites and ca. 245–241 Ma adakites nearby form a rock association in response to slab break-off at that time, immediately after the initial stage of the Sukhothai-Indochina collision. The occurrence of this rock association could mark not only the cessation of eastward subduction of the Nan back-arc basin but also the initiation of the Sukhothai-Indochina collision.
中文翻译:
泰国东北部黎府褶皱带中三叠世闪长岩:古生代俯冲背景下的成岩作用和构造意义
泰国的印度支那地区出现了两条早中三叠世岩浆弧带,即南邦火山带和黎府-碧差汶火山带,它们相距约150公里,并且相互平行。南邦火山带已被广泛研究,并被认为是由向东的Paleotethyan俯冲带引起的,而黎-碧差汶火山带由于年代学和地球化学数据的缺乏而没有受到很好的限制。在这里,我们报告了最近在泰国东北部黎府发现的Phu Rai重晶石的锆石U Pb年代,元素地球化学和Sr Nd同位素的详细研究。Phu Rai闪长岩产生了中三叠纪(约239 Ma)的侵占年龄。它们是钙碱性岩石,其特征是弧形的痕量元素图案和贫化的SrNd同位素组成((87 SR / 86 SR)我 = 0.70371-0.70392;ε钕(吨)= 1.65到2.54)。这些地球化学和同位素特征表明,Phu Rai闪长岩最有可能来自贫化的地幔楔,其由俯冲的沉积物衍生的熔体和板状衍生的流体交代,并受到有限的有限度的分级结晶的修饰,其中包括次氯环吡喃,闪石和铁钛氧化物与较弱的斜长石沉积相结合。根据我们的研究结果和文献中的其他资料,我们建议在泰国东北部存在早中三叠世(约250–239 Ma)岩浆弧带,它与东Paleotethyan俯冲不直接相关,但可能与东俯冲俯冲有关南弧后盆地向东俯冲。具体来说,239 Ma Phu Rai diorites and ca. 素可泰-印度支那碰撞初期之后,当时的板状断裂响应附近的245-241 Ma Maakakites形成了岩石协会。这种岩石组合的出现不仅标志着南后弧盆地向东俯冲的停止,而且标志着素可泰-印度支那碰撞的开始。