Moonpa Kritsada, Motanated Kannipa
Department of Geological Sciences, Faculty of Science, Chiang Mai University, 239 Huay Kaew Road, Suthep, Mueang, Chiang Mai, 50200, Thailand.
Heliyon. 2018 Feb 1;4(1):e00517. doi: 10.1016/j.heliyon.2018.e00517. eCollection 2018 Jan.
The Nam Pat Group of the Nam Pat Basin, Uttaradit Province, Thailand is situated in the Nan Suture Zone. Two contrasting tectonic framework models of the Nan Suture have previously been proposed: as a main Paleo-Tethyan suture and as a remnant of a closed back-arc basin. The goal of this study is to analyze the tectonic framework of the Nan Suture and reevaluate the existing tectonic models. This research infers the tectonic setting of the basin based on basin-filled lithofacies distributions, provenance, and paleocurrents. Three facies groups are identified. Facies A, B, and C are polymictic conglomerate, interbedded sandstone and mudstone, and mudstone with thin-bedded sandstone, respectively. Generally, the strata strike NE-SW, steeply dip NW, and fine toward the SE. Petrographic results of sandstone samples show that the majority of lithic fragments are volcanic rocks with lesser amount of metamorphic rocks and sedimentary rocks. The modal compositions of sandstones are analyzed on QFL, QmFLt, QmPK, LmLvLs, and QpLvmLsm ternary diagrams. The plots indicate that the sandstones of the Nam Pat Group have high proportions of volcanic-arc detritus. Paleocurrents, determined from the orientation of clast imbrications and cross-stratification, are toward the SE. The results suggest that large quantities of sediment traveled southeastward from a nearby volcanic arc into the basin. The Nam Pat Group stratigraphically overlies the Pak Pat Volcanics. The chemical features of the Pak Pat Volcanics, located to the west of the basin, show that they are andesitic volcanic rocks formed as a magmatic arc. Thus, the nearby Pak Pat Volcanics are the main sediment source of the Nam Pat Group, and the basin is best interpreted as back-arc basin rather than as a forearc basin.
泰国乌泰他尼府难河盆地的难帕群位于难河缝合带。先前已提出难河缝合带的两种截然不同的构造框架模型：作为主要的古特提斯缝合带和作为封闭弧后盆地的残余部分。本研究的目的是分析难河缝合带的构造框架并重新评估现有的构造模型。本研究根据盆地充填岩相分布、物源和古水流推断盆地的构造背景。识别出三个相组。相A、B和C分别为多成分砾岩、砂岩与泥岩互层以及含薄层砂岩的泥岩。总体而言，地层走向为东北 - 西南，向西北陡倾，向东南变细。砂岩样品的岩石学结果表明，大多数岩屑为火山岩，变质岩和沉积岩较少。在QFL、QmFLt、QmPK、LmLvLs和QpLvmLsm三元图上分析砂岩的模态成分。这些图表明难帕群的砂岩具有高比例的火山弧碎屑。根据碎屑叠瓦状排列方向和交错层理确定的古水流方向为东南。结果表明大量沉积物从附近的火山弧向东南搬运至盆地。难帕群在地层上覆于帕帕火山岩之上。位于盆地西部的帕帕火山岩的化学特征表明它们是作为岩浆弧形成的安山质火山岩。因此，附近的帕帕火山岩是难帕群的主要沉积物来源，该盆地最好解释为弧后盆地而非弧前盆地。
