A new rock complex has been discovered from the Tsuwano area of Southwest Japan. This granitic rock complex namely, Tsuwano Complex contains foliated granitic gneiss, massive granitoids, and metaquartzite, forming a distinct unit at the westernmost end of the east-west elongate Maizuru Terrane. The above-mentioned litho-assemblage is characteristically different in appearance from the typical rocks of the Maizuru Terrane as well as the surrounding Jurassic and Permian accretionary rocks. We report here the zircon U-Pb LA-ICP-MS geochronological data of the rocks of this Tsuwano Complex. The comprehensive geochronological data indicate that this complex is much older than the surrounding rocks of the Maizuru Terrane. Zircon cores of the granitic gneiss yield possible magmatic age at ca. 2700 and 2500 Ma, while rim parts show a possible metamorphic age of ca. 1850 Ma. Associated dioritic to tonalitic granitoids also show a comparable age of crystallization at ca. 1850 Ma, indicating Neoarchean granitic rocks suffering a thermal overprinting and associated granitoid magmatism at Paleoproterozoic era. The exposed metaquartzite also yielded Neoarchean detrital zircon grains with the calculated maximum age of deposition at ca. 2430 Ma. While, all the other studied rocks including the grayish granitoids, felsic tuff, and metagabbro yield Paleozoic to Mesozoic ages. This is the first discovery of a Precambrian basement rock complex from the Japanese main islands. Based on the present geochronological dataset, we propose for a correlation and paleo-positioning of these basement rocks on the East Asian cratonic margin and a possible tectonic model of its evolution.

从日本西南部的Tsuwano地区发现了一个新的岩石综合体。这个花岗岩岩体，即Tsuwano岩体，包含叶状花岗岩片麻岩，块状花岗岩和变石英岩，在东西向细长的Maizuru Terrane的最西端形成了一个独特的单元。上述岩石组合在外观上与舞鹤山地的典型岩石以及周围的侏罗纪和二叠纪增生岩石特征不同。我们在此报告该Tsuwano复杂地带的锆石U-Pb LA-ICP-MS年代学数据。全面的年代学数据表明，该复合体比Maizuru Terrane的围岩要古老得多。花岗岩片麻岩的锆石岩心可能在大约30℃产生岩浆年龄。2700和2500 Ma，轮缘部分显示出大约为的变质年龄。1850年。伴有闪长岩到tonalitic的类固醇也显示出大约可比的结晶年龄。1850 Ma，表明新元古代的花岗岩在古元古代时代遭受热套印和相关的花岗岩类岩浆作用。暴露的偏石英岩还产生了新阿尔巴纪碎屑锆石晶粒，其计算出的最大沉积年龄为约200℃。2430马。同时，所有其他研究过的岩石，包括浅灰色的花岗岩，长石凝灰岩和变质岩，都产生了古生代至中生代的年龄。这是来自日本主要岛屿的前寒武纪基底岩层的首次发现。根据当前的年代数据集，