班公湖—怒江缝合带东段八宿地区古生代地层碎屑锆石U-Pb年龄：物源分析及构造意义

八宿微陆块位于班公湖—怒江缝合带东部，其古生代地层的构造属性存在争议，有增生楔和微陆块两种观点。古生代地层（邦达组和错绒沟口组）岩性为板岩、千枚岩，夹灰岩、砂岩等岩块。本文对八宿地区邦达组和错绒沟口组进行了野外调查、砂岩镜下观察以及碎屑锆石U-Pb年代学研究，结果表明：1）地层中砂岩的地层最大沉积年龄为510.2±2.5 Ma，结合岩块中古生物化石、玄武岩和辉绿岩锆石年龄，其沉积时代初步限定为寒武纪—早石炭世。2）地层属于具有变质基底的微陆块，而不是增生楔。3）邦达组和错绒沟口组中碎屑锆石多为岩浆成因，测得U-Pb年龄可划分为650~500 Ma、1 200~700 Ma、1 850~1 550 Ma和2 600~2 400 Ma，表明物源区存在强烈的泛非期和格林威尔造山期构造岩浆事件。4）邦达组和错绒沟口组所在的微陆块与南羌塘地体具有相近的物源区，经历了相似的构造演化，属于冈瓦纳大陆的一部分。

Detrital zircon U-Pb ages from Paleozoic strata in the eastern Bangong Lake-Nujiang suture zone,Basu area: Provenance analysis and tectonic affinity

The tectonic affinity of the Paleozoic basement of the Basu microcontinent in eastern Tibet remains controversial, with two views of accretionary wedge and microcontinent. The Paleozoic strata(Bangda and Cuoronggoukou formations)is composed of slate and phyllite with blocks of limestones and sandstones. This paper presents detailed field mapping, petrographic and detrital zircon U-Pb data from Bangda and Cuoronggoukou formations in the eastern Bangong-Nujiang suture zone. Our results show that: 1)the maximum depositional age of the sandstones is 510.2±2.5 Ma. Combined with Early Carboniferous age from fossils of limestone blocks and zircon ages of basalt and gabbro blocks, the depositional age is tentatively limited to the Cambrian-Early Carboniferous. 2) The Cambrian-Carboniferous strata is interpreted to belong to microcontinent, rather than accretionary wedge. 3) Most of the detrital zircons in the Bangda and the Cuoronggoukou formations are of magmatic origin, and the U-Pb age spectra and are dominated by peaks at 650~500 Ma, 1 200~700 Ma, 1 850~1 550 Ma and 2 600 ~ 2 400 Ma. These detrital zircons were derived from Pan-African and Greenville orogenic belt in the Gondwana continent. 4) Our data indicated that the Bangda and the Cuoronggoukou formations have similar source areas and tectonic evolution with the South Qiangtang terrane.