中文摘要：

柴北缘乌兰县二郎洞地区的达肯大坂岩群主要由黑云斜长片麻岩、混合岩、黑云母石英片岩、斜长角闪岩和大理岩、花岗片麻岩等共同组成。本文首次对两件混合岩化黑云斜长片麻岩样品中的锆石进行了内部结构分析和SHRIMP测年，黑云斜长片麻岩中的锆石大多具有核一边结构，核部和边部分别表现为典型的岩浆和变质成因锆石特征。一件样品中错石核部206Pb／238U加权平均年龄为503．8±5．1Ma，边部206Pb／238U加权平均年龄为449±9．9Ma；另一件样品核部206Pb／238U加权平均年龄为493．6±4．5Ma。这些结果表明，乌兰县二郎洞地区达肯大坂岩群中的混合岩化黑云斜长片麻岩原岩形成年龄为504～494Ma，属于晚寒武世岩浆活动的产物，变质年龄为449Ma，分别与柴北缘岛弧岩浆作用和超高压变质作用的时限相一致。研究表明，二郎洞地区达肯大坂岩群不仅有新太古代一古元古代基底岩石，还包含早古生代的岩石组合，为一套不同性质和不同时代的混杂岩。

英文摘要：

The Dakendaban Group was mainly composed of biotite plagiogneiss, migmatite, biotite- quartz schist, plagioclase amphibolite and marble in the Erlangdong area at the northern margin of Qaidam Basin. Internal structure analysis show that most of them exhibit core-rim structure. The core and rim of zircon are typical magmatic and metamorphic zircon, respectively. Zircon dating yielded Early Cambrian age of 503.8±5.1 Ma and 493.6±4.5 Ma for the core, but Late Ordovician age of 449 ± 9.9 Ma for the rim. The former represented the protolith age of migmatite biotite plagioclase gneiss, and the later reflected the time for metamorphism. The protolith and metamorphism age of the migmatitic biotite plagioclase gneiss were consistent with the time of arc magmatism and ultra-pressure metamorphism on the northern margin of Qaidam Basin. Our research proved the Dakendaban Group was not only comprised of Neoarchean- Paleoproterozoic rocks, but also contained Early Paleozoic rock assemblage, which is a melange composed of different times and different genesis rocks.