中文摘要：

本文对秦岭勉略（勉县—略阳）构造混杂带康县—勉县段的铁镁质岩块或蛇绿岩块进行了系统的锆石SHRIMP U-Pb年代学研究。测年结果表明，勉略构造混杂带康县—勉县段铁镁质岩块的形成时代为841±16-812±11Ma，蛇绿混杂岩中的辉长岩和辉绿岩块的形成时代为827±14-808±10Ma。从西向东，勉略构造混杂带不同地段蛇绿岩块或铁镁质岩块的锆石U-Pb同位素年龄在误差范围内相同，表明勉略混杂岩带中的蛇绿岩块所代表的是新元古代古洋壳残片。中部三岔子斜长花岗岩的形成年龄（923Ma±13）大于其他铁镁质岩块和蛇绿岩。

英文摘要：

Traditionally, the Mianxian--Lueyang mélange（MLM） was interpreted to be a suture when the south and north China blocks collided in the early Mesozoic. The ophiolitic and mafic blocks in the MLM were considered as the remnants of a Devonian regenerated oceanic basin. SHRIMP U-Pb analyses for zircon grains in this paper showed that the ophiolitic blocks （sample SCZ-11, XKY-8 and GYY-1） in the Kangxian--Mianxian section of the MLM were formed in the Neoproterozoic, ca 841±16 - 812±11Ma. SHRIMP dating results yielded ages of 827±14-808±10Ma to the mafic blocks （sample B126, B136 and B175） in the MLM. However, a plagiogranite block （sample SCZ-9） in the middle of the MLM near a small town Sancazi was dated at ca 923±13Ma, significantly older than other ophiolitic and mafic blocks. The ages of the ophiolitic and mafic blocks are greatly excellent with each other within the errors. As a result, the update results in the present paper indicated that those ophiolitic and mafic blocks in the MLM are actually the remnants of a Neoproterozoic ocean basin, rather than the so-called Devonian regenerated ocean basin as previously.