中文摘要：

为探讨扬子陆块东南缘新元古代岩浆活动的性质,选择浙江金华罗店深成杂岩中的中基性岩石,开展了系统的岩石学、地球化学、同位素地球化学和年代学研究,发现该深成杂岩中存在富铌辉长岩和高镁闪长岩等典型的岛弧地区岩浆岩。富铌辉长岩相对富P2O5、Ti O2和Nb,原始地幔标准化La/Nb〈1.3,类似于太古宙和古生代富铌玄武岩。采用LA-ICP-MS技术测得高镁闪长岩的锆石U-Pb年龄为848±10Ma,相对富Mg O、低Ti O2,Mg～#〉62.5,富Cr而贫Sr、Y和重稀土元素,接近于日本Setouchi火山岩带的中新世高镁安山岩和阿留申西部的Piip型高镁安山岩。而且,二者均富集Rb、Ba、K、Pb等大离子亲石元素,亏损Nb、Ta、Ti等高场强元素,εNd（t）〉＋2.92,相应的ISr介于0.70308～0.70474之间,推测二者成因均与俯冲板片部分熔融的熔体交代地幔楔橄榄岩再熔融有关。综合区域地质资料及前人研究成果认为,扬子陆块东南缘至848Ma左右仍存在明显的岛弧岩浆活动,这对认识华南前寒武纪的大地构造格局及其演化具有重要意义。

英文摘要：

In order to probe into the Neoproterozoic magmatic activity along the southeastern margin of Yangtze Block, the authors conducted petrographic, geochemical and chronologic studies of the first-discovered Nb-enriched gabbros （NEGs） and high-Mg diorites （HMDs） in the Jinhua plutonic complex, Zhejiang Province. The NEGs show relatively high P 2O5, TiO2 and Nb values with （La/Nb）N less than 1.3, similar to features of Archean and Palaeozoic Nb-enriched basalts. The HMDs have relatively higher MgO content with Mg# higher than 62.5 and lower TiO2 content, and are enriched in Cr but depleted in Sr, Y and HREE, consistent with features of Miocene high-Mg andesites of Setouchi volcanic belt in Japan and Piip-type HMAs in west Aleutian. The enrichment of LILE （e.g., Rb, Ba, K and Pb） and depletion of HFSE （e.g., Nb, Ta and Ti） with dataεNd（t）〉＋2.92 and ISr=0.70308～0.70474, probably indicate that the NEGs and the HMDs were formed by partial melting of mantle wedge peridotite with slab fluid metasomatism. The HMD yielded a weighted mean 206Pb/238U age of 848± 10Ma （measured by LA-ICP-MS）. Based on the regional geology and previous studies, the authors hold that obvious island arc magmatic activity still existed along the southeast margin of Yangtze Block at Ca.848Ma, and hence the Precambrian geotectonic evolution history of south China should be reconsidered.