摘要
江南造山带西段湖南中、新元古代火山-侵入岩具有截然不同的地球化学特征。中元古代火山-侵入岩多属亚碱性玄武岩类,MgO、Ni、Cr含量及Al_2O_3/TiO_2比值高,稀土元素分馏形式多样,更多地具有岛弧火山岩的特征。新元古代中基性火山-侵入岩MgO、Ni、Cr含量较低;其中的基性岩大多属碱性玄武岩类,并较富TiO_2,Al_2O_3/TiO_2比值较低,HFSE明显富集,微量元素标准化曲线与OIB类似,具有裂谷玄武岩的特征。 中元古代南桥玄武岩ε_(Nd)(t)为6.86～8.98,具明显的N-MORB特征,是俯冲带附近的古洋壳残片,为九岭古岛弧提供了新的证据。中元古代的益阳玄武岩ε_(Nd)(t)为1.56～1.76,Nb、Ti、Zr亏损,Th相对富集,具俯冲带火山岩的地球化学特征,同时这些玄武岩具高MgO、高Al_2O_3/TiO_2比值和Ni、Cr含量,具科马提质玄武岩的特性,可能是局部地幔柱-弧相互作用的产物。新元古代早期益阳安山质集块岩Th、La、Sm和Nd富集,Nb、Ti、Zr和Hf亏损,ε_(Nd)(t)值为-0.53～-1.05,是格林威尔造山运动的产物。新元古代黔阳、古丈、高桥火山-侵入岩原始地幔标准化曲线近似于OIB,具裂谷玄武岩的特征,黔阳、古丈基性岩ε_(Nd)(t)值在1.09～1.69,来源于软流圈地幔。湖南这些中-新元古代火山-侵入岩的地球化学特征记录了
The Meso-Neoproterozoic volcanic-intrusive rocks from Hunan in west section of Jiangnan orogen show very different geochemistry features. The Mesoproterozoic volcanic-intrusive rocks have narrow SiO2 contents varying from 49.95% to 53.91%. They are mainly sub-alkaline basalts with low TiO2 and Zr/Y ratios, high MgO, Ni, Cr, and Al2O3/TiO2 ratios. They have different types of REE patterns, and display characteristics of arc volcanic rocks. The Neoproterozoic volcanic intrusive rocks are alkaline and sub-alkaline basalts with broad SiO2 varying 45.56% to 60.37%. They have high Zr/Y ratios and low MgO, Ni, Cr. Among them, the Neoproterozoic basic rocks are mostly alkaline basalts, with high TiO2 contents and low Al2O3/TiO2 ratios. They are obviously enriched in HFSE and show typical patterns of OIB, similar to the rift-basalts. Mesoproterozoic basalts from Nanqiao exhibit typical N-MORB features with high epsilon(Nd)(t) values (6.86similar to8.98), and may represent the residual slab, which provides a new important evidence for Jiuling Island Arc in the middle section of Jiangnan orogen. Mesoproterozoic basalts from Yiyang show enrichment in Th and depletion in Nb and Ti with low epsilon(Nd)(t) values (1.56 similar to1.76), similar to arc island volcanic rocks. On the other hand, they are enriched in MgO, Ni, and Cr with komatiitic basalts signatures, implying that they might be a product of interaction between the plume induced by subduction and the arc in the area. Early Neoproterozoic andesites from Yiyang are enriched in Th, La, Sm and Nd and depleted in Nb, Ti, Zr and Hf showing arc volcanic features. They suggest that they are the products of Grenville orogeny. Patterns normalized by primitive mantle of Neoproterozoic volcanic-intrusive rocks from Qianyang, Guzhang and Gaoqiao are similar to OIB, the epsilon(Nd)(t) of basic rocks from Qianyang and Guzhang are 1.69similar to1.05, indicating that they might be originated from asthenospheric mantle. The geochemistry of these Meso-Neoproterozoic volcanic-intrusive
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2003年第1期49-60,共12页
Acta Petrologica Sinica
基金
国家自然科学基金(批准号:49872030)
