摘要
北秦岭拉圾庙苏长辉长岩体由辉长岩和苏长辉长岩组成。它们分属两个不同的岩浆系列:辉长岩属拉斑系列,TiO_2,Fe^(3+)/Fe^(2+)和REE丰度较高;苏长辉长岩属钙碱系列,低TiO_2,Fe^(3+)/Fe^(2+)和REE,特别是HREE。这说明后者源区较深并受榴辉岩相控制。两种岩石均有与岛弧玄武岩类似的地球化学特征,如较高的Ba,Pb,Sr和较低的Nb、Zr、Ni含量等。拉圾庙辉长岩和苏长辉长岩的Sr,Nd同位素特征与蛇绿岩类似,其ε_(Nd)值恒定在+2左右,ε^(Sr)变化范围较大(-6.4—+31.2),并与Na_2O,H_2O+,CO_2含量和Fe^(3+)/Fe^(2+)有正相关关系。在ε_(Nd—Nb/Th,ε_(Nd)-La/Nb和ε_(Nd)-Ba/Nb图中,清楚显示了该岩体的地幔源含较多的陆源沉积物组分。它说明古秦岭海板块在古生代俯冲时,携带有较多沉积物进入地幔。
The Lajimiao norite-gabbro complex, as a part of the ophiolites on the southern side of the North Qinling belt, consists of gabbro and norite-gabbro. They were derived from different magma series: the gabbro was derived from tholeiitic magma series with higher TiO_2, REE abundance and Fe^(3+)/Fe(2+) ratio; norite-gabbro was derived from calc-alkalic magma series with lower TiO_2, Fe^(3+)/Fe^(2+) ratio and REE abundance and much lower HREE abundance, which suggests that the source of the norite-gabbro magma was deeper and controlled by eclogite facies. Geochemical characteristics of both plutonic rocks are similar to those of island-arc basalts, such as higher Ba, Pb and Sr and lower Nb, Zr and Ni contents.The Sr, Nd isotopic characteristics of the Lajimiao norite-gabbro complex are similar to those of ophiolites. Its ε_(Nd) values are constant, about+2; whereas ε_(sr) values have wide variation from -6.4 to +31.2 and positively correlate with Na_2O, H_2O^+ and CO_2 contents and the Fe^(3+)/Fe^(2+) ratio. The ε_(Nd)-Nd/Th, ε_(Nd)-La/Nb and ε_(Nd)-Ba/Nb diagrams clearly show that the terrigenous sediments are an important component in the mantle source of the Lajimiao norite-gabbro complex. It suggests that large amount of sediments had been carried into the mantle by the subducted ancient Qinling sea plate during the Palaeozoic.
出处
《地质学报》
EI
CAS
CSCD
北大核心
1993年第4期310-322,共13页
Acta Geologica Sinica
基金
国家自然科学基金(编号 49070165)
关键词
痕量元素
苏长辉长岩
同位素地质学
trace element, Sr/Nd isotopes, norite-gabbro, Lajimiao, North Qinling
