摘要
辽宁宽甸、河北汉诺坝及福建明溪碱性玄武岩中普通辉石巨晶的^(87)Sr/^(86)Sr值是0.70387—0.70401,^(143)Nd/^(144)Nd值是0.51282—0.51295,宽甸石榴石巨晶的^(143)Nd/^(144)Nd值是0.51282—0.51293,巨晶的εNd值与载体玄武岩相似。辉石的^(207)Pb/^(204)Pb值是15.6017—15.6649,^(206)Pb/^(204)Pb值是18.5604—18.8359,石榴石的^(207)Pb/^(204)Pb值是15.6046—15.7792,^(206)Pb/^(204)Pb值是18.1849—19.0345。巨晶放射性Pb同位素明显高于载体玄武岩,表明两者之间未达到同位素平衡。巨晶母岩浆可能产生于二元混合体系,端元之一可能与岛弧物质有关。
The Pb, Sr and Nd isotopic compositions of Al-augite and garnet megacrysts in alkali basalts from Kuandian, Liaoning Province, Hannobar, Hebei Province and Mingxi, Fujian Province have been reported in this paper. 87Sr/86Sr ratios in the Al-augites range from 0.70387 to 0.70401, with εSr varying from-6.96 to -8.94 while 143Nd/144Nd ratios vary from 0.51282 to 0.51295, with εNd ranging from 3.51 to 6.05. Four garnet megacrysts from Xuandian have 143Nd/144Nd ratios ranging from 0.51282 to 0.51293, with εNd = 3.51-5.66. The εNd values of megacrysts are similar to those of their host alkali basalts.The Pb isotopic composition of five Al-augite megacrysts is: 207Pb/206Pb = 15.6017-15.6649 and 206Pb/204Pb = 18.5604-18.8359. Four garnet megacrysts have 206Pb/204Pb ratios ranging from 18.1849 to 19.0345 and 207Pb/204Pb ratios varying from 15.6046 to 15.7792. Similarities in Pb isotopic compositions of all megacrysts suggest that Al-augite and garnet megacrysts from the three locations might be of the same origion. The fact that the Pb isotopic composition is obviously higher than that of the host basalts shows that no isotopic equilibrium has been achieved betwen the megacrysts and the host basalts.The primary magma of megacrysts might be produced from a two-component-mixing system one of them might be related with the material of underthrusting oceanic plate.
出处
《地球化学》
CAS
CSCD
北大核心
1992年第1期9-18,共10页
Geochimica
