鄂北地区碱性岩的时代及成因

AGE AND GENESIS OF THE ALKALINE ROCKS IN NORTHERN HUBEI PROVINCE

产于鄂北的花山寨、观子山、杀熊洞和庙垭四个碱性岩体,其K-Ar、U-Pb和Rb-Sr同位素年龄值为215～306Ma,成岩时代属海西—印支期。根据^(87)Sr/^(86)Sr初始值,杀熊洞岩体(0.7032)和庙垭岩体(0.7029)的成岩物资来源于上地幔,观子山岩体(0.7041)的成岩物质属幔壳混源型,但仍以幔源为主,花山寨岩体(0.7092)的成岩物质则主要来源于下地壳。

In the present paper, petrology, petrochemistry, REE geochemistry, especially age and geneses of four alkaline rock bodies, i. e., Huashanzhai nordmarkite body, Guanzishan jadeite-cancrinite syenite body, Shaxiong dong cancrinite syenite-carbonatite complex and Miaoya syenite-carbonatite complex located in Northern Hubei Province, have been studied. K-At, U-Pb and Rb-Sr datings give the isotopic age of these rock bodies in a range of 215-306Ma, indicating that they were formed during Hersynian-Indosinian period. Initial ^(87)Sr/^(86)Sr ratios in Shaxiongdong complex and Miaoya complex are 0.7032 and 0.7029 respectively, showing that their rock-forming materials were derived from the upper mantle. The ratio in Guanzishan body is 0.7041, and hence its rock-forming materials came from a mixed source in the upper mantle predominantly with lower crustal materials. The ratio in Huashanzhai body is 0.7092, so its rock-forming materials is mainly derived from the lower crust.