鄂北地区碱性岩的时代及成因

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。

AGE AND GENESIS OF THE ALKALINE ROCKS IN NORTHERN HUBEI PROVINCE

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.