摘要
白音诺铅锌矿床主要受中生代演化完善的一个火山-深成杂岩控制。在该区,受同一构造机制控制,一套中酸性火山岩、次火山/超浅成侵入体和花岗岩类深成侵入体,在空间上密切相伴,时间上有先后,但时距不大。它们在岩相和结构上逐渐变化,化学成分具明显相似性和继承性的演化特点。作者根据这一套火山-深成杂岩的岩石学及地球化学特点,讨论了它们的岩浆起源、演化及成岩机制。
The Bayan Nut volcano-plutonic complex occurs in the Mesozoic Greater Khingan volcanic down-faulted region in the eastern part of Inner Mongolia. Controlled by the same tectonic mechanism, the volcanic rocks, subvolcanic and/or ultra-shallow intrusions and plutons are spatially related. Though they originated at different times, the time spans were short, thus forming an igneous complex.
This complex consists of volcanic rocks (which are mainly rhyolitic crystal tuffolavas and dacitic crystal tuffolavas), subvolcanic and/or ultra-shallow intrusions ranging from subbasic dacite-porphyry and granodiorite-porphyry through acid rhyolite-porphyry and granite-porphyry to alkali quartz syenite-porphyry, and plutonic rocks, including granite and granodiorite. Their petrofacies and textures change gradually, and their chemical compositions show obvious similarity and inheritance.
The ∑REE and REE distribution patterns of the granitoids of the complex are similar to those of the early Yanshanian granitoids in the Greater Khingan Range region and early Yanshanian syntectonic granitoids in South China. The relatively low initial ^(87)Sr/^(86)Sr ratio and δ^(18)O value(I_0=0.7028—0.7077 and δ^(18)O=6.1‰ -SMOW) of the volcanic rocks and granitoids show that the primitive magma forming the complex originated mainly in the lower crust and upper mantle, and a certain materials of the upper crust were mixed in the process of the ascent of the magma.
The contents of the transitional elements and large-ion lithophile elements and the chondrite-normalized REE patterns of various rocks change regularly with the change in the ratios of Ga/AI and Li/Mg, which suggests that as a result of three separations of melts from the deep to shallow magma chambers and relatively complete differentiation in the shallow magma chamber, the product of each magmatic activity must be composed of subbasic, acid and alkali rocks. Haring a powerful thermodynamic system, the early magma was able to erupt at the earth's surface. With the tectonic and magmatic evolution, the thermodynamic force decreased and the resistance increased, and hence ultra-shallow intrusions and plutons formed successively. The period from the volcanic eruption to plutonic intrusion lasted for about 20Ma.
出处
《地质论评》
CAS
CSCD
北大核心
1990年第4期289-297,共9页
Geological Review
