ND, SR, PB ISOTOPIC CHARACTERISTICS OF THE MESOZOIC INTRUSIVE ROCKS IN THE TAIHANG - DA HINGGAN MOUNTAINS TECTONOMAGMATIC BELT AND THEIR SOURCE REGION

Abstract

The Taihang-Da Hinggan Mountains Tectonomagmatic Belt is the Mesozoic magmaeric activities concentrating area in eastern China, which passes through the two tectonic units of the North China Craton and the Inn Mongolian Orogenic Zone. In this paper a systematic geochemical study on Nd, Sr and Pb isotopic characteristics from more than 40 typical complexes along the tectonomagmatic belt is presented to indicate that the Mesozoic intrusives in different sections of this belt (mainly the north, south Taihang Mountains and the middle-south Da Hinggan Mountains), even those of different stages (mainly three stages) in the same section have entirely different Nd, Sr and Pb isotopic characteristics, which reveals that their source regions are different. The source rocks in the southern section of Taihang Mountains are related to materials from the enriched mantle reservoir. In the northern section the early stage basic-intermediate rocks are mainly formed by the partial melting of materials from the enriched mantle, the main stage intermediate-acid ones have a close connection to materials from the lower crust, while the late stage alkali-rich ones are even derived from those from the lower-middle crust. And the intermediate-acid magma in the middle-south Da Hinggan Mountains is mainly originated from depleted mantle materials. These also reveal that the lithospheric mantle below the North China Craton is enriched and that below the Inner Mongolia Orogenic Zone is depleted. In addition, implicated by Nd depleted mantle model ages (T_(DM)), 2543～1485Ma probably represents the time for mantle enrichment beneath the North China Craton, and 983～540Ma (Proterozoic to early Palaeozoic period) suggests one of the main stages for the crust growth in Da Hinggan Mountains area.