Characteristics And Petrogenesis Of The Jiangmiao And Gushan Intrusions In The Ningwu Basin, Eastern China

In the Ningwu basin located in the Lower-Middle Valley of Yangtze River is exposed a suite of subalkaline to alkaline igneous rocks, of which the intrusive rocks are gabbro and pyroxene diorite, represented by the Jiangmiao and Gushan intrusions. A field geologic investigation combined with a petrographic, petro-geochemical and isotopic study has been carried out on these two intrusions. The general features of the intrusions have been ascertained through this study, which gives a clue to better understanding the background and process for the formation of these two intrusive bodies.The following are achievements obtained through the study in this thesis.1. The lithologies of the Jiangmiao intrusion are predominated by gabbro and diabase, with less diorite-porphyrite and diorite, while those of the Gushan intrusion by pyroxene diorite.2. The Major element, trace element and rare earth element analyses show that these two intrusions consist of subalkaline to alkaline basic to intermediate-basic rocks with close genetic relation.3. The rare earth element and isotope data support the formation of these two intrusions through slight crustal material contamination combined with little fractional crystallization of basaltic magma derived from upper mantle and derivation of basaltic magma in Jiangmiao from deeper part of the upper mantle.4 The Jiangmiao intrusion is dated at 127.2±1.9Ma using Rb-Sr isochron method and represents product generated in the initial stage of the Ningwu volcanic basin formation.