内蒙石炭纪锡林浩特辉长岩成因—对地幔源区性质及深部流体循环的初步制约

石炭纪基性岩的成因是理解兴蒙造山带演化的关键之一，但是目前对于其岩石成因及动力学背景仍存在较大争议，缺乏对其地幔源区的系统研究是造成争议的主要原因。前期工作表明内蒙锡林浩特地区出露晚石炭世含角闪石辉长岩，是示踪地幔源区性质的重要窗口。因此，本项目拟以晚石炭世锡林浩特辉长岩为研究对象，通过全岩微量元素和矿物比例以及单斜辉石原位微量元素分析，反演母岩浆的微量元素组成；根据斜长石、单斜辉石、斜方辉石和角闪石的主量元素含量，确定母岩浆的温压条件和水含量，分析水在岩浆形成和演化过程中的作用；通过橄榄石主量元素和氧同位素以及全岩Sr-Nd-Hf同位素分析，确定地幔源区中再循环地壳组分的演化。这些信息是揭示地幔源区水来源及其循环过程的关键。结合已有的成果，本研究将初步建立深部水循环与兴蒙造山带晚古生代岩浆活动的成因联系，探讨形成锡林浩特辉长岩的动力学过程，为解决兴蒙造山带演化的关键科学问题提供重要制约。

Although the petrogenesis of the Carboniferous-aged gabbros is crucial for an understanding the evolution of the Xing’an-Mongolia orogenic belt, there is neither consensus on their origin nor on the tectonic setting of their emplacement. The principle problems appear to be the lack of detailed information on their mantle-source characteristics, partial-melting conditions as well as an understanding of magma evolution. Integrated whole-rock geochemical and isotopic analyses, in situ mineral chemical and isotopic compositions, and petrographic examination of selected rock units can address those problems. Previous studies have shown that Late Carboniferous amphibole-bearing gabbroic rocks crop out over a wide area near Xilinhot, Inner Mongolia, China, and can provide key information for understanding the characteristics of the mantle source. Therefore, this study will focus on those Late Carboniferous, in order to determine the thermal and chemical state of their mantle source, and to provide preliminary constraints on deep-Earth geodynamics of the Xing’an-Mongolia orogenic belt during the Late Paleozoic. This study will analyse clinopyroxene and whole-rock trace-element compositions, and mineral modes in order to constrain the trace-element compositions of the parental magmas. The proposed study will further determine pressure and temperature conditions, and water contents of the parental magmas through the major-element contents of plagioclase, clinopyroxene, orthopyroxene and amphibole, and thereby reveal the role of water in the generation and subsequent evolution of parental magmas. Combined whole-rock Sr-Nd-Hf isotopic compositions, major-element contents and oxygen isotopic composition of olivine will be used to determine the evolution of recycled crustal components in the mantle source. These results will provide crucial constraints on the understanding of the source of water and on associated cycling process beneath the Xing’an-Mongolia orogenic belt. Together with available data, the outcomes of this study will provide new perspectives on the mantle source and geodynamic processes related to these Carboniferous mafic igneous rocks. This study will help to establish a dynamic link between deep-Earth fluid cycling and Late Paleozoic magmatism in Xing’an-Mongolia orogenic belt, and provide an independent constraint on the tectonic evolution of Xing’an-Mongolia orogenic belt.