A synthesis and new perspective on the petrogenesis of kamafugites from West Qinling, China, in a global context
详细信息 查看全文
- 作者：Pengyuan Guo ; Yaoling Niu ; Xuehui Yu
- 关键词：West Qinling ; Kamafugite ; Petrogenesis ; Geochemistry ; Immiscibility
- 刊名：Journal of Asian Earth Sciences
- 出版年：5 January, 2014
- 年：2014
- 卷：79
- 期：part_PA
- 页码：86-96
- 全文大小：3549 K
文摘
We discuss the overall characteristics of a recently recognized kamafugite province in West Qinling, China, using field observations and geochemical data. We discuss the petrogenesis of the kamafugites using new bulk-rock major and trace element data and Sr-Nd isotope compositions of representative samples together with the literature data (in Chinese) and comparing them with type kamafugite suites from Italy, Brazil and Uganda. All these four kamafugite suites show OIB-like rare earth element (REE) patterns, but are much more enriched than OIB in the progressively more incompatible elements. The West Qinling kamafugite samples resemble closely the Ugandan and Brazilian suites in having a negative anomaly of K, P and Ti and a positive Nb-Ta anomaly, yet the Italian suite shows conspicuously a negative Nb-Ta anomaly. The four kamafugite suites have different 蔚Nd(t) values and 87Sr/86Sri ratios, implying their distinct sources and source histories. We consider that the ideal sources for kamafugite magmas are most likely metasomatized sub-continental lithosphere with components of ancient seafloor subducted calcareous terrigenous sediments. The close association of kamafugite with carbonatite worldwide, including the West Qinling suite, is consistent with both being derived from a single CO2-rich silicate parental magma segregated during ascent as a result of decompression-induced immiscibility. In terms of both sources (or source histories) and processes, our simple interpretation can effectively explain the petrogenesis of all the apparently different kamafugite suites suggests that the petrogenesis of kamafugites may actually be simple. Further effort should aim to test whether our interpretation is indeed valid globally.