Yang Zong-Feng, Zhou Jun-Hong
State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing. 100083, China.
Sci Rep. 2013;3:1856. doi: 10.1038/srep01856.
The nature of source rocks of basaltic magmas plays a fundamental role in understanding the composition, structure and evolution of the solid earth. However, identification of source lithology of basalts remains uncertainty. Using a parameterization of multi-decadal melting experiments on a variety of peridotite and pyroxenite, we show here that a parameter called FC3MS value (FeO/CaO-3*MgO/SiO2, all in wt%) can identify most pyroxenite-derived basalts. The continental oceanic island basalt-like volcanic rocks (MgO>7.5%) (C-OIB) in eastern China and Mongolia are too high in the FC3MS value to be derived from peridotite source. The majority of the C-OIB in phase diagrams are equilibrium with garnet and clinopyroxene, indicating that garnet pyroxenite is the dominant source lithology. Our results demonstrate that many reputed evolved low magnesian C-OIBs in fact represent primary pyroxenite melts, suggesting that many previous geological and petrological interpretations of basalts based on the single peridotite model need to be reconsidered.
玄武质岩浆源岩的性质在理解固体地球的组成、结构和演化方面起着基础性作用。然而，玄武岩源岩岩性的识别仍然存在不确定性。通过对多种橄榄岩和辉石岩进行的数十年熔融实验的参数化研究，我们在此表明，一个名为FC3MS值（FeO/CaO - 3*MgO/SiO2，均以重量百分比计）的参数能够识别出大多数源自辉石岩的玄武岩。中国东部和蒙古的类似大陆大洋岛玄武岩的火山岩（MgO>7.5%）（C - OIB）的FC3MS值过高，无法源自橄榄岩源。相图中的大多数C - OIB与石榴石和单斜辉石处于平衡状态，这表明石榴石辉石岩是主要的源岩岩性。我们的结果表明，许多著名的演化程度较低的低镁C - OIB实际上代表了原生辉石岩熔体，这表明许多先前基于单一橄榄岩模型对玄武岩进行的地质和岩石学解释需要重新考虑。
