Tracing Recycled Paleo-Asian Ocean Carbonates Using Magnesium Isotope Systematics
The low δ26Mg values in basaltic lavas are generally thought to be derived from mantle sources modified by subducted carbonates,making Mg isotopes a potential tool for tracing subducted plates.To investigate the fate of ancient subduction carbonate and its control on the composition of Cenozoic basalts in the west of Daxing'anling-Taihang Gravity Lineament(DTGL),we report Mg isotope data of Dariganga Cenozoic basalts in Eastern Mongolia.The δ26Mg values(-0.35‰ to-0.30‰)of the studied basalts are systematically lower than that of the terrestrial mantle(δ26Mg=-0.25‰±0.04‰),which cannot be explained by post-eruption alteration,crustal contamination,fractional crystallization,and partial melting.The low δ26Mg compositions of the basalts may be related to subduction carbonates in the mantle sources.Modeling of the Mg-Sr isotopic data indicates that the addition of 3%to 6%dolomitic carbonates to the pyroxenite source can explain the Mg isotopic anomalies and 87Sr/86Sr ratios in the Dariganga Cenozoic basalts.Based on the seismic tomography data and the distribution of Mg-Zn data in the DTGL cross-section,the Paleo-Pacific plate is excluded as a possible source of recycled carbonates.Combined with the regional tectonic history,we suggest that the recycled carbonates in the mantle source were carried by another subducting oceanic plate,namely,the Paleo-Asian Ocean subduction.
万方数据
维普
