Chen, X.; Wu, T.; Gao, Q.; Lai, Y. Recycling of Marine Carbonate Induced Calcium Isotope Heterogeneity of Arc Magmas in Subduction Zones. Preprints2021, 2021070523. https://doi.org/10.20944/preprints202107.0523.v1
APA Style
Chen, X., Wu, T., Gao, Q., & Lai, Y. (2021). Recycling of Marine Carbonate Induced Calcium Isotope Heterogeneity of Arc Magmas in Subduction Zones. Preprints. https://doi.org/10.20944/preprints202107.0523.v1
Chicago/Turabian Style
Chen, X., Qin Gao and Yu-Ming Lai. 2021 "Recycling of Marine Carbonate Induced Calcium Isotope Heterogeneity of Arc Magmas in Subduction Zones" Preprints. https://doi.org/10.20944/preprints202107.0523.v1
Abstract
Calcium (Ca) is an essential element constituting sedimentary carbonate in subducting sediments. Ca isotopic characteristics of subduction-related rocks could provide insight into the behavior and budget of carbonate and carbon cycles in subduction zones, due to the distinctive δ44/40Ca ranges of sedimentary carbonate with respect to the mantle. Here, we studied the Ca isotopic compositions of arc magmas from the Northern Luzon arc (NLA), which are evolved from a depleted mantle metasomatized by slab-derived fluids and sediment melts. The δ44/40Ca values range from 0.76 ± 0.04‰ to 1.01 ± 0.03‰ and cover the typical ranges for bulk silica earth (BSE, ~ 0.94‰) and fresh mid-ocean ridge basalt (MORB, ~ 0.83‰). The Ca isotopes of NLA volcanics are not dominantly determined by the effects of mantle partial melting or fractional crystallization, nor significantly modified by secondary alteration. Instead, the δ44/40Ca values of NLA volcanics are controlled by the subduction-related metasomatism. The metasomatism by slab-derived fluids (mainly expelled from altered oceanic crust, AOC) dramatically elevated the contents of fluid-mobile elements (e.g., Ba and Pb) with respect to fluid-immobile elements (e.g., Ce). This process, however, rarely modified the Ca isotopes, possibly ascribed to the δ44/40Ca similarity between AOC and the depleted mantle. The δ44/40Ca values significantly correlated with subduction indicators (e.g., Sr-Nd isotopes, Ba/Nb, Ce/Pb, and Nb/La), demonstrating the Ca isotopes of NLA volcanics are mainly controlled by the metasomatism of sediment melts subducting from the South China Sea (SCS). Based on the thermal structures and chemical compositions of sediments subducting into global trenches, we propose that carbonate Ca isotopic signals can only be observed in the arcs with high sedimentary Ca fluxes and temperature-pressure conditions well beyond the solidus of H2O-saturated sediment melting, e.g., NLA, Nicaragua, Guatemala, Colombia, Peru, South Chile, North Vanuatu, New Zealand, and Kermadec. The absence of such signals in other arcs suggests either limited sedimentary fluxes or much of the subducting sedimentary carbonate has been survived during plate subduction to enter the deep mantle.
Environmental and Earth Sciences, Atmospheric Science and Meteorology
Copyright:
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Received:
17 December 2021
Commenter:
Kang Liu
The commenter has declared there is no conflict of interests.
Comment:
Goog job! based on your result, it seems like that carbonate cycling in hot subduction zones is reasonable. and i also agree with it, but in my opinion, only under very high temperature (such as more than 1000℃) can the carbonate-saturated slab materials (sediments or altered oceanic crust) produce high CaO silicate melts by partial melting (from the experiments of skora et al. (2015)) , and under low temperature, is it possible to generate high CaO silicate melt? by the way, can you share your TableS5 in your preprint? it is unaviable in the online prints.
Commenter: Kang Liu
The commenter has declared there is no conflict of interests.
with congratulations and thanks!
Kang