Sulfur Isotope Systematics of Mid-Ocean Ridge Basalts

本研究旨在评估硫同位素对全球大洋中脊玄武岩(MORB)形成的几种地质作用的敏感性，并利用硫同位素变化来约束大洋中脊玄武岩及其地幔来源的同化和再循环过程。硫的稳定同位素(主要是32S和34S)被化学蚀变、脱气和岩石-海水相互作用等低温过程分馏，但不被部分熔融和分离结晶等高温过程分馏。因此，MORB中的硫同位素可以作为(1)大洋中脊岩浆室对海水硫的同化和(2)沉积物和洋壳通过上地幔循环回到MORB源区的灵敏示踪剂。我们将使用高精度离子微探针测量世界各地MORB玻璃原始不混溶硫化物中的硫同位素，以确定MORB中硫同位素的全球变异性，并研究这些变异性与同化作用、地壳厚度、扩散速率和热点附近的关系。

This proposal is to evaluate the sensitivity of sulfur isotopes to several geologic processes which contribute to the formation of mid-ocean ridge basalts (MORB) on a global scale, and to use sulfur isotope variations to constrain the processes of assimilation and recycling in MORB and their mantle sources. The stable isotopes of sulfur (mainly 32S and 34S) are fractionated by many low-temperature processes such as chemical alteration, degassing and rock-seawater interactions, but are not fractionated by high-temperature processes such as partial melting and fractional crystallization. As a result, sulfur isotopes in MORB can be used as sensitive tracers of (1) assimilation of seawater sulfur in mid-ocean ridge magma chambers, and (2) recycling of sediments and oceanic crust through the upper mantle and back into the source regions of MORB. We will use high-precision ion microprobe measurements of sulfur isotopes in primitive immiscible sulfides from MORB glasses worldwide to define the global variability of sulfur isotopes in MORB, and examine the relationships of these variations to assimilation, crustal thickness, spreading rate, and proximity to hotspots.