Behavior of apatite in granitic melts derived from partial melting of muscovite in metasedimentary sources

ABSTRACT: Fluid-absent and fluid-fluxed melting of muscovite in metasedimentary sources are two types of crustal anatexis to produce the Himalaya Cenozoic leucogranites. Apatite grains separated from melts derived from the two types of parting melting have different geochemical compositions. The leucogranites derived from fluid-fluxed melting have relict apatite grains and magmatic crystallized apatite grains, by contrast, there are only crystallized apatite grains in the leucogranites derived from fluid-absent melting. Moreover, apatite grains crystallized from fluid-fluxed melting of muscovite contain higher Sr, but lower Th and LREE than those from fluid-absent melting of muscovite, which could be controlled by the distribution of partitioning coefficient (DAp/Melt) between apatite and leucogranite. DAp/Melt in granites derived from fluid-absent melting is higher than those from fluid-fluxed melting. So, not only SiO2 and A/CNK, but also types of crustal anatexis are sensitive to trace element partition coefficients for apatite. In addition, due to being not susceptible to alteration, apatite has a high potential to yield information about petrogenetic processes that are invisible at the whole-rock scale and thus is a useful tool as a petrogenetic indicator.©2021 China Geology Editorial Office.