Abstract
Arc magmas originate in subduction zones as partial melts of the mantle, induced by aqueous fluids/melts liberated by the subducted slab. Subsequently, they rise through and evolve within the overriding plate crust. Aside from broadly similar features that distinguish them from magmas of other geodynamic settings (e.g., mid-ocean ridges, intraplate), arc magmas display variably high Sr/Y values. Elucidating the debated origin of high Sr/Y signatures in arc magmas, whether due to mantle-source, slab melting or intracrustal processes, is instrumental for models of crustal growth and ore genesis. Here, using a statistical treatment of >23000 whole rock geochemical data, I show that average Sr/Y values and degree of maturation (MgO depletion at peak Sr/Y values) of 19 out of 22 Pliocene-Quaternary arcs correlate positively with arc thickness. This suggests that crustal thickness exerts a first order control on the Sr/Y variability of arc magmas through the stabilization or destabilization of mineral phases that fractionate Sr (plagioclase) and Y (amphibole ± garnet). In fact, the stability of these mineral phases is function of the pressure at which magma evolves, which depends on crustal thickness. The data presented show also that high Sr/Y Pliocene-Quaternary intermediate-felsic arc rocks have a distinct origin from their Archean counterparts.
Highlights
Correspondence and requests for materials should be addressed to Crustal thickness control on Sr/Y signatures of recent arc magmas: an Earth scale perspective
Elucidating the debated origin of high Sr/Y signatures in arc magmas is essential to develop a comprehensive model of arc magma genesis[34], constrain models of crust formation[6,7,8,9] and understand magmatic processes leading to the genesis of porphyry-type deposits[10,11,12,13,14,15]
If the high Sr/Y signatures of arc magmas are due to intracrustal processes a systematic control by crustal thickness on Sr/Y values should be expected, because crustal thickness is the main parameter controlling the development of adakite-like signatures in the intracrustal model, through stabilisation of magmatic (6residual) amphibole 6 garnet and destabilization of plagioclase in a thick crust[23,24,30,31,32]
Summary
Correspondence and requests for materials should be addressed to Crustal thickness control on Sr/Y signatures of recent arc magmas: an Earth scale perspective. Using a statistical treatment of .23000 whole rock geochemical data, I show that average Sr/Y values and degree of maturation (MgO depletion at peak Sr/Y values) of 19 out of 22 Pliocene-Quaternary arcs correlate positively with arc thickness This suggests that crustal thickness exerts a first order control on the Sr/Y variability of arc magmas through the stabilization or destabilization of mineral phases that fractionate Sr (plagioclase) and Y (amphibole 6 garnet). If the high Sr/Y signatures of arc magmas are due to intracrustal processes a systematic control by crustal thickness on Sr/Y values should be expected, because crustal thickness is the main parameter controlling the development of adakite-like signatures in the intracrustal model, through stabilisation of magmatic (6residual) amphibole 6 garnet and destabilization of plagioclase in a thick crust[23,24,30,31,32]
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