An iron isotope perspective on back-arc basin development: Messages from Mariana Trough basalts

The geology and magmatism of the northern Mariana Trough (NMT) represent a type example for development back-arc basin (BAB). It is mature spreading center in south propagating northward via rifting arc rear lithosphere response to trench retreat overriding plate extension space time. thus essential fully characterize its tectonomagmatic processes that are potentially global significance. For this reason, we carried out comprehensive geochemical study on basaltic samples (glasses) from NMT axis 17 23°N by analyzing full suite major trace elements, Sr–Nd–Pb–Hf radiogenic isotopes stable Fe isotopes. isotopes, particular, have potential offer novel perspectives beyond aforementioned variables. From north, ?56Fe basalts (NMTB) decrease systematically, varying MOR-like value +0.12‰ an arc-like 0.00‰. Importantly, incompatible element abundances isotope compositions NMTB also show systematic along-latitude variations. Positively correlated with ?56Fe, fluid-insoluble elements (e.g., Nb, Ta, Zr, Hf, Ti heavy rare earth elements) south-to-north decrease, suggesting systematics inherited magma source variation. variation most consistent asthenosphere progressively more depleted harzburgitic prior melt depletion towards north. On other hand, there scattered but significant enrichment trends north terms fluid-soluble Ba, Rb, Cs, Th, U, K, Pb, Sr light elements), which increase slab material fluids, sediments etc.) contribution. These north-to-south defined can be readily understood as tectonic time initial arc-magmatism dominated sub-arc lithospheric mantle melting contributions characterized increasing asthenospheric melting, decreasing contribution diminishing participation. This tectonic-magma evolution manifested snapshot geology, petrology geochemistry. values unaffected materials, controlled residues previous extraction these low at early stage MORB characteristics well-developed system. observations affirm understanding compositionally physically buoyant prerequisite subduction initiation edges.