The lack of zircon inheritance in the magmatic products and rather high zircon ε Hf t values (all >+3, but for most samples > +8) as well as whole-rock Sr–Nd isotopic compositions imply that the arc was not founded on mature continental crust. Over time, partial melting of older, lower crustal metabasic rocks became increasingly significant, again with a strong subduction signature. Magma mixing with, or without, exchange of xenocrysts between compositionally dissimilar melt batches was also important. Multiple intrusions of basic magma derived from a subduction-modified depleted mantle developed by fractional crystallization and/or accumulation of (Ol, Cpx) Amp + Bt, later joined by Pl.
The (normal-) calc-alkaline signature and characteristic trace-element enrichment in hydrous-fluid mobile large-ion lithophile elements (LILE) relative to high-field strength elements (HFSE) suggest an origin within a magmatic arc. 538–495 Ma) and are mostly geochemically primitive (Mg# ~ 50), Na-rich and metaluminous. The magmatic rocks were emplaced during most of the Cambrian ( c. 0.35–0.5 GPa) to shallower crustal levels dominated by Amp–Bt tonalites ( c. The Khantaishir Magmatic Complex (KMC) (south–central Mongolia) exposes a section of a magmatic system consisting of deep crustal, ultramafic cumulates (coarse-grained Amp gabbros and hornblendites c.
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