Formation of Continental Crust by Diapiric Melting of Recycled Crustal Materials in the Mantle Wedge

The compositional similarity between high‐Mg andesite‐dacite from accretionary orogens and bulk continental crust (CC) provides an opportunity to unravel the CC formation paradox. Compositional data from a global compilation of Quaternary magmatic arcs indicate the presence of low‐Mg series (LMS) and high‐Mg series (HMS). The LMS show trends of crystal fractionation and can be subdivided into high Ba/Th and high La/Sm groups, which likely originate from fluid‐ and sediment melt‐modified mantle wedge, respectively. In contrast, the HMS have variably mixed compositions (e.g., high Mg#, Ba/Th, and La/Sm) and can be explained by partial melting of mélange diapirs rising into the mantle wedge, which are mixtures of subducted sediment, eroded arc crust or CC, buoyant oceanic crust, and peridotite. We, therefore, propose a two‐step process for creating CC involving extraction of LMS from the mantle followed by re‐melting of recycled LMS in the mantle to generate HMS and thus CC. Plain Language Summary Continental crust (CC) is extracted from the mantle primarily by subduction‐related magmatism in accretionary orogens. However, igneous rocks sourced from the mantle have low SiO2 (basalt), whereas average CC has high SiO2 (andesite) and high MgO. To resolve this paradox, we analyzed Quaternary subduction‐related igneous rocks worldwide and find that they can be divided into low‐Mg series (LMS) and high‐Mg series (HMS). We compare existing compositional data for LMS and HMS and find that LMS are dominated by basalt whereas HMS are dominated by andesite and similar to the average CC. Petrogenetic analyses reveal that LMS likely originate from the mantle and represent primitive CC, whereas HMS likely originate from recycled crustal materials in the mantle and represent mature CC. We propose a two‐step process for creating CC, involving extraction of LMS from the mantle followed by re‐melting of recycled LMS to generate HMS and thus CC. Our results provide a new solution to the CC formation paradox. Key Points Low‐Mg series (LMS) arc igneous rocks originate from fluid‐/sediment melt‐modified mantle wedge, followed by crystal fractionation High‐Mg series (HMS) arc igneous rocks likely originate from recycled crustal materials as mélange diapirs rising into the mantle wedge Continental crust is formed by extracting LMS from the mantle followed by re‐melting of recycled LMS in the mantle wedge to generate HMS