A Neoarchean subduction polarity reversal event in the North China Craton

Abstract

Subduction polarity reversal events following arc–continent, arc–arc or continent–continent collisions have been well-documented from Cenozoic, Mesozoic, and Paleozoic orogens, but not from the Archean. We here document a Neoarchean subduction reversal event after an arc–continent collision between the Eastern Block of the North China Craton (NCC) and the Fuping arc using field, geochemical and geochronological data. We focus our work on the Wangjiazhuang granite in the Zanhuang massif located along the eastern margin of the Central Orogenic Belt (COB) of the NCC, and a regional tectonic comparison with other granitic rocks with similar ages, geochemical and petrogenetic characteristics. The ca. 2.5Ga A-type Wangjiazhuang granite intrudes the Neoarchean Zanhuang mélange belt and contains mafic and felsic inclusions. It has positive εNd(t) values (+0.12 to +1.13) and TDM2 ages between 2784Ma and 2869Ma. This work shows clearly, from field structural relationships, geochemistry and geochronology, that the Wangjiazhuang granite formed after an arc–continent collision between the Eastern Block which is defined as a continental block and the Fuping arc, after a subduction polarity reversal event placed a new slab beneath the collisionally modified margin of the Eastern Block and converted it to an Andean-type margin. The subduction polarity reversal event at ca. 2.5Ga resulted in melting of the enriched mantle. Meanwhile, the rising magma induced partial melting of the old and thickened TTG crust leading to the intrusion of ca. 2.5Ga Wangjiazhuang granite into the Neoarchean Zanhuang mélange. There are other granitic rocks with similar ages and geochemical and petrogenetic features in the Central Orogenic Belt and Eastern Block of the North China Craton, suggesting that they formed in a similar tectonic setting as the circa 2.5Ga granites across the Eastern Block. The Neoarchean subduction polarity reversal event and prior arc–continent collision provide strong evidence that plate tectonics was operating by the end of the Neoarchean.