A long-lived magma chamber in the Paleoproterozoic North China Craton: Evidence from the Damiao gabbro-anorthosite suite

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The Damiao igneous complex is a composite gabbro-anorthosite suite that was emplaced during the post-collisional extensional stage following the amalgamation of the Eastern and Western Blocks within the North China Craton (NCC). This magmatic suite is composed of anorthosite, leuconorite, gabbroic anorthosite, norite, gabbronorite, noritic gabbro, ferrodiorite, Fe-Ti-(P) rich gabbro and Fe-Ti ore. We present zircon LA-ICP-MS U–Pb age data on noritic gabbro, norite, leuconorite, gabbronorite, and gabbroic anorthosite from the Damiao suite. The data yield weighted mean 207Pb/206Pb ages of 1725±13Ma, 1687±18Ma, 1751±15Ma and 1693±24Ma, 1721±17Ma, and 1729±14Ma respectively suggesting a relatively long-lived crystallization process within the magma chamber during late Paleoproterozoic. The different lithologies show similar rare earth element patterns indicating a co-magmatic nature and derivation from the same magma chamber through polybaric crystallization and differentiation. The high alumina dykes of gabbronorite and noritic gabbro which are chemically identical to the parental magmas of high alumina gabbros from elsewhere and exhibit an upper mantle origin with high degree melting of spinel-bearing mantle facies. Their zircon ɛHf(t) compositions plot along the evolution line of the 2.5–3.0Ga Neo- to Mesoarchean basement rocks in the NCC (−9.2 to −3.3) and the relatively low Cr, Ni contents (Cr: 9.33–338ppm; Ni: 8.62–182ppm), high Th/Ta (>2.90), Ba/Zr (>20.18), and low Nb anomaly (Nb/Nb*=NbPM/(ThPM×LaPM)<0.50) for chemically equivalent parental rocks deviate from typical mantle-derived melts, suggesting the input of Archean crustal components. We propose that the magma was sourced from spinel-bearing sub-continental lithospheric mantle at depths of up to 60km, within a post-collisional extensional setting, and assimilated Archean crustal components before ascent. The heat input for the extensive melting might have come from upwelling asthenosphere triggered by the break-off of the subducted oceanic slab following the collision between the Eastern and Western Blocks of the NCC. The deep seated magma was channeled to mid-crust depth along rift zone and underwent low pressure crystallization and differentiation to form the Damiao suite.