RECYCLING OF NOBLE GASES BY CONTINENTAL DEEP SUBDUCTION
Postcollisional mafic igneous rocks are common in collisional orogens, which may have bearing on the recycling of subducted contiental crust into the mantle. The noble gas extracted from minerals in the postcollisional mafic igneous rocks may provide important information about the recycling during continental deep subduction. In this contribution, we report for the first time the mineral noble gas isotope compositions of postcollisional mafic igneous rocks from the Dabie orogeny in east-central China. The He and Ar isotope analyses of pyroxene from these postcollisional mafic rocks yield extremely low 3He/4He of 0.002 to 1.8 Ra and air-like 40Ar/36Ar ratios of 393.6 to 1599.8. There are also correlations between mineral noble gas isotope and whole-rock geochemical compositions. These observations demonstrate the mass transfer from the deeply subducted continental crust to the overlying mantle wedge, witnessing the source mixing between the crust-derived melt and the mantle peridotite in the continental subduction channel. A direct addition of the crustal He via crust-derived melt to the mantle leads to the extremely low 3He/4He ratios in orogenic lithospheric mantle, and the dissolved atmospheric Ar in the subducted supracrustal rocks results in the air-like 40Ar/36Ar ratios. It is demonstrated that the recycling of noble gases into the mantle by the deep subduction of continental crust. Our findings also establish the slab-mantle interaction model for the recycling of noble gases in the continental subduction zone.