Tectonic development from oceanic subduction to continental collision: Geochemical evidence from postcollisional mafic rocks in the Hong'an–Dabie orogens

Two types of the crust-mantle interaction in continental subduction zones

“…Partial melting of the mantle metasomatites gives rise to various mafic igneous rocks above subduction zones. As such, their petrogenesis can be accounted for by the slab-mantle interaction model (Zheng, 2012;Zhao et al, 2013;Chen et al, 2014;Dai et al, , 2015aDai et al, , 2015b.…”

“…Reaction of these melts with the overlying mantle wedge peridotite would generate pyroxene/amphibole-rich metasomatites. The metasomatites could be stored in the lithospheric mantle for a long time, and then become partially melted to give rise to mafic igneous rocks, which have OIB-like trace element distribution patterns, depleted radiogenic isotope compositions and H-O isotope compositions different from those of the normal mantle (Zheng, 2012;Dai et al, 2014Dai et al, , 2015aDai et al, , 2015bXu et al, 2014aXu et al, , 2014b.…”

“…The produced felsic melts are remarkably enriched in LILE and LREE but depleted in HFSE and HREE due to the stability of rutile and garnet during the dehydration melting. If the accessory minerals of rutile and garnet decompose, the resulted melts would be not depleted and even enriched in HFSE and HREE (Ringwood, 1990;Zheng, 2012;Dai et al, 2014Dai et al, , 2015b. In any case, these felsic melts would metasomatize the overlying mantle wedge above subduction channel, generating the mantle sources of mafic igneous rocks in deep subduction zones.…”

“…Coexisting UHP oceanic and continental crustal rocks have been found in many continental subduction zones (Beltrando et al, 2010;Wu and Zheng, 2013;Song et al, 2014;Zhou et al, 2015). In addition, postcollisional mafic igneous rocks have recorded the recycling of not only the oceanic crust but also the continental crust (Dai et al, 2011(Dai et al, , 2015a(Dai et al, , 2015bMerle et al, 2014). Therefore, it is necessary to decipher the petrological and geochemical records of the recycling of different types of crustal rocks and crust-mantle interaction during continental collision, to probe into similarities and differences in the slab-mantle interaction between continental subduction and fossil oceanic subduction, and to advance the understanding of chemical geodynamics for the recycling of crustal materials.…”

“…The main rock types in the Hong'an orogen are granitoid and volcanics of Early Cretaceous ages (Yang et al, 2012d;Gao et al, 2013). There are only sporadic occurrences of mafic igneous rocks in late Early Cretaceous to Late Cretaceous ages, such as dolerite dykes in the Macheng area Dai et al, 2015b), basalts in the Cehu, Sanjiadian and Duanjiawan areas of the Huangshi city (Lu et al, 2006). In-situ zircon U-Pb dating indicates that the Macheng mafic dykes formed in the Early Cretaceous of 112 to 115 Ma, and contain abundant residual zircons with mainly Neoproterozoic and Paleozoic ages Dai et al, 2015b).…”