Genesis of Garnet-Bearing Granites in UHP Terrane of Dabie-Sulu Orogenic Belt, Central China

Dabie-Sulu UHP terrane, central China, extends from western Tongbai Mountains through the Dabie Mountains to Sulu. The garnet-bearing granites account for more than 85% in volume in the UHP units, with a mineral assemblage of Or+Ab+Q+Bi+Mc+Grt+Zr+Ep+Ae+Hb. In some profiles where larger eclogute bodies occurred, there is a gradual transition from eclogite →amphibolite (frequently with symplecites of plagioclase+ amphibole) →garnet-bearing gneisses→garnet-bearing granite. The gneisses occur as relics or bands of several centimeters to several meters in the garnet-bearing granites. The bands are parallel to the foliation of garnet-bearing granites. All these spatial distributions result from the partial melting and transformation of structural regime. The garnet-bearing granites have w(SiO₂)=71.73%-79.15%; A/CNK=0.83-1.09; w(K₂O+Na₂O)=6.15%-9.00%, w(K₂O)/w(Na₂O)=0.16-1.54. They are in the range of weakly peralkaline to weakly peraluminous series. In trace elements, the garnet-bearing granites have w(Zr)/w(Hf)=20.40~48.99 (averaging 35.13), w(Nb)/w(Ta)=6.93-22.28 (averaging 13.24), w(Zr)/w (Nb)=7.42-226.82 (averaging 37.34), and w(∑REE) =56.61×10^-6-795.58×10^-6. All samples of the garnet-bearing granites show obvious Eu negative (anomaly). While in primitive mantle-normalized spider diagram, the garnet-bearing granites are relatively rich in K, Ba, Pb, Nd, Y and La and relatively depleted in Nb, Ta, Sr, Ti, Zr and P. Combined with another characteristics such as high SiO₂, (K₂O+Na₂O), Ga and low Al₂O₃, CaO, MgO, the garnet-bearing foliated granites are similar to A-type granites. From Dabie to Sulu, the content of SiO₂, (K₂O+Na₂O), ∑REE, Ga and the ratios of w(K₂O)/w(Na₂O), (Fe/Mg)_M and w(Zr)/w(Hf) increase gradually; the content of Al₂O₃, CaO, MgO, Sr and the ratio of w(Nb)/w(Ta) decrease gradually. The emplacement level for garnet-bearing granites in Sulu is lower than that in Dabie.