Aluminous granulites from the Pulur complex, NE Turkey: A case of partial melting, efficient melt extraction and crystallisation

In the Pulur complex, NE Turkey, a heterogeneous rock sequence ranging from quartz-rich mesocratic gneisses to silica- and alkali-deficient, Fe-, Mg- and Al-rich melanocratic rocks is characterized by granulite-facies assemblages involving garnet, cordierite, sillimanite, ilmenite, ±spinel, ±plagioclase, ±quartz, ±biotite, ±corundum, rutile and monazite. Textural evidence for partial melting in the aluminous granulites, particularly leucosomes, is largely absent or strongly obliterated by a late-stage hydrothermal overprint. However, inclusion relations, high peak P - T conditions, the refractory modes, bulk and biotite compositions of the melanocratic rocks strongly support a model of partial melting. The melt was almost completely removed from the melanocratic rocks and crystallised within the adjacent mesocratic gneisses which are silica-rich, bear evidence of former feldspar and show a large range in major element concentrations as well as a negative correlation of most elements with SiO₂. Peak conditions are estimated to be ≥800 °C and 0.7-0.8 GPa. Subsequent near-isothermal decompression to ∼0.4-0.5 GPa at 800-730 °C is suggested by the formation of cordierite coronas and cordierite-spinel symplectites around garnet and in the matrix. Sm-Nd, Rb-Sr and ⁴⁰Ar/³⁹Ar isotope data indicate peak conditions at ∼330 Ma and cooling below 300 °C at ∼310 Ma.