Qian, QingHermann, Jörg2025-02-112025-02-11researchoutputwizard:f5625xPUB3404Scopus:84877834008WOS:319009600009https://dspace-test.anu.edu.au/handle/1885/733713540The pressure-temperature (P-T) conditions for producing adakite/tonalite-trondhjemite-granodiorite (TTG) magmas from lower crust compositions are still open to debate. We have carried out partial melting experiments of mafic lower crust in the piston-cylinder apparatus at 10-15 kbar and 800-1,050 °C to investigate the major and trace elements of melts and residual minerals and further constrain the P-T range appropriate for adakite/TTG formation. The experimental residues include the following: amphibolite (plagioclase + amphibole ± garnet) at 10-15 kbar and 800 °C, garnet granulite (plagioclase + amphibole + garnet + clinopyroxene + orthopyroxene) at 12.5 kbar and 900 °C, two-pyroxene granulite (plagioclase + clinopyroxene + orthopyroxene ± amphibole) at 10 kbar and 900 °C and 10-12.5 kbar and 1,000 °C, garnet pyroxenite (garnet + clinopyroxene ± amphibole) at 13.5-15 kbar and 900-1,000 °C, and pyroxenite (clinopyroxene + orthopyroxene) at 15 kbar and 1,050 °C. The partial melts change from granodiorite to tonalite with increasing melt proportions. Sr enrichment occurs in partial melts in equilibrium with <20 wt% plagioclase, whereas depletions of Ti, Sr, and heavy rare earth elements (HREE) occur relative to the starting material when the amounts of residual amphibole, plagioclase, and garnet are >20 wt%, respectively. Major elements and trace element patterns of partial melts produced by 10-40 wt% melting of lower crust composition at 10-12.5 kbar and 800-900 °C and 15 kbar and 800 °C closely resemble adakite/TTG rocks. TiO2 contents of the 1,000-1,050 °C melts are higher than that of pristine adakite/TTG. In comparison with natural adakite/TTG, partial melts produced at 10-12.5 kbar and 1,000 °C and 15 kbar and 1,050 °C have elevated HREE, whereas partial melts at 13.5-15 kbar and 900-1,000 °C in equilibrium with >20 wt% garnet have depressed Yb and elevated La/Yb and Gd/Yb. It is suggested that the most appropriate P-T conditions for producing adakite/TTG from mafic lower crust are 800-950 °C and 10-12.5 kbar (corresponding to a depth of 30-40 km), whereas a depth of >45-50 km is unfavorable. Consequently, an overthickened crust and eclogite residue are not necessarily required for producing adakite/TTG from lower crust. The lower crust delamination model, which has been embraced for intra-continental adakite/TTG formation, should be reappraised.Acknowledgments D. Scott, D. Clark and W.O. Hibberson are acknowledged for technical assistance during the piston-cylinder experiments. We are grateful to F. Brink, C. Allen, G. Hunter, H. Cheng, and L. Li for help during the LA-ICP-MS and SEM analyses. R. Rapp, J.J. Yang, J.H. Guo, F. Liu, H.St.C. O’Neill, and T.G. Lan provided constructive suggestions. J. Adam and two anonymous reviewers provided very helpful comments. We thank J. Hoefs for efficient handling of the manuscript. The experiments were funded by the Australian Research Council to J.H. Q.Q. has been financially supported by the National Natural Science Foundation of China [41172065, 90914008, 41023009, 40872057] and the Chinese Academy of Sciences (XDB03010201).30EnglishAdakiteLower continental crustPartial melting experimentTTGTrace element201310.1007/s00410-013-0854-9http://www.scopus.com/inward/record.url?scp=84877834008&partnerID=8YFLogxK