TY - JOUR
T1 - Late Cretaceous (100-89Ma) magnesian charnockites with adakitic affinities in the Milin area, Eastern Gangdese
T2 - partial melting of subducted oceanic crust and implications for crustal growth in Southern Tibet
AU - Ma, Lin
AU - Wang, Qiang
AU - Wyman, Derek A.
AU - Li, Zheng-Xiang
AU - Jiang, Zi Qi
AU - Yang, Jin Hui
AU - Gou, Guo Ning
AU - Guo, Hai Feng
PY - 2013/8/15
Y1 - 2013/8/15
N2 - Rapid Mesozoic-Early Cenozoic crustal growth in the Gangdese area, southern Tibet, has commonly been attributed to pre-collisional and syn-collisional underplating of mantle-derived magmas. Here, we report on adakitic magnesian charnockites (i.e., hypersthene-bearing diorites and granodiorites) near Milin, in eastern Gangdese, that provide new insights into the crustal growth process of the region. Zircon U-Pb analyses of seven charnockite samples indicate that they were generated in the Late Cretaceous (100-89Ma). They exhibit variable SiO2 (53.9 to 65.7wt.%) contents, high Na2O/K2O (1.6 to 14.4) and Sr/Y (27.2 to 138.7) ratios, low Y (6.5 to 18.5ppm), heavy rare earth element (e.g., Yb=0.6 to 1.6ppm) and Th (0.20-2.39ppm) contents and Th/La (0.02-0.23) ratios, with relatively high Mg# (46 to 56) and MgO (2.0 to 4.5wt.%) values. They are characterized isotopically by high and slightly variable εNd(t) (+2.4 to +4.0) and εHf(t) (+10.1 to +15.8) values with relatively low and consistent (87Sr/86Sr)i (0.7042 to 0.7043) ratios. Their pyroxenes have high crystallization temperatures (876 to 949°C). The Milin charnockites were most probably produced by partial melting of subducted Neo-Tethyan oceanic crust that was followed by adakitic melt-mantle interaction, minor crustal assimilation and fractional crystallization of amphibole+plagioclase. The upwelling asthenosphere, triggered by the roll-back of subducted Neo-Tethyan oceanic lithosphere, provided the heat for slab melting. Therefore, we suggest that, in addition to pre-collisional and syn-collisional underplating of mantle-derived magmas, the recycling of subducted oceanic crust has also played an important role in continental crustal growth in southern Tibet.
AB - Rapid Mesozoic-Early Cenozoic crustal growth in the Gangdese area, southern Tibet, has commonly been attributed to pre-collisional and syn-collisional underplating of mantle-derived magmas. Here, we report on adakitic magnesian charnockites (i.e., hypersthene-bearing diorites and granodiorites) near Milin, in eastern Gangdese, that provide new insights into the crustal growth process of the region. Zircon U-Pb analyses of seven charnockite samples indicate that they were generated in the Late Cretaceous (100-89Ma). They exhibit variable SiO2 (53.9 to 65.7wt.%) contents, high Na2O/K2O (1.6 to 14.4) and Sr/Y (27.2 to 138.7) ratios, low Y (6.5 to 18.5ppm), heavy rare earth element (e.g., Yb=0.6 to 1.6ppm) and Th (0.20-2.39ppm) contents and Th/La (0.02-0.23) ratios, with relatively high Mg# (46 to 56) and MgO (2.0 to 4.5wt.%) values. They are characterized isotopically by high and slightly variable εNd(t) (+2.4 to +4.0) and εHf(t) (+10.1 to +15.8) values with relatively low and consistent (87Sr/86Sr)i (0.7042 to 0.7043) ratios. Their pyroxenes have high crystallization temperatures (876 to 949°C). The Milin charnockites were most probably produced by partial melting of subducted Neo-Tethyan oceanic crust that was followed by adakitic melt-mantle interaction, minor crustal assimilation and fractional crystallization of amphibole+plagioclase. The upwelling asthenosphere, triggered by the roll-back of subducted Neo-Tethyan oceanic lithosphere, provided the heat for slab melting. Therefore, we suggest that, in addition to pre-collisional and syn-collisional underplating of mantle-derived magmas, the recycling of subducted oceanic crust has also played an important role in continental crustal growth in southern Tibet.
KW - adakitic charnockite
KW - crust growth
KW - gangdese batholith
KW - roll-back
KW - slab melting
KW - Tibet
UR - http://www.scopus.com/inward/record.url?scp=84880045280&partnerID=8YFLogxK
U2 - 10.1016/j.lithos.2013.04.006
DO - 10.1016/j.lithos.2013.04.006
M3 - Article
AN - SCOPUS:84880045280
SN - 0024-4937
VL - 175-176
SP - 315
EP - 332
JO - Lithos
JF - Lithos
ER -