TY - JOUR
KW - alkaline Pluton
KW - Central Asian Orogenic Belt
KW - geochemistry
KW - Lake Zone
KW - U-Pb zircon dating
AU - D. Burianek
AU - Vojtěch Janoušek
AU - Pavel Hanžl
AU - Yingde Jiang
AU - Karel Schulmann
AU - Ondrej Lexa
AU - Battushig Altanbaatar
AB - Sagsai Pluton intruded the low-grade metavolcanosedimentary complex of the Cambrian Tugrug Fm. in the Sagsai river valley SW of Tsogt soum, Gobi-Altai aimag (SE Mongolian Altai). This oval body ( 9 × 12 km) is composed mainly of amphibole monzogabbros to quartz diorites, biotite to amphibole-biotite syenites to quartz monzonites. It is intruded by anatectic two-mica granites along the W rim. The abundant mafic microgranular enclaves enclosed by syenites to quartz monzonites are interpreted as an evidence of vigorous magma mingling and mixing. The newly obtained LA ICP-MS zircon ages for two samples of quartz monzonites gave emplacement ages of 307 ± 1 Ma and 309 ± 2 Ma (2σ), respectively. They have εtHf values varying broadly from +2.4 to +11.6 ruling out a participation of an old, mature crust. One gabbro body gave zircon U-Pb age of 322 ± 2 Ma with positive εtHf values of +7.4 to +11.5. The latter suggest an exclusively juvenile, depleted mantle-derived magma source. According to calculated P-T conditions, we propose three main stages in the Sagsai Pluton evolution. The gabbro started to grow at >1000 °C and 0.8-0.9 GPa. The ensuing magma mixing with crustal melts and final crystallization of gabbro occurred at similar P-T conditions (740-830 °C and 0.5-0.6 GPa) as partial melting of migmatite xenoliths in the Sagsai Pluton. The P-T conditions of the Sagsai Pluton final emplacement calculated from quartz syenite (c. 600 to 670 °C and 0.4-0.5 GPa) are consistent with the mineral assemblage in the contact aureole (cordierite-biotite and biotite-chlorite schists). The magmatic evolution of Sagsai Pluton confirms a model of deep lithosphere thermal anomaly associated with heterogeneous melting of crust in a post-subduction extensional regime, perhaps shortly after the slab break-off.
BT - Journal of GEOsciences
DO - http://dx.doi.org/10.3190/jgeosci.207
N2 - Sagsai Pluton intruded the low-grade metavolcanosedimentary complex of the Cambrian Tugrug Fm. in the Sagsai river valley SW of Tsogt soum, Gobi-Altai aimag (SE Mongolian Altai). This oval body ( 9 × 12 km) is composed mainly of amphibole monzogabbros to quartz diorites, biotite to amphibole-biotite syenites to quartz monzonites. It is intruded by anatectic two-mica granites along the W rim. The abundant mafic microgranular enclaves enclosed by syenites to quartz monzonites are interpreted as an evidence of vigorous magma mingling and mixing. The newly obtained LA ICP-MS zircon ages for two samples of quartz monzonites gave emplacement ages of 307 ± 1 Ma and 309 ± 2 Ma (2σ), respectively. They have εtHf values varying broadly from +2.4 to +11.6 ruling out a participation of an old, mature crust. One gabbro body gave zircon U-Pb age of 322 ± 2 Ma with positive εtHf values of +7.4 to +11.5. The latter suggest an exclusively juvenile, depleted mantle-derived magma source. According to calculated P-T conditions, we propose three main stages in the Sagsai Pluton evolution. The gabbro started to grow at >1000 °C and 0.8-0.9 GPa. The ensuing magma mixing with crustal melts and final crystallization of gabbro occurred at similar P-T conditions (740-830 °C and 0.5-0.6 GPa) as partial melting of migmatite xenoliths in the Sagsai Pluton. The P-T conditions of the Sagsai Pluton final emplacement calculated from quartz syenite (c. 600 to 670 °C and 0.4-0.5 GPa) are consistent with the mineral assemblage in the contact aureole (cordierite-biotite and biotite-chlorite schists). The magmatic evolution of Sagsai Pluton confirms a model of deep lithosphere thermal anomaly associated with heterogeneous melting of crust in a post-subduction extensional regime, perhaps shortly after the slab break-off.
PY - 2016
EP - 67–92
T2 - Journal of GEOsciences
TI - Petrogenesis of the Late Carboniferous Sagsai Pluton in the SE Mongolian Altai
UR - http://www.jgeosci.org/detail/jgeosci.207/abstract
VL - 61
ER -