Blueschists in Damenglong, Jinghong City, southwestern Yunnan, China: Petrology and metamorphism and their implications for the Paleo-Tethys

This paper is the result of geological survey engineering.

Objective Bluesschist is the product of subduction of ancient oceanic crust and collage of ocean-continental and land-continental collisions. It is of great significance to further explore the subduction metamorphism of oceanic crust or continental crust and the formation and evolution of orogenic belts. In this paper, the newly discovered bluesschist in Damenglong area, Jinghong, western Yunnan, is selected as the research object, and its restriction on the Changning-Menglian Paleo-Tethys Ocean subduction-orogenic setting is discussed.

Methods Through petrography and mineral chemistry analysis, two different types of bluesschist in the study area are identified according to different mineral combinations, and the P-T trajectory of metamorphic evolution is initially established. Combined with regional geological data, the genetic mechanism and dynamic background of bluesschist are analyzed to constrain the evolution of Changning-Menglian Paleo-Tethys Ocean subduction and orogeny.

Results The results show that the peak metamorphic temperature and pressure conditions of muscovite-garnet-glaucophane-quartz schists are T =450-490℃, P=0.90-1.45 GPa, and chlorite-epidote-actinolite-glaucophane schist with the low peak metamorphic temperature and pressure conditions are T = 430-470℃, P = 0.69-0.73 GPa. The P-T tracks of metamorphic evolution of two different types of bluesschist are preliminarily established.

Conclusions The metamorphic differences of the two types of blueschists occur might because the metamorphic rocks subducted to different depths were uplifted to the surface via subduction tunnels through the exhumation mechanism. The results of this study will provide an important basis for further exploring the subduction and closure of the Paleo-Tethys Ocean in the Changning-Menglian suture zone.