Post-Meeting Field Trip 1

Ultrahigh-pressure metamorphism in the Dabie orogen: Tracing the continental crust into the mantle 

Time Duration：25-27, October,2024 

Leader:  Prof. WANG Qin, Nanjing University 

Major cities or towns on the line:  Beijing City (start), Hefei City, Nanjing City (end) 

Geological features for observation and investigation: 

 The Dabie-Sulu orogen is one of the largest (~30,000 km2) and best exposed ultrahigh-pressure (UHP) metamorphic terranes in the world. It was formed by northward subduction of the Yangtze craton beneath the North China craton in the Triassic. The central Dabie UHP metamorphic belt consists of interlayered pelitic and granitic gneisses, phengite-quartz schist, quartzite, marble, eclogite and garnet peridotite. These rocks commonly contain coesite and occasionally microdiamond as inclusions, and was subjected to the peak metamorphism under P-T conditions of 3.0-4.0 GPa and 700-850 ºC (i.e., >120 km) at 234-240 Ma. After a rapid syn-convergence exhumation under eclogite facies, these rocks experienced slow exhumation under amphibolite to greenschist facies conditions from the Latest Triassic to the Jurassic. In the Early Cretaceous, large amounts of granitic rocks intruded into the Dabie Mountains and resulted in a domal structure and the final unroofing of the UHP rocks. 

During this field trip, we will visit four classic outcrops to see different types of eclogites and their country rocks: the Bixiling eclogite-garnet peridotite complex, the Xindian microdiamond-bearing eclogites within marbles, the Yezhai folded eclogites and eclogite-facies breccia, and a kilometer-scale eclogitic sheath fold in Shuanghe. These UHP metamorphic rocks provide a window to trace deep subduction and exhumation processes of continental supracrustal materials during continental collision.

 Costs:  3000 CNY per-person (2400 CNY if share a standard room with two beds), which covers： 
       1. High-speed train ticket from Beijing to Hefei (first class); 
       2. Hotel stay (2 nights in Qianshan County on Oct. 25-26, one night in Nanjing University on Oct. 27), four-star hotel, meals and water in the field; 
       3. Field vehicle rental/gasoline/toll, travel insurance; 
       4. Administrative fees for preparing and setting up the field trip;
       5. Fees for entering private properties during the field excursion without sightseeing, etc.