Post-conference field trip -1

Post-collisional granitoids and migmatites in the Dabie orogen, east-central China 

Time: Saturday October 19th – Tuesday October 22nd October, 2019 

Price: $500 US dollars

The Dabie orogen in east-central China is a continent-continent collisional orogen that was produced by northward subduction of the South China Block beneath the North China Block in the Triassic. It is characterized by the occurrence of ultrahigh-pressure (UHP) metamorphic rocks with index minerals such as coesite and microdiamond. These characteristics demonstrate deep subduction of the continental crust to subarc depths. Numerouspost-collisional granitoids were produced in the Early Cretaceous, contemporaneously with migmatites. Relict zircons in both granitoids and migmatites have similar U–Pb ages indicating that they were derived from reworking of the deeply subducted continental crust in the post-collisional stage. The post-collisional granitoids in the Dabie orogen can be subdivided into two magmatic phases. The early phase was emplaced at 130–143 Ma, and exhibits an adakitic affinity and varying degrees of structural deformation. In contrast, the late phase was emplaced at 120–130 Ma and exhibits neither adakitic affinity nor considerable deformation. Multiple lines of evidence indicate the formation of granulite–migmatite–granite associations in the Early Cretaceous. This four-day field trip will focus on the post-collisional granitoids and migmatites in the Dabie orogen. During the field trip, we will visit representative outcrops of granitic batholiths, a granite-hosted Mo deposit, migmatites, and granulites that occur in the same lithotectonic zone.

Fig. 10 Photograph of the Tianzhu Mountain in the Dabie orogen.

Fig. 11 Simplified geologic map of the Dabie orogen showing the distribution of post-collisional magmatic rocks. The insert shows the location of the area within the Triassic Qinling–Dabie–Sulu orogenic belt in east-central China. BHYZ = Beihuaiyang low-T/low-P greenschist- facies zone, NDZ = North Dabie high-T/UHP granulite-facies zone, CDZ = Central Dabie mid-T/UHP eclogite facies zone, SDZ = South Dabie low-T/UHP eclogite-facies zone, SZ = Susong low-T/HP blueschist- facies zone, XMF = Xiaotian–Mozitan fault, WSF = Wuhe–Shuihou fault, HMF = Hualiangting–Mituo fault, TMF = Taihu–Mamiao fault.

Day 1 (Oct. 19):

Morning: Depart from Nanjing to Jinzhai County by bus.

Afternoon: Depart from Jinzhai County to Shapinggou village. We will visit the Early Cretaceous quartz syenite porphyry and associated Mo deposit, 

which formed in the post-collisional stage. Afterwards we will go to the hotel in Jinzhai County.

Day 2 (Oct. 20):

Morning: Depart from hotel at 8:30 am to Tiantangzhai village and visit the Early Cretaceous Tiantangzhai granitic batholith, which was emplaced at

130–143 Ma. The batholith exhibits an adakitic affinity and varying degrees of structural deformation. Afterwards we will move to Yanzhihe village to visit a

migmatite outcrop that also formed in the Early Cretaceous.

Afternoon: We will go to the Daoshichong and Manshuihe villages, and examine the migmatites that occur there. These migmatites formed in the Early Cretaceous and associated with the granitic magmatism.

Evening: We will arrive at the hotel in Huoshan County.

Day 3 (Oct. 21):

Morning: Depart from the hotel at 8:30 am to visit the Baimajian granitic batholith and the migmatite at Qingtian.

Afternoon: We will visit the Zhubuyuan granitic batholith. Both Baimajian and Zhubuyuan granitoids were emplaced at 120–130 Ma, neither of which

 exhibit the adakitic affinity or considerable deformation.

Evening: We will arrive at the hotel in Qianshan County.

Day 4 (Oct. 22):

Morning: Depart from hotel at 8:30 am to visit the Tianzhushan granitic pluton, which was emplaced in the Early Cretaceous into the UHP granitic 

gneisses of Triassic age, and these gneisses have the igneous protoliths of Neoproterozoic age.

Afternoon: Depart from Qianshan County to Nanjing by bus.