Pre-conference field trip -1

Paleoproterozoic and Late Mesozoic Granitic rocks in Beijing, North China Craton

Time:Wednesday October 9th – Sunday October 13th, 2019 

Price: $450 US dollars

The North China Craton (NCC) is the largest Archean craton in China. It was stabilized in the Paleoproterozoic and was subsequently covered by a thick sequence of Proterozoic to Paleozoic sediments. It was destabilized during the Mesozoic and since then experienced intense compressional–extensional deformation, magmatism (i.e., decratonization). This trip offers an excellent opportunity to examine the cratonization and decratonization processes of the NCC through visits to the ancient basement rocks, the sedimentary cover, the Paleoproterozoic rapakivi pluton, and the Late Mesozoic plutons associated with the Late Mesozoic Yunmenshan metamorphic core complex (MCC) around Beijing.

Fig. 1 Simplified geological map for the granitoids in the Beijing area.

The regional Archean basement rocks comprise magnetite quartzite, granulite, and tonalite gneiss with zircon U–Pb ages of about 2.52 Ga. These rocks were intruded by the 1.68 Ga rapakivi pluton at Miyun. The Late Mesozoic Yunmenshan MCC is the first recognized MCC in China. Late Jurassic dioritic to granitic rocks and Early Cretaceous granodiorite to granite intruded the Archean basement and its sedimentary cover. They make up the majority of the core of the Yunmengshan MCC. The ductile extensional shear zone along the southeastern margin developed between 131–114 Ma. It is overprinted by the brittle Hefangkou normal fault, which is associated with the development of the Huairou rift basin on the hanging wall. There will be plenty of opportunities to examine the relationships between the emplacement of the granitic plutons and the ductile–brittle structures that they contain. As an additional benefit, because the trip will take place during Beijing’s golden season, there will be excellent opportunities to see and photograph the beautiful Great Wall. 

Fig. 2 An overall view of the Great Wall in the field.

Day 1 (Oct. 9):

Participants should arrange their own transportation to Beijing and arrive before October 9th. We will provide the name and address of the hotel to all of the participants.

Morning: Depart from hotel to the Miyun district of Beijing at 8:30 am.

We will examine the Archean basement rocks (~2.5 Ga Kf granite) and the unconformity between the basement and its Proterozoic sandstone cover. A ~1.68 Ga rapakivi stock intruded into the Proterozoic sandstones.

Afternoon: We will visit the Miyun (or Shachang) rapakivi pluton that intruded into the ~2.52 Ga Archean magnetite quartzite and tonalite.

If time permits, we will visit the Early Cretaceous diorite–granodiorite–granite Siganding pluton.

Evening: We will arrive at the hotel at the University of Chinese Academy of Sciences in the Huairou District of Beijing. 

Day 2 (Oct. 10):

Morning: Departure at 8:30 am.

This day will focus on the Late Jurassic to Early Cretaceous Yunmengshan diorite and granite pluton that represents syn-tectonic magmatism, as well as the Yunmengshan metamorphic core complex. They are all related to the decratonization of the North China Craton. We will also have an opportunity to visit the Great Wall.

Evening: Arrive at the hotels in the Changping District of Beijing.

Day 3 (Oct. 11):

Morning: We will meet in front of the hotel and depart for Badaling batholith at 8:30 am. We will examine the Early Cretaceous gabbros, diorites, and granites, as well as the gabbro-related iron ores. We will be able to observe beautiful textures that serve as evidence for magma mingling/mixing. These textures illustrate the complex relationships between these rocks.

Evening: We will arrive at the hotels in Changping District of Beijing. This is the end of the field trip.

Day 4 (Oct. 12):

Depart from Beijing to Nanjing.