Post-Meeting Field Trip 2

Introduction 

Late Mesozoic tectonics in the Daqingshan orogen, north margin of the North China Craton

The Late Mesozoic orogenic processes in East Asia were characterized by continent–continent collision, large-scale thrusting, strike-slip faulting and intense crustal shortening, crustal thickening, regional anatexis and metamorphism, followed by large-scale lithospheric extension, rifting and magmatism (Fig. 1). These significant tectonic activities, marked by widespread intracontinental orogeny and continental reconstruction, are commonly termed the Yanshan Revolution (Movement) in the Chinese literature.

Fig.1 Simplified map outlining the distribution of Late Mesozoic contractional tectonic features in China (depicted by red zones) and its surrounding convergent orogenic margins marked by yellow zones (located in the inset map at lower left corner). Tectonic elements in the Trans-Baikal orogen and along the Mongo-Okhotsk suture are complied after Donskaya et al. (2013), and those in the far-east Russia after Faure et al. (1986, 1995). Abbreviations: TBO: Trans-Baikal Orogen; CAOB: Central Asia Orogenic Belt; NCC: North China Craton; SCB: South China Block; BJKB: Bureya-Jiamusi Khanka Block; MDJ: Mudanjiang suture.

The construction of the East Asian continent in the Late Mesozoic occurred in two major stages. In the first stage (ca. 170–135 Ma), plate convergence was dominated by continental margin accretion, multi-plate collision, extensive orogenic activity, metamorphism and compressional deformation. In the second stage (ca. 135–120 Ma), the collapse of thickened lithosphere led to large-scale crustal extension and the development of vast metamorphic core complexes, pull-apart basins and broad volcano-magmatic belts (Fig. 2).

Fig.2 Late Jurassic and Early Cretaceous tectonic activity, sedimentation, magmatism, and deformation in the East Asian continent. JLSF, Middle Jurassic Jiulongshan Formation; TJSF, Late Jurassic Tiaojishan Formation in North China; ZJKF, Early Cretaceous Zhangjiakou Formation in North China; SMSG, Middle Cretaceous Shimaoshan Group in SE China.

During the construction of the East Asian plate in the Late Mesozoic, the transition from orogenic collision to postorogenic extension occurred at ca. 135 Ma. Magmatic activity between ca. 135 and 120 Ma was much more intense at this time, with voluminous magmatism of varied composition, and with a wider spatial distribution. As collisional orogenesis changed to post-orogenic extension, the orogenic belts were subjected to regional melting. During the post-orogenic period,alkaline, peralkaline and other mantle-derived magmas were mainly formed ca. 135–120 Ma, and this was accompanied by uplift and deformation of rocks of the middle and lower crust via the formation of metamorphic core complexes.

Here our structural and geochronologic analysis in the Daqingshan structural belt define the Middle-Late Jurassic-Eearly Cretaceous compressional structures including the Middle Jurassic growth strata and nappes related intracontinental compression and Early-Middle Cretaceous extensional structures typical of the Early Cretaceous thermal upwelling-extensional structure and detachment structure system associated with the Early Cretaceous extension., marking the Late Mesozoic intracontinent deformation in East Asia.

• The Middle Jurassic growth strata to the Baotou city constituted a roughly forward thrusting sequence with a slow uplift rate in the early stages and a suddenly accelerated uplift rate in the final stage, responding to the initiation of Yanshanian deformation during 170–160 Ma due to N-S compression driven by the closure of the Mongol-Okhotsk Ocean.  

• The Hohhot “MCC” to the north of Hohhot City, records top-to-southeast normal-sense exhumation of the deformed Archean-Proterozoic metamorphic basement that was intruded by Jurassic-Cretaceous complex granite mass. The basement was intruded by deformed Jurassic adakitic and undeformed Cretaceous A-type intrusions in the footwall. The mylonitic shear zone (S1) located between undeformed Cretaceous granite and low-angle detachment faults with pervasively top-to-SE simple shearing (ca. 146-141 Ma). Here the three units composed the Hohhot “MCC” and reestablished Hohhot thermal upwelling-extensional structure (TUES) model: (a) the core-granite composed of Early Cretaceous (136-127 Ma) A-type granites; (b) the pure-shear-dominated shear zone (S21) distributed in the core-granite periphery, with foliation (no lineation); (c) the low-angle detachment system (S22) characterized by low-angle normal faults separating the footwall top-to-the-SE ductile structures and microbreccia zone from the hanging-wall Cretaceous supra-detachment basin along the flank of domal S1. 
  

Field Trip Price 

3200  per-person, which covers：

• Hotel stay (3 nights stay in Hohhot City, 25th-28th October 2024), meals and water in the field.  

• Field vehicle rental/gasoline/toll. Train fee between Beijing and Hohhot.

• Administrative fees for preparing and setting up the field trip.

• Fees for entering private properties during the field excursion without sightseeing, etc.

• Except oversea invited speakers whom got the financial support from the DEEP-2024 with the official supporting letter, the other participants should pay the field-trip fees before October 10, 2024 for the preparation of the vehicle and booking the train tickets. 

Field Trip Schedule 

• Time Duration：25~28 October, 2024

• Participant：Min. 16 / Max. 20

• Departing from Beijing to Hohhot City: at 9:00, 25 Oct. from Beijing beijing station or Qinghe station by train.

• Returning Beijing from Hohhot City：at 9:00, 27 Oct. from Hohhot East station by train.

Day 1: 25 October, 2024 

• 9:00, Participants depart from Beijing to Hohhot City, Inner Mongolia by train (at Beijing Bei station or Qinghe station).

• 12:00-13:00, Have lunch at the Hotel.

• 13:30-16:00, Go to the Jiulongwan section (northeast of Hohhot City) to observe Hohhot thermal upwelling-extensional structure in Daqingshan.

• 16:00-18:00, Go to the Qixiaying section (northeast of Hohhot City) to observe the Early Cretaceous extensional structures.

• 18:30-20:00, have dinner at the Hotel.

Day 2: 26 October, 2024 

• 7:00-9:00, Have breakfast at the Hotel.

• 9:00-17:30, Go to Zhaogou section and Ximawan section in the Shiguai Basin (north of Baotou City) to observe the Middle-Late Jurassic growth strata, and have snack in field. We have a long travel from Hohhot City to Baotou City, which will takes 2.5 hours.

• 18:00-20:00, Have dinner at the Hotel.  

Day 3: 27 October, 2024 

• 7:00-9:00, Have breakfast at the Hotel.

• 9:00-12:30, Go to the Bikeqi section (east of Hohhot City) to observe Bikeqi nappes..

• 12:30-13:30, Have lunch at the Hotel 

• 14:00-18:00, visit Inner Mongolia Museum and Saishang Lao Street to understand Mongolia culture.

• 18:30-20:00, Have dinner at the Hotel.  

Day 4: 28 October, 2024 

• 7:00-9:00, Have breakfast at the Hotel.

• 9:00-12:00, Participants depart from Hohhot City to Beijing by train. 

Contact Information： 

Any inquiry about the Field trip 2, please contact with:

Prof. SHI Wei, Email: shiweinmg@163.com

Dr. Zhang Yu，Email: yuzhang000@126.com