发布时间：2019-11-27 浏览次数：29
Cretaceous adakitic quartz diorite and sedimentations around Nanjing
Time: Wednesday October 16th, 2019
Price: This mid-conference field trip is included in the registration fee.
The mid-conference field trip will include excursions to the Anjishan pluton, the Upper Cretaceous Pukou Formation, and cultural heritage sites around Nanjing.
The Anjishan pluton is located in the Ningzhen area of the Lower Yangtze region. It is composed of porphyritic granodiorite and quartz diorite. New LA-ICP-MS U–Pb zircon ages suggest that the Anjishan granodiorite formed at 108.8 ± 1.2 Ma (Liu JM et al., 2014, Geol. Rev.). The Anjishan rocks are characterized by geochemical features typical of adakitic rocks (i.e., high Mg#, Sr/Y, La/Yb, and low Y and Yb). These geochemical features suggest that the thickness of the crust in this area exceeded 40 km in the Early Cretaceous, which is greater than the present-day thickness of ~30 km. This indicates that the crust had been thinned by at least 10 km since the Early Cretaceous (Xu JF et al., 2002, Geology).
The second component of this field trip is a visit to the Yanziji Park on the southern bank of the Changjiang (Yangtze) River, where continental conglomerates deposited in an alluvial fan are well exposed. The conglomerates belong to the Late Cretaceous Pukou Formation and were deposited in an extensional sedimentary basin. They are gray-red in colour, poorly sorted, and poorly graded. The Yanziji Park is also an excellent scenic vantage point for the Changjiang River.
Fig. 9 Photograph showing a view in Yanziji Park.
During the field trip, we will visit the Nanjing Homo Museum, as well as the ape man cave that preserves the bones of Nanjing Homo erectus that lived around 300,000 years ago. In addition, as a Ming Dynasty cultural experience, we will visit the Yangshan Stele park – one of the largest steles in the world, which is Permian in age and composed of micritic limestones originally deposited in hemi-pelagic marine environment. These are famous tourist attractions in Nanjing and are close to the Xianlin campus of Nanjing University.