SHRIMP ages of detrital zircons from the Changcheng System in the Ming Tombs area, Beijing: Constraints on the protolith nature and maximum depositional age of the Mesoproterozoic cover of the North China Craton

摘要

The Mesoproterozoic Changcheng System is widely distributed in the North China Craton. Determining its time of deposition and sources is important to understand the Precambrian crustal evolution of the North China Craton. This paper suggests age distribution patterns for detrital zircons from clastic sediments of the Changcheng System in the Ming Tombs area, Beijing. Samples of feldspar-bearing sandstone (CHc-2) and pure sandstone (CHc-9) were collected from the Changzhougou Formation, which constitutes the basal part of the Changcheng System. Detrital zircons show an age range from 2.35 to 2.60 Ga. However, sample CHc-9 in the upper Changzhougou Formation also contains some zircons with ages of 1.9 — 1.8 Ga and 2.3 — 2.1 Ga. The age patterns lead to the following conclusions: (1) Most of the detrital material came from a source area composed predominantly of ～2.5 Ga continental crust of the North China Craton; (2) 1.9 — 1.8 Ga reflects the age record of Palaeopro-terozoic continent-continent collisional event in the North China Craton; and (3) the oldest age for deposition of the Changcheng System is 1.8 Ga.