Earliest paleoproterozoic supracrustal rocks in the north china craton recognized from the daqingshan area of the khondalite belt: Constraints on craton evolution

Abstract The Upper Wulashan “Subgroup” at Daqingshan in the Khondalite Belt of the Western Block of the North China Craton contains an Early Paleoproterozoic (2.5–2.45 Ga) supracrustal sequence, incorporating banded iron formations, which we refer to as the Daqingshan Supracrustal Rocks. They contain rounded to elliptical zircon grains that commonly show core–rim or core–mantle–rim structures and precise SHRIMP U–Pb dating of these domains allows the discrimination of a series of tectono-thermal events that straddle the Archean/Proterozoic boundary. Detrital zircon cores with oscillatory zoning have formation ages ranging from 2.55 to 2.50 Ga, indicating derivation from Late Neoarchean magmatic rocks. As a result of exhumation and erosion, these became incorporated in earliest Paleoproterozoic sediments that were deposited between 2.50 and 2.45 Ga and then underwent high-grade metamorphism at 2.45–2.40 Ga. This event variously recrystallized the cores into two main domains: a dark inner domain and a gray outer domain, as imaged in cathodoluminescence. The gray domains commonly show sector zoning and have Th/U ratios of 0.1–0.5, a feature commonly noted in zircons recrystallized under high-grade metamorphic conditions. Metamorphic mantles are generally more homogeneous in structure and have lower Th/U ratios (commonly