Paleogeographical reconstruction of the South China Block during Gondwana assembly using detrital apatite: Pan-African source affinity concealed by detrital zircon

Abstract

Detrital zircon provenance analysis plays a key role in reconstructions of past tectonic and sedimentary environments. However, non-unique (or even erroneous) interpretations can be introduced due to the inherent limitations of both zircon provenance analysis (fertility bias, recycling) and those of single-proxy provenance systems in general. Apatite crystallizes in a wider range of lithologies than zircon, and can thus facilitate more detailed source reconstructions. In this study, detrital apatite analysis of Cryogenian to Ordovician sandstones in the Cathaysia Block was carried out in comparison with detrital zircon data for a better understanding of the source-sink process on the northern margin of Gondwana. In contrast to the abundant Grenvillian (1300−900 Ma) detrital zircons of igneous origin, detrital apatites show major Pan-African (650−500 Ma) age peaks that are mostly derived from metamorphic rocks (52%−72%). The apatite data show that the Cathaysia Block mainly received detritus from western Australia and India during the late Neoproterozoic to early Paleozoic, with much lower affinities to East Antarctica and the terranes of Iran-Turkey. Provenance variations include a shift with time in the major age populations from ca. 900 Ma to 600 Ma with a decrease in metamorphic apatite (from 72% to 52% of all grains) in the late Cryogenian, an increase in high-grade metamorphic apatite (from 27% to 56%) in the late Ediacaran−Cambrian, and an increase in igneous apatite (from 33% to 45% of all grains) in the Early Ordovician. In contrast, detrital zircon data could only reveal the source change in the late Ediacaran. These provenance switches were likely caused by the unroofing of Pan-African orogens (640−490 Ma) and subsequent erosion of their exposed cores, due to the rapid uplift of source rocks formed in the Pan-African orogens during the Gondwana assembly.