Detrital zircon U–Pb geochronology, Hf-isotopes and geochemistry—New clues for the Precambrian crustal evolution of Cathaysia Block, South China

Abstract

This paper reports some new results from U–Pb geochronological, Hf isotopic and REE geochemical studies of detrital zircons in the Ordovician sandstones from South Jiangxi within Cathaysia. 426 groups of U–Pb age determinations define five major age populations: 2560–2380 Ma (a peak of 2460 Ma), 1930–1520 Ma (a peak of 1700 Ma), 1300–900 Ma (a major peak at 970 Ma and two subordinate peaks at 1250 Ma and 1130 Ma), 850–730 Ma (a prominent peak of 780 Ma) and 670–530 Ma (a major peak at 540 Ma and a subordinate peak at 650 Ma). We also report zircon U–Pb concordia age of 3.96 Ga, which is the oldest age so far obtained from Cathaysia. The age peak at 2460 Ma correlates with similar ages reported for Neoarchean global continental growth. The 1930–1520 Ma population broadly overlaps with the time of amalgamation and disruption of the Columbia supercontinent. The major age peak at 970 Ma and two secondary peaks at 1250 Ma and 1130 Ma reflect multiple tectonothermal events associated with the assembly of Rodinia. Similar ages are widely reported from the South China Craton (SCC). Our study reveals that the 850–730 Ma population is consistent with the breakup period of Rodinia, suggesting that the SCC within Rodinia began to break up since 850 Ma. Geologically, the evidence for this breakup event is widespread and presented by Neoproterozoic granites, bimodal igneous rocks, basic dyke swarms and formation of continental rift type basins. Our study also reveals a 670–530 Ma population that correlates well with the assembly of Gondwana during end Neoproterozoic. However, direct geological evidence for this event has not yet been found within the studied area. Furthermore, the Hf isotopic model age data suggest two major stages of crustal evolution within Cathaysia. The first is the event dated at 1.6–2.8 Ga and the second one at 3.5–3.9 Ga. The zircons show a large range of εHf(t) values from + 8.64 to − 30.54, suggesting that they have different origins with a similar age of crystallization. The fact that most detrital zircons show negative εHf(t) values suggests the ancient provenances of Cathaysia were dominated by reworked crustal materials.