Rare-earth and trace elements of the lower Cambrian–Lower Cretaceous siliciclastic succession of NE Gondwana in Jordan : from provenance to metasomatism

The present bulk-rock geochemical study aims to answer some questions concerning the distribution and variability of trace elements (TEs) and rare earth elements (REEs) in the lower Cambrian–Lower Cretaceous sandstones and mudstones of NE Gondwana in Jordan. The study proved that the REE and the TE distribution patterns in both detrital and authigenic, light and heavy minerals are controlled principally by the source-rock provenance, followed by an interplay of many factors: chemical weathering, recycling, hydraulic sorting, locally low-temperature, hydrothermal metasomatism, depositional environment and redox conditions, and diagenesis. On the basis of specific trace elements, trace-element ratios, and petrographic proxies, the provenance is constrained to be mainly felsic-, rarely mafic granitoids of the Arabian-Nubian Shield, and less commonly, recycled Palaeozoic and Mesozoic siliciclastic strata. REEs are hosted mainly in zircon, Ti-bearing minerals, and partly in clay minerals. They were depleted by both chemical weathering and recycling; nevertheless, they were enriched by subsequent hydraulic sorting and low-temperature, hydrothermal metasomatism. Chemical weathering initially depleted zirconium. However, this was counteracted by subsequent enrichment through recycling, hydraulic sorting, and low-temperature, hydrothermal metasomatism. The fractionation of the other TEs, due to these sedimentological factors during the genesis of subarkosic arenites, quartz arenites and mudstones, is discussed and some conclusions are derived. The Eu negative anomaly was enhanced significantly by recycling and low-temperature, hydrothermal metasomatism. Scandium abundance increased with decreasing grain size from coarse sand to the mud fraction. The recorded REE and TE fractionation might also apply to siliciclastics in similar, geological environments.