Application of blocky calcite vein LA-MC-ICP-MS U–Pb dating and geochemical analysis to the study of tectonic–fault–fluid evolutionary history of the Tabei Uplift, Tarim Basin

Abstract

In this work, blocky calcite veins in drilling cores were studied by integrating petrography, in-situ laser ablation multiple collector inductively coupled plasma mass spectrometry U–Pb dating and trace element analysis to investigate whether calcites without obvious syn-kinematic features can constrain the timing of local fault/fracture activity and far-field tectonic movement. On this basis, a synergistic ‘tectonic–fault–fluid’ evolution model in the Tabei Uplift, Tarim Basin was developed. Cathodoluminescence characteristics, rare earth elements and U–Pb ages allow the subdivision of calcite veins into three categories. The much shorter timescales for sealing the studied calcite vein than the uncertainties of current carbonate U–Pb dating (<5 %) attest to a temporal link between calcite precipitation and fracture activity. The consistency between calcite U–Pb ages and the timing of terminal collisions of the Tarim Craton with surrounding terranes demonstrates the potential of blocky calcites to record far-field tectonics. The information on the origin of fluids and the timing of fracture activity revealed by the calcite veins is placed within the established tectonic evolutionary history of the study area, allowing the tectonic–fracture–fluid evolutionary history of the study area to be recovered. From ~466 Ma to ~454 Ma, accompanying the formation of strike-slip faults under compressional stresses resulting from the closure of the Kudi Ocean, seawater and formation fluids seeped down into the carbonate strata and eventually precipitated along the fracture walls. From ~383 Ma to ~366 Ma, continued northward subduction of the eastern Kunlun–Altyn Tagh terrane caused tectonic uplift and fault reactivation. Circulating meteoric fluid and downward seeping seawater transported by advection eventually precipitated blocky calcites. From ~287 Ma to ~232 Ma, activation of the early faults along with the closure of the Paleo-Asian Ocean promoted the formation fluids buffered by the host limestones to flow into open fractures and precipitated. This work, in a practical geological context, confirms that centimeter-scale blocky calcite veins have the potential to constrain the timing of fault slip and associated fracturing, which further boost confidence in the applicability of calcite U–Pb geochronology in dating of brittle faulting episodes.