Geology Seminar Series - Yumeng Wang: Large-scale fluid convection revealed by coupled quartz dissolution-precipitation pattern

Wed., Mar. 24, 2021 4:00 p.m.

Location: https://uregina-ca.zoom.us/j/92337163072?pwd=b2xnMFpVYXRUQnlRYnZaWEF2WDlnUT09

Title: Large-scale fluid convection revealed by coupled quartz dissolution-precipitation pattern in the Athabasca Basin, Saskatchewan, Canada

Speaker: Yumeng Wang, PhD student, Department of Geology, University of Regina

Abstract:

Thermal convection is one of the most important forms of fluid flow and heat transport in the earth, and has been shown to be operating in many magmatic-hydrothermal systems, but whether thermal convection driven by thermal gradient occurs in sedimentary basins devoid of magmatic activities remain controversial. Here we report a case study of the Proterozoic Athabasca Basin in which the thermal convection hypothesis is strongly supported by petrographic observations and reactive mass transport modeling. The basin is renowned for its large accommodation of high-grade unconformity-related uranium deposits, and is stratigraphically characterized by thick (up to 1500 m) sandstone successions separated by relatively thin (<300 m), mud-rich intervals. The top of the sandstone successions is characterized by extensive quartz overgrowths and point contacts of detrital grains, whereas the basal part contains little cement and shows extensive dissolution features and sutured contacts. This spatial distribution pattern of diagenetic features cannot be explained by gradual burial of the basin, and is instead interpreted as a result of simultaneous quartz precipitation at the top and dissolution (followed by compaction) at the bottom due to fluid convection. Numerical modeling of reactive mass transport of SiO₂ indicates that this quartz precipitation-dissolution pattern can be produced only if the sandstones are sufficiently permeable and thick so that the Rayleigh number exceeds the critical value for convection. Thus, the development of such a coupled quartz cementation-dissolution pattern can be used as an indicator of thermal convection. This recognition is of great importance for explaining the large amounts of fluids required to form the unconformity-related uranium deposits in the Athabasca Basin.