Diagnostic rock textures in fault-controlled dolomite bodies: insights from hyperspectral imaging and the integration of petrographical, geochemical, and geomechanical analyses

Abstract

Fault-controlled, often hydrothermal, dolomitization is typically accompanied by a series of "diagnostic" rock textures that are considered to be indicative of elevated pressure (P) and temperature (T) conditions. Zebra textures, for example, comprise alternating, mm- to cm-scale, bands of replacement dolomite (RD) and saddle dolomite (SD) that form symmetrical RD-SD-SD-RD patterns. Such rock textures are closely related to boxwork textures that form similarly banded textures with highly irregular orientations, as well as cement-supported breccias that include floating clasts of RD that are fully surrounded and supported by SD. Recent studies of hydrothermal dolomite (HTD) bodies have focused on the dimensions of their associated geobodies, the timing of dolomitization, and the source of the dolomitizing fluid. Nevertheless, the sedimentological, tectonic, and metasomatic controls on the formation of these diagnostic rock textures have received limited attention. This Ph.D. thesis presents a multi-proxy approach to determine the genesis of zebra textures, cement-supported breccias, and boxwork textures in HTD bodies. First, shortwave infrared hyperspectral imaging was used to discern the several phases of RD and SD that form these rock textures, as well as to map their spatial distributions in the field (Chapter IV). Next, axisymmetric rock deformation experiments were used to establish an empirical framework by which the stress states that contribute to their formation can be interpreted (Chapter V). Lastly, a conceptual model for the formation of these rock textures is presented, incorporating a range of field, petrographical, and geochemical evidence (Chapter VI). Zebra textures, cement-supported breccias, and boxwork textures are closely associated with faults and carbonate-hosted ore deposits (e.g., magnesite, rare earth element, and Mississippi Valley-type mineralization), thus providing invaluable information regarding the hydrogeological evolution of a sedimentary basin and the metasomatism of carbonate sedimentary rocks under elevated P/T conditions.

Date of Award	1 Aug 2023
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Ernest Rutter (Supervisor) & Catherine Hollis (Supervisor)