Monazite Growth in Response to Metamorphic and Deformation Events at Different Structural Levels
Abstract
The central zone of Damara Orogen formed by the continent-continent collision between Congo and Kalahari cratons has been the research focus for decades due to its significance for Gondwana supercontinent assembly. Nine episodic deformation events (D1cz-D9cz) were identified by dating the syn-kinematic localized sills and regional granite and pegmatite. However, such a method is not a direct constraint on the deformation and metamorphic history because detailed information recorded inside of the metamorphic rocks themselves is not obtained. Monazite is a sensitive mineral that can help reveal details of multi-stage metamorphic events based on its chemical zoning patterns. In this study, monazite-bearing samples from the central Damara zone at different structural depths, i.e., the basal, mid-level and top-level Lower Plate, the Okahandja Detachment and the Upper Plate, were mapped by EPMA for Y, Th, U, Ca and Ce elements. Results indicate that, for garnet-absent samples, monazites from Lower Plate generally show up to 4 zones with increasing Y patterns, representing the retrograde metamorphism related with post-peak along orogen shortening events (D6cz-D7cz) and extensional exhumation events (D8cz-D9cz). However, for garnet-present samples, monazites from Lower Plate (basically the mid- to top-level) exhibit up to 7 growth zones with both decreasing and increasing Y patterns, indicating the prograde and peak Damaran events (D1cz-D5cz) and retrograde metamorphism (D6cz-D9cz). The missing 2 growth zones can be explained by the fact that some deformation events did not promote metamorphism. The absence of prograde and peak metamorphic records for monazites in garnet-absent samples from Lower Plate can be ascribed to the complete dissolution of monazite due to partial melting during peak metamorphism. However, regardless of whether garnet is present, monazites from Upper Plate show uniformly increasing Y patterns, and reveal 2-3 growth zones that correspond to the retrograde metamorphism aforementioned. Furthermore, monazites from the Okahandja Detachment present only 1-2 growth zones that basically record the faulting activity. Ongoing research work will be to date these monazites, trace its growth environment change, and explore its further implications on structural and tectonic evolution.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.V52B..03J
- Keywords:
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- 1031 Subduction zone processes;
- GEOCHEMISTRY;
- 8031 Rheology: crust and lithosphere;
- STRUCTURAL GEOLOGY;
- 8150 Plate boundary: general;
- TECTONOPHYSICS;
- 8178 Tectonics and magmatism;
- TECTONOPHYSICS