Dissertation
U-Pb, Lu-Hf and Sm-Nd isotope systematics of accessory minerals and the applications in subduction zone processes
Doctor of Philosophy (PhD), Washington State University
01/2018
Handle:
https://hdl.handle.net/2376/117227
Abstract
The utility of U-Pb, Lu-Hf and Sm-Nd isotope systems in accessory and metamorphic minerals provides both age and isotope constraints on the processes of subduction zone metamorphism. The combined use of coupled garnet Lu-Hf and Sm-Nd dates and zircon, titanite, and monazite U-Pb ages, with geothermometer and the temperature information recorded by the closure of isotope systems, adds direct timing constraints on the pressure-temperature conditions of the metamorphism in the subduction zone. Natural rock samples of eclogite from the Sulu ultra-high pressure terrane in eastern China have been studied using this approach, which presents the P-T-t path for the eclogite formation and subsequent retrogression. Radiogenic isotopes also have been widely used as powerful tracers to investigate crustal evolution and subduction-zone processes, including magma genesis, recycling of crustal materials, and crustal melting. This dissertation focuses on using in-situ Sm-Nd isotopes of titanite and monazite – systems that have not been widely employed – to constrain the crustal melting processes in the subduction zone. Understanding partial melting in subduction zones is critically important, as the melt could affect the rheology of subducted crust dramatically and thus provides insights into the processes of chemical differentiation of the continental crust. By applying in-situ Sm-Nd isotope measurements in REE-rich minerals (i.e., titanite, monazite, etc.), integrated with their inherent U-Pb chronologic information, this dissertation observed 1) Homogenous Nd isotope in titanite from the host rocks with vastly different protoliths (Triassic eclogite, Archean amphibolite, and leucogranite), which links the source, migration and emplacement of the partial melt; 2) Nd isotope disequilibrium between anatectic monazite and garnet/host rocks, which illustrates that the melt-source disequilibrium may not be uncommon during crustal anatexis, and thus whole-rock Nd isotope data may not preserve the signatures of the source, which may be biased by preferential dissolution of one LREE-hosting phase during partial melting. This dissertation sheds new lights on the behaviors of Sm-Nd isotope system during the crustal melting processes in the subduction zone, and presents new approaches of integrating multi-mineral and multi-system to the studies of crustal evolution.
Metrics
3 File views/ downloads
22 Record Views
Details
- Title
- U-Pb, Lu-Hf and Sm-Nd isotope systematics of accessory minerals and the applications in subduction zone processes
- Creators
- Da Wang
- Contributors
- Jeffrey D Vervoort (Advisor)Jeffrey D Vervoort (Committee Member)Sean P Long (Committee Member)Catherine M Cooper (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- School of the Environment (CAHNRS)
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Number of pages
- 176
- Identifiers
- 99900581507501842
- Language
- English
- Resource Type
- Dissertation