Project Details
Projekt
Kinematic evolution of crustal mylonites from southern Mexico during Pangea breakup and beyond – a microstructural and geochronologic approach combining electron backscatter diffraction (EBSD) and secondary ion mass spectrometry (SIMS).
Subject Area
Mineralogy, Petrology and Geochemistry
Term
since 2025
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 565882959
The aim of this research project is to apply the latest technical advances in both microstructure analysis and geochronology to a specific geological problem that has been driving scientists for decades. How can the overlap of large parts of Mexico with the northern Andes of South America be explained in Pangea reconstructions? Although there is a consensus that different crustal blocks shifted along lateral shear zones, it is still unclear exactly how and when this occurred. Basically, the situation is due to various tectonic processes that were active in the Mesozoic during and after the breakup of western equatorial Pangea: (1) the opening of the Gulf of Mexico and the Caribbean Sea, which produced rift basins and dextral shear zones in eastern Mexico, and (2) the onset of oblique subduction of the Pacific Plate along the western plate boundary of Mexico, which is held responsible for hypothetical left-lateral so-called mega-shears in Mexico. In addition, there is (3) a more recent hypothesis that considers most of central and southern Mexico as a large peninsula in the early Mesozoic, which was formed by hyperextension of a doubled crust in response of the Permian orogeny, which in turn could explain most of the abovementioned overlap. All these tectonic processes have different effects on rocks of the mid-continental crust, which can be studied in deep shear zones that are exposed today in the form of mylonites. The whole problem is particularly evident in the Sierra de Juárez Mylonite Complex, which has long been the subject of controversy, as well as in the Chiapas Massif, which has a partly comparable geological history. Mylonites from both areas will be examined here with regard to their kinematics and timing. State-of-the-art EBSD analytics are used to (1) determine shear sense and physical conditions of deformation based on microstructural features and (2) analyze datable accessory phases (e.g., zircon and titanite) for intracrystalline effects on the crystal domains affected by deformation. This is crucial to understand the influence of deformation on chemical diffusion and to accurately document these domains. In the next step, U-Pb isotopes of the deformed domains of individual zircons with a beam diameter of only 3-4 micrometers will be measured using an ion probe (SIMS) and the new, high-energy ion beam in order to precisely determine the age of the deformation. In addition, titanite will also be investigated in a similar way, with an additional focus on changes in the chemical and isotopic (delta18O) composition to draw conclusions about P-T conditions and the influence of fluids during deformation.
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