The Paleoarchean East Pilbara Terrane (NW Australia): structural and geo-thermochronologic tests of early Earth tectonic models

• Applicant: Professor Dr. Lothar Ratschbacher
• Subject Area: Geology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 545110442

The tectonics of early Earth is described by (1) plate tectonics with dominantly horizontal motions or (2) diapiric processes (partial convective overturn) with dominantly vertical movements. The Paleoarchean East Pilbara Terrane (NW Australia) likely is the key locality to discriminate between these models. There, massive granitoid domes and surrounding greenstone belts have been interpreted by non-plate tectonic dome-and-keel geometry formed by granitoid-up and greenstone-down movements. Others have described the Pilbara Terrane as a well-preserved fragment of a plate-tectonic style convergent margin with the earliest deformation showing the greenstones overthrusting the granitoids (i.e., greenstone-up). This preparatory project has two aims: (1) Based on the long-term experience of the applicants with structural studies in the classic Cenozoic Alpine-Himalayan plate-tectonic accretion-collision belt, we will check the available structural data and work on new data in two domes of the East Pilbara Terrane (Mt Edgar and Shaw domes). We will map and study key localities around the domes to elucidate the structural geometry, kinematics, and structural superpositions. (2) We will examine which datable mineral phases are associated with the key structures, focusing on new approaches provided by the LA-ICPMS U-Pb technique. In the field-related subproject, we will obtain field and microscopic (optical, SEM-EBSD) structural data from deformed granitoids and greenstones; the lab work is a necessary aspect due to the outcrop geometry and commonly strong weathering. The data will enable exploration of deformation temperatures, shear senses, fabric orientations, and 3D strain geometries at micro- to macro-scales. A large deviation from horizontal deformation patterns would imply the dominance of non-plate tectonic processes. In the second, lab-related sub-project, we will characterize the syn-tectonic mineralization to explore how deformation can be dated under a wide range of temperature conditions. We will use optical microscopy, SEM-MLA, and in part Raman spectroscopy to detect syn-tectonic minerals that can constrain the age of the shear/fault zones via various approaches, starting with the LA-ICPMS-based U-Pb dating approach. The information gained in this preparatory proposal should provide key information for a funding application led by PI A.A.G. Webb that will focus on the age dating of the shear/fault zones and greenstone stratigraphy with the goals to test the early Earth models proposed for the East Pilbara Terrane.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr. A. Alexander G. Webb