Abstract

Recent advances in petroleum exploration off the southern coast of Timor-Leste and emerging mineral discoveries onshore have underscored the need for a more comprehensive structural understanding of the nation's geology. Although new structural models have been proposed for other parts of Timor, limited progress has been made toward developing detailed models for the Ramelau Mountains, which presents the highest structural relief of the Timor Ranges. Previous mapping in this area has been largely reconnaissance in nature and focused primarily on surface bedrock geology. This study presents a new 1:62,500-scale geologic map and a geometric structural analysis of the Ramelau region aimed at testing various subsurface interpretations in the absence of extensive seismic or geophysical data. Mapping and structural assessments reveal multiple shear zones associated with major thrust sheets of Mesozoic Gondwana-affinity strata, which have been uplifted and exhumed through earlier Permian roof thrusts emplaced during the initial stages of collision. However, modern oblique convergence that involves strain partitioning, arcuate segments, and collided inherited grabens with variable unit thicknesses prevent simple tectonic restorations. The shear zones appear to represent reactivated structures inherited from the pre-collisional development of the Australian passive margin, evidenced by matching orientation to original basin architecture, and unit thickness variability across domain boundaries within a mountain scale. Observed fold and thrust structures in the Ramelau Mountains are predominantly NE-SW-striking, and oblique-normal faults characterized by boudinage, slickenlines, Riedel shears, and en echelon fractures. The distribution and geometry of these shear zones indicate a southeastward younging in thrust sheet emplacement and exhumation. Measured line-length shortening of up to 50%, with SE-directed vergence, is observed in the southern forelimbs of most thrust sheets. Shortening occurs through a combination of kink folding, flexural slip, flexural flow, dissolution, and anticlinal folding, consistent with fault-propagation folding where deformation is concentrated in the forelimb. The most prominent and deeply eroded of these uplifted grabens forms the Ramelau Anticline or culmination, where pronounced thickening accounts for the high topographic relief separating Mount Ramelau, the island's highest peak, from the adjacent deep river valleys. The culmination likely developed under structural confinement imposed by the Asian-affinity Banda Terrane roof thrust, which is exposed in a synform immediately south of the Ramelau Mountains. The results highlight the importance of structural inheritance in shaping the Ramelau Mountains, which encompass six distinct structural regimes reflecting a progressive tectonic evolution: (1) overthrusting of the Banda Terrane, (2) emplacement of the Permian roof thrust, (3) thrust emplacement of the Aileu low-grade metamorphic complex over the Permian roof, (4) shortening and folding of Triassic-Jurassic sequences, (5) uplift and exhumation of Triassic units through the Permian sheet and broken mélange, and (6) normal and oblique strike-slip faulting caused by collision obliquity between the NNE trending subducting Australian passive margin and Banda forearc. This evolution involving various structural domains indicates complex polyphase deformation involving a range of reactivated structures and cross-cutting relationships, acquired in response to varying tectonic stresses with different orientations.

Degree

MS

College and Department

Geological Sciences; Computational, Mathematical, and Physical Sciences

Rights

https://lib.byu.edu/about/copyright/

Date Submitted

2025-12-19

Document Type

Thesis

Keywords

Timor-Leste, Tectonics, Banda Orogen, Geometric Analysis, Geologic Mapping, Inherited Structures, Bonaparte Basin

Language

english

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