Abstract

This study presents a structural analysis of the brittle and ductile features within the Aileu Metamorphic Complex of Timor Leste, located in the active Banda Arc–Australian continental collision zone. The deformation history of the complex is interpreted from the Permian–Jurassic deposition of sediments and basalts into intra-arc basins of Gondwana, through to the present- day collision of the Australian continental margin. This collision led to the development of the Wetar Suture and subsequent back-thrusting of the Aileu metamorphic rocks northward over the Banda forearc. Field evidence confirms that the Laclo Fault is currently active, with the most recent movement exhibiting oblique right-lateral displacement. Furthermore, mapping shows that the Laclo Fault extends farther west than previously documented. Along its length, the fault delineates key lithological boundaries: in the westernmost and easternmost regions, it separates metamorphosed and unmetamorphosed units of the Gondwana Sequence, while in its central segment, it divides higher- and lower-grade metamorphic rocks. Measurements of S1 and S2 cleavage, fold axes and axial planes, normal and thrust faults, and joint orientations were collected from metamorphic units along Timor Leste’s northern coast. Structural data were grouped into four geographic zones, beginning in the westernmost portion of the study area. Zones I and III exhibit ductile structures consistent with a NW–SE maximum principal stress (σ1) direction, while Zones II and IV show a NE–SW σ1 orientation. The NW–SE stress direction aligns with the inferred orientation of the Australian continental margin at the onset of collision. To explain the anomalous stress orientations in Zones II and IV, this study proposes four potential mechanisms: (1) strike-slip motion along the Laclo Fault, (2) localized stress changes caused by gabbro intrusions, (3) a lateral thrust ramp influenced by pre-existing structures within the Australian margin, and (4) buoyancy-driven domal uplift of the metamorphic rocks. Previous studies that aimed to constrain exhumation rates have identified circular uplift patterns across the eastern Aileu Complex. These observations align with the concept of buoyancy-driven domal uplift of metamorphic rocks. As such, this study favors this mechanism as the most likely explanation for the rotated stress orientations observed in Zones II and IV.

Degree

MS

College and Department

Computational, Mathematical, and Physical Sciences; Geological Sciences

Rights

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

Date Submitted

2025-06-10

Document Type

Thesis

Handle

http://hdl.lib.byu.edu/1877/etd13698

Keywords

Timor Leste, Laclo Fault, structural analysis, Banda Arc, Banda Orogen

Language

english

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