Timing of early Andean uplift inferred from a detailed provenance analysis: a methodical approach that can be used to emphasise the quality of hydrocarbon reservoirs in the Levantine Basin

The tectonic evolution of the western margin of South America is controlled by the continuous subduction of the Nazca plate. The Central Andes, which reach altitudes of 6500 m, are characterised by continental crust up to 70 km thick. Two major pulses of surface uplift are recognised: a first episode during Oligocene to Early Miocene (Isacks, 1988) and a second one during Late Miocene (Lamb and Hoke, 1997). Crustal thickening started in mid-Eocene time and is accepted to be responsible for the Oligocene to Early Miocene uplift. However, the timing of this early uplift phase is not well constrained.

Since the early Paleozoic the Central Andes have been a locus for synorogenic sedimentary basins development. The focus of this study is on Cenozoic continental siliciclastic formations, named the Moquegua Group, deposited between the Western Cordillera and the Coastal Cordillera in southern Peru. Techniques employed include geochemistry analysis of single detrital heavy mineral grains (amphibole and Fe-Ti oxide), U-Pb dating of detrital zircon using LA-SF-ICP-MS as well as zircon fission-track thermochronology. The data are used to develop a sediment provenance model from which the timing of the early episode of Andean uplift can be better constrained.

The combination of field observations, stratigraphic and petrographic descriptions taken from the literature, and our geochemical, geochronological and thermochronological data indicates uplift induced a significant change in provenance at around 35 to 30 Ma. This change in provenance is related to major reorganisation of the drainage sytem due to the formation of relief. This reorganisation directly affects the nature of the deposited sediments in a basin and thus the quality of any potential hydrocarbon reservoirs.

This study demonstrates the value of detailed provenance analysis based on a variety of techniques for reconstruction of regional tectonic history, drainage systems evolution and the link to hydrocarbon reservoir quality.

On the eastern part of the Levantine Basin, offshore Lebanon, a detailed provenance based study is planned which will allow us to better constrain the timing of uplift of the Mount Lebanon and Anti-Lebanon. The provenance model will be used to describe the evolution of the regional drainage systems and thus, estimate the quality of the potential hydrocarbon reservoirs offshore Lebanon.