Uplift history of the Troodos ophiolite inferred from integrating thermomechanical models, submarine and deltaic fan clast content and serpentinites

Uplift history of the Troodos ophiolite inferred from integrating thermomechanical models, submarine and deltaic fan clast content and serpentinites

Schutte, Demi (Utrecht University)

Utrecht University

Molengraaff Fonds

2024-01

Uplift of the Troodos ophiolite from its time of formation (~90 Ma) to the present-day is currently poorly constrained, due to its complex multi-phase uplift history involving multiple uplift mechanisms. The aim of this study is to quantify the amount of uplift and uplift rates in the different phases, to construct a more complete timeline of the uplift phases and their mechanisms. The recent (9-0 Ma) uplift history of the Troodos is investigated through analysis of clast content and clast characteristics of submarine and deltaic fans. Thermomechanical models are run to evaluate through which mechanisms serpentinization can contribute to uplift. Serpentinite samples from the Troodos are studied to put temporal constraints on serpentinization. The four formations studied in the fans show four different uplift phases, with uplift rates ranging from 0.025 to 0.4 cm/yr, resulting in 5.8-10.4km total uplift in the past 9Ma. The uplift phases are interpreted to have resulted from regional tectonics: major changes in plate motion, modern subduction initiation and the underthrusting of the Eratosthenes Seamount. The models show 1-12.5 km uplift after 10 myr and uplift rates ranging from 0.1-0.9 cm/yr. In the models, thick or light serpentinite wedges create higher topography compared to thin or dense serpentinite wedges. Erosion decreases the amount of uplift in models with a shallow slab, but it increases the amount of uplift in models with a steep slab, when comparing those models to the ones without erosion. Uplift in the models usually lasts 2-5 million years, before subsidence starts. Steep slab models generally experience less subsidence when erosion is applied. Interpretation of the models show that serpentinite can contribute to uplift by enabling decoupling, as serpentinite has a weak rheology and lowers the frictional strength of a rock. Its buoyancy helps to maintain the already formed topography. The serpentinite samples show a high degree of serpentinization, with very few relict minerals. The serpentine minerals present are predominantly lizardite and minor chrysotile. The most prevalent non-serpentine mineral is magnetite. The samples are interpreted to have formed between 200-4000C in close proximity to the spreading ridge. Previous studies have found antigorite and meteoric indicators in the serpentinite, implying at least three serpentinization phases. The models and field data are then combined to infer the uplift history of the Troodos ophiolite. It seems likely that serpentinization has aided early obduction of the Troodos crust, by necking, breaking and providing buoyancy. This enabled transport of the ophiolitic crust across the subduction zone. After this first period of uplift, a period of relative tectonic quiescence followed, and uplift resumed in the Miocene with the four uplift phases inferred from the fans.

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