Tectonics and Metallogenesis of the Western Tethys

Abstract

Geological events driven by plate tectonics affect human society in various ways. Understanding the driving forces allows explanation as to why particular events (earthquakes, volcanic eruptions, basin formation, orogenesis) occur at certain times and specific location(s). The prolonged Mediterranean subduction zone under Africa-Europe convergence is an ideal candidate to understand subduction evolution. This prolonged, continuous subduction occurred since the Late Cretaceous provides valuable insights into geological events that take longer to develop (e.g., orogenesis) as well as events that only occur at a specific time in subduction zone evolution (e.g., intermediate-deep earthquakes during slab boudinage).

Decades of research across the Mediterranean region have produced controversial tectonic evolution models, and several questions remain. How many oceanic basins were involved in the episodic closure of Mediterranean West Tethys? Can they be observed as subducted slabs? What is their pre-subduction areal extent? Within the accreted terrane stacks, what components are of Gondwanan (Africa) affinity and what were Europe-derived? Is there sufficient 'space' in the suture zone to accommodate their presence and subsequent accretion? How are the region's oroclines created? What is the subduction architecture at depth? And how does this affect the mode of subduction and the region's superficial tectonic deformation?

This research systematically constructed 3D slab models beneath the modern Mediterranean basins and linked them with 2D+time tectonic reconstructions on the planet surface. Structures at depth are related to surface crustal deformation events, both at present and in the past. The computer-modelled results are tested for their ability to 'predict' occurrence of tectono-thermal events observed in the field.

The twisting motion of a slab segment in the eastern Cyprus arc is identified as the driver of the overall SW-ward lithospheric collapse of Central Anatolia into the Cyprus Arc. This is the precursor to major earthquake events such as the Mw 7.8 then Mw 7.6 2023 Kahramanmaras earthquake series. The presence of slab boudinage beneath the Vrancea region, Romania is identified by analysing intermediate depth earthquakes unique to the locality in addition to the 'necking' geometry observed in the tomography data. This admits to the occurrence of slab stretching before dropping off, as opposed to the 'mantle drip' concept. Possible causes to the differential ore enrichment across the region are also discussed.

This study further identifies two deeper slab segments beneath the 660 km transition zone in the Aegean Arc region. These slab segments are identified as the subducted Paleo-Tethys and Neo-Tethys from which the Rhodope ophiolites and the Vardar ophiolites were off-scraped. The two deeper slab segments do not extend into the Black Sea regime, being the Neo-Tethys back arc basin. When regional ore deposits are mapped onto the slab models, deposit occurrences reduce significantly in the Central Anatolia region where the two deeper slabs terminate. This study suggests the Black Sea form in the expanse of the subducted Paleo- and Neo-Tethys lithosphere beneath Anatolia and in doing so, breaks the 'impermeable' lithospheric seal essential for orogenesis through 'trapping' of metal-enriched mantle fluid. Show more