Neotethyan Ophiolites and Their Geodynamic Evolution During the Mesozoic: A Global Overview
Authors: DILEK Yildirim 
Published: November 2020

Neotethyan ophiolites evolved in multiple seaways separated by Gondwana–derived ribbon continents within an eastward widening, latitudinal oceanic realm (Neotethys) throughout the Mesozoic. Opening and closure of these seaways were diachronous events, resulting in E–W variations in the timing of oceanic crust production and ophiolite emplacement. The Neotethyan ophiolites are highly diverse in their crustal–mantle structures and compositions, isotopic fingerprints, and sedimentary cover types, pointing to major differences in their mantle melt sources and tectonic and paleogeographic settings of magmatic construction (Dilek and Furnes, 2019). The Jurassic Western Alpine and Ligurian ophiolites in Europe and their counterparts in southern and northern Iberia formed in a narrow basin (Western Tethys) that developed between Europe and North Africa–Adria–Iberia. Their peridotites represent exhumed, continental lithospheric mantle, and the ophiolites display a Hess–type oceanic crustal architecture with MORB geochemical signatures (Dilek and Furnes, 2011). All these ophiolites were incorporated into continental margins from the downgoing oceanic lithosphere of the Western Tethys. Triassic, Jurassic and Cretaceous ophiolites east of Adria formed in different Neotethyan seaways (Dilek et al., 1990), and their rift– drift, seafloor spreading and suprasubduction zone (SSZ) magmatic construction involved multiple episodes of melting, depletion and refertilization of previously or actively subduction metasomatized mantle sources. Deep mantle recycling processes through subduction zone tectonics and / or plume activities played a major role in their melt evolution, and in the incorporation of mantle transition zone (MTZ) materials into their peridotites (Fig. 1; Dilek and Yang, 2018; Xiong et al., 2019). Tectonic mélanges structurally beneath these ophiolites include Permo–Triassic, OIB–type extrusive rocks, indicating that the initial dismantling of the Pangea supercontinent that led to the opening of the Triassic and Jurassic ocean basins within the Neotethyan realm was associated with plume magmatism (Dilek, 2003a; Yang and Dilek, 2015). This plume signature is absent in the Permo–Triassic magmatic record of the Western Tethys to the west.

The Cretaceous ophiolites around the Arabia (Dilek et al., 1990; Dilek and Delaloye, 1992; Dilek and Eddy, 1992) and India sub‐continents (Fareeduddin and Dilek, 2015) occur discontinuously along a ∼9000‐km‐long belt from SW Anatolia to SE Tibet and Indo‐China. The majority of these ophiolites have a Penrose–type oceanic crustal architecture (Dilek, 2003b) and display SSZ geochemical affinities, complete with a MORB–IAT–BON progression of their chemo‐stratigraphy (Fig. 1; Dilek and Thy, 1998; Dilek et al., 1999; Dilek and Furnes, 2014; Saccani et al., 2018). They evolved above a N–dipping, Trans–Tethyan subduction–accretion system that was situated in sub‐tropical latitudes within the Neotethyan realm. The Trans–Tethyan subduction–accretion system was segmented into two major domains (Western and Eastern domains) by the NNE–SSW–oriented, sinistral Chaman–Omach–Nal transform fault plate boundary. This Cretaceous intraoceanic arc–trench system was analogous to the modern Izu–Bonin–Mariana (IBM) and Tonga arc–trench systems in the western Pacific in terms of its size. Diachronous collisions of the Arabia and India sub‐continents with this segmented Trans‐Tethyan arc–trench system resulted in the southward emplacement of the SSZ Neotethyan ophiolites onto their passive margins in the latest Mesozoic (Dilek and Furnes, 2019). A separate N–dipping subduction system, dipping beneath Eurasia to the north during much of the Jurassic and Cretaceous, was consuming the Neotethyan oceanic lithosphere and was responsible for the construction of a composite magmatic arc belt extending discontinuously from Southern Tibet to Northern Iran. Slab rollback along this northern subduction system produced locally developed forearc–backarc oceanic lithosphere that was subsequently collapsed into the southern margin of Eurasia. The existence of these two contemporaneous, N‐dipping subduction systems within Neotethys led to its rapid contraction and the fast convergence of India towards Eurasia during the late Mesozoic–early Cenozoic (Dilek and Furnes, 2019). It was the collision with Eurasia of the India sub‐continent with the accreted ophiolites around its periphery in the Late Paleogene that produced the Himalayan orogeny.