Tethyan ophiolites have played a major role in the development of the ophiolite concept during the past 200 years, and contributed significantly to the formulations of the suprasubduction-zone (SSZ) ophiolite paradigm and the plate-tectonics theory. Their melt evolution and magmatic construction witnessed the dispersal of the supercontinent Pangaea via continental rifting and seafloor spreading, opening and closure of multiple seaways in an eastward widening, latitudinal ocean basin (Neotethys), and deep mantle recycling processes through subduction-zone tectonics and plume activities. Neotethyan ophiolites are highly diverse in their crustal–mantle structures and compositions, pointing to major differences in their melt sources and tectonic settings of magmatic construction. The papers in this thematic set demonstrate these differences in the Neotethyan ophiolite record through new structural, geochemical, isotopic and geochronological data and interpretations. The Jurassic Western Alpine Ophiolites formed in a narrow basin (Alpine Tethys) that developed between Europe and North Africa–Adria–Iberia. Their peridotites represent exhumed, continental lithospheric mantle. The Triassic, Jurassic and Cretaceous ophiolites east of Adria formed in different Neotethyan seaways, and their SSZ magmatic construction involved multiple episodes of melting, depletion and refertilization of subduction-modified oceanic mantle. The Late Cretaceous peri-Arabian and peri-Indian ophiolites, which are discontinuously exposed along a c. 9000 km long belt from SW Anatolia to SE Tibet, formed above a Trans-Tethyan subduction–accretion system within Southern Neotethys. Diachronous collisions of Arabia and India with this intraoceanic subduction–accretion system in the latest Mesozoic and the Paleogene (respectively) resulted in diachronous ophiolite emplacement in the Mediterranean and Tibetan–Himalayan orogenic belts. Thematic collection: This article is part of the ‘Tethyan ophiolites and Tethyan seaways collection’ available at: https://www.lyellcollection.org/cc/tethyan-ophiolites-and-tethyan-seaways

We present a comprehensive overview of the melt evolution of the upper mantle peridotites and different lava types occurring in the Jurassic Albanide-Hellenide ophiolites, based on new and extant geochemical data and trace element modeling. Peridotites consist of lherzolites and harzburgites that are variably depleted, and show increasing light rare earth element (LREE) enrichment with increasing whole-rock depletion. The spatial-temporal relationships of volcanic rocks indicate four discrete types with progressively younging ages: (1) normal midoceanic ridge basalts (N-MORBs); (2) medium-Ti basalts (MTBs); (3) island arc tholeiitic (IAT) basalts; (4) boninitic rocks. Our REE modeling reveals the following results. (1) Moderately depleted lherzolites represent N-MORB mantle residua produced by 10%–20% partial melting of a depleted MORB mantle source. Melt extraction formed N-MORB lavas. (2) Residual lherzolite underwent 5%–8% partial melting without any subduction influence, producing MTB magmas. (3) Following subduction initiation, these refractory lherzolites were enriched in LREEs by subduction-derived fluids. Their partial melting (∼10%–20%) generated IAT magmas. (4) With continued subduction, the highly depleted residual mantle left after the previous melting events underwent significant LREE enrichment and high degree (15%–25%) partial melting, producing the youngest, boninitic rocks. The residual mantle after boninitic melt extraction is represented by extremely refractory harzburgites. This progressive melt evolution of the upper mantle peridotites and volcanic rock types is compatible with that of the subduction initiation–related magmatism and mantle dynamics in the Izu-Bonin-Mariana arc-trench rollback system, and indicates a time-progressive mantle-melt evolution in the upper plate of the Tethyan subduction system.

We present a regional synthesis of the structural architecture and tectonic evolution of the Western Alpine Ophiolites (WAO), exposed in NW Italy. The WAO represent the remnants of Alpine Tethys (Ligurian–Piedmont Ocean) that opened between Europe and Adria, and developed in four stages from the Middle Jurassic to Early Cretaceous. Emplacement of gabbroic intrusions into the extending lithospheric mantle of Europe–Adria marked the main magmatic event (Stage 1). Coalescent shear zones in the fossil upper mantle form lithospheric-scale detachment faults, which led to the exhumation of upper mantle peridotites and gabbros on the seafloor, and extensive serpentinization (Stage 2). Detachment faults, and serpentinized peridotites–gabbros in their footwalls, represent preserved fossil oceanic core complexes within the WAO. Emplacement of ophiolitic breccias and basaltic lava flows marked the syn-extensional phase (Stage 3). Radiolarian chert and limestone were deposited unconformably on this syn-extensional volcanic–sedimentary sequence, marking the post-extensional phase (Stage 4). Magmatic ages of gabbroic intrusions and mafic–felsic dykes, and depositional ages of post-extensional sequences in the WAO constrain the timing of the opening of the Ligurian–Piedmont Ocean to the Middle Jurassic ( c. 170–168 Ma), followed by a tectonic quiescence stage in the Late Jurassic–Early Cretaceous. Thematic collection: This article is part of the ‘Tethyan ophiolites and Tethyan seaways collection' available at: https://www.lyellcollection.org/cc/tethyan-ophiolites-and-tethyan-seaways

Ophiolitic peridotites represent variously depleted residues of the primitive mantle after multiple episodes of partial melting, melt extraction, and melt-rock interactions. They display a wide range of compositional and geochemical heterogeneities at different scales, and their incompatible bulk-rock compositions and mineral chemistries are commonly inconsistent with their evolution through simple partial melting processes at shallow mantle depths. Approaching these issues from different perspectives, the papers in this volume concentrate on (1) melt evolution and magmatic construction of ophiolites in various tectonic settings, and (2) the occurrence of microdiamonds, ultrahigh-pressure (UHP) minerals, and crustal material as inclusions in ophiolitic chromitites and peridotites. Crustal and mantle rock units exposed in different ophiolites show that the mantle melt sources of ophiolitic magmas undergo progressive melting, depletion, and enrichment events, constantly modifying the melt compositions and the mineralogical and chemical makeup of residual peridotites. Formation and incorporation of microdiamonds and UHP minerals into chromite grains occurs at depths of 350–660 km in highly reducing conditions of the mantle transition zone. Carbon for microdiamonds and crustal minerals are derived from subduction-driven recycling of surface material. Host peridotites with their UHP mineral and diamond inclusions are transported into shallow mantle depths by asthenospheric upwelling, associated with either slab rollback–induced channel flow or superplumes. Decompression melting of transported mantle rocks beneath oceanic spreading centers and their subsequent flux melting in mantle wedges result in late-stage formation of podiform chromitites during the upper mantle petrogenesis of ophiolites. Future studies should demonstrate whether diamonds and UHP minerals also occur in peridotites and chromitites of nonsubduction-related ophiolites.