Geochemical and geochronologic data are presented for meta-mafic to meta-felsic rocks along the Paleo-Tethys Suture in the Binalood Mountains east of Neyshabur, NE Iran. The rocks have a late Cambrian age (U–Pb zircon, ~ 490 Ma) and were metamorphosed in the Early Jurassic (40Ar/39Ar amphibole and plagioclase, 199–192 Ma). The rocks of this suite are alkaline and sub-alkaline (tholeiitic). The alkaline rocks are enriched in light relative to heavy rare earth elements, and do not show depletion of high-field strength elements on primitive mantle-normalized multi-element diagrams; they are similar to ocean island basalts (OIB). The tholeiitic rocks are depleted in Nb and Ta and have higher MgO and lower TiO2 than the alkaline rocks. Both types have similar, high and variable 87Sr/86Sr(i) isotopic compositions of 0.7044 to 0.7082 and 143Nd/144Nd(i) values of 0.5118 to 0.5122. The alkaline rocks are lower-degree partial melts than the tholeiitic rocks and were generated at greater depths; they likely originated from a garnet pyroxenite-rich source. The spatial, temporal, and geochemical relationships of early Paleozoic meta-mafic to felsic rocks along the Paleo-Tethys Suture (e.g., Shahrud, Jajarm, Binalood, Torbat-e-Jam) substantiate the role of a mantle plume in continental breakup along the northern margin of Gondwana and a late Cambrian-Ordovician onset of rifting that resulted in the opening of the Paleo-Tethys Ocean. The Early Jurassic metamorphism post-dates its closure.

basalts (MORB) and their intrusive equivalents, gabbros, are the characteristic igneous rocks formed at mid-ocean ridges. They are tholeiitic basalts Basalt (UK: BAH-salt); US: buh-SALT) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90% of all volcanic rock on Earth is basalt. Rapid-cooling, fine-grained basalt has the same chemical composition and mineralogy as slow-coo Tholeiitic basalt, which is relatively rich in iron and poor in alkali metals and aluminium, include most basalts of the ocean floor, most large oceanic islands, and continental flood basalts such as the Columbia River Plateau. High- and low-titanium basalt rocks, which are sometimes classified based on their titanium (Ti) content in High-Ti and Low-Ti varieties. High-Ti and Low-Ti basalt have been distinguished from each other in the Paraná and Etendeka traps and the Emeishan Traps. Mid-ocean ridge basalt (MORB) is a tholeiitic basalt that has almost exclusively erupted at ocean ridges; it is characteristically low in incompatible elements. Although all MORBs are chemically similar, geologists recognize that they vary significantly in how depleted they are in incompatible elements. When they are present in close proximity along mid-ocean ridges, that is seen as evidence for mantle inhomogeneity. Enriched MORB (E-MORB) is defined as MORB that is relatively undepleted in incompatible elements. It was once thought to be mostly located in hot spots along mid-ocean ridges, such as Iceland, but it is now known to be located in many other places along those ridges. Normal MORB (N-MORB) is defined as MORB that has an average amount of incompatible elements. D-MORB, depleted MORB, is defined as MORB that is highly depleted in incompatible elements. Alkali basalt is relatively rich in alkali metals. It is silica-undersaturated and may contain feldspathoids, alkali feldspar, phlogopite, and kaersutite. Augite in alkali basalts is titanium-enriched augite; low-calcium pyroxenes are never present. They are characteristic of continental rifting and hotspot volcanism. High-alumina basalt has greater than 17% alumina (Al2O3) and is intermediate in composition between tholeiitic basalt and alkali basalt. Its relatively alumina-rich composition is based on rocks without phenocrysts of plagioclase. These represent the low-silica end of the calc-alkaline magma series and are characteristic of volcanic arcs above subduction zones. Boninite is a high-magnesium form of basalt that is erupted generally in back-arc basins; it is distinguished by its low titanium content and… The… During…