Description: Ophiolites, and discussions on their origin and significance in Earth's history, have been instrumental in the formulation, testing, and establishment of hypotheses and theories in earth sciences. The definition, tectonic origin, and emplacement mechanisms of ophiolites have been the subject of a dynamic and continually evolving concept since the nineteenth century. Here, we present a review of these ideas as well as a new classification of ophiolites, incorporating the diversity in their structural architecture and geochemical signatures that results from variations in petrological, geochemical, and tectonic processes during formation in different geodynamic settings. We define ophiolites as suites of temporally and spatially associated ultramafic to felsic rocks related to separate melting episodes and processes of magmatic differentiation in particular tectonic environments. Their geochemical characteristics, internal structure, and thickness vary with spreading rate, proximity to plumes or trenches, mantle temperature, mantle fertility, and the availability of fluids. Subduction-related ophiolites include suprasubduction-zone and volcanic-arc types, the evolution of which is governed by slab dehydration and accompanying metasomatism of the mantle, melting of the subducting sediments, and repeated episodes of partial melting of metasomatized peridotites. Subduction-unrelated ophiolites include continental-margin, mid-ocean-ridge (plume-proximal, plume-distal, and trench-distal), and plume-type (plume-proximal ridge and oceanic plateau) ophiolites that generally have mid-ocean-ridge basalt (MORB) compositions. Subduction-related lithosphere and ophiolites develop during the closure of ocean basins, whereas subduction-unrelated types evolve during rift drift and seafloor spreading. The peak times of ophiolite genesis and emplacement in Earth history coincided with collisional events leading to the construction of supercontinents, continental breakup, and plume-related supermagmatic events. Geochemical and tectonic fingerprinting of Phanerozoic ophiolites within the framework of this new ophiolite classification is an effective tool for identification of the geodynamic settings of oceanic crust formation in Earth history, and it can be extended into Precambrian greenstone belts in order to investigate the ways in which oceanic crust formed in the Archean.

Description: The Late Ordovician (443 Ma) Solund-Stavfjord ophiolite complex in west Norway represents the youngest phase of oceanic crust formation in the western Norwegian Caledonides. It contains three structural domains with different crustal architecture that formed during two episodes of seafloor spreading evolution of a Late Ordovician marginal basin. The fossil oceanic crust of the younger episode contains pillow lavas, massive sheet flows, and hyaloclastites, NE-trending sheeted dikes, and high-level isotropic gabbros. The pillow lava versus massive sheet flow distribution and the occurrence of an extensive sheeted dike complex in the Solund-Stavfjord ophiolite complex are typical of in situ oceanic crust developed at modern intermediate-spreading mid-ocean ridges. The Solund-Stavfjord ophiolite complex lavas and dikes are composed predominantly of normal mid-ocean-ridge basalt (N-MORB) Fe-Ti basalts, and their trace-element patterns indicate a weak subduction influence. The Nd isotope data of these rocks suggest derivation of their magmas from an isotopically homogeneous melt source with no indication of continental crustal contamination. The Solund-Stavfjord ophiolite complex extrusive sequence contains phyllite interlayers and is conformably overlain by a continentally derived, quartz-rich metasandstone that is intercalated with sills of N-MORB basaltic lavas and shallow-level intrusions. The geochemical features of the upper-crustal rocks of the Solund-Stavfjord ophiolite complex indicate their formation from magmas in which the melt evolution involved only minor or no slab-derived fluids. The evolution of the Solund-Stavfjord ophiolite complex oceanic crust occurred in a short-lived (

Description: The U-Pb age and Hf isotope data on detrital zircons from Paleozoic metasedimentary rocks in the Lhasa terrane (Tibet) define a distinctive age population of ca. 1170 Ma with {varepsilon}Hf(t) values identical to the coeval detrital zircons from Western Australia, but those from the western Qiangtang and Tethyan Himalaya terranes define an age population of ca. 950 Ma with a similar {varepsilon}Hf(t) range. The ca. 1170 Ma detrital zircons in the Lhasa terrane were most likely derived from the Albany-Fraser belt in southwest Australia, whereas the ca. 950 Ma detrital zircons from both the western Qiangtang and Tethyan Himalaya terranes might have been sourced from the High Himalaya to the south. Such detrital zircon connections enable us to propose that the Lhasa terrane is exotic to the Tibetan Plateau system, and should no longer be considered as part of the Qiangtang-Greater India-Tethyan Himalaya continental margin system in the Paleozoic reconstruction of the Indian plate, as current models show; rather, it should be placed at the northwestern margin of Australia. These results provide new constraints on the paleogeographic reconstruction and tectonic evolution of southern Tibet, and indicate that the Lhasa terrane evolved as part of the late Precambrian-early Paleozoic evolution as part of Australia in a different paleogeographical setting than that of the Qiangtang-Greater India-Tethyan Himalaya system.

Description: We present a detailed structural and stratigraphic record of a Neogene-Quaternary supradetachment sedimentary succession in the Aegean extensional province of western Anatolia, and we compare its tectonic features and evolution to those of other well-documented supradetachment basins around the world. The sedimentary fill of the Alasehir basin records the uplift and exhumation of a core complex in the footwall of a detachment fault within the Central Menderes Massif. Accumulation of footwall-derived clastic sediments in this basin started ca. 20 Ma, shortly after the initiation of the approximately E-W-trending Alasehir detachment and its shear zone, and continued until ca. 2 Ma. Major sedimentary facies types include fluvial and alluvial-fan deposits, debris-flow and mass-flow deposits, and locally developed lacustrine rocks. These sedimentary units were accumulated largely in distal depocenters within the extending basin, as the low-angle (15{degrees}-28{degrees}) detachment faulting created little accommodation space near the basin margins while producing high back-shed topography in the uplifted Menderes core complex. The drainage system was dominated mainly by extension-parallel transverse streams during the main phases of basin evolution. Extension-parallel, scissor (hinge) faulting produced differential uplift and subsidence in the adjacent fault blocks, changed the direction of sediment transport and drainage patterns over short distances, and resulted in the local uplift of the older basin strata. These processes led to the development of subbasins with lateral variations in basement topography, strata thickness, and sedimentary facies distribution, and generated a segmented basin architecture. High-angle synthetic and antithetic faults that formed extensively after 3 Ma caused back-tilting of the sedimentary strata, formation of half grabens with their own axial drainage systems, and development of angular unconformities. With the onset of this crustal-scale block faulting, the detachment fault ceased to operate, and the Quaternary Gediz graben started to develop at the northern end of the Alasehir supradetachment basin. Our comparative evaluation of select basins shows a maximum sediment thickness of 3 km, average extension rates of 6 to 8-9 mm yr-1, and accumulation rates of 0.1-0.2 mm yr-1 (uncorrected for compaction) in supradetachment basins in general. The rates and amounts of extension, the geometry of detachment faulting, the rates of footwall uplift, and the kinematics and interplay of different fault systems are the most important factors controlling three-dimensional structural architecture and evolution of supradetachment basins.