Statistics and Data Analysis in Geology

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.

Ophiolite genesis and global tectonics: Geochemical and tectonic fingerprinting of ancient oceanic lithosphere

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Reconciling plate-tectonic reconstructions of Alpine Tethys with the geological–geophysical record of spreading and subduction in the Alps

This paper presents a synthetic view of the geodynamic evolution of the Zagros orogen within the frame of the Arabia-Eurasia collision. The Zagros orogen and the Iranian plateau preserve a record of the long-standing convergence history between Eurasia and Arabia across the Neo-Tethys, from subduction/obduction processes to present-day collision (from ~ 150 to 0 Ma). We herein combine the results obtained on several geodynamic issues, namely the location of the oceanic suture zone, the age of oceanic closure and collision, the magmatic and geochemical evolution of the Eurasian upper plate during convergence (as testified by the successive Sanandaj-Sirjan, Kermanshah and Urumieh-Dokhtar magmatic arcs), the P-T-t history of the few Zagros blueschists, the convergence characteristics across the Neo-Tethys (kinematic velocities, tomographic constraints, subduction zones and obduction processes), together with a survey of recent results gathered by others. We provide lithospheric-scale reconstructions of the Zagros orogen from ~ 150 to 0 Ma across two SW-NE transects. The evolution of the Zagros orogen is also compared to those of the nearby Turkish and Himalayan orogens. In our geotectonic scenario for the Zagros convergence, we outline three main periods/regimes: (1) the Mid to Late Cretaceous (115-85 Ma) corresponds to a distinctive period of perturbation of subduction processes and interplate mechanical coupling marked by blueschist exhumation and upper-plate fragmentation, (2) the Paleocene-Eocene (60-40 Ma) witnesses slab break-off, major shifts in arc magmatism and distributed extension within the upper plate, and (3) from the Oligocene onwards (~ 30-0 Ma), collision develops with a progressive SW migration of deformation and topographic build-up (Sanandaj-Sirjan Zone: 20-15 Ma, High Zagros: ~12-8 Ma; Simply Folded Belt: 5-0 Ma) and with partial slab tear at depths (~10 Ma to present). Our reconstructions underline the key role played by subduction throughout the whole convergence history. We finally stress that such a long-lasting subduction system with changing boundary conditions also makes the Zagros orogen an ideal natural laboratory for subduction processes.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/66E4243B7AFD642333291037F213B38E/S001675681100046Xa.pdf/div-class-title-zagros-orogeny-a-subduction-dominated-process-div.pdf

Zagros orogeny: a subduction-dominated process

Principles of Isotope Geology

Petrogenesis and tectonic setting of the Roman Volcanic Province, Italy

Clinopyroxene composition of ophiolite basalts as petrogenetic indicator

New geochemical data integrated in a petrogenetic model indicate that the 30Ma Northern Ethiopian continental flood basalts (CFBs) preserve a record of magmas generated from the centre to the flanks of a plume head, currently corresponding to the ‘ Afar hotspot’ . Basaltic lavas appear zonally arranged with Low-Ti tholeiites (LT) in the west, High-Ti tholeiites (HT1) to the east and very High-Ti transitional basalts and picrites (HT2,TiO2 4^6 wt %) closer to the Afar triple junction. Modelling provides estimates of the P^T^X conditions of magma generation showing that the Ethiopian CFBs could be generated in the pressure range 1 3^3 0 GPa at an approximate depth of 40^100 km from mantle sources that were increasingly metasomatized and hotter (1200^15008C) from west to east; that is, from the outer zones (LT) to the core of the plume head (HT2 ultra-titaniferous basalts and picrites). Metasomatizing agents can be envisaged as alkali^silicate melts that integrate various geochemical components (e.g. Ti and related high field strength elements, low field strength elements, light rare earth elements, H2O, noble gases, etc.) scavenged and pooled along the plume axis, and derived from heterogeneous mantle materials mixed during the plume rise. This has significant implications for the current debate about mantle plumes, as the modelled compositionally and thermally zoned plume head (Texcess 3008C with respect to ambient mantle) is in accordance with seismic tomography and buoyancy flux, as well as geochemical characteristics, thus supporting a deep provenance of the Afar plume, which possibly originated in the transition zone or lower mantle.

http://www.mantleplumes.org/WebDocuments/Beccaluva2009.pdf

Continental Flood Basalts and Mantle Plumes: a Case Study of the Northern Ethiopian Plateau

Amphibole genesis via metasomatic reaction with clinopyroxene in mantle xenoliths from Victoria Land, Antarctica

Geochemistry and petrology of the Kermanshah ophiolites (Iran): Implication for the interaction between passive rifting, oceanic accretion, and OIB-type components in the Southern Neo-Tethys Ocean

Luigi Beccaluva

Papers

Petrogenesis and tectonic setting of the Roman Volcanic Province, Italy

Clinopyroxene composition of ophiolite basalts as petrogenetic indicator

Continental Flood Basalts and Mantle Plumes: a Case Study of the Northern Ethiopian Plateau

Amphibole genesis via metasomatic reaction with clinopyroxene in mantle xenoliths from Victoria Land, Antarctica

Geochemistry and petrology of the Kermanshah ophiolites (Iran): Implication for the interaction between passive rifting, oceanic accretion, and OIB-type components in the Southern Neo-Tethys Ocean