Fluid driven processes in the crust – the formation of anorthositic dykes in the Troodos ophiolite (Cyprus)

Anorthositic dykes related with the Upper Cretaceous Troodos ophiolite are described for the first time. An entire anorthosite dyke swarm appears within the Limassol Forest Complex, crosscutting the supply channels of late Troodos extrusives. As inferred from crosscutting relations, the intrusion of dykes must be related to a very late magmatic stage of oceanic crust formation. The appearance of anorthosites as dykes, imply that their composition had to be liquid at the time of intrusion. Melting experiments of such compositions show that even under H2O saturated conditions, temperatures required for whole-sale melting are well above 1250 °C at 500 MPa, which is unrealistic for a derivative melt. Pivotal aspect of the present work is the development of a genetic model, based on petrological, geochemical and experimental observations. Complex, multi-stage, open system phenomena are unrevealed, involving differentiation and unmixing of magmatic fluids and melts such as the enrolment of hydrothermal fluids. Anorthositic dykes are interpreted to represent precipitates of a magmatic liquid that intruded the upper crust as a crystal mush. The anorthosite liquid is derived from unmixing of a highly evolved melt at depth. The fluid thereby is considered as a viscous gel, highly enriched in silicate solute, high field strength elements and rare earth elements. The solubility of the different species is granted by the saline, probably chloride rich composition of the liquid. Normative bulk compositions of dykes range 80 - 100 wt.% plagioclase such that they are classified as anorthosites. Primary magmatic plagioclase approaches pure end member anorthite composition (XAn = 0.76 - 1.0). Anorthite, calcic pyroxene and accessory phases (titanite, rutile and zircon) are inferred as liquidus phases. The observed mineral textures such as the trace element- and isotope composition confirms the intrusion of anorthosites to be related with a highly viscous magmatic fluid having a mutual source in boninites. A perfect correlation between lutetium content and the 176Lu/177Hf isotope ratio is observed in anorthosite rocks but does not appear in other Troodos extrusives emphasizing its unique generation history. Liquidus experiments in the hydrous anorthosite system reveal melting temperatures of the bulk assembly exceeding 1150 °C; and anorthite (XAn = 1) as liquidus phase. Phase relation experiments in the H2O saturated anorthite - diopside - forsterite system aim to duplicate and quantify the process responsible for the enrichment of the plagioclase component in the melt. It is demonstrated that the presence of a H2O saturated melt coexisting with a H2O-dominated fluid phase largely suppresses the crystallisation of anorthite from the fluid saturated melt. Simple system experiments further reveal the separation of a melt saturated fluid from the fluid saturated melt at conditions below the second critical point of water. Decompression recrystallisation experiments with hydrous tholeiite compositions reconcile that fractionation of a mafic melt prior to unmixing of a fluid phase results in accumulation of the anorthite component and hence could represent the parental magma composition

Impacto del Programa Prevenir de la Agencia Alemana para la Cooperación Internacional (GIZ) en El Salvador: Estrategias de Prevención de Violencia para el Aumento de la Inserción Escolar y Laboral durante los años 2009-2017.

Análisis del Marco Jurídico Internacional y Nacional en el Cumplimiento de Compromisos del Estado Salvadoreño en Materia de Prevención de la Violencia y su Relación con el Programa Prevenir -- Programa Prevenir como Cooperación Internacional y su Coordinación con las Municipalidades de El Salvador – Impacto del Programa Prevenir en El Salvador. Estrategia y Mecanismos de la Cooperación Internacional Enfocada en la Prevención de la Violencia

Comparisons between Tethyan Anorthosite-bearing Ophiolites and Archean Anorthosite-bearing Layered Intrusions: Implications for Archean Geodynamic Processes

Elucidating the petrogenesis and geodynamic setting(s) of anorthosites in Archean layered intrusions and Tethyan ophiolites has significant implications for crustal evolution and growth throughout Earth history. Archean anorthosite-bearing layered intrusions occur on every continent. Tethyan ophiolites occur in Europe, Africa, and Asia. In this contribution, the field, petrographic, petrological, and geochemical characteristics of 100 Tethyan anorthosite-bearing ophiolites and 155 Archean anorthosite-bearing layered intrusions are compared. Tethyan anorthosite-bearing ophiolites range from Devonian to Paleocene in age, are variably composite, contain anorthosites with highly calcic (An44-100) plagioclase and magmatic amphibole. These ophiolites formed predominantly at convergent plate margins, with some forming in mid-ocean ridge, continental rift, and mantle plume settings. The predominantly convergent plate margin tectonic setting of Tethyan anorthosite-bearing ophiolites is indicated by negative Nb and Ti anomalies and magmatic amphibole. Archean anorthosite-bearing layered intrusions are Eoarchean to Neoarchean in age, have megacrystic anorthosites with highly calcic (An20-100) plagioclase and magmatic amphibole and are interlayered with gabbros and leucogabbros and intrude pillow basalts. These Archean layered intrusions are interpreted to have predominantly formed at convergent plate margins, with the remainder forming in mantle plume, continental rift, oceanic plateau, post-orogenic, anorogenic, mid-ocean ridge, and passive continental margin settings. These layered intrusions predominantly crystallized from hydrous Ca- and Al-rich tholeiitic magmas. The field, petrographic and geochemical similarities between Archean and Tethyan anorthosites indicate that they were produced by similar geodynamic processes mainly in suprasubduction zone settings. We suggest that Archean anorthosite-bearing layered intrusions and spatially associated greenstone belts represent dismembered subduction-related Archean ophiolites

Spheroidal textures in igneous rocks - Textural consequences of H2O saturation in basaltic melts

When melts reach H2O saturation before they are emplaced at the Earth's surface, they exsolve a hydrous fluid phase. At elevated pressure and high temperature, a hydrous fluid is not pure H2O but can contain some quantities of silicate and metal oxide solute, notably if fluid saturation occurs at high pressure. Chemically and physically, fluid-saturated basalts behave like any other system with liquid immiscibility. Textures that can result after solidification are globules of former fluid dispersed in a former silicate melt, or silicate melt orbs embedded in a former fluid matrix. The Troodos ophiolite on the island of Cyprus, generated in a back arc basin above a wet intra oceanic subduction zone, carries in its magmatic stratigraphy lithologies distinctly orbicular and globular in shape. Many melt compositions parental to the ophiolite were H2O-saturated near their liquidus temperatures before they reached their depths of emplacement within the ophiolite sequence. Spheroids are not uncommon in magmatic rocks but still debated as to how they form. We propose that globular and orbicular textures in igneous worldwide may result when melts reach H2O saturation and exsolve an immiscible solute-bearing H2O-dominated fluid phase at elevated temperature and pressure, before or while they are emplaced. (C) 2015 Elsevier Ltd. All rights reserved

Rare earth elements in apatite as a monitor of magmatic and metasomatic processes : the Ilímaussaq complex, South Greenland

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