The history of petrogenesis has been the history of re-interpretations of origins -Peter J. Wyllie important enriched geochemical reservoir.We argue that ancient subducted metasomatized mantle lithosphere (SML) provides the major source component for OIB.The metasomatic agent is an H 2 O-CO 2 -rich silicate melt derived from within the LVZ.Upward migration and concentration of the melt at the lithosphere-LVZ interface (i.e., the lithosphere-asthenosphere boundary or LAB) results in chemical stratification in the LVZ with the deeper portion being more depleted (i.e., DMM), providing the source for MORB.The widespread metasomatized peridotites, pyroxenites and hornblendites from xenolith suites exhumed from the deep lithosphere (both oceanic and continental) and in orogenic peridotite massifs confirm the role of a low-F silicate melt phase as the metasomatic agent.The SOC, if subducted into the lower mantle, will be too dense to return in bulk to the upper mantle source regions of oceanic basalts, and may have contributed to the two large low shear wave velocity provinces (LLSVPs) at the base of the mantle beneath the Pacific and Africa over Earth's history.
Research Article| October 01, 2010 Aragonite in olivine from Calatrava, Spain—Evidence for mantle carbonatite melts from >100 km depth Emma R. Humphreys; Emma R. Humphreys 1Department of Earth Sciences, University of Bristol, Wills Memorial Building, Bristol BS8 1RJ, UK2Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK Search for other works by this author on: GSW Google Scholar Ken Bailey; Ken Bailey 1Department of Earth Sciences, University of Bristol, Wills Memorial Building, Bristol BS8 1RJ, UK Search for other works by this author on: GSW Google Scholar Chris J. Hawkesworth; Chris J. Hawkesworth 1Department of Earth Sciences, University of Bristol, Wills Memorial Building, Bristol BS8 1RJ, UK3University of St Andrews, College Gate, North Street, St Andrews, Fife KY16 9AJ, UK Search for other works by this author on: GSW Google Scholar Frances Wall; Frances Wall 2Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK4Camborne School of Mines, University of Exeter, Cornwall Campus, Penryn, Cornwall TR10 9EZ, UK Search for other works by this author on: GSW Google Scholar Jens Najorka; Jens Najorka 2Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK Search for other works by this author on: GSW Google Scholar Andrew H. Rankin Andrew H. Rankin 5School of Geography, Geology and the Environment, Kingston University, Surrey KT1 2EE, UK Search for other works by this author on: GSW Google Scholar Geology (2010) 38 (10): 911–914. https://doi.org/10.1130/G31199.1 Article history received: 09 Mar 2010 rev-recd: 07 May 2010 accepted: 20 May 2010 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Emma R. Humphreys, Ken Bailey, Chris J. Hawkesworth, Frances Wall, Jens Najorka, Andrew H. Rankin; Aragonite in olivine from Calatrava, Spain—Evidence for mantle carbonatite melts from >100 km depth. Geology 2010;; 38 (10): 911–914. doi: https://doi.org/10.1130/G31199.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Aragonite, as an inclusion in olivine from a leucitite lava flow, provides evidence for high-pressure crystallization and carbonatitic activity beneath the geophysical lithosphere in Calatrava, Spain. The aragonite occurs as a single crystal within olivine (Fo87), interpreted to have crystallized from a carbonated silicate melt at mantle depths. Experimental data constrain the stability of aragonite to depths of >100 km at CO2-H2O-bearing mantle solidus temperatures. This is the first documented evidence of magmatic aragonite crystallized in the mantle. Entrained as xenocrysts, the olivines have not crystallized from the carrier melts, which must have formed deeper within the mantle. Lead isotope data of the leucitite and carbonate inclusions indicate that the source melts show isotopic enrichment relative to mid-oceanic ridge basalt and most ocean island basalt. Our evidence strengthens the argument for direct and deep mantle-derived volcanic carbonatite in alkaline volcanic provinces containing maar-type volcanism, such as Calatrava. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
Based on an evaluation of major and trace element data for ocean island basalts (OIB), we demonstrate that oceanic lithosphere thickness variation, which we refer to as the lid effect, exerts the primary control on OIB geochemistry on a global scale. The lid effect caps the final depth (pressure) of melting or melt equilibration. OIB erupted on thick lithosphere have geochemical characteristics consistent with a low extent and high pressure of partial melting, whereas those erupted on thin lithosphere exhibit the reverse; that is, a high extent and low pressure of melting cessation. This observation requires that mantle melting beneath intra-plate volcanic islands takes place in the asthenosphere and results from dynamic upwelling and decompression. Melting beneath all ocean islands begins in the garnet peridotite facies, imparting the familiar 'garnet signature' to all OIB melts (e.g. [Sm/Yb]N > 1); however, the intensity of this signature decreases with increasing extent of melting beneath thinner lithospheric lids as a result of dilution. The dilution effect is also recorded in the radiogenic isotope composition of OIB, consistent with the notion that their mantle source regions are heterogeneous with an enriched component of lower solidus temperature dispersed in a more refractory matrix. High-quality data on the compositions of olivine phenocrysts from mid-ocean ridge basalt and global OIB sample suites are wholly consistent with the lid effect without the need to invoke olivine-free pyroxenite as a major source component for OIB. Caution is necessary when using basalt-based thermobarometry approaches to estimate mantle potential temperatures and solidus depth because OIB do not unequivocally record such information. For plate ages up to ∼80 Ma, we demonstrate that the geophysically defined base of the growing oceanic lithosphere corresponds to both an isotherm (∼1100°C) and the pargasite (amphibole) dehydration solidus of fertile mantle peridotite. As pargasite in H2O–CO2-bearing mantle peridotite is stable under conditions of T ≤ 1100°C and P ≤ 3 GPa (∼90 km), this solidus is essentially isothermal (i.e. dT/dP ∼ 0 in P–T space) with T ∼ 1100°C) at depths ≤90 km, but becomes isobaric (i.e. dP/dT ∼ 0 in P–T space) at the ∼90 km depth. The latter explains why older (>70 Ma) oceanic lithosphere cannot be thicker than ∼90 km without the need to invoke physically complex processes such as convective removal.
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