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Journal ArticleDOI

Genesis of Archean Peridotitic Magmas and Constraints on Archean Geothermal Gradients and Tectonics

01 Jan 1975-Geology (Geological Society of America)-Vol. 3, Iss: 1, pp 15-18
TL;DR: In this article, a model of peridotitic komatiite magma was developed in which selective removal of garnet during ascent produces CaO/Al 2 O 3 > 1 and heavy rare-earth element depletion in the resultant peridoteitic or mafic extrusions.
Abstract: The experimentally determined extrusion temperature (1650° ± 20°C) for Archean peridotitic komatiite magma implies diapirism of upper mantle peridotite from a depth of at least 200 km. Models of magma genesis are developed in which selective removal of garnet during ascent produces CaO/Al 2 O 3 > 1 and heavy rare-earth element depletion in the resultant peridotitic or mafic extrusions. Magma genesis can be interpreted with a model of the Archean geotherm, lithosphere, and plate tectonics processes resembling the modern Earth, but this does not account for the distinctive preservation and character of Archean greenstone belts. A preferred model of a steeper Archean geotherm, thin lithosphere (≃50 km), and asthenosphere with approximately 5 percent melting does not allow eclogitization and subduction of basaltic oceanic crust, but it postulates scraping off of such crust against and between primitive sialic nucleii. This model may account for the distinctive characteristics of the Archean greenstone and “granite” terranes.
Citations
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Journal ArticleDOI
TL;DR: In this article, Pollack et al. constructed a global map of lithospheric thickness based on the regional variation of surface heat flow, geotherms, and lithosphere thickness, and identified the lid as synonymous with the lithosphere.

969 citations


Cites background from "Genesis of Archean Peridotitic Magm..."

  • ...…ubiquitously distributed in the ancient cratonic elements of several continents may be the characteristic tectonic style and petrologic assemblage to develop in a 40 km high heat flow continental lithosphere interacting with an extremely mobile asthenosphere (Green, 1975; McKenzie and Weiss, 1975)....

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Book ChapterDOI
TL;DR: In this article, the IUGS definition of trondhjemite as leucotonalite was followed, except that andesine-bearing leucomorphalite be termed calcic trondhmite.
Abstract: Goldschmidt's definition (1916) of the rock name “trondhjemite,” unfortunately, was not quantitative. Furthermore, the trondhjemite intrusives of the type area, south of Trondheim, Norway, have had much of their original mineralogy obliterated by metamorphism to greenschist facies. The author suggests that the IUGS definition of trondhjemite as leucotonalite be followed, except that andesine-bearing leucotonalite be termed calcic trondhjemite, and that albite-bearing leucotonalite, as well as the oligoclase variety, be termed trondhjemite.

857 citations

Journal ArticleDOI
TL;DR: In this paper, a diapiric model was proposed for the genesis of komatiite magma by partial melting of mantle peridotite at 150-200 km depth.
Abstract: Melting phase relations of a fertile lherzolite KLB-1 have been studied in the pressure range from 1 atm to 14 GPa (140 kbar). Olivine is the liquidus phase at all pressures studied. The second mineral to crystallize changes with increasing pressure; chromian spinel (1 atm), Ca-poor orthopyroxene (up to 3 GPa), pigeonitic clinopyroxene (up to 7 GPa), pyrope-rich garnet (above 7 GPa). The melting temperature interval of the peridotite is more than 600°C wide at 1 atm but narrows to about 150°C at 14 GPa. The partial melts along the peridotite solidus become increasingly more MgO-rich as pressure increases throughout the pressure range studied. At 5–7 GPa, the partial melts formed within 50°C of the solidus contain more than 30 wt % MgO and are very similar to Al-undepleted-type peridotitic komatiite which is common in Archean volcanic terrains. Due to the increase of enstatite component in clinopyroxene solid solution at high pressure and temperature, the orthopyroxene liquidus field narrows as pressure increases and disappears at 3.5 GPa. Harzburgites which are common in the basal peridotite in ophiolite suites may have been produced as residues by partial melting at relatively shallower depths ( 100 km). A diapiric model is consistent with the genesis of komatiite magma by partial melting of mantle peridotite at 150–200 km depth. Based on the following observations, (1) convergence of the liquidus and solidus of the peridotite at pressures > 14 GPa, (2) the near solidus partial melt composition very close to the bulk rock at 14 GPa, and (3) change in liquidus mineral from olivine to majorite garnet at pressures between 16 and 20 GPa in preliminary experiments, it is proposed that the upper mantle peridotite was generated originally as a magma (or magmas) by partial melting of the primitive earth at 400–500 km depth.

742 citations

Book
01 Jan 1990
TL;DR: The authors provides a basic understanding of the formative processes of igneous and metamorphic rock through quantitative applications of simple physical and chemical principles, and encourages a deeper comprehension of the subject by explaining the petrologic principles.
Abstract: This textbook provides a basic understanding of the formative processes of igneous and metamorphic rock through quantitative applications of simple physical and chemical principles. The book encourages a deeper comprehension of the subject by explaining the petrologic principles rather than simply presenting the student with petrologic facts and terminology. Assuming knowledge of only introductory college-level courses in physics, chemistry, and calculus, it lucidly outlines mathematical derivations fully and at an elementary level, and is ideal for intermediate and advanced courses in igneous and metamorphic petrology. The end-of-chapter quantitative problem sets facilitate student learning by working through simple applications. They also introduce several widely-used thermodynamic software programs for calculating igneous and metamorphic phase equilibria and image analysis software. With over 350 illustrations, this revised edition contains valuable new material on the structure of the Earth's mantle and core, the properties and behaviour of magmas, recent results from satellite imaging, and more.

607 citations