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dc.contributor.authorCarswell, Dennis Anthonyen
dc.date.accessioned2018-01-31T11:41:10Z
dc.date.available2018-01-31T11:41:10Z
dc.date.issued1988en
dc.identifier.urihttp://hdl.handle.net/1842/27764
dc.description.abstracten
dc.description.abstractHigh pressure metamorphic rocks in two contrasting geological settings have been studied and interpreted.en
dc.description.abstractOccurrences in exposed high grade gneiss complexes (especially in west Norway) have been documented. Petrogenetic interpretations of these rocks have involved the integration of field, mineralogical and microstructural observations with whole rock and mineral composition data, isotopic age data and calculated equilibration temperature and pressure values. Deduced pressure - temperature -time paths for both the prograde (subduction related) and retrograde (uplift related) metamorphic stages have been used to establish tectonothermal models for the formation and survival of such high pressure rocks in orogenic belts involving collision between continental lithospheric plates. Particular emphasis has been placed on interpretation of the chemical, mineralogical and tectonic evolution of alpine -type Mg -Cr rich peridotites of deduced sub -continental mantle origin. However, it has been shown that high pressure mineral asemblages have also developed in original, low pressure, crustal protoliths due to the imposition of high lithostatic pressures during transient A -type subduction.en
dc.description.abstractComplementary studies of high pressure assemblages in xenoliths, brought up in volatile charged magmas of deep mantle origin, have provided important data on the chemical and mineralogical composition of the lower crust and uppermost mantle beneath continental cratonic areas. Particular attention has been paid to evaluation of the reliability of the application of mineral exchange reaction thermometers and barometers to assessment of the pressure - temperature conditions for formation, and depths of origin, of the various xenolith types. It has been demonstrated that, for the garnet lherzolite xenolith suite in the kimberlites of northern Lesotho, earlier pressure - temperature estimates purported to indicate a marked thermal perturbation in the upper mantle palaeogeotherm are invalid. Instead revised pressure - temperature estimates are interpreted to be indicative of only a slightly elevated craton margin geotherm, compatible with derivation of the higher temperature deformed xenoliths in a thermally convecting asthenosphere beneath a ca. 150 kms. thick, thermally conductive, lithosphere.en
dc.description.abstractA revised, three fold, temperature based classification scheme for the formation of high pressure, eclogite facies, mineral assemblages in proposed. Low temperature (<550 °C) eclogites have formed in subordinate, fluid deficient, rocks associated with blueschists in B -type subduction zones. Medium temperature (550- 900 °C) eclogites have been stabilised in tectonically thickened continental crust sequences in A -type subduction zones. High temperature ( >900 °C) eclogites and associated garnet lherzolites, as witnessed as xenoliths in kimberlites, have equilibrated in the upper mantle.en
dc.publisherThe University of Edinburghen
dc.relation.ispartofAnnexe Thesis Digitisation Project 2017 Block 16en
dc.relation.isreferencedbyAlready catalogueden
dc.titlePetrology, whole rock and mineral chemistry, thermobarometry and interpretation of high pressure metamorphic rocksen
dc.typeThesis or Dissertationen
dc.type.qualificationlevelen
dc.type.qualificationnameDSc Doctor of Scienceen


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