Edinburgh Research Archive logo

Edinburgh Research Archive

University of Edinburgh homecrest
View Item 
  •   ERA Home
  • Chemistry, School of
  • Chemistry thesis and dissertation collection
  • View Item
  •   ERA Home
  • Chemistry, School of
  • Chemistry thesis and dissertation collection
  • View Item
  • Login
JavaScript is disabled for your browser. Some features of this site may not work without it.

Petrology, whole rock and mineral chemistry, thermobarometry and interpretation of high pressure metamorphic rocks

View/Open
CarswellDA_1988redux.pdf (91.49Mb)
Date
1988
Author
Carswell, Dennis Anthony
Metadata
Show full item record
Abstract
 
 
High pressure metamorphic rocks in two contrasting geological settings have been studied and interpreted.
 
Occurrences 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.
 
Complementary 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.
 
A 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.
 
URI
http://hdl.handle.net/1842/27764
Collections
  • Chemistry thesis and dissertation collection

Library & University Collections HomeUniversity of Edinburgh Information Services Home
Privacy & Cookies | Takedown Policy | Accessibility | Contact
Privacy & Cookies
Takedown Policy
Accessibility
Contact
feed RSS Feeds

RSS Feed not available for this page

 

 

All of ERACommunities & CollectionsBy Issue DateAuthorsTitlesSubjectsPublication TypeSponsorSupervisorsThis CollectionBy Issue DateAuthorsTitlesSubjectsPublication TypeSponsorSupervisors
LoginRegister

Library & University Collections HomeUniversity of Edinburgh Information Services Home
Privacy & Cookies | Takedown Policy | Accessibility | Contact
Privacy & Cookies
Takedown Policy
Accessibility
Contact
feed RSS Feeds

RSS Feed not available for this page