Garnet-Clinopyroxene Assemblages in the Earth's Mantle


(2007) Garnet-Clinopyroxene Assemblages in the Earth's Mantle.

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For over 100 years eclogites have played a vital role in the development of partial melting models, crustal-mantle systems and geodynamic models involving subduction/recycling processes. However their origin remains controversial from one involving subducted basaltic protoliths to polybaric fractionates of basaltic melts with the added complexity of post-formational metamorphic processes. This thesis presents new chemical data on eclogite and pyroxenite samples from varied geological settings: a classic craton [Kaapvaal Craton (e.g., Roberts Victor, Kimberley and Bultfontein pipes)], circum-cratonic localities (Chino Valley – USA) and oceanic environments (Malaita, New Zealand and Hawaii). Apart from petrographic data, mineral chemistry has been constrained using the electron microprobe and laser ablation ICP-MS for major, minor and trace element data, laser ablation for oxygen isotope data and ICP-MS and TIMS for radiogenic isotopes (Sm-Nd, Lu-Hf and Sr). Garnet pyroxenites have normalised trace element patterns and O isotopes consistent with derivation from silicate melts or by reaction between melts and peridotite. On-craton eclogites and garnet clinopyroxenites have normalised trace element patterns and heterogeneous O isotopes indicative of lower temperature processes either as (a) a “basaltic” protolith altered at low temperatures and subducted to form eclogite or (b) an eclogite retrograded to garnet pyroxenite pre- or syn-entrainment. Modeling of Hf-Nd-Sr isotopes indicates that the Kaapvaal eclogites were derived from Archean protoliths whose isotopic signatures have been disturbed by extensive metasomatism. Four aspects of the thesis are noteworthy: (1) the extreme Hf-Nd-Sr heterogeneity shown by eclogites and pyroxenites relative to MORB and OIB, (2) the heavy O isotope ratios for on- and off-craton samples from Chino Valley and Lovedale, (3) the unique Archean (3.15 Ga) low Hf, Nd and Sr reservoir represented by a Roberts Victor eclogite, and (4) the Lu-Hf system is more robust than the Sm-Nd system.

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This is a Accepted version
This version's date is: 11/2007
This item is not peer reviewed

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Item TypeThesis (Doctoral)
TitleGarnet-Clinopyroxene Assemblages in the Earth's Mantle
Uncontrolled Keywordseclogites; pyroxene; garnet pyroxenites; Chino Valley; Lovedale
DepartmentsFaculty of Science\Earth Sciences

Deposited by Leanne Workman (UXYL007) on 13-Apr-2015 in Royal Holloway Research Online.Last modified on 05-Feb-2017


©2007 Ruth Goretti Gonzaga. Short sections of text, not to exceed two paragraphs, may be quoted without explicit permission provided that full credit including © notice, is given to the source.