Crystallisation temperatures of the most Mg-rich magmas of the Karoo LIP on the basis of Al-in-olivine thermometry

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http://hdl.handle.net/10138/156273

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Heinonen , J S , Jennings , E S & Riley , T R 2015 , ' Crystallisation temperatures of the most Mg-rich magmas of the Karoo LIP on the basis of Al-in-olivine thermometry ' , Chemical Geology , vol. 411 , pp. 26-35 . https://doi.org/10.1016/j.chemgeo.2015.06.015

Julkaisun nimi: Crystallisation temperatures of the most Mg-rich magmas of the Karoo LIP on the basis of Al-in-olivine thermometry
Toissijainen nimi: Karoon suuren magmaprovinssin Mg-rikkaimpien magmojen kiteytymislämpötilat Al-oliviini termometrin perusteella
Tekijä: Heinonen, Jussi S.; Jennings, Eleanor S.; Riley, Teal R.
Tekijän organisaatio: Finnish Museum of Natural History
Natural Sciences Unit
Päiväys: 2015-09-14
Kieli: eng
Sivumäärä: 10
Kuuluu julkaisusarjaan: Chemical Geology
ISSN: 0009-2541
DOI-tunniste: https://doi.org/10.1016/j.chemgeo.2015.06.015
URI: http://hdl.handle.net/10138/156273
Tiivistelmä: Calculating reliable temperatures of Mg-rich magmas is problematic because melt composition and KD(Fe-Mg)ol-liq, the key parameters of many traditional thermometers, are difficult to constrain precisely. The recently developed Al-in-olivine thermometer [Coogan, L.A., Saunders, A.D., Wilson, R.N., 2014. Aluminum-in-olivine thermometry of primitive basalts: Evidence of an anomalously hot mantle source for large igneous provinces. Chemical Geology 368, 1–10] circumvents these problems by relying on the temperature-dependent exchange of Al between olivine and spinel crystallising in equilibrium with each other. This thermometer is used to re-evaluate the crystallisation temperatures of the most Mg-rich magma type identified from the Karoo large igneous province (LIP), known as the Vestfjella depleted ferropicrite suite. Previous temperature estimates for the suite were based on olivine-melt equilibria and indicated anomalously high crystallisation temperatures in excess of 1600 °C. We also present crystallisation temperatures for another Antarctic Karoo magma type, Group 3 dykes from Ahlmannryggen, which are derived from a pyroxene-rich mantle source. Our high-precision analysis of Al in olivine-spinel pairs indicate crystallisation temperatures from 1391±42 °C to 1481±35 °C for the Vestfjella depleted ferropicrite suite (Fo88–92) and from 1253±64 °C to 1303±40 °C for the Group 3 dykes (Fo79–82). Although the maximum temperature estimates for the former are over 100 °C lower than the previously presented estimates, they are still ~200 °C higher than those calculated for mid-ocean ridge basalts using the same method. Although exact mantle potential temperatures are difficult to estimate, the presented results support elevated sub-Gondwanan upper mantle temperatures (generated by a mantle plume or internal mantle heating) during the generation of the Karoo LIP.Calculating reliable temperatures of Mg-rich magmas is problematic because melt composition and KD(Fe-Mg)ol-liq, the key parameters of many traditional thermometers, are difficult to constrain precisely. The recently developed Al-in-olivine thermometer [Coogan, L.A., Saunders, A.D., Wilson, R.N., 2014. Aluminum-in-olivine thermometry of primitive basalts: Evidence of an anomalously hot mantle source for large igneous provinces. Chemical Geology 368, 1–10] circumvents these problems by relying on the temperature-dependent exchange of Al between olivine and spinel crystallising in equilibrium with each other. This thermometer is used to re-evaluate the crystallisation temperatures of the most Mg-rich magma type identified from the Karoo large igneous province (LIP), known as the Vestfjella depleted ferropicrite suite. Previous temperature estimates for the suite were based on olivine-melt equilibria and indicated anomalously high crystallisation temperatures in excess of 1600 °C. We also present crystallisation temperatures for another Antarctic Karoo magma type, Group 3 dykes from Ahlmannryggen, which are derived from a pyroxene-rich mantle source. Our high-precision analysis of Al in olivine-spinel pairs indicate crystallisation temperatures from 1391±42 °C to 1481±35 °C for the Vestfjella depleted ferropicrite suite (Fo88–92) and from 1253±64 °C to 1303±40 °C for the Group 3 dykes (Fo79–82). Although the maximum temperature estimates for the former are over 100 °C lower than the previously presented estimates, they are still ~200 °C higher than those calculated for mid-ocean ridge basalts using the same method. Although exact mantle potential temperatures are difficult to estimate, the presented results support elevated sub-Gondwanan upper mantle temperatures (generated by a mantle plume or internal mantle heating) during the generation of the Karoo LIP.
Avainsanat: 119 Other natural sciences
Karoo magmatism
LARGE IGNEOUS PROVINCE
CONTINENTAL FLOOD BASALTS
picrite
THERMOMETRY
Vertaisarvioitu: Kyllä
Pääsyrajoitteet: openAccess
Rinnakkaistallennettu versio: acceptedVersion


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