|کد مقاله||کد نشریه||سال انتشار||مقاله انگلیسی||ترجمه فارسی||نسخه تمام متن|
|6436310||1637563||2015||10 صفحه PDF||سفارش دهید||دانلود رایگان|
- Re-evaluation of the crystallisation temperatures of the most Mg-rich magmas of the Karoo LIP
- Most primitive magmas crystallised at temperatures of 1400-1500Â Â°C
- Sublithospheric sources of the Karoo LIP heated above ambient upper mantle temperatures
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. Aluminium-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 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 1600Â Â°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 1391Â Â±Â 42Â Â°C to 1481Â Â±Â 35Â Â°C for the Vestfjella depleted ferropicrite suite (Fo88-92) and from 1253Â Â±Â 64Â Â°C to 1303Â Â±Â 40Â Â°C for the Group 3 dykes (Fo79-82). Although the maximum temperature estimates for the former are over 100Â Â°C lower than the previously presented estimates, they are still ~Â 200Â Â°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.
Journal: Chemical Geology - Volume 411, 14 September 2015, Pages 26-35