TY - JOUR

T1 - Differentiation and crystallization conditions of basalts from the Kerguelen large igneous province

T2 - An experimental study

AU - Freise, Marcus

AU - Holtz, Francois

AU - Nowak, Marcus

AU - Scoates, James S.

AU - Strauss, Holger

N1 - Funding Information: Acknowledgments This research was carried out in the framework of the ODP ‘‘Schwerpunktprogramm’’ supported by the German Science Foundation (DFG, Ho1337). The ODP is sponsored by the US National Science Foundation (NSF) and participating countries under management of Joint Oceanographic Institutions (JOI), Inc. Sample 35R2 was collected during ODP Leg 183 and sample OB93-190 was collected on the Kerguelen Archipelago by D. Weis and D. Damasceno. We thank Dominique Weis for help in selecting the appropriate samples for the experimental study. We thank O. Diedrich for preparing the samples and W. Hurkuck and B. Aichinger for technical assistance. Copyright: Copyright 2009 Elsevier B.V., All rights reserved.

PY - 2009/4/18

Y1 - 2009/4/18

N2 - Phase relations of basalts from the Kerguelen large igneous province have been investigated experimentally to understand the effect of temperature, fO2, and fugacity of volatiles (e.g., H2O and CO2) on the differentiation path of LIP basalts. The starting rock samples were a tholeiitic basalt from the Northern Kerguelen Plateau (ODP Leg 183 Site 1140) and mildly alkalic basalt evolved from the Kerguelen Archipelago (Mt. Crozier on the Courbet Peninsula), representing different differentiation stages of basalts related to the Kerguelen mantle plume. The influence of temperature, water and oxygen fugacity on phase stability and composition was investigated at 500 MPa and all experiments were fluid-saturated. Crystallization experiments were performed at temperatures between 900 and 1,160°C under oxidizing (log fO2 ∼ ΔQFM + 4) and reducing conditions (log fO2 ∼ QFM) in an internally heated gas-pressure vessel equipped with a rapid quench device and a Pt-Membrane for monitoring the fH2. In all experiments, a significant influence of the fO2 on the composition and stability of the Mg/Fe-bearing mineral phases could be observed. Under reducing conditions, the residual melts follow a tholeiitic differentiation trend. In contrast, melts have high Mg# [Mg2+/(Mg2+ + Fe2+)] and follow a calk-alkalic differentiation trend at oxidizing conditions. The comparison of the natural phenocryst assemblages with the experimental products allows us to constrain the differentiation and pre-eruptive conditions of these magmas. The pre-eruptive temperature of the alkalic basalt was about 950-1,050°C. The water content of the melt was below 2.5 wt% H2O and strongly oxidizing conditions (log fO2 ∼ ΔQFM + 2) were prevailing in the magma chamber prior to eruption. The temperature of the tholeiitic melt was above 1,060°C, with a water content below 2 wt% H2O and a log fO2 ∼ Δ QFM + 1. Early fractionation of clinopyroxene is a crucial step resulting in the generation of silica-poor and alkali-rich residual melts (e.g., alkali basalt). The enrichment of alkalis in residual melts is enhanced at high fO2 and low aH2O.

AB - Phase relations of basalts from the Kerguelen large igneous province have been investigated experimentally to understand the effect of temperature, fO2, and fugacity of volatiles (e.g., H2O and CO2) on the differentiation path of LIP basalts. The starting rock samples were a tholeiitic basalt from the Northern Kerguelen Plateau (ODP Leg 183 Site 1140) and mildly alkalic basalt evolved from the Kerguelen Archipelago (Mt. Crozier on the Courbet Peninsula), representing different differentiation stages of basalts related to the Kerguelen mantle plume. The influence of temperature, water and oxygen fugacity on phase stability and composition was investigated at 500 MPa and all experiments were fluid-saturated. Crystallization experiments were performed at temperatures between 900 and 1,160°C under oxidizing (log fO2 ∼ ΔQFM + 4) and reducing conditions (log fO2 ∼ QFM) in an internally heated gas-pressure vessel equipped with a rapid quench device and a Pt-Membrane for monitoring the fH2. In all experiments, a significant influence of the fO2 on the composition and stability of the Mg/Fe-bearing mineral phases could be observed. Under reducing conditions, the residual melts follow a tholeiitic differentiation trend. In contrast, melts have high Mg# [Mg2+/(Mg2+ + Fe2+)] and follow a calk-alkalic differentiation trend at oxidizing conditions. The comparison of the natural phenocryst assemblages with the experimental products allows us to constrain the differentiation and pre-eruptive conditions of these magmas. The pre-eruptive temperature of the alkalic basalt was about 950-1,050°C. The water content of the melt was below 2.5 wt% H2O and strongly oxidizing conditions (log fO2 ∼ ΔQFM + 2) were prevailing in the magma chamber prior to eruption. The temperature of the tholeiitic melt was above 1,060°C, with a water content below 2 wt% H2O and a log fO2 ∼ Δ QFM + 1. Early fractionation of clinopyroxene is a crucial step resulting in the generation of silica-poor and alkali-rich residual melts (e.g., alkali basalt). The enrichment of alkalis in residual melts is enhanced at high fO2 and low aH2O.

KW - Basalt

KW - Crystallization experiments

KW - Large igneous provinces

KW - Liquid lines of descent

KW - Oxygen fugacity

KW - Phase relations

UR - http://www.scopus.com/inward/record.url?scp=69849087386&partnerID=8YFLogxK

U2 - 10.1007/s00410-009-0394-5

DO - 10.1007/s00410-009-0394-5

M3 - Article

AN - SCOPUS:69849087386

VL - 158

SP - 505

EP - 527

JO - Contributions to Mineralogy and Petrology

JF - Contributions to Mineralogy and Petrology

SN - 0010-7999

IS - 4

ER -