Details
| Original language | English |
|---|---|
| Pages (from-to) | 25-45 |
| Number of pages | 21 |
| Journal | Journal of Petrology |
| Volume | 49 |
| Issue number | 1 |
| Publication status | Published - 27 Nov 2007 |
Abstract
Phase equilibria simulations were performed on naturally quenched basaltic glasses to determine crystallization conditions prior to eruption of magmas at the Mid-Atlantic Ridge (MAR) east of Ascension Island (7-11°S). The results indicate that mid-ocean ridge basalt (MORB) magmas beneath different segments of the MAR have crystallized over a wide range of pressures (100-900 MPa). However, each segment seems to have a specific crystallization history. Nearly isobaric crystallization conditions (100-300 MPa) were obtained for the geochemically enriched MORB magmas of the central segments, whereas normal (N)-MORB magmas of the bounding segments are characterized by polybaric crystallization conditions (200-900 MPa). In addition, our results demonstrate close to anhydrous crystallization conditions of N-MORBs, whereas geochemically enriched MORBs were successfully modeled in the presence of 0.4-1 wt% H2O in the parental melts. These estimates are in agreement with direct (Fourier transform IR) measurements of H2O abundances in basaltic glasses and melt inclusions for selected samples. Water contents determined in the parental melts are in the range 0.04-0.09 and 0.30-0.55 wt% H2O for depleted and enriched MORBs, respectively. Our results are in general agreement (within ±200 MPa) with previous approaches used to evaluate pressure estimates in MORB. However, the determination of pre-eruptive conditions of MORBs, including temperature and water content in addition to pressure, requires the improvement of magma crystallization models to simulate liquid lines of descent in the presence of small amounts of water.
Keywords
- Cotectic crystallization, Depth of crystallization, Mid-Atlantic Ridge, MORB, Phase equilibria calculations, Polybaric fractionation, Pressure estimates, Water abundances
ASJC Scopus subject areas
- Earth and Planetary Sciences(all)
- Geophysics
- Earth and Planetary Sciences(all)
- Geochemistry and Petrology
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In: Journal of Petrology, Vol. 49, No. 1, 27.11.2007, p. 25-45.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - Depths of partial crystallization of H2O-bearing MORB
T2 - Phase equilibria simulations of basalts at the MAR near Ascension Island (7-11°S)
AU - Almeev, Renat
AU - Holtz, François
AU - Koepke, Jürgen
AU - Haase, Karsten
AU - Devey, Colin
N1 - Funding Information: This is publication 14 of the priority program SPP1144 ‘From Mantle to Ocean: Energy-, Material-and Life-cycles at Spreading Axes’ of the German Science Foundation (DFG) (Project Ho1337/10). We thank Alexei Ariskin and Jun-Ichi Kimura for helpful reviews of an earlier draft. The authors wish to thank Othmar Mu« ntener and three anonymous reviewers for their suggestions, which allowed us to improve the clarity and quality of the paper considerably. The authors acknowledge Wendy Bohrson for her editorial comments and efforts. Copyright: Copyright 2008 Elsevier B.V., All rights reserved.
PY - 2007/11/27
Y1 - 2007/11/27
N2 - Phase equilibria simulations were performed on naturally quenched basaltic glasses to determine crystallization conditions prior to eruption of magmas at the Mid-Atlantic Ridge (MAR) east of Ascension Island (7-11°S). The results indicate that mid-ocean ridge basalt (MORB) magmas beneath different segments of the MAR have crystallized over a wide range of pressures (100-900 MPa). However, each segment seems to have a specific crystallization history. Nearly isobaric crystallization conditions (100-300 MPa) were obtained for the geochemically enriched MORB magmas of the central segments, whereas normal (N)-MORB magmas of the bounding segments are characterized by polybaric crystallization conditions (200-900 MPa). In addition, our results demonstrate close to anhydrous crystallization conditions of N-MORBs, whereas geochemically enriched MORBs were successfully modeled in the presence of 0.4-1 wt% H2O in the parental melts. These estimates are in agreement with direct (Fourier transform IR) measurements of H2O abundances in basaltic glasses and melt inclusions for selected samples. Water contents determined in the parental melts are in the range 0.04-0.09 and 0.30-0.55 wt% H2O for depleted and enriched MORBs, respectively. Our results are in general agreement (within ±200 MPa) with previous approaches used to evaluate pressure estimates in MORB. However, the determination of pre-eruptive conditions of MORBs, including temperature and water content in addition to pressure, requires the improvement of magma crystallization models to simulate liquid lines of descent in the presence of small amounts of water.
AB - Phase equilibria simulations were performed on naturally quenched basaltic glasses to determine crystallization conditions prior to eruption of magmas at the Mid-Atlantic Ridge (MAR) east of Ascension Island (7-11°S). The results indicate that mid-ocean ridge basalt (MORB) magmas beneath different segments of the MAR have crystallized over a wide range of pressures (100-900 MPa). However, each segment seems to have a specific crystallization history. Nearly isobaric crystallization conditions (100-300 MPa) were obtained for the geochemically enriched MORB magmas of the central segments, whereas normal (N)-MORB magmas of the bounding segments are characterized by polybaric crystallization conditions (200-900 MPa). In addition, our results demonstrate close to anhydrous crystallization conditions of N-MORBs, whereas geochemically enriched MORBs were successfully modeled in the presence of 0.4-1 wt% H2O in the parental melts. These estimates are in agreement with direct (Fourier transform IR) measurements of H2O abundances in basaltic glasses and melt inclusions for selected samples. Water contents determined in the parental melts are in the range 0.04-0.09 and 0.30-0.55 wt% H2O for depleted and enriched MORBs, respectively. Our results are in general agreement (within ±200 MPa) with previous approaches used to evaluate pressure estimates in MORB. However, the determination of pre-eruptive conditions of MORBs, including temperature and water content in addition to pressure, requires the improvement of magma crystallization models to simulate liquid lines of descent in the presence of small amounts of water.
KW - Cotectic crystallization
KW - Depth of crystallization
KW - Mid-Atlantic Ridge
KW - MORB
KW - Phase equilibria calculations
KW - Polybaric fractionation
KW - Pressure estimates
KW - Water abundances
UR - http://www.scopus.com/inward/record.url?scp=37449022346&partnerID=8YFLogxK
U2 - 10.1093/petrology/egm068
DO - 10.1093/petrology/egm068
M3 - Article
AN - SCOPUS:37449022346
VL - 49
SP - 25
EP - 45
JO - Journal of Petrology
JF - Journal of Petrology
SN - 0022-3530
IS - 1
ER -