Citation:

PANGAEA.727453

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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 midocean ridge basalt (MORB) magmas beneath different segments of the MAR have crystallized over a wide range of pressures (100-900MPa). However, each segment seems to have a specific crystallization history. Nearly isobaric crystallization conditions (100-300MPa) 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 (200-900MPa). In addition, our results demonstrate close to anhydrous crystallization conditions of N-MORBs, whereas geochemically enriched MORBs were successfully modeled in the presence of 0.4-1wt% 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 ±200MPa) 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.

KEY WORDS: MORB; Mid-Atlantic Ridge; depth of crystallization; water abundances; phase equilibria calculations; cotectic crystallization; pressure estimates; polybaric fractionation

Related to:

Almeev, Renat; Holtz, François; Koepke, Jürgen; Haase, Karsten M; Devey, Colin W (2008): Depth of partial crystallization of H2O-bearing MORB: Phase equilibria simulations of basalts at the MAR near Ascension Island (7-11°S). Journal of Petrology, 49, 25-45, https://doi.org/10.1093/petrology/egm068

Project(s):

From Mantle to Ocean: Energy-, Material- and Life-cycles at Spreading Axes (DERIDGE)

Funding:

German Research Foundation (DFG), grant/award no. 5471797 : From Mantle to Ocean: Energy-, Material- and Life-cycles at Spreading Axes

Coverage:

Median Latitude: -9.254670 * Median Longitude: -13.294863 * South-bound Latitude: -10.887800 * West-bound Longitude: -13.616200 * North-bound Latitude: -7.665800 * East-bound Longitude: -13.021800

Event(s):

M41/2_132 * Latitude Start: -7.665800 * Longitude Start: -13.456000 * Latitude End: -7.674500 * Longitude End: -13.450800 * Elevation Start: -3925.0 m * Elevation End: -3991.0 m * Location: Mid-Atlantic Ridge at 4-11°S * Campaign: * Basis: * Method/Device: Dredge (DRG) * Comment: Mid Atlantic Ridge, south of Ascension Fracture Zone, segment A1

M41/2_133 * Latitude Start: -7.718000 * Longitude Start: -13.444000 * Latitude End: -7.726000 * Longitude End: -13.424200 * Elevation Start: -3980.0 m * Elevation End: -3809.0 m * Location: Mid-Atlantic Ridge at 4-11°S * Campaign: * Basis: * Method/Device: Dredge (DRG) * Comment: Mid Atlantic Ridge, south of Ascension Fracture Zone, segment A1

M41/2_136 * Latitude Start: -7.772500 * Longitude Start: -13.431500 * Latitude End: -7.774200 * Longitude End: -13.435200 * Elevation Start: -3727.0 m * Elevation End: -3719.0 m * Location: Mid-Atlantic Ridge at 4-11°S * Campaign: * Basis: * Method/Device: Dredge (DRG) * Comment: Mid Atlantic Ridge, south of Ascension Fracture Zone, segment A1

License:

Creative Commons Attribution 3.0 Unported (CC-BY-3.0)

Size:

3 datasets

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Datasets listed in this publication series

Almeev, R; Holtz, F; Koepke, J et al. (2009): Crystallization conditions and compositions of residual melts from the Mid Atlantic Ridge near Ascension Island. https://doi.org/10.1594/PANGAEA.727431
Almeev, R; Holtz, F; Koepke, J et al. (2009): Crystallization conditions obtained after inverse and forward calculations and pressures of partial crystallization of melts from the Mid Atlantic Ridge near Ascension Island. https://doi.org/10.1594/PANGAEA.727433
Almeev, R; Holtz, F; Koepke, J et al. (2009): Geochemical composition of basaltic glasses and glass inclusions from the Mid Atlantic Ridge near Ascension Island. https://doi.org/10.1594/PANGAEA.727391