Recent volcanism in the Siqueiros transform fault

Picritic basalts and implications for MORB magma genesis

M. R. Perfit, D. J. Fornari, W. I. Ridley, P. D. Kirk, J. Casey, K. A. Kastens, J. R. Reynolds, M. Edwards, D. Desonie, Robert D Shuster, S. Paradis

Research output: Contribution to journalArticle

110 Citations (Scopus)

Abstract

Small constructional volcanic landforms and very fresh-looking lava flows are present along one of the inferred active strike-slip faults that connect two small spreading centers (A and B) in the western portion of the Siqueiros transform domain. The most primitive lavas (picritic and olivine-phyric basalts), exclusively recovered from the young-looking flows within the A-B strike-slip fault, contain millimeter-sized olivine phenocrysts (up to 20 modal%) that have a limited compositional range (Fo 91.5 -Fo 89.5 ) and complexly zoned Cr-Al spinels. High-MgO (9.5-10.6 wt%) glasses sampled from the young lava flows contain 1-7% olivine phenocrysts (Fo 90.5 -Fo 89 ) that could have formed by equilibrium crystallization from basaltic melts with Mg# values between 71 and 74. These high MgO (and high Al 2 O 3 ) glasses may be near-primary melts from incompatible-element depleted oceanic mantle and little modified by crustal mixing and/or fractionation processes. Phase chemistry and major element systematics indicate that the picritic basalts are not primary liquids and formed by the accumulation of olivine and minor spinel from high-MgO melts (10% < MgO < 14%). Compared to typical N-MORB from the East Pacific Rise, the Siqueiros lavas are more primitive and depleted in incompatible elements. Phase equilibria calculations and comparisons with experimental data and trace element modeling support this hypothesis. They indicate such primary mid-ocean ridge basalt magmas formed by 10-18% accumulative decompression melting in the spinel peridotite field (but small amounts of melting in the garnet peridotite field are not precluded). The compositional variations of the primitive magmas may result from the accumulation of different small batch melt fractions from a polybaric melting column.

Original languageEnglish (US)
Pages (from-to)91-108
Number of pages18
JournalEarth and Planetary Science Letters
Volume141
Issue number1-4
StatePublished - Jan 1 1996

Fingerprint

Transform faults
transform fault
mid-ocean ridge basalt
olivine
basalt
magma
volcanism
Strike-slip faults
melt
Melting
melting
peridotite
lava
strike-slip fault
lava flow
spinel
slip
volcanic landform
glass
Landforms

Keywords

  • Geochemistry
  • Magmas
  • Olivine
  • Olivine basalt
  • Phase equilibria
  • Picrite
  • Siqueiros fracture zone

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

Cite this

Perfit, M. R., Fornari, D. J., Ridley, W. I., Kirk, P. D., Casey, J., Kastens, K. A., ... Paradis, S. (1996). Recent volcanism in the Siqueiros transform fault: Picritic basalts and implications for MORB magma genesis. Earth and Planetary Science Letters, 141(1-4), 91-108.

Recent volcanism in the Siqueiros transform fault : Picritic basalts and implications for MORB magma genesis. / Perfit, M. R.; Fornari, D. J.; Ridley, W. I.; Kirk, P. D.; Casey, J.; Kastens, K. A.; Reynolds, J. R.; Edwards, M.; Desonie, D.; Shuster, Robert D; Paradis, S.

In: Earth and Planetary Science Letters, Vol. 141, No. 1-4, 01.01.1996, p. 91-108.

Research output: Contribution to journalArticle

Perfit, MR, Fornari, DJ, Ridley, WI, Kirk, PD, Casey, J, Kastens, KA, Reynolds, JR, Edwards, M, Desonie, D, Shuster, RD & Paradis, S 1996, 'Recent volcanism in the Siqueiros transform fault: Picritic basalts and implications for MORB magma genesis', Earth and Planetary Science Letters, vol. 141, no. 1-4, pp. 91-108.
Perfit MR, Fornari DJ, Ridley WI, Kirk PD, Casey J, Kastens KA et al. Recent volcanism in the Siqueiros transform fault: Picritic basalts and implications for MORB magma genesis. Earth and Planetary Science Letters. 1996 Jan 1;141(1-4):91-108.
Perfit, M. R. ; Fornari, D. J. ; Ridley, W. I. ; Kirk, P. D. ; Casey, J. ; Kastens, K. A. ; Reynolds, J. R. ; Edwards, M. ; Desonie, D. ; Shuster, Robert D ; Paradis, S. / Recent volcanism in the Siqueiros transform fault : Picritic basalts and implications for MORB magma genesis. In: Earth and Planetary Science Letters. 1996 ; Vol. 141, No. 1-4. pp. 91-108.
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