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 language | English (US) |
|---|---|
| Pages (from-to) | 91-108 |
| Number of pages | 18 |
| Journal | Earth and Planetary Science Letters |
| Volume | 141 |
| Issue number | 1-4 |
| State | Published - Jun 1996 |
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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
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, 06.1996, p. 91-108.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Recent volcanism in the Siqueiros transform fault
T2 - Picritic basalts and implications for MORB magma genesis
AU - Perfit, M. R.
AU - Fornari, D. J.
AU - Ridley, W. I.
AU - Kirk, P. D.
AU - Casey, J.
AU - Kastens, K. A.
AU - Reynolds, J. R.
AU - Edwards, M.
AU - Desonie, D.
AU - Shuster, Robert D
AU - Paradis, S.
PY - 1996/6
Y1 - 1996/6
N2 - 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.
AB - 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.
KW - Geochemistry
KW - Magmas
KW - Olivine
KW - Olivine basalt
KW - Phase equilibria
KW - Picrite
KW - Siqueiros fracture zone
UR - http://www.scopus.com/inward/record.url?scp=0029751343&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0029751343&partnerID=8YFLogxK
M3 - Article
AN - SCOPUS:0029751343
VL - 141
SP - 91
EP - 108
JO - Earth and Planetary Sciences Letters
JF - Earth and Planetary Sciences Letters
SN - 0012-821X
IS - 1-4
ER -