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Petrological relationships among lavas, dikes, and gabbros from Integrated Ocean Drilling Program Hole 1256D: Insight into the magma plumbing system beneath the East Pacific Rise

Petrological relationships among lavas, dikes, and gabbros from Integrated Ocean Drilling Program Hole 1256D: Insight into the magma plumbing system beneath the East Pacific Rise
Petrological relationships among lavas, dikes, and gabbros from Integrated Ocean Drilling Program Hole 1256D: Insight into the magma plumbing system beneath the East Pacific Rise
A continuous section from extrusive lavas, through sheeted dikes, and uppermost gabbros recovered from Integrated Ocean Drilling Program Hole 1256D provides important information regarding magma plumbing systems beneath superfast spreading ridges. Petrological examination demonstrates that a model of fractional crystallization from a magma of composition similar to one of the more primitive gabbros in a shallow (?50–100 MPa) melt lens reasonably explains mineral and whole rock compositions of many lavas and dikes. Elevated concentrations of trace elements in some rocks appear to have resulted from mixing between primitive magma and highly evolved magma. About half of the dike samples have more evolved Fe-rich compositions than the extrusive lava samples. Magma densities of the Fe-rich dikes are a little higher (?30 kg/m3) than those of lavas, suggesting that these dike magmas would not reach the surface. Mineralogical investigations reveal that both lavas and dikes contain oscillatory zoned plagioclase xenocrysts, implying magma mixing caused by successive episodes of fractionation and magma replenishment in the melt lens. The plagioclase xenocrysts contain high-Anorthite sections [An: 100 × Ca/(Ca+Na) in mole percent] whose compositions are not in equilibrium with host liquids. The high-An sections were likely crystallized when primitive magmas with high CaO/Na2O were injected in the melt lens. Since the oscillatory zoned plagioclase generally forms crystal clots, they were probably accumulated in a mush zone. The petrographical examination favors a model suggesting that injection of primitive magma into the melt lens broke the mush zone and pushed out the oscillatory zoned plagioclase.
1525-2027
Q06013
Sano, Takashi
9175ab5f-a44f-462a-8a57-b43fe3807308
Sakuyama, Tetsuya
8d559dac-1711-4079-96e9-423bf20b03a4
Ingle, Stephanie
290ddc48-9f8a-4639-86a7-d552434de4e8
Rodriguez, Sedelia
6359f2a9-7415-4b64-89f6-55fa4fe5ec30
Yamasaki, Toru
d98f06d9-ccca-4379-9998-866f9e4b3674
Sano, Takashi
9175ab5f-a44f-462a-8a57-b43fe3807308
Sakuyama, Tetsuya
8d559dac-1711-4079-96e9-423bf20b03a4
Ingle, Stephanie
290ddc48-9f8a-4639-86a7-d552434de4e8
Rodriguez, Sedelia
6359f2a9-7415-4b64-89f6-55fa4fe5ec30
Yamasaki, Toru
d98f06d9-ccca-4379-9998-866f9e4b3674

Sano, Takashi, Sakuyama, Tetsuya, Ingle, Stephanie, Rodriguez, Sedelia and Yamasaki, Toru (2011) Petrological relationships among lavas, dikes, and gabbros from Integrated Ocean Drilling Program Hole 1256D: Insight into the magma plumbing system beneath the East Pacific Rise. Geochemistry, Geophysics, Geosystems, 12 (6), Q06013. (doi:10.1029/2011GC003548).

Record type: Article

Abstract

A continuous section from extrusive lavas, through sheeted dikes, and uppermost gabbros recovered from Integrated Ocean Drilling Program Hole 1256D provides important information regarding magma plumbing systems beneath superfast spreading ridges. Petrological examination demonstrates that a model of fractional crystallization from a magma of composition similar to one of the more primitive gabbros in a shallow (?50–100 MPa) melt lens reasonably explains mineral and whole rock compositions of many lavas and dikes. Elevated concentrations of trace elements in some rocks appear to have resulted from mixing between primitive magma and highly evolved magma. About half of the dike samples have more evolved Fe-rich compositions than the extrusive lava samples. Magma densities of the Fe-rich dikes are a little higher (?30 kg/m3) than those of lavas, suggesting that these dike magmas would not reach the surface. Mineralogical investigations reveal that both lavas and dikes contain oscillatory zoned plagioclase xenocrysts, implying magma mixing caused by successive episodes of fractionation and magma replenishment in the melt lens. The plagioclase xenocrysts contain high-Anorthite sections [An: 100 × Ca/(Ca+Na) in mole percent] whose compositions are not in equilibrium with host liquids. The high-An sections were likely crystallized when primitive magmas with high CaO/Na2O were injected in the melt lens. Since the oscillatory zoned plagioclase generally forms crystal clots, they were probably accumulated in a mush zone. The petrographical examination favors a model suggesting that injection of primitive magma into the melt lens broke the mush zone and pushed out the oscillatory zoned plagioclase.

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Published date: 2011

Identifiers

Local EPrints ID: 193803
URI: http://eprints.soton.ac.uk/id/eprint/193803
ISSN: 1525-2027
PURE UUID: cb0d990c-332b-4bd7-9837-2a3799223943

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Date deposited: 20 Jul 2011 12:59
Last modified: 16 Jul 2019 23:25

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