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

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doi: 10.1029/2011GC003548
Author(s): Sano, Takashi; Sakuyama, Tetsuya; Ingle, Stephanie; Rodriguez, Sedelia; Yamasaki, Toru
Author Affiliation(s): Primary:
National Museum of Nature and Science, Department of Geology and Paleontology, Tokyo, Japan
Japan Agency of Marine-Earth Science and Technology, Japan
University of Southampton, United Kingdom
Lamont-Doherty Earth Observatory, United States
Geological Survey of Japan, Japan
Volume Title: Geochemistry, Geophysics, Geosystems - G<sup>3</sup>
Source: Geochemistry, Geophysics, Geosystems - G>3`, 12(6). Publisher: American Geophysical Union and The Geochemical Society, United States. ISSN: 1525-2027
Note: In English. 131 refs.; illus., incl. 2 tables, sketch map
Summary: 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.
Year of Publication: 2011
Research Program: IODP Integrated Ocean Drilling Program
ODP Ocean Drilling Program
Key Words: 05 Petrology, Igneous and Metamorphic; Anorthite; Basalts; Chemical composition; Cocos Plate; Crust; Density; Dikes; East Pacific; East Pacific Rise; Equatorial Pacific; Expedition 309; Expeditions 309/312; Feldspar group; Framework silicates; Gabbros; Guatemala Basin; Igneous rocks; Integrated Ocean Drilling Program; Intrusions; Lava; Magmas; Mid-ocean ridge basalts; Mid-ocean ridges; Nazca Plate; North Pacific; Northeast Pacific; ODP Site 1256; Ocean Drilling Program; Ocean floors; Oceanic crust; Oscillatory zoning; Pacific Ocean; Petrography; Phase equilibria; Plagioclase; Plate tectonics; Plutonic rocks; Silicates; Upper crust; Volcanic rocks; Xenocrysts; Zoning
Coordinates: N064400 N064400 W0915600 W0915600
Record ID: 2012021838
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