Petrology and geochemistry of primitive lower oceanic crust from Pito Deep; implications for the accretion of the lower crust at the southern East Pacific Rise

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doi: 10.1007/s00410-007-0210-z
Authors:Perk, Neil W.; Coogan, Laurence A.; Karson, Jeffrey A.; Klein, Emily M.; Hanna, Heather D.
Author Affiliations:Primary:
University of Victoria, School of Earth and Ocean Sciences, Victoria, BC, Canada
Syracuse University, United States
Duke University, United States
North Carolina Geological Survey, United States
Volume Title:Contributions to Mineralogy and Petrology
Source:Contributions to Mineralogy and Petrology, 154(5), p.575-590. Publisher: Springer International, Heidelberg - New York, International. ISSN: 0010-7999
Publication Date:2007
Note:In English. 76 refs.; illus., incl. sketch map
Summary:A suite of samples collected from the uppermost part of the plutonic section of the oceanic crust formed at the S East Pacific Rise (EPR) and exposed at the Pito Deep has been examined. These rocks were sampled in situ by a remotely operated vehicle and lie beneath a complete upper crustal section. This is only the second area (after the Hess Deep) in which a substantial depth into the plutonic complex formed at the EPR has been sampled in situ and reveals significant spatial heterogeneity in the plutonic complex. In contrast to the uppermost plutonic rocks at Hess Deep, the rocks studied here are generally primitive with olivine forsterite contents mainly between 85 and 88 and including many troctolites. The majority of the samples crystallized from a melt that was aggregated normal MORB. High Mg# clinopyroxene is common despite model predictions that clinopyroxene should not reach the liquidus early during low-P crystallization of MORB. Stochastic modelling of melt crystallisation at various levels in the crust suggests that it is unlikely that a significant melt mass crystallized in the deeper crust (for example in sills) because this would lead to more evolved shallow level plutonic rocks. Similar to the upper plutonic section of the Hess Deep and the Oman ophiolite, many samples show a steeply dipping, axis-parallel, magmatic fabric. This suggests that vertical magmatic flow is an important process in the upper part of the seismic low-velocity zone beneath fast-spreading ridges. It is suggested that both temporal and spatial (along-axis) variability in the magmatic and hydrothermal systems can explain the differences observed between the Hess Deep and Pito Deep plutonics. [G.L.B.]
Sections:Geochemistry; Petrology
Subsections:Igneous rocks; Oceanic petrology
Subjects:Basalts; Crust; Crystal chemistry; Crystallization; Gabbros; Geochemistry; ICP mass spectra; Igneous rocks; Intrusions; Lithophile elements; Low pressure; Lower crust; Magma chambers; Magmas; Mass spectra; Metals; Mid-ocean ridge basalts; Mid-ocean ridges; Mineral composition; Models; Ocean floors; Oceanic crust; Ophiolite; P-T conditions; Petrology; Phase transitions; Plate tectonics; Plutonic rocks; Prediction; Pressure; Rare earths; Sea-floor spreading; Sills; Spectra; Spreading centers; Trace elements; Troctolite; Volcanic rocks; Whole rock; Arabian Peninsula; Asia; East Pacific; East Pacific Rise; Equatorial Pacific; Hess Deep; North Pacific; Northeast Pacific; Oman; Pacific Ocean; Pito Deep
Coordinates:S225900 S225800 W1115300 W1115400
Abstract Numbers:07M/4304
Record ID:2008075990
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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