Mineral chemistry, whole-rock compositions, and petrogenesis of leg 176 gabbros: Data and discussion

Niu, Yaoling, Gilmore, Trinity, Mackie, Suzie, Greig, Alan and Bach, Wolfgang (2002) Mineral chemistry, whole-rock compositions, and petrogenesis of leg 176 gabbros: Data and discussion. Ocean Drilling Program. Scientific Results. Proceedings. Scientific Results, 176 1-60.


Author Niu, Yaoling
Gilmore, Trinity
Mackie, Suzie
Greig, Alan
Bach, Wolfgang
Title Mineral chemistry, whole-rock compositions, and petrogenesis of leg 176 gabbros: Data and discussion
Journal name Ocean Drilling Program. Scientific Results. Proceedings. Scientific Results
ISSN 0884-5891
Publication date 2002
Sub-type Article (original research)
Volume 176
Start page 1
End page 60
Total pages 60
Editor A. Miller
Place of publication Boulder, Colo. U.S.A.
Publisher National Science Foundation, Joint Oceanographic Institutions, Inc.
Collection year 2002
Language eng
Subject C1
780104 Earth sciences
260102 Igneous and Metamorphic Petrology
Abstract We report mineral chemistry, whole-rock major element compositions, and trace element analyses on Hole 735B samples drilled and selected during Leg 176. We discuss these data, together with Leg 176 shipboard data and Leg 118 sample data from the literature, in terms of primary igneous petrogenesis. Despite mineral compositional variation in a given sample, major constituent minerals in Hole 735B gabbroic rocks display good chemical equilibrium as shown by significant correlations among Mg# (= Mg/[Mg+Fe2+]) of olivine, clinopyroxene, and orthopyroxene and An (=Ca/[Ca+Na]) of plagioclase. This indicates that the mineral assemblages olivine + plagioclase in troctolite, plagioclase + clinopyroxene in gabbro, plagioclases + clinopyroxene + olivine in olivine gabbro, and plagioclase + clinopyroxene + olivine + orthopyroxene in gabbronorite, and so on, have all coprecipitated from their respective parental melts. Fe-Ti oxides (ilmenite and titanomagnetite), which are ubiquitous in most of these rocks, are not in chemical equilibrium with olivine, clinopyroxene, and plagioclase, but precipitated later at lower temperatures. Disseminated oxides in some samples may have precipitated from trapped Fe-Ti–rich melts. Oxides that concentrate along shear bands/zones may mark zones of melt coalescence/transport expelled from the cumulate sequence as a result of compaction or filter pressing. Bulk Hole 735B is of cumulate composition. The most primitive olivine, with Fo = 0.842, in Hole 735B suggests that the most primitive melt parental to Hole 735B lithologies must have Mg# ≤ 0.637, which is significantly less than Mg# = 0.714 of bulk Hole 735B.
Q-Index Code C1

Document type: Journal Article
Sub-type: Article (original research)
Collection: School of Earth Sciences Publications
 
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Created: Tue, 14 Aug 2007, 18:12:00 EST