Graduate Thesis Or Dissertation

 

Partial melting of tonalite at the margins of a Columbia River Basalt Group dike, Wallowa Mountains, northeastern Oregon Public Deposited

Downloadable Content

Download PDF
https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/z029p782s

Descriptions

Attribute NameValues
Creator
Abstract
  • Columbia River Basalt Group dikes cut the tonalite-granodiorite Wallowa Batholith in northeastern Oregon, providing a natural setting in which to examine partial melting. Many dikes have up to 5 m-wide zones of quenched partially melted wallrock at their margins. This paper examines the progressive partial melting reactions in biotite-and hornblende-bearing tonalite at the margin of a near-vertical Grande Ronde dike in the vicinity of Maxwell Lake. Paleodepth at the time of dike emplacement is estimated at 1- 2 km, and dike temperature was about 1140°C. Samples collected from the dike margin represent five successive stages of melt reaction over a distance of about 5 m from unmolten wallrock (Stage 1) to about 40 volume percent (vol%) quenched melt (Stage 5). This melt is now represented by about 31 vol% silicic glass that has undergone little to no devitrification and about 9 vol% plagioclase, pyroxene, and Fe-Ti oxide quench crystals. Whole rock major and trace element bulk compositional data are nearly identical to unmolten rock at each stage, suggesting that the melt did not separate from the restite and each stage represents essentially a chemically closed system. With progressive melting, primary hornblende, biotite, and orthoclase are entirely consumed but residual plagioclase, quartz, Fe-Ti oxides and apatite persist in the restite. Hornblende dehydration initially produces a dusty intergrowth of augite, pigeonite, lesser enstatite, and sparse Fe-Ti oxides. Initial biotite dehydration produces titaniferous magnetite and lesser ilmenite aligned in bands in an intergrowth of enstatite and plagioclase. Andesine plagioclase develops a spongy texture as the albite component is lost to the melt. Reaction of hornblende, quartz, and feldspar produces sparse tonalitic (high-Ca) glass, while the reaction of biotite, quartz, and feldspar produces abundant granitic (high-K) glass. The two glass types are irregularly distributed around mafic reaction sites and in up to 2 mm seams on quartz-feldspar contacts. With progressive melting, replacement phases become compositionally more homogeneous, clinopyroxene is consumed, the proportion of plagioclase decreases, and glasses become slightly more mafic. Granitic and tonalitic glasses persist in just over 31 vol% glass suggesting that deformation is required to mix these melt types.
Resource Type
Date Available
Date Copyright
Date Issued
Degree Level
Degree Name
Degree Field
Degree Grantor
Commencement Year
Advisor
Academic Affiliation
Non-Academic Affiliation
Subject
Rights Statement
Language
Digitization Specifications
  • File scanned at 300 ppi (Monochrome, 256 Grayscale, 24-bit Color) using Capture Perfect 3.0.82 on a Canon DR-9080C in PDF format. CVista PdfCompressor 4.0 was used for pdf compression and textual OCR.
Replaces
Additional Information
  • description.provenance : Approved for entry into archive by Patricia Black(patricia.black@oregonstate.edu) on 2011-04-18T18:57:21Z (GMT) No. of bitstreams: 1 PetcovicHeatherL2001.pdf: 16936509 bytes, checksum: 488facf53c34f297e1a11a674ca634a2 (MD5)
  • description.provenance : Approved for entry into archive by Patricia Black(patricia.black@oregonstate.edu) on 2011-04-18T19:50:46Z (GMT) No. of bitstreams: 1 PetcovicHeatherL2001.pdf: 16936509 bytes, checksum: 488facf53c34f297e1a11a674ca634a2 (MD5)
  • description.provenance : Made available in DSpace on 2011-04-18T19:50:46Z (GMT). No. of bitstreams: 1 PetcovicHeatherL2001.pdf: 16936509 bytes, checksum: 488facf53c34f297e1a11a674ca634a2 (MD5) Previous issue date: 2000-07-07
  • description.provenance : Submitted by Erin Clark (ecscannerosu@gmail.com) on 2011-04-18T18:45:39Z No. of bitstreams: 1 PetcovicHeatherL2001.pdf: 16936509 bytes, checksum: 488facf53c34f297e1a11a674ca634a2 (MD5)

Relationships

Parents:

This work has no parents.

Items