Presentation Type

Poster

Location

Portland State University, Portland, Oregon

Start Date

5-12-2015 11:00 AM

End Date

5-12-2015 1:00 PM

Subjects

Meteorites -- Research, Geochemistry

Abstract

Northwest Africa 8614 is classified as a winonaite on the basis of oxygen isotope ratios, mineralogy, and highly reduced chemistry. Unlike other winonaites, it contains numerous and readily apparent chondrules. Here we discuss various features of NWA 8614 and the possible significance of the meteorite.

Petrological and chemical analyses were performed using optical microscopy with a DM2500 Leica petrographic microscope and a Zeiss Sigma VP-FEG scanning electron microscope (SEM) with a high-efficiency energy dispersive spectrometer (EDS). Oxygen isotopes were analyzed by Karen Ziegler at the University of New Mexico on acid-washed samples to remove terrestrial weathering products.

Owing to the abundance of chondrules, NWA 8641 may be one of the least heated winonaites, and therefore may provide clues to the chondritic protolith of the winonaite parent body. Overall textures are similar to those found in type 6 chondrites that escaped significant melting.

Despite similar geothermometer temperatures for various mineral pairs, NWA 8614 apparently did not attain Fe-Mg equilibrium between olivine and pyroxene. Like other winonaites, NWA 8614 has olivine compositions that are too magnesian for equilibrium relative to low-Ca pyroxene. Among winonaites as a whole, there is no evidence for a curved trend between Fa and Fs compositions as would be expected for FeO-reduction during metamorphism [Benedix, et al 1998], nor for mineral compositions that correlate with geothermometry temperatures. This argues against a single metamorphic FeO-reduction trend from a common chondritic precursor. Instead, protoliths for different winonaites may have varied slightly in composition.

Rights

© Copyright the author(s)

IN COPYRIGHT:
http://rightsstatements.org/vocab/InC/1.0/
This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).

DISCLAIMER:
The purpose of this statement is to help the public understand how this Item may be used. When there is a (non-standard) License or contract that governs re-use of the associated Item, this statement only summarizes the effects of some of its terms. It is not a License, and should not be used to license your Work. To license your own Work, use a License offered at https://creativecommons.org/

Persistent Identifier

http://archives.pdx.edu/ds/psu/19822

Share

COinS
 
May 12th, 11:00 AM May 12th, 1:00 PM

NWA 8614: The Least Heated Winonaite

Portland State University, Portland, Oregon

Northwest Africa 8614 is classified as a winonaite on the basis of oxygen isotope ratios, mineralogy, and highly reduced chemistry. Unlike other winonaites, it contains numerous and readily apparent chondrules. Here we discuss various features of NWA 8614 and the possible significance of the meteorite.

Petrological and chemical analyses were performed using optical microscopy with a DM2500 Leica petrographic microscope and a Zeiss Sigma VP-FEG scanning electron microscope (SEM) with a high-efficiency energy dispersive spectrometer (EDS). Oxygen isotopes were analyzed by Karen Ziegler at the University of New Mexico on acid-washed samples to remove terrestrial weathering products.

Owing to the abundance of chondrules, NWA 8641 may be one of the least heated winonaites, and therefore may provide clues to the chondritic protolith of the winonaite parent body. Overall textures are similar to those found in type 6 chondrites that escaped significant melting.

Despite similar geothermometer temperatures for various mineral pairs, NWA 8614 apparently did not attain Fe-Mg equilibrium between olivine and pyroxene. Like other winonaites, NWA 8614 has olivine compositions that are too magnesian for equilibrium relative to low-Ca pyroxene. Among winonaites as a whole, there is no evidence for a curved trend between Fa and Fs compositions as would be expected for FeO-reduction during metamorphism [Benedix, et al 1998], nor for mineral compositions that correlate with geothermometry temperatures. This argues against a single metamorphic FeO-reduction trend from a common chondritic precursor. Instead, protoliths for different winonaites may have varied slightly in composition.