Albitization of plagioclase crystals in the Stevens sandstone (Miocene), San Joaquin Basin, California, and the Frio Formation (Oligocene), Gulf Coast, Texas. A TEM/AEM study

Journal Article · Tue Jun 01 00:00:00 EDT 1993 · Geological Society of America, Bulletin; (United States)

DOI:https://doi.org/10.1130/0016-7606(1993)105<0708:AOPCIT>2.3.CO;2· OSTI ID:6316201

Hirt, W G ^[1]; Wenk, H R ^[2]; Boles, J R ^[3]

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1. Center for Higher Education, San Ramon, CA (United States)
2. Univ. of California, Berkeley (United States)
3. Univ. of California, Santa Barbara (United States)

Conventional Transmission Electron Microscopy (CTEM) and Analytical Electron Microscopy (AEM) studies of partially albitized plagioclase crystals taken from drill cores from the Stevens sandstone (Miocene), San Joaquin, California, and the Frio Formation (Oligocene), Gulf Coast, Texas, reveal that replacement of Ca-rich plagioclase cores by nearly pure albite (Ab[sub 96]-Ab[sub 100]) occurs along submicroscopic ([minus]15 nm wide) en echelon (001) and (110) cleavages. The cleavages are the result of changes in the localized stress regime created by dissolution of adjacent phases. Photomicrographs show albite-lined brittle cleavage crosscutting albitized semibrittle fractures. Such crosscutting relationships can be explained by a reduction in effective stress associated with the albitization process. On a macroscopic scale, this reduction in effective stress implies that the transition from hydrostatic to lithostatic pressure is discontinuous. 30 refs., 7 figs.

• OSTI ID: 6316201
• Journal Information: Geological Society of America, Bulletin; (United States), Vol. 105:6; ISSN 0016-7606
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
58 GEOSCIENCES
ALBITE
ELECTRON MICROSCOPY
PHOTOMICROGRAPHY
ANORTHOSITES
MIOCENE EPOCH
PETROLEUM GEOLOGY
SANDSTONES
STRESSES
TERTIARY PERIOD
CENOZOIC ERA
FELDSPARS
GABBROS
GEOLOGIC AGES
GEOLOGY
IGNEOUS ROCKS
MICROSCOPY
MINERALS
PHOTOGRAPHY
PLUTONIC ROCKS
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SEDIMENTARY ROCKS
SILICATE MINERALS
020200* - Petroleum- Reserves
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580000 - Geosciences