(Energy related studies utilizing microline thermochronology)
In our first year of the current funding cycle, we have investigated three interrelated aspects of K-feldspar thermochronology; (1) the Ar diffusion properties and microstructures of K-feldspars, (2) the thermal evolution of the Valles Caldera and (3) the continued development of microanalysis. Results of TEM and light microscopy on heated and unheated samples of MH-10 K-feldspar reveal three classes of substructure are present: (1) cross hatched extinction is common and there is almost no albite/pericline twinning, only tweed microstructure; (2) 5--10 vol. % of this K-feldspar are turbid zones with complex twin and tweed structures at the sub-micron scale and numerous dislocation and strain features; (3) about 20% of the K-feldspar is comprised of 0.01 {times} 0.2-1{mu}m albite exsolution lamellae. The network of fractured/turbid zones divides the sample into blocks of approximately 50 {mu}m and the separation between albite exsolution lamellae produce K-feldspar domains of the order 0.1 {mu}m. Independent crushing and diffusion experiments suggest the scale of the largest domain is order ten's of micron whereas the smallest domain size is inferred to be {approximately}0.1 {mu}m. Many, and perhaps most, alkali feldspars contain diffusion domains with activation energies that may vary by as much as 8 kcal/mol. An extraordinary consequence of even relatively small variations in activation energy between domains is that the shape of an age spectrum can change dramatically by varying the laboratory heating schedule. We have performed {sup 40}Ar/{sup 39}Ar age spectrum experiments on K-feldspar separated from Proterozoic quartz monzonite taken from a depth of 1.76 km down the VC-2B drill hole, Valles Caldera, north-central New Mexcio.
- Research Organization:
- Univ. of California, Los Angeles, CA (United States)
- Sponsoring Organization:
- USDOE; USDOE, Washington, DC (United States)
- DOE Contract Number:
- FG03-89ER14049
- OSTI ID:
- 5440729
- Report Number(s):
- DOE/ER/14049-T1; ON: DE92012239
- Country of Publication:
- United States
- Language:
- English
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(Energy related studies utilizing K-feldspar thermochronology)
[Energy related studies utilizing K-feldspar thermochronology]. Progress report, 1991--1992