Fission track thermochronology and its tectonic applications
Reseacher(s): Dumitru and graduate students
Fission track thermochronology is a geochronologic method that yields the time when rock rose through the 2 to 5 km depth window or ~80°-120°C (for apatite). This low-temperature thermochronometer allows us to collect data at the regional scale to study time-space patterns of mountain building and their uplift or on detailed scales to understand the slip history of faults in the brittle crust. The best studies utilizing low temperature thermochronology involve careful integration of field-based structural studies and balanced cross-sections with laboratory-collected thermochronology data. Transects of ten or more samples are keyed to detailed structural cross-sections. Because the thermal histories of samples in a specific transect must be linked, such data arrrays provide a solid measure of the cooling history of the structural section sampled. The Fission Track Laboratory at Stanford has applied these approaches in a variety of tectonic settings, including reconstructing time-space patterns of extension across the Basin and Range province, analyzing margin-wide shortening across the San Andreas fault system, reconstructing mountain-building in China during the India-Asia collision, and analyzing exhumation of high-pressure rocks within the Franciscan subduction complex. This work has been funded by a series of grants from the NSF Tectonics Division including EAR9417939, EAR-9725371, EAR-029854 and EAR-0809226.
(U-Th)/He thermochonology is a more recently developed and highly complimentary method for dating exhumation from even shallower depths (~40-85°C) intervals. The (U-Th)/He laboratory resides in our Noble Gas Laboratory. The two methods paired together provide a powerful means of solving many tectonic questions about the P-T path of the upper 10 km of the crust. This laboratory was initially funded through NSF's Instrumentation Division.
How the method works for normal faults:
Cross-section of a polished and etched apatite crystal showing schematic tracks that intersect the polished surface of the grain and confined tracks that cross cracks or tracks in the subsurface of the grain. The length of these confined tracks are measured and statistically they determine the cooling rate of the sample through the apatite partial annealing zone. This data provides information and a robust analysis as to what an obtained fission track "age" means.
Fission track mineral separation and sample preparation
Our mineral separation and sample preparation facilities, intended primarily for Stanford faculty, staff, students and visitors, include rock crusher, rock grinder, Gemeni table, sieves, Ro-tap, drying ovens, fume hoods, Frantz electrodynamic separators, LMT and MEI apparatus (heavy liquid density separations), binocular microscopes, etc.
Fission track sample preparation facilities include epoxy and teflon grain mounting, slide grinding wheels, slide polishing wheels, fume hoods. All other specialized fission track sample preparation facilities are also available.
Fission track microscope facilities
We have a Zeiss Axioskop microscope specially configured for FT work; 32.5x. 125x, 250x, 625x, and 1250x magnifications; transmitted and reflected light; objectives designed for use without cover-slips; no polarized light capability. The microscope is fitted with a drawing tube and computerized digitizing system which permits measurements of track lengths with an accuracy of 0.15 microns. The microscope is also fitted with a computer-automated stage system which permits locating and relocating objects with an accuracy of 3 microns.
For further information, contact Trevor Dumitru.
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Dumitru, T. A., E. L. Miller, P. B. OSULLIVAN, J. M. Amato, K. A. Hannula, et al. 1995. “CRETACEOUS TO RECENT EXTENSION IN THE BERING STRAIT REGION, ALASKA.” TECTONICS 14 (3). AMER GEOPHYSICAL UNION: 549–63.
Colgan, J. P., T. A. Dumitru, and E. L. Miller. 2004. “Diachroneity of Basin and Range Extension and Yellowstone Hotspot Volcanism in Northwestern Nevada.” GEOLOGY 32 (2). GEOLOGICAL SOC AMER, INC: 121–24. DOI: 10.1130/G20037.1
Egger, Anne E., and Elizabeth L. Miller. 2011. “Evolution of the Northwestern Margin of the Basin and Range: The Geology and Extensional History of the Warner Range and Environs, Northeastern California.” GEOSPHERE 7 (3). GEOLOGICAL SOC AMER, INC: 756–73. DOI: 10.1130/GES00620.1
Miller, E. L., T. A. Dumitru, R. W. Brown, and P. B. Gans. 1999. “Rapid Miocene Slip on the Snake Range-Deep Creek Range Fault System, East-Central Nevada.” GEOLOGICAL SOCIETY OF AMERICA BULLETIN 111 (6). GEOLOGICAL SOC AMER, INC: 886–905.
Dumitru, T. A., P. B. Gans, D. A. Foster, and E. L. Miller. 1991. “REFRIGERATION OF THE WESTERN CORDILLERAN LITHOSPHERE DURING LARAMIDE SHALLOW-ANGLE SUBDUCTION.” GEOLOGY 19 (11). GEOLOGICAL SOC AMERICA: 1145–48.
Miller, E. L. 1998. “Structural Geology.” GEOTIMES 43 (2). AMER GEOLOGICAL INST: 26–27.
Egger, A. E., T. A. Dumitru, E. L. Miller, C. FI Savage, and J. L. Wooden. 2003. “Timing and Nature of Tertiary Plutonism and Extension in the Grouse Creek Mountains, Utah.” INTERNATIONAL GEOLOGY REVIEW 45 (6). BELLWETHER PUBL LTD: 497–532.
Colgan, J. P., T. A. Dumitru, M. McWilliams, and E. L. Miller. 2006. “Timing of Cenozoic Volcanism and Basin and Range Extension in Northwestern Nevada: New Constraints from the Northern Pine Forest Range.” GEOLOGICAL SOCIETY OF AMERICA BULLETIN 118 (1-2). GEOLOGICAL SOC AMER, INC: 126–39. DOI: 10.1130/1325681.1
Surpless, B. E., D. F. Stockli, T. A. Dumitru, and E. L. Miller. 2002. “Two-Phase Westward Encroachment of Basin and Range Extension into the Northern Sierra Nevada.” TECTONICS 21 (1). AMER GEOPHYSICAL UNION. DOI: 10.1029/2000TC001257