Thermochronology and Exhumation History
Constructing pressure-temperature-time (P-T-t) trajectories of rock masses is crucial in understanding tectonic processes and exhumation histories. The variation of the P-T conditions is deduced from phase relations, reaction textures and geothermobarometric studies, whereas the timing and rate of such P-T changes can be estimated from thermochronometers, particularly 40Ar/39Ar and (U-Th)/He methods. The inferred P-T-t path provides fundamental input parameters for thermo-geodynamic modeling.
The exhumation process (upward movement relative to Earth¡¯s surface) is mainly controlled by upward tectonic force or erosion-induced isostatic equilibrium. Estimating exhumation rates links the dynamics and origin of surficial processes, such as development of topography and climatic evolution, with lithospheric plate motions and their large scale origins such as mantle convection. The (U-Th)/He thermochronometer is sensitive enough to constrain exhumation history in the temperature range of ~70-200 ¨¬C corresponding to ~3-10 km depth. Complementary constraints from other thermochronometers, including apatite and zircon fission track dating and 40Ar/39Ar dating of various phases, can also provide highly detailed thermal histories over a wide range of temperatures for rocks that have experienced even complex orogenic histories.
I have studied one of the
metamorphic belts in Korean peninsular. From petrographic observation,
phase equilibria (mineral assemblages and EPM, X-ray analyses),
isotopic dating (K/Ar and 40Ar/39Ar methods) and fluid inclusion
analyses, a clockwise P-T-t path was inferred with peak metamorphic
conditions of 5-8 kbar and 520-590 ¢ªC, corresponding amphibolite facies
metamorphism. These features are most likely accounted for by
intracontinental extension followed by closure of an aborted rift
rather than an intercontinental collision processes. The Korean
peninsular is also an interesting area for low-temperature
thermochronology because its main mountain belts have very asymmetric
topographic features with gentle slope to the west and steep one to the
east. Another target area would be metamorphic gneiss complex in Norway
which has exhumed with domal shape during Cretaceous. Our preliminary
examination of U, Th and He concentrations in zircon and apatite
crystals revealed intensive zoning patterns, thus yielding scattered
(U-Th)/He ages. For such samples, it would be ideal to obtain spatial
distribution of the U,Th and He contents using in-situ analyses.
Recently an excimer laser ablation system was installed at Yale, and I
hope these new techniques give reliable (U-Th)/He age distributions in
single grains. I am willing to develop new projects related with P-T-t
path and exhumation processes of sedimentary basins, orogenic belts and
Min K, Cho M, Reiners P (2008) Exhumation History of the Taebaek Mountain Range in Korean Peninsula: Implications for Miocene Tectonic Evolution of East Asia. EOS Trans. AGU, 89(53), Fall Meeting Suppl., Abstract T53B-1922.
Hu S, Raza A, Min K, Kohn BP, Ketcham RA, Reiners PW, Wang J, Gleadow AJW (2006) Late Mesozoic and Cenozoic thermotectonic evolution along a transect from the north China craton through the Qinling orogen into the Yangtze craton, central China. Tectonics, v. 25, TC6009, doi: 10.1029/2006TC001985.
Min K and Cho M (1998) Metamorphic evolution of the northwestern Ogcheon metamorphic belt, South Korea. Lithos, v. 43, p. 31-51.
Cho M, Kim IJ, Kim H, Min K, Ahn J-H and Nagao K (1995) K-Ar biotite ages of pelitic schists in the Jeungpyeong-Deokpyeong area, central Ogcheon metamorphic belt, Korea. Journal of Petrological Society of Korea, v. 4, p. 178-185.
Min K, Cho M, Kwon S-T, Kim IJ, Nagao K and Nakamura E (1995) K-Ar ages of metamorphic rocks in the Chungju area: Late Proterozoic (675 Ma) metamorphism of the Ogcheon metamorphic belt. Journal of Geological Society of Korea, v. 31, p. 315-327.