Comparative thermometry on pelitic rocks and marbles of the Llano uplift, Texas

Conference · Wed Jan 01 04:00:00 EST 1992 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5690624

Letargo, C M.R.; Lamb, W M ^[1]

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1. Texas A and M Univ., College Station, TX (United States). Dept. of Geology

The Llano Uplift in central Texas is a Grenville-aged metamorphic complex consisting of amphibolite facies assemblages whose development has been attributed to the emplacement of granite plutons between 1.0--1.1 Ga. Temperatures have been obtained from garnet-biotite, garnet-ilmenite, and calcite-dolomite pairs as well as from various silicate equilibria. Application of these geothermometers yield consistent results and are thus indicative of peak conditions attending the amphibolite facies metamorphism. Temperature determined using garnet-biotite and garnet-ilmenite thermometry compare favorably with calcite-dolomite temperatures obtained from marbles in contact with granite plutons in the southeastern part of the uplift. The highest calcite-dolomite temperatures of [approximately]600 C are obtained from marbles containing an isobarically invariant assemblage consisting of calcite + dolomite + diopside + tremolite + forsterite. At pressures of 2--3 kbar, this isobarically invariant assemblage will be stable at a temperature range of [approximately]600--650 C. Also in close proximity to granites in the southeast uplift is the assemblage muscovite + quartz + k-feldspar + sillimanite [approximately] andalusite which indicate T 650 C and P 2.5 kbar. Assemblages consisting of garnet + sillimanite + quartz + plagioclase (GASP) and garnet + rutile + ilmenite + plagioclase + quartz (GRIPS) are currently being studied to provide additional constraints on pressures of amphibolite facies metamorphism.

• OSTI ID: 5690624
• Report Number(s): CONF-921058--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 24:7
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
BIOTITE
CALCITE
CARBONATE MINERALS
COMPARATIVE EVALUATIONS
DEVELOPED COUNTRIES
DOLOMITE
EVALUATION
GARNETS
GEOLOGIC FORMATIONS
GEOLOGIC HISTORY
GEOTHERMOMETERS
GEOTHERMOMETRY
ILMENITE
MEASURING INSTRUMENTS
METAMORPHISM
MICA
MINERALOGY
MINERALS
NORTH AMERICA
OXIDE MINERALS
OXYGEN COMPOUNDS
RESERVOIR TEMPERATURE
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
TEXAS
THERMOMETERS
USA