Rb--Sr, K--Ar, and fission-track geochronological studies of samples from LASL drill holes GT-1, GT-2, and EE-1

Technical Report · Wed Jun 01 04:00:00 EDT 1977

DOI:https://doi.org/10.2172/7212084· OSTI ID:7212084

Brookins, D G; Forbes, R B; Turner, D L; Laughlin, A W; Naeser, C W

Geochronological investigations using the Rb-Sr, K-Ar, and fission-track methods have been completed on core samples from the three LASL deep drill holes, GT-1, GT-2, and EE-1. This work indicates a complex history for these Precambrian rocks beginning with a metamorphic event at 1.66 b.y. which generated the gneisses and schists from older sedimentary and igneous rocks. The metamorphic complex was intruded by at least two different magmas at 1.3--1.4 b.y. producing thin felsic dikes and a major biotite granodiorite pluton. This igneous activity caused pervasive argon loss to occur, lowering the K-Ar ages to about 1.4 b.y. Plio-Pleistocene igneous activity related to formation of the Valles Caldera increased the local geothermal gradient to 50--60/sup 0/C/km and produced fission track annealing in apatite and again argon loss from the biotite in deeper samples.

• Research Organization: Los Alamos Scientific Lab., NM (USA)
• DOE Contract Number: W-7405-ENG-36
• OSTI ID: 7212084
• Report Number(s): LA-6829-MS
• Country of Publication: United States
• Language: English

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