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- Usage in publication:
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- Tillman Mountain Tonalite
- Modifications:
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- Named
- Dominant lithology:
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- Tonalite
- AAPG geologic province:
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- Okanogan province
Summary:
Tillman Mountain Tonalite. Name proposed for unit in /Toats Coulee magma series [informal] (new). Mapped in Toats Coulee Creek region, Okanogan Range, Washington. Described as dark-gray, chiefly medium-grained tonalite. Contains more hornblende and biotite than Loomis granodiorite (new) of Toats Coulee magma series. Secondary cataclastic gneissose structures are common. Age is Late Triassic, based on radiometric (K-Ar, hornblende) age of 194 +/-6 Ma of Loomis granodiorite (new) of Toats Coulee magma series (citing Rinehart and Fox [1972]). [Age is Early Jurassic, based on 1983 DNAG Geologic Time Scale and 1986 USGS Geologic Time Chart.]
Type locality not stated by author. Named from Tillman Mountain, in T. 38 N., R. 24 E., Okanogan Co., WA.
["Toats Coulee magma series" considered informal. Term "Series" is applied formally only to chronostratigraphic units (ACSN, 1961, 1970; NACSN, 1983, 2005, 2021). US geologic names lexicon (USGS Bull. 1520, p. 308) lists Tillman Mountain Tonalite of Toats Coulee Group (explanation not given).]
Source: GNU records (USGS DDS-6; Menlo GNULEX); US geologic names lexicon (USGS Bull. 1520, p. 308).
For more information, please contact Nancy Stamm, Geologic Names Committee Secretary.
Asterisk (*) indicates published by U.S. Geological Survey authors.
"No current usage" (†) implies that a name has been abandoned or has fallen into disuse. Former usage and, if known, replacement name given in parentheses ( ).
Slash (/) indicates name conflicts with nomenclatural guidelines (CSN, 1933; ACSN, 1961, 1970; NACSN, 1983, 2005, 2021). May be explained within brackets ([ ]).