Accession Number : AD0721194

Title :   The Age and Probable Anatectic Origin of the Brant Lake Gneiss, Southeastern Adirondack Mountains, New York.

Descriptive Note : Final rept. 15 Aug 69-31 Dec 70,

Corporate Author : KANSAS UNIV LAWRENCE DEPT OF GEOLOGY

Personal Author(s) : Bickford,Marion E.

Report Date : 31 JAN 1971

Pagination or Media Count : 31

Abstract : The Brant Lake Gneiss is exposed in the cores of two structural domes in the northwestern portion of the Bolton Landing, N.Y. quadrangle (15'). Overlying the gneiss are metasedimentary rocks which may be correlated respectively with the 'Older Paragneisses' (lowest), the Paradox Lake Marble, and the Treadway Mountain Formation (highest) of Walton. Rb-Sr isochrons from whole-rock samples yield the following: (1) Corerocks of the larger dome are 1119 plus or minus 39 m.y. old with (Sr87/Sr86) sub o = 0.7073 plus or minus .0021; (2) Core-rocks of the smaller dome are 1144 plus or minus 11 m.y. old with (Sr87/Sr86) sub o = 0.7055 plus or minus .0006; (3) Samples of the 'Older Paragneisses', collected from the same outcrop, are 1210 plus or minus 45 m.y. old with (Sr87/Sr86) sub o = 0.7023 plus or minus .0015. All errors are given at 80 percent confidence limits. The rocks in the cores of the domes are clearly not the basement upon which the precursors of the 'Older Paragneisses' were deposited. They are younger and probably represent intrusive masses; their initial Sr87/Sr86 ratios suggest derivation from pre-existing crustal material. (Author)

Descriptors :   (*METAMORPHIC ROCK, GEOLOGIC AGE DETERMINATION), RADIOACTIVE ISOTOPES, RUBIDIUM, STRONTIUM, SAMPLING, CORRELATION TECHNIQUES, STRUCTURAL GEOLOGY, MOUNTAINS, STRATIGRAPHY, PETROLOGY, OROGENY, NEW YORK

Subject Categories : Geology, Geochemistry and Mineralogy

Distribution Statement : APPROVED FOR PUBLIC RELEASE