Nd, O and Sr isotopic constraints on the origin of Precambrian rocks, southern Black Hills, South Dakota
The Nd, O and Sr isotopic characteristics of Precambrian metasedimentary, metavolcanic and granitic rocks from the Black Hills of South Dakota are examined. Two late-Archean granites (2.5-2.6 Ga) have T/sub DM/ ages of 3.05 and 3.30 Ga, suggesting that at least one of the granites was derived through the melting of significantly older crust. Early-Proterozoic metasedimentary rocks have T/sub DM/ ages that range from 2.32 to 2.45 Ga. These model ages, in conjunction with probable stratigraphic ages ranging from 1.9 to 2.2 Ga, indicate that mantle-derived material was added to the continental crust of this region during the early-Proterozoic. Previous studies of the Harney Peak Granite complex have reported U-Pb and Rb-Sr ages of about 1.71 Ga, and most granite samples examined in this study have Sr isotopic compositions consistent with that age. Two granite samples taken from the same sill, however, give two-point Rb-Sr and Sm-Nd ages of 2.08 +/- 0.08 and 2.20 +/- 0.20 Ga, respectively. In addition, whole-rock and apatite samples of the spatially associated Tin Mountain pegmatite give a Sm-Nd isochron age of 2000 +/- 100 Ma.
- Research Organization:
- State Univ. of New York, Stony Brook
- DOE Contract Number:
- AC02-79ER10412; AS03-82ER12040; FG01-84ER13259
- OSTI ID:
- 6691580
- Journal Information:
- Geochim. Cosmochim. Acta; (United States), Vol. 50:12
- Country of Publication:
- United States
- Language:
- English
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GRANITES
ORIGIN
METAMORPHIC ROCKS
SOUTH DAKOTA
ISOTOPE RATIO
NEODYMIUM ISOTOPES
OXYGEN ISOTOPES
STRONTIUM ISOTOPES
ALKALINE EARTH ISOTOPES
FEDERAL REGION VIII
IGNEOUS ROCKS
ISOTOPES
NORTH AMERICA
PLUTONIC ROCKS
ROCKS
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580300* - Mineralogy
Petrology
& Rock Mechanics- (-1989)
580400 - Geochemistry- (-1989)