Reinterpretation of Rb/Sr isotopic data for the Little Elk Granite: Implications for the timing of deformational events, Black Hills, South Dakota
- Kent State Univ., OH (United States). Dept. of Geology
Early Proterozoic rift sediments in the Black Hills were multiply deformed (into refolded nappe structures) during the Trans-Hudson Orogeny, which culminated in Harney Peak Granite (HPG) emplacement at 1,715--1,697 Ma. A reset whole-rock Rb/Sr age of 1,840 [+-] 70 Ma obtained from the Archean (2,549 [+-] 11 Ma) Little Elk Granite (LEG, Zartman and Stern, 1967) is widely interpreted as being coeval with D2, based upon parallelism of gneissic foliation in the granite and F2 foliation predominant elsewhere in the Black Hills. However, the authors have recalculated the whole-rock Rb/Sr age by applying the IUGS-recommended [sup 87]Rb decay constant (Steiger and Jager, 1977) to the original isotopic data, obtaining a revised age of 1,905 [+-] 59 Ma. The authors interpret this age as representing a whole-rock isotopic resetting event associated with Early Proterozoic (2,170--1,880 Ma) rifting in the Black Hills. The authors envision the LEG to have experienced a convective hydrothermal fluid-flow regime associated with the rifting. This scenario would allow for the sustained heating and isotopic exchange between granite and abundant water-rich fluid (seawater ) that would be required to effect complete resetting of an Rb/Sr whole-rock isochron. They favor an age for the refolding event and the development of F2 structures that is more closely linked in time with HPG emplacement. Such an age is more compatible with published field/petrologic observations and Proterozoic tectonothermal models for the Black Hills.
- OSTI ID:
- 5342267
- Report Number(s):
- CONF-9305259-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 25:5; Conference: 89. annual meeting of the Cordilleran Section and the 46th annual meeting of the Rocky Mountain Section of the Geological Society of America (GSA), Reno, NV (United States), 19-21 May 1993; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
Similar Records
Nd, O and Sr isotopic constraints on the origin of Precambrian rocks, southern Black Hills, South Dakota
Isotopic and structural responses of granite to successive deformation and metamorphism
Related Subjects
GEOLOGIC FORMATIONS
ISOTOPE DATING
PETROGENESIS
GRANITES
SOUTH DAKOTA
DEFORMATION
GEOCHEMISTRY
GEOLOGIC HISTORY
ISOTOPE RATIO
PRECAMBRIAN ERA
RIFT ZONES
RUBIDIUM ISOTOPES
STRONTIUM ISOTOPES
AGE ESTIMATION
ALKALI METAL ISOTOPES
ALKALINE EARTH ISOTOPES
CHEMISTRY
DEVELOPED COUNTRIES
GEOLOGIC AGES
GEOLOGIC STRUCTURES
GEOLOGY
IGNEOUS ROCKS
ISOTOPES
NORTH AMERICA
PETROLOGY
PLUTONIC ROCKS
ROCKS
USA
580000* - Geosciences