Interpretation of whole-rock Rb-Sr geochronology in the high grade rocks of the Adirondack Mountains, New York

Conference · Wed Jan 01 04:00:00 EST 1992 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5724812

Yang, Y; Grant, N K ^[1]

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1. Miami Univ., Oxford, OH (United States). Dept. of Geology

Published and new Rb-Sr whole-rock isochrons for high grade metaigneous, gneissic and mylonitic rocks from the Adirondack Mountains have been evaluated in two ways. In the first, the Rb-Sr ages are compared to the published U-Pb zircon ages for metaigneous rocks. In the second, the ages are compared with forward modeling that employs Monte Carlo simulation and solid diffusion calculations to determine the probabilities of Rb-Sr resetting under various conditions of channelized and homogeneous fluid flow. The first comparison shows that the Rb-Sr isochrons fall into three groups. The first comprises isochrons of ca. 1050 Ma for mylonitic and metaigneous rocks from the Carthage-Colton Mylonite Zone that separates the Highlands from the Lowlands, and the zone of Trans-Adirondack Structural Discontinuities that separate the southern from the northern Highlands. These ages can be interpreted to the result of complete resetting during the Ottawan phase of the Grenville orogeny. The second group comprises isochrons that are concordant or consistent with the U-Pb zircon ages, and the third group isochrons with ages intermediate between the U-Pb zircon ages and that for high grade metamorphism at 1150 Ma and 1050 Ma in the Lowlands and Highlands respectively. The forward modeling suggests that complete resetting of Rb-Sr isochrons was associated with high fluid/rock ratios (>2) under conditions of homogeneous flow, and that fluid/rock ratios were low (<0.25) in cases where no resetting has occurred. Partial resetting, as can be demonstrated in the Lowlands, requires conditions intermediate between the first two cases or extremely heterogeneous fluid flow. These results show that whole-rock Rb-Sr age determination can recover useful information from high grade rocks, providing the samples are collected from clearly documented tectonic domains.

• OSTI ID: 5724812
• Report Number(s): CONF-921058--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 24:7
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ACTINIDES
ADIRONDACK MOUNTAINS
AGE ESTIMATION
ALKALI METAL ISOTOPES
ALKALINE EARTH ISOTOPES
APPALACHIAN MOUNTAINS
DEVELOPED COUNTRIES
ELEMENTS
FLUID FLOW
FLUIDS
GEOLOGIC HISTORY
GEOLOGIC MODELS
ISOTOPE DATING
ISOTOPES
LEAD
METALS
METAMORPHISM
MINERALS
MOUNTAINS
NEW YORK
NORTH AMERICA
OROGENESIS
RESERVOIR FLUIDS
RUBIDIUM ISOTOPES
SILICATE MINERALS
STRONTIUM ISOTOPES
TECTONICS
URANIUM
USA
ZIRCON