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Title: Nature and origin of authigenic K-feldspar in Precambrian basement rocks of the North American midcontinent

Abstract

Authigenic K-feldspar occurs in alteration profiles in uppermost Precambrian igneous and metamorphic basement rocks of the midcontinent. The K-feldspar is widespread and has been identified in six states. The profiles occur directly below the Cambrian-Precambrian unconformity and range from about <1 to 8 m in thickness. Authigenic K-feldspar occurs throughout the profile. The K-feldspar is monoclinic or triclinic by X-ray diffraction, of end-member composition, and may compose 63% of rock volume. Much of the K-feldspar formed by replacement of primary feldspar. A sample of wholly authigenic K-feldspar from altered basement in southern Illinois gives a K/Ar data of 549 {plus minus} 18 Ma (Early Cambrian). This data is in agreement with Early Cambrian Rb/Sr dates for potassic alteration of uppermost Precambrian basement in Ohio. Dated authigenic K-feldspars from both Ohio and Illinois give identical {delta}{sup 18}O values of 17.5, suggesting formation from a very similar fluid. Concordancy of both dates and {delta}{sup 18}O values suggests that the K-feldspar formed during an episode of potassic alteration during Early Cambrian time that affected much of midcontinent North America. The dates and {delta}{sup 18}O values for K-feldspar, when considered together, do not fit any of the hypotheses presented here.

Authors:
 [1]
  1. Univ. of Illinois, Urbana (USA)
Publication Date:
OSTI Identifier:
6967065
Resource Type:
Journal Article
Journal Name:
Geology; (USA)
Additional Journal Information:
Journal Volume: 17:8; Journal ID: ISSN 0091-7613
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; FELDSPARS; ORIGIN; GEOLOGIC DEPOSITS; GEOCHEMISTRY; ILLINOIS; OHIO; ARGON; BASEMENT ROCK; GEOLOGIC HISTORY; GEOLOGIC MODELS; ISOTOPE DATING; ISOTOPE RATIO; OXYGEN 18; POTASSIUM; PRECAMBRIAN ERA; RUBIDIUM; SAMPLING; STRONTIUM; THICKNESS; X-RAY DIFFRACTION; AGE ESTIMATION; ALKALI METALS; ALKALINE EARTH METALS; CHEMISTRY; COHERENT SCATTERING; DIFFRACTION; DIMENSIONS; ELEMENTS; EVEN-EVEN NUCLEI; FEDERAL REGION V; FLUIDS; GASES; GEOLOGIC AGES; ISOTOPES; LIGHT NUCLEI; METALS; MINERALS; NONMETALS; NORTH AMERICA; NUCLEI; OXYGEN ISOTOPES; RARE GASES; SCATTERING; STABLE ISOTOPES; USA; 580000* - Geosciences

Citation Formats

Duffin, M E. Nature and origin of authigenic K-feldspar in Precambrian basement rocks of the North American midcontinent. United States: N. p., 1989. Web. doi:10.1130/0091-7613(1989)017<0765:NAOOAK>2.3.CO;2.
Duffin, M E. Nature and origin of authigenic K-feldspar in Precambrian basement rocks of the North American midcontinent. United States. https://doi.org/10.1130/0091-7613(1989)017<0765:NAOOAK>2.3.CO;2
Duffin, M E. 1989. "Nature and origin of authigenic K-feldspar in Precambrian basement rocks of the North American midcontinent". United States. https://doi.org/10.1130/0091-7613(1989)017<0765:NAOOAK>2.3.CO;2.
@article{osti_6967065,
title = {Nature and origin of authigenic K-feldspar in Precambrian basement rocks of the North American midcontinent},
author = {Duffin, M E},
abstractNote = {Authigenic K-feldspar occurs in alteration profiles in uppermost Precambrian igneous and metamorphic basement rocks of the midcontinent. The K-feldspar is widespread and has been identified in six states. The profiles occur directly below the Cambrian-Precambrian unconformity and range from about <1 to 8 m in thickness. Authigenic K-feldspar occurs throughout the profile. The K-feldspar is monoclinic or triclinic by X-ray diffraction, of end-member composition, and may compose 63% of rock volume. Much of the K-feldspar formed by replacement of primary feldspar. A sample of wholly authigenic K-feldspar from altered basement in southern Illinois gives a K/Ar data of 549 {plus minus} 18 Ma (Early Cambrian). This data is in agreement with Early Cambrian Rb/Sr dates for potassic alteration of uppermost Precambrian basement in Ohio. Dated authigenic K-feldspars from both Ohio and Illinois give identical {delta}{sup 18}O values of 17.5, suggesting formation from a very similar fluid. Concordancy of both dates and {delta}{sup 18}O values suggests that the K-feldspar formed during an episode of potassic alteration during Early Cambrian time that affected much of midcontinent North America. The dates and {delta}{sup 18}O values for K-feldspar, when considered together, do not fit any of the hypotheses presented here.},
doi = {10.1130/0091-7613(1989)017<0765:NAOOAK>2.3.CO;2},
url = {https://www.osti.gov/biblio/6967065}, journal = {Geology; (USA)},
issn = {0091-7613},
number = ,
volume = 17:8,
place = {United States},
year = {Tue Aug 01 00:00:00 EDT 1989},
month = {Tue Aug 01 00:00:00 EDT 1989}
}