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

Journal Article · Tue Aug 01 00:00:00 EDT 1989 · Geology; (USA)

DOI:https://doi.org/10.1130/0091-7613(1989)017<0765:NAOOAK>2.3.CO;2· OSTI ID:6967065

Duffin, M E ^[1]

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1. Univ. of Illinois, Urbana (USA)

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.

• OSTI ID: 6967065
• Journal Information: Geology; (USA), Vol. 17:8; ISSN 0091-7613
• Country of Publication: United States
• Language: English

Related Subjects

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