Petrology and geochemistry of Ordovician K-bentonites in New York State: Constraints on the nature of a volcanic arc

Journal Article · Thu Mar 01 00:00:00 EST 1990 · Journal of Geology; (USA)

DOI:https://doi.org/10.1086/629391· OSTI ID:6250461

Delano, J W; Schirnick, C; Bock, B; Kidd, W S.F.; Heizler, M T; Putman, G W; De Long, S E; Ohr, M ^[1]

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1. State Univ. of New York, Albany (USA)

Altered volcanic ashes (K-bentonites) in the late Ordovician (Caradocian) Utica shale of New York State are the product of explosive arc volcanism. Most of the 30 K-bentonites examined in this investigation contain fragmental crystals and rock fragments (microliths) up to 600 {mu}m in diameter that generally are neither detrital contamination from the surrounding black shale nor igneous phenocrysts. The dominant phases are garnet (two groups; Gr{sub 15-20}Alm{sub 45-75}Py{sub 35-0}Sp{sub 2-5}; Gr{sub 2-5}Alm{sub 55-85}Py{sub 10-40}Sp{sub 1}), plagioclase feldspar (An{sub 80-10}), alkali feldspar (Or{sub 99-0}), clinopyroxene (Wo{sub 50-40}En{sub 50-30}Fs{sub 0-30}), and orthopyroxene (Wo{sub 1-2}En{sub 77-32}Fs{sub 32-66}), accompanied by lesser quantities of hornblende, aluminosilicate, quartz, sphene, Fe-Ti oxides, apatite, and zircon. Most of the fragmental crystals appear to be derived from the same source as the metamorphic microliths, which possess minerals with similar compositions. Both crystals and microliths are interpreted as xenocrysts and xenoliths from the ancient continental crust on which the Ordovician arc was constructed. They became entrained in the volcanic plume during explosive eruptions. A Precambrian age acquired on K-feldspars from one K-bentonite using the {sup 40}Ar/{sub 39}Ar method shows that these xenocrysts were derived from depths of less than 5-10 km in the microcontinent at the time of late Ordovician volcanism. The occurrence of xenocrysts and xenoliths in these K-bentonites underscores the importance of performing detailed petrology on ash layers prior to the onset of more sophisticated tasks (e.g., isotopic age determinations; regional stratigraphic correlations of K-bentonites based upon chemical compositions).

• OSTI ID: 6250461
• Journal Information: Journal of Geology; (USA), Vol. 98:2; ISSN 0022-1376
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
NEW YORK
VOLCANIC REGIONS
GEOCHEMISTRY
PETROLOGY
ALUMINIUM SILICATES
ANORTHOSITES
APATITES
ARGON 39
ARGON 40
BENTONITE
BLACK SHALES
CONTINENTAL CRUST
FELDSPARS
GARNETS
HORNBLENDE
IRON OXIDES
ISOTOPE DATING
ISOTOPE RATIO
ORDOVICIAN PERIOD
ORIGIN
OXIDE MINERALS
POTASSIUM COMPOUNDS
PYROXENES
QUARTZ
SHALES
TITANIUM OXIDES
VOLCANIC ROCKS
VOLCANISM
ZIRCON
AGE ESTIMATION
ALKALI METAL COMPOUNDS
ALUMINIUM COMPOUNDS
AMPHIBOLE
ARGON ISOTOPES
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BITUMINOUS MATERIALS
CARBONACEOUS MATERIALS
CHALCOGENIDES
CHATTANOOGA FORMATION
CHEMISTRY
CLAYS
EARTH CRUST
ENERGY SOURCES
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
FEDERAL REGION II
FOSSIL FUELS
FUELS
GABBROS
GEOLOGIC AGES
GEOLOGIC FORMATIONS
GEOLOGY
IGNEOUS ROCKS
IRON COMPOUNDS
ISOTOPES
LIGHT NUCLEI
MATERIALS
MINERALS
NORTH AMERICA
NUCLEI
OIL SHALES
OXIDES
OXYGEN COMPOUNDS
PALEOZOIC ERA
PHOSPHATE MINERALS
PLUTONIC ROCKS
RADIOISOTOPES
ROCKS
SEDIMENTARY ROCKS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SILICON OXIDES
STABLE ISOTOPES
TITANIUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
USA
YEARS LIVING RADIOISOTOPES
ZIRCONIUM COMPOUNDS
ZIRCONIUM SILICATES
580000* - Geosciences