The use of geochemistry in interpreting the origin of metavolcanic rocks in the northern Appalachians

Conference · Mon Mar 01 04:00:00 EST 1993 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5933989

Coish, R A ^[1]

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1. Middlebury College, VT (United States). Geology Dept.

Major elements, trace elements and isotopes have been used to fingerprint the tectonic origin of metavolcanic rocks in the northern Appalachians. Two examples show the failure and success of this approach. In the first example, some unusual volcanic rocks (boninites) found in many ophiolites are not easily assigned to a tectonic environment by classic chemical diagrams. Boninites are rare, high-Mg volcanic rocks found in arc regions of the western Pacific and identified in the Thetford Mines ophiolite in Quebec and the Betts Cove ophiolite, Newfoundland. The extremely low contents of Ti, Zr and Y of boninites invalidates the use of standard geochemical diagrams to pinpoint their tectonic environment. However, in other diagrams trace element and isotopic compositions show that the boninites must have originated in a arc/subduction environment. In the second example, the chemistry of greenstones (metavolcanic rocks) in Vermont provides a good example of the successful use of standard chemical discriminant diagrams along with geological evidence to support tectonic interpretations. Diagrams involving Ti, Zr, Y, Cr and P have been used to show that the greenstones and dikes in western Vermont (Pinnacle and Underhill formations) and eastern New York formed in a young rift valley, whereas greenstones in central Vermont (Stowe Formation) formed in an oceanic ridge environment. Furthermore, regional trends in geochemistry indicate that greenstones located between the western and central outcrops have a range of chemistries overlapping with those on either side and may have formed in an incipient setting. Recent Nd-isotopic work on the Pinnacle and Stowe formations supports this interpretation. Nd isotopes from Pinnacle greenstones are like those from the Catoctin volcanics in the southern Appalachians and from modern rift basalts in East Africa.

• OSTI ID: 5933989
• Report Number(s): CONF-9303211--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 25:2
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
APPALACHIAN MOUNTAINS
CANADA
CHEMISTRY
COMPARATIVE EVALUATIONS
DEVELOPED COUNTRIES
DIAGRAMS
EVALUATION
GEOCHEMISTRY
GEOLOGIC DEPOSITS
GEOLOGIC FORMATIONS
GEOLOGIC HISTORY
GEOLOGY
IGNEOUS ROCKS
ISLANDS
ISOTOPE RATIO
METAMORPHIC ROCKS
MOUNTAINS
NEW YORK
NEWFOUNDLAND
NORTH AMERICA
PETROCHEMISTRY
PETROGENESIS
PETROLOGY
PLATE TECTONICS
QUEBEC
ROCKS
SUBDUCTION ZONES
TECTONICS
THERMOCHEMICAL DIAGRAMS
TRACE AMOUNTS
USA
VERMONT
VOLCANIC ROCKS