Geochemistry of the Newbury Volcanic Complex, northeastern, Massachusetts

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

OSTI ID:5579526

McKenna, J M; Hepburn, J C; Hon, R ^[1]

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1. Boston Coll., Chestnut Hill, MA (United States). Dept. of Geology and Geophysics

The Newbury Volcanic Complex consists of 3,000+ meters of subaerial volcanic flows, tuffs and minor admixed sediment (Shride, 1976), contained entirely within fault blocks between the Nashoba and Boston-Avalon tectonic terrane. Fossils date these essentially unmetamorphosed and unpenetratively deformed volcanic rocks as latest Silurian to earliest Devonian. The rocks fall into two general compositional groups: a more mafic group of basalts, basaltic andesites and andesites with SiO[sub 2] values ranging from 50% to 59%; and a second, rhyolitic group with SiO[sub 2] ranging from 75% to 77%. The mafic rocks have high Al[sub 2]O[sub 3] (15% to 19%) and Zr/Hf ratios between 38 and 41. The REE abundances of both groups show marked LREE enrichment with La/Lu ratios ranging from 4.7 to 11. Tectonic discrimination diagrams, including, AFM, Ti-Zr-Y, Hf-Th-Ta, and Nb-Zr-Y, applied to the mafic rocks, all indicate a calc-alkaline chemistry and a volcanic arc origin for the Newbury Volcanic Complex. Depletions in Ta and Nb on MORB-normalized spidergrams further support this conclusion. High Zr/Y ratios suggest that the arc was erupted through continental crust. The authors geochemical data strengthens correlations along the eastern margin of the Appalachians and reinforces the existence of Silurian arc volcanism on or adjacent to the Avalon Zone.

• OSTI ID: 5579526
• 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
AGE ESTIMATION
CHEMISTRY
DEVELOPED COUNTRIES
DEVONIAN PERIOD
ELEMENTS
FOSSILS
GEOCHEMISTRY
GEOLOGIC AGES
GEOLOGIC FORMATIONS
GEOLOGY
IGNEOUS ROCKS
MASSACHUSETTS
METALS
NORTH AMERICA
PALEOZOIC ERA
PETROGENESIS
PETROLOGY
RARE EARTHS
ROCKS
SILURIAN PERIOD
USA
VOLCANIC ROCKS