Extensional deformation in the lower to middle continental crust is increasingly recognized and s... more Extensional deformation in the lower to middle continental crust is increasingly recognized and shown to have significant impact on crustal architecture, magma emplacement, fluid flow, and ore deposits. Application of the concept of extensional strain to ancient orogenic systems, like the Grenville province of eastern North America, has helped decipher the structural evolution of these regions. The Marcy massif is a ∼3000 km2 Mesoproterozoic anorthosite batholith in the Adirondack Mountains (New York, USA) of the southern Grenville province. Bedrock geology mapping at 1:24,000 scale paired with characterization of bedrock exposed by recent landslides provides a glimpse into the structural architecture of the massif and its margin. New data demonstrate granulite- to amphibolite-facies deformational fabrics parallel the margin of the batholith, and that the Marcy massif is draped by a southeast-directed detachment zone. Within the massif, strain is localized into mutually offsetting c...
Guidebook for field trips in Vermont: New England Intercollegiate Geological Conference, 79th ann... more Guidebook for field trips in Vermont: New England Intercollegiate Geological Conference, 79th annual meeting, October 16, 17 and 18, 1987: Trips B-8; C-
U-Pb zircon geochronology by sensitive high-resolution ion microprobe–reverse geometry (SHRIMP-RG... more U-Pb zircon geochronology by sensitive high-resolution ion microprobe–reverse geometry (SHRIMP-RG) on 11 plutonic rocks and two volcanic rocks from the Bronson Hill arc in western New Hampshire yielded Early to Late Ordovician ages ranging from 475 to 445 Ma. Ages from Oliverian Plutonic Suite rocks that intrude a largely mafic lower section of the Ammonoosuc Volcanics ranged from 474.8 ± 5.2 to 460.2 ± 3.4 Ma. Metamorphosed felsic volcanic rocks from within the Ammonoosuc Volcanics yielded ages of 460.1 ± 2.4 and 455.0 ± 11 Ma. Younger Oliverian Plutonic Suite rocks that either intrude both the upper and lower Ammonoosuc Volcanics or Partridge Formation ranged in age from 456.1 ± 6.7 Ma to 445.2 ± 6.7 Ma. These new data and previously published results document extended magmatism for >30 m.y. The ages, along with the lack of mappable structural discontinuities between the plutons and their volcanic cover, suggest that the Bronson Hill arc was part of a relatively long-lived comp...
The eastern Adirondack Highlands of northern New York host dozens of iron oxide-apatite (IOA) dep... more The eastern Adirondack Highlands of northern New York host dozens of iron oxide-apatite (IOA) deposits containing magnetite and rare earth element (REE)-bearing apatite. We use new aeromagnetic, aeroradiometric, ground gravity, and sample petrophysical and geochemical data to image and understand these deposits and their geologic framework. Aeromagnetic total field data reflect highly magnetic leucogranite host rock and major structures that likely served as fluid conduits for the hydrothermal system. Band-pass filtering of the aeromagnetic data reveals locations of individual deposits that were verified in the field or from historical records. A 3D inversion for magnetic susceptibility images these deposits at depth, allowing the inference of plunge directions and relative size. Radiometric data highlight variations in the surface geology and several large tailings piles that contain REE-bearing apatite. Within the host rock, eTh (equivalent Th), K, and the eTh/K ratio are variable...
The trip will examine the Nashua and Rockingham sub-belts of the Merrimack terrane (Fig. 1) in li... more The trip will examine the Nashua and Rockingham sub-belts of the Merrimack terrane (Fig. 1) in light of recent geologic mapping, structural analysis, metamorphic petrology, and Ar-Ar and U-Pb geochronology sponsored by the National Cooperative Geologic Mapping Program (NCGMP). The first half of the day will be spent visiting outcrops of multiply-folded metaturbidites of the Paxton, Oakdale, and Worcester formations at different metamorphic grades. The second half of the day will be spent examining phases of the New Hampshire Plutonic Suite including the Ayer Granodiorite and the Chelmsford Granite, and their intrusive relationships with the Berwick Formation. The trip will travel from Leominster to Tyngsborough (Fig. 1) with the aim of examining the main stratigraphic units in the eastern part of the belt, the Devonian plutons which crosscut these units, and the Acadian and Alleghanian structures preserved in both packages of rock.
This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey e... more This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards (or with the North American Stratigraphic Code). Any use of trade, product, or firm names is for descriptive purposes only and does not constitute endorsement by the USGS. Although this database has been used by the U.S. Geological Survey, no warranty, expressed or implied, is made by the USGS as to the accuracy and functioning of the database and related program material, nor shall the fact of distribution constitute any such warranty, and no responsibility is assumed by the USGS in connection therewith.
Extensional deformation in the lower to middle continental crust is increasingly recognized and s... more Extensional deformation in the lower to middle continental crust is increasingly recognized and shown to have significant impact on crustal architecture, magma emplacement, fluid flow, and ore deposits. Application of the concept of extensional strain to ancient orogenic systems, like the Grenville province of eastern North America, has helped decipher the structural evolution of these regions. The Marcy massif is a ∼3000 km2 Mesoproterozoic anorthosite batholith in the Adirondack Mountains (New York, USA) of the southern Grenville province. Bedrock geology mapping at 1:24,000 scale paired with characterization of bedrock exposed by recent landslides provides a glimpse into the structural architecture of the massif and its margin. New data demonstrate granulite- to amphibolite-facies deformational fabrics parallel the margin of the batholith, and that the Marcy massif is draped by a southeast-directed detachment zone. Within the massif, strain is localized into mutually offsetting c...
Guidebook for field trips in Vermont: New England Intercollegiate Geological Conference, 79th ann... more Guidebook for field trips in Vermont: New England Intercollegiate Geological Conference, 79th annual meeting, October 16, 17 and 18, 1987: Trips B-8; C-
U-Pb zircon geochronology by sensitive high-resolution ion microprobe–reverse geometry (SHRIMP-RG... more U-Pb zircon geochronology by sensitive high-resolution ion microprobe–reverse geometry (SHRIMP-RG) on 11 plutonic rocks and two volcanic rocks from the Bronson Hill arc in western New Hampshire yielded Early to Late Ordovician ages ranging from 475 to 445 Ma. Ages from Oliverian Plutonic Suite rocks that intrude a largely mafic lower section of the Ammonoosuc Volcanics ranged from 474.8 ± 5.2 to 460.2 ± 3.4 Ma. Metamorphosed felsic volcanic rocks from within the Ammonoosuc Volcanics yielded ages of 460.1 ± 2.4 and 455.0 ± 11 Ma. Younger Oliverian Plutonic Suite rocks that either intrude both the upper and lower Ammonoosuc Volcanics or Partridge Formation ranged in age from 456.1 ± 6.7 Ma to 445.2 ± 6.7 Ma. These new data and previously published results document extended magmatism for >30 m.y. The ages, along with the lack of mappable structural discontinuities between the plutons and their volcanic cover, suggest that the Bronson Hill arc was part of a relatively long-lived comp...
The eastern Adirondack Highlands of northern New York host dozens of iron oxide-apatite (IOA) dep... more The eastern Adirondack Highlands of northern New York host dozens of iron oxide-apatite (IOA) deposits containing magnetite and rare earth element (REE)-bearing apatite. We use new aeromagnetic, aeroradiometric, ground gravity, and sample petrophysical and geochemical data to image and understand these deposits and their geologic framework. Aeromagnetic total field data reflect highly magnetic leucogranite host rock and major structures that likely served as fluid conduits for the hydrothermal system. Band-pass filtering of the aeromagnetic data reveals locations of individual deposits that were verified in the field or from historical records. A 3D inversion for magnetic susceptibility images these deposits at depth, allowing the inference of plunge directions and relative size. Radiometric data highlight variations in the surface geology and several large tailings piles that contain REE-bearing apatite. Within the host rock, eTh (equivalent Th), K, and the eTh/K ratio are variable...
The trip will examine the Nashua and Rockingham sub-belts of the Merrimack terrane (Fig. 1) in li... more The trip will examine the Nashua and Rockingham sub-belts of the Merrimack terrane (Fig. 1) in light of recent geologic mapping, structural analysis, metamorphic petrology, and Ar-Ar and U-Pb geochronology sponsored by the National Cooperative Geologic Mapping Program (NCGMP). The first half of the day will be spent visiting outcrops of multiply-folded metaturbidites of the Paxton, Oakdale, and Worcester formations at different metamorphic grades. The second half of the day will be spent examining phases of the New Hampshire Plutonic Suite including the Ayer Granodiorite and the Chelmsford Granite, and their intrusive relationships with the Berwick Formation. The trip will travel from Leominster to Tyngsborough (Fig. 1) with the aim of examining the main stratigraphic units in the eastern part of the belt, the Devonian plutons which crosscut these units, and the Acadian and Alleghanian structures preserved in both packages of rock.
This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey e... more This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards (or with the North American Stratigraphic Code). Any use of trade, product, or firm names is for descriptive purposes only and does not constitute endorsement by the USGS. Although this database has been used by the U.S. Geological Survey, no warranty, expressed or implied, is made by the USGS as to the accuracy and functioning of the database and related program material, nor shall the fact of distribution constitute any such warranty, and no responsibility is assumed by the USGS in connection therewith.
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