Probing the depths of Oliverian magmas: Implications for Paleozoic tectonics'in the northeastern United States

Matthew J. Kohn; Frank Spear

doi:10.1130/0091-7613(1999)027<0803:PTDOOM>2.3.CO;2

Probing the depths of Oliverian magmas: Implications for Paleozoic tectonics'in the northeastern United States

Matthew J. Kohn
, Frank Spear

Geosciences Department

University of South Carolina

Research output: Contribution to journal › Article › peer-review

10 Scopus citations

Abstract

Oliverian Magma Series gneisses (442-454 Ma) in the cores of domes in southwestern New Hampshire have an igneous mineralogy that crystallized at pressures (P) of 9-11 kbar and temperatures (T) of 650-775°C, whereas the cover (Ammonoosuc Volcanics) has the same formation age (453 ± 2 Ma) yet is clearly extrusive. A significant crustal section, -30 km thick, must have originally separated the two units, a recognition that demands tectonic reinterpretation of this classic orogen. Acadian age (ca. 400 Ma) metamorphism at P -4-6 kbar, T > 625 °C is well documented in the cover, but the absence of expected diffusional reequilibration in Oliverian garnets indicates that they never exceeded -550°C after formation. Juxtaposition of the Oliverian Magma Series gneisses and their cover must have occurred after the cover had cooled below 550°C, and was likely via either (neo-)Acadian or Alleghanian thrusting.

Original language	English
Pages (from-to)	803-806
Number of pages	4
Journal	Geology
Volume	27
Issue number	9
DOIs	https://doi.org/10.1130/0091-7613(1999)027<0803:PTDOOM>2.3.CO;2
State	Published - 1999

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10.1130/0091-7613(1999)027<0803:PTDOOM>2.3.CO;2

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title = "Probing the depths of Oliverian magmas: Implications for Paleozoic tectonics'in the northeastern United States",

abstract = "Oliverian Magma Series gneisses (442-454 Ma) in the cores of domes in southwestern New Hampshire have an igneous mineralogy that crystallized at pressures (P) of 9-11 kbar and temperatures (T) of 650-775°C, whereas the cover (Ammonoosuc Volcanics) has the same formation age (453 ± 2 Ma) yet is clearly extrusive. A significant crustal section, -30 km thick, must have originally separated the two units, a recognition that demands tectonic reinterpretation of this classic orogen. Acadian age (ca. 400 Ma) metamorphism at P -4-6 kbar, T > 625 °C is well documented in the cover, but the absence of expected diffusional reequilibration in Oliverian garnets indicates that they never exceeded -550°C after formation. Juxtaposition of the Oliverian Magma Series gneisses and their cover must have occurred after the cover had cooled below 550°C, and was likely via either (neo-)Acadian or Alleghanian thrusting.",

author = "Kohn, \{Matthew J.\} and Frank Spear",

year = "1999",

doi = "10.1130/0091-7613(1999)027<0803:PTDOOM>2.3.CO;2",

language = "English",

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journal = "Geology",

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publisher = "Geological Society of America",

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T1 - Probing the depths of Oliverian magmas

T2 - Implications for Paleozoic tectonics'in the northeastern United States

AU - Kohn, Matthew J.

AU - Spear, Frank

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N2 - Oliverian Magma Series gneisses (442-454 Ma) in the cores of domes in southwestern New Hampshire have an igneous mineralogy that crystallized at pressures (P) of 9-11 kbar and temperatures (T) of 650-775°C, whereas the cover (Ammonoosuc Volcanics) has the same formation age (453 ± 2 Ma) yet is clearly extrusive. A significant crustal section, -30 km thick, must have originally separated the two units, a recognition that demands tectonic reinterpretation of this classic orogen. Acadian age (ca. 400 Ma) metamorphism at P -4-6 kbar, T > 625 °C is well documented in the cover, but the absence of expected diffusional reequilibration in Oliverian garnets indicates that they never exceeded -550°C after formation. Juxtaposition of the Oliverian Magma Series gneisses and their cover must have occurred after the cover had cooled below 550°C, and was likely via either (neo-)Acadian or Alleghanian thrusting.

AB - Oliverian Magma Series gneisses (442-454 Ma) in the cores of domes in southwestern New Hampshire have an igneous mineralogy that crystallized at pressures (P) of 9-11 kbar and temperatures (T) of 650-775°C, whereas the cover (Ammonoosuc Volcanics) has the same formation age (453 ± 2 Ma) yet is clearly extrusive. A significant crustal section, -30 km thick, must have originally separated the two units, a recognition that demands tectonic reinterpretation of this classic orogen. Acadian age (ca. 400 Ma) metamorphism at P -4-6 kbar, T > 625 °C is well documented in the cover, but the absence of expected diffusional reequilibration in Oliverian garnets indicates that they never exceeded -550°C after formation. Juxtaposition of the Oliverian Magma Series gneisses and their cover must have occurred after the cover had cooled below 550°C, and was likely via either (neo-)Acadian or Alleghanian thrusting.

UR - https://www.scopus.com/pages/publications/0033377999

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DO - 10.1130/0091-7613(1999)027<0803:PTDOOM>2.3.CO;2

M3 - Article

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JO - Geology

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IS - 9

ER -

Probing the depths of Oliverian magmas: Implications for Paleozoic tectonics'in the northeastern United States

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