TY - JOUR
T1 - Probing the depths of Oliverian magmas
T2 - Implications for Paleozoic tectonics'in the northeastern United States
AU - Kohn, Matthew J.
AU - Spear, Frank
PY - 1999
Y1 - 1999
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 - http://www.scopus.com/inward/record.url?scp=0033377999&partnerID=8YFLogxK
U2 - 10.1130/0091-7613(1999)027<0803:PTDOOM>2.3.CO;2
DO - 10.1130/0091-7613(1999)027<0803:PTDOOM>2.3.CO;2
M3 - Article
AN - SCOPUS:0033377999
SN - 0091-7613
VL - 27
SP - 803
EP - 806
JO - Geology
JF - Geology
IS - 9
ER -