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N. M. Ratcliffe

Publications and source records attributed to N. M. Ratcliffe.

At least 19 recordsLinked to original sources
USGS1996

Preliminary bedrock geologic map of the Vermont part of the 7.5 x 15 minute Mount Ascutney and Springfield quadrangles, Windsor County, Vermont

Bedrock in the Vermont part of the Mount Ascutney and Springfield quadrangles consists largely of, from west to east, Middle Proterozoic gneisses in the core of the Chester Dome, pre-Silurian metasedimentary, metavolcanic, and meta-igneous rocks as a cover sequence immediately above the dome, Silurian and Devonian metasedimentary and metavolcanic rocks of the Connecticut Valley sequence, and Ordovician to Silurian and Devonian metasedimentary rocks informally referred to as the New Hampshire sequence. In addition, the rocks are intruded by granitic dikes of the Devonian New Hampshire Plutonic Suite and, at Mount Ascutney, the Cretaceous White Mountain Plutonic - Volcanic Suite. The primary purpose of this report is to present preliminary results on the stratigraphic and structural relationships in the Connecticut Valley and New Hampshire sequence rocks.

Vermont↗
USGS1991

Trondhjemitic, 1.35-1.31 Ga gneisses of the Mount Holly Complex of Vermont: evidence for an Elzevirian event in the Grenville Basement of the United States Appalachians

A newly recognized suite of trondhjemite–tonalite and dacitic gneiss forms a 10 km wide belt of rocks within the Mount Holly Complex in the central part of the Green Mountain massif of Vermont. Field relationships and chemistry indicate that these gneisses are calc-alkaline, volcanic, and hypabyssal plutonic rocks older than the Middle Proterozoic regional deformation that affected the Mount Holly Complex. U–Pb zircon dates indicate ages as great as 1.35 Ga for crystallization of the volcanic protoliths and for intrusion of crosscutting trondhjemite. Tonalitic plutonism continued until 1.31 Ga.Map-scale contacts between the trondhjemitic–tonalitic–dacitic gneisses and the paragneiss sequence of the Mount Holly Complex are sharp, suggesting that the volcanic rocks of the trondhjemite–tonalite suite underlie the paragneiss units and do not intrude them. These relationships suggest that the trondhjemite–tonalite suite is either considerably older than, and unconformable beneath, the paragneiss cover rocks or represents a volcanic edifice slightly older than the deposition of the sedimentary precursor to the paragneiss units. The paragneiss and tonalite–trondhjemite gneisses are both intruded by younger granitoids that were intruded at about 1.25 Ga during strong dynamothermal metamorphism.The trondhjemitic gneisses of the Mount Holly Complex of Vermont have high Al 2 O 3 and low Yb contents and light rare-earth element enrichment patterns that are more characteristic of continental than oceanic volcanic arcs. The Mount Holly intrusives and volcanics may have formed during 1.35–1.31 Ga ensialic volcanic-arc activity, contemporaneous with ensimatic arc activity during the early part of the Elzevirian phase of the Grenville orogeny. In Vermont, later deformation and granite intrusion at about 1.25 Ga coincide with the major pulse of the Elzevirian orogeny and associated trondhjemitic plutonism in the Central Metasedimentary Belt of eastern Canada.

Vermont↗