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N. M. Ratcliffe

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

31 records · Page 2Linked to original sources
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↗
USGS1985

40Ar/39Ar and K-Ar data bearing on the metamorphic and tectonic history of western New England

40 Ar/ 39 Ar ages of coexisting biotite and hornblende from Proterozoic Y gneisses of the Berkshire and Green Mountain massifs, as well as 40 Ar/ 39 Ar and K-Ar mineral and whole-rock ages from Paleozoic metamorphic rocks, suggest that the thermal peak for the dominant metamorphic recrystallization in western New England occurred 465 ± 5 m.y. ago (Taconian). Although textural data indicate a complex metamorphic-tectonic history for Paleozoic rocks, no evidence in rocks at least as high as kyanite grade dictates an Acadian age for the Barrovian metamorphism. Available 40 Ar/ 39 Ar and K-Ar data suggest that the low-grade metamorphism and cleavage formation in Taconic allochthons and the higher-grade metamorphism and emplacement of the Berkshire massif allochthon are Taconian. 40 Ar/ 39 Ar age data from a poorly defined terrane beginning near the east margin of the Green Mountain massif and extending along the eastern one-third of the Berkshire massif as far south as Otis, Massachusetts, suggest that the area has been retrograded during a metamorphism that peaked at least 376 ± 5 m.y. ago (Acadian). Available age and petrologic data from western New England indicate the presence of at least three separate metamorphic-structural domains of Taconian age: (1) a small area of relict high-pressure and low-temperature metamorphism in northern Vermont (T-1 domain), (2) a broad area in Vermont and eastern New York of normal Barrovian metamorphism from chlorite to garnet grade and characterized by a gentle metamorphic gradient (T-2 domain), and (3) a rather narrow belt of steep-gradient, Barrovian series metamorphic rocks extending from near the Cortlandt Complex northeastward through Dutchess County, New York, to the Berkshire massif in western Massachusetts (T-3 domain). Areas of maximum metamorphic intensity within the T-3 domain coincide with areas of maximum crustal thickening resulting from imbricate thrusting (Berkshire massif) or from recumbent folding (Manhattan Prong) of remobilized North American continental crust in the later stages of the Taconic orogeny.

Geological Society of America Bulletin↗
USGS1985

Attitude, movement history, and structure of cataclastic rocks of the Flemington Fault results of core drilling near Oldwick, New Jersey

Since 1978, the U.S. Geological Survey (USGS) has cored cataclastic rocks at six localities along border faults of the Early Mesozoic Newark basin in New York and New Jersey. This drilling was done as part of fault definition studies for the USGS Earthquake and Reactor Hazard Programs. The purposes of these studies are to: (1) determine the attitude and location of major faults, (2) assess evidence for recent reactivation, and (3) identify the movement history and depth of formation of the faults. The results of these studies up to 1980 are summarized in Ratcliffe (1980) and a study of a site in Rockland County, N.Y. appears in Ratcliffe 1982). The attitude and movement history of these faults is particularly important because of the possible association of recent low-level seismicity in the New York-New Jersey area with the Ramapo-Flemington fault system (Aggarwal and Sykes, 1978). Previous studies have shown that the Ramapo fault dips to the southeast at angles varying from 70° to 45° and strikes N. 40° E. to N. 10° E. In all of the cored fault zones, the actual contact of hanging-wall and footwall blocks is expressed as a relatively narrow zone, 3 to 8 inches thick, of dark, finely comminuted, fluxionbanded gouge. The intensity of cataclasis decreases rapidly upwards so that rocks 60 ft or so above the fault are not strongly cataclastic. Gneiss, dolostone, and phyllonite in the footwall block are generally weakly deformed more than 30 ft below the fault. Movement sense on the Ramapo fault is largely dip-slip and right-oblique normal faulting. In the summer of 1983, two holes were drilled through the border fault of the Newark basin near Oldwick, New Jersey, in the Gladstone 7.5minute quadrangle. Figure 1A shows the location of the drill site in relation to regional geology and the major faults. The fault drilled in this study connects to the south with the Flemington fault, which trends southwestward across the Newark basin, as shown. To the north, the fault can be traced along the valley that extends towards Mendham, N. J., beyond the limits of exposed Mesozoic rocks, to connect with the Ramapo fault near Morristown N. J. (fig. 1A; Ratcliffe, 1980). For this reason, we use the name "Flemington" for the border fault in the region of the drill site. A detailed map (fig. 1B) shows the local geology along the border fault from Pottersville, N. J. southward to the axis of the Oldwick syncline.

New Jersey↗