255:. In 1993, Southworth and others give a date of 35.0 ± 0.5 Ma for basalt of Trimble Knob In 2012, Bulas and others studied the other igneous rocks and sampled them to obtain the mineral separates and perform age dating. The amphibole minerals composing the volcanic rock Trachydacite were dated utilizing the Ar-Ar age dating method and found them to be 48.86±.37 million years of age. The age of the volcanic eruption is not explained by the age of the formation of amphibole minerals which formed at a time before the volcanic eruption occurred. There may have been a bi-model or two-stage eruption mechanism responsible for producing the different varieties of mafic and felsic volcanic rock that have been discovered and associated with this volcanism. Both age dates place the earliest age of the eruption to be during the
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Southworth, C.S., Gray, K.J., and Sutter, J.F., 1993, Middle Eocene intrusive igneous rocks of the central
Appalachian Valley and Ridge province; Setting, chemistry, and implications for crustal structure: U.S. Geological Survey Bulletin 1839, p. J1–J24.
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Rader, E.K. and Wilkes, G.P., 2001, Geologic map of the
Virginia portion of the Staunton 30 X 60 minute quadrangle: Virginia Division of Mineral Resources, Publication 163, scale 1:100000.
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Trimble Knob is an isolated conical hill in an otherwise relatively flat valley, surrounded by farmland. The peak of the hill has an elevation of 3123 ft (952m).
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epoch and further research is needed to better understand the timing and eruption mechanisms responsible for these rock types.
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lies along the southeast flank of the hill. Trimble Knob is the most obvious of many igneous intrusions in the area.
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that last erupted approximately 35 million years ago, making it one of the youngest volcanos on the east coast of
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Jonathan L. Tso; Ronald R. McDowell; Katharine Lee Avary; David L. Matchen & Gerald P. Wilkes (2004).
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378:"Evidence for a Two-Stage Eruption at Trimble Knob, an Eocene Volcanic Plug in Highland County, VA"
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332:"Trimble Knob United States on the Elevation Map. Topographic Map of Trimble Knob United States"
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309:"Middle Eocene Igneous Rocks in the Valley and Ridge of Virginia and West Virginia"
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with a diameter of approximately 150 metres (160 yd). The basalt
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shale and calcareous mudstone), and is near the axis of a
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243:The basalt at Trimble Knob (and other igneous rock
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247:in the area) were originally thought to be of
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33:Photo of Trimble Knob, taken December 2011
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440:Landforms of Highland County, Virginia
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460:Cinder cones of the United States
251:age by relative age dating using
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317:United States Geological Survey
445:Diatremes of the United States
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235:in the center of the valley.
253:cross-cutting relationships
220:through the gently dipping
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153:, located southwest of
16:Virginian conical hill
450:Volcanoes of Virginia
416:38.40472°N 79.58778°W
67:38.40472°N 79.58778°W
376:Guzman and Johnson.
421:38.40472; -79.58778
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72:38.40472; -79.58778
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330:elevationmap.net.
225:Needmore Formation
93:Monterey, Virginia
39:Highest point
267:Rockingham County
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455:Eocene volcanoes
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137:Last eruption
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384:. Retrieved
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339:. Retrieved
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169:composed of
167:conical hill
151:Trimble Knob
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22:Trimble Knob
419: /
273:rocks near
201:Description
109:35.0 ± 0.5
105:Age of rock
70: /
45:Coordinates
434:Categories
407:79°35′16″W
404:38°24′17″N
341:2018-06-11
289:References
58:79°35′16″W
55:38°24′17″N
263:Mole Hill
249:Paleozoic
177:rock, of
83:Geography
233:syncline
222:Devonian
218:intrudes
191:diatreme
183:Tertiary
175:volcanic
163:Virginia
155:Monterey
130:diatreme
88:Location
386:11 June
271:igneous
187:volcano
181:(early
165:, is a
126:volcano
99:Geology
257:Eocene
214:basalt
179:Eocene
171:basalt
123:Eroded
381:(PDF)
245:dikes
388:2018
173:, a
277:in
239:Age
189:or
157:in
141:35
128:or
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143:Ma
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