- Usage in publication:
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- Hitt Mountain Alkali Feldspar Syenite
- Modifications:
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- First used
- Dominant lithology:
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- Syenite
- AAPG geologic province:
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- Piedmont-Blue Ridge province
Summary:
Tollo and Arav (in press) propose that Robertson River Formation of Allen (1963) be revised as Robertson River Igneous Suite to emphasize the lithologic diversity that characterizes this belt. Rocks range in composition from alkali syenite to alkali feldspar granite to granite. This suite is the largest group of intrusives within the Blue Ridge province of VA. Extends from near Upperville, 70 mi southwest to northern suburbs of Charlottesville. Includes at least nine mappable lithologic units, among them, Hitt Mountain Alkali Feldspar Syenite. Unit is poorly exposed but has been mapped across a broad area of the southern segment of the Robertson River outcrop belt. Includes medium- to coarse-grained, amphibole-bearing alkali feldspar quartz syenite and alkali feldspar syenite. Quartz-poor nature of mineralogic assemblage is distinctive. Intrudes the Laurel Mills Granite.
Source: GNU records (USGS DDS-6; Reston GNULEX).
- Usage in publication:
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- Hitt Mountain Alkali Feldspar Syenite*
- Modifications:
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- Named
- Dominant lithology:
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- Syenite
- AAPG geologic province:
-
- Piedmont-Blue Ridge province
Summary:
Recent detailed mapping and petrologic analysis indicate rocks previously assigned to Robertson River Formation include a series of granitoids, syenitoids, and felsites emplaced sequentially during 30 m.y. episode of magmatism. Collectively, the rocks form a dike-like mass of intrusions extending nearly 100 km from vicinity of Charlottesville, VA to north-northwest of Ashby Gap, VA. Therefore, name is revised to Robertson River Igneous Suite. At least 8 units of the suite are distinguishable by mineral composition, texture, bulk chemical composition, and U-Pb-determined isotopic age, and can be mapped at 1:24,000 scale. Hitt Mountain Alkali Feldspar Syenite is named for Hitt Mountain. Type locality is series of small outcrops on southwest slope of Hitt Mountain west of VA Hwy 607, approx 1.4 km (0.9 mi) northeast of intersection of VA Hwys 607 and 606, Brightwood 7.5-min quad, northern VA. Consists of light-gray, coarse-grained, amphibole-bearing alkali feldspar syenite. Dikes of Hitt Mountain rocks cut Laurel Mills Granite near Novum, VA. Age is Late Proterozoic. Report includes geologic map.
Source: GNU records (USGS DDS-6; Reston GNULEX).
- Usage in publication:
-
- Hitt Mountain Alkali Feldspar Syenite*
- Modifications:
-
- Geochronologic dating
- AAPG geologic province:
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- Piedmont-Blue Ridge province
Summary:
U-Pb zircon age of Hitt Mountain Alkali Feldspar Syenite is 706+/-2 Ma.
Source: GNU records (USGS DDS-6; Reston GNULEX).
For more information, please contact Nancy Stamm, Geologic Names Committee Secretary.
Asterisk (*) indicates published by U.S. Geological Survey authors.
"No current usage" (†) implies that a name has been abandoned or has fallen into disuse. Former usage and, if known, replacement name given in parentheses ( ).
Slash (/) indicates name conflicts with nomenclatural guidelines (CSN, 1933; ACSN, 1961, 1970; NACSN, 1983, 2005, 2021). May be explained within brackets ([ ]).