Английская Википедия:Guilford Quartz Monzonite

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Шаблон:Short description Шаблон:Infobox rockunit

Файл:Guilford Quartz Monzonite.jpg
Outcrop of Guilford Quartz Monzonite in Kings Contrivance Village, Columbia, Maryland
Файл:Bulletin 426 Plate VI B Guilford and Waltersville Granite Company Quarry.jpg
Historical photo c. 1910 of the Guilford Quarry while in operation
Файл:Fine grained granite plateXVI MD Geol Survey 1898.jpg
Polished slab from the Guilford Quarry (1898). Width is approximately 10.7 cm.
Файл:Guilford Quarry Jan2013.jpg
The old Guilford Quarry in January 2013, facing north.

The Guilford Quartz Monzonite is a Silurian or Ordovician quartz monzonite pluton in Howard County, Maryland. It is described as a biotite-muscovite-quartz monzonite which occurs as discontinuous lenticular bodies[1] which intrude mainly through the Wissahickon Formation (gneiss).

The extent of this intrusion was originally mapped in 1940[2] as the "Guilford granite". It was given its current name in 1964 by C. A. Hopson.[3] Hopson grouped the Guilford Quartz Monzonite with the Ellicott City Granodiorite and the Woodstock Quartz Monzonite as "Late-kinematic intrusive masses."

Description

The Guilford Quartz Monzonite was described in 1898 as "perhaps the most attractive stone in the state" by Edward B. Mathews of the Maryland Geological Survey.[4] He provides this detailed description of the granite: Шаблон:Quotation

Hopson[3] reported the chemical composition (by %) of the Guilford Quartz Diorite from 1.5 miles west-southwest of Guilford along the Middle Patuxent River, as follows:

Chemical % Chemical %
SiO2 73.08 CaO 1.71
TiO2 0.27 Na2O 3.70
Al2O3 13.86 K2O 4.09
Fe2O3 0.65 H2O+ 0.46
FeO 1.40 H2O− 0.10
MnO 0.05 CO2 0.05
MgO 0.48 P2O5 0.06

Early quarrying

The 1898 account of Edward B. Mathews of the Maryland Geological Survey[4] of the quarry at Guilford (now within the town of Columbia) is as follows: Шаблон:Quotation

Age

A. A. Drake argued that the Guilford is of Ordovician age[5] because it is probably comagmatic with the Woodstock Quartz Monzonite dated at 444 Ma. An earlier source gives the date of 420 +/-50 Ma.[6] More recently, radiometric dating (U-Pb-TIMS) of zircon crystals extracted from the Guilford Quartz Monzonite yielded an age of 362 +/- 3 Ma (Devonian).[7]

References

Шаблон:Reflist

Партнерские ресурсы
Криптовалюты
Магазины
Хостинг
Разное

  1. ↑ USGS Mineral Resources On-Line Spatial Data
  2. ↑ Cloos, Ernst, and Broedel, C.H., 1940, Geologic map of Howard County and adjacent parts of Montgomery and Baltimore Counties (Maryland): Maryland Geological Survey County Geologic Map, 1 sheet, scale 1:62,500
  3. ↑ 3,0 3,1 Hopson, C. A., 1964, The crystalline rocks of Howard and Montgomery Counties: Maryland Geological Survey County Report, 337 p., (Reprinted from Cloos, Ernst, and others, "Geology of Howard and Montgomery Counties," p. 27-215)
  4. ↑ 4,0 4,1 Maryland Geological Survey Volume 2, 1898, The Johns Hopkins Press, Baltimore.
  5. ↑ Drake, A.A., Jr., 1998, Geologic map of the Kensington quadrangle, Montgomery County, Maryland: U.S. Geological Survey Geologic Quadrangle Map, GQ-1774, scale 1:24,000
  6. ↑ Wetherill, G.W., Tilton, G.R., Davis, G.L., Hart, S.R., and Hopson, C.A., 1966, Age measurements in the Maryland Piedmont: Journal of Geophysical Research, v. 71, p. 2139-2155.
  7. ↑ John N. Aleinikoff, J. Wright Horton, Avery Ala Drake, C. Mark Fanning, 2002, SHRIMP and Conventional U-Pb ages of Ordovician granites and tonalites in the central Appalachian Piedmont: Implications for Paleozoic tectonic events: American Journal of Science, 302 (1) 50-75; DOI: 10.2475/ajs.302.1.50
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