(DUCO) Barrovian Metamorphic Sequence -- Dutchess County, New York

Title

(DUCO) Barrovian Metamorphic Sequence -- Dutchess County, New York

Description

A classic example of Barrovian-type metamorphism in Dutchess County, NY associated with the Taconic orogeny. A Barrovian metamorphic sequence displays gradual pressure and temperature increase along the metamorphic gradient, and occurs during regional metamorphism. These zones of pressure and temperature increase are recognizable by the characteristic minerals that accompany them. Dutchess County, NY contains an unusually complete sequence.

This collection contains metamorphic rocks from chlorite grade to sillimanite grade in a tight spatial window which records the regional metamorphic gradient increasing from WNW to ESE. This collection also contains some rocks that mirror the protoliths of the schists and quartzites of the sequence (shales and graywacke).

Date

1970

Contributor

Western Minerals, Inc.

Spatial Coverage

Dutchess County, New York

Temporal Coverage

450-430 Ma

Accrual Method

Purchased from Western Minerals, Inc.

References

Start Here:
Vollmer, F. W., and Walker, J., 2009, The classic Barrovian metamorphic sequence of Dutchess County and its structural and stratigraphic context in the Taconic Orogeny. In Guidebook—New York State Geological Association Meeting, v. 81, p. 11-1. 
http://www2.newpaltz.edu/~vollmerf/papers/Vollmer_and_Walker_2009_NYSGA.pdf (accessed March 15th, 2015)

  • A useful field trip guide across the Barrovian metamorphic sequence of Dutchess county. Good general introduction to the geology of the area.
Additional Resources:
Whitney, D.L., Mechum, T.A., Keuhner, S.M., and Dilek, Y.R., 1996, Progressive metamorphism of pelitic rocks from protolith to granulite facies, Dutchess County, New York, USA: constraints on the timing of fluid infiltration during regional metamorphism, Journal of Metamorphic Geology, v. 14, p. 163-181. http://dx.doi.org/10.1046/j.1525-1314.1996.05836.x

  • A fairly general look at the progressive metamorphism in Dutchess County by one of the foremost workers in the area.

Knopf, E.B., 1927, Some recent work in the Taconic area: American Journal of Science, v. 41, p. 42-458. http://dx.doi.org/10.2475/ajs.s5-14.84.429

  • One of the first articles to describle the Dutchess County rocks as a "classic" Barrovian sequence. 

Ghent, E.D., Stout, M.Z., 1981, Geobarometry and geothermometry of plagioclase-biotite-garnet-muscovite assemblages, Contributions to Mineralogy and Petrology, v. 76, p. 92-97. http://dx.doi.org/10.1007/BF00373688


  • Work constraining the pressure and temperature paths of metamorphism in the sequence through equilibrium assemblages. This work was found to be in agreement with other equilibrium assemblage PT paths.

Whitney, D.L., Mechum, T.A., Dilek, Y.R., and Keuhner, S.M., 1996, Modification of garnet during regional metamorphism in garnet through sillimanite-zone rocks, Dutchess County, New York, American Mineralogist, v. 81, p. 696-705. http://www.minsocam.org/MSA/AmMin/TOC/Articles_Free/1996/Whitney_p696-705_96.pdf

  • Work by Whitney on changes in PTX conditions leading to modification of garnet in the metamorphic sequence. Garnet is widely distributed through the sequence, which makes it a useful marker for tracking these changes.

Items in the (DUCO) Barrovian Metamorphic Sequence -- Dutchess County, New York Collection

Barrovian Metamorphic Sequence--Dutchess County, NY Western Minerals Supplementary Information
OCR PDF of supplemental information for the Barrovian Metamorphic Sequence--Dutchess County, NY

Marble
Metamorphised Balmville limestone with visible phlogopite crystals. Also contains tremolite visible at the outcrop level. Within nose of anticline of Walloomsac schist.

The PPL thin section shows a large irregular calcite grain with tremolite at…

Marble
Metamorphised Balmville limestone with visible phlogopite crystals. Also contains actinolite.

Thin section shows calcite with interspersed pleochroic phlogopite.

Marble
Metamorphised Briarcliff dolostone with visible micas. Contains diopside, tremollite, and phlogopite. At the metamorphic grade of the first sillimanite isograd.

Thin section shows irregular dolomite grains in the center, with pleochroic…

Marble
Metamorphised Briarcliff dolostone.

The thin section shows well-twinned dolomite grains with diopside at the bottom.

Muscovite schist
Extremely coarse-grained muscovite schist. Large garnets visible in hand sample. Sillimanite is not recognizable in hand sample, however.

The thin section shows muscovite (with minor sillimanite) in a large band, biotite, staurolite, and…

Kyanite biotite garnet schist
Schist with coarse biotite controlling foliation. Garnets visible in some hand samples. Kyanite blades without preferred orientation--at higher concentration within folds. Possibly from the Walloomsac schist.

The PPL thin section shows biotite,…

Quartzite
Metamorphised sandstone with a gray, glassy appearance. From the Paughquag quartzite, a late Cambrian formation. The basal Cambrian quartzite rests on pre-Cambrian gneisses.

The thin section shows quartz and plag with some biotite and grain…

Staurolite schist
Schist with coarse staurolite grains. This outcropping is approximately on the strike of the chloritoid schists (sample 7). Also contains garnet, muscovite, feldspar, and quartz. Presumed to be from the Everett Schist.

The thin section shows…

Staurolite chloritoid schist
Schist bearing both staurolite and chloritoid. This marks the first appearance of staurolite in the metamorphic sequence. Also contains garnet, muscovite, chlorite, biotite, feldspar, and quartz. The assemblage in not in equilibrium.

The thin…

Chloritoid schist
Schist with coarse chloritoid crystals (up to 1/8 inch) without preferred orientation. These crystals grow across the foliation developed in the schist, but appear deformed. Chloritoid is a silicate mineral made in metamorphism. It also contains…

Garnet biotite schist
Schist with sparse garnet. This schist is darker and graphitic. It also contains biotite, chlorite, muscovite, feldspar, and quartz.

The thin section shows several large biotite grains with an included garnet, small quartz grains, muscovite, and…

Graphitic slate
A highly graphitic slate in the Walloomsac slates. Contains pyrite. This rock also contains biotite, chlorite, muscovite, quartz, ilmenite, and pyrite.

The thin section shows large biotite grains, and chlorite muscovite, and quartz. Fluid…

Slate
Kink fold in a slate from the Mt. Merino Member.

This rock is from the chlorite zone of the Barrovian metamorphic sequence (low metamorphism).

Graywacke
The graywacke facies in the Mt. Merino member (where sample 4 also comes from). Graywacke is a hard, dark-colored sandstone. This sandstone represents a similar rock to the protolith for the quartzite of sample 10.

The thin section shows quartz,…

Green shale
Green shale of the Indian River member of the Normanskill formation. This shale contains muscovite, chlorite, plagioclase, and quartz.

The thin section shows quartz and biotite with some minor opaques.

This rock is from the chlorite zone of the…

Red shale
Red shale from the Indian River member of the Normanskill formation. This rock contains hematite, chlorite, muscovite, plagioclase, and quartz.

The thin section shows muscovite and biotite with some larger quartz grains visible and minor hematite…

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