Post by 1dave on Dec 29, 2017 15:34:03 GMT -5
jamesp is this the red quartzite you mention?
www.lpi.usra.edu/meetings/lpsc2008/pdf/2506.pdf
www.lpi.usra.edu/meetings/lpsc2006/pdf/2375.pdf
COSMIC IMPACT IN THE PIEDMONT OF GEORGIA? THE WOODBURY STRUCTURE.
E. F. Albin,1 D. T. King, Jr.,2 R. S. Harris,3 L. W. Petruny,4 S. J. Jaret,1 J. C. Gibson.2
1 Dept. of Space Sciences, Fernbank Sci. Center, Atlanta, GA 30307 [ed.albin@fernbank.edu],
2 Dept. of Geology, Auburn Univ., Auburn, AL 36849,
3 Dept. of Geol. Sci, Brown Univ., Providence, RI 02912,
4 AstraTerra Research, Auburn, AL 36831-3323.
Introduction:
The Woodbury structure (also known as Cove Dome) is located 6 km SSE of the town of Woodbury, Meriwether County, Georgia. The center of the structure is located approximately 32o 55’N; 84o
32’W. A nearly circular structure almost 7 km in diameter (Fig.1), it is a conspicuous feature in the eastern Pine Mountain terrane which skirts the southern edge of the Appalachian Piedmont.
Geologic Setting:
The structure consists of an elevated quartzite rim and rather flat floor comprised of schist and gneiss. Relief from floor to rim ranges from 100 to 150 meters (Fig. 2).
The Flint River, an antecedent stream, cuts through the rim in the northeastern quadrant and exits through the structure’s rim in the southeastern quadrant.
The Woodbury structure has been previously interpreted as a “structural dome which post-
dates the development of regional metamorphic foliation” [1].
The age of the Late Paleozoic rim rocks (Hollis Quartzite) is quite different from the
underlying Grenvillian rocks (Woodland Gneiss) of the structure’s floor [1]. This relationship has
been interpreted as a tectonic contact and/or a major unconformity[1].
The Hollis Quartzite dips radially away from the center of the structure; the average Hollis dip is approximately 20 degrees [2]. Rocks on the eastern rim show
overturned folding that also dips away from the structure’s center (Fig. 3).
Other arcuate ridges of uplifted and tightly folded Hollis Quartzite occur in the region; but unlike those occurrences the Woodbury “dome” does not appear to coincide with an obvious positive magnetic anomaly belying the source of the uplift [3]. Gravity data of sufficient quality to investigate the structure has not been available.
Pseudotachylitic Breccia:
Streamcuts into the northern limb of the structure, near Dixon Mountain, expose an unusual reddish quartzite which crops out beneath the steeply dipping white quartzites comprising the rim. Thin sections reveal that the red color is due to iron oxide staining and replacement of a dense network of pseudotachylitic veins.
www.lpi.usra.edu/meetings/lpsc2008/pdf/2506.pdf
Introduction:
Located 6 km SSE of the town of Woodbury (Meriwether County, Georgia) is a feature known informally as “Cove Dome” (herein called the Woodbury structure). It lies at the eastern end of the Pine Mountain terrane along the southern edge of the Appalachian Piedmont. The structure, centered at 32o55’N; 84o 32’W, is a 7 km diameter circular depression with a conspicuous rim (Fig. 1). Previously, we presented preliminary evidence suggesting that an impact event should be considered to explain the structure [1]. Here we present additional evidence that shock processes likely have played a role in its origin.
. . .
Coesite Occuurence with Shocked Zircon:
While investigating these zircons with a micro-Raman spectrometer at Auburn University, we found that the spectra of quartz immediately around one of them (see Fig.3) contains a relatively strong 521cm- line diagnostic [5] of coesite (Fig.4).
Conclusions:
The occurrence of zircons containing PDFs and their association with coesite strongly suggest that at least some of the rocks associated with the Woodbury structure experienced an impact event sometime between deposition of the quartzite protoliths and Alleghanian metamorphism.
We continue to investigate the structure and currently are analyzing gravity and magnetic data.
Located 6 km SSE of the town of Woodbury (Meriwether County, Georgia) is a feature known informally as “Cove Dome” (herein called the Woodbury structure). It lies at the eastern end of the Pine Mountain terrane along the southern edge of the Appalachian Piedmont. The structure, centered at 32o55’N; 84o 32’W, is a 7 km diameter circular depression with a conspicuous rim (Fig. 1). Previously, we presented preliminary evidence suggesting that an impact event should be considered to explain the structure [1]. Here we present additional evidence that shock processes likely have played a role in its origin.
. . .
Coesite Occuurence with Shocked Zircon:
While investigating these zircons with a micro-Raman spectrometer at Auburn University, we found that the spectra of quartz immediately around one of them (see Fig.3) contains a relatively strong 521cm- line diagnostic [5] of coesite (Fig.4).
Conclusions:
The occurrence of zircons containing PDFs and their association with coesite strongly suggest that at least some of the rocks associated with the Woodbury structure experienced an impact event sometime between deposition of the quartzite protoliths and Alleghanian metamorphism.
We continue to investigate the structure and currently are analyzing gravity and magnetic data.
www.lpi.usra.edu/meetings/lpsc2006/pdf/2375.pdf
COSMIC IMPACT IN THE PIEDMONT OF GEORGIA? THE WOODBURY STRUCTURE.
E. F. Albin,1 D. T. King, Jr.,2 R. S. Harris,3 L. W. Petruny,4 S. J. Jaret,1 J. C. Gibson.2
1 Dept. of Space Sciences, Fernbank Sci. Center, Atlanta, GA 30307 [ed.albin@fernbank.edu],
2 Dept. of Geology, Auburn Univ., Auburn, AL 36849,
3 Dept. of Geol. Sci, Brown Univ., Providence, RI 02912,
4 AstraTerra Research, Auburn, AL 36831-3323.
Introduction:
The Woodbury structure (also known as Cove Dome) is located 6 km SSE of the town of Woodbury, Meriwether County, Georgia. The center of the structure is located approximately 32o 55’N; 84o
32’W. A nearly circular structure almost 7 km in diameter (Fig.1), it is a conspicuous feature in the eastern Pine Mountain terrane which skirts the southern edge of the Appalachian Piedmont.
Geologic Setting:
The structure consists of an elevated quartzite rim and rather flat floor comprised of schist and gneiss. Relief from floor to rim ranges from 100 to 150 meters (Fig. 2).
The Flint River, an antecedent stream, cuts through the rim in the northeastern quadrant and exits through the structure’s rim in the southeastern quadrant.
The Woodbury structure has been previously interpreted as a “structural dome which post-
dates the development of regional metamorphic foliation” [1].
The age of the Late Paleozoic rim rocks (Hollis Quartzite) is quite different from the
underlying Grenvillian rocks (Woodland Gneiss) of the structure’s floor [1]. This relationship has
been interpreted as a tectonic contact and/or a major unconformity[1].
The Hollis Quartzite dips radially away from the center of the structure; the average Hollis dip is approximately 20 degrees [2]. Rocks on the eastern rim show
overturned folding that also dips away from the structure’s center (Fig. 3).
Other arcuate ridges of uplifted and tightly folded Hollis Quartzite occur in the region; but unlike those occurrences the Woodbury “dome” does not appear to coincide with an obvious positive magnetic anomaly belying the source of the uplift [3]. Gravity data of sufficient quality to investigate the structure has not been available.
Pseudotachylitic Breccia:
Streamcuts into the northern limb of the structure, near Dixon Mountain, expose an unusual reddish quartzite which crops out beneath the steeply dipping white quartzites comprising the rim. Thin sections reveal that the red color is due to iron oxide staining and replacement of a dense network of pseudotachylitic veins.
