GO 240 Field Trip Reflections

Formerly GO 240 Hand Specimen Petrology

Emporia State University

http://www.emporia.edu/earthsci/amber/go240/trip06.htm

2006 Spring Semester Field Trip

by Susan Ward Aber and James S. Aber

Students enrolled in GO 240 Hand-specimen Petrology have been introduced to rocks and minerals through participation in weekly course work and a field excursion. The field trip was taken April 7, 2006. Follow along through images and text. Click on any image to see it enlarged.

Left to right-
Sitting first row-Stephanie, Susie, Erin, Kallie, Kathleen, Jenica, Brandon
Sitting second row-John, Tyler, Dallas, Andy, Cara, Andy
Standing third row-Scott, Tyson, Jerritt, Gayla, John, Shawn

Photo © by J.S. Aber, April 7, 2006

Upland Chert Gravel Silver City Rose Dome Links References

Upland Chert Gravel
The first stop of the field trip was south of Burlington, Coffey County, Kansas. Students collected chert, milky quartz nodules, Permian fossils, and exotic quartzose or quartzite pebbles in an abandoned gravel pit. The exotic quartzites were likely transported from High Plains and Rocky Mountain sources by streams that flowed across the Flint Hills (Aber, 1988), and these gravel deposits are Neogene, Tertiary in age.
Students pondered the question of how river gravel become deposited on a high hill overlooking the Neosho River drainage valley? Besides the explanation of exotic quartzites, consider the following clues. This region is located in the Osage Cuestas physiographic province. To the west is the province known as the Flint Hills, which is made up of flint or chert-rich limestones interbedded with shales. Chert is a microcrystalline quartz and has a higher resistance to weathering than its limestone host or shale.

Photo © by J.S. Aber, 4/2006
These chert gravels in Coffey County resemble the Leon Gravel, which is a name assigned by Dr. J.S. Aber (1992) to chert gravel deposits in Butler and Cowley counties. Leon Gravel is associated with the Olpe or Olpe-Norge soils and found on high terraces and hill tops, about 1-2 m thick and resting on bedrock.

The field trip continued south on US Highway 75 to Woodson and Wilson counties. Much of the surficial bedrock in these two counties is Pennsylvanian. For example, the Weston Shale within the Stranger Formation was examined at a roadcut along the highway, as was the Stanton Formation at Wilson County Lake, in the spillway and road cuts. In addition to sedimentary rock, the class collected igneous and metamorphic rock in Woodson County.
Cretaceous age intrusive igneous rock created a structural dome, which on the surface appears as a topographic basin. This structure is responsible for gently dipping strata away from the center of the dome. The intrusive rock is responsible for a narrow zone of metamorphic rock as well as the xenoliths found at both Rose Dome and Silver City (Aber and Aber, 2001).

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Silver City Silver City was named for a small mining settlement and scandel in the 1870s. Shares in a silver mine were sold to investors; the silver to bronze colored phlogopite mica sparkles in the sun and from a distance has a metallic look. Students examined the igneous intrusive material in detail at the Micro-Lite Quarry in Woodson County, Kansas, west and north of Buffalo (right).		Photo © by J.S. Aber, 4/2006
The Micro-Lite distribution plant is directly west of Buffalo and a short distance farther is a water filled open pit that resulted from quarrying rock from the Weston Shale to create bricks. The brick plant was fueled by the abundant natural gas in the area but when the gas played out, the brick plant closed. The Micro-Lite Quarry is located a few miles on to the west and north. Micro-Lite is quarrying a weathered lamproite deposit, an intrusive igneous rock that moved up toward the surface some 88-91 million years ago. A visit to an external link from a Kansas Geological Survey field trip, http://www.kgs.ku.edu/Extension/fieldtrips/guidebooks/SCKS/SCKS3.html, provides additional information including a schematic diagram of a carrot-shaped lamproite deposit intruding through the granite basement rock and layers of sedimentary rock.
Photo © by J.S. Aber, 4/2006	Today, the lamproite is mostly taken from the eastern end of the quarry. The product is gathered by the earthmover and dropped onto a conveyor belt that moves the material to a large tank for drying.	Photo © by J.S. Aber, 4/2006
Then the product is loaded into dump trucks and hauled to the Buffalo plant, where it is bagged and distributed. Micro-Lite has operated the plant since 1982 and the KGS reported in 1996 70,000 tons of lamproite were removed (www.kgs.ku.edu/Extension/fieldtrips/guidebooks/SCKS/SCKS3.html). Lamproite deposits in Australia and along the Colorado-Wyoming border contain diamonds in sufficient quantities to mine. It may never be publically known if Kansas lamproite deposits hold diamond, but Micro-Lite company is mining this weathered serpentinized clay and marketing it as a mineral supplement for cattle feed.
Photo © by J.S. Aber, 4/2006	The lamproite deposit is on the floor of the mine, while the slope represents the surrounding zone of contact metamorphic rock. Faults can be seen along the north face of the quarry.	Photo © by J.S. Aber, 4/2006
Wagner (1954) described the lamproite as the Hills Pond Peridotite that was medium-grained, olive-gray when fresh and grayish-yellow when weathered. Zartman, Brock, Heyl, and Thomas (1967) dated the material to Late Cretaceous, 88-91 million years using K-Ar on samples of phlogopite mica. O'Connor (1968) reported the Hills Pond rocks were in contact with late Pennsylvanian age Lansing and Douglas Group at the surface (in D.E. Zeller, p. 68). As research into this igneous intrusion, Cullers, Bamakrishnan, Berendsen, and Griffin (1985) were the first to note the peridotite was really lamproite (p. 1383-1402).
Photo © by J.S. Aber, 4/2006	The lamproite contains about one-fourth phlogopite mica and 15 percent olivine, diopsidic augite, red-brown amphibole, all in a serpentinized clay groundmass. A different assemblage of rocks occur along the margin of the lamproite (right image).	Photo © by J.S. Aber, 4/2006
The lamproite is up to 20 meters thick in the northern part of the Silver City Dome. Overall, this deposit represents a network of sills that came out from a main lamproite pipe structure. The KGS reported other "sills extend away from the main pipe and have been encountered at depths of about 1,300 feet during core drilling, and drilling for oil and gas, in the area around the dome" (Micro-Lite Quarry/Silver City Dome). Intruding hot lamproite magma into the surrounding Pennsylvanian sandstones and shales has created a odd assemblage of metamorphic rocks. Resulting quartzite, skarn, and slate are confined to a narrow zone and are brightly colored blue, green, gray, brown, and pink specimens.
Photo © by J.S. Aber, 4/2006	Contact metamorphic rocks are shown in these images. In detail, these hornfels-grade metamorphics can be horizontally layered or brecciated and folded masses.	Photo © by J.S. Aber, 2/2006
Photo © by J.S. Aber, 4/2006	In addition to the lamproite deposit and contact metamorphics ringing the igneous intrusion, limestone xenoliths were first reported at the far west end of the pit in 2000 (Aber and Aber, 2001).	Photo © by J.S. Aber, 4/2006
Unusual limestone xenoliths containing areas of gray and brown limestone with fossils and criss-crossed with white quartz veins. Pieter Berendsen reported drilling a core hole on the ridge to the south of the open-pit mine that first, encountered rocks in the Stranger Formation and second, encountered rocks in the Stanton Limeston at a depth of 69 meters.
Photo © by J.S. Aber, 4/2006	"Within the Stranger Formation, thin beds of limestone and brecciated limestone were noted at several levels. The limestone may have been uplifted along the fault that marks the southern edge of the sill at this location" (Aber and Aber, 2001, p. 126-127).	Photo © by J.S. Aber, 4/2006
Thus, Aber and Aber concluded that the limestone xenoliths were derived from shallow Pennsylvanian sources within the sill complex (p. 127). "Genesis of the xenoliths began as quartz veins were precipitated in highly fractures wall rocks. Some fragments of the wall rocks were detached, transported a short distance (10s of meters), and emplaced at the rapidly cooling margin of the sill" (p. 127). Return to Table of Contents

Rose Dome

Although the limestone xenoliths were a relatively new discovery, other foreign rock types had been known from a nearby area for many years. The field trip concluded at Rose Dome where students were introduced to the Rose Dome granite, the only in-situ granite exposed at the surface in Kansas. The texture is phaneritic to brecciated, and the granite was dated with Rb-Sr to about 1.2 billion years or middle Proterozoic (Bickford et al. 1971).

This Kansas basement rock is a brecciated granite with 30 percent blue-gray quartz, 45 percent sanidine feldspar, 25 percent albite, and less than one percent biotite (Franks et al. 1971). It is unlike most granite. One student collected this specimen of Rose Dome Granite, which had a vug of euhedral amethyst crystals. What an unusual and beautiful find!

Photo © by J.S. Aber, 4/2006

Through the years, researchers had speculated on how this granite came to be in Kansas, with proposals from Pleistocene glacial erractics to displaced basement rock along a major thrust fault. Others suggested a grantitic intrusion or iceberg rafting from glacial centers in Gondwana in the Pennsylvanian. As late as 1998, Luczaj argued that the granite was the uplifted center of an meteorite impact crater, where the meteorite skipped along the 38 degree lineament crossing through several states.

While the presence of the granite is difficult to understand, knowing about the nearby Silver City intrusion provides a great clue. The best and accepted interpretation today comes from test drilling at Rose Dome that showed the lamproite intrusive rock is just beneath the surface (Berendsen and Blair, 1991). Here the intrusion brought up granite and various sedimentary rock types, which were altered as they were carried toward the surface and subjected to high temperatures.

If the greater regional structures are considered, evidence points to lamproite intrusions at Silver City and Rose Dome taking place along deep crust, pre-existing fractures. The intrusions are isolated but widespread mid-Cretaceous igneous activity events across the central US, which may be related to sea-floor spreading in the Atlantic or rifting of the Mississippi Embayment. Although origins of the intrusions are at least 100 km deep, recurrent crustal movements have led to measurable joints in the sill at Hills Pond. Finally, there is absolutely no physical evidence at Rose Dome for meteorite impact origin and the connection between Rose Dome and the 38 degree lineament is only a coincidence.

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References

Aber, J.S. 1988. Upland chert gravels of east-central Kansas. Kansas Geological Survey Guidebook Series 6: 19-19.
Aber, J.S. 1992. Chert gravel, drainage development, and sinkholes in the Walnut basin, south-central Kansas. Kansas Academy Science, Transactions 95:109-121. Online at www.emporia.edu/kas/trans095/trans095.htm#aber.
Aber, J.S., and Aber, S.W. 2001. Limestone xenoliths in Hills Pond Lamproite, Woodson County, Kansas. Transactions of the Kansas Academy of Science 104(1/2):123-128. Online at www.kansasacademyscience.org/TKAS/trans104/aber2/aber2.htm.
Berendsen, P., and Blair, K.P. 1991. Interpretive subcrop map of the Precambrian basement in the Joplin 1 degree x 2 degree quadrangle. Kansas Geol. Survey, Subsurfae Geology Series 14, 10pp.
Bickford, M.E., Mose, D.G., Wetherill, G.W., and Franks, P.C. 1971. Metamorphism of Precambrian granitic xenoliths in a mica peridotite at Rose Dome, Woodson County, Kansas: Part 1, Rb-Sr isotopic studies. Geological Society of America Bulletin 82:2863-2868.
Cullers, R.L., Ramakrishnan, S., Berendsen, P., and Griffin, T. 1985. Geochimica et Cosmochimica Acta, 49:1383-1402. In Lexicon of Geologic Names of Kansas (through 1995), D.L. Baars and C.G. Maples (editors), KGS Bulletin 231, 1998, p. 107.
Franks, P.C., Bickford, M.E., and Wagner, H.C. 1971. Metamorphism of Precambrian granitic xenoliths in a mica peridottite at Rose Dome, Woodson County, Kansas: Part 2, petrologic and mineralogic studies. Geological Society of America Bulletin 82:2869-2890.
Luczaj, J. 1998. Argument supporting explosive igneous activity for the origin of cryptoexplosion structures in the midcontinent, United States. Geology 26(4): 295-298.
O'Connor, H. 1968. Kansas Geological Survey Bulletin 189, edited by D.E. Zeller. In Lexicon of Geologic Names of Kansas (through 1995), D.L. Baars and C.G. Maples (editors), KGS Bulletin 231, 1998, p. 106.
Wagner, H.C. 1954. U.S. Geological Survey, Geological Quadrangle Map GQ-49. In Lexicon of Geologic Names of Kansas (through 1995), D.L. Baars and C.G. Maples (editors), KGS Bulletin 231, 1998, p. 106.
Zarman, R.E., Brock, M.R., Heyl, A.U., and Thomas, H.H. 1967. American Journal of Science, 265:848-870. In Lexicon of Geologic Names of Kansas (through 1995), D.L. Baars and C.G. Maples (editors), KGS Bulletin 231, 1998, p. 106.
Zeller, D.E. 1968. The stratigraphic succession in Kansas. Kansas Geological Survey, Bulletin 189, 81p.

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This page originates from the Earth Science department for the use and benefit of students enrolled at Emporia State University. The curriculum is © by the author, 2006-2008. Creation and last update 14 August 2008. For more information contact the course instructor, S. W. Aber, e-mail: saber@emporia.edu