Mesozoic rocks in the Transantarctic Mountains Triassic-Jurassic sandstones in foreground; Jurassic plateau basalts at top in background. See Hanson and Elliot (1996).	Campsite in Namibia Rocks in field of view are granite and syenite within a Neoproterozoic intraplate igneous complex emplaced prior to continental breakup along the western margin of the Kalahari craton.

Table of Contents

• Proterozoic Tectonic Evolution of Southern Africa
• Northern Sierra Nevada, California
• Paleovolcanological Studies in Southernmost South America and Antarctica
• Cambrian Rhyolites, Southern Oklahoma
• West Texas

Reworked basement along southern margin of Zambezi belt in Zambia. Mesoproterozoic gneissic banding folded and sheared by Neoproterozoic Zambezi deformation. See Hanson et al. (1994).	Umkondo igneous province, southern Africa. 1.1 Ga diabase sill (top of hill) intruding Paleoproterozoic sedimentary strata, eastern Botswana. See Hanson et al. (2004).

Southern Africa is of crucial importance in understanding global Proterozoic plate dynamics and supercontinent configurations, both with regard to assembly and breakup of the Mesoproterozoic Rodinia supercontinent, and with regard to the assembly of Gondwana near the end of the Neoproterozoic. Much of my work in this region has consisted of structural, petrological, and geochronological studies of major basement terrains in Zambia and Zimbabwe in relation to regional Proterozoic crustal evolution. One exciting project involved geochronological study of remote, isolated basement exposures in the Kalahari Desert in Botswana. This work has helped to constrain the distribution and tectonic relations of Precambrian crustal provinces in a large part of southern Africa where the basement geology is almost completely blanketed by Kalahari sands.

Other, more recent work has focused on the geochronology, geochemistry, paleomagnetism, and tectonic relations of a poorly understood 1.1-billion-year-old large igneous province that developed over an area of some two million square kilometers in southern Africa and originally contiguous parts of Antarctica. Collaborators in this project included Sam Bowring (MIT), Wulf Gose and Ian Dalziel (Univ. of Texas, Austin), and Peter Hall and Dean Bullen (Univ. of Portsmouth). Our work suggests that the African igneous province is temporally and perhaps spatially linked to widespread, coeval within-plate magmatism in North America (including the Midcontinent rift). This linkage has important implications for proposed reconstructions of Rodinia, and for relations between mantle convection and supercontinent assembly and dispersal.

I am now collaborating with Bowring, Gose and Davi Evans at Yale on a new project in Africa, which seeks to obtain robust, well-dated paleomagnetic poles from Neoproterozoic intraplate igneous rocks in the Kalahari and Congo cratons, two of the main building blocks of the Gondwana supercontinent. The resulting data will be used to test models for assembly of the central part of Gondwana.

Relevant Publications:

2006 Gose, W.A., Hanson, R.E., Dalziel, I.W.D., Pancake, J.A., and Seidel, E.K., Paleomagnetism of the 1.1 Ga Umkondo large igneous province in southern Africa: Journal of Geophysical Research, v. 111, 18 p. (doi:10.1029/2005JB003897).

2004 Hanson, R.E., Crowley, J.L., Bowring, S.A., Ramezani, J., Gose, W.A., Dalziel, I.W.D., Pancake, J.A., Seidel, E.K., Blenkinsop, T.G., and Mukwakwami, J., Coeval large-scale magmatism in the Kalahari and Laurentian cratons during Rodinia assembly: Science, v. 304, p. 1126-1129. Reprint available at: http://www.sciencemag.org/cgi/reprint/1096329v1?ijkey=svPbmTcHfQwjs&keytype=ref&siteid=sci

2004 Hanson, R.E., Gose, W.A., Crowley, J.L., Ramezani, J., Bowring, S.A., Bullen, D.S., Hall, R.P., Pancake, J.A., and Mukwakwami, J., Paleoproterozoic intraplate magmatism and basin development on the Kaapvaal craton: age, paleomagnetism and geochemistry of ~1.93 to ~1.87 Ga post-Waterberg dolerites: South African Journal of Geology, v. 107, p. 233-254.

2003 Hanson, R.E., Proterozoic geochronology and tectonic evolution of southern Africa, in Yoshida, M., Windley, B.F., and Dasgupta, S. (eds.), Proterozoic East Gondwana: supercontinent assembly and breakup: Geological Society of London Special Publication 206, p. 427-463.

2003 Hargrove, U.S., Hanson, R.E., Martin, M.W., Blenkinsop, T.G., Bowring, S.A., Walker, N., and Munyanyiwa, H., Tectonic evolution of the Zambezi orogenic belt: geochronological, structural, and petrological constraints from northern Zimbabwe: Precambrian Research, v. 123, p. 159-186.

2003 Singletary, S.J., Hanson, R.E., Martin, M.W., Crowley, J.L., Bowring, S.A., Key, R.M., Ramokate, L.V., Direng, B.B., and Krol, M.A., Geochronology of basement rocks in the Kalahari Desert, Botswana, and implications for regional Proterozoic tectonics: Precambrian Research, v. 121, p. 47-71.

2001 Majaule, T., Hanson, R.E., Key, R.M., Singletary, S.J., Martin, M.W., and Bowring, S.A., The Magondi belt in northeast Botswana: regional relations and new geochronological data from the Sua Pan area: Journal of African Earth Sciences, v. 32, p. 257-267.

2001 Vinyu, M.L., Hanson, R.E., Martin, M.W., Bowring, S.A., Jelsma, H.A., and Dirks, P.H.G.M., U-Pb zircon ages from a craton-margin Archaean orogenic belt in northern Zimbabwe: Journal of African Earth Sciences, v. 32, p. 103-114.

1999 Vinyu, M.L., Hanson, R.E., Martin, M.W., Bowring, S.A., Jelsma, H.A., Krol, M.A., and Dirks, P.H.G.M., U-Pb and 40Ar/39Ar geochronological constraints on the tectonic evolution of the easternmost part of the Zambezi orogenic belt, northeast Zimbabwe: Precambrian Research, v. 98, p. 67-82.

1998 Hanson, R.E., Martin, M.A., Bowring, S.A., and Munyanyiwa, H., U-Pb zircon age for the Umkondo dolerites, eastern Zimbabwe: 1.1 Ga large igneous province in southern Africa/East Antarctica and possible Rodinia correlations: Geology, v. 26, p. 1143-1146.

1998 Hanson, R.E., Singletary, S.J., Martin, M.A., Bowring, S.A., Key, R.M., Majaule, T., Mapeo, R.B.M., Ramokate, L.V., Direng, B., and McMullan, S.R., Geochronology of Proterozoic basement terranes in the Kalahari region of Botswana: progress report: Abstracts, International Conference on the Role of a National Geological Survey in Sustainable Development (Geological Survey of Botswana, Gaborone, Botswana, June 23-25), p. 41-43.

1998 Hanson, R.E., Hargrove, U.S., Martin, M.A., Bowring, S.A., Krol, M.A., Hodges, K.V., Munyanyiwa, H., and Blenkinsop, T.G., New geochronological constraints on the tectonic evolution of the Pan-African Zambezi belt, south-central Africa: Journal of African Earth Sciences, v. 27, no. 1A, p. 104-105 (special abstract issue for 10th International Gondwana Conference, Capetown, South Africa, June 28-July 4).

1997 Munyanyiwa, H., Hanson, R.E., Blenkinsop, T.G., and Treloar, P.J., Geochemistry of amphibolites and quartzofeldspathic gneisses in the Pan-African Zambezi belt, NW Zimbabwe: evidence for bimodal magmatism in a continental rift setting: Precambrian Research, v. 81, p. 179-196.

1997 Wilson, T.J., Grunow, A.M., and Hanson, R.E., Gondwana assembly: the view from southern Africa and East Gondwana: Journal of Geodynamics, v. 23, p. 263-286.

1996 Grunow, A., Hanson, R.E., and Wilson, T.J., Were aspects of Pan-African deformation linked to Iapetus opening? Geology, v. 24, p. 1063-1066.

1994 Hanson, R.E., Wilson, T.J., and Munyanyiwa, H., Geologic evolution of the Neoproterozoic Zambezi orogenic belt in Zambia: Journal of African Earth Sciences, v. 18, p. 135-150.

1993 Hanson, R.E., Wardlaw, M.S., Wilson, T.J., and Mwale, G., U-Pb zircon ages from the Hook granite massif and Mwembeshi dislocation: constraints on Pan-African deformation, plutonism, and transcurrent shearing in central Zambia: Precambrian Research, v. 63, p. 189-209.

1993 Wilson, T.J., Hanson, R.E., and Wardlaw, M.S., Late Proterozoic evolution of the Zambezi belt, Zambia: implications for regional Pan-African tectonics and shear displacements in Gondwana, in Findlay, R.H., Unrug, R., Banks, M.R., and Veevers, J.J. (eds.), Gondwana 8 - assembly, evolution, and dispersal (Gondwana 8 Symposium Volume): Balkema, Rotterdam, p. 69-82.

1988 Hanson, R.E., Wilson, T.J., and Wardlaw, M.S., Deformed batholiths in the Pan-African Zambezi belt, Zambia: age and implications for regional Proterozoic tectonics: Geology, v. 16, p. 1134-1137.

1988 Hanson, R.E., Wilson, T.J., Brueckner, H.K., Onstott, T.C., Wardlaw, M.S., Johns, C.C., and Hardcastle, K.C., Reconnaissance geochronology, tectonothermal evolution, and regional significance of the Middle Proterozoic Choma-Kalomo block, southern Zambia: Precambrian Research, v. 42, p. 39-61.

1988 Munyanyiwa, H., and Hanson, R.E., Geochemistry of marbles and calc-silicate rocks in the Pan-African Zambezi belt, Zambia: Precambrian Research, v. 38, p. 177-200.

Northern Sierran geology: Jurassic granodiorite (light-colored outcrops to left) intruding Jurassic island-arc deposits to right. See Hanson et al. (1996).	Paleozoic submarine island-arc strata, northern Sierra Nevada. Submarine volcaniclastic debris-flow deposit interbedded with radiolarian chert in Upper Devonian Sierra Buttes Formation. See Hanson et al. (2000).

Northern Sierra Nevada, California

My interest in this region began with my Ph.D. research, which focused on Paleozoic island-arc rocks in the Northern Sierra terrane and included documentation of a tilted Late Devonian volcano-plutonic system exposed in cross section. More recently, my students and I have studied the nature, timing, and interrelations of volcanic arc construction, regional deformation, and batholith emplacement during the Jurassic and Cretaceous evolution of this part of the Sierra Nevada. One result of our detailed mapping has been the recognition of complex, large-scale masses of quenched and disrupted intrusive rock that formed when magma was injected into and intermixed with wet sediment at shallow levels beneath the sea floor. Although still poorly understood, such quenched, high-level intrusive complexes are likely to be common facies elements in submarine arc sequences and provide important insights into processes involved in the initiation of explosive hydrovolcanic eruptions. Another significant result has been the discovery that voluminous granitoid plutons previously considered as Cretaceous parts of the Sierra Nevada batholith were emplaced in the Middle Jurassic during a major episode of contractional deformation along the convergent margin, which has implications for regional models of Jurassic terrane accretion and interrelations between plutonism and orogenic pulses in arc systems.

Relevant Publications:

2004 Berkebile, M.S., Hanson, R.E., Gose, W.A., and Harwood, D.S., Geologic and paleomagnetic studies of a Pliocene volcanic debris-avalanche deposit in the northern Sierra Nevada, California: Geological Society of America Abstracts with Programs, v. 36, no. 4, p. 9.

2003 Templeton, J.H., and Hanson, R.E., Jurassic submarine arc-apron deposits and associated magma/wet-sediment interaction, northern Sierra Nevada, California: Journal of Volcanology and Geothermal Research, v. 128, p. 299-326.

2000 Hanson, R.E., Girty, G.H., Harwood, D.S., and Schweickert, R.A., Paleozoic subduction complex and Paleozoic-Mesozoic island-arc volcano-plutonic assemblages in the northern Sierra terrane, in Lageson, D.R., Peters, S.G., and Lahren, M.M. (eds.), Great Basin and Sierra Nevada: Geological Society of America Field Guide Series, v. 2, 255-277.

1999 Hanson, R.E., and Hargrove, U.S., Processes of magma/wet sediment interaction in a large-scale Jurassic andesitic peperite complex, northern Sierra Nevada, California: Bulletin of Volcanology, v. 60, p. 610-626.

1999 Schweickert, R.A., Hanson, R.E., and Girty, G.H., Accretionary tectonics of the Western Sierra Nevada Metamorphic Belt, in Wagner, D.L., and Graham, S.A. (eds.), Geologic Field Trips in Northern California (for Centennial Meeting of the Cordilleran Section of the Geological Society of America: California Division of Mines and Geology Special Publication 119, p. 33-79.

1998 Hargrove, U.S., and Hanson, R.E., Large-scale peperites associated with a multiphase andesitic sill intruded into wet sediments, Jurassic, northern Sierra terrane, California: The Compass (Journal of Earth Sciences, Sigma Gamma Epsilon), v. 74, p. 95-102.

1998 Kulow, M.J., Hanson, R.E., Girty, G.H., Girty, M.S., and Harwood, D.S., Cretaceous plutonic rocks in the Donner Lake-Cisco Grove area, northern Sierra Nevada, California: The Compass (Journal of Earth Sciences, Sigma Gamma Epsilon), v. 74, p. 69-76.

1998 Mielke, K.L., Hanson, R.E., Girty, G.H., Girty, M.S., and Schweickert, R.A., Jurassic island-arc rocks in the Webber Peak and Meadow Lake areas, northern Sierra terrane, California: The Compass (Journal of Earth Sciences, Sigma Gamma Epsilon), v. 74, p. 77-86.

1998 Phillipson, S.E., Hanson, R.E., Girty, G.H., and Girty, M.S., Petrology and geochronology of the intrusive suite of Haypress Creek (Middle Jurassic), northern Sierra terrane, California: The Compass (Journal of Earth Sciences, Sigma Gamma Epsilon), v. 74, p. 87-94.

1997 Hargrove, U.S., and Hanson, R.E., Geology of the Huntley Mill Lake sill complex: a multiphase peperitic sill intruded into wet sediments, Jurassic, northern Sierra Nevada, California, in Girty, G.H., Hanson, R.E., and Cooper, J.D. (eds.), Geological evolution of the western Cordillera: perspectives from undergraduate research: Society for Sedimentary Geology (SEPM), Pacific Section, Book 82, p. 111-122.

1997 Kulow, M.J., Hanson, R.E., and Girty, G.H., The Big Bend shear zone: Early Cretaceous ductile deformation associated with pluton emplacement in the Northern Sierra terrane, California, in Girty, G.H., Hanson, R.E., and Cooper, J.D. (eds.), Geological evolution of the western Cordillera: perspectives from undergraduate research: Society for Sedimentary Geology (SEPM), Pacific Section, Book 82, p. 79-90.

1996 Hanson, R.E., Girty, G.H., Girty, M.S., Hargrove, U.S., Harwood, D.S., Kulow, M.J., Mielke, K.L., Phillipson, S.E., Schweickert, R.A., and Templeton, J.H., Paleozoic and Mesozoic arc rocks in the Northern Sierra terrane, in Girty, G.H., Hanson, R.E., Harwood, D.S., and Schweickert, R.A. (eds.), The Northern Sierra terrane and associated Mesozoic magmatic units: implications for the tectonic history of the western Cordillera: Society for Sedimentary Geology (SEPM), Pacific Section, Book 81, p. 25-55.

1995 Girty, G.H., Hanson, R.E., Girty, M.S., Schweickert, R.A., Harwood, D.S., Yoshinobu, A.S., Bryan, K.A., Skinner, J.E., and Hill, C.A., Timing of emplacement of the Haypress Creek and Emigrant Gap plutons: implications for the timing and controls of Jurassic orogenesis, northern Sierra Nevada, California, in Miller, D.M., and Busby, C. (eds.), Jurassic magmatism and tectonics of the North American Cordillera: Geological Society of America Special Paper 299, 191-201.

1993 Hanson, R.E., Girty, G.H., Harwood, D.S., Schweickert, R.A., Templeton, J.H., Yoshinobu, A.S., Wracher, M.D., and Girty, M.S., Devonian and Jurassic volcano-plutonic associations in the Northern Sierra terrane: implications for arc evolution and Mesozoic deformation, in Lahren, M.M., Trexler, J.H., Jr., and Spinosa, C. (eds.), Crustal evolution of the Great Basin and the Sierra Nevada: Geological Society of America, Field Trip Guidebook for 1993 Cordilleran/Rocky Mountain Sections Joint Meeting, p. 97-128.

1991 Hanson, R.E., Quenching and hydroclastic disruption of andesitic to rhyolitic intrusions in a submarine island-arc sequence, northern Sierra Nevada, California: Geological Society of America Bulletin, v. 103, p. 804-816.

1988 Hanson, R.E., Saleeby, J.B., and Schweickert, R.A., Composite Devonian island-arc batholith in the northern Sierra Nevada, California: Geological Society of America Bulletin, v. 100, p. 446-457.

1986 Hanson, R.E., and Schweickert, R.A., Stratigraphy of mid-Paleozoic island-arc rocks in part of the northern Sierra Nevada, Sierra and Nevada Counties, California: Geological Society of America Bulletin, v. 97, p. 986-998.

1984 Schweickert, R.A., Bogen, N.L., Girty, G.H., Hanson, R.E., and Merguerian, C., Timing and structural expression of the Nevadan orogeny, Sierra Nevada, California: Geological Society of America Bulletin, v. 95, p. 967-979.

1982 Hanson, R.E., and Schweickert, R.A., Chilling and brecciation of a Devonian rhyolite sill intruded into wet sediments, northern Sierra Nevada, California: Journal of Geology, v. 90, p. 717-724.

Jurassic rhyolite peperite, southern Chile. Quenched, brecciated rhyolite (light-colored) in a matrix of black, disrupted mudstone. See Hanson and Wilson (1993).	Jurassic volcanic rocks, Transantarctic Mountains. Flood basalts (black) at top of Mt. Kirkpatrick rest on basaltic pyroclastic deposits (dark brown, immediately below black cliffs). See Hanson and Elliot (1996).

My work in southern South America has primarily focused on the paleovolcanology of voluminous submarine rhyolites emplaced within a Jurassic proto-marginal basin in the southern Andes. The rocks show a number of unusual features that reflect extensive interaction between rhyolitic magma and seawater or wet sediment, and the sequence as a whole contrasts markedly with better known subaerial rhyolitic ignimbrite fields associated with continental extension.

In Antarctica I have worked on widespread Jurassic subaerial basaltic pyroclastic deposits that formed just before outpouring of flood basalts along the length of the Transantarctic Mountains. Our work has shown that these unusual pyroclastic deposits reflect explosive subterranean interaction between basaltic magma and groundwater within a continental-scale volcano-tectonic rift zone related to incipient stages in Gondwana fragmentation. This has implications for models dealing with relations between plume-generated mafic magmatism and continental extension during supercontinent breakup. Similar deposits are now being recognized in other flood-basalt provinces, suggesting that explosive phreatomagmatic volcanism may be much more common in such provinces than previously realized.

2001 Elliot, D.H., and Hanson, R.E., Origin of widespread, exceptionally thick phreatomagmatic tuff breccia in the Middle Jurassic Prebble and Mawson Formations, Antarctica: Journal of Volcanology and Geothermal Research, v. 111, p. 183-201.

1996 Hanson, R.E., and Elliot, D.H., Rift-related Jurassic basaltic phreatomagmatism in the central Transantarctic Mountains: precursory stage to flood-basalt volcanism: Bulletin of Volcanology, v. 58, p. 327-347.

1994 Miller, C.A., Barton, M., Hanson, R.E., and Fleming, T.H., An Early Cretaceous volcanic arc/marginal basin transition zone, Peninsula Hardy, southernmost Chile: Journal of Volcanology and Geothermal Research, v. 63, p. 33-58.

1993 Hanson, R.E., and Wilson, T.J., Large-scale rhyolite peperites (Jurassic, southern Chile): Journal of Volcanology and Geothermal Research, v. 54, p. 247-264.

1991 Hanson, R.E., and Wilson, T.J., Submarine rhyolitic volcanism in a Jurassic proto-marginal basin, southern Andes, Chile and Argentina, in Harmon, R.S., and Rapela, C.W. (eds.), Andean magmatism and its tectonic setting: Geological Society of America Special Paper 265, p. 13-27.

Cambrian Rhyolites, Southern Oklahoma Flow banding crossed by columnar jointing in Cambrian rhyolite lava, Bally Mountain area, SW Oklahoma.	Cambrian rhyolite flow Rhyolite lava flow 400 m thick exposed on top of Bally Mountain, north of main mass of Wichita Mountains in SW Oklahoma.

I have supervised several B.S. and M.S. theses on the physical volcanology of extensive Cambrian rhyolites emplaced during rifting within the Southern Oklahoma aulacogen.Working in the Wichita Mountains in southwestern Oklahoma, we have established a volcanic stratigraphy and have mapped out individual flows within parts of this ancient volcanic field for the first time. Our work indicates that the rhyolites may be analogous to laterally extensive felsic lava flows ("flood rhyolites") documented in some other continental volcanic provinces. The rhyolites show a complex textural evolution reflecting vertical variations in degassing, primary crystallization, and devitrification histories within individual thick cooling units. The ultimate goal of our work is to develop a general model for the emplacement and textural evolution of the southern Oklahoma rhyolites that would help in the recognition and interpretation of other examples of these types of poorly understood felsic flood lavas, for which there are no modern analogues.

Relevant Publications:

2010 McCleery, D.A., and Hanson, R.E., Geochemistry of Cambrian rhyolites in the Wichita Mountains, southwestern Oklahoma: A-type felsic volcanism within the southern Oklahoma aulacogen: Geological Society of America Abstracts with Programs, v. 42, no. 2, p. 105-106.

2009 Hanson, R.E., McCleery, D.A., Crowley, J.L, Bowring, S.A., Burkholder, B.A., Finegan, S.A., Philips, C.M., and Pollard, J.B., Large-scale Cambrian rhyolitic volcanism in southern Oklahoma related to opening of Iapetus: Geological Society of America Abstracts with Programs, v. 41, no. 2, p. 14.

2006 Burkholder, B.K., and Hanson, R.E., Carlton Rhyolite on Zodletone Mountain, southern Oklahoma: Geological Society of America Abstracts with Programs, v. 38, no. 1, p. 30.

2006 Finegan, S.A., and Hanson, R.E., Field relations of the Carlton Rhyolite in the Fort Sill area, southwestern Oklahoma: Geological Society of America Abstracts with Programs, v. 38, no. 1, p. 30.

2001 Philips, C.M., and Hanson, R.E., Anatomy of an A-type Cambrian felsic volcanic field: Carlton Rhyolite in the Blue Creek Canyon area, Wichita Mountains, southern Oklahoma: Geological Society of America Abstracts with Programs, v. 33, no. 5, p. A24.

2000 Pollard, J., and Hanson, R.E., Carlton Rhyolite at Bally Mountain, Southwest Oklahoma: evidence for extensive A-type Cambrian felsic flows in the Southern Oklahoma aulacogen: Geological Society of America Abstracts with Programs, v. 32, no. 3, p. A39.

1992 Bigger, S.E., and Hanson, R.E., Devitrification textures and related features in the Carlton Rhyolite in the Blue Creek Canyon area, Wichita Mountains, southwestern Oklahoma: Oklahoma Geology Notes, v. 52, p. 124-142.

Explosive Eocene phreatomagmatic volcanism, West Texas Small basaltic volcanic neck cutting Cretaceous strata north of Big Bend National Park. See Befus et al. (2009).	Eocene hypabyssal basaltic dike/sill network Basalt intrusions are dark gray to black and intrude Cretaceous to Paleocene sedimentary strata near Study Butte. See Dietz et al. (2010).

West Texas

Volcanological studies in West Texas have partly focused on detailed mapping and facies analysis of recently discovered Cretaceous near-vent basaltic maar deposits in the Big Bend region of the Trans-Pecos igneous province, in collaboration with John Breyer and Art Busbey at TCU and Tom Lehman at Texas Tech. We infer that the maar deposits were erupted from subaerial phreatomagmatic volcanoes within a western extension of the intraplate Balcones igneous province.

Other recent work in West Texas deals with Eocene alkaline hypabyssal intrusions that exhibit a range of nonexplosive to explosive interactions between magma and unconsolidated, groundwater-rich host sediment. Of particular interest are complex diatreme root zones inferred to have fed phreatomagmatic volcanoes now eroded away. This work suggests that Trans-Pecos Texas may represent an important locale for the study of phreatomagmatic processes at shallow levels in the subsurface.

Relevant Publications:

2010 Dietz, J.E., Hanson, R.E., Miggins, D.P, and Winkler, C.E., Eocene(?) basaltic dike-sill network and phreatomagmatic vents emplaced into unlithified Cretaceous to Paleocene strata, Study Butte area, Big Bend National Park, west Texas: Geological Society of America Abstracts with Programs, v. 42, no. 2, p. 106.

2009 Befus, K.S., Hanson, R.E., Miggins, D.P., Breyer, J.A., and Busbey, A.B., Nonexplosive and explosive magma/wet-sediment interaction during emplacement of Eocene intrusions into Cretaceous to Eocene strata, Trans-Pecos igneous province, West Texas: Journal of Volcanology and Geothermal Research, v. 181, p. 155-172.

2009 Winkler, C.E., Hanson, R.E., and Miggins, D.P., A newly discovered Eocene(?) basaltic phreatomagmatic vent complex in Big Bend National Park, Trans-Pecos Texas: Geological Society of America Abstracts with Programs, v. 41, no. 2, p. 10-11.

2008 Befus, K.S., Hanson, R.E., Lehman, T.M., and Griffin, W.R., Cretaceous basaltic phreatomagmatic volcanism in West Texas: maar complex at Peña Mountain, Big Bend National Park: Journal of Volcanology and Geothermal Research, v. 173, p. 245-264.

2007 Breyer, J.A., Busbey, A.B., Hanson, R.E., Befus, K.E., Griffin, W.R., Hargrove, U.S., and Bergman, S.C., Evidence for Late Cretaceous volcanism in Trans-Pecos Texas: Journal of Geology, v. 115, p. 243-251.