Boulder, CO, USA - Geosphere articles published online 22 Nov. 2011 are provided below. Highlights include additions to two themed issues: (1) New Developments in Grenville Geology and (2) ANDRILL McMurdo Ice Shelf (MIS) and Southern McMurdo Sound (SMS) Drilling Projects. Other articles include two studies in Mexico - one in Sonora and one in Acapulco; a study of Pleistocene Lake Bonneville; and modeling studies of magma "plumbing systems."
Keywords: New York State, Adirondack Lowlands, kinematics, ANDRILL, McMurdo, Pleistocene, Lake Bonneville, Idaho, Sonora, Laramide magmatic arc, Tarahumara Formation, rapakivi, Acapulco, Mexico, modeling studies.
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Timing and kinematics of deformation in the northwest Adirondack Lowlands, New York State: Implications for terrane relationships in the southern Grenville Province
Graham B. Baird and Catherine H. Shrady, Earth Sciences, University of Northern Colorado, Campus Box 100, Greeley, Colorado 80639, USA. Posted online 22 Nov. 2011; doi: 10.1130/GS689.1.
Mountain belts are constructed of blocks of crust with different geologic histories. Understanding the relationship between the blocks of crust is key in determining how the mountain belt is formed. A portion of the deeply eroded 1700-980 million-year-old mountain belt called the Grenville Province was studied southeast of the St. Lawrence River in New York State to better understand when the rocks were deformed and metamorphosed. It was found that the rocks were deformed and metamorphosed at about 1185-1145 million years ago during what is called the Shawinigan Orogeny, one of the periods of mountain building that helped form the Grenville Province. This information and a study of the current knowledge regarding the Grenville rocks of northwestern New York State and southeast Ontario, Canada, reveal that the rocks in these two regions are different blocks of crust with different geologic histories. This article is a new addition to the themed issue: New Developments in Grenville Geology.
Thermal properties of the AND-2A borehole in the southern Victoria Land Basin, McMurdo Sound, Antarctica
H. Schroder et al., Leibniz Institute for Applied Geophysics, Stilleweg 2, D-30655 Hannover, Germany. Posted online 22 Nov. 2011; doi: 10.1130/GS690.1.
The ANDRILL (Antarctic Geological Drilling Program) Southern McMurdo Sound Project (SMS) drilled an 1138-m-deep borehole (AND-2A) in the southern Victoria Land Basin in the Ross Sea, Antarctica, during the 2007-2008 austral spring. As part of the project, an extensive downhole logging program was carried out in this borehole, including logs of temperature and natural radioactivity. These logging data were combined with lab measurements of the thermal conductivity of core samples to deduce several thermal parameters of the borehole country rock. Our intent is to present the results of these analyses, which provide important new constraints on thermal properties that have a general bearing on understanding the geodynamic evolution of the Victoria Land Basin within this sector of the West Antarctic Rift system. Tectonic records from the Antarctic continent are sparse but of widespread interest, yet there are only a few temperature logs from boreholes in this area. This article is an addition to the ANDRILL McMurdo Ice Shelf (MIS) and Southern McMurdo Sound (SMS) Drilling Projects themed issue.
Short- and long-term effects in the school system of a research immersion experience for science educators: An example from ANDRILL (Antarctic Geological Drilling)
Matteo Cattadori et al., Museo Tridentino di Scienze Naturali (Tridentine Museum of Natural Sciences), Via Calepina, 14, Trento, Italy. Posted online 22 Nov. 2011; doi: 10.1130/GS678.1.
The ANtarctic geological DRILLing (ANDRILL) program is a multinational initiative, involving collaboration among the Antarctic programs of Germany, Italy, New Zealand, and USA. ANDRILL has implemented an innovative educational and public outreach program known as ARISE (ANDRILL Research Immersion for Science Educators), which has actively immersed a group of selected educators in every phase of the research, from participation in field activities to discussion of the scientific results. This method of research immersion has led to an impressive list of achievements, including the development of quality outreach initiatives and diverse educational materials, the involvement of a large number of schools using these resources, the creation of an international network of strongly motivated polar geoscience educators, and the realization of new and unexpected professional opportunities for educators. This article illustrates the short-, middle- and long-term impacts of the ARISE Program, primarily as observed in the scholastic system of Italy and more generally with respect to Earth System Sciences education, and it is an addition to the ANDRILL McMurdo Ice Shelf (MIS) and Southern McMurdo Sound (SMS) Drilling Projects themed issue.
New insights into the outlet conditions of late Pleistocene Lake Bonneville, southeastern Idaho, USA
Susanne U. Janecke and Robert Q. Oaks, Jr., Dept. of Geology, 4505 Old Main Hill, Utah State University, Logan, Utah 84322-4505, USA. Posted online 22 Nov. 2011; doi: 10.1130/GS587.1.
During the last ice age, the world's premier pluvial lake, Lake Bonneville, formed in Utah and parts of southeastern Idaho. The lake had no outlet for most of its history, but rose to an overflow point in SE Idaho about 18 thousand years ago. After stable overflow for roughly one thousand years, the outlet failed, produced the huge Bonneville flood, and the lake dropped 100 m. There is evidence for a large earthquake on the Riverdale normal fault, near the outlet, about the time of the flood. This raises the possibility that a large earthquake triggered the Bonneville flood and that the weight of the extra water in the short-lived, deep-lake episode induced the earthquake and the flood. After the flood, the north shore of Lake Bonneville was at Swan Lake, ~11 km south of the modern drainage divide. A dry and warm climate oscillation called the Heinrich 1 event may have incised the outlet and caused the lake to shift its northern shore and outlet even farther south, from Swan Lake to the Clifton, Idaho, area for a fairly short period of time at about 16,000 years ago. A major meandering river flowed northward from this outlet, and its abandoned riverbed is preserved in Round Valley. These outlets for the Provo levels of Lake Bonneville are far south of Red Rock Pass, the location favored by most researchers except G.K. Gilbert (1890). The Great Basin's modern drainage divide at Red Rock Pass formed in the Holocene when a small alluvial fan filled the dry bed of the north-flowing paleoriver.
Stratigraphy, geochronology, and geochemistry of the Laramide magmatic arc in north-central Sonora, Mexico
Carlos M. González-León et al., Instituto de Geología, Estación Regional del Noroeste, Universidad Nacional Autónoma de México, Apartado Postal 1039, Hermosillo, Sonora, México 83000. Posted online 22 Nov. 2011; doi: 10.1130/GS679.1.
Widespread outcrops of a volcanic succession and related plutonic rocks of Late Cretaceous to Eocene age compose the Laramide magmatic arc in the state of Sonora, northwestern Mexico. We studied these rocks in the Arizpe-Mazocahui quadrangle located in the north-central part of Sonora where the more-than-4-km-thick volcanic succession is composed of stratified rhyolitic to dacitic ignimbrite, andesite flows, tuffs, volcaniclastic rocks, and subordinate lacustrine strata. This succession is assigned to the Tarahumara Formation, and its age is constrained between ca. 80 and 59 Ma. The Tarahumara shows marked lateral facies change within the study area, and toward northeastern Sonora, it grades into the coeval, fluvial, and lacustrine rocks of the Cabullona Group. Several monzonitic to granitic plutons that intrude this formation have ages between 71 and 50 Ma, including the El Jaralito batholith in the southern part of the area. The Laramide magmatic rocks show calcalkaline differentiation trends typical of continental magmatic arcs, and the isotope geochemistry indicates a strong contribution from a mature continental crust to the magmas. The Laramide arc in the study region was built over juxtaposed basements of the Proterozoic Caborca and Mazatzal provinces, and the Nd, Sr and Pb isotope data help to better constrain this crustal boundary. The data also permit comparison with previously defined Laramide isotopic provinces of Sonora and Arizona. A basal conglomerate of the Tarahumara Formation that unconformably overlies deformed Proterozoic igneous rocks and Neoproterozoic to Lower Cretaceous strata constrains the age of the younger contractional tectonic event of Sonora between Cenomanian and early Campanivan time.
Petrogenesis and thermobarometry of the ~50 Ma rapakivi granite-syenite Acapulco intrusive: Implications for post-Laramide magmatism in southern Mexico
Guillermo A. Hernandez-Pineda et al., Instituto de Geología, Universidad Nacional Autonoma de Mexico, Ciudad Universitaria, 04510 Mexico, D.F., Mexico. Posted online 22 Nov. 2011; doi: 10.1130/GS744.1.
About 50 million years ago, the Acapulco intrusion took place in a complex tectonic scenario in Southern Mexico. This intrusion is part of what is known as the 50-60 Ma magmatic event that is related to the final stage of the Laramide orogeny. Based on a comprehensive technique application to Acapulco's rocks, this work represents a contribution to the regional geological understanding of this topic.
Magma addition and flux calculations of incrementally constructed magma chambers in continental margin arcs: Combined field, geochronologic, and thermal modeling studies
Scott R. Paterson et al., Dept. of Earth Sciences, University of Southern California, Los Angeles, California 90089-0740, USA. Posted online 22 Nov. 2011; doi: 10.1130/GS696.1.
Plutons, the now frozen parts of magma plumbing systems underneath volcanoes, are thought to be largely constructed by the amalgamation of many different pulses of magma (melt plus crystals) that rose through the crust and then got trapped at the pluton construction site. This paper by Scott R. Paterson of the University of Southern California and colleagues addresses the challenges of determining how these "magma plumbing systems" and plutons evolve over time, their potential thermal histories, and under what geologic circumstances large magma chambers can form.
Journal
Geosphere