Earth Sciences Commons^™

Evidence For Monazite Growth At ~1.6 Ga And ~1.4 Ga In Proterozoic Migmatites Of The Santa Fe Range, North-Central New Mexico, Dan Heuer, Christopher Daniel

Dan Heuer

Supracrustal Proterozoic migmatites exposed in the Aspen Basin area of the Santa Fe Range represent the northernmost exposure of the Mazatzal (~1.65 Ga) crustal province. Two migmatite samples (plag-bt-ms-qtz-hem±grt) yield preliminary in-situ electron microprobe U-Th-total Pb ages from monazite that are ~1.4 Ga; however, 1 grain yields a core age of ~1.6 Ga.

Monazite are generally aligned subparallel to a regional moderately, south-dipping foliation (S1), indicating monazite growth was pre- or synkinematic. X-ray mapping of monazite shows variable U, Th, Pb, Y, and Ce zoning, interpreted to reflect three periods of monazite growth. Xenotime are relatively unzoned in most elements, …

Monazite Thermochronometry In Migmatites From North-Central New Mexico: Contact Metamorphism Or A Regional Mid-Crustal Melt-Rich Layer?, Dan Heuer, Christopher Daniel, Joseph Pyle

Dan Heuer

Monazite thermochronometry demonstrates that Proterozoic migmatites exposed in the central Santa Fe range and the Rincon range of north-central New Mexico preserve high-temperature monazite that crystallized near 1.4 Ga. No 1.4 Ga plutons are exposed in the Rincon range; however, undated plutons are present in the Santa Fe Range and a contact metamorphic setting is possible. Alternatively, partial melting in these two areas may represent a regional, mid-crustal, melt-rich layer.

Subhedral monazite in both areas are commonly aligned subparallel with the dominant regional foliation. Monazite from the central Santa Fe range show three distinct compositional domains. Relatively high-Y cores yield …

Evidence For A Normal P-T Gradient And Top-North Displacement In The Central Bhutan Himalaya: Shear Sense And P-T Estimates From The Chekha Fm. And The Greater Himalayan Sequence, Dan Heuer, John Witmer, Adam Kahler, M. Ryan Delaney, Adam Dennis, Djordje Grugic, Christopher Daniel

Dan Heuer

Upper amphibolite facies metasedimentary rocks at the base of the Chekha Fm overlie the partially melted Greater Himalaya Sequence (GHS) and likely correlate with the Everest Series in the Mt. Everest massif. From the base of the Chekha Fm, metamorphic grade decreases to slates and unmetamorphosed rocks of the Tethyan sedimentary series (TSS) with increasing elevation. The Chekha Fm is separated from both the GHS and the overlying TSS by normal-sense shear zones related to the south Tibetan Detachment zone (STDZ).

Five samples from near the base of the Chekha Fm are characterized by the mineral assemblage Grt-Bt-St. Garnet crystals …

Overview Of Radiometric Ages In Three Allochthonous Belts Of Northern Venezuela: Old Ones, New Ones, And Their Impact On Regional Geology, V Sisson, H Lallemant, M Ostos, Ann Blythe, L Snee, P Copeland, J Wright, R Donelick, L Guth

Ann Blythe

No abstract provided.

Exploring The Persistence Of Sorted Bedforms On The Inner-Shelf Of Wrightsville Beach, North Carolina, Benjamin Gutierez, George Voulgaris, Robert Thieler

George Voulgaris

Geological studies offshore of Wrightsville Beach, North Carolina reveal subtle large-scale regions of coarse sand with gravel and shell hash (widths between 100 and 200 m and negative relief of ∼1 m) that trend obliquely to the coast. It was previously suggested that these regions serve as conduits for sand exchange between the shoreface and inner shelf during storm-associated downwelling. Consequently they were classified as rippled scour depressions. More recently, the role of alongshore flows and self-organization as a result of inhibited settling of fine sand has been discussed. In this study, 45 days of near-bed current measurements were analyzed …

Effect Of Channel Bifurcation On Residual Estuarine Circulation: Winyah Bay, South Carolina, Yong Kim, George Voulgaris

George Voulgaris

The residual circulation pattern of Winyah Bay, the fourth largest estuary on the eastern coast of the US, is examined using stationary and shipborne current measurements during periods of low freshwater discharge. The estuary has a complex morphology with a single channel and narrow banks at the river entrance and the bay mouth, and a bifurcated channel system (main and western channels, respectively) in the middle part that appears to affect the residual circulation. Overall, the upper (single channel morphology) and middle (dual-channel morphology) parts of the estuary exhibit a baroclinic residual circulation. The presence of bifurcated channels in the …

Sustainable Development And Natural Governance: The Challenges Ahead, John Dernbach, Dan Tarlock

John C. Dernbach

No abstract provided.

Integrating High-Precision Aftershock Locations And Geodetic Observations To Model Coseismic Deformation Associated With The 1995 Kozani-Grevena Earthquake, Greece, Phillip G. Resor, David Pollard, T J. Wright, G C. Beroza

Phillip G Resor

We integrate high-precision aftershock locations with geodetic inverse modeling to create a more complete kinematic model for the Kozani-Grevena earthquake sequence. Using the double-difference algorithm, we have improved relative hypocentral locations by a factor of ∼7 and thus imaged the details of the fault network associated with the seismic sequence. The interpreted fault network consists of multiple segments including (1) a master normal fault that strikes nearly due west and dips toward the north at 43°, extending from 6 to 15 km depth; (2) an upper segment that connects the top of the seismicity to the observed surface ruptures and …

Inverting For Slip On Three-Dimensional Fault Surfaces Using Angular Dislocations, Phillip G. Resor, David Pollard, Frantz Maerten, Laurent Maerten

Phillip G Resor

The increasing quality of geodetic data (synthetic aperture radar interferometry [INSAR] dense Global Positioning System [GPS] arrays) now available to geophysicists and geologists are not fully exploited in slip-inversion procedures. Most common methods of inversion use rectangular dislocation segments to model fault ruptures and therefore oversimplify fault geometries. These geometric simplifications can lead to inconsistencies when inverting for slip on earthquake faults, and they preclude a more complete understanding of the role of fault geometry in the earthquake process. We have developed a new three-dimensional slip-inversion method based on the analytical solution for an angular dislocation in a linear-elastic, homogeneous, …

Hartford Basin Cross Section – Southington To Portland, Ct, Phillip G. Resor, J Z. Deboer

Phillip G Resor

No abstract provided.

Laramie Peak Shear System, Central Laramie Mountains, Wyoming, Usa: Regeneration Of The Archean Wyoming Province During Palaeoproterozoic Accretion, Phillip G. Resor, Arthur W. Snoke

Phillip G Resor

The Laramie Peak shear system (LPSS) is a 10 km-thick zone of heterogeneous general shear (non-coaxial) that records significant tectonic regeneration of middle-lower crustal rocks of the Archean Wyoming province. The shear system is related to the 1.78–1.74 Ga Medicine Bow orogeny that involved the collision of an oceanic-arc terrane (Colorado province or Green Mountain block or arc) with the rifted, southern margin of the Wyoming province. The style and character of deformation associated with the LPSS is distinctive: a strong, penetrative (mylonitic) foliation commonly containing a moderately steep, SW-plunging elongation lineation. In mylonitic quartzo-feldspathic gneisses of the Fletcher Park …

Western End Of The Honey Hill Fault Along The Eastern Bank Of The Connecticut River, Phillip G. Resor, J Z. Deboer

Phillip G Resor

No abstract provided.

Knowledge Discovery From Multispectral Satellite Images, Arun D. Kulkarni

Arun Kulkarni

Constraining The Exhumation And Burial History Of The Safod Pilot Hole With Apatite Fission Track And (U-Th)/He Thermochronometry, Ann Blythe, M D’Alessio, R Bürgmann

Ann Blythe

[1] The San Andreas Fault Observatory at Depth (SAFOD) pilot hole traverses the upper 2 km of a site 1.8 km west of the San Andreas fault (SAF) near Parkfield, California. In order to evaluate the burial and exhumation history of the site and its relationship to the kinematics and mechanics of the SAF, we use 15 apatite fission-track (FT) and 5 (U-Th)/He analyses from pilot hole samples to document their thermal history. Sample ages decrease with depth: FT and (U-Th)/He ages range from ∼60 and ∼31 Ma, respectively, in the upper 800 m of the hole to ∼3 and …

Structural Correction Of Paleomagnetic Vectors Dispersed About Two Fold Axes And Application To The Duke Island (Alaska) Ultramafic Complex, Scott Bogue, C. Sherman Gromme

Scott Bogue

A new analysis of paleomagnetic data from the mid-Cretaceous (∼110 Ma) ultramafic complex at Duke Island (southeast Alaska) supports large poleward transport of the Insular superterrane relative to North America consistent with the Baja British Columbia hypothesis. Previous paleomagnetic work has shown that the characteristic remanence of the ultramafic complex predates kilometer-scale deformation of the very well developed cumulate layering but that the layering was not horizontal everywhere before the folding. It is possible, however, to estimate paleohorizontal for the Duke Island ultramafic complex because the postremanence deformation of the intrusion occurred about two well-defined and spatially separate fold axes. …

Decoupling Of Erosion And Precipitation In The Himalayas, D Burbank, Ann Blythe, J Putkonen, B Pratt-Sitaula, E Gabet, M Oskin, A Barros, T Ohja

Ann Blythe

The hypothesis that abrupt spatial gradients in erosion can cause high strain rates in active orogens has been supported by numerical models that couple erosional processes with lithospheric deformation via gravitational feedbacks1, 2, 3. Most such models invoke a 'stream-power' rule, in which either increased discharge or steeper channel slopes cause higher erosion rates. Spatial variations in precipitation and slopes are therefore predicted to correlate with gradients in both erosion rates and crustal strain. Here we combine observations from a meteorological network across the Greater Himalaya, Nepal, along with estimates of erosion rates at geologic timescales (greater than 100,000 yr) …

Using Information Literacy Standards To Improve Geoscience Courses, Aimee Dechambeau, Ira Sasowsky

Aimee deChambeau

Information literacy (IL) is the set of skills that enables a person to find, evaluate, and use information. Although IL is important in the geosciences, it is hard to teach because the information comes in so many forms. Most geoscience courses include work that implicitly addresses some IL issues. However, because of the importance of IL, it is worthwhile to explicitly include it as part of the curriculum. The Association of College and Research Libraries has developed Information Literacy Standards for Higher Education that may be used to assess an individual's level of information literacy. We introduce a method for …

Implications Of Distributed Crustal Deformation For Exhumation In A Portion Of A Transpressional Plate Boundary, Western Transverse Ranges, Southern California, Andrew Meigs, Dong Yule, Ann Blythe, Doug Burbank

Ann Blythe

Spatial and temporal patterns of exhumation are inextricably linked to patterns of crustal deformation because crustal deformation drives rock uplift. A new interpretation of a segment of the Pacific-North America transpressional plate boundary in southern California is analyzed in the context of crustal shortening, rock uplift, and exhumation. Deformation is partitioned between two structural anticlinoria formed above thrust faults that root into a mid-crustal décollement. The southern anticlinorium began growing after 5 Ma and is characterized by almost no topographic expression, rock uplift of ∼3 km, and exhumation of <1.2 km. Deposition in the Los Angeles basin on the south generally kept pace with growth of this anticlinorium. In contrast, the northern anticlinorium is younger, has a significant topographic expression, rock uplift of 2.5–4.0 km, and exhumation of ∼1.5–2 km. On-going surface uplift above the northern anticlinorium is suggested by the mismatch between the magnitude of rock uplift relative to the exhumation. These data emphasize that the distribution of deformation between faults in the upper and middle crust, crustal root formation in the lower crust, and flexural subsidence are primary controls of patterns of exhumation, which together dictate net surface uplift in active orogenic belts.

Geochemistry Of Kauai Shield-Stage Lavas: Implications For The Chemical Evolution Of The Hawaiian Plume, Scott Bogue, S. Mukhopadhyay, J.C. Lassiter, K.A. Farley

Scott Bogue

We measured He, Sr, Nd, Pb, and Os isotope ratios and major and trace element concentrations in stratigraphically and paleomagnetically controlled shield-stage lavas from Kauai, Hawaii. The range of 3He/4He ratios (17–28 RA) from Kauai is similar to that reported from Loihi and thus challenges the prevailing notion that high 3He/4He ratios are restricted to the preshield stage of Hawaiian magmatism. 3He/4He ratios vary erratically with stratigraphic position, and chronostratigraphic control from paleomagnetic data indicates very rapid changes in the 3He/4He ratios (up to 8 RA in ∼102 years). These variations in helium isotopic ratios are correlated with variations in …

No Frictional Heat Along The San Gabriel Fault, California: Evidence From Fission-Track Thermochronology, M.A. D’Alessio, Ann Blythe, R Bu¨Rgmann

Ann Blythe

Large earthquakes generate frictional heat, and the magnitude of heating is related to the slip magnitude, the applied effective normal stress, and the frictional strength of the fault. We looked for evidence of this heating in apatite fission-track age and track-length distributions of samples from adjacent to and within the San Gabriel fault zone in southern California. The fault is thought to be an abandoned major trace of the San Andreas fault system active from 13 to 4 Ma and has since been exhumed from depths of 2–5 km. At our sample locality, as much as 40 km of total …

Cretaceous−Cenozoic History Of The Southern Tan-Lu Fault Zone: Apatite Fission-Track And Structural Constraints From The Dabie Shan (Eastern China), J Grimmer, R Jonckheere, E Enkelmann, L Ratschbacher, B Hacker, Ann Blythe, G Wagner, Q Wue, S Liu, S Dong

Ann Blythe

Apatite fission-track (AFT) and structural data outline the Late Cretaceous−Cenozoic history of the southern Tan-Lu fault zone (TLFZ), one of Asia's major faults, the Triassic–Jurassic Dabie orogen, Earth's largest track of ultrahigh-pressure rock exposure, and its foreland, the Yangtze foreland fold-thrust belt. The fission-track analyses utilized the independent (φ-), Z- and ξ-methods for age determination, which yielded within error identical ages. Ages from Triassic–Jurassic syn-orogenic foreland sediments are younger than their depositional age and thus were reset. A group of ages records rapid cooling following shallow emplacement of granitoids of the widespread latest Jurassic−Early Cretaceous “Yanshanian” magmatism. Most ages are …

Controls On The Erosion And Geomorphic Evolution Of The San Bernardino And San Gabriel Mountains, Southern California, J Spotila, M House, Ann Blythe, N Niemi, G Bank

Ann Blythe

No abstract provided.

Low-Temperature Thermochronology Of The San Gabriel And San Bernardino Mountains, Southern California: Constraining Structural Evolution, Ann Blythe, M House, J Spotila

Ann Blythe

No abstract provided.

Geomagnetic Field Behavior Before And After The Kauai Reverse-Normal Polarity Transition, Scott Bogue

Scott Bogue

New paleomagnetic results from 4 m.y. old lava flows from Kauai, Hawaii, suggest that strong poloidal field is associated with an unusual state of the geodynamo that follows attempts at polarity reversal (successful or not). The new data comprise 50 paleomagnetic sites from superposed lava flows occurring just below and above the Kauai reverse-normal polarity transition. A composite record of 45 distinct field determinations was constructed by combining sites that record similar ancient field and correlating them to previously published results from Kauai. Of the 45 data, 25 include paleointensity estimates derived from double-heating experiments. A comparison of the composite …

Structural And Topographic Evolution Of The Central Transverse Ranges, California, From Apatite Fission- Track, (U-Th)/He And Digital Elevation Model Analyses, Ann Blythe, D Burbank, K Farley, E Fielding

Ann Blythe

No abstract provided.

Internal Waves Revealed By Synthetic Aperture Radar (Sar) Imagery In The Vicinity Of The Eastern Cretan Arc Straits (Eastern Mediterranean), Adonis Velegrakis, E. Oikonomou, A. Theocharis, M Collins, H Kontoyannis, V Papadopoulos, George Voulgaris, T. Wells, E. Balopoulos

George Voulgaris

Internal waves have been detected on ERS-1 SAR images obtained during late summer over the eastern Cretan Straits, an area characterised by complex regional physiography, bottom topography, flow regime and stratification patterns of the upper part of the water column. Analysis of the imaged characteristics of the internal waves has revealed a strong diversity in form, propagation direction and type of sea surface modulation, which indicates various mechanisms of generation. Analysis of the currents recorded over the area shows that, although semi-diurnal tidal currents are present, these are of low magnitude in comparison with the overall flow and, therefore, tidal …

Radiocarbon Chronology And Δ13c Analysis Of Mid-To Late-Holocene Aeolian Environments, Guadalupe Mountains National Park, Texas, Usa, David Wilkins, Donald Currey

David E. Wilkins

The Red Dunes of Guadalupe Mountains National Park are quartzose sand sheets and dunes stabilized by sparse plant cover. Stratigraphy, radiocarbon dating, and δ13C analysis were examined in two of the larger arroyos for correlating evidence of aeolian deposition, which in this basin is taken as an indication of arid conditions. Four quartz-sand lithostratigraphic units, representing intervals of aeolian activity, are identified. Radiocarbon dates provide constraint on the timing of the three youngest quartz-sand units. A mid-Holocene aeolian interval, represented by a single radiocarbon date of 6350± 70 BP, is interpreted as transitional to an altithermal regime. A neopluvial period, …

Experimental Studies Of Fe-Mg Carbonates And Their Role In Petrogenesis

Andrea M. Koziol

Active Tectonics And Ultrahigh-Pressure Rocks, Ann Blythe

Ann Blythe

This chapter compares modern exhumation and surface uplift rates with the rates needed for the preservation of ultrahigh pressure (UHP) metamorphic rocks. The highest recorded exhumation rates of ~ 5–10 mm/a are inferred from isotopic and fission-track analyses in the Himalaya, Southern Alps of New Zealand, and D’Entrecasteaux Islands. Similar rates (~7 mm/a) of surface uplift are measured from leveling surveys in Nepal and correlations of marine terraces in the Southern Alps. In Nepal, however, this surface uplift rate is occurring despite erosion, and the true rate of surface uplift is probably considerably higher. In restraining bends along the San …

Longitudinal Study Of Dental Development In Chimpanzees Of Known Chronological Age: Implications For Understanding The Age At Death Of Plio-Pleistocene Hominids, Robert Anemone, Mark Mooney

Robert L. Anemone

Reconstruction of life history variables of fossil hominids on the basis of dental development requires understanding of and comparison with the pattern and timing of dental development among both living humans and pongids. Whether dental development among living apes or humans provides a better model for comparison with that of Plio-Pleistocene hominids of the genus Australopithecus remains a contentious point. This paper presents new data on chimpanzees documenting developmental differences in the dentitions of modern humans and apes and discusses their significance in light of recent controversies over the human or pongid nature of australopithecine dental development. Longitudinal analysis of …