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Oral Presentations
The origin of trachytes and pantellerites at the
Eburru volcanic complex, Kenya, Africa
Beltran, J. M. V., Department of Geological
Sciences, University of Texas at El Paso
The Eburru volcanic field is located in the Kenya
Rift, where it is part of the very young axial volcanic
activity. The Eburru field belongs to the complex of
volcanoes -- Menengai, Eburru, Olkaria, Longonot,
and Suswa -- that are centered on the Kenya Dome.
All of these volcanoes are prime targets for
geothermal energy, with Kenya’s one geothermal
plant at Olkaria. Correlation with dated volcanism
implies that the activity at Eburru is at most
approximately 500,000 years. The surfaces preserved
on the youngest flows suggest that they erupted
within the last 1,000 years. Mapping indicates that
the volcanic field is divided into an older western
section, composed of pantellerites (Er1) and
overlying, faulted trachytes (Et1), and a younger
eastern section. The eastern section has a mapable
ring structure, and is composed of trachytes (Et2) and
pantellerites (Er2). Some of these flows may be
contemporaneous, but the final phase of eruption is
exclusively pantellerite.
We have chemical data for all units except
the older pantellerites. The data indicate that the
trachytes and rhyolites are both pantelleritic in terms
of their alumina and iron contents. This is in
contradistinction to the rhyolites immediately
adjacent at Olkaria, which are comenditic.
Concentrations for all elements are highly elevated,
except for Ba, Sr, K, P, and Ti that show deep
negative anomalies. The relationship between the
trachytes (Et2) and pantellerites (Er2) is one in which
the pantellerites consistently have the highest
concentrations in all elements, including those with
negative anomalies. Correlation coefficients for pairs
such as Zr and Rb support the field evidence for the
western Et1 trachytes being a separate magmatic
event from the Et2 and Er2 units of the eastern field.
Spatially restricted deformation around the 1.4
Ga Eolus Granite, Needle Mountains, Colorado:
Constraints on regional deformation fields at 1.4
Ga
Dean, R.L., Andronicos, C.L., Noel, M.E. and
Mansfield, M., Department of Geological Sciences,
The University of Texas at El Paso, 79968
Understanding the strain field around 1.4 Ga Plutons
is critical to correctly deciphering the processes
responsible for the generation of this enigmatic
magmatic belt. Here we present structural data from
the northeast fringe of the 1440 Ma Eolus Granite in
the Needle Mountains of SW Colorado which record
regional deformation fields in a thermally softened
aureole.
The eastern side of the Eolus granite in the Vallecito
River valley is north striking and subvertical,
concordant with the bulk of fabrics in country rock
gneisses. However, near the plutons margin domains
of migmatic gneisses occur which contain an eastwest striking, steeply dipping foliation. This foliation
is defined by migmatitic banding and sillimanite,
both spatially restricted to the aureole of the pluton.
These relationships suggest that this foliation formed
during contact metamorphism at 1.4 Ga.
Furthermore, since this fabric intersects the pluton
contact at a high angle, it cannot have been produced
by expansion of the pluton.
At Sunlight Creek, the orientation of the margin of
the pluton changes from north striking to east-west
striking with a steep southern dip. Quartzites at the
contact of the pluton are isoclinally folded as
indicated by reversals in facing direction recorded by
cross-bedding along this margin. In schist layers, a
crenulation cleavage is present which is east-west
striking and sub-vertical similar to that seen in
migmatite farther south. Thin leucosomes developed
in these schists are intruded into shallowly dipping
vein arrays, suggesting vertical incremental
extension. Sillimanite defined stretching lineations
are down dip, consistent with the observations from
the veins.
Taken together, the fabrics within the contact aureole
record approximately north-south shortening during
pluton emplacement. The apparent restriction of these
fabrics to the aureole of the pluton combined with the
lack of pervasive solid state fabrics in the interior of
the pluton suggests the regionally imposed deviatoric
stresses may have been small. This in turn may have
lead to focusing of deformation into the aureoles of
1.4 Ga plutons.
Determination of the lithospheric structure of
Lake Baikal, Russia
Dena, O., Department of Geological Sciences,
University of Texas at El Paso
[email protected]
Lake Baikal is located in the southern part of Russia
between the Precambrian Siberian Platform and the
India-Tibet collision zone. It is the deepest lake in the
world and contains over 23,000 cubic meters of fresh
water, or roughly 20 percent of the total fresh water
available in the world. Lake Baikal is the main rift of
the Baikal Rift system (BRS) and is considered to be
a phase in a more general and complex rifting
process. The lithospheric structure of the Lake Baikal
is very important to decipher the tectonic regime that
resulted in the formation of this far and enigmatic
intraplate rift. Data from a wide-angle reflection
survey carried out in Siberia in 1992 is being
analyzed in order to produce a velocity model along
the Lake’s Northern Basin to determine if southward
crustal thinning is present, as is expected according to
the proposed rift evolution models.
Microbial Survival Rates in Soil under Sub-Zero,
Low-Pressure and UV conditions
Diaz, B. R. and Schulze-Makuch, D., Department of
Geological Sciences, University of Texas at El Paso
Evidence of life has been found in sub-zero
cold environments on Earth. Microorganisms of
different types have been identified living in
microscopic pockets of brine (Gilichinsky et al.
1993), encased in ice cores many thousands of years
old (Siegert 2000) and in porous sandstone and
surface pavements in the Antarctic Dry Valleys
(Doran et al. 1998, Wynn-Williams 2000). It is also
accepted that microbes can remain viable and can be
cultured after being preserved for extended periods of
time by deep-freezing or lypohilization and ultrafreezing (Heckley 1985, MacKenzle 1977). However,
the question remains whether microorganisms can
remain viable for extended periods under subzero
conditions when also exposed to near-vacuum
conditions and UV radiation. Experiments were
designed to test whether certain selected
microorganisms can remain viable under these
conditions, and if so at what rate.
The experiments started with a series of tests to study
sublimation rates and microbial viability rates under
simulated sub-zero, low-pressure conditions. A
vacuum system was created to stimulate a lowpressure atmosphere using a GAST Model DAA oil
less diaphragm vacuum pump, and subzero
temperatures were simulated using an upright
compact commercial freezer and a 3 quart capacity
Dry-Ice Cold Trap. A high radiation environment
was simulated using an UV-lamp, because UV
radiation is most detrimental to bacterial survival
(Shaw 1987, Harris 2000). First, we measured the
sublimation rates of salt water (30,000mg/L total
dissolved solids), fresh water (1,000mg/L) and
deionized water, respectively. In the next set we
measured the sublimation rates for various soil/water
mixtures using Mars-1 Martian regolith simulant soil
provided by the Johnson Space Center under a
vacuum of 20 mbar of pressure. Then, we introduced
into the soil slurry a generic microbe (E. coli), a
radiation
resistant
microbe
(Deinococcus
radiodurans), a common spore-forming soil microbe
(Bacillus subtillus) and a halophilic microbe
(Halobacterium salinarium), and measured the
number of microbes that were still viable after a
freezing period of 10 days. The next steps of the
experiments will include a radiation source, UV light,
to determine the effect of the radiation on microbial
viability. The microbial viability will be provided as
a function of depth in the soil-mixture. The results of
our analysis will assist in evaluating whether
microorganisms can remain viable in extreme, high
radiation and below freezing environments,
somewhat analogous to the Martian and Europan
surface and near-subsurface (upper 10cm). It will
also quantify how efficient UV radiation is to destroy
microbes under these environmental conditions.
The Shallow Seismicity of Cook Inlet
Flores, C. H., and Doser, D. I., Department of
Geological Sciences, University of Texas at El Paso,
[email protected]
The city of Anchorage, Alaska sits on a peninsula at
the northern end of Cook Inlet. Recent seismic
studies by Page et al. and Haussler et al. show that
there are seismic hazards in the surrounding region
that can present themselves as medium to high
magnitude (ML>=4.5) shallow (depth < 15 km)
earthquakes. This study uses earthquake data from
the Alaska Earthquake Information Center from 1987
to 1999 to identify structures using refined
earthquake locations.
The largest magnitude
earthquake in this cluster in Cook Inlet is M L = 4.3
that occurred in February1991. The combined results
of Double-Difference relocations and the AURA
Project (Saltus et al.) seem to suggest there is a linear
structure underneath Cook Inlet defined by both the
earthquakes and magnetics data. We believe the
linear feature we see is an actual structure located 5
to 15 km beneath the surface and is not an artifact of
the analysis techniques used.
Lithology, alteration, and mineralization in the
Eastern Mexican Alkaline Province
Hamblock, J., Department of Geological Sciences,
The University of Texas at El Paso
The Eastern Mexican Alkaline Province (EMAP) is a
NNW-SSE trending belt of Tertiary alkaline igneous
intrusions extending from northern Coahuila to
Veracruz. Rock types within the EMAP vary from
highly alkalic carbonatites, ijolites, and nepheline
syenites to marginally alkaline granodiorites and
monzogabbros. Mineralization includes F  Be
associated with felsic lithologies, Mo  Cu related to
porphyries and pegmatites, Fe-oxide  Cu skarn and
Au associated with dioritic-monzonitic intrusions,
REE  Th related to carbonatites, and base metal 
Ag peripheral to igneous centers of diverse types.
Two recurring geologic features observed in the
EMAP are (1) early andradite-grossular garnet +
magnetite skarn and endoskarn ( vesuvianite,
clinopyroxene,
tremolite,
epidote,
marialitic
scapolite, albite, and sphene) with late Cu and Fe
sulfides and oxides, and (2) large zones of sodium 
calcium-rich alteration (chlorite, actinolite, albite,
diopside). These features resemble Fe-oxide(Cu-AuREE) systems (e.g. Olympic Dam-type deposits),
whose origins are controversial but increasingly
associated with external saline fluids. The presence
of Mesozoic evaporites in eastern Mexico supports
the likelihood of evaporitic fluid involvement in
mineralization.
However, observations that (1)
mineralization styles are strongly correlated with
magma type and (2) certain alteration styles (e.g. Ksilicate) are reminiscent of alteration by magmatic
fluids, suggest that hydrothermal systems of eastern
Mexico involve magmatic fluids as well. Thus, the
styles of alteration and mineralization present in
eastern Mexico appear to be hybrids of Fe-oxide(CuAu-REE) systems and alkaline magmatichydrothermal systems, with both external and
magmatic fluids being important in the formation of
the styles and volumes of hydrothermal features
observed.
Results from the Bromide Tracer test at Rio
Bosque
Reyes, Joel, Abdel-Fattah, A.,, Langford, R. P., and
Schulze-Makuch, D., Department of Geological
Sciences, University of Texas at El Paso
An experiment site constructed along an artificial
channel of the Rio Grande in El Paso, Texas is being
used in an experiment funded by the EPA and that is
designed to measure the effectiveness of bank
filtration in an arid environment. The experiment is
important because of the hundreds of thousands of
people drinking water from shallow wells drilled in
close proximity to septic systems. A pumping well
was drilled 17 meters from the stream bank and
screened from 3.5 to 8 m depth. An array of
observation wells with several multilevel completions
allows detection of downstream and vertical
movement of water as well as flow from the stream
to the well. Prior to pumping, measurements showed
a flat water table 2 meters below the water in the
channel. The background concentration of Bromide
was 4 to 5 ppm in both the wells and the stream prior
to injection.
This abstract describes the results of a tracer test
where bromide was injected into one of the wells
near the stream bank. Bromide was injected into well
“2”. However, the water level in the well was 2 m
below the surface of the stream. Bromine first
appears in the stream water 30 minutes after
injection. From 30 minutes to approximately 100
hours after injection, the stream contained the highest
concentrations of Bromide. This indicates effective
and rapid diffusion against hydraulic head from the
aquifer into the stream. Bromide concentrations
began to rise in the wells between the injection and
pumping well 2 hours after injection. Bromine rose
to peak values of 9 to 10 ppm several times.
Prominent peaks occurred at 18 to 29, 35, 160 to 170
hours. Bromide returns to background in all wells
except for the deep completions by approximately
100 hours. The deep wells continued to increase
their bromine concentrations to 300 to 350 hour.
These results indicate rapid flushing of the upper
channel sand, but much slower drainage of the deeper
sand. We conclude that the upper sand is in effective
communication with the channel and the pumping
well. The deeper aquifer is only slowly drained by
the pumping well.
Laramide age basins of central Colorado: An
Integrated Geophysical Study
Treviño, L., Department of Geological Sciences,
University of Texas at El Paso,
[email protected]
The compressive environment of the Laramide
orogeny (70-35Ma) produced North Park, South Park
and the Raton basins of central Colorado. Rugged
intermontane topography defines the basins of North
and South Park. The Raton basin, bordered on the
west by the Sangre de Cristo Range, is the
easternmost of the Laramide age basins of central
Colorado. The purpose of this study is to determine
the structure and origin of these basins by integration
of several geophysical techniques; detailed
subsurface studies of these basins are few.
An extensive gravity database housed at the
University of Texas El Paso was used to produce
smoothed and filtered gravity maps and 2.5D gravity
profiles of these basins. Gravity profiles indicate that
the North Park and Raton basins are asymmetrical
synclines. Smoothed and filtered maps indicate that
the gravity low over North Park is the result of basin
fill. The gravity gradient on the eastern edge of South
Park can be attributed to the Elkhorn Thrust fault or
to a change in rock composition between South Park
and the Front Range. The Sangre de Cristo range is
cut through by many faults. ASTER images acquired
for the area under study are being analyzed and will
be integrated to this study.
A Study of the 1995 Waitangi Day Outer Rise
Seismic Sequence,
North Island, New Zealand
Treviño, L., Department of Geological Sciences,
University of Texas at El Paso
[email protected]
In the space of several weeks in February 1995 the
New Zealand digital seismic network recorded a
sequence of earthquakes, between 3.0-4.5 in
magnitude and on occasion exceeding over 200 a
day. This series of earthquakes, known as the
Waitangi Day sequence, occurred on the outer rise of
the Hikurangi Margin. The outer rise (also known as
the outer swell) is an uplifted portion of the oceanic
plate just in front of the subduction zone. The
Hikurangi Margin (or Trough) is the southerly
extension of the Tonga-Kermadec subduction arc
complex. The trough gently curves offshore along
the eastern edge of the North Island and the northern
extension of the South Island near the Chatham rise.
The subduction zone has been the main influence on
the present topography of New Zealand; in particular
the North Island displays a classic sequence
associated with subduction zone complexes.
Furthermore, the subduction zone has also affected
seismicity patterns on the North Island. Outer rise
events are known to often precede larger events in
subduction zones. Events plotted over a ten-day
period show that the Waitangi Day sequence is
composed of two small clusters. Also, a plot of the
seismic moment demonstrates that the Waitangi Day
sequence does not follow Omori’s Law. Focal
mechanisms for the larger events indicate a change in
strain distribution for the Trough. The objectives of
this study are to properly locate the earthquake
swarm using relocation algorithm, HypoDD;
determine the stress field for the region; and use a
variety of other techniques to better understand the
implications of outer rise earthquakes.
Poster Presentations
Phytoremediation as an Alternative for the
Remediation of Lead (Pb) Soil Contamination in
El Paso, Texas
Arias, J. A. [email protected]
Contaminated soils around the world present a major
environmental, human, and animal health problem
that
may
be
partially
eliminated
with
Phytoremediation. Lead is considered one of the most
frequently
encountered
heavy
metals
of
environmental concern and remediation research.
Lead-contaminated soils may result in environmental
problems such as loss of vegetation, groundwater
contamination, toxicity in-humans, plants, and
animals, and mental retardation in children (Salt et
al., 1995). Due to the use of lead in Industries,
ammunition, paints, gasoline, explosives, and in raw
sewage, outbreaks of contamination frequently occur.
The clean up of lead-contaminated soils represents a
significant expense to many government agencies
and private entities.
Today, lead poisoning is the number one
environmental disease of children in the United
States. It affects nearly one million children under the
age of six. Lead poisoning is not only an expensive
societal problem but more importantly it prevents
children from reaching their full potential and denies
the community they live in of their long term
contributions.
Also, scientific studies have shown a clear link
between lead poisoning and aggressive or violent
behavior in teenagers or young adults who were
poisoned as children. Children poisoned by lead often
find it difficult to learn and are seven times more
likely to drop out of school.
Phytoremediation is the use of plants to decrease
metal (Pb in this case) concentrations in the soil.
Through cultivation of suitable plants, the sites could
eventually become decontaminated. Plant cultivation
and harvesting are rather inexpensive processes,
compared to traditional engineering practices that
rely on intensive soil manipulation or excavation.
This makes Phytoremediation an attractive form of
clean up for Pb-contaminated soils (Jorgensen, 1993).
Chelates (chemical) have been used in soils and
nutrient solutions to increase the solubility of metal
cations in plant growth media. They are reported to
have significant effects on metal solubility of metal
cations in plant growth media. For this reason it has
been used together with the Phytoremediation. They
are reported to have significant effects on metal
accumulation in plants (Wallace et al., 1977).
Overwhelmingly positive results continue to become
available regarding the ability of plants to degrade
certain organic and inorganic compounds.
Phytoremediation appears a very promising
technology for the removal of metals from
contaminated areas.
The Use of Gravity Models to Constrain Regional
Velocity Models for the Libya Area
Brown, W. A., Doser, D. I. and Keller, G. R.,
Department of Geological Sciences, University of
Texas at El Paso
The tectonic evolution of Libya has yielded a
complex crustal structure, which is composed of a
series of basins and uplifts. A considerable amount of
oil exploration has been undertaken in the area and
numerous studies have been published on the shallow
(<10km depth) geology and geophysics of the region.
In addition, over 6000 gravity measurements are
available for the northern Libya region. We are using
these data in conjunction with other geologic and
geophysical control to construct a 3-D model of
density/geology for northern Libya and surrounding
regions. This 3-D model will then be used to develop
a regional velocity model that can be
verified/modified by analysis of regional waveform
data we are collecting from earthquakes occurring
within northern Libya.
Northern Libya is the most seismologically active
and highly faulted portion of the country. This poster
also incorporates remotely sensed Landsat 4 and
Landsat 5 images in an effort to better understand
structural features such as recent faults in the area.
Conceptual Model of Olkaria
Geolthermal Field, Kenya: A Re-Interpretation of
Geophysics Data
Bw’Obuya, M., Kenya Electricity Generating
Company Ltd, Geothermal Division Olkaria, Kenya
Review of the structure of the Olkaria Volcanic area,
Kenya, strongly indicates that the complex is the
remnant of an older caldera that has been filled by
later volcanic material along the rim of the caldera
and along N-S striking faults. Development of the
conceptual reservoir model of Olkaria Geothermal
Field has been done regularly since 1976 as
additional information became available from the
field. The geophysical model relating to the observed
subsurface resistivity variations, gravity and
magnetic anomalies and seismology data shows
marked contrasts defined by sharp boundaries. The
geophysical anomalies suggest a relation to the
geological and structural evolution of the geothermal
system and the proximity to the heat source. Micro-
earthquake monitoring for epicentre and hypocentre
locations show that Olkaria is a high temperature
geothermal field characterized by a relatively high
level of micro-earthquake activity. The geothermal
resource occurs within a low gravity anomaly.
Residual aeromagnetic data acquired within the Rift
Valley shows that the Greater Olkaria Geothermal
Area has a positive anomaly that has a NW-SE trend.
Latest studies show that the geothermal system
mostly occurs as discrete units that are controlled by
the tectonic and geological structures and the
proximity to the heat source. The systems occur in
either NW-SE or NE-SW trends that are separated by
north-south structural discontinuities.
Controls on Morphology of the Parabolic Dunes in
White Sands National Monument, New Mexico
Crocker, L.
Brock, M.
and Langford, R.,
Department of Geological Sciences, University of
Texas at El Paso, [email protected]
Parabolic dunes are one of the major types of eolian
dunes, but little is know of their origin and the
controls on their movement. White Sands National
Monument has one of the largest clusters of parabolic
dunes in the world. This study describes six different
classes of parabolic dunes at White Sands. Groups
are distinguished by differences in the length, width,
interdune morphology, and length-to-width ratios.
Group A consists of widely spaced, very long dunes
(857 meters long and 123 meters wide). These dunes
are associated with well-vegetated interdunes and
extend far from sand sources. Group B are an older
generation of parabolic dunes that have been
overridden by younger transverse and parabolic
dunes. Group C consist of closely spaced wide and
short dunes with straight fronts that are transitional to
transverse dunes.
Group D are intermediate
between groups E and A in their size and shape.
Group E are dunes emerging from transverse ridges
of the interior White Sands dunes. Group F are small
(80.1 meters long by 38.7 meters wide) that are
forming on the arms of the dunes of Group A.
Different methods are applied to distinguish between
the six classes. The distribution of vegetation on the
dunes does not seem to correlate with differences in
dune shape and movement. Interdune vegetation
correlates with increased dune spacing and dune
length. The parabolic dunes have formed through
several different processes. Group C and D start as
blowouts of transverse dune ridges and may be
observed forming today. Group B seems to have
formed from excavation of the interdunes upwind of
them. Group A has a more problematic origin and
may represent reactivation of older generations of
parabolic dunes.
Groundwater exploration in central Chihuahua,
Mexico using ASTER and Landsat Imagery and
GIS
Gutierrez Jurado, H. A., Goodell, P., Hurtado J.,
Department of Geological Sciences, The University
of Texas at El Paso, J. M., Reyes, I., Departamento
de Geología, Universidad Autónoma de Chihuahua
The surface water resources of the area adjacent to
the City of Chihuahua, Mexico --an area within 100
km from the City-- are insufficient in volume to
supply the amount needed for the activities of the
region. Water used to satisfy the city requirements is
obtained by exploiting aquifers near the city. The
water supply of the city is thus directly dependent on
the state of the aquifers in the area. The aquifers that
are tapped for city use are selected on the basis of
proximity to the city, yield capacity and low cost of
water extraction in the short term. The aquifers are
exploited until exhaustion, followed by further
exploitation of aquifers farther away. This process
does not consider sustainable use of the water
resources. Overall, this approach does not represent a
long-term solution to the water supply scarcity
problem faced by the City of Chihuahua.
There are two main aims of this study. First is to
identify the major basins in the region of interest. So
far twenty-one have been identified. The second
objective is to obtain hydrologic parameters relevant
to future water supply from these basins. The
integration of these two objectives will result in a
matrix of hydrologic parameters for the basins
identified.
Remote sensing data from ASTER and Landsat will
be employed to create thematic maps of drainage
density, stream bifurcation ratios, stream frequency,
vegetation cover, soils, slope, and precipitation. The
resulting thematic maps will then be integrated and
analyzed in a GIS. The data products generated from
the GIS analyses will be used to assess the values of
the variables in the parameter matrix. This matrix
will be used to quantitatively evaluate the hydrologic
parameters of each basin. The overall goal is to
understand the basins in the vicinity of Chihuahua
City to the extent that they can be exploited at a level
appropriate given their rate of recharge. We believe
that this process can lead to a greater sustainability of
groundwater utilization in the Chihuahua City area.
Lithospheric heterogeneity beneath the East
African Rift System interpreted from major and
trace element analyses of mafic rocks
Hamblock, J., Department of Geological Sciences,
The University of Texas at El Paso
Chemical analyses are reported for tholeiites from the
axial region of the East African Rift System (EARS)
and tholeiites and basanites from the Chyulu Hills
Volcanic Province (CHVP), located on the SE flank
of the Kenya Rift. The purpose of the study is to: i)
explore contrasts in lithospheric composition from
the axial region, where seismic velocities imply high
temperatures and presence of melt at shallow depths,
to the flanks, where geophysical studies indicate
thick lithosphere and a zone of partial melt centered
under the CHVP (Ritter and Kaspar, 1997,
Tectonophysics 278, 149-169). ii) investigate plume
components and plume-lithosphere interactions in the
different settings. This study complements the
characterization of lithosphere along the axis of the
Rift by MacDonald et al. (2001, J. Petrol. 42, 877900) and the study of temporal evolution of the
CHVP by Späth et al. (2001, J. Petrol. 42, 765-787).
Basanites within the CHVP are similar to OIB in
their trace-element patterns, but with a pronounced
negative K-anomaly. Späth et al. attribute this
anomaly to melting of a lithospheric mantle source
containing amphibole. They postulate, based on
radiogenic isotopes (Sr, Pb, Nd), recent
metasomatism due to interaction of the lithosphere
with the EARS plume. High La/Yb suggests a source
within the garnet-peridotite field. Tholeiites from the
CHVP are distinct in trace-element chemistry from
basanites, with flatter multi-element patterns and
generally lower elemental concentrations. The CHVP
tholeiites have La/Yb indicative of a spinel peridotite
source. The role of crustal contamination for
tholeiites remains open; however, substantial
evidence exists for lithospheric heterogeneity beneath
the CHVP. Axial lavas show similar elemental
behavior as the CHVP: basanites have negative Kanomalies (MacDonald et al., 2001), whereas
tholeiites do not. Tholeiites have flat multi-element
patterns with low overall concentrations, similar to
those from the CHVP, with one significant difference
– tholeiites from the axial region have variable and
high concentrations of Ba, K, and Ta, which may
represent a more pervasive plume component. The
Mg-number of lavas from the axial region are
significantly lower than lavas in the CHVP,
suggesting greater degrees of crystal fractionation
and potentially longer residence times in crustal
magma chambers. In conclusion, evidence exists in
both areas for lithospheric mantle heterogeneity, but
in both areas the elemental signature is highly
correlated to silica saturation. For a given group of
lavas of similar silica saturation, the elemental
patterns are similar from the axis to the flank. This
observation implies that there are not strong lateral
contrasts in lithospheric composition across the
EARS.
Exploring Himalaya Seismicity in the Kingdom of
Bhutan Utilizing a Temporary Seismic Network.
Hernandez, D., Velasco, A. A., and Miller, K. C.,
Department of Geological Sciences, The University
of Texas at El Paso
We are recording and processing data from a
temporary seismic network within the Kingdom of
Bhutan to gain a better understanding of the seismic
activity and hazards in the region. Before the
temporary network deployment in the Bhutan
Himalaya, event data from global catalogs was
limited. We deployed a five station temporary
seismic network in January 2002 and will record until
March 2003. Initial results from processing the first
6 months of data show that the region is dramatically
more active than previously known.
We
automatically detected, associated, and located
approximately 1600 teleseismic, regional, local
events over this six-month period, and discovered
that approximately 700 events were not in the global
United States Geological Survey earthquake catalog.
These 700 local and regional events must be
relocated, since the initial locations were made on a
coarse grid. We manually picked P- and S-waves for
each event and performed event locations using a
global velocity model.
We also computed
magnitudes for each of the relocated events, finding a
broad range of magnitudes. However, we find that
there is a high level of microseismicity (events with
magnitude less than two) recorded within the
network. We also find evidence of event clustering,
which suggests the location of active faults. Future
work will include processing data from the complete
deployment (until March 2003), adding data from
other seismic stations in the region, developing a
better 1-D velocity model, and performing highresolution earthquake locations.
Characterization of the Continental
Mantle in an Active Rift Zone: Kilbourne Hole,
New Mexico
Kappus, Eric J., Anthony, E., and Andronicos, C.,
Department of Geological Sciences, The University
of Texas at El Paso, [email protected]
The mantle xenoliths from the Kilbourne
Hole maar, which is situated in the southern New
Mexico portion of the Rio Grande Rift, have held
fascination for decades. They have been the source of
several seminal studies that characterize their
chemistry and petrology. These studies have focused
primarily on fertile lherzolite samples (i.e. with
modal clinopyroxene greater than 40 percent) and
composite samples, which typically have Group II
wehrlites and clinopyroxenites as veins in the fertile
lherzolite. The present study continues to characterize
these lithologies and also includes a previously
neglected, less fertile lithology. This lithology, which
is texturally distinct from the fertile lherzolite,
typically has modal olivine greater than 70 percent,
and includes lherzolite, harzburgite, and dunite.
Major and trace element compositions for whole rock
and constituent minerals show the expected trends
which accompany greater degrees of partial melt
extraction. For example, forsterite content in olivine
is an average of Fo92 for this lithology compared to
Fo89 in the fertile lherzolite; whole rock CaO content
is less than 1 %, and MgO content greater than 45 %.
Superposed on both this less fertile lithology and the
composite samples is LREE and alkali element
enrichment, requiring a multi-stage history. Sr and
Nd isotopic studies of these samples suggest that the
enrichment is both Proterozoic and recent.
Preliminary thermobarometric data indicate
that the more fertile samples are shallower and cooler
than the less fertile samples. This finding is in
contradistinction to many xenoliths studies,
particularly of the Archean, which document less
fertile samples immediately below the Moho. Re/Os
isotopes indicate that the shallow fertile mantle
stabilized at 1.6 Ga or earlier, an age similar to the
crustal stabilization for the region established by Nd
isotopic data. Modal differences between the 2
groups can account for 0.2 to 0.3 km/sec difference in
P wave velocities. Velocities, calculated at P-T from
our thermobarometric data, indicate velocities as low
as 7.7 km/sec for the more fertile upper mantle and
7.9 km/sec for the deeper olivine-rich mantle. This
result implies that the low velocities in the Rio
Grande Rift in this region can be explained by high
temperature alone, without recourse to hypothesizing
presence of partial melt. This agrees with petrologic
studies that indicate that magmas are generated in
garnet peridotite, and eruptive centers are fed by
small magma batches which ascend to the crust from
the zone of magma generation.
Dinosaur Footprints from the Lower Cretaceous
Anapra Sandstone at Cerro de Cristo Rey, Dona
Ana County, New Mexico
Kappus, E. J., Department of Geological Sciences,
University of Texas at El Paso, Lucas, S. G., Heckert,
A. B., Hunt, Adrian, P., New Mexico Museum of
Natural History, [email protected]
Dinosaur tracks and swimming traces have been
discovered at three localities in the latest Albian
“Anapra Sandstone” (= Sarten Member of the
Mojado Formation, Bisbee Group) at Cerro de Cristo
Rey in Sunland Park, New Mexico, southernmost
Doña Ana County. At one locality, NMMNH
locality #5293, many underprints (over 400) of the
ichnogenus Caririchnium (and ornithopod dinosaur)
are preserved in concave relief on top of a hematized,
bioturbated sandstone bed in the lower part of the
Anapra, ~ 9m above its basal contact with the
underlying Mesilla Valley Shale. The exposure is
approximately 400 m2, although ~150 m2 is partially
covered by erosional debris. These tracks are
tridactyl, relatively large (up to 65 cm footprint
length), have wide, blunt toes, and a square bilobate
heel, all of which are characteristic of the ichnogenus
Caririchnium.
The second and third localities are two
quarries adjacent to each other and are designated
NMMNH localities #5291 and #5292. These are
linear quarries exposing two track-bearing beds 9m
apart stratigraphically in the upper third of the
Anapra Sandstone. The lower bed of this second
locality also preserves large Caririchnium tracks in
concave relief with small manus impressions. Also
preserved are large (40-60 cm footprint length) tracks
of the ichnogenus Magnoavipes (a theropod
dinosaur), characterized by extremely thin, pointed
toes. These theropod tracks are preserved in convex
epirelief in a hematized, bioturbated sandstone as
well. The upper bed of these two localities preserves
Caririchnium tracks in convex hyporelief as well as
numerous
swimming
traces—possibly
from
reptilians.
These are scratch marks and other
parallel, linear grooves. These two upper Anapra
track beds can be traced over a total strike of ~750 m
and as many as 350 distinct footprints are exposed,
including at least 12 pairs of swimming traces.
The Anapra Sandstone is of latest Albian
age (Plesioturrillites brazoensis ammonite zone), so
the Cerro de Cristo Rey tracks are slightly younger
than the well known late Albian tracksites of
northeastern New Mexico, which are in strata
equivalent to the Mortoniceras equidistans ammonite
zone, or slightly younger. At Cerro de Cristo Rey,
the dominance of ornithopod tracks and absence of
sauropod tracks fits regional patterns of late AlbianCenomanian track distribution consistent with North
American extirpation of sauropods before late Albian
time. The deltaic/coastal plan depositional setting of
the Anapra Sandstone is also remarkably similar to
the track-bearing late Albian-Cenomanian sandstones
of NE New Mexico, Oklahoma, and SE Colorado,
which also have a tetrapod footprint ichnofacies
dominated by ornithopod (Caririchnium) tracks.
Gravity Studies to Detect Faults Controlling
Groundwater Movement within the Lower Mesilla
Basin, West Texas
Khatun, S., Ekal, M. C. I., Doser, D. I., Department
of Geological Sciences, University of Texas at El
Paso
A project has been undertaken to determine the
location of faults and their roles as conduits or
barriers to fluid flow in the Mesilla basin, West
Texas and Southern New Mexico. This study area has
been selected because it has good well control and
easy access and serves as an important aquifer for the
El Paso urban region. The study has focused on
finding smaller faults within the basin, which are
believed to be a major control on ground water flow.
Precision gravity and DC surface resistivity methods
have been used to determine the location of faults and
their role in ground water flow.
The faults control grain size variations of sediments
deposited in the basin and hydraulic conductivity of
these sediments. Away from faults, significant soil
profiles can develop and the clays associated with
these soils inhibit the vertical flow of ground water.
The faults also act as conduit for ground water
recharge and barriers to horizontal fluid flow. Thus
difference in water salinity can exist across these
faults. Because density, grain size and salinity
variations exist across many of these faults, we have
found gravity and resistivity studies particularly well
suited for fault detection. Our results will be used to
develop a model of ground water flow that can be
tested against observations in the Canutillo well field
of the Mesilla valley that is operated by the El Paso
Water Utilities.
Filtration of Pathogenic Parasites using Laterites
and Surfactant-Modified Zeolites
Lehner, T. and Schulze-Makuch, D., Department of
Geological Sciences, University of Texas at El Paso
Sewage effluent can leak into groundwater and
contaminate the drinking wells with pathogenic
microbes. The problem is evident in small
US/Mexico border towns called colonias where there
are no wastewater facilities. Cryptosporidium and
Giardia are parasites that cause moderate to severe
intestinal illness that may persist from one to two
weeks. In children, elderly, and immunodeficient
persons the infection may result in death.
Previous studies by Schulze-Makuch et al. (2002)
indicate that surfactant-modified zeolites (SMZ)
removed all of the bacteria and most viruses in lab
experiments. The paper also indicates that Fe-oxide
coated sand removed most microbes in lab
experiments.
In the current research we are running experiments
with SMZ and laterite as barriers to pathogen
movement in the groundwater to test their efficiency
to remove protozoans. Laterite, a highly leached
iron-oxide soil, is tested for the removal of viruses,
bacteria and protozoans. Laboratory experiments are
conducted in a plexiglass model aquifer to simulate
natural
groundwater
movement.
Since
Cryptosporidium and Giardia are hazardous to
humans, polystyrene microspheres of similar sizes
are used as analogues for protozoa. Water samples
are analyzed for microbe concentrations at UTEP and
microsphere concentrations at New Mexico Tech.
Deciphering the Nature of the Seri-Tauhe Terrane
Boundary, Northwestern Mexico
McDonough, C., Department of the Geological
Sciences, The University of Texas at El Paso
A terrane boundary is a fault that separates two
distinct geologic packages.
Remote sensing,
petrology and field observations can be used to
decipher the nature of a terrane boundary. There
have been several studies on the terranes of Mexico
(Campa and Coney, 1983; Coney, 1989; Sedlock et.
al, 1993). In northwestern Mexico, Sedlock et
al(1993), inferred an east-west trending terrane
boundary located at the 28th parallel in southern
Sonora and labeled it as the boundary between the
Seri-Tauhe terranes.
One of the controversies
surrounding the proposed terranes is that the fault has
not been mapped out.
The regional geology consists of Precambrian
continental crust to the north (Anderson et al, 1979,
Anderson and Silver, 1981) and the late Triassic crust
to the south (Anderson and Schmidt, 1983). The
Late Triassic is intruded by Cretaceous as well. A
unique opportunity to observe the geology and the
terrane boundary was created in 1995 with the
erection of a second dam Rio Fuerte in Sonora. It has
opened a lake of 23,000 navigable acres which
extend eastward towards the Sinforosa Lineament, a
suspect locale of the terrane boundary.
Convincing geochemical and isotope data point to the
existence of a terreane boundary in northwestern
Mexico. With the use of ASTER data and careful
field observations it can be discerned. I propose to
determine the nature and exact location of the terrane
boundary.
Erosion and transport potential of sediment
obstructing the flow of the Rio Grande into the
Gulf of Mexico
Neu, R., Langford, R., Jepsen, R., Chapin, D. M.,
Buhalts, R., and Roberts, J., Department of the
Geological Sciences, The University of Texas at El
Paso
The mouth of the Rio Grande has become silted up,
obstructing its flow into the Gulf of Mexico. This is
problematic in that it has created extensive flooding.
The purpose of the study was to determine the
erosion and transport potential of the sediments
obstructing the flow. This was done using a unique
Mobile High Shear Stress flume developed by
Sandia’s Carlsbad Programs Group for the US Army
Corps of Engineers. The flume measures in-situ
sediment erosion properties at shear stresses ranging
form normal flow to flood conditions for a variable
depth sediment core. The flume is in a self-contained
trailer that can be placed on site in the field. Erosion
rates and sediment grain size distributions were
determined from sediment samples collected in and
around the obstruction. This data was used to
characterize the erosion potential of the sediments of
concern.
Kinematic Analysis of low angle normal faulting
during basin development in the southern Rio
Grande rift
Ruiz, A. and Andronicos, C., Department of the
Geological Sciences, The University of Texas at El
Paso
The Rio Grande Rift consists of a series of
interconnected, asymmetrical grabens extending from
Leadville, Colorado to Presidio, Texas and
Chihuahua, Mexico which may follow zones of
crustal weakness. Rifting has been active for about
the last 30 Ma and has resulted in the production of
the major basins. Understanding the kinematic
development of these basins has far reaching
implications for basin development in extensional
settings. This study is focused on the development of
the Rio Grande Rift in southern New Mexico and far
west Texas where crustal extension has been greatest,
and some of the largest basins in the Rift have
developed. Our study area is centered on the Franklin
Mountains along the New Mexico-Texas State line in
between the Mesilla and Hueco Basins. We have
focused on the kinematic development of faults in the
Franklin Mountains as these faults are the most direct
evidence for structural processes in the deep basins
on either side of the range.
In the northern Franklin Mountains two phases of
deformation are recognized. The first phase is best
recorded in Permian and Pennsylvanian rocks found
along the western side of the range. Folds found
within these rocks are upright with northwestsoutheast trending hinges. Geometric analysis of the
bedding data presented in Figures (1987) suggests
that similarly oriented folds are present within
Paleozoic rocks in the Franklins and are cross cut by
moderate to shallowly dipping normal faults.
Moderate to shallow dipping normal faults are the
most dramatic structural feature in the northern
Franklin Mountains. Structural analysis suggests that
the faults currently dip between ~30 and 40 degrees.
We focused on what Figures (1987) referred to as the
Main boundary fault of the Pipeline complex.
Stratigraphic separation on the fault is ~750 meters.
Assuming the fault slipped with its current dip of ~30
o
suggests a displacement of ~1500 meters.
Calcite filled tension veins are well developed around
the fault. We used the geometry of these veins to
estimate the orientations of the principal stresses
during faulting. Tension veins are best developed
near the fault and appear to post date the
development of a fault propagation syncline in the
hanging wall of the fault. These veins suggest that the
least compressive stress plunged 4º to 095º the
intermediate stress plunged 55º to 182º, and the
greatest compressive stress plunged 36º to 003º
during low angel normal faulting. These orientations
suggest a strike slip component to a strain field
dominated by east-west extension.
Enhancing Structural Features through Satellite
Imagery
Schiek, C., Department of Geological Sciences, The
University of Texas at El Paso
The Davis Mountains are part of the Trans-Pecos
region just north of the Big Bend National Park in
southwest Texas. The area consists of a suite of
peralkaline rhyolites, which are thought to originate
from the subduction of the Farallon Plate (Barker,
1987). Traditional theories on peralkaline rhyolites
prefer paragenesis from continental hot spots or
extensional settings. Dikes intruded into the country
rock contemporaneous with the emplacement of the
peralkaline rhyolites. By studying the positions of
these dikes along with fractures, veins, and faults in
this locality the true tectonic setting for the placement
of these peralkaline rhyolites will be revealed.
Satellite imagery of the Davis Mountains can be used
to depict linear geological features such as geologic
contacts, faults, and fractures. When this imagery
has been directionally filtered, these linear features
are intensified and when coupled with geologic
mapping overall structural trends can be identified.
By recognizing this structural trend the principle
direction of the greatest stress can be estimated along
with what tectonic event had the greatest influence
over this area. This preliminary study will aid in
where to find these linear features in the field as well
as a possible hypothesis of the stress regime.
Contact Metamorphism around the 1.4 Ga Eolus
Granite, Needle Mountains, Southwest Colorado
Silva, A., Andronicos, C. L., Noel, M. E., Dean, R.
L., and Mansfield, M., Department of Geological
Sciences, The University of Texas at El Paso,
[email protected]
We are investigating contact metamorphism around
the NE margin of the Eolus granite in the Vallecito
River valley, Needle Mountains Colorado. In the
Vallecito Valley, the Eolus granite intrudes a diverse
package of metavolcanic and metasedimentary rocks.
A well developed contact aureole is present and
records an andalusite-sillimanite type field gradient.
Amphibolites in the southern part of the study area
contain chlorite, biotite, and actinolite at distances
greater than 1 km form the pluton margin. Near the
pluton margin, both chlorite and actinolite have been
replaced by hornblende, indicating amphibolite to
upper amphibolite facies metamorphic conditions.
In the northern part of the study area the granite
intrudes quartzites and schists. At distances greater
than 1 km from the pluton andalusite is present with
chlorite, biotite and muscovite. Closer to the pluton
sillimanite appears with muscovite, and at the pluton
margin muscovite is eliminated from the assemblage.
Taken together, the mineral assemblages suggest that
contact metamorphism occurred at pressures between
2 and 4 kbar, with peak temperatures near 650 C. We
are working to refine these pressure and temperature
estimates using quantitative thermobarometry. These
results suggest that like many 1.4 Ga plutons, the
Eolus granite was emplaced at relatively shallow
levels within the crust.
Regional Discrimination between Earthquakes
and Explosions from the Nevada Test Site
VanDeMark, T. F., Department of Geological
Sciences, University of Texas at El Paso
My research is based on using the Pn, Pg, and Lg
regional seismic phases to discriminate natural
seismic events from un-natural seismic events (i.e.
nuclear explosions) at regional distances. My data
includes 37 nuclear explosions, 34 earthquakes, and 1
chemical explosion which all took place in or around
the Nevada Test Site between 1988 and 1997. The
stations used for this study were Pasadena, CA (PAS)
and Goldstone, CA (GSC). The magnitudes of all
events range from 3 to 6 Mb. The discrimination of
the events was accomplished by using the following
methods.
The first method is executed by band passing a
signal at several frequencies and then comparing the
Pn or Pg phase to the Lg phase at each frequency and
plotting it against the magnitude of the event.
Through these means Phase Ratio diagrams that
include several events can be created and interpreted.
I have found that the explosions will separate from
the natural events at certain frequencies and by
creating a Phase Ratio diagram that includes events
for each frequency range we can determine which
ranges work the best.
Another method used to discriminate the events was
the creation of P-Wave and S-Wave Spectral Ratios.
This was done by comparing each phase individually
at 1-2 Hz and 6-8 Hz and plotting the results against
the magnitude of the event. Once again I found the
explosions separated from the natural events.
Source Processes of Western Washington
Intraslab Earthquakes (1939-1965)
Wiest, K., and Doser, D., Department of Geological
Sciences, University of Texas at El Paso, Zollweg, J.,
Department of Geological Sciences, Boise State
University
The Cascadia Subduction Zone in Washington and
Oregon is created by the Juan de Fuca plate
subducting beneath the North American plate at a
rate of about 4 cm/year. Earthquake hazards in the
region are associated with plate interface, intraslab,
and crustal earthquakes. All have potential to cause
significant physical and monetary damage. As
population and infrastructure continue to grow, the
possibility of more extensive damage from seismicity
in the region also grows. In this study, we will
examine and model regional and teleseismic
seismograms for historic intraslab and crustal events
of M > 5.5 occurring within the Pacific Northwest
region to better determine source locations, source
mechanisms, and rupture histories of these events.
Our first year of research deals with seismograms for
four intraslab earthquakes (1930-1965) of M > 5.7
located in Western Washington. We are using digital
seismograms of recent (post 1990) intraslab events
(with well determined focal depths and mechanisms)
that were recorded in the same locations to aid in the
interpretation of the historical seismograms. We are
confident that some of the recent events may be used
as empirical Greens functions to more accurately
determine the rupture processes of the historic
earthquakes. Preliminary work has focused on the
analysis of seismograms recorded in Pasadena,
California and College, Alaska for the April 1949
Olympia and January 2001 Nisqually events. The
earthquakes appear to have similar waveforms,
although the 1949 event generated more damaging
ground motions than the Nisqually event.
Statistical Geochemistry of Stream Sediments of
the Sierra de Pena Blanca
Zamarron, I., and Goodell, P., Department of
Geological Sciences, University of Texas at El Paso,
[email protected]
The Sierra de Peña Blanca is located 50 km to the
north of Chihuahua City and it contains the largest
amount of uranium (U) reserves known in Mexico.
Three of its deposits, El Nopal, Margaritas, and
Puerto 3, were in an active stage of development.
During the industrial development and scientific
study, several geological and geochemistry databases
were generated, but all activities were terminated in
1983; therefore, the study and understanding of the
results were never undertaken. The present research
activities are engaged in completing one of these
investigations.
The Sierra de Peña Blanca is a 60 km long, northsouth trending range, which constitutes the surface
expression of the Peña Blanca block, a small coherent
tectonic fragment that ranges from Mid-Tertiary
volcanics (45 to 35 million years) at the northern end.
The Peña Blanca deposits are found in Tertiary ash
flow tuffs near the western margin of the Rio Grande
Rift. The area is broken by various district faults,
which dip to the east.
As a method of geochemical exploration for
additional uranium resources 160 stream sediment
samples where obtained from the Peña Blanca region
and analyzed for 28 chemical elements. Statistical
analyses of this data are in progress and will be
reported here. They will include standard descriptive
statistics,
correlation
coefficients,
pairwise
correlations, factor analysis, and spacial analysis.
The spacial analysis will include the study of
chemical results in many maps in relationship to the
known mineral deposits.
The results will be
integrated and summarized.