Monday, May
14, 2012
6:00 - 7:30 pm
Pellissippi
State Technical Community College
10915 Hardin
Valley Road, Knoxville
J.L Goins Administration Building, Cafeteria Annex
MAY PRESENTATION
Award-Winning
Student Presentations
This month ETGS meeting will follow a slightly different format than is usual. Instead of having one speaker give a 50-minute-long presentation, we will be featuring three "mini" presentations, each approximately 15 minutes long, by graduate students from the Department of Earth and Planetary Sciences (EPS) at the University of Tennessee - Knoxville. Each year EPS offers a course on Professional Presentations (Geology 596) to provide a formal opportunity for students to develop their oral communication skills. This one-credit course involves writing an abstract and preparing, practicing, and delivering a professional presentation on any geological topic of interest, usually a portion of their dissertation/thesis research. The students present their talks at a departmental seminar and they are ranked by the seminar attendees and a five-person committee consisting of faculty, post-doc, and students. Once again, ETGS is partnering with EPS to further broaden this valuable experience by offering awards to the student presenters and inviting them to give their talks to a professional geology audience at the May ETGS meeting. We hope you can join us to support this new generation of geologists and see their presentations.
Microgravity and
Micromagnetic Evidence for Shallow Subsurface
Termination of the Northeast Dike at Ship Rock, NM
Carolyn
Tewksbury-Christle
Department of Earth & Planetary Sciences, University
of Tennessee
Knoxville, Tennessee
The northeast dike at Ship
Rock, NM is composed of en echelon segments whose offsets do not
appear to be formed by post-emplacement deformation. Delaney and
Pollard (1981) modeled the subsurface structure of the northeast
dike based on the surface expression and concluded that the en
echelon segments formed due to rotation of the maximum horizontal
compressive stress direction as the dike propagated vertically.
They proposed that a main dike is located at depth, connecting
the en echelon segments.
I modeled the structure under the northeast dike based on gravity
and magnetic field measurements I gathered over a pair of en
echelon dike segments and used that modeling to constrain the
emplacement mechanism. Though the reduced the gravity data
appears to be random, suggesting that the actual gravity anomaly
is within the error of the Lacoste and Romberg gravimeter used
for this study, the magnetics show a distinct anomaly along the
dike. For this reason, I developed several models of the
subsurface using the University of British Columbia's Mag3D
programs and determined a best fit between modeled and field
data. The initial models, based off of Delaney and Pollard's
research, produced anomalies that are both larger and wider than
the anomalies in the measured field data. To produce a smaller
and narrower anomaly, dike material must be removed from the
model. In the best-fit model for the magnetic field data, the
dike terminates at approximately six meters below the surface.
This surprising result suggests that the northeast dike was
originally emplaced above the present-day land surface and
propagated both upwards and downwards. The remnants of the
northeast dike appear to be the base, not the top, of the
original dike, which has since been eroded away, and the en
echelon segments formed due to rotation of the maximum horizontal
compressive stress direction at the bottom edge of the dike.
Comparative
Functional Analysis of Microbial Sulfide Oxidation
and its Impact on Environmental Geochemistry
Brendan Headd
Department of Earth &
Planetary Sciences, University of Tennessee
Knoxville, Tennessee
Numerous metabolic strategies
have evolved in Bacteria and Archaea to utilize reduced sulfur
compounds as electron donors for energy transformation and the
fixation of carbon dioxide for either chemolithoautotrophy or
anoxygenic photosynthesis. As such, different enzymes, pathways,
and mechanisms for the oxidation of reduced sulfur compounds are
known and complicate detection and phylogenetic descriptions of
sulfur-oxidizing microbes in natural systems. The extent to which
gene nucleotide variation in any of the sulfur oxidation pathways
affects enzyme and pathway function are not well understood. Gene
variations among different sulfur bacteria in close proximity to
one another, even if utilizing the same metabolic pathway, likely
yield distinct and quantifiable metabolic potentials and
byproducts. Because the sulfur oxidation (Sox) system is present
in diverse guilds of sulfur bacteria, the purpose of this study
was to examine the distribution of soxB genes along a geochemical
gradient to identify how different variations of this particular
gene are partitioned in a natural, flowing sulfidic spring-stream
complex where H2S concentration decreased away from the spring
orifice (from 188 to 0 µmol/L), dissolved O2 increased (from 5.6
to 150 µmol/L), and the pH increased (from 6.8 to 7.8) toward
the end of the outflow channel 14 m downstream. soxB genes were
retrieved from microbial mats and sediments in all areas of the
spring outflow channel. However, soxB gene clusters were
heterogeneously distributed within the spring-stream system. For
instance, soxB OTUs related to the genus Chlorobium were found
only in microbial mats at the spring orifice, but several soxB
OTUs related to the genera Halothiobacillus and Paracoccus were
retrieved from sediment microbial communities underlying the mats
throughout the outflow channel. The upper and middle sections of
the outflow channel, where sulfide concentrations were moderate,
were dominated by a single soxB OTU related to the genus
Thiothrix. Only where sulfide concentrations were low to
undetectable were soxB OTUs distantly related (70-80% similarity)
to the genera Bradyrhizobium, Rhodovulum, and Thiobacillus
identified. The end of the outflow channel was dominated by soxB
OTUs only found at the end of the outflow channel and distantly
related to the genus Rhodovulum. The nucleotide sequence
variations were specific to certain phylogenetic groups and
metabolic pathways occuring within the spring outflow channel.
These results suggest that the distribution of sulfur-oxidizing
bacteria along this geochemical gradient is a function of
substrate preference and availability in order to maintain
optimal enzyme function. Consequently, efforts are underway to
measure the concentrations of intermediate sulfur species and to
express the different variations of the soxB gene clusters in the
laboratory to test the currently hypothesized model for metabolic
variability among the sulfur-oxidizing bacteria in this spring.
The
Curecanti Pluton: A ~1.4 Ga Laccolith in the
Black Canyon of the Gunnison, CO
Donnie Hicks
Department of Earth & Planetary Sciences, University
of Tennessee
Knoxville, Tennessee
The 1420±15 Ma Curecanti pluton, exposed in the Black Canyon of the Gunnison, Colorado, is a 6-km-long discordant sheet of undeformed fine-grained quartz monzonite. The pluton was emplaced as a tabular body into amphibolite facies quartzofeldspathic migmatites, gneisses, and schists. Its floor dips 10-25º to the northeast, its roof undulates between vertical and subhorizontal as it tapers towards the intrusion's margins, and all contacts are highly discordant with the subvertical foliation in the host rock. Floor and roof contacts are characterized by an agmatic zone where wall rocks are injected with leucosome along preexisting foliations, leading to paleosomes entirely surrounded by leucosome, some of which are then stoped into the main body of the Curecanti and digested. A pervasive set of east-west striking and vertically dipping pegmatites cross-cut the Curecanti pluton and are interpreted as recording the last stage of crystallization. The Curecanti pluton&rsquos geometry is interpreted as a laccolith with emplacement facilitated by extensive brecciation, assimilation, and lifting of roof rocks. Field observations suggest that the emplacement depth and geometry of the Curecanti pluton was likely a function of magma ascent being arrested in the mid-crust, perhaps at the brittle-ductile-transition, and forcibly lifting its roof rocks. Further investigation will help to demonstrate these emplacement mechanisms and determine how this fine-grained pluton relates to a global suite of megacrystic 1.4 Ga granites, providing insights into the tectonic setting of 1.4 Ga magmatism throughout southern Laurentia.
Page updated May 26, 2018 |