Geology Commons^™

Climate Change And Late Pliocene Acceleration Of Erosion In The Himalaya, Katharine Huntington, Ann Blythe, Kip Hodges

Ann Blythe

Studies of active mountain ranges suggest that atmospheric and geodynamic processes may be strongly coupled through erosion — a hypothesis that has led to a debate over the relative importance of climate and far-field tectonic forcing in influencing erosion. We addressed this debate by developing the detailed long-term erosional history of a transect in the central Annapurna Range of Nepal for comparison with the climate and tectonic forcing histories of the region. Patterns of apatite fission-track and muscovite 40Ar/39Ar apparent ages with elevation indicate a five-fold increase in apparent erosion rate between 2.5 and 0.9 Ma ago. The time frame …

The Karst Of West-Central Florida, Lee J. Florea

Lee J Florea, PhD, P.G.

Caves, the cornerstone feature of karst aquifers, are little understood in Florida. This dissertation, which analyzes the morphology, elevation, lithologic setting, and hydrology of caves in west-central Florida, demonstrates that the karst of the unconfined Floridan aquifer differs from the paradigm view of karst presented in modern geology textbooks. The differences reflect setting: eogenetic (west-central Florida) vs. telogenetic (conventional).

Climatic Forcing Of Erosion, Landscape, And Tectonics In The Bhutan Himalayas, Djordje Grujic, Isabelle Coutand, Bodo Bookhagen, Stéphane Bonnet, Ann Blythe, Chris Duncan

Ann Blythe

A fundamental objective in studies of climate-erosion-tectonics coupling is to document convincing correlation between observable indicators of these processes on the scale of a mountain range. The eastern Himalayas are a unique range to quantify the contribution of tectonics and climate to long-term erosion rates, because uniform and steady tectonics have persisted for several million years, while monsoonal precipitation patterns have varied in space and time. Specifically, the rise of the Shillong plateau, the only orographic barrier in the Himalayan foreland, has reduced the mean annual precipitation downwind in the eastern Bhutan Himalaya at the Miocene-Pliocene transition. Apatite fission-track (AFT) …

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 …

Formation And Maintenance Of Shear Zones, Caleb Holyoke, Jan Tullis

Caleb Holyoke

No abstract provided.

Mechanisms Of Weak Phase Interconnection And The Effects Of Phase Strength Contrast On Fabric Development, Caleb Holyoke, Jan Tullis

Caleb Holyoke

No abstract provided.

The Interaction Between Reaction And Deformation: An Experimental Study Using A Biotite + Plagioclase + Quartz Gneiss, Caleb Holyoke, Jan Tullis

Caleb Holyoke

No abstract provided.