Thomas Mooney | Geology Reports

USGS2007

Observations of chlorine monoxide over Scott Base, Antarctica, during the ozone hole, 1996-2005

We report observations of chlorine monoxide, ClO, in the lower stratosphere, made from Scott Base (77.85º S, 166.77º E) in springtime during each year, 1996-2005. The ClO amounts in the atmosphere are retrieved from remote measurements of microwave emission spectra. ClO column densities of up to about 2.5 × 1015 cm-2 are recorded during September, when chlorine is present in chemically active forms due to reactions on the surface of Polar Stratospheric Cloud (PSC) particles. Maximum mixing ratios of ClO are approximately 2 ppbv. The annual average of ClO column density during the activation period is anticorrelated with similar averages of ozone column measured at nearby Arrival Heights, with correlation coefficient of –0.81, and with averages of ozone mass integrated over the entire polar region, with similar correlation coefficients. There was a substantial decrease in ClO amounts during 2002-2004. There has been no systematic change in the timing of chlorine deactivation attributable to secular change in the Antarctic vortex

Open-File Report↗

USGS2006

Seismic characteristics of central Brazil crust and upper mantle: A deep seismic refraction study

[1] A two‐dimensional model of the Brazilian central crust and upper mantle was obtained from the traveltime interpretation of deep seismic refraction data from the Porangatu and Cavalcante lines, each approximately 300 km long. When the lines were deployed, they overlapped by 50 km, forming an E‐W transect approximately 530 km long across the Tocantins Province and western São Francisco Craton. The Tocantins Province formed during the Neoproterozoic when the São Francisco, the Paranapanema, and the Amazon cratons collided, following the subduction of the former Goiás ocean basin. Average crustal V P and V P /V S ratios, Moho topography, and lateral discontinuities within crustal layers suggest that the crust beneath central Brazil can be associated with major geological domains recognized at the surface. The Moho is an irregular interface, between 36 and 44 km deep, that shows evidences of first‐order tectonic structures. The 8.05 and 8.23 km s −1 P wave velocities identify the upper mantle beneath the Porangatu and Cavalcante lines, respectively. The observed seismic features allow for the identification of (1) the crust has largely felsic composition in the studied region, (2) the absence of the mafic‐ultramafic root beneath the Goiás magmatic arc, and (3) block tectonics in the foreland fold‐and‐thrust belt of the northern Brasília Belt during the Neoproterozoic. Seismic data also suggested that the Bouguer gravimetric discontinuities are mainly compensated by differences in mass distribution within the lithospheric mantle. Finally, the Goiás‐Tocantins seismic belt can be interpreted as a natural seismic alignment related to the Neoproterozoic mantle domain.

Journal of Geophysical Research B: Solid Earth↗