Interaction of mantle-derived magma with island crust? Trace element and oxygen isotope data from the Diego Hernandez Formation, Las Cañadas, Tenerife

The Quaternary Diego Hernandez Formation consists of interbedded phonolitic pyroclastics and basanite lavas and scoria beds. Most of the phonolites are mingled-magma units that contain a minor mafic component. The phonolites fall into two stratigraphically bounded groups, based on major and trace element abundances. Nb contents are especially distinctive, due to a varying role for titanite during petrogenesis. Nepheline syenite xenoliths, which are plentiful in some of the phonolitic ignimbrites, fall into the same two compositional groupings but are typically more strongly differentiated. Major and trace element variations during evolution of the phonolites can be modelled by fractional crystallization, by melting of syenite, or by some combination of the two such as AFC. Trace element variations among the basanites require the addition of a highly fractionated felsic component, either phonolitic magma or nepheline syenite. δ¹⁸O values of phonolites vary across twice the range of the basanites, inconsistent with an origin by pure fractional crystallization of a basanitic parent. We conclude that recycling of differentiated rocks within the Tenerife island edifice has played a significant role in Quaternary magmatism on Tenerife.     

Metop-GRAS in-orbit instrument performance

The GRAS instrument on the Metop-A satellite provides more than 600 radio occultation measurement profiles per day. The instrument is characterized by its wide antenna coverage, high signal-to-noise ratio and an ultra-stable clock reference. The conventional dual-frequency tracking of GPS signals is under dynamic atmosphere conditions complemented by open loop tracking with sampling of the signal at a 1 kHz rate, providing an unprecedented view of the signal spectral environment. This paper presents the instrument performance as derived from analysis of in-orbit measurement data. We show that the noise figure is low enough to enable mapping of external radio noise variations over the earth’s surface. An error propagation model is presented to relate instrument characteristics to bending angle performance. This model is also used to illustrate the relation between filter bandwidth, resolution and measurement noise. The Doppler model, guiding open loop measurements, is found to be accurate to better than 20 Hz with a possibility for improvement to 10 Hz. The high performance at low altitudes enables the presence of surface reflections at the −20-dB level to be identified in more than 50% of the occultations. The potential performance improvements for next generation receivers are discussed.     

GPS seismology

GPS seismology uses convential geodetic models to analyze GPS data at high sampling rates, such as 1 Hz. GPS seismology results are shown for the Denali, San Simeon, Tokachi-oki, and Chuetsu earthquakes. Records for these earthquakes indicate that GPS is an excellent instrument for measuring large displacements near earthquake ruptures. GPS systems can be improved for seismic applications if their sampling rates are increased from 1 to 10 Hz.     

Late Holocene sea-level rise in Tampa Bay: Integrated reconstruction using biomarkers,pollen, organic-walled dinoflagellate cysts,and diatoms

A suite of organic geochemical, micropaleontological and palynological proxies was applied to sediments from Southwest Florida, to study the Holocene environmental changes associated with sea-level rise. Sediments were recovered from Hillsborough Bay, part of Tampa Bay, and studied using biomarkers, pollen, organic-walled dinoflagellate cysts and diatoms. Analyses show that the site flooded around 7.5 ka as a consequence of Holocene transgression, progressively turning a fresh/brackish marl-marsh into a shallow, restricted marine environment. Immediately after the marine transgression started, limited water circulation and high amounts of runoff caused stratification of the water column. A shift in dinocysts and diatom assemblages to more marine species, increasing concentrations of marine biomarkers and a shift in the Diol Index indicate increasing salinity between 7.5 ka and the present, which is likely a consequence of progressing sea-level rise. Reconstructed sea surface temperatures for the past 4 kyrs are between 25 and 26 ° C, and indicate stable temperatures during the Late Holocene. A sharp increase in sedimentation rate in the top ∼50 cm of the core is attributed to human impact. The results are in agreement with parallel studies from the area, but this study further refines the environmental reconstructions having the advantage of simultaneously investigating changes in the terrestrial and marine environment.