Hydrothermal activity and magma genesis along a propagating back-arc basin: Valu Fa Ridge (southern Lau Basin)

Valu Fa Ridge is an intraoceanic back-arc spreading center located at the southern prolongation of the Lau basin. Bathymetric observations as well as detailed sampling have been carried out along the spreading axis in order to trace hydrothermal and volcanic activity and to study magma generation processes. The survey shows that widespread lava flows from recent volcanic eruptions covered most of the Vai Lili hydrothermal vent field; only diffuse low-temperature discharge and the formation of thin layers of siliceous precipitates have been observed. Evidence of present-day hydrothermal activity at the Hine Hina site is indicated by a thermal anomaly in the overlying water column. Our studies did not reveal any signs of hydrothermal activity either above the seismically imaged magma chamber at 22°25′S or across the southern rift fault zone (22°51′S). Lavas recovered along the Valu Fa Ridge range from basaltic andesites to rhyolites with SiO2 contents higher than reported from any other intraoceanic back-arc basin. On the basis of the highly variable degrees of crystal fractionation along axis, the development of small disconnected magma bodies is suggested. In addition, the geochemical character of the volcanic rocks shows that the transition zone from oceanic spreading to propagating rifting is located south of the Hine Hina vent field in the vicinity of 22°35′S

Exploring patterns of recurrent melanoma in Northeast Scotland to inform the introduction a digital self-examination intervention

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Along- and Across-Arc Variations in the Southern Volcanic Zone, Chile

Within Collaborative Research Center (SFB574), we are studying the changes in the chemistry of olivinebearing volcanic rocks along the volcanic front of the Southern Volcanic Zone (SVZ) in Chile and in the rear and backarc in Argentina. Samples from the volcanic front (VF) have typical trace element signatures of subduction zone volcanic rocks, characterized, for example, by negative Nb and Ta anomalies and positive Pb, Sr, Cs, Rb, Ba, Th and U anomalies on incompatible element (spider) diagrams. Samples from Longavi in the forearc are distinct in having lower abundances of the HREE's, high Sr/Y and geochemical signatures characteristic of adakitic rocks believed to be derived through melting of the subducting slab. The northern Southern Volcanic Zone (NSVZ) samples from Tupungatito and San José have the most enriched highly to moderately incompatible element ratios, high Rb/Ba and low La/Ta and Ba/La, suggesting involvement of lower crust in the petrogenesis of these rocks. We observe systematic variations in Sr and Nd isotopic compositions along the arc, with Sr isotopes showing a dramatic increase and Nd isotopes showing a dramatic decrease in the NSVZ, which is where the crust begins to thicken significantly. The increase in Sr and decrease in Nd in the VF is coupled with an increase in the degree of differentiation of the Tupungatito and San José (SiO2 > 58%, MgO = 2-4%) volcanoes. On the Pb isotope diagrams, the VF rocks trend from MORB-like compositions to the field for pelagic sediments, consistent with involvement of subducted sediments in generating the VF rocks. Interestingly, samples from the NSVZ form the lower end of the VF array (have the least radiogenic Pb isotopic compositions) on the uranogenic Pb isotope diagram, but extend to the left of the rest of the VF array on the thorogenic Pb isotope diagram, showing evidence of at least a second enriched component. The presence of the second enriched component could reflect assimilation of lower crust or addition of lower crust through subduction erosion into the manlte wedge. Quaternary backarc samples in Argentina also show subduction signatures in their incompatible elements but generally show lower fluid signatures than the VF samples. Although the Pb isotopic compositions of backarc rocks are similar to MORB, the low Nd isotopic compositions indicate the presence of enriched material within the backarc. Although no systematic variation is seen in Sr and Nd isotopic composition from north to souths, the Pb isotope ratios show systematic spatial variations with the northern samples having the most enriched Pb isotope ratios. The lower fluid signatures in the backarc volcanoes, coupled with less radiogenic Pb isotopic compositions are consistent with a decreasing influence of the subduction signature into the backarc. With the addition of Hf and O isotope data we should be able to better constrain the different reservoirs involved in generating the diverse geochemical compositions of the SVZ volcanic rocks

Post-Collisional Transition from Subduction to Intraplate-type Magmatism in the Westernmost Mediterranean: Evidence for Continental-Edge Delamination of Subcontinental Lithosphere

Post-collisional magmatism in the southern Iberian and northwestern African continental margins contains important clues for the understanding of a possible causal connection between movements in the Earth's upper mantle, the uplift of continental lithosphere and the origin of circum-Mediterranean igneous activity. Systematic geochemical and geochronological studies (major and trace element, Sr–Nd–Pb-isotope analysis and laser 40Ar/39Ar-age dating) on igneous rocks provide constraints for understanding the post-collisional history of the southern Iberian and northwestern African continental margins. Two groups of magmatic rocks can be distinguished: (1) an Upper Miocene to Lower Pliocene (8·2–4·8 Ma), Si–K-rich group including high-K (calc-alkaline) and shoshonitic series rocks; (2) an Upper Miocene to Pleistocene (6·3–0·65 Ma), Si-poor, Na-rich group including basanites and alkali basalts to hawaiites and tephrites. Mafic samples from the Si–K-rich group generally show geochemical affinities with volcanic rocks from active subduction zones (e.g. Izu–Bonin and Aeolian island arcs), whereas mafic samples from the Si-poor, Na-rich group are geochemically similar to lavas found in intraplate volcanic settings derived from sub-lithospheric mantle sources (e.g. Canary Islands). The transition from Si-rich (subduction-related) to Si-poor (intraplate-type) magmatism between 6·3 Ma (first alkali basalt) and 4·8 Ma (latest shoshonite) can be observed both on a regional scale and in individual volcanic systems. Si–K-rich and Si-poor igneous rocks from the continental margins of southern Iberia and northwestern Africa are, respectively, proposed to have been derived from metasomatized subcontinental lithosphere and sub-lithospheric mantle that was contaminated with plume material. A three-dimensional geodynamic model for the westernmost Mediterranean is presented in which subduction of oceanic lithosphere is inferred to have caused continental-edge delamination of subcontinental lithosphere associated with upwelling of plume-contaminated sub-lithospheric mantle and lithospheric uplift. This process may operate worldwide in areas where subduction-related and intraplate-type magmatism are spatially and temporally associated

Sr/Ca and δ¹⁸O in a fast-growing Diploria strigosa coral - evaluation of a new climate archive for the tropical Atlantic

This study provides the first monthly resolved, 41-year record of geochemical variations (δ18O and Sr/Ca) in a fast-growing Diploria strigosa brain coral from Guadeloupe, Caribbean Sea. Linear regression yields a significant correlation of coral Sr/Ca (δ18O) with instrumental sea surface temperature (SST) on both monthly and mean annual scales (e.g., r = −0.59 for correlation between Simple Ocean Data Assimilation (SODA) SST and Sr/Ca, and r = −0.66 for δ18O; mean annual scale, p < 0.0001). The generated coral Sr/Ca (δ18O)-SST calibration equations are consistent with each other and with published equations using other coral species from different regions. Moreover, a high correlation of coral Sr/Ca and δ18O with local air temperature on a mean annual scale (r = −0.78 for Sr/Ca; r = −0.73 for δ18O; p < 0.0001) demonstrates the applicability of geochemical proxies measured from Diploria strigosa corals as reliable recorders for interannual temperature variability. Both coral proxies are highly correlated with annual and seasonal mean time series of major SST indices in the northern tropical Atlantic (e.g., r = −0.71 for correlation between the index of North Tropical Atlantic SST anomaly and Sr/Ca, and r = −0.70 for δ18O; mean annual scale, p < 0.001). Furthermore, the coral proxies capture the impact of the El Niño–Southern Oscillation on the northern tropical Atlantic during boreal spring. Thus fast-growing Diploria strigosa corals are a promising new archive for the Atlantic Ocean

Pliocene mixed-layer oceanography for Site 1241, using combined Mg/Ca and δ¹⁸O analyses of Globigerinoides sacculifer

To reconstruct changes in tropical Pacific surface hydrography, we used samples from Site 1241 (5°50′N, 86°26′W; 2027-m water depth) to establish high-resolution records of Mg/Ca and δ18O for the mixed-layer dwelling planktonic foraminifer Globigerinoides sacculifer for the Pliocene time interval from 4.8 to 2.4 Ma. An increase in average seasurface temperatures (SSTs) (24.5°–25.5°C) between 4.8 and 3.7 Ma can probably be explained by a southward shift of the Intertropical Convergence Zone, thereby increasing the influence of the warmer North Equatorial Countercurrent. The general global cooling trend, a response to intensification of Northern Hemisphere glaciation (NHG), started at ~3.2 Ma (shown by the δ18Obenthic record) and is paralleled by tropical east Pacific cooling (indicated by SSTMg/Ca). Tropical east Pacific cooling, however, had already commenced by ~3.7 Ma, suggesting that global cooling, probably related to decreasing atmospheric CO2 concentrations, might have started well before intensification of NHG. Relative changes in local sea-surface salinity (indicated by δ18Osalinity) show a decoupling from global high-latitude processes (shown by the δ18Obenthic record). Long-term regional freshening started with decreasing SSTMg/Ca at ~3.7 Ma, suggesting that changes in the tropical wind field combined with latitudinal shifts of the tropical rainbelt were related to general decreases in tropical east Pacific SST-controlled δ18Osalinity. The similarity of Pliocene SSTMg/Ca for G. sacculifer with modern SSTs in the east Pacific, in combination with the early development of a shallow thermocline at Site 1241, gives no direct support to the idea that a permanent El Niño-like Pliocene climate might have existed during the early Pliocene

Impact of warming events on reef-scale temperature variability as captured in two Little Cayman coral Sr/Ca records

The rising temperature of the world’s oceans is affecting coral reef ecosystems by increasing the frequency and severity of bleaching and mortality events. The susceptibility of corals to temperature stress varies on local and regional scales. Insights into potential controlling parameters are hampered by a lack of long term in situ data in most coral reef environments and sea surface temperature (SST) products often do not resolve reef-scale variations. Here we use 42 years (1970–2012) of coral Sr/Ca data to reconstruct seasonal- to decadal-scale SST variations in two adjacent but distinct reef environments at Little Cayman, Cayman Islands. Our results indicate that two massive Diploria strigosa corals growing in the lagoon and in the fore reef responded differently to past warming events. Coral Sr/Ca data from the shallow lagoon successfully record high summer temperatures confirmed by in situ observations (>338C). Surprisingly, coral Sr/Ca from the deeper fore reef is strongly affected by thermal stress events, although seasonal temperature extremes and mean SSTs at this site are reduced compared to the lagoon. The shallow lagoon coral showed decadal variations in Sr/Ca, supposedly related to the modulation of lagoonal temperature through varying tidal water exchange, influenced by the 18.6 year lunar nodal cycle. Our results show that reef-scale SST variability can be much larger than suggested by satellite SST measurements. Thus, using coral SST proxy records from different reef zones combined with in situ observations will improve conservation programs that are developed to monitor and predict potential thermal stress on coral reefs

Effects of the fibers distribution in the human eardrum: A biomechanical study

The eardrum separates the external ear from the middle ear and it is responsible to convert the acoustical energy into mechanical energy. It is divided by pars tensa and pars flaccida. The aim of this work is to analyze the susceptibility of the four quadrants of the pars tensa under negative pressure, to different lamina propria fibers distribution. The development of associated ear pathology, in particular the formation of retraction pockets, is also evaluated. To analyze these effects, a computational biomechanical model of the tympano-ossicular chain was constructed using computerized tomography images and based on the finite element method. Three fibers distributions in the eardrum middle layer were compared: case 1 (eardrum with a circular band of fibers surrounding all quadrants equally), case 2 (eardrum with a circular band of fibers that decreases in thickness in posterior quadrants), case 3 (eardrum without circular fibers in the posterior/superior quadrant). A static analysis was performed by applying approximately 3000Pa in the eardrum. The pars tensa of the eardrum was divided in four quadrants and the displacement of a central point of each quadrant analyzed. The largest displacements of the eardrum were obtained for the eardrum without circular fibers in the posterior/superior quadrant