Contact metamorphism of roof pendants at Hope Valley,Alpine County,California, USA

Calcareous hornfelses and marbles all contain calcite+K-feldspar+quartz+sphene±diopside±plagioclase ±scapolite±clinozoisite. In addition, rocks on one side of a fault contain combinations of biotite, amphibole, and muscovite while those on the other side contain combinations of grossular, wollastonite, and axinite. At bars, mineral-fluid equilibria in biotite and amphibole-bearing rocks record T= 440° C and garnet-bearing rocks record T=540° C and Conventional volumetric fluid-rock ratios were calculated using measured progress of prograde decarbonation reactions and the conditions of metamorphism: marbles, 0–0.4; amphibole-bearing hornfelses, 1.0–1.4; garnet-bearing hornfelses, 2.8–6.7. Decarbonation reactions were driven by pervasive infiltration of rock by reactive aqueous fluids. Differences in fluid-rock ratio between interbedded marble and hornfels and lack of correlation between fluid-rock ratio and whole-rock Cl-content, however, argue for channelized fluid flow along lithologic layers. A new analysis of reaction progress allows estimation of time-integrated fluxes for a specified temperature gradient along the direction of flow. Results are: marbles, 0–0.1×10⁵ cm³/cm²; amphibole-bearing hornfelses, 0.8–1.3×10⁵ cm³/cm²; garnet-bearing hornfelses, 1.2–2.5 × 10⁵ cm³/cm². Fluid flowed from regions of low to regions of high temperature. Using a simple thermal model for the area, the duration of contact metamorphism was estimated as 10⁵ years. Assuming the time of fluid flow was the same as the duration of the thermal event, the first measurements of average metamorphic fluxes (q) and permeabilities (k) are: average marbles, q=0–0.3×10^–8 cm/s and k =2×10^–6 darcy; hornfels, q=3–8×10^–8 cm/s and k =20–53×10^–6 darcy. Estimated premeabilities are within the range of values measured for metamorphic rocks in the laboratory. Fluxes, permeabilities, and whole-system fluidrock ratios are similar to those estimated for the Skaergaard hydrothermal system by Norton and Taylor (1979).     

Hydrothermal alteration of Tertiary igneous rocks from the Isle of Skye,northwest Scotland

Hydrothermal alteration of Tertiary gabbros from Skye involved the reaction of igneous olivine, augite, hypersthene, plagioclase, magnetite, and ilmenite with aqueous fluid primarily to combinations of talc, chlorite, montmorillonite, calcic amphibole, biotite, and secondary magnetite. Lesser amounts of calcite, epidote, quartz, sphene, prehnite, and garnet also developed. During mineralogical alteration of gabbro there was a net addition to rock of K, Na, Sr, and H₂O and a net loss of Mg. Gabbro was oxidized early in the hydrothermal event and later reduced. Iron and silicon were probably initially lost and later added. There is no evidence for significant change in the Al or Ca content of the gabbros. Hydrothermal alteration of Skye gabbro involved not only large-scale migration of ¹⁸O, ¹⁶O, D and H but also of K, Na, Sr, Mg, and probably Fe and Si.Mineral thermometry indicates that pyroxenes in the gabbros crystallized at 1000° C–1150° C and were very resistent chemically as well as isotopically to later hydrothermal alteration. Hypothetical equilibrium between primary and secondary mafic silicates suggests that mineralogical alteration of gabbro occurred at 450°–550° C. The lack of correlation between mineralogical and isotopic alteration of gabbro requires that much isotopic alteration occurred at temepratures above those at which the secondary minerals developed, 550°–1000° C. The chemical alteration of gabbro is correlated with its mineralogical alteration and therefore occurred at 450°–550° C.Measured progress of the mineral-fluid reactions was used to estimate the amount of H₂O fluid that infiltrated the gabbro as primary olivine was converted to talc+magnetite at 525°–550° C. Calculated fluid-rock ratios are in the range 0.2–6 (volume basis) and are smaller than values estimated from isotopic data (fluid/rock 1–10, volume basis). Both isotopic and petrologic data point to pervasive flow of fluid through crystalline rock at elevated temperatures of 500°–1000° C. Isotopic fluid-rock ratios are larger than petrologic fluid-rock ratios because isotopic alteration of cooling gabbro began earlier and at higher temperatures than did the mineralogical alteration.     

Condensed water in tropical cyclone “Oliver”, 8 February 1993

On February 8, 1993, the NASA DC-8 aircraft profiled from 10,000 to 37,000 feet (3.1–11.3 km) pressure altitude in a stratified section of tropical cyclone “Oliver” over the Coral Sea northeast of Australia. Size, shape and phase of cloud and precipitation particles were measured with a 2-D Greyscale probe. Cloud/ precipitation particles changed from liquid to ice as soon as the freezing level was reached near 17,000 feet (5.2 km) pressure altitude. The cloud was completely glaciated at −5°C. There was no correlation between ice particle habit and ambient temperature. In the liquid phase, the precipitation-cloud drop concentration was 4.0 × 10³ m⁻³, the geometric mean diameter D_g=0.5−0.7 mm, and the liquid water content 0.7−1.9 g m⁻³. The largest particles anywhere in the cloud, dominated by fused dendrites at concentrations similar to that of raindrops (2.5 × 10³ m⁻³) but a higher condensed water content (5.4 g m⁻³ estimated) were found in the mixed phase; condensed water is removed very effectively from the mixed layer due to high settling velocities of the large mixed particles. The highest number concentration (4.9 × 10⁴ m⁻³), smallest size (D_g=0.3−0.4 mm), largest surface area (up to 2.6 × 10² cm² m⁻³ at 0.4−1.0 g m⁻³ of condensate) existed in the ice phase at the coldest temperature (−40°C) at 35,000 feet (10.7 km). Each cloud contained aerosol (haze particles) in addition to cloud particles. The aerosol total surface area exceeded that of the cirrus particles at the coldest temperature. Thus, aerosols must play a significant role in the upscattering of solar radiation. Light extinction (6.2 km⁻¹) and backscatter (0.8 sr⁻¹ km⁻¹) was highest in the coldest portion of the cirrus cloud at the highest altitude.     

A 48-kyr-long slip rate history for the Jordan Valley segment of the Dead Sea Fault

We investigate the late Quaternary active deformation along the Jordan Valley segment of the left-lateral Dead Sea Fault and provide new insights on the behaviour of major continental faults. The 110-km-long fault segment shows systematic offsets of drainage systems surveyed at three sites along its southern section. The isotopic dating of six paleoclimatic events yields a precise chronology for the onset of six generations of gully incisions at 47.5 ka BP, 37.5 ka BP, 13 ka BP, 9 ka BP, 7 ka BP, and 5 ka BP. Additionally, detailed mapping and reconstructions provide cumulative displacements for 20 dated incisions along the fault trace. The individual amounts of cumulative slip consistently fall into six distinct classes. This yields: i) an average constant slip rate of 4.7 to 5.1 mm/yr for the last 47.5 kyr and ii) a variable slip rate ranging from 3.5 mm/yr to 11 mm/yr over 2-kyr- to 24-kyr-long intervals. Taking into account that the last large earthquake occurred in AD 1033, we infer 3.5 to 5 m of present-day slip deficit which corresponds to a Mw  7.4 earthquake along the Jordan Valley fault segment. The timing of cumulative offsets reveals slip rate variations critical to our understanding of the slip deficit and seismic cycle along major continental faults.     

Thermodynamics of rare events and impulsive relaxation events in the magnetospheric substorm dynamics

The magnetosphere dynamics shows fast relaxation events following power-law distribution for many observable quantities during magnetic substorms. The emergence of such power-law distributions has been widely discussed in the framework of self-organized criticality and/or turbulence. Here, a different approach to the statistical features of these impulsive dynamical events is proposed in the framework of the thermodynamics of rare events [Lavenda, B.H., Florio, A., 1992. Thermodynamics of rare events, Int. J. Theor. Phys. 31, 1455–1475; Lavenda, B.H., 1995. Thermodynamics of Extremes. Albion]. In detail, an application of such a novel approach to the magnetospheric substorm avalanching dynamics as monitored by the auroral electroject index is discussed.     

Revisiting wintertime cold air intrusions at the east of the Andes: propagating features from subtropical Argentina to Peruvian Amazon and relationship with large-scale circulation patterns

This study investigates the spatial and temporal characteristics of cold surges that propagates northward along the eastern flank of the Andes from subtropical to tropical South America analysing wintertime in situ daily minimum temperature observations from Argentina, Bolivia and Peru and ERA-40 reanalysis over the 1975–2001 period. Cold surges usually last 2 or 3 days but are generally less persistent in the southern La Plata basin compared to tropical regions. On average, three to four cold surges are reported each year. Our analysis reveals that 52 % of cold episodes registered in the south of La Plata basin propagate northward to the northern Peruvian Amazon at a speed of around 20 m s^?1. In comparison to cold surges that do not reach the tropical region, we demonstrate that these cold surges are characterized, before they reach the tropical region, by a higher occurrence of a specific circulation pattern associated to southern low-level winds progression toward low latitudes combined with subsidence and dry condition in the middle and low troposphere that reinforce the cold episode through a radiative effect. Finally, the relationship between cold surges and atmosphere dynamics is illustrated for the two most severe cold intrusions that reached the Peruvian and Bolivian Amazon in the last 20 years.     

Correlation of reefal Oxfordian episodes and climatic implications in the eastern Paris Basin (France)

Oxfordian reefal episodes of Lorraine and Burgundy have a long time been considered as contemporaneous. Biostratigraphic data and sequential evolutions peculiar to each region indicate their structural autonomy during Oxfordian times. A north‐south‐oriented well‐logging transect shows that, during the Middle Oxfordian, a shallow reefal platform developed in Lorraine while thin deeper deposits occurred in Burgundy. In spite of their different ages, reefal episodes of Middle Oxfordian in Lorraine and Upper Oxfordian in Burgundy exhibit a broadly similar vertical evolution of coral communities. During the Late Oxfordian, the contemporaneous occurrence of a diversified assemblage in the Burgundy region, a colder coral assemblage characterized by eurytopic genera and the decrease in seawater isotopic temperatures in Lorraine can be explained by a shift in trophic conditions, a climatic change related to structural rearrangements in this strategic place and a modification of oceanic circulations between the arctic and the Tethyan regions.