The latest geodynamics in Asia: Synthesis of data on volcanic evolution,lithosphere motion,and mantle velocities in the Baikal-Mongolian region

From a synthesis of data on volcanic evolution,movement of the lithosphere,and mantle velocities in the Baikal-Mongolian region,we propose a comprehensive model for deep dynamics of Asia that assumes an important role of the Gobi,Baikal,and North Transbaikal transition-layer melting anomalies.This layer was distorted by lower-mantle fluxes at the beginning of the latest geodynamic stage(i.e.in the early late Cretaceous) due to avalanches of slab material that were stagnated beneath the closed fragments of the Solonker,Ural-Mongolian paleoceans and Mongol-Okhotsk Gulf of Paleo-Pacific.At the latest geodynamic stage,Asia was involved in east-southeast movement,and the Pacific plate moved in the opposite direction with subduction under Asia.The weakened upper mantle region of the Gobi melting anomaly provided a counterflow connected with rollback in the Japan Sea area.These dynamics resulted in the formation of the Honshu-Korea flexure of the Pacific slab.A similar weakened upper mantle region of the North Transbaikal melting anomaly was associated with the formation of the Hokkaido-Amur flexure of the Pacific slab,formed due to progressive pull-down of the slab material into the transition layer in the direction of the Pacific plate and Asia convergence.The early—middle Miocene structural reorganization of the mantle processes in Asia resulted in the development of upper mantle low-velocity domains associated with the development of rifts and orogens.We propose that extension at the Baikal Rift was caused by deviator flowing mantle material,initiated under the moving lithosphere in the Baikal melting anomaly.Contraction at the Hangay orogen was created by facilitation of the tectonic stress transfer from the Indo-Asian interaction zone due to the low-viscosity mantle in the Gobi melting anomaly.     

The chemical variability at the surface of Mars: Implication for sediment formation and rock weathering

Compositional data analysis was performed on chemical compositions of martian surface materials in order to unravel scenarios of past and present weathering and to evaluate the role of meteoritic accumulation. The observed chemical variability is analyzed by means of principal component analysis. Potential reservoirs that may have contributed primary material to soil formation are assessed. Chemical alteration in the course of in situ weathering is described in terms of alteration vectors that link the compositions of fresh rocks and their weathering crusts. The interplay of localized chemical alteration and global scale re-distribution and mixing of fines material is documented through the identification of different soil forming branches. These branches emanate from distinct compositional domains, which comprise basaltic and basalt-andesitic primary materials, and they converge to a global dust composition, which represents the product of chemical and physical disintegration and subsequent global mixing. Mass balance considerations applied to localized weathering phenomena are in line with findings from experimental acid-sulfate weathering on olivine-bearing basalts and the persistence of secondary silica in evaporitic rocks. In addition the composition and oxidation state of involved volcanic gases is deduced. Our findings corroborate the past activity of volcanic exhalation products in combination with liquid water. We conclude that average martian crust is dominated by basaltic materials at its topmost level and that the amount of meteoritic accumulation may contribute about 6 wt% to the martian fines. From the meteoritic contribution minimum soil formation rates of 60±20 cm/Gyr are derived. Sequestration of atmospheric oxygen during weathering of primary materials may account for the oxygen deficiency of the martian atmosphere. A 4-14-m-thick layer of oxidized martian fines may account for the estimated deficit of 1.7×¹⁰¹⁸ mol O₂ in the martian atmosphere depending on the primary oxidation state of volatile volcanic emanations.     

Late Miocene–Quaternary volcanism, tectonics and drainage system evolution in the East Carpathians, Romania

Middle Miocene (Sarmatian) convergence created the fold and thrust belt of the Eastern Carpathians of Romania, which subsequently experienced post-collisional crustal deformation combined with calc-alkaline and alkalic-basaltic volcanism in late Miocene–Quaternary time. This deformation led to the rise of the Cǎlimani–Gurghiu–Harghita volcanic mountains and to the subsidence of the N–S-oriented intramontane Borsec/Bilbor–Gheorgheni–Ciuc and Braşov pull-apart basins, and the E-oriented monocline-related Fǎgǎraş basin. The regional drainage network is the composite of:

(1) Older E-, SE- and S-flowing rivers, which cross the Carpathians, radiate towards the foreland and were probably established during the Middle Miocene (Sarmatian) collision event.

(2) A more recent drainage system related to the contemporaneous development of the volcanoes and intramontaneous basins, which generally drains westward into the Transylvanian Basin since late Miocene time and has been capturing the older river system.

The older river drainage system has also been modified by Late Pliocene–Quaternary folding, thrusting and monoclinal tilting along the Pericarpathian orogenic front and by reactivated transverse high angle basement faults, which cross the Eastern Carpathian foreland.     

HiRISE observations of gas sublimation-driven activity in Mars’ southern polar regions: IV. Fluid dynamics models of CO2 jets

The High Resolution Imaging Science Experiment (HiRISE) onboard Mars Reconnaissance Orbiter (MRO) has been used to monitor the seasonal evolution of several regions at high southern latitudes on Mars and, in particular, the jet-like activity which may result from the process described by Kieffer (Kieffer, H.H. [2007]. J. Geophys. Res. (Planets) 112, E08005. doi:10.1029/2006JE002816) involving translucent CO₂ ice. In this work, we concentrate on attempting to model the dusty CO₂ gas jets using a computational fluid dynamics code. Models that included surface slopes of up to 20° (as an analogy to the jet activity seen in “Inca City”, 81°S, 296°E), wind (from 0 to 6 m s⁻¹), variable vent cross-section and length, particles (including a particle size distribution) and mass loading (with dust to gas ratios exceeding 1) were investigated. The structure of the resulting gas jets, the particle distribution within the jets, the deposition patterns (including their dependence on particle size), and the appearance of jets when viewed from different orientations (including from a nadir-pointing camera) have been investigated for a range of input parameters. The results provide predictions for the size-dependency of altitudes of particles within a plume and the distribution of particle sizes in the deposition fans. Where slopes are a dominant influence, larger particles are expected to be seen furthest from the vent. Where wind is dominant, smaller particles should travel to larger distances. Models producing deposition patterns consistent in length (∼80 m) and form with fans observed by HiRISE on MRO have been demonstrated. The models also suggest that downward flow of gas produced by drag effects from particles falling from the jet under gravity could provide a mechanism for the production of bright haloes which are observed to surround dark fan deposits in MOC, HiRISE and CRISM.     

Morphology, temperature, and eruption dynamics at Pele

The Pele region of Io has been the site of vigorous volcanic activity from the time of the first Voyager I observations in 1979 up through the final Galileo ones in 2001. There is high-temperature thermal emission from a visibly dark area that is thought to be a rapidly overturning lava lake, and is also the source of a large sulfur-rich plume. We present a new analysis of Voyager I visible wavelength images, and Galileo Solid State Imager (SSI) and Near Infrared Mapping Spectrometer (NIMS) thermal emission observations which better define the morphology of the region and the intensity of the emission. The observations show remarkable correlations between the locations of the emission and the features seen in the Voyager images, which provide insight into eruption mechanisms and constrain the longevity of the activity. We also analyze an additional wavelength channel of NIMS data (1.87 μm) which paradoxically, because of reduced sensitivity, allows us to estimate temperatures at the peak locations of emission. Measurements of eruption temperatures on Io are crucial because they provide our best clues to the composition of the magma. High color temperatures indicative of ultramafic composition have been reported for the Pillan hot spot and possibly for Pele, although recent work has called into question the requirement for magma temperatures above those expected for ordinary basalts. Our new analysis of the Pele emission near the peak of the hot spot shows color temperatures near the upper end of the basalt range during the I27 and I32 encounters. In order to analyze the observed color temperatures we also present an analytical model for the thermal emission from fire-fountains, which should prove generally useful for analyzing similar data. This is a modification of the lava flow emission model presented in Howell (Howell, R.R. [1997]. Icarus 127, 394-407), adapted to the fire-fountain cooling curves first discussed in Keszthelyi et al. (Keszthelyi, L., Jaeger, W., Milazzo, M., Radebaugh, J., Davies, A.G., Mitchell, K.L. [2007]. Icarus 192, 491-502). When applied to the I32 observations we obtain a fire-fountain mass eruption rate of 5.1 × 10⁵ kg s⁻¹ for the main vent area and 1.4 × 10⁴ kg s⁻¹ for each of two smaller vent regions to the west. These fire-fountain rates suggest a solution to the puzzling lack of extensive lava flows in the Pele region. Much of the erupted lava may be ejected at high speed into the fire-fountains and plumes, creating dispersed pyroclastic deposits rather than flows. We compare gas and silicate mass eruption rates and discuss briefly the dynamics of this ejection model and the observational evidence.     

The variability of volcanic activity at Zamama, Culann, and Tupan Patera on Io as seen by the Galileo Near Infrared Mapping Spectrometer

Zamama, Culann, and Tupan Patera are three large, persistent volcanic centers on the jovian moon Io. As part of an ongoing project to quantify contributions from individual volcanic centers to Io’s thermal budget, we have quantified the radiant flux from all suitable observations made by the Galileo Near Infrared Mapping Spectrometer (NIMS) of these volcanoes, in some cases filling omissions in previous analyses. At Zamama, after a long period of cooling, we see a peak in thermal emission that corresponds with new plume activity. Subsequently, toward the end of the Galileo epoch, thermal emission from Zamama drops off in a manner consistent with a greatly reduced eruption rate and the cooling of emplaced flows. Culann exhibits possible episodic activity. We present the full Tupan Patera NIMS dataset and derive new estimates of thermal output and temporal behavior. Eruption rates at these three volcanoes are on the order of 30 m³ s⁻¹, consistent with a previous analysis of NIMS observations of Prometheus, and nearly an order of magnitude greater than Kilauea volcano, Hawai’i, Earth’s most active volcano. We propose that future missions to the jovian system could better constrain activity at these volcanoes and others where similar styles of activity are taking place by obtaining data on a time scale of, ideally, at least one observation per day. Observations at similar or even shorter timescales are desirable during initial waxing phases of eruption episodes. These eruptions are identifiable from their characteristic spectral signatures and temporal behavior.     

青藏高原北羌塘榴辉岩质下地质及富集型地幔源区——来自新生代火山岩的岩石地球化学证据

利用岩石地球化学的方法，研究了北羌塘新生代火山岩，结果表明，北羌塘第三纪火山岩可区分为碱性（钾玄岩质）和高钾钙碱两套不同的火山岩组合，它们分别起源于一个特殊的，不均一的富集型上地幔和一个加厚陆壳的榴辉岩质下地壳，由于青藏陆块之下软流层物质的上涌而形成幔源碱性岩浆活动，而幔源岩浆在Mobo面的底侵作用又为下地壳中酸性高钾钙碱系列火山岩的起源提供了热动力条件，该区两套不同系列和源区类型的火山岩正是在这种特殊的构造环境中形成。     

The Deccan tholeiite lavas and dykes of Ghatkopar–Powai area,Mumbai, Panvel flexure zone: Geochemistry,stratigraphic status,and tectonic significance

Mumbai City, situated on the western Indian coast, is well known for exposures of late-stage Deccan pillow basalts and spilites, pyroclastic rocks, rhyolite lavas, and trachyte intrusions. These rock units, and a little-studied sequence of tholeiitic flows and dykes in the eastern part of Mumbai City, constitute the west-dipping limb of a regional tectonic structure called the Panvel flexure. Here we present field, petrographic, major and trace element and Sr–Nd isotopic data on these tholeiitic flows and dykes, best exposed in the Ghatkopar–Powai area. The flows closely resemble the Mahabaleshwar Formation of the thick Western Ghats sequence to the east, in Sr–Nd isotopic ratios and multielement patterns, but have other geochemical characteristics (e.g., incompatible trace element ratios) unlike the Mahabaleshwar or any other Formation. The flows may have originated from a nearby eruptive center, possibly offshore of Mumbai. Two dykes resemble the Ambenali Formation of the Western Ghats in all geochemical characteristics, though they may not represent feeders of the Ambenali Formation lavas. Most dykes are distinct from any of the Western Ghats stratigraphic units. Some show partial (e.g., Sr–Nd isotopic) similarities to the Mahabaleshwar Formation, and these include several dykes with unusual, concave-downward REE patterns suggesting residual amphibole and thus a lithospheric source. The flows and dykes are inferred to have undergone little or no contamination, by lower continental crust. Most dykes are almost vertical, suggesting emplacement after the formation of the Panvel flexure, and indicate considerable east–west lithospheric extension during this late but magmatically vigorous stage of Deccan volcanism.