Basaltic Units Research Articles

Ruthenium Variation in Chromite from Komatiites and Komatiitic Basalts--A Potential Mineralogical Indicator for Nickel Sulfide Mineralization

More than 390 chromite grains from komatiites and komatiitic basalts from the Yilgarn craton of Western Australia and the Finnish part of the Fennoscandian Shield were analyzed using in situ laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to identify ruthenium (Ru) signatures in chromite associated with nickel sulfide-bearing rocks. Results indicate a potential method to discriminate mineralized and barren komatiite and komatiitic basalt units based on Ru concentrations in chromite and indicate potential for chromite to be used as a resistate indicator mineral in exploration for komatiite-associated nickel sulfide deposits. Chromites from barren komatiites and komatiitic basalts display Ru concentrations mostly between ∼150 and 600 ppb. Chromites from mineralized units have distinctly lower Ru contents (<150 ppb). These results can be interpreted in terms of the much higher partition coefficient for Ru into sulfide liquid compared to that of Ru into chromite, resulting in much lower Ru concentrations in chromite where both chromite and sulfide liquid are present and competing for Ru. As a result, the Ru content of chromite can be used to determine if a komatiite melt equilibrated with a sulfide liquid during crystallization, and therefore, if a system and/or sequence is prospective for nickel sulfide mineralization. The strength of this method compared to previous whole-rock exploration techniques derives from combining (1) the geochemical properties of a chalcophile element that records an ore-forming process while being strongly immobile during postmagmatic processes, with (2) the in situ analysis of a mineral that is generally preserved even in highly altered and mildly weathered komatiites and that is a common constituent of detrital heavy mineral samples. Chromite Ru content has potential as a prospectivity indicator, applicable to a wide range of media including bedrock, laterites, and detrital resistates heavy mineral samples.

Mineralogy of Mare Serenitatis on the near side of the Moon based on Chandrayaan-1 Moon Mineralogy Mapper (M3) observations

Spectral analysis of Mare Serenitatis has been carried out using Chandrayaan-1 Moon Mineralogy Mapper (M3) data in order to map the compositional diversity of the basaltic units that exist in the basin. Mare Serenitatis is characterized by multiple basaltic flows of different ages indicating a prolonged volcanism subsequent to the basin formation event. Reflectance spectra of fresh craters from the Mare Serenitatis have been analyzed to study the nature and location of the spectral absorption features around 1- and 2-μm respectively, arising due to the electronic charge transition of Fe2+ in the crystal lattice of pyroxenes and/or olivine. Chandrayaan-1 M3 data have been utilized to obtain an Integrated Band Depth (IBD) mosaic of the Serenitatis basin. Based on the spectral variations observed in the IBD mosaic, 13 spectral units have been mapped in the Mare Serenitatis. In the present study, we have also derived spectral band parameters, namely, band center, band strength, band area and band area ratio from the M3 data to study the mineralogical and compositional variations amongst the basaltic units of the studied basin. On the basis of spectral band parameter analysis, the pyroxene compositions of the basaltic units have been determined, which vary from low to intermediate end of the high-Ca pyroxene and probably represent a sub-calcic to calcic augite compositional range. Detailed spectral analyses reveal little variations in the mafic mineralogy of the mare basalts in terms of pyroxene chemistry. The uniformity in pyroxene composition across the basaltic units of Mare Serenitatis, therefore, suggest a probably stable basaltic source region, which might not have experienced large-scale fractionation during the prolonged volcanism that resulted in filling of the large Serenitatis basin.

A late Mesozoic high plateau in eastern China: Evidence from basalt vesicular paleoaltimetry

Eastern China is made of a number of large and small continental fragments throughout late Paleozoic and Mesozoic time, and is still the best natural laboratory for examining kinematic models of continent tectonics. The paleoelevation history of eastern China provides direct insight into the tectonic processes in China. Here we present basalt-vesicularity based estimates of the paleoaltimetry of the early Cretaceous basalts in northern East China, which indicate that the studied basalt units were at an elevation of more than 4 kilometers in late Mesozoic. Two vesicular basaltic rocks have been collected form bottom to top along the lava flow outcrop in eastern Inner Mongolia. After the digital precessing to the sample cross-sections, and taking advantage of the stereological conversion method to acquire the bubble size distributions, paleoelevation estimate was calculated for East China in the early Cretaceous. The results show that the elevation has been near 4700±750 m when the lava flows was cooling, implying that there were highland regions in the northern part of the East China Plateau during the early Cretaceous. Combined with other geological evidence, we conclude that there was a high plateau with elevation near 5000 m above sea level in Eastern China during the late Mesozoic. This ancient high plateau in eastern China was most likely formed by the collision of the north and south China blocks.

Ferruginous and manganiferous haloes around massive sulphide deposits of the Urals

Proximal brecciform ferruginous and manganiferous rocks related to VMS deposits of the Urals are subdivided into jasperites, gossanites, and umbers, in addition to thin-bedded jaspers and cherts. The coherence of host rock composition and Mn–Fe-fertility of the sediments have been established. Fe-poor pink hematitic and gray sulphidic chert are typical of the felsic class of VMS deposits. In contrast the contents of Fe vary from high to moderate in ferruginous rocks enclosed in basaltic units associate with VMS deposits. Fe- and Mn-rich ferruginous rocks and umbers occur in association with limestones and calcareous sedimentary rocks in both types of volcanic sequences. A common feature of jasperites and umbers is the abundance of replacement textures of hyaloclastites and carbonates by hematite and silica. In addition, replacement of clastic sulphides by hematite and magnetite is a characteristic genetic feature of gossanites. All of these sedimentary rocks are accompanied by pseudomorphs of hematite and quartz formed after bacterial filaments. The abundance of replacement textures are supportive of the halmyrolysis model, in addition to hydrothermal sedimentary and sub-seafloor hydrothermal replacement theories. Study of chemical zonation of altered hyaloclasts shows depletion of their rims, not only in mobile Na, K, Mg, but also in immobile Al, Ti, and REE; whereas Si and Fe are concentrated in situ. The halmyrolysis model presented here, involving organic-rich calcareous hyaloclastic sediments, resolves the problem of subtraction of Al, Ti, REE and other elements, which are commonly immobile under hydrothermal conditions. The evolution of the halmyrolysis process from acidic reducing to alkaline oxidized conditions infers a possible range in transformation from FeII–Mg smectites to Fe-silicates and Fe-Si oxides as precursors of brecciform jasperite and thin-bedded jasper. The higher acidic, initial stage, of gossanite formation seems to be required for oxidation of organic matter and/or pyrite. The acidic condition facilitates the temporal preservation of “immobile” elements (Al, Ti, REE) in “immature”chlorite–hematite gossanites. Another peculiarity of the gossanite-forming processes is the likely sorption of P, U and V by iron hydroxides displacing sulphides. The general evolution of all ferruginous sediments results in complete Fe2+ oxidation and silicification accompanied by subtraction of other elements. The vertical diagenetic differentiation leads to concentration of Mn-carbonates, silicates and oxyhydroxides into the tops of jasperite and gossanite layers. Mn oxyhydroxides scavenge positively charged hydrated cations like Co and Ni. Near-vent bacterial communities may activate the processes of volcanic glass and sulphide degradation. The proposed processes of halmyrolysis followed by silicification, in situ, may resolve the enigma of silica-rich sediment formation in a silica undersaturated ocean. The discrimination between gossanite and jasperite is useful for elaboration of new criteria for local exploration of VMS- and Mn-deposits. Halo dispersion of gossanites covering an area about two to three times that of the massive sulphide deposit is a good vector for ore body discovery. Proximal gossanites can be differentiated from jasperites by presence of relic sulphide clasts or elevated contents of chalcophile elements (Cu, Fe, Zn, Pb, Bi, Te, As, Sb, Ba), noble metals (Au, Ag) and distinct REE patterns with La and Eu positive anomalies. The development of halmyrolysis and biomineralization models merit further elaboration and testing in on-going research, in order to add or revise theories of iron and manganese deposit formation.

Platinum-group elements and geochemical characteristics of the Permian continental flood basalts in the Tarim Basin, northwest China: Implications for the evolution of the Tarim Large Igneous Province

Permian continental flood basalts (CFBs), as a main component for Tarim Large Igneous Province (TLIP), are widely distributed in the western and central parts of the Tarim Basin. Here we present a systematic study of platinum-group elements (PGEs) combined with conventional major, trace and Sr–Nd isotopic geochemistry to characterize the Tarim CFBs from the Yingan section in the Keping area, west of the Tarim Basin. The basaltic units with a total thickness of ca. 400m in the section can be divided into two basaltic sequences: the lower Kupukuziman and the upper Kaipaizileike sequences. Both of the sequences display extremely low PGE concentrations, with Os, Ir, Ru, Rh, Pt and Pd contents of 0.014–0.106, 0.007–0.072, 0.035–0.253, 0.011–0.078, 0.043–0.149 and 0.026–0.124ppb, respectively. The Keping basalts exhibit a marked increase in Cu/Pd ratios (>105) albeit with a narrow range of lower Pd/Ir ratios (<50), different from the PGE-undepleted basalts of the Siberian Traps, Emeishan Large Igneous Province (ELIP), East Greenland CFBs and Deccan Traps. Furthermore, the Tarim CFBs in Keping and elsewhere in the basin have very low Cu/Zr ratios (<0.5 commonly), indicating that their parent magmas were significantly depleted in chalcophile elements. The Tarim CFB magmas are estimated to have formed by <5% partial melting, and were probably S-saturated during partial melting, leaving residual sulfide in the mantle source. The differences in Th/Yb and (Th/Nb)N ratios between the Kupukuziman and Kaipaizileike sequences suggest that the Keping basalts incorporated variable degrees of assimilated crustal components from the Precambrian basement in the Tarim Basin. Modeling indicates that the earlier erupted Kupukuziman lavas witnessed relatively larger extent of assimilation than the later Kaipaizileike lavas. Nevertheless, the crustal assimilation did not trigger sulfur saturation and sulfide segregation for the basaltic magma in the crust. Furthermore, a magma mixing process between the relatively primitive and more evolved residual magmas of the same lineage during magma chamber replenishment is suggested according to the PGEs and Sr–Nd isotope variations in the Kaipaizileike sequence. This process might have also induced limited sulfur saturation and sulfide segregation in the late stage of the magmatic evolution. A comparison of the chalcophile element characteristics between the basalts in the Tarim Basin and the mafic–ultramafic rocks in the Eastern Tianshan and Beishan Rift areas indicates that the degree of partial melting plays an important role on the PGE geochemistry and potential PGE–(Ni–Cu) ore deposits in the TLIP.

Subvolcanic subsidence and caldera formation during subaerial seafloor spreading in Iceland

Many caldera systems worldwide are interpreted to form as a result of catastrophic subsidence into space vacated by eruption. Some basaltic calderas, however, both associated with modern active volcanoes and in ancient, deeply eroded terranes, lack evidence for catastrophic formation and thus may have formed incrementally. The Vatnsdalur structural basin in northern Iceland is one such caldera-like volcanic depression. The Vatnsdalur structural basin is an elliptical depression with dimensions of ∼6 km × ∼3 km and a structural depth of ∼1.5 km. It occurs within the gently west-dipping, Tertiary basaltic lava sequences of the Skagi region, northern Iceland. Tilted basaltic to rhyolitic lava flows define a large-scale, rim monocline surrounding the basin. Exposures that form the southern rim of the Vatnsdalur structural basin reveal details of the pre-, syn-, and postsubsidence volcanic and tectonic processes during basin evolution. In these exposures, the dips of lava flows steepen continuously from horizontal to as much as 60°W, toward the center of the basin. Basaltic lava flows and mass-flow breccia units were deposited unconformably over the dipping lava flows and thicken substantially downdip, toward the basin center. The dip of bedding and flow contacts in these overlying units decreases up section, gradually becoming conformable with the regional lava-flow stratigraphy. Brittle folding of the lava flows within the rim monocline occurred by a combination of slip on minor faults and syntectonic dike intrusion. Based on structural evidence and comparisons to worldwide caldera systems, we conclude that the Vatnsdalur structural basin formed as a result of either (1) loading of the subsurface by dense, intrusive material or (2) shallow crustal magma redistribution accommodating many small subsidence events. In the context of crustal construction in Iceland, the Vatnsdalur structural basin and adjacent areas demonstrate significant along-strike variability in the mechanism(s) of crustal construction that occurs during subaerial seafloor spreading.

The layered structure of lunar maria: Identification of the HF-radar reflector in Mare Serenitatis using multiband optical images

Comparison of the Lunar Radar Sounder (LRS) data to the Multiband Imager (MI) data is performed to identify the subsurface reflectors in Mare Serenitatis. The LRS is FM-CW radar (4–6MHz) and the 2MHz bandwidth leads to the range resolution of 75m in a vacuum, whereas the sampling interval in the flight direction is about 75m when an altitude of the spacecraft with polar orbit is nominal (100km). Horizontally continuous reflectors were clearly detected by LRS in limited areas that consist of about 9% of the whole maria. The typical depth of the reflectors is estimated to be a few hundred meters. Layered structures of mare basalts are also discernible on some crater walls in the MI data of the visible bands (VIS). The VIS range has nine wavelengths of 415, 750, 900, 950, and 1000nm, and their spatial resolution is 20m/pixel at a nominal altitude. The stratigraphies around Bessel and Bessel-H craters in Mare Serenitatis are examined in this paper. It was revealed that the subsurface reflectors lie on the boundaries between basalt units with different chemical compositions. In addition, model calculations using the simplified radar equation indicate that the subsurface reflectors are not compositional interfaces but layer boundaries with a high-porosity contrast. These results suggest that the detected reflectors in Mare Serenitatis are regolith accumulated during so long hiatus of mare volcanisms enough for chemical composition of magma to change, not instantaneously. Therefore combination of the LRS and MI data has a potential to reveal characteristics of a series of magmatism forming each lithostratigraphic unit in Mare Serenitatis and other maria.

Source, evolution and emplacement of Permian Tarim Basalts: Evidence from U–Pb dating, Sr–Nd–Pb–Hf isotope systematics and whole rock geochemistry of basalts from the Keping area, Xinjiang Uygur Autonomous region, northwest China

Permian basalts distribute at least 250,000km2, and underlie the southwest Tarim Basin in Xinjiang Uygur Autonomous region, northwest China. This vast accumulation of basalt is the main part of the Tarim Large Igneous Province (LIP). The basaltic units in the Lower Permian Kupukuziman and Kaipaizileike Formations in the Keping area, Tarim Basin; were the best exposure of the Permian basalt sequence in the basin. LA–ICP–MS U–Pb dating of zircon from the basal basaltic unit in the section gives an age of 291.9±2.2Ma (MSWD=0.30, n=17); this age, combined with previously published geochronological data, indicates that the basalts in the Tarim Basin were emplaced between 292Ma and 272Ma, with about 90% of the basalts being emplaced between 292 and 287Ma. Basalts from the Keping area have high FeOT (10.8–18.6wt.%), low Mg#s (0.26–0.60), and exhibit primitive mantle normalized patterns with positive Pb, P and Ti but negative Zr, Y and Ta anomalies.The basalts from both formations have similar 206Pb/204Pb (18.192–18.934), 207Pb/204Pb (15.555–15.598) and 208Pb/204Pb (38.643–38.793) ratios. The basalts also have high εSr(t) (45.7–62.1), low εNd(t) (−3.6 to −2.2) and low zircon εHf(t) (−4.84 to −0.65) values. These characteristics are typical of alkali basalts and suggest that the basalts within the Tarim Basin were derived from an OIB-type mantle source and interacted with enriched mantle (EMI-type) before emplacement. Rare earth element systematics indicate that the parental melts for the basalts were high-degree partial melts derived from garnet lherzolite mantle at the base of the lithosphere. Prior to emplacement, the Tarim Permian Basalts (TPB) underwent fractional crystallization and assimilated crustal material; the basalts were finally emplaced during crustal extension in an intra-plate setting. The wide distribution, deep source and high degree partial melting of the TPB was consistent with a mantle plume origin. The TPB and other coeval igneous rocks in the Tarim Basin constitute a Permian LIP formed by a mantle plume in a similar fashion to the plume-related Emeishan LIP in southwest China.

Integrated hydrochemical and geophysical studies for assessment of groundwater pollution in basaltic settings in Central India

The Pithampur Industrial sectors I, II, and III, located approximately, 45km from Indore in Central India have emerged as one of the largest industrial clusters in the region. Various types of industries ranging from automobiles to chemicals and pharmaceuticals have been set up in the region since 1990. Most of the industries have effluent treatment plants (ETP) for treating wastewater before its disposal on land and/or in water body. The present study is an attempt to assess the groundwater quality in the watersheds surrounding these industrial sectors to develop the baseline groundwater quality in order to enable the policy makers to facilitate decisions on the development of industries in this region. The industries are located in two sub-watersheds, namely, Gambhir river sub-watershed and Chambal river sub-watershed. Geologically, the study area is located in the Deccan traps of Cretaceous to Paleocene age. The different basaltic flow units underlie clayey soils varying in thickness from 2-3m. The aquifer is mostly of unconfined nature. Samples have been collected from a network of observation wells set up in the watersheds. The water quality analysis of the groundwater samples has been carried out six times during three hydrological cycles of 2004, 2005, and 2006. The results indicate that a few observation wells in the vicinity of the industrial clusters have very high TDS concentration and exceed the Bureau of Indian Standards (BIS) guideline for TDS concentration. The contamination of groundwater has been more severe in the Gambhir watershed as compared to the Chambal watershed. The presence of the impermeable clay layers has resulted in a slow migration of contaminants from the sources. The findings reveal that there is no significant groundwater contamination in the Pithampur industrial sectors except in the vicinity of the industrial clusters, which indicates that there is good environmental space available for the expansion of industrial units in the Pithampur industrial hub.

PETROGRAPHY, GEOCHEMISTRY AND GEOCHRONOLOGY OF THE METAVOLCANIC ROCKS OF THE MESOPROTEROZOIC LEERKRANS FORMATION, WILGENHOUTSDRIF GROUP, SOUTH AFRICA - BACK-ARC BASIN TO THE AREACHAP VOLCANIC ARC

The Leerkrans Formation of the Wilgenhoutsdrif Group is a succession of highly sheared metasedimentary and metavolcanic rocks separating the western margin of the Archean Kaapvaal Craton from the polydeformed and highly metamorphosed Proterozoic Namaqua Sector of the Namaqua-Natal Province. This study presents the results of a comprehensive petrographic, geochemical and isotopic study of the metavolcanic rocks of the Leerkrans Formation. Rocks of a basaltic member, a quartz porphyry and a second stratigraphically higher basaltic unit were sampled, with those of the lower basaltic member further subdivided based on their petrographic features and geochemical characteristics. Extensive alteration (chloritisation and epidotisation) of the volcanic rocks make identification of the precursor lithology difficult. Highly chloritised and epidotised metabasalts from the Lower Basalt are typically flow-banded, massive, vesicular or amygdaloidal, and have primitive tholeiitic, MORB-like geochemical characteristics and positive epsilon Nd(t) (e Nd(t) ) values (+4.2 to +6.1), with enriched large ion lithophile element (LILE) contents relative to primitive mantle suggesting derivation from a depleted mantle source. Some of the basalts of this unit have alkaline within-plate tholeiite characteristics. The Upper Quartz Porphyry is comprised of less altered felsic volcanic rocks which have pyroclastic or tuffaceous textures. The geochemistry of these rocks, which display a tholeiitic affinity with fractioned REE patterns and LILE enrichment relative to the high field strength elements (HFSE) and primitive mantle, along with negative e Nd(t) values (−4.8) indicate that the rocks are derived from crustal melting. U-Pb single zircon SHRIMP dating of zircons from a felsic pyroclastic rock from this unit yields an age of 1289 ± 9 Ma. The Upper Basalt and Mixed Zone of the Leerkrans Formation are comprised of basaltic lavas showing similar geochemical features to the Lower Basalt. The metavolcanic rocks of the Leerkrans Formation overlap in age with the oldest units of the ~1.3 to ~1.23 Ga Areachap Group, the polydeformed and highly metamorphosed remnants of a volcanic arc that separates the western margin of the Kaapvaal Craton from the Namaqua Sector. The Leerkrans Formation likely represents the remnants of a related back-arc basin to the volcanic arc which was accreted onto the western margin of the craton. The Leerkrans Formation escaped high-grade metamorphism and polyphase deformation that affected the Areachap arc during the Namaquan Orogeny due to being thrust back onto the Kaapvaal Craton during early arc accretion.

Mathematical modeling of thermomechanical erosion beneath Proterozoic komatiitic basaltic sinuous rilles in the Cape Smith Belt, New Québec, Canada

Virtually all of the economic Ni–Cu–(platinum group element (PGE)) mineralization in the central part of the Cape Smith Belt of New Quebec is hosted by thick olivine cumulate units in the Katinniq Member of the Raglan Formation at the base of the 1.9 Ga Chukotat Group. These units transgress underlying gabbros and pelitic metasediments, forming 50–200-m deep and 300–1,000-m wide V-shaped embayments and have been interpreted on the basis of surface geology, deep diamond core drilling, and magnetic inversion models to represent the remnants of one or more large, long (at least 20 km, possibly ≥50 km), sinuous, komatiitic basalt lava channels that formed by thermomechanical erosion of their substrates. We have used a mathematical model to test these hypotheses regarding komatiitic lava emplacement and erosion by lava. Our modeling predicts that an initially 10-m thick komatiitic basalt flow should have flowed turbulently near the vent and should have thermomechanically eroded unconsolidated pelitic sediment during emplacement to reach the observed degree of contamination of ≤10% at distances of ~30–60 km downstream from the source. Furthermore, our models predict that, at these distances downstream, a fully inflated 100-m thick komatiitic basalt flow would have had thermal erosion rates over consolidated gabbroic substrate of ~0.7–1.5 m/day, requiring ~70–140 days to incise a 100-m deep channel, depending on the initial temperature of the lava, the paleoslope, and the initial temperature and solidus temperature of the gabbro. These erosion rates would have been associated with volumetric flow rates of >105–106 m3/s and eruption volumes of >103–104 km3. Although these flow rates are orders of magnitude larger than those of most modern terrestrial basaltic flows, they are of the same order as those estimated for the largest terrestrial flood basalt flows and with those inferred for some of the largest extraterrestrial flows. Our predicted flow volumes are also of the same order as those of the largest terrestrial flood basalt units, consistent with the great thickness and widespread distribution of the Chukotat Group. Our modeling of thermomechanical erosion of gabbro by komatiitic basalt results in negligible contamination ( Middle REE–Heavy REE > Nb–Ta–Ti represent contamination by underlying Povungnituk semipelites. This result is consistent with present models for the genesis of the Ni–Cu–(PGE) mineralization in the Raglan Formation that involve thermomechanical erosion of unconsolidated, sulfidic semipelitic sediments, and decoupling of the miscible silicate and immiscible sulfide components.

Integration of K–Ar geochronology and remote sensing: Mapping volcanic rocks and constraining the timing of alteration processes (Al-Lajat Plateau, Syria)

The Al-Lajat plateau (southern Syria) is a Quaternary volcanic field hosting numerous historical and archaeological sites. Based on the integration of K–Ar geochronology and remote sensing methods, a new map is presented for Al-Lajat plateau volcanic field, and a chronological model for alteration processes (such as weathering) in relation to Quaternary paleoclimatic changes. Potential use of the geological data in archaeological investigations is discussed. The alteration patterns of ferric, ferrous, and clay minerals were identified by using Landsat Enhanced Thematic Mapper data (ETM+) methods and ratio images of 3/1, 5/4 and 5/7. Principal Components Analysis (PCA), combined with “Crosta technique” interpretation was used to gauge the response of weathered minerals. Using this technique, high concentrations of ferrous minerals appear brightly colored in the third axis of the Principal Components Analysis (‘PC3’), while oxides show the opposite in PC4. Composite images consisting of ratio images (3/1, 4/5, and 5/7), shown in blue, green, and red respectively, appear to be the most useful for mapping the lithologic boundaries of the main lava flows. Based on new K–Ar ages, the timing of the volcanic activity appears to have been between 56 ± 9 ka and 266 ± 6 ka. Three distinct groups of ages can be identified, confirming the sequence of the basaltic units defined by remote sensing: 1) the youngest unit belongs to Tyrrhenian, between 71 ka and 56 ka, 2) the intermediate unit, Pre-Tyrrhenian to Tyrrhenian between 114 ka and 139 ka, and 3) the oldest basaltic unit, surrounding the Al-Lajat plateau, is dated to at least 266 ka. A chrono-alteration model highlights the role of climatic changes in the distribution of the minerals at the surface of the volcanic rocks as a function of the ages. Weathering conditions during the post-glaciation phase are responsible for clay removal in the study area. Integrating dating and remote sensing data are important for mapping the location and timing of past volcanic activity, but can also be used to identify the sources of archaeological tools and architecture in volcanic areas such as the Al-Lajat plateau.

Lunar mare deposits associated with the Orientale impact basin: New insights into mineralogy, history, mode of emplacement, and relation to Orientale Basin evolution from Moon Mineralogy Mapper (M3) data from Chandrayaan-1

[1] Moon Mineralogy Mapper (M3) image and spectral reflectance data are combined to analyze mare basalt units in and adjacent to the Orientale multiring impact basin. Models are assessed for the relationships between basin formation and mare basalt emplacement. Mare basalt emplacement on the western nearside limb began prior to the Orientale event as evidenced by the presence of cryptomaria. The earliest post-Orientale-event mare basalt emplacement occurred in the center of the basin (Mare Orientale) and postdated the formation of the Orientale Basin by about 60–100 Ma. Over the next several hundred million years, basalt patches were emplaced first along the base of the Outer Rook ring (Lacus Veris) and then along the base of the Cordillera ring (Lacus Autumni), with some overlap in ages. The latest basalt patches are as young as some of the youngest basalt deposits on the lunar nearside. M3 data show several previously undetected mare patches on the southwestern margins of the basin interior. Regardless, the previously documented increase in mare abundance from the southwest toward the northeast is still prominent. We attribute this to crustal and lithospheric trends moving from the farside to the nearside, with correspondingly shallower density and thermal barriers to basaltic magma ascent and eruption toward the nearside. The wide range of model ages for Orientale mare deposits (3.70–1.66 Ga) mirrors the range of nearside mare ages, indicating that the small amount of mare fill in Orientale is not due to early cessation of mare emplacement but rather to limited volumes of extrusion for each phase during the entire period of nearside mare basalt volcanism. This suggests that nearside and farside source regions may be similar but that other factors, such as thermal and crustal thickness barriers to magma ascent and eruption, may be determining the abundance of surface deposits on the limbs and farside. The sequence, timing, and elevation of mare basalt deposits suggest that regional basin-related stresses exerted control on their distribution. Our analysis clearly shows that Orientale serves as an excellent example of the early stages of the filling of impact basins with mare basalt.

Geology of the Moscoviense Basin

[1] The Moscoviense Basin, on the northern portion of the lunar farside, displays topography with a partial peak ring, in addition to rings that are offset to the southeast. These rings do not follow the typical concentric ring spacing that is recognized with other basins, suggesting that they may have formed as a result of an oblique impact or perhaps multiple impacts. In addition to the unusual ring spacing present, the Moscoviense Basin contains diverse mare basalt units covering the basin floor and a few highland mafic exposures within its rings. New analysis of previously mapped mare units suggests that the oldest mare unit is the remnant of the impact melt sheet. The Moscoviense Basin provides a glimpse into the lunar highlands terrain and an opportunity to explore the geologic context of initial lunar crustal development and modification.

Tholeiitic to calc-alkaline cyclic volcanism in the Roy Group, Chibougamau area, Abitibi Greenstone Belt — revised stratigraphy and implications for VHMS explorationGeological Survey of Canada Contribution 20100254. Ministère des Ressources naturelles et de la Faune Contribution 8439-2010-2011-17.

The Roy Group in the Chibougamau area of the Abitibi subprovince, Southeastern Superior craton, Quebec, exemplifies Archean volcanic evolution. The Roy Group formed in two volcanic cycles, with voluminous basal mafic tholeiitic volcanic rocks being capped by a thin succession of calc-alkaline felsic volcanic rocks, banded iron formations, and cherts that represent regional stratigraphic markers. The Gilman Formation is thought to represent the mafic base of the 2nd Roy Group volcanic cycle. Our new mapping reveals that the Gilman Formation (North of the Lac Doré Layered intrusive complex) can be subdivided into a tholeiitic lower part (David member), a calc-alkaline extrusive sequence (Allard member), and a tholeiitic, more mafic upper part (Bruneau Formation, newly defined here). New U–Pb zircon ages on Allard member tuffs (2726.6 ± 0.7 Ma) are within error of those obtained from rhyolites of the Waconichi Formation (2728.2–2728.7 Ma), which underlies the Gilman Formation. These ages, along with geochemical and lithological similarities, imply that the Allard member belongs to the Waconichi Formation and that the David member occupies the same stratigraphic position as the Obatogamau Formation. The upper part of the former Gilman Formation is reassigned to the new Bruneau Formation. A thin transitional calc-alkaline basalt unit at the base of the Allard member is geochemically similar to basalts occurring at the top of the Lemoine member of the Waconichi Formation near the Lemoine mine, suggesting that the Allard member is slightly younger than the Lemoine member, and that its base (also associated with iron formation, breccia, and chert) represents a regional stratigraphic break favourable for volcanogenic-hosted massive sulphide (VHMS) exploration.

A geotechnical study on the landslides in the Trabzon Province, NE, Turkey

In the Trabzon province at the Eastern Black Sea region in Turkey, there are small and large landslides, especially following heavy rainfall periods in every year. These landslides regularly result in the loss of lives and properties. In this study, an assessment on the geotechnical characteristics of the areas where the landslides occur and the immediate vicinity were compared with the characteristics of non-landslides areas. A total of 50 landslides occurring in different locations were studied. As a result of the geotechnical investigations, the average of liquid limit values were between 49% and 69%, and the average plasticity index of the units ranged from 9% to 19% in the overlying materials in the landslide areas. Heavy rainfall exceeding boundary saturation of soils plays a critical role in causing landslides. According to the Unified Soil Classification System, the soils were “silts of high plasticity and silts, silty or clayey fine sands of low plasticity”. 80% of the total landslides occurred within very high and completely weathered units of basalt, andesite, or pyroclastics, and intercalations of sandstone, clayey limestone and siltstone. This study shows that the shear strength parameters decreased with increasing moisture content and that the number of landslides increased in relation to the particle size distribution of the clay.

Magnetic anomalies and rock magnetism of basalts from Reykjanes (SW-Iceland)

This study presents rock magnetic properties along with magnetic field measurements of different stratigraphic and lithologic basalt units from Reykjanes, the southwestern promontory of the Reykjanes peninsula, where the submarine Reykjanes Ridge passes over into the rift zone of southwestern Iceland. The basaltic fissure eruptions and shield lava of tholeiitic composition (less than 11500 a old) show a high natural remanent magnetization (NRM, Jr) up to 33.6 A/m and high Koenigsberger ratio (Q) up to 52.2 indicating a clear dominance of the NRM compared to the induced part of the magnetization. Pillow basalts and picritic shield lava show distinctly lower Jr values below 10 A/m. Magnetic susceptibility (κ) ranges for all lithologies from 2.5 to 26×10−3 SI.

Permian flood basalts from the Tarim Basin, Northwest China: SHRIMP zircon U–Pb dating and geochemical characteristics

This study documents the Permian basalts from the Tarim large igneous province, northwest China. Detailed field work has led to recognition of eight basalt units (BU) in the Permian sequences exposed in the Keping area, northern Tarim Basin. These basalt units are interbedded with terrestrial clastics, and thus represent eight discrete eruptive episodes. The basalt sequence is divided into two major eruption cycles, with an earlier cycle comprising two BUs within the uppermost Kupukuziman Formation, separated by ~ 1000 m of clastic sediments from an upper eruptive cycle represented by a further six BUs in the upper part of the Kaipaizileike Formation. SHRIMP U–Pb zircon ages of 289.5 ± 2.0 Ma (MSWD = 2.2) for the lowermost BU1 and 288 ± 2.0 Ma (MSWD = 3.1) for the uppermost BU8 are statistically indistinguishable, and limit the duration of the entire eruptive phase to no more than 5.5 Ma. The Keping basalts exhibit OIB-like trace element patterns, enrichment of LILE and HFSE, high ( 87Sr/ 86Sr) i ratios and negative εNd( t) values — all of which are consistent with the mantle plume derivation. The parental magmas for these basalts were extracted from spinel to garnet lherzolite by low-degree (less than 8%) partial melting. The magmas underwent pre-eruption fractional crystallization, but did not experience significant crustal contamination.

U–Pb baddeleyite ages linking major Archean dyke swarms to volcanic-rift forming events in the Kaapvaal craton (South Africa), and a precise age for the Bushveld Complex

The Archean basement in the northeastern part of the Kaapvaal craton is intruded by a large number of mafic dykes, defining three major dyke swarms, which collectively appear to fan out from the Bushveld Complex. Herein we present U–Pb baddeleyite ages for two of these dyke swarms, the northwest trending Badplaas Dyke Swarm and the east-west trending Rykoppies Dyke Swarm, and infer their correlation with tectonic events in the Kaapvaal craton. We also present a U–Pb baddeleyite age for a noritic phase of the Marginal Zone of the Rustenburg Layered Suite (Bushveld Complex). The age of the Badplaas swarm is determined from two dolerites dated at 2965.9 ± 0.7 Ma and 2967.0 ± 1.1 Ma. These ages coincide with units of the Nsuze Group lavas (2967–2985 Ma), which constitute the world's oldest preserved rift basin, and suggest that dykes of this swarm are feeders to basaltic units of this group. Similarly, the E–W trending Rykoppies swarm has earlier been interpreted as a potential feeder system to the Bushveld Complex. However, the emplacement ages of six dolerites fall in the range 2.66–2.68 Ga, thus ∼600 Myr earlier than the intrusion of the Bushveld Complex (herein dated at 2057.7 ± 1.6 Ma). Rather, these ages coincide with the Allanridge Formation at the uppermost part of the Ventersdorp Supergroup as well as volcanic rocks of the “protobasinal” sequences preserved at the base of the overlying Transvaal Basin. The Rykoppies Dyke Swarm probably marks the initial stages of rifting of the Transvaal Basin and reflects a major shift from a NW–SE to an E–W trending tectonic setting. The origin of the Rykoppies Dyke Swarm can be linked either to prolonged mantle plume activity or to the onset of back-arc extension associated with south-directed subduction of oceanic lithosphere in a compressional setting along the northern margin of the Kaapvaal craton.

Ages and stratigraphy of lunar mare basalts in Mare Frigoris and other nearside maria based on crater size‐frequency distribution measurements

We report on ages derived from impact crater counts for exposed mare basalt units in the northern part of the lunar nearside hemisphere (Mare Frigoris), the eastern and northeastern part of the nearside hemisphere (Lacus Temporis, Joliot, Hubble, Goddard, Mare Marginis, and Mare Smythii), the central part of the nearside hemisphere (Palus Putredinis, Mare Vaporum, and Sinus Medii), and the southwestern part of the nearside hemisphere (Grimaldi, Crüger, Rocca A, Lacus Aestatis, and Schickard). In Mare Frigoris, we dated 37 basalt units, showing ages from 2.61 to 3.77 Gyr, with most units being formed in the late Imbrian period between 3.4 and 3.8 Gyr ago. In Mare Vaporum we dated six spectrally homogeneous units that show model ages of 3.10 to 3.61 Gyr. Our model ages of basalts in Mare Marginis range from 3.38 to 3.88 Gyr and are mostly older than basalts in Mare Smythii (3.14–3.48 Gyr). The model ages of four units in Sinus Medii indicate that the basalts in this region formed 3.63 to 3.79 Gyr ago. We find an excellent agreement of our crater size‐frequency model ages of the Palus Putredinis area, which contains the Apollo 15 landing site, with the radiometric ages of Apollo 15 samples. According to our crater counts, basalts in Palus Putredinis are 3.34 Gyr old and this compares favorably with the radiometric ages of 3.30–3.35 Gyr of the olivine‐normative and quartz‐normative basalts of the Apollo 15 landing site. Lacus Aestatis is a small irregular‐shaped mare patch in the southwestern nearside and shows an Imbrian age of 3.50 Gyr; basalts in Lacus Temporis in the northeastern nearside formed between 3.62 and 3.74 Gyr ago and are, therefore, older than the basalts in Lacus Aestatis. We found that basalts in craters of the southwestern nearside (Schickard, Grimaldi, Crüger, and Rocca A) are also mostly younger than basalts in craters of the northeastern nearside (Hubble, Joliot, and Goddard). While basalt ages vary between 3.16 and 3.75 Gyr in the southwest, basalts in the northeast are 3.60–3.79 Gyr old. These results confirm and extend the general distribution of ages of mare basalt volcanism and further underline the predominance of older mare basalt ages in the eastern and southern nearside and in patches of mare peripheral to the larger maria, in contrast to the younger basalt ages on the western nearside (Oceanus Procellarum).