Volcanic Units Research Articles

Using Rover-analogous Methodology to Discriminate between Volcanic and Sedimentary Origins in Successions Dominated by Igneous Composition

We tested rover science operations strategies to determine best practices for interrogating geologic sections where the bulk composition is igneous but depositional/emplacement processes range from sedimentary to volcanic. This scenario may mirror locations on Mars interrogated by mobile vehicles (e.g., Perseverance rover in Jezero crater). Two field teams studied a 60 m vertical outcrop on Iceland’s Tjörnes peninsula as an analog for a Martian site containing interleaved layers of sedimentary and volcanic units. A Rover team commanded a human rover to execute observations based on common Mars rover sequences; the resulting data were used to characterize the geologic history of the location. Results were compared to that of a Tiger team using traditional terrestrial field methods to interrogate the same site. The goal was to understand which instruments, at what resolution, are required to assess the provenance of volcanic or sedimentary layers of similar chemical composition. Results suggest that, in a succession dominated by rocks having basaltic composition, current rover-driven decision-making protocols are sufficient to support a first-order interpretation of a sequence of sedimentary and volcanic layers. Two crucial data sets in maximizing science return in this scenario are (1) handlens-scale images revealing grain morphology and relationships and (2) data sets that allow comparison between surface and bulk geochemistry. Certain sedimentary features can be difficult to confidently identify if not viewed at a specific angle and resolution, and confident interpretations appear to require lateral scanning of beds at meter scales. This work illuminates the need for strategic planning, particularly of resource-intensive observations.

The Kupol Epithermal Au-Ag Vein District, Chukotka, Far Eastern Russia

Abstract The Kupol epithermal Au-Ag vein district is located in the northern part of the Okhotsk-Chukotka volcanic belt, a Late Cretaceous subduction-related continental volcanic arc exposed for >3,000 km along the eastern coast of Russia. High-grade veins are hosted in the Kupol andesite sequence, a 300- to 1,000-m-thick, subhorizontal, layered sequence of andesite flows, sills, and ash tuffs, dated at 97 to 96 Ma (Cenomanian). The Kupol andesite sequence is underlain by mixed mafic-felsic volcanic units plus sedimentary rocks (“older volcanics”) and overlain by a >1-km-thick “upper felsic” sequence of dacitic-rhyolitic tuffs and associated dikes and flow domes, dated at 95 to 85 Ma, with local sequences of fluvio-lacustrine sedimentary rocks. The epithermal veins occupy N-striking, steeply dipping normal faults that cut thick coherent andesite flows and sills in the central-upper part of the Kupol andesite sequence. The district is dominated by the large Kupol vein (180.7 tonnes (t) Au and 1,986 t Ag produced to 2020), hosted by the 5.5-km-long Kupol fault, which accommodates normal, east-side-down displacement of up to 190 m. The Moroshka and Providence veins, 5 km east-southeast of Kupol, occupy shorter faults (1- to 2-km strike) with smaller vertical displacements (to 70 m). The Moroshka vein is dated at 93.5 ± 1.5 Ma (Turonian; 40Ar/39Ar method on adularia), and the timing of vein mineralization here and at Kupol overlaps with the early stage of upper felsic sequence magmatism. Veins contain subhorizontal ore shoots, controlled by the intersection of the steep faults with flat-lying Kupol andesite sequence stratigraphy and by steepening of the faults to a more dilational orientation as the inferred paleosurface is approached. Local structural controls are also evident, reflecting a component of oblique slip on the Kupol fault, with the thickest vein segments at steeply pitching jogs and relays. Main-stage veins grew via repeated encrustation by quartz-chalcedony ± amethyst ± lattice bladed calcite (replaced by quartz), with Au-Ag–bearing crustiform adularia ± clays ± sulfides/sulfosalts/electrum ± chlorite ± hematite bands. The main controls on Au grade are inferred to have been boiling, resulting in sharp vertical limits to high metal grades typical of epithermal veins, coupled with optimal dilation of the vein system where the hosting normal fault steepens near surface with decreasing differential stress. Although much of the displacement on the controlling faults is pre-mineralization in timing, lithified cataclastic breccia, coeval with some vein stages, and vein geometry patterns indicate that some vein development occurred contemporaneously during late normal displacement along the fault system. Waning of the hydrothermal system is marked by late carbonate fill, initially Fe dolomite, then coarse calcite as veins, matrix to vein breccia, and central vein cavity fill. The Kupol district veins have proximal adularia-quartz alteration (haloes meters wide), within an extensive (hundreds of meters in scale) clay alteration halo. Clays are zoned both vertically and laterally with respect to veins, with inner illite-chlorite that was magnetite-destructive (at highest paleotemperature; >220°C), grading outward and upward to illite/interlayered illite-smectite with kaolinite, then to an outer zone (or upper blanket) of smectite, at lowest paleo-temperature (<150°C). The boundary between the illite and smectite zones is interpreted to mark the interaction limit of paleo-hydrothermal systems with cooler groundwater. District-scale pathfinder element zonation correlates with clays, with S-Te-Bi-As in the illite-chlorite core and Sb-Cs-Tl(-As-Li) in the smectite blanket. Pathfinder zonation patterns at Kupol point to a magmatic source at depth or, more likely given the scale of the anomalies, multiple magmatic sources, with the surface clay zonation indicating the extent of coalesced paleo-hydrothermal systems associated with upflow plumes. This is the best-defined alteration record with geochemical signature for a complete district hosting a large, high-grade vein deposit. Early definition of clay and pathfinder element patterns across an entire epithermal district can be carried out at low cost to provide useful constraints on vein targeting.

High-precision 40Ar/39Ar geochronology and volumetric investigation of volcanism and resurgence following eruption of the Tshirege Member, Bandelier Tuff, at the Valles caldera

Despite recognition as a significant volcanic threat to the southwestern United States, the post-caldera history of Valles caldera is poorly constrained. This study provides 49 new high-precision 40Ar/39Ar sanidine ages and volume estimations that reveal insights into eruptive timescales and resurgence. Caldera collapse and deposition of the Tshirege Member of the Bandelier Tuff at 1231.9 ± 1.3 ka was followed by eruption of 34 volcanic units from vents on the resurgent dome and along the caldera ring-fracture. New ages indicate post-caldera dome complexes are characterized by dominantly polygenetic and minor monogenetic emplacement. The Deer Canyon eruptions immediately followed caldera formation between 1231.6 ± 4.1 ka and 1212.0 ± 5.6 ka, for a total lifespan of 19.6 ± 6.9 kyr. Similarly, Redondo Creek eruptions occurred between 1199.9 ± 5.6 ka and 1186.8 ± 2.9 ka, a lifespan of 13.1 ± 6.3 kyr. Cerro del Medio is the longest-lived dome complex, erupting during a 24.5 ± 5.5 kyr lifespan between 1158.0 ± 3.1 and 1133.5 ± 4.6 ka. Following Cerro del Medio, Cerros del Abrigo erupted between 1010.1 ± 1.7 and 997.7 ± 1.7 ka. These longer-lived dome complexes are located within structurally complex zones of the caldera, suggesting the dense network of faults facilitate magma transport to the surface, producing long-lived eruptions. Conversely, the six dome and vent complexes that erupted between 932.5 ± 1.1 ka and 68.9 ± 1.0 ka have shorter eruptive lifespans than early post-caldera eruptions. Three of the complexes—San Antonio Mountain, South Mountain, and the East Fork Member—are polygenetic with lifespans ranging from 4.9 to 5.4 kyr with measurable repose periods. Dating of Cerro Santa Rosa 2, Cerro San Luis, and Cerro Seco domes yields a suite of indistinguishable ages, constraining rapid emplacement of each dome complex between 804.7 ± 2.0 ka and 800.3 ± 2.7 ka. The post-caldera volcanic units are grouped into a total of 17 temporally distinguishable eruptive events emplaced during 93.9 kyr of intra-dome volcanic activity. The eruptive frequency is 1 event per 5.5 ka for when Valles caldera enters periods of dome activity. A combination of new and published volumes of the dome and vent complexes indicate that these eruptions range from 0.8 km3 to 14.1 km3. In contrast, the average eruptive flux for each volcanic complex has nearly systematically increased from 0.05 ± 0.02 to 2.66 ± 0.75 km3/kyr during post-caldera evolution. Using new ages of the Tshirege Member, a syn-resurgent lava, and the oldest post-resurgent eruption, resurgence durations at Valles caldera are constrained between 73.9 ± 3.4 and 41.9 ± 6.4 kyr. Average magmatic flux during resurgence is between 0.52 ± 0.02 and 0.92 ± 0.14 km3/kyr, similar to pluton-filling rates, suggesting that resurgence is partly caused by significant decreases in magmatic flux following higher fluxes that sustain caldera-forming magma bodies. The eruptive frequency during dome activity and increasing flux has important implications should Valles caldera enter a new volcanic phase.

Cambrian rift magmatism recorded in subvolcanic sills of the Ediacaran-Cambrian La Ciénega Formation, NW Mexico

Mafic-ultramafic subvolcanic metabasalt sills intrude Ediacaran and Cambrian strata of the La Ciénega Formation of Sonora, Mexico. Sills are typically 1–7.5 m thick, with minor associated thin (∼10 cm thick) intrusions. Sills are typically bed parallel with upper and/or lower tempered (quenched) borders and porphyritic textures characterized by abundant olivine and pyroxene pseudomorphs that have been transformed to clay and carbonate minerals. Metamorphic halos in adjacent dolostones and quartzites occur at the bottom and top contacts, and metabasalt sills contain carbonate veins typical of hydrothermal alteration and mobilization. Unlike surface flows of the overlying Cerro Rajón Formation, all sills in the La Ciénega Formation lack evidence of crystal settling, yet evidence for assimilation of country rocks is present. Assimilation is more typical of sills rather than flows and is diagnostic of sills in the El Arpa Formation, a stratigraphically lower unit in the succession. Actinolite-chlorite-albite metamorphic mineral paragenesis suggests low-grade greenschist facies metamorphism for these metabasaltic rocks. Although their primary mineralogy is obscured due to alteration, olivine and clinopyroxene pseudomorphs are present and their major and trace element geochemistry suggest they were derived from alkaline basaltic magmas with low (normalized) SiO2N (22.7–43.1 wt%), high MgON (7.25–16.6 wt%), and high TiO2N (4.04–6.27 wt%). Immobile trace elements suggest these sills were originally alkaline rift-related basalts with OIB-type signatures. Tectonic discrimination diagrams suggest continental rift magmatism with low geochemical evolution ratios and relatively low mantle melting rates when compared to contemporaneous rift related magmatism. Sr-Hf-Nd-Pb isotopes suggest the metabasalts originated from an Enriched Mantle I (EMI) reservoir and melting occurred during adiabatic decompression. These geochemical characteristics are remarkably similar to volcanic rocks of the Cerro Rajón Formation. The inferred magmatic composition, mantle melting rates, petrography and field relations of the La Ciénega Formation metabasalt are consistent with a low viscosity feeder system like that envisaged to have sourced volcanic rocks of the overlying Cambrian (Terreneuvian) Cerro Rajón Formation. Together, evidence from these two volcanic units is consistent with a Cambrian continental rift event close to the onset of the Sauk transgression.

Eocene Volcanic Complex from Central British Columbia: The Role of Fractional Crystallization during the Magmatic Evolution

Abstract The Challis-Kamloops belt of south-central British Columbia is a regionally extensive (>65,000 km2) magmatic province that erupted within the North American Cordillera during the Eocene (55-45 Ma). The inland volcanic belt runs parallel to the coast, and the rocks were emplaced mainly within extensional basins indicating volcanism was attributed to rift-related decompressional melting. The rocks include both calc-alkaline and tholeiitic mafic and intermediate types (i.e., low-Fe, medium-Fe, and high-Fe suites). Voluminous volcanic units (Buck Creek, Goosly Lake, Swans Lake) of the Buck Creek volcanic complex (~3,000 km2 in area) within the Nechako plateau erupted within 1-2 million years and show significant internal chemical variability. All rock types have similar Sr-Nd isotopic (87Sr/86Sri=0.70435-0.70487; εNdt=+2.6-+4.0) ratios indicating they originated from the same sub-Cordilleran mantle source. Petrological modeling using the most primitive rocks of the Buck Creek, Goosly Lake, and Swans Lake magmatic pulses demonstrates that the chemical variability observed in each system can be explained by hydrous fractional crystallization in the upper crust (≤0.1 GPa) under moderately oxidizing to oxidizing conditions (ΔFMQ 0 to +0.7). The primary difference between the low-Fe to medium-Fe (calc-alkaline) Buck Creek suite model and the high-Fe to medium-Fe (tholeiitic) Swans Lake suite model is water content as the Swans Lake model has lower (H2O=0.75 wt.%) starting water than the Buck Creek and also the Goosly Lake models (H2O=1.25-2.00 wt.%). Moreover, the intermediate to silicic rocks of the complexes are compositionally similar to rocks associated with “slab failure” suggesting that rifting and mantle melting were related to asthenospheric upwelling through a slab tear. The implications are that the chemical variability of the rock suites are primarily related to fractional crystallization and that the mantle source is heterogeneous with respect to water content which is likely due to heterogeneities in the processes related to pre-Eocene subduction.

Age and significance of the Fire Bay assemblage: an Ordovician arc fragment within the Clements Markham belt, northwestern Ellesmere Island, Canada

The Fire Bay Formation of Trettin (1998), Clements Markham belt, Ellesmere Island, Canada, includes volcanic rocks described as Silurian in age based on Llandovery graptolites in adjacent clastic rocks. New field observations suggest the Llandovery fossils are from packages of the Silurian Danish River and/or Lands Lokk formations that are fault-bounded rather than stratigraphically tied to Ordovician sections that contain a 470.0 ± 0.2 Ma lithic tuff, volcaniclastic units with maximum depositional ages (MDAs) of 466 ± 2 and 462 ± 2 Ma based on detrital zircon, volcanic clasts with ages of 498 ± 6, 478 ± 4, and 477 ± 8 Ma, and Ordovician conodonts and graptolites of Darriwilian and Sandbian age, respectively. Since the Fire Bay Formation of Trettin (1998) lacks a type section and is fault-bounded with ambiguous age relationships, Ordovician volcanic units and fault-bounded clastic rocks correlated with the Hazen Formation are both included in the Fire Bay assemblage following the original interpretations of Trettin and Nowlan (1990). The Fire Bay assemblage records juvenile Ordovician arc magmatism proximal to the Pearya terrane. The adjacent Lands Lokk Formation yields bimodal age peaks at 440–430 and 465 Ma, MDA of 424 ± 3 Ma, and εHf(t) values of −5 to +10. The signature matches Ordovician Pearya units and Silurian circum-Arctic arc sources but there is no evidence for Silurian arc magmatism between the Pearya terrane and Laurentian margin, compatible with Pearya accretion during oblique Ordovician arc collision and Silurian sinistral translation along the northern Laurentian margin.

Terrestrial martian analogues from the Indian subcontinent: Implications for hydrological activity on Mars

Martian geology and surface geomorphic features are grouped under Noachian, Hesperian, and Amazonian eras, based on the crater retention ages and resurfacing ages by crater densities. Comparing the similarities and differences between Martian landforms and their terrestrial analogues promotes an understanding of how surface processes operated on both planets. The study focusses on the processes responsible for the evolution of fluvial valleys on the flanks of volcanic craters and the fluvial terraces with an objective towards ascertaining the role of changing climate, tectonic, and volcanic conditions. We have studied the channels that developed on the flank of volcanic crater Ceraunius Tholus and compared with the monogenetic volcanic field of Dhinodhar Hill which have been significantly modified by fluvial processes. Similarly, the fluvial basins developed on the Hesperian volcanic units of Echus plateau were compared with the Alaldari drainage of Upper Tapi river basin, showing the development of theater-headed channels and valleys, and relative fluvial features showing the strong influence of catastrophic climate and tectonic, which is also supported by the morphometric analysis in modulating the topography. The fluvial terraces developed in the Nubra and Shyok rivers of Ladakh and Upper and Middle reaches of Satluj in Central Himalayas are compared with Noctis fossae on Mars both developed due to the interplay of tectonism and climate.

Paleomagnetic and rock-magnetic study of Los Azufres lava flows (central Mexico)

We report a detailed rock-magnetic and paleomagnetic investigation on seventeen volcanic units (160 standard paleomagnetic cores) belonging to essentially Plio-Pleistocene Azufres Volcanic Field, located in the central part of the Trans-Mexican Volcanic Belt. Titanium-poor titanomagnetite is responsible for thermoremanence in the most lava flows, while unstable titanomaghemites presumably dominate in the less than half of the analyzed lava flows. The mean paleodirections are calculated for 15 sites, discarding apparently transitional flow and poorly defined (scattered) units yielding Dec = 357.23°, Inc = 38.62°, α95 = 4.89°, k = 55. These values are concordant with the expected paleodirections derived from the stable North America reference paleomagnetic poles. Secular variation parameters calculated through the dispersion of the site-mean virtual geomagnetic poles and the inclination anomaly are found slightly different to the available models. Within the 17 paleodirections obtained, four lava flows are normally magnetized between 1.14 and 1.23 Ma. These paleodirections may tentatively be assigned to the worldwide observable Cobb Mountain Geomagnetic event (subchron). This presumably short-lived episode seems to be characterized by apparently major duration than previously reported.

Age and petrology of Eocene-Oligocene calc-alkaline volcanism in Biga Peninsula (NW Turkey): Implications for magma origin and geodynamic evolution

In NW Anatolia, Eocene-Oligocene post-collisional volcanism is represented by K-rich volcanic rocks, including high K calc-alkaline products. Magmatic rocks in the Dededağ area (Biga Peninsula, NW Turkey) can be classified into 6 different groups with lithostratigraphic and chronostratigraphic data using 40Ar/39Ar methods (Eocene-early Oligocene, 42.08 ± 0.09 to 29.02 ± 0.29 Ma). From the Eocene period, there are calc-alkaline Laledağ granodiorite, Beyçayır volcanics with andesite and dacite composition, and also Kızıldam volcanics with alkaline and basic character (basaltic trachyandesite, trachybasalt). Furthermore, in the Oligocene period, calc-alkaline volcanism started with Dededağ volcanics with dacite and rhyolite intermediate-acidic composition, continued with Kırcalar volcanics consisting of basalt and basaltic andesite, and Harmancık volcanics ranging from basalt to rhyolite. The calc-alkaline Çamyayla pluton with quartz monzonite composition intruded into Oligocene Dededağ and Harmancık volcanics in the region. Alkaline lavas in the region are classified as high-K and shoshonitic, and calc-alkaline lavas are medium-high-K. On N-type mid-ocean ridge basalt and chondrite-normalized trace element diagrams, enrichment was observed for all volcanic units with regard to large ion lithophile elements and light rare earth elements. High field strength elements and heavy rare earth elements were depleted in all volcanic units. These compositions reveal the participation of a mantle source that was enriched by subduction components. Using geochemical data, all the volcanic rocks differentiated as a result of magma mixing/replenishment and contamination/assimilation processes. Consequently, the source of volcanism is thought to derive from the compressional regime associated with collision during the Eocene-Oligocene, and from a previously-enriched lithospheric mantle source with subsequent effects of the extensional regime.

Geochemical and geochronological constraints on origin of the Sawlava ophiolite (NW Iran): Evidence for oceanic mantle evolution beneath Iran-Iraq border

The Sawlava ophiolite is situated on the Iran–Iraq border within the Walash-Kermanshah ophiolitic belt and represents remnants of the Cenozoic southern Neo-Tethys Ocean, which was located between the Arabian plate and the Sanandaj–Sirjan zone. It contains a complete ophiolitic sequence started from harzburgites with foliated/discordant dunites, gabbroic bodies, a dyke complex, and pillow as well as massive basaltic lavas. The whole-rock and mineral chemistry of the Sawlava peridotites suggest that they are a mantle residuum after ca. 20–30% partial melting and melt extraction in the suprasubduction zone (SSZ) setting. The volcanic rocks generally range from island arc tholeiite to calc-alkaline affinities. Whole-rock chemistry indicates that volcanic units have compositions akin to depleted- and enriched-types mid-ocean ridge basalts (E-MORB). Layered- and isotropic gabbros show geochemical affinity similar to the normal mid-ocean ridge basalt (N-MORB) and E-MORB compositions, respectively. Their llight rare earth elements (LREE) observed in both N-MORB-like and E-MORB-like rocks, define two main basic geochemical types (LREE-enriched and LREE-depleted), suggesting several magmatic pulses from different mantle compositions that reveal mantle evolution and heterogeneity across the study area. Basaltic lavas weakly depleted in LREE show relatively flat REE patterns and (La/Yb)N values of 0.77 to 1.24, whereas LREE-enriched rocks have a (La/Yb)N mean values of 1.7, and lack an Eu anomaly. These subgroups of basaltic rocks show different extrusion ages – Paleocene–Eocene (59–50 Ma) and Oligocene (29 Ma), respectively. Petrogenetic modeling shows that mafic N- and E-MORB type rocks of Sawlava, which have (La/Yb)N = 0.97 and 1.7 and (Dy/Yb)N = 1.13 and 1.1, respectively, formed due to partial melting of a mantle source less enriched in LREE than an garnet lherzolite ((La/Yb)N = 0.88 and (Dy/Yb)N = 0.94) source or, alternatively, from very low degree (<2%) partial melting of a spinel-bearing DMM. The La/Yb–Dy/Yb systematics of these rocks are interpreted to be compatible with ~2 to 10% and ~ 20% of partial melting of a garnet bearing spinel lherzolite source for the N- and E-MORB type rocks, respectively. The geochemical data and results reveal that magmatic-originated rocks from both Paleocene-Eocene and Oligocene lavas seem to be less heterogeneous compared with the mantle sources of the Walash-Kermanshah ophiolites, likely due to different slab-fluid components and variations of partial melting degrees. The studied volcanic rocks therefore possibly record chemical heterogeneity due to magmatic activity at an oceanic spreading center alongside slab rollback and back-arc extension at the Eurasian continental margin.

Volcanostratigraphy Study of Way Ratai Geothermal Prospect in Pesawaran Regency, Lampung Province

Way Ratai geothermal area is volcanogenic geothermal system located in Pesawaran Regency, Lampung Province, Indonesia. The presence of the geothermal system in this area is indicated by the distribution of geothermal manifestations such as hot pools and hydrothermal alteration. Understanding the geological setting of this area plays an important role in considering the prospect of geothermal resources. This paper aims to determine the prospect of the geothermal area by investigating the relationship between volcanic units, geological structures, and geothermal systems in the Way Ratai. The study was conducted with remote sensing analysis and volcanostratigraphy study to interpret the stress regime, the permeability zone analyzed by the lineament density, the lithological unit, and the dimension of the volcanoes. Three groups of structural lineaments are identified from remote sensing analysis: NW-SE trend, NNE-SSW trend, and circular feature. Mount Ratai Volcanic Crown consists of 19 lithological units such as lava dome, lava flow, pyroclastic products, and surface deposit. The estimation of the volcanic product dimension is about 55 km3 that widespread radially which indicates the presence of a significant heat source beneath the surface. The volcanic activities occurred during the Pleistocene to Holocene with andesitic composition. Based on the lineament density extraction, the prospect area located on the southern flank of Mount Ratai has good permeability. Lineament maps that are overlaid by volcanic rock distribution maps will result in the relationship between the volcanostratigraphy units and the geological structure pattern of the area. From this study, the characteristics of the area show that this area has a good geothermal prospect to be developed and needs further investigation.

Interaction between volcanic and non-volcanic systems and its implication for prospectivity in the Faroe–Shetland Basin, NE Atlantic continental margin

Exploration in the Faroe–Shetland Basin on the Faroese Continental Shelf has revealed thick and complex volcanic successions and discovery of inter-volcanic oil-bearing siliciclastic sandstone fan deposits in the central parts of the basin. The possibility for such play types at the fringe of the North Atlantic Igneous Province requires a better understanding of the interaction between competing sedimentary and volcanic depositional transport systems. We have re-examined volcanic units in cuttings from exploration wells in the greater Judd Sub-basin area for evaluation of facies and geochemical affinity. This allows for chemostratigraphical correlation of wells to the absolute radiometrically age-constrained Faroe Islands Basalt Group. The collective well data were subsequently tied to a regional interpretation of 2D seismic data which facilitated a detailed interpretation of temporal development of the volcanic successions in the Judd Sub-basin area in terms of geometry, volcanic facies, depositional environment, and interdigitation with non-volcanic sedimentary units. The Judd Sub-basin was influenced by major volcanic phases during pre-breakup and syn-breakup. The influence was both direct, in the form of volcanic deposits, and indirect, in the form of obstructing established sedimentary transport systems and creating new provenance areas. The volcanic transport systems reached different areas of the Judd Sub-basin at different times during pre-breakup volcanism. The earliest incursion in the west was during late Mid Paleocene (T-sequence T31/T32). With at least three stratigraphically discrete incursions of volcanic material into the Judd Sub-basin, possibilities arise for sub- and inter-volcanic stratigraphic and structural traps for each incursion.

A method to collect representative samples from water-driven percussion drilling techniques: examples from RoXplorer® coiled tubing drill rig

Water-driven percussion drilling techniques, such as that used by the RoXplorer® coiled tubing drill rig, return a rock sample as cuttings that are carried to the surface by the circulating drilling fluid. This drilling technique does not deliver a core sample. In order for the RoXplorer® to be effective as a mineral-exploration drill rig, it is critical to develop robust, representative and repeatable sampling techniques for the rock cuttings and to establish with confidence the depth interval from which the sample was derived. The RoXplorer® produces more than 7 kg/m of cuttings every few minutes (rate of penetration dependent) that are carried to the surface by the drilling fluid with a fluid return rate of 80–150 L/min. The cuttings, which range in size from <10 µm to 5 mm, require extraction from the drilling fluid and preparation prior to analysis. Subsampling of the fluid/cuttings stream can reduce the sample size to allow easier processing. A modified static cone splitter and ancillary flow-control system were designed and tested during field deployment of the RoXplorer® drill rig in South Australia in February 2017. We drilled a vertical hole with RoXplorer® starting 10 m to the northeast of an existing vertical diamond drill hole with well-characterised, shallow-dipping sedimentary and volcanic units. This allows comparison of drilling performance and sample quality against industry-standard drilling and sampling techniques. The performance of the splitter to take a representative continuous 1/8th subsample of drilling fluid and cuttings by volume was assessed based on its ability to resolve a 1 m interval of low-grade Cu mineralisation (0.74–1.03 wt% Cu) at 398 m that was detected in the reference diamond drill hole. The coiled tubing samples produced an equivalent and unbiased (chemistry and particle-size distribution) subsample, with sub-metre depth accuracy and comparable signal magnitude of the mineralisation at 398 m as detected in the diamond core. KEY POINTS Samples from the RoXplorer® drilling system were benchmarked against a twin diamond core hole that intersected a narrow band of copper mineralisation at 398 m depth A representative subsample was achieved through taking a split of cuttings as a slurry prior to dewatering Samples collected over key stratigraphic boundaries, including the narrow band of mineralisation, were accurately depth-constrained and had minimal carryover or mixing of cuttings when compared with the twin diamond core hole

Coda Wave Spatial Variation in Eastern Anatolia, Turkey

Eastern Anatolia is a tectonically active area, where continent-to-continent collision and accretion processes are shaping the crust and leading to high seismic characteristics. The main motivation of this research is to calculate the Coda Wave Spatial Variation in the depth and horizontal plane using 3438 events recorded by 26 seismic stations. The Coda Q features from 1 to 16 Hz are computed for various lapse times, which determine the coda waves depth distribution. The contours of Q-variation in the regional crust at different depths are obtained. The Coda-Q values range from ~180±120 at 1 Hz to ~800±500 at 16 Hz in the study area. The Q characteristics are interpreted concerning tectonics, crustal anomalies, and possible geothermal regime variations. Low Q values are observed in and around major fault-lines, zones of high tectonic activity, and geothermal spots. The results suggest that 8 Hz coda-Q distribution may be associated with the Curie point depth distribution. Low Coda-Q values specifies high attenuation features, while low-frequency exponent can define clear principal attenuation according to molten lower crust along Arabian-Anatolian plate collision zone and presence old volcanic units, such as Tendürek, Agri, Süphan, and Nemrut Mountains scattered all around the study area, as well as geothermal reservoirs.

Geologic map of Slate Range Crossing area, California, USA

This detailed geologic map and supplemental digital data set1 examine and demonstrate the complex Neogene–Quaternary deformation in the Slate Range Crossing area (California, USA) of the active dextral transtension of the Death Valley region and Walker Lane belt. This map integrates the late Cenozoic structures and geologic units with the Mesozoic geologic units and deformation as a data set to examine the controls on reactivation of older structures. These geologic data were collected to study pre-, syn-, and post-kinematic rocks to examine the deformation history of the area and to find palinspastic markers to examine the late Cenozoic fault displacement and displacement history across Panamint Valley to the east, as reported in Andrew and Walker (2009). The study focused on defining the Miocene and Pliocene rocks and deposits and examining lateral changes and depositional sources of clasts. There are two different volcanic-sedimentary sequences in this area. A Miocene section contains mafic to felsic volcanic units, numerous debris-flow to laharic deposits, and several associated conglomerates and breccias containing exotic clasts. The exotic clasts are matched to rocks in the Panamint Range on the east side of Panamint Valley as reported in Andrew and Walker (2009) as displacement vectors for palinspastic reconstructions. These Miocene strata ubiquitously dip eastward 20–40º. A younger volcanic-sedimentary sequence contains relatively thin mafic lava flows and associated locally derived, coarse-grained mass wasting deposits. These younger basaltic lavas generally have gentle dipping lava flow features and foliation. Numerous faults cut the different age deposits allowing a chronology of Neogene to Quaternary faulting; additionally, there are numerous fabrics associated with Jurassic contraction and Cretaceous(?) dextral shear. The area near Slate Range Crossing has a conspicuous zone of earthquake foci; this study found that some of this seismic activity coincides with a zone of southwest-striking, moderately dipping to the north, sinistral-oblique normal faults, which cut across the northernmost Slate Range. These faults form a structural boundary between the Argus and Slate Ranges and link the fault networks in Panamint Valley with those in Searles Valley. This mapping and structural data demonstrate the two-stage Neogene fault history of the Walker Lane belt deformation in this area and show that regional tilting of rocks occurred after ca. 13 Ma and before ca. 4 Ma; this eastward down-tilting appears to be a discrete event and may mark the change from extension to transtension. This detailed geologic mapping and collection of structural data for the rocks in the eastern Argus and northern Slate Ranges and Panamint Valley were created using digital in-the-field geographic information systems software running on a field-hardened laptop computer. This map is a simplification of detailed geologic mapping data collected at 1:6000 scale and reduced to 1:20000 scale. Structural data includes kinematic and relative timing of deformation information.

Geology of the Simlipal Volcano-sedimentary Basin of Singhbhum Revisited: A Simplistic Interpretation

Abstract The status of the Proterozoic volcano-sedimentary Simlipal complex (covering latitudes 21°14’-22°20’N and longitudes 86°03’-86°35’E) of Singhbhum, eastern India remains unclear till date. The Simlipal complex has classically been designated to represent three layers of alternate spilitic volcanics and quartzite deposited in a geosyncline that unconformably overlies the meta-sedimentary Singhbhum Group of rocks. The study of the authors (entailing digital elevation map) bring out that the concentric ring-like outcrop pattern of Simlipal complex is only topography-controlled and repetitive bands of quartzite and volcanics do not exist. Further, it has been documented that the Simlipal complex comprises basemental weakly metamorphosed quartzite-phyllite (~450m thick) heterolith unit (proposed Lulung Formation), which is followed upward by fresh, sub-horizontal (~250m thick) volcanic unit (proposed Barehipani Formation) with local presence of peridotite-gabbro, and finally to quartz arenite unit (~150m thick) as the topmost layer (proposed Jurunda Formation). The heterolith unit (proposed Lulung Formation) has been envisaged as a part of the older Singhbhum Group. The basaltic rocks (Barehipani Formation) correspond to calc-alkaline tectonic affinity based on geochemistry. We propose an arc-subduction related setting for the Simlipal complex which may be further confirmed through detailed major/trace elements and isotopic studies.

Mid‐Pleistocene to Recent Crustal Extension in the Inner Graben of the Northern Kenya Rift

AbstractMagmatic continental rifts often constitute nascent plate boundaries, yet long‐term extension rates and transient rate changes associated with these early stages of continental breakup remain difficult to determine. Here, we derive a time‐averaged minimum extension rate for the inner graben of the Northern Kenya Rift (NKR) of the East African Rift System for the last 0.5 m.y. We use the TanDEM‐X science digital elevation model to evaluate fault‐scarp geometries and determine fault throws across the volcano‐tectonic axis of the inner graben of the NKR. Along rift‐perpendicular profiles, amounts of cumulative extension are determined, and by integrating four new 40Ar/39Ar radiometric dates for the Silali volcano into the existing geochronology of the faulted volcanic units, time‐averaged extension rates are calculated. This study reveals that in the inner graben of the NKR, the long‐term extension rate based on mid‐Pleistocene to recent brittle deformation has minimum values of 1.0–1.6 mm yr−1, locally with values up to 2.0 mm yr−1. A comparison with the decadal, geodetically determined extension rate reveals that at least 65% of the extension must be accommodated within a narrow, 20‐km‐wide zone of the inner rift. In light of virtually inactive border faults of the NKR, we show that extension is focused in the region of the active volcano‐tectonic axis in the inner graben, thus highlighting the maturing of continental rifting in the NKR.

CL LEVELS ANALYSIS IN SG-12 AND SG-18 WELLS IN CILODONG AND SURROUNDING AREAS CILODONG DISTRICT DEPOK CITY EAST JAVA

This Research was conducted in the Cilodong area and its surroundings, Cilodong district, Depok, West Java. The geology in this research area consists of Qa (alluvium), Qav ( alluvium fan), and Qv (young volcanic unit). The groundwater level in this study area ranged from 76.2-86.14 dml. This research area has a high Cl (chloride) value with a minimum value of 11,846 mg/l at SG-12 and a maximum value of 70,517 mg/l at SG-19. The difference in Cl (chloride) levels is also supported by differences in the study area such as TDS values of 40 mg/l at SG-12 and 200 mg/l at SG-18 and EC of 40 µmhos/cm at SG-12 and 400 µmhos/cm at SG-18.

A first regional model of the past Earth's magnetic field from Africa for the last 4000 years

The understanding of the Earth's magnetic field variations over time on the African continent is fundamental for several reasons. For instance, the most important feature of the present geomagnetic field, the South Atlantic Anomaly (SAA) characterized by weaker geomagnetic strength values than those expected for their latitudes, may have emerged in South Africa at the beginning of the second millennium CE. Here, we first selected the available volcanic and archaeomagnetic data following a set of three criteria inspired by the FAIR principles. We then built a first regional geomagnetic model for Africa covering the last 4000 years, using a revised version of the spherical cap harmonic (SCH) analysis in 2 dimensions. The new regional model shows, at the Earth's surface, the westward migration of the SAA from the Indian Ocean over Africa since 1100 CE. In addition, the regional model is tested as a paleomagnetic dating tool by re-dating previous archaeomagnetic data from Africa and thus can be used to date other African archeological sites and the numerous active and dormant volcanoes of the East African System. Plain language summaryThe spatial and temporal evolution of the Earth's magnetic (geomagnetic) field is based on direct historical or instrumental data and the indirect information extracted from rocks and archeological artifacts (palaeo- and archaeomagnetic data). While the present field is well sampled at both spatial and temporal domains, this is not the case for the past evolution of the geomagnetic field, where the paleomagnetic data are not globally distributed. There are large areas in the Southern Hemisphere yet to be investigated. However, recent data from Africa enables us the building of the first regional geomagnetic model for the last 4000 years. The new regional model sheds light on the past evolution of the most remarkable feature of the present geomagnetic field, the South Atlantic Anomaly (SAA), showing details of the westward migration of the SAA from the Indian Ocean over Africa since 1100 CE. Moreover, the new model refines the use of paleomagnetism as a dating tool for volcanic units from East African Rift System and for the abundant African archeological sites improving the knowledge of the history of human civilizations.

Utilizing cores for characterising the temperature and permeability regimes in a litho-stratigraphic model of the Montserrat geothermal system, Montserrat (Lesser Antilles arc, West Indies)

Cores samples are vital in the characterization of heterogeneous volcanic geothermal environments. Continuous cored intervals, representative of the subsurface formation, can help to validate geological and thermal classifications previously interpreted from drill cuttings. More importantly, core samples can help to improve our understanding of controls on fluid flow, as direct permeability measurements are attainable. In this study, we conduct petrological and petrophysical analyses on three cores (Core 1, Core 2 and Core 3) obtained from the well MON-3, drilled within the hydrothermal system located in Montserrat, Lesser Antilles arc, West Indies. We present a litho-stratigraphic model of the geothermal system. Contrasting lithologies (sandstone, limestone and interbedded silicified tuff) and mineralogies (calcite vs plagioclase) from Core 3 (2109 – 2116.5 mbsl) contributed to constraining a volcanic-sedimentary unit (∼1900 – 2200 mbsl) while pumice textures of Core 1 (1478 – 1482.6 mbsl) and Core 2 (1700 – 1705.3 mbsl) helped to classify a subaerial volcanic unit (∼1200 – 1900 mbsl). Integrating classified alteration assemblages in the model with downhole temperature logs, we propose that the thermal regime of the hydrothermal system was hotter in the past based on evidence of epidote and actinolite observed at depths less than 1200 mbsl. Lastly, we infer that the primary permeability of carbonate formations or secondary fracture permeability developed by a SW and WNW fault zone in a shallower volcanic sedimentary unit (∼900 – 1200 mbsl) could be influences on potential feedzone locations in the wellbore. This could be supported by the relatively highest measured permeabilities (10−18 – 10−17 m2) in a carbonate sample of Core 3 and fractured samples of Core 2. Overall, the improved characterization of litho-units, alteration assemblages and permeable zones with possible influences on fluid flow, can be used to enhance previous numerical and geophysical models of Montserrat's geothermal system.