Pahoehoe Lava Research Articles

Lithofacies association and stratigraphy of the Quixaba and Remédios formations, Fernando de Noronha archipelago, Brazil

This work presents facies analysis of pyroclastic and effusive deposits present in areas of the Fernando de Noronha Archipelago (FNA), South Atlantic Ocean. A detailed stratigraphic study was carried out for the Remédios Formation at the Caieira beach and the Quixaba Formation at the Capim-Açu Edge, Americano, and Bode beaches. The lithofacies association for the deposits of the Remédios Formation characterizes non-welded ignimbrites of phonolitic composition generated by concentrated ground-hugging density currents originated from collapses of a buoyant eruption column. Possibly, this phase was followed by a caldera collapse and the exposition of a complex system of dikes at Caieira Beach. For the deposits of the Quixaba Formation, the lithofacies association characterizes scoria and ash flow/grain avalanching deposits, proximal fallout deposits, and Pahoehoe lava flows. The Quixaba volcanism shows evidence of pulses of Strombolian and possibly Violent Strombolian activity alternated with effusive Hawaiian activity. A later stage of magma-water interaction during the Quixaba volcanism led to the formation of a sustained eruption column and fallout deposits with ash aggregates formed through wet aggregation.

3D Paleogeographic Reconstruction of the Cabiúnas formation lava flows in Campos basin, SE Brazil

Hydrocarbon production from volcanic reservoir rocks in Brazil is rare but it was successfully achieved in the Badejo field, Campos Basin. The volcanic rocks are basalts of the Cabiúnas Formation, related with the voluminous lava flows that erupted prior and during the Gondwana breakup in the Early Cretaceous. Despite their widespread distribution in Campos Basin, volcanic facies architectures and studies of physical volcanology regarding the Cabiúnas basalts are still scarce. The cores recovered from wells BD-02, BD-04 and BD-08, drilled in the Badejo field, provided an excellent material to reconstruct the 3D geometries of the volcanic lava flows in the area. Two compound-braided sequences (Sequence 1 and 3) and a tabular-classic sequence (Sequence 2) were identified in the studied wells. Lithofacies associations or morphologies include classical, hummocky, sheet and rubbly pahoehoe lavas. Coherent, brecciated, peperites and volcanogenic lithofacies were also described in the well cores. Estimated vesicle deformation values (parameter D) for hummocky lavas are higher than those for classical pahoehoe lavas, pointing to porosities and permeabilities adequate to the best potential plays in Sequence 3. The compound-braided Sequence 3 have reach 89.5 m, much thicker than the 40 m thick tabular-classical sequence (Sequence 2). The volcanic paleoenvironment corresponds to subaerial lava flows interacting with wet sediments in all sequences. This information can be of great importance for better characterization of potential offshore volcanic reservoirs within Campos and other sedimentary basins associated with the Gondwana breakup in SE Brazil.

Vikrahraun—the 1961 basaltic lava flow eruption at Askja, Iceland: morphology, geochemistry, and planetary analogs

We examine the morphology and chemistry of the Vikrahraun basaltic eruption emplaced at Askja Volcano, Iceland, from Oct. 26–Dec. 17, 1961. The eruption had three eruptive events, initiating with aʻa and followed by alternating aʻa and pahoehoe lava flow emplacement. We determine that while the eruption is chemically homogenous (Fe/Mg = 1.9–2.2, 47–52 wt.% SiO2), it demonstrates transitions from high to low viscosity lava flow morphologies. Aʻa flows have a total crystallinity (phenocryst and microlite abundance by area) ranging from 85–100%, which increases by 1% per km from the vents, while pahoehoe flows range from 55–86% and increase at a higher rate of 5% per km. Vesicularity systematically decreases with distance from the vent by 3% per km. Pahoehoe and vent samples have calculated temperatures 50 °C higher than aʻa samples, which we interpret to be due to the difference between tube fed pahoehoe and open channel aʻa lavas. The homogenous nature of the Vikrahraun lava makes it an excellent testbed to study the effects of observational scale and satellite resolution on the interpretation of surficial textures. Festoons, which are downslope pointed convex ridges from 1 to 5 m high and ~ 10 m long, are observed in event 2 aʻa lavas in satellite imagery and topographic profiles. Features of this scale have previously only been documented in terrestrial rhyolitic lavas, leading planetary researchers to infer that festooned lava flows on Venus and Mars may be silicic. The diverse morphologies and homogenous composition make Vikrahraun an important planetary analog, where morphological complexity is over-attributed to chemical variation and suggests the need to re-evaluation planetary lava flow interpretations.Graphical

Review of geology and geomorphology of the Xalapa Monogenetic Volcanic Field, eastern Trans-Mexican Volcanic Belt

Monogenetic volcanic fields have associated volcanic hazards that are not always well constrained due to the lack of complete and well established geological and geomorphological studies, field boundaries, volcano inventories, and of detailed reconstruction of individual volcano eruptive histories. This work presents a detailed review and further insights into geology and geomorphology of the Xalapa Monogenetic Volcanic Field (XMVF), achieved by completing a comprehensive revision of all previous works on the XMVF, along with new data produced from extensive fieldwork, field and digital mapping, radiocarbon dating, and morphometric and density analyses. The main results are: (i) a renewed inventory of 72 XMVF monogenetic volcanoes - a total number larger than previously recorded (59); (ii) identification of six new and not previously identified monogenetic volcanoes: La Natividad, La Pedrera, El Puente, Rancho Sicomoro, and Puentecillas scoria cones, and the Tenampa maar; (iii) recognition of four possible new volcanoes integrating the Macuiltépetl cluster, recorded in historical documents; (iv) corrections and new volcanoes identified in the volcano clusters of Pextlan, La Joya, Ocotepec, and Cruz Negra; (v) geological mapping of all lava flows associated with the 72 monogenetic volcanoes; (vi) comprehensive morphometric analyses of all 72 reported volcanoes; (vii) three new radiocarbon ages corresponding to 780 ± 60 BP and 1340 ± 60 BP lava flows of El Volcancillo scoria cone, and to 1300 ± 60 BP and 1115 ± 80 BP lavas of La Pedrera volcano; (viii) new evidence of the late Pleistocene to Holocene age of the Acatlán scoria cone; (ix) new outline of the boundaries of the XMVF based on fieldwork and remote sensing; and (x) volcanoes and lava flows density and distribution maps. From these results, we conclude that, in case of renewed monogenetic activity in the XMVF, the most likely deterministic hazard model would comprise effusion of lavas of variable length (3–40 km), of up to extremely long tube-fed pahoehoe lava flows; explosive activity ranging from typical to violent Strombolian style eruptions producing scoria cones, extensive fallouts, and associated pyroclastic density currents; and phreatomagmatic style activity producing maars, tuff rings and/or tuff cones, and sequences of wet pyroclastic density currents. Hazard distributions in these scenarios would be mainly controlled by topography, local tectonics, groundwater level and basement rocks lithology, and would mostly affect the north and south flanks of Cofre de Perote volcano, as well as central XMVF sectors where the metropolitan area of the city of Xalapa and towns of Naolinco and Acatlán locate. From this review, we conclude that without any further studies of geology and chemistry of every single volcano, the western boundaries of the XMVF will remain unclear, and the associated volcanic risk will remain underestimated. This work provides a fundamental basis from which further and more detailed work could be attained.

Characterization of volcanic reservoirs; insights from the Badejo and Linguado oil field, Campos Basin, Brazil

The Badejo and Linguado oil fields are hosted within non-conventional volcanic reservoirs which produced commercial hydrocarbons from the Lower Cretaceous Cabiúnas Formation, Campos Basin, offshore Brazil. Despite over 30 years of production, limited characterization of the nature and reservoir properties of the volcanic reservoirs have been presented to date. A comprehensive reappraisal of the Cabiúnas Formation volcanic reservoirs is presented in this study incorporating extensive existing and new data including core descriptions, laboratory petrophysical analyses, petrography, QEMSCAN, SEM, wireline, and microtomography results from five cored intervals of wells spanning the main reservoirs of the Badejo and Linguado fields. Volcanic facies analyses of the sequences reveal a predominance of subaerial effusive basic volcanic rocks interbedded with sediment and in several cases comprising peperites revealing intricate lava-sediment interaction products. Four volcano-sedimentary units are identified, showing alternations between low (compound pahoehoe lava dominated Units 1 and 3) and high (tabular rubbly pahoehoe lava dominated Units 2 and 4) effusion rates. Paleoenvironmental conditions also varied between units with extensive oxidation present in Unit 1 inferred to relate to extended periods of subaerial exposure and weathering in an arid environment. Overlying Units 2–4 reveal an increase in humidity evidenced by an increase in the presence of well sorted fine-grained sediment interlayers, peperites, and non-marine ostracods. Both original facies and alteration reveal key controls on reservoir properties. Extensive weathering and alteration of Unit 1 caused pervasive filling of original porosity (vesicles and fractures) and resulted in reservoir degradation. Lesser weathering of overlying Units 2, 3 and 4, resulted in improved reservoir properties which can be clearly linked to volcanic intra-facies including vesiculated and autobrecciated lava flow tops which commonly reveal extensive oil staining. This study reveals the intricate interplay between primary volcanic facies and subsequent alteration history in dictating volcanic reservoir properties in a successful offshore oil field development.

Morphology, Textures and Thicknesses of Rubbly Pahoehoe Lavas from the ~117 Ma Sylhet Traps, India

Abstract The Sylhet Traps and the larger outcrops of the Rajmahal Traps in India constitute an important remnant of a large Continental Flood Basalt (CFB) province related to the Kerguelen hotspot. A composite log of lava flows across the southern margin of the Meghalaya plateau is presented where the Sylhet Traps are best exposed. Lavas in the lower part of stratigraphic sequence (~480 to 700 m above mean sea level) are compound and contain pahoehoe sheet lobes intruded by thin basaltic dykes constituting a swarm. These lavas record variable degrees of inflation at low effusive rates. In the upper parts, several rubbly pahoehoe lavas are interspersed with sheet lobes. These represent transitional lava types (between pahoehoe and aa) and occur due to steep gradients and/or increased effusive rates. The vesicles from within these lavas impinge and coalesce, indicating that they had time to form and grow in an insulated environment. The vesicle deformation index (VDI) ranges from 0.2 to 0.53, indicating moderate but variable shear strain on the lavas during emplacement. The coexistence of pahoehoe-rubbly pahoehoe lavas is also recorded in the surface outcrops of Rajmahal Traps and the IODP drill cores along the Kerguelen Plateau. It is postulated that the Sylhet lavas represent the distal edge of a lava-shield evolving into a flood basalt setting, dominated by pahoehoe in the lower stratigraphy with few lavas transitioning to rubbly pahoehoe towards the top. Such an architecture is in keeping with other CFB provinces worldwide.

GEOHERITAGE POTENTIAL AS GEOTOURISM SPOT BASED ON QUANTITATIVE AND QUALITATIVE ANALYSIS IN BANDUNG, WEST JAVA


 
 
 
 Bandung is one of area with abundant geodiversity which also indicates high geotourism potential. One of Bandung geodiversity attractive aspect is the high scientific value related to Tectono-Volcanic History of Bandung which have a good Geoheritage potential. This research intends to assess the Geoheritage potential for Geotourism purposes in Ban-dung City. Research methods such as field observation, literature study, quantitative and qualitative analysis aimed toward at seven geoheritage potentials: Sunda Ignimbrite at Goa Jepang, Sunda Ignimbrite at Goa Belanda, Lava Tube at Cikapundung River, Pahoehoe Lava at Cikapundung River, Ropy Lava at Curug Lalay, Columnar Joint Lava at Curug Omas and Lembang Fault Scarp at Keraton Cliff. Quantita-tive Analysis is based on classification for geotourism pur-poses which includes Intrinsic and Scientific Value, Educa-tional Value, Economic Value, Conservation Value, etc. Quantitative analysis indicates that Geoheritages in Bandung City have a good potential for Geotourism purposes with mean percentage score of >59%.
 
 
 

Magmatic and hydrothermal evolution of mafic pegmatites and their host basalts, Paraná Large Igneous Province, Brazil

The high-Ti Paranapanema sequence in the Paraná Large Igneous Province consists of a succession of pahoehoe lava flows. Some of these flows host mafic segregation structures, such as horizontal pegmatitic sheet layers and vesicular cylinders. Geochronology, whole-rock and mineral chemistry of two pegmatite occurrences and their host basalts permit characterizing crystal-melt segregation processes that occur during magmatic differentiation after lava flow emplacement. The mineralogy of the pegmatites is similar to that of the host basalts, and it includes plagioclase, pyroxene and titanomagnetite-ilmenite crystals; the only observable difference is the coarser grain size of primary phases and an increase in the volume fraction of clay minerals derived from glass devitrification and vesicle infilling in the pegmatites (~15 vol% clay in the pegmatites vs. ~6 vol% clay in the basalts). The pegmatites from both sites are more fractionated than the enclosing lavas and are enriched in TiO2, FeOtotal, K2O, P2O5 and incompatible trace elements (e.g., Ba, Rb, Nb, Hf, Y, Zr, La, Ce, Yb). Thermodynamic modeling of whole-rock compositional data suggests that the Barracão pegmatites were formed after ~8–27 wt% fractional crystallization of the host basalt, whereas the Capanema pegmatites formed after ~38–43 wt% fractional crystallization of the host basalt. 40Ar/39Ar geochronology indicates slight yet significant age differences between plagioclase phenocrysts from the pegmatites and whole-rock fragments from the enclosing lavas (Capanema: 133.56 ± 0.52 pegmatite vs. 134.30 ± 0.46 Ma enclosing lava; Barracão: 133.23 ± 0.88 pegmatite vs. 134.49 ± 0.31 Ma enclosing lava). These age differences likely result from hydrothermal alteration of the plagioclase phenocrysts (e.g., secondary albite and K-feldspar), and they are not due to resolvable differences in crystallization age. Smectite-celadonite aggregates recovered from the Capanema basalt suggest that hydrothermalism occurred at 123.18 ± 0.61 Ma, approximately ten million years after rock crystallization.

Englacial lake dynamics within a Pleistocene cordilleran ice sheet at Kima' Kho tuya (British Columbia, Canada)

Passage zones are stratigraphic surfaces found in littoral settings separating deposits diagnostic of subaqueous environments from overlying sequences of subaerial deposits. In glaciovolcanic settings, passage zone surfaces are unequivocal records of the heights and depths of paleo-englacial lakes at a specific point in time and space, thereby, informing on the presence and nature of the enclosing ice sheet. Kima' Kho, a Pleistocene glaciovolcano (i.e. tuya) located in the northern Cordillera of British Columbia, features multiple and diverse passage zones. The basaltic volcano comprises four main stratigraphic packages: i) subaqueously and subaerially deposited lapilli tuffs (Lt1/Lt2) forming a central tephra cone and representing an explosive onset to the eruption, ii) subaqueously deposited, steeply-inclined beds of tuff breccia dominated by pillow lava fragments (Tb1-3), iii) stacked sheets of subaerial pahoehoe lavas (L1-3), and iv) dykes and sills (I) intruding all units. Stratigraphic and geochemical relationships suggest that Kima' Kho volcanism was continuous and 40Ar/39Ar geochronometry on three samples yields a mean age of 1949 ± 63 ka. Three temporally distinct passage zones record the interplay between growth of the volcanic edifice, syn-volcanic melting of the enclosing ice sheet, and fluctuations in the depth of the englacial lake. The earliest passage zone (PZ1) is expressed in two different ways marking a transition from explosive to effusive eruption: (i) within pyroclastic deposits of the tephra cone (<1800 masl), and (ii) by pillow lava tuff breccia deposits overlain by subaerial lavas. Together they record a peak, sustained lake depth of 320–340 m that constrains the enclosing Cordilleran ice sheet to a minimum thickness of ∼400 m. Two subsequent passage zones (PZ2-3), also defined by sequences of subaerial lavas resting on dipping beds of pillow lava tuff breccias, occur at lower elevations: 1690-1640 masl and 1740-1720 masl, respectively. The latter two passage zones indicate a major draining of the englacial lake followed by refilling to depths of 230–180 m and 260–280 m, respectively. The substantial decline in lake level between PZ1 and PZ2 suggests a massive, catastrophic deluge (i.e. jökulhlaup) of 1–2 km3. Lastly, the reconstructed glaciovolcanic evolution of Kima' Kho demands the presence of a regionally extensive ice sheet overlying the Kawdy plateau at ∼1.9 Ma and representing an earlier incarnation of the Cordilleran Ice Sheet (CIS).

The Magnificent of Geosites as Geoheritage Potential in Djuanda Grand Forest Park Area, Bandung, Indonesia

Djuanda Grand Forest Park (Tahura Djuanda) at Bandung, West Java Province, built-in 1985, has functioned as a conservation area concerning Indonesia’s biodiversity. It is the first Grand Forest Park among 27 of them, which was built in Indonesia. In addition, Djuanda Grand Forest Park potential for geodiversity and geoheritage concerning the geological history of the Tangkuban Parahu volcano formation since ancient times, so that conservation is needed. The Indonesian Geological Association (IAGI), in collaboration with the Djuanda Grand Forest Park Institution and the Geological Agency, researched the geoheritage potential of the Djuanda Grand Forest Park for accelerating the Tahura Djuanda to be a geoheritage area. The method used in this study consist of inventorying, identifying, analyzing, and mapping each geodiversity/geoheritage. The finding is that the Djuanda Grand Forest Park area has seven geoheritage potentials: the Dago Waterfall Lava, Pahoehoe Lava, Lalay Waterfall Lava, Omas Waterfall Lava, Ignimbrite at “Gua Belanda” and “Gua Jepang” and the Kraton Cliff Fault Scarp. By establishing the Djuanda Grand Forest Park area as a geoheritage area will expose more information about the geological history of Tangkuban Parahu Volcano’s formation through some interpretation boards (signboards) installed at each geoheritage location for conservation and education purposes through tourists visit points. In addition, West Java will be the second province to have a geoheritage after the Geoheritage of Pandeglang Regency, located in Banten Province.

The Thórólfsfell tuya, South Iceland – A new type of basaltic glaciovolcano

Basaltic tuyas are glaciovolcanoes that form when substantial focused eruptions take place beneath thick ice. None have been witnessed, so models reconstructing tuya formation are grounded in detailed fieldwork. A key feature of many basaltic tuyas is the presence of volcanic and volcaniclastic rocks that indicate the sustained presence of an encircling meltwater lake during the eruption.Here we provide the first description of Þórólfsfell (Thórólfsfell), a basaltic tuya from Iceland, which is sufficiently distinct from previously described tuyas to be considered a new type of basaltic glaciovolcano.Thórólfsfell is an asymmetric tuya with an area of c.8 km2, base-to-top height of c.450 m, and volume of c.2.2 ± 0.4 km3 that has been emplaced onto the approximately 12o sloping lower southern flanks of Tindfjallajökull central volcano.Thórólfsfell shares only two major morphological characteristics with other basaltic tuyas: (1) a sub-horizontal top comprising subaerial lavas; (2) a clear vertical topographic expression, which reflects preferential upwards edifice growth due to lateral confinement by encircling ice and/or meltwater. There is no evidence for the presence of a large and long-lived syn-eruptive meltwater lake.The Thórólfsfell eruption is effusion-dominated, and there is a gradual reduction in cooling fractures in lavas with elevation. The eruption is divided into three Stages. Stage I forms a c.110 m thick drape onto an irregular but persistently c.12o dipping basement of older basaltic tuffs; Stage I consists of palaeoslope-parallel lava lobes with abundant cooling fractures, accompanied by abundant breccias. Stage II comprises a c.240 m thick stack of c.12o dipping stacked lava lobes with abundant cooling fractures, and occasional autobreccias. Stage III is c.110 m thick, and whilst early lavas have cooling fractures, the final Stage III lavas are sub-horizontal, subaerial pahoehoe lava flows.Our model for the formation of Thórólfsfell has two key features. The first is that the inclined basement has facilitated the downslope movement of meltwater away from the eruption site into an efficient gravity-assisted subglacial meltwater drainage system. The second is that there is a close connection between the vertical growth of the tuya and the ice above, with each successive lava in the growing stack being close to and/or in contact with the overlying ice. This repeated process provides the regular (but transient) meltwater supply necessary to produce a c.350 m stack of similarly-cooled lava carapaces.From a hazards perspective, a Thórólfsfell-style eruption is of little concern as rapid and steady meltwater drainage away from the eruption site would prevent the high-magnitude glacial outburst floods that require accumulated meltwater. The Thórólfsfell eruption provides a new perspective on effective meltwater dispersal away from tuya-building eruptions on dipping palaeoslopes, and on lava-ice interactions during subglacial eruptions. The products of other subglacial eruptions onto dipping basements, producing Thórólfsfell-type tuyas, await study.This first description of a new type of basaltic glaciovolcano may aid in the identification and interpretation of similar glaciovolcanoes on Earth and Mars that have yet to be discovered.

Lithostratigraphy of the Serra Geral Formation in the northern portion of the Paraná-Etendeka Igneous Province: A tool for tracking Early Cretaceous paleoenvironmental changes

A detailed lithofacies analysis in Continental Flood Basalt Provinces allows the comprehension of their evolution and paleoenvironmental significance. In the northern portion of the Paraná-Etendeka Igneous Province (PEIP), in Brazil (Uberlândia-Araguari area), a volcanological and stratigraphic approach provided evidence that the basaltic volcanic succession is not monotonous, involving different lava flow morphologies and architecture. The volcanic succession reaches a thickness of ca. 300 m and includes four lithofacies associations: pillow lavas, compound pahoehoe, simple pahoehoe, and sediment-matrix basalt breccia. Pillow lavas, simple pahoehoe, and compound pahoehoe characterize the onset of volcanic activity in the area. Sediment-matrix basalt breccia and thick simple pahoehoe lavas occur in upper stratigraphic levels. Some of these thick igneous bodies can represent invasive lavas or shallow intrusions. In the study area, the common presence of volcanic deposits and structures formed in wet conditions is evidenced by the occurrence of pillow lavas, undulatory columns, and interleaved lacustrine and fluvial sedimentary rocks. These deposits reflect different environmental conditions from those previously described as arid in other portions of the PEIP. Low-temperature post-depositional alteration has affected the volcanic and sedimentary rocks of the study area, obliterating many of the primary sedimentary structures. The subaerial and subaqueous lavas are chemically similar, and compatible with high-TiO2 Pitanga magma type. The Uberlândia-Araguari area and the southern part of the PEIP have a similar stratigraphic style both characterized by the dominance of compound pahoehoe lavas at the base and by an intermittent volcanism, which is evidenced by the intercalation of sedimentary deposits with lavas.

Experimental evidence for lava-like mud flows under Martian surface conditions

Large outflow channels on ancient terrains of Mars have been interpreted as the products of catastrophic flood events. The rapid burial of water-rich sediments after such flooding could have led to sedimentary volcanism, in which mixtures of sediment and water (mud) erupt to the surface. Tens of thousands of volcano-like landforms populate the northern lowlands and other local sedimentary depocentres on Mars. However, it is difficult to determine whether the edifices are related to igneous or mud extrusions, partly because the behaviour of extruded mud under Martian surface conditions is poorly constrained. Here we investigate the mechanisms of mud propagation on Mars using experiments performed inside a low-pressure chamber at cold temperatures. We found that low viscosity mud under Martian conditions propagates differently from that on Earth, because of a rapid freezing and the formation of an icy crust. Instead, the experimental mud flows propagate like terrestrial pahoehoe lava flows, with liquid mud spilling from ruptures in the frozen crust, and then refreezing to form a new flow lobe. We suggest that mud volcanism can explain the formation of some lava-like flow morphologies on Mars, and that similar processes may apply to cryovolcanic extrusions on icy bodies in the Solar System.

Characterising the Bushe-Poladpur Contact across the Western Deccan Traps and Implications for Mapping the K-Pg Boundary?

Abstract The Bushe-Poladpur contact is one of the most important stratigraphic boundary separating the middle Lonavala Sub-group from upper Wai Sub-group in the Western Deccan Traps. In this paper, physical volcanology textural and petrochemical finger printing, crystal size distribution and shape preferred orientation studies (SPO) is integrated with paleomagnetic and AMS studies to correlate lavas across five localities transcending the Bushe-Poladpur boundary, south of Pune city. The flows belonging to the Bushe Formation are highly inflated, compound pahoehoe lavas, with plagioclase-olivine-phyric, coarse grained diktytaxitic textures. The flows belonging to the Poladpur Formation are transitional between pahoehoe and aa (rubbly pahoehoe lavas), with or without multi-tiered entablature showing fine-grained, olivine-phyric glassy textures. CSD studies indicate that the Bushe lavas have lower plagioclase crystals per unit area (1.11x10-4/μm2), low average effective nucleation rates (2.60x 10-12/μm3s) and high average effective growth rates (1.22x10-5μm2/s) for intact crust time than the Poladpur lavas that have higher plagioclase crystals per unit area (8.31x10-4/μm2), high average effective nucleation rates (3.46x10-11/μm3s) and lower average effective growth rates (2.24x10-6μm2/s) akin to their emplacement dynamics and cooling histories. There is a stark contrast in the magnetic susceptibilities (Bushe- 24759.8 x 10-6 SI; Poladpur-29178.02 x10-6 SI) across the Bushe-Poladpur contact. There is a general similarity between the SPO of the primary silicates (plagioclase) to the AMS derived directions. The divergence in AMS directions across the Bushe-Poladpur contact in the study area can be attributed to complex interplay of local paleotopography and slope, lava flow field dynamics, inflation and inversion of topography, style and emplacement mechanism of flow units. Generalisations and over simplifications of delineating lavas and deciphering their flow direction on a single criteria (tool) or single ghat (road section), outcrop or sample will have disastrous consequences while mapping large and complex lava flow fields. Thus, a multi-disciplinary approach needs to be the norm for characterising, correlating and mapping lavas across formations that transcend the K-Pg boundary in highly dissected ancient continental flood basalt province like the Deccan Traps.

Ovda Fluctus, the Festoon Lava Flow on Ovda Regio, Venus: Not Silica‐Rich

AbstractOvda Fluctus (6.1°S, 95.5°E) is a lava flow complex on the equatorial tessera highlands of Ovda Regio, Venus. We examined its morphology and geologic setting to determine if its apparent emplacement rheology is consistent with silica‐rich (e.g., rhyolitic) lava; this has significant implications for the compositions of Venus's tesserae. Using Magellan radar data, we find that the radar properties (emissivity, roughness, and backscatter) of Ovda Fluctus are similar to those of the surrounding tessera, although the flow is smoother at multiple scales. Ovda Fluctus is a “festoon flow complex,” whose surface is rumpled into arcuate folds. The flow includes multiple flow lobes and at least two distinct flow units. The flow complex includes a portion at high altitude (~5 km above mean planetary radius) that has low radar backscatter and high radar emissivity compared with lower‐altitude portions of the complex. The high‐altitude region of Ovda Fluctus is continuous with the lower‐elevation portions: the change in radar properties does not represent different flows. Outlines of Ovda Fluctus flow lobes have fractal dimensions consistent with basaltic pahoehoe lavas. The margin of Ovda Fluctus is at significantly higher elevation than its center, a characteristic seen in basalt flows on Earth, but not on more silica‐rich flows. Thus, the available evidence suggests that Ovda Fluctus had an emplacement rheology consistent with a basaltic composition; this result provides no support for hypotheses that Ovda Regio (a highlands tessera terrain) is composed of granitic rock.

Volcanic succession, petrology, and geochemistry of the Sujiagou komatiite from the North China Craton

The ~2.7‐Ga Taishan greenstone belt from the Eastern Block of the North China Craton has well‐exposed komatiite sections. The komatiite outcrops at Sujiagou have well‐preserved primary volcanic texture although they have experienced amphibolite‐facies metamorphism. Two komatiite lava flows are identified in the Sujiagou outcrops: “Flow Ι,” with a thickness of 55 m, is characterized by poly‐sutured crust at the top, spinifex texture in the middle, and olivine cumulates at the flow bottom. “Flow ΙΙ” consists of abundant pahoehoe lava lobes with no interstitial materials. These volcanic characteristics, as well as the interbedding with terrestrial sediments, suggest that the Sujiagou komatiite erupted in a subaerial continental environment. The olivine–chromite geothermometer gives peak metamorphic temperatures from 684°C to 764°C. Phase equilibria modelling suggests that the mineral proportions and mineral compositions are consistent with a retrograde temperature of ~488°C, at which the komatiite would have low olivine Fo (79–89) and high bulk‐rock Mg# (83–90). Linear mixing of the in situ trace element compositions of the metamorphic olivine, augite, tremolite, serpentine, and chlorite from Sujiagou komatiite samples can reproduce the trace elements of representative komatiite compositions, suggesting that later metamorphism and fluid–rock interactions played key roles in trace element variations in the bulk‐rock komatiite samples. These results also imply that the “arc signature” of the Sujiagou komatiite may be an overprint from posteruption fluid alteration rather than a primary subduction geochemical feature. Therefore, the Sujiagou komatiites may belong to a part of the global plume‐related greenstone belts at ~2.7 Ga.

A unique ~12 ka subaerial record of rift-transform triple-junction tectonics, NE Iceland

In northern Iceland the European-North American plate boundary is broad and complex but includes a remarkable subaerial triple-junction intersection between the Husavik-Flatey Fault (HFF) dextral transform and rifting in the Northern Volcanic Zone. Fortuitously, the triple junction occurs in a sheet of ~12 ka pahoehoe lavas; a tabula rasa recording innumerable fault features displayed in exquisite detail. High-resolution drone imagery, coupled with 120 field measurements of fault slip directions and opening amounts, made possible the mapping and analysis of this detail and, importantly, enabled recognition and exclusion of potentially misleading primary deformation features associated with emplacement of the lavas. Rift-transform interactions in this natural laboratory have remained spatially stable throughout post-glacial time, although with transform-affinity faults reactivated to accommodate rift extension and transform ‘encroachment’ into the rift domain. First-order en-echelon Riedel fault complexes are recognised, linked by transpressional faulting and compressional strike-slip relay ramps, as well as second-order R shears, R’ and P shears, and previously undescribed R’ Riedel-in-Riedel relationships. A pahoehoe flow front offset along a first-order Riedel fault complex records slip at ~3.8 mm a−1, which may be consistent with the published GPS-based current slip-rate estimate of ~6.8 mm a−1 across the HFF as a whole.

The geological site characterisation of the Mandla region, Eastern Deccan Volcanic Province, Central India

Detailed geological studies were carried out on the basaltic sequences along the Jabalpur–Niwas, Jabalpur–Chutka and Jabalpur–Mandla traverses covering an area of about $$12\hbox { km} \times 15\hbox { km}$$ to characterise various basaltic lava flows and their behaviour on seismotectonics and geodynamic setting of their formation in the Mandla region of the Eastern Deccan Volcanic Province (EDVP). The studies involve an analysis of the satellite images for the identification of lineaments/faults and field geological studies consisting of geological controls such as ground check, thickness of fractures and orientation along the acknowledged lineaments/faults. The results of the present research comprising 65 lineaments/faults mainly belonging to two geometric groups, minor and major dominantly in the NW–SE and the NE–SW and altered strata varying lithology (weathered to compact basalts) are recognised in the study area. Based on their extent, 57 lineaments have been classified as minor ( 300 km) lineaments are noticed in the study region. The field geological investigations have facilitated the recognition of 10 flows with different characteristic features and a variety of volcanic structures such as columnar, vesicular, amygdaloidal, inflated pahoehoe lava flows and red bole interflow horizons have been documented. Basement rocks of these Deccan basalt lavas are represented by Tirodi Biotite gneisses, quartzite, quartz–mica schists and crystalline limestone in the SE part of the study area of the Mandla region. The present study will help evaluate the localised site characterisation for urban planning and setting up major civil structures.

Teledetección aplicada al mapeo geomorfológico de los volcanes de la cuenca alta del río Chaschuil, provincia de Catamarca, Argentina

Contexto: La cuenca alta del río Chaschuil se encuentra en las provincias geomorfológicas de codillera Frontal y sistema de Famatina, se extiende desde el límite superior de la cuenca, a los 26° 45' 6,35" de latitud S y 68° 2'22 15" de longitud O, hasta el volcán Aguas Calientes, a los 27° 13' 25,81" de latitud S y 68° 19'5 48" de longitud O. La zona se inserta en el Cinturón de Fuego del Pacífico, que se caracteriza por concentrar algunas zonas de subducción más importantes del mundo, donde se genera una intensa actividad sísmica y volcánica.&#x0D; Método: A través de operaciones estadísticas y numéricas aplicadas sobre los datos de las matrices que componen una imagen satelital, se generó la cartografía geomorfológica volcánica. Para dicho análisis, se utilizó el software libre SoPI 3.0, en el que se procesaron las imágenes satelitales Landsat 7 y 8, de los años 2002 y 2015. La cartografía fue elaborada en el software libre QGIS 3.2.2, con el apoyo del software libre Google Earth Pro.&#x0D; Resultados: Los mejores resultados del procesamiento digital se dieron en las bandas de rango visible y mediante distintas combinaciones de bandas en RGB. Se describen 13 aparatos volcánicos principales, altamente erosionados, con lavas pahoehoe asociadas; y erupciones secundarias, con lavas rugosas tipo aa sobrepuestas a las lavas más fluidas.&#x0D; Conclusiones: La aplicación del procesamiento digital de imágenes satelitales es una herramienta óptima para el estudio de estructuras volcánicas, que permite su delimitación y clasificación.

Geomorphological Classification and Landforms Inventory of the Middle-Atlas Volcanic Province (Morocco): Scientific Value and Educational Potential

Abstract Through the tabular morphology of northwestern part of the Middle-Atlas in Morocco, numerous uncovered monogenetic volcanoes arise structured of pyroclastic product layers and lava flows. Our fieldwork results witness a wide-ranging volcanic shape spectrum, as cones, maars, tuff-rings, and cone-maar mixes, generally associated with a later lava flow discharge that could develop many surfaces and appearances. There are withal sundry eruptive products such as pahoehoe lava, scoria, tuff, lapilli, peperites, base-surges, bombs, etc. This monogenetic volcanic field of practically 1000 km2 offers remarkable eruptive landforms, referred to as the largest, and the youngest volcanic field in Morocco, which consists of a large area within the Ifrane National Park. This fieldwork study provides a renewed volcanic geomorphological classification table and GIS data to be used by a wide public range for both educational and geo-touristic interest and access effectively to such a high-mountain natural museum. In the event that these volcanic structures were appropriately dealt with, the high educational scientific content and the notable touristic vocation would almost certainly create business openings and new financial wages for neighborhood populaces. This work focuses to share our outcomes and emphases the scientific value about the monogenetic volcanic field around the tabular Middle-Atlas in Morocco.