Lithic Clasts Research Articles

Conduit armouring preceding explosive activity at an andesitic stratovolcano, an example from Taranaki Mounga, New Zealand

The strength and permeability of volcanic conduits can directly influence eruption dynamics via moderating the outgassing of ascending magma and the density of eruption plumes. Lithic clasts in pyroclastic ejecta can be used to understand the dynamic evolution of conduit walls because they are incorporated into the ascending melt-gas-particle mixture during volcanic eruptions. We examine the 1655 CE Burrell eruption of Taranaki Mounga, which transitioned from effusive activity to an explosive sub-Plinian phase and ended in unsteady columns. This episode was followed by a series of effusive eruptions of lower explosivity. Using textural analysis and physical properties, we distinguish five dominant lithic clast types within Burrell deposits that represent different regions of the shallow conduit and vent. Lithic types 1–3 represent juvenile (‘intrusive cognate’) and older (‘intrusive accessory’) conduit-filling plug materials. Lithic type 4 represents juvenile (‘extrusive cognate’) vent-filling lava dome extruded at the eruption onset, while Type 5 lithics (‘extrusive cognate’) represent sintered/compacted cognate material from the shallow vent accumulated during transitions in eruptive style. Crystalline andesite lithics (type 1) show a microlite-dominated groundmass. Hydrothermally altered andesite lithics (type 2) show breakdown of phenocrysts and increased seismic velocity relative to type 1 lithics. Brecciated andesite lithics (type 3) comprise fractured and sintered clasts of crystalline andesite. Glassy andesite lithics (type 4) show sub-rounded vesicles and glass-hosted microlites. Banded vitrophyre lithics (type 5) show bands of varying vesicularity, crystallinity and clast load. Physical property data reveals porosity, fracturing, sintering and alteration extent dictate dynamic changes in conduit permeability and potentially strength. Our results show how, during the explosive phase of the Burrell eruption, the conduit was lined with juvenile and remnant shallow plug material that was variably fractured, sintered and altered before being eroded and ejected. Comparison with previous work on Taranaki and dome-plug material from around the world shows how fracturing and sintering of conduit walls, combined with lining with dense juvenile material, cause overall permeability reduction and strengthening of the conduit. This inhibits outgassing and preserves conduit structure, facilitating the transition to explosive activity and the establishment of a stable eruption column.

The subaqueous felsic volcanism from the Upper Member of the Cordón de Lila Complex, Antofagasta region, northern Chile

This contribution presents the study of an Ordovician subaqueous felsic succession, formed by the ~400 m-thick Upper Member of the Cordón de Lila Complex (CISL), northern Chile. From bottom to top, the succession starts with two dacitic sills that intruded into the sediments of the lowermost part of the Upper Member. Then, it is followed by a thick sedimentary deposit, two rhyolitic lavas, a volcanoclastic felsic breccia with pyroclastic clasts, and ends with a red rhyolitic lava. The first rhyolitic lava shows centimetric to metric folds with a north-northwestern vergence, evidence of flow in that direction. In the volcanoclastic breccia, an abundant pumice-and-fiamme-rich green matrix wraps around lithic clasts, giving the rock an eutaxitic texture at the outcrop scale. This matrix and texture evidence is characteristic of hot pyroclastic flows deposited under subaqueous conditions. The described section of the breccia is formed by four coarsening-up sequences, reflecting respectively four pulses of building up energy. The lack of internal erosional features points to a single and continuous explosive eruption. An accidental granite clast in the upper part of the breccia suggests a connection with a granitic body, possibly the Pingo-Pingo monzogranite. The geochemical character of the felsic succession is calc-alkaline. The tectonic setting diagram shows a within-plate setting for the succession. This suggests a shift from the arc position inferred for the Lower Member of the CISL to a forearc continental setting for the Upper Member of the CISL.

Mineralogy and Geochemistry of Upper Miocene Igneous Rocks, Kos Island, Greece: Extension during Strike-Slip Faulting and Subduction Rollback

Upper Miocene volcanic and plutonic rocks on Kos island preserve a record of magmatic and tectonic events in the transition zone between the Aegean and Anatolian microplates. Their field setting, syn-intrusion deformation, mineralogy, and geochemistry were investigated. Volcanic rocks, including trachyandesite flows and trachyandesite to rhyolite domes, were extruded on a central E–W horst and directly overlie Alpine basement. Thick successions of trachytic flow tuffs are interbedded with fluvial and lacustrine basinal sediments to the south of this horst. Volcanism was synchronous with the emplacement of the Dikeos monzonite pluton, which is geochemically similar to some lithic clasts in the thick flow tuffs and is cut by mafic dykes including lamprophyres. Two main types of mafic magma were present: a K-rich lamprophyric magma that evolved to trachyandesite and more calc-alkaline magma similar to mafic enclaves in the monzonite. Syn-intrusion structures in the monzonite indicate emplacement during E–W sinistral strike-slip faulting that created local transtensional deformation, providing accommodation for a Dikeos magma reservoir. A change in the style of deformation in the Late Miocene led to NW-striking extension in the footwall, occupied by mafic dykes and mineralized veins, and extensional detachment of the hanging wall, resulting in unroofing of the monzonite.

Petrology and chronology of mare components in lunar basaltic breccia meteorite Northwest Africa 12384

AbstractNorthwest Africa (NWA) 12384 is a lunar polymict breccia composed almost entirely of basaltic components. The clast content includes low‐ to very‐low‐Ti volcanic picritic glass, basaltic vitrophyre, and crystalline pigeonite basalt—an assemblage of volcanic materials that can be tested for petrogenetic relationships. We present the inferred history of select mare components of NWA 12384 as suggested by texture, mineralogy, and petrography, and compare them to Apollo samples and other lunar meteorites. In addition, we used the volcanic glasses in the breccia as a primary composition for crystallization modeling and comparison to the lithic clast compositions. We find that the mafic clasts in NWA 12384 cannot be derived from the picritic glass through a common liquid line of descent because of higher Ti content, though they may have crystallized from a separate, common liquid line of descent. These clasts could represent local source‐region heterogeneity or differential assimilation of more Ti‐rich material. Pb‐Pb SIMS analyses of a large basalt clast in NWA 12384 reveal an age of 3044 ± 41 Ma (2σ), which is used together with the chemical data and 4π cosmic ray exposure age of less than 20 kyr and terrestrial age of between 3.1 and 17.3 kyr to constrain the possible locations of provenance for this meteorite.

Compositional analysis of Apollo 12 Granitic Breccia 12013: Insights into protoliths and formation

We report bulk rock composition and mineral chemistry of previously unstudied fragments and thin sections of lunar granitic breccia 12013. Instrumental Neutron Activation Analysis data on 25 fragments indicate that the 12013 breccia can be described as a three-component system comprising granitic, rare earth element (REE)-rich, and mafic components. The granitic component is low in FeO and REE but rich in K2O, Th, and associated incompatible elements. The REE-rich component has an elevated concentration of REE, moderate FeO, and low concentrations of those elements that are high in the granitic component, in other words, its composition is complementary to that of the granitic component. The mafic component is richest in FeO, and low in those elements that are concentrated in the granitic and REE-rich components. Petrographically, the REE-rich component is an impact melt breccia with a composition unique to Apollo 12 impact melt breccias. Trace-element concentrations in the REE-rich component indicate that its protolith is possibly monzogabbro, although its composition is significantly more magnesian than other known lunar monzogabbros. The mafic component is dominated by fine-grained pyroxene and plagioclase that appear to have recrystallized after impact. However, preserved lithic clasts with an igneous texture occur in the mafic component and are inferred to represent its protolith. The textures of the preserved mafic lithic fragments and lack of Mg-Fe zoning in pyroxene indicate that the protolith of the mafic component formed either as a crustal intrusion or at the bottom of a thick lava flow. The composition of the mafic component is unlike any previously studied mare basalt samples. Textures of this complex breccia suggest that the granitic breccia was first incorporated with the mafic component to form the “gray breccia”, and that the gray breccia was then incorporated with the REE-rich component while the components were still in a hot, plastic state. The complementary trace-element compositions, including the REE patterns, indicate that the petrogenesis of the granitic and REE-rich components are related. We infer that silicate-liquid immiscibility is likely not the formation mechanism for the 12013 components. Instead, bimodal volcanism owing to basaltic underplating may have led to the formation of the 12013 components.

Provenance of Coastal and Seabed Sediments Relative to Mining and Processing Wastes: The Case of Lavrion, Attiki Peninsula, Greece

A detailed textural, mineralogical, and geochemical investigation of beach sands and seabed sediments from Thorikos and Oxygono bays of the eastern coast of Lavrion is performed, with the objective the provenance of the ore types exploited, the processing and beneficiation types employed, and the respective exploitation periods. The Oxygono Bay beach and seabed sands are highly heterogeneous, predominated by lithic clasts originating from surrounding lithologies. Examination of the fine-grained fraction from the seabed core revealed that only the upper 50 cm was affected by recent and ancient mining activity. Combining the mineralogy and geochemistry of Oxygono Bay sands with the radiochronological model of Pappa et al. (2018), four periods of recent exploitation (mid-19th—late 20th century) are distinguished: (1) The “1860–1875 A.D.”, involving exploitation of the ancient smelter slags, (2) the “1875–1900 A.D.”, with ongoing ancient smelter slag processing and the commencement of underground sulfide ore exploitation, (3) the “1900–1930 A.D.”, where heavy mining of the carbonate-hosted Pb–Zn–Ag ore occurs, (4) the “1930–1980”), where the implementation of flotation-type processing assisted in the exploitation of the poor skarn and porphyry-type ores. The latest “1980 A.D.—to date” period depicts the cessation of all mining and processing activities. The southern Thorikos Bay beach sands are homogeneous and fine-grained, are mainly composed of gangue and pyrite, and show elevated Fe, As, Pb, Zn, and Mn content. The southern Thorikos Bay beach sands clearly point to exploitation and processing by flotation of the carbonate-hosted Pb–Zn–Ag sulfide ore, and the tailings were disposed of from the nearby facilities to southern Thorikos Bay without any environmental concern during the “1930–1980 A.D.” period.

Impact-related chemical modifications of the Chang’E-5 lunar regolith

Impact events on the Moon have been recognized as modifying the composition of surface materials through processes such as shock metamorphism and mixing with exotic components. Previous studies have indicated that the regolith sampled by the Chinese Chang’E-5 mission was primarily evolved from local mare basalts, likely originating from a single episode of effusive volcanism. The relatively simple and monotonic protolith of the Chang’E-5 regolith presents a unique opportunity to investigate the chemical modifications induced by impact events. In this study, we conducted detailed petrographic and mineralogical analyses on a diverse set of lunar regolith samples, including thirty-three small impact glass particles (39–227 μm), one large agglutinate (∼1.6 mm), and sixteen basaltic clasts (0.1–1.6 mm). Numerical modeling was also conducted to quantitatively assess the melting behavior of basaltic clasts under different impact conditions. Our primary objective was to evaluate the chemical variations of impact glass in relation to lithic clasts. While the majority of homogeneous impact glass spherules and larger basaltic clasts (≥1 mm) exhibit similar bulk compositions (e.g., Al2O3, CaO and FeO) to the local regolith, we recognize additional effects of impact processes, including impact comminution, impact melting and crystallization, differential volatilization, and potentially selective melting. These processes have modified the texture and geochemistry of lunar regolith components. The chemical signatures of small clasts in the Chang’E-5 regolith indicate that the fine size fractions (e.g., those with diameters of ≤ 300 μm) are predominantly composed of lithic and monomineralic fragments with a substantial proportion being dominated by mesostasis. Melting of these sub-millimeter fractions may lead to the formation of impact glass with chemical compositions deviating from the average local regolith. These results have implications for understanding the compositional evolution of the Chang’E-5 regolith. Notably, our study suggests that impact glasses spherules with different major (e.g., TiO2, MgO) and minor (e.g., REEs, Zr, Th and U) element compositions could be derived from the same protolith of local mare basalts, instead of being exclusively attributed to exotic impact ejecta. In this case, small-scale local impacts may have played a crucial role in the impact history of the Chang'E-5 landing site.

Carbonate sediment dynamics in the Abu Dhabi lagoon - implications for low-angle inner-to-middle ramp models

Carbonate ramps are prominent features of continental margins and intrashelf basins throughout much of Earth's history. Among the limited number of recent analogues of ancient carbonate ramps, the Persian/Arabian Gulf stands out due to its morphologically complex array of open coastal to sabkha environments. This study presents detailed field and laboratory data on spatial facies variability linked to different hydrodynamic regimes spanning from open coastal to inner lagoon settings in Abu Dhabi. Sediment transport and deposition are determined by waves and tidal currents, with spatially and temporally complex variations in the hydrodynamic regime, resulting in a complex facies mosaic. The open coastal domain is subject to persistent north-westerly trade (Shamal) winds and episodic winter storms, generating waves that affect the deposition of ooids, peloids, lithic clasts and bioclasts. In the outer lagoon, these waves interact with tidal currents and thus become less dominant towards the middle lagoon. Tidal currents are more important in the restricted inner lagoon. The outer lagoonal sediments primarily consist of ooids, bioclasts and lithic clasts and are peloid- and micrite-lean. Bimodal tidal currents, locally with velocities of two or more metres per second, are present in the relatively open regime of the middle lagoon and accumulate bar complexes dominated by skeletal carbonates. Seagrass and biofilms locally stabilise muddy carbonates and limit sediment entrainment even where significant tidal currents exist. In a landward direction, and with decreasing hydrodynamic levels, carbonate mud (micrite) is increasingly abundant, reflecting the lower hydrodynamic conditions in the restricted regime of the mid-and inner lagoon. Data shown here provide a facies distribution model in the shallow coastal portions of what might be one of the few modern analogues of a ‘marginal epeiric’ sea, shedding light on the complex interplay between coastal morphology, wave and tide energy and biological processes. This study discusses how hydrodynamics and seafloor bio-stabilisation influence the spatial carbonate facies of this highly dynamic ramp system by comparing data shown here with data from the Kuwait and Doha coasts, which have different orientations to the prevailing winds. The quantitative and refined composite inner ramp model shown here has wider significance for coastal dynamics and carbonate stratigraphy.

Quantitative evidence for Arctic continental freezing in a high-CO 2 world: Junggar Basin, NW China

Abstract We show that the Late Triassic–Early Jurassic continental Arctic experienced wintertime freezing conditions, despite the exceptionally high atmospheric CO 2 levels, by quantifying common lake ice-rafted debris (L-IRD) identified in the Junggar Basin of Xinjian, NW China. This L-IRD consists of outsized (0.1–12 mm) lithic clasts ‘floating’ in otherwise fine-grained, profundal lake sediment matrix. Laser-diffraction grain-size analysis demonstrates that the grain-size distribution for lacustrine strata of Junggar Basin is very similar to modern sediments from the seasonally ice-covered Sea of Okhotsk, reflecting a similar depositional mechanism. Three-dimensional computed tomography and two-dimensional thin sections demonstrate that the outsized clasts are dispersed, rather than confined to sand lenses or layers. These results are inconsistent with alternative methods of bimodal sediment deposition such as mud flows, algae rafting or root rafting. The discovery of Triassic–Jurassic continental freezing provides new context for understanding global climate during periods with high-CO 2 conditions and climate and biotic changes in the Mesozoic Era.

Fluid‐Mantle Interaction Along the Mariana Convergent Margin

AbstractActive serpentinite mud volcanoes in the forearc region of the Izu‐Bonin‐Mariana system represent an excellent natural laboratory for studying the geochemical processes along convergent plate margins and the associated forearc. During IODP Expedition 366, serpentinite mud with lithic clasts from the underlying forearc crust and mantle as well as from the subducting Pacific Plate was recovered. Ultramafic clasts from Fantangisña Seamount reveal very high degrees of serpentinization with mesh and bastite textures as well as development of late lizardite and chrysotile veins, which suggests serpentinization temperatures below 200°C. On the other hand, recovered harzburgites and, on occasion, dunites from Asùt Tesoru Seamount show a well‐preserved primary assemblage with low degrees of serpentinization and forearc peridotite characteristics. Fine‐grained antigorite associating with lizardite has been identified throughout the serpentine mud matrix, suggesting an alteration temperature of c. 340°C. Furthermore, alteration conditions during rodingitization point to temperatures of at least 228°C, estimated via chlorite geothermometry. Additionally, a rare ophicarbonate clast containing andraditic as well as Cr‐rich hydrogarnets from Asút Tesoru Seamount indicates crystallization temperatures of at least 230°C. Hence, a trend of lower temperature of serpentinization and higher degree of alteration closer to the trench. The detailed characterization of the fluid‐rock alteration conditions as well as fluids composition and transport permits a better constraining of the fluid–rock interactions and related mass transfers within subduction zones and during ascent of serpentinite fault gouge within mud volcano conduits and in mudflows after their emplacement on the flanks of the edifices.

Mobility and emplacement of an ancient, large-volume pyroclastic flow, Ongatiti Ignimbrite, North Island, New Zealand

Pyroclastic flows are the most devastating phenomena of explosive volcanic eruptions. These hazardous fast-moving, hot, concentrated density currents are able to travel several tens of kilometers radially away from their source. Due to an enveloping ash cloud, it is still impossible to directly study pyroclastic flows. However, their deposits (i.e., ignimbrites) provide useful insight into their internal processes of emplacement. This study focuses on the Ongatiti Ignimbrite, which is sourced from Mangakino caldera (i.e., the oldest volcanic centre in the Taupo Volcanic Zone, North Island, New Zealand dated at 1600–950 ka) and offers a unique opportunity to understand the emplacement processes of an ancient and large-volume pyroclastic flow. It is a welded to non-welded, columnar-jointed, cliff-forming deposit, that has been divided into nine facies based on the variation in pumice and lithic clast abundance, and degree of welding.Our results constrain the minimum deposit volume for the Ongatiti Ignimbrite to ca. 1400 km3, or 1000 km3 dense-rock equivalent. Zircon (UTh)/He data suggest an eruption age of 1.37 ± 0.04 Ma, which is in good agreement with the previous proposed eruption age. The topographic controls on the spatial distribution of the ignimbrite have been determined to understand pyroclastic flow pathways through valleys and over hills. The ignimbrite covered hills up to ∼900 m (about 650 m above the caldera height) to around 40 km from the Mangakino volcanic center (MVC) and, the pyroclastic flow travelled to beyond 90 km from the vent. The Ongatiti Ignimbrite was a landscape-modifying event that covered at least the western North Island and as far away as Auckland and Wellington.

Timescale of Emplacement and Rheomorphism of the Green Tuff Ignimbrite (Pantelleria, Italy)

AbstractWe present a multidisciplinary study based on Differential Scanning Calorimetry (DSC), paleomagnetic analysis, and numerical modeling to gain information on the timescales of syn‐ and post‐depositional ductile deformation of the strongly welded and rheomorphic Green Tuff ignimbrite (GT; Pantelleria, Italy). DSC measurements allow the determination of glass fictive temperatures (Tf; i.e., the parameter accounting for the cooling dependence of glass structure and properties). Using a Tf‐based geospeedometry procedure, we infer the cooling rate (qc) experienced by the glassy phases in different lithofacies within the GT formation. Glass shards from the basal pumice fall deposit record a fast qc of ∼10°C/s. In contrast, the ignimbrite body returns slow qc values depending on the stratigraphic position and lithofacies (basal/upper vitrophyres, fiamme‐rich and rheomorphic layers), ranging from ∼10−2 to ∼10−6 °C/s. Moreover, paleomagnetic analyses of the natural remanent magnetization of ignimbrite matrix and embedded lithic clasts indicate an emplacement temperature higher than 550–600°C. By integrating calorimetric and paleomagnetic datasets, we constrain a conductive cooling model, describing the ignimbrite's temperature‐time‐viscosity (T–t–η) evolution from the eruptive temperature to below Tf. Outcomes suggest that the upper and basal vitrophyres deformed and quenched over hours, indicating that the entire GT underwent intense syn‐depositional ductile deformation. Furthermore, the central body remained above Tf for a much longer timespan (>1 month), enabling post‐emplacement rheomorphic flow. Lastly, we discuss the critical role of mechanisms such as shear heating and retrograde solubility of volatiles, in locally controlling the rheological behavior of the GT.

Depositional and diagenetic controls over reservoir quality of tight sandstone and conglomerate in the lower Cretaceous Shahezi formation, Xujiaweizi fault depression, Songliao basin, China

The distribution of high-quality reservoirs restricts the exploration and development of tight gas in the Shahezi Formation in the Xujiaweizi Fault Depression, but the complex sedimentary composition and abundant diagenesis make it difficult to determine which rocks are high-quality reservoirs. In this paper, the petrological, mineralogical, and pore structure characteristics of sandstone and conglomerate were investigated to elucidate how depositional and diagenetic processes jointly control reservoir quality and identify favorable sequences in which high-quality reservoirs are distributed. The results showed that the content and type of matrix and lithic clasts in the sedimentary rock unit controlled the effects of the following diagenetic sequence, which in turn controlled the reservoir porosity, permeability and pore size distribution. Conglomerate and coarse-to medium-grained sandstone, both with a low muddy matrix content and high intermediate–basic volcanic lithic clast content, underwent extensive dissolution or grain fracturing during diagenesis, resulting in a reservoir with pore spaces >0.1 μm in diameter, which is considered as a high-quality reservoir for tight gas exploration. Conglomerate and fine-grained silty sandstone, both with a high muddy matrix content and low intermediate–basic volcanic lithic clasts, or those reservoir units directly adjacent to mudstone often experienced severe mechanical compaction or cementation during diagenesis. This resulted in a reservoir dominated by micropores (<0.1 μm) and therefore formed nonreservoir areas for tight gas exploration. High-quality reservoirs are more likely to be developed in the lacustrine transgressive systems tract and regressive systems tract in sequence four of the Shahezi Formation in the Xujiaweizi Fault Depression.

Aspects of Aktuo-Paläontologie of the rocky beaches of the eastern Isle of Mull, UK

Conglomerates are, commonly, only poorly fossiliferous at best. Yet beaches with common lithic clasts can be used to model the taphonomy of fossils in conglomeratic settings. Four beaches on the east coast of the Isle of Mull, Inner Hebrides, are clast-rich, with lithic pebbles, cobbles and boulders, but poor in shells, many of which are poorly preserved. There is ample evidence of shells being bored and encrusted, yet many or most of these were infested after death of the host. Of the ‘boring trinity’, Caulostrepsis Clarke, Entobia Bronn and Gastrochaenolites Leymerie, so typical of the Trypanites Ichnofacies around Britain's coasts, only the last ichnogenus was not present, most probably owing to the absence of suitable mobile substrates (such as limestone cobbles and oysters). Encrusters including Balanus , serpulids and spirorbids show different patterns of preservation, probably owing to multiple factors. Bored wood ( Apectoichnus ) was found at only one locality, which may be due to hydrodynamic sorting. Whelk shells show a range of patterns of breakage, most probably caused by mechanical damage. But conglomerates commonly preserve fossil snails either complete or not at all. The results from these sites suggest that they represent an intermediate condition rarely preserved in the rock record.

Petrology and mineralogy of mesosiderite Northwest Africa 12949: Implications for geological history on its parent body

AbstractMesosiderites are breccias composed of roughly equal parts of metal phases and silicate clasts. However, the parent body and formation process of mesosiderites remain enigmatic. Northwest Africa (NWA) 12949 is a newly found mesosiderite belonging to type 2A. One type of ultramafic clasts and four types of mafic clasts (gabbroic, poikilitic, subophitic, and cataclastic), compositionally consistent with diogenites and eucrites, have been identified in NWA 12949. However, these clasts have undergone different thermal histories, with cooling rates varying from ~0.0044 °C year−1 to a few °C h−1, and equilibrium temperatures varying from ~880 to 910 °C to ~1000 to 1100 °C. All the lithic clasts have undergone redox reactions during extensive metamorphism, forming excess troilite, chromite, merrillite, tridymite, and pyroxene with lower Fe/Mg and Fe/Mn. The petrology and mineralogy of NWA 12949 support a formation scenario involving two major impact events, and a candidate parent body of 4 Vesta.

Subsolidus breakdown of armalcolite: Constraints on thermal effects during shock lithification of lunar regolith

Abstract Shock lithification of regolith breccias is a ubiquitous process on the surfaces of airless planetary bodies and may induce thermal effects, including melting on regolith breccia minerals. However, potential thermal effects on lithic and mineral clasts in regolith breccias have seldom been quantitatively constrained. Here, we report two types of micro-textures of armalcolite [(Mg,Fe2+)Ti2O5] in an Mg-suite lithic clast from lunar regolith breccia meteorite Northwest Africa 8182. One type of armalcolite contains oriented fine-grained ilmenite grains; the other occurs as an aggregate of ilmenite, rutile, spinel, and loveringite. We propose that the two types of micro-textures formed through subsolidus breakdown of armalcolite by different processes. The formation of ilmenite inclusions in armalcolite is related to slow cooling after the solidification of its source rock, whereas the ilmenite-rutile-spinel-loveringite aggregates probably formed during the shock lithification event of NWA 8182. The results indicate that the temperature at the margin of lithic clasts could be raised up to at least 600 °C during strong shock lithification of lunar regolith and has profound thermal effects on the mineralogical and isotopic behaviors of lithic and mineral fragments in lunar regolith breccias.

Petrochemical and geochronological data of Permian-Lower Triassic clastic sedimentary rocks in the northwestern Junggar basin, NW China: Implications for provenance, tectonism and paleoclimate

The Permian clastic sediments in the Mahu sag offer outstanding conditions to test the control of tectonism and paleoclimate on sedimentation in a rift basin. A synthesis of petrological and geochemical analyses of sandstones, zircon U–Pb geochronology of granitic conglomerates, and principal component analysis have been used to investigate the source composition and chemical weathering indices. The rare earth and trace element compositions of 16 sandstone samples are consistent with first cycle sources from the Carboniferous–Lower Permian mafic and felsic igneous rocks in West Junggar. Lower Permian sandstones contain abundant volcanic lithic clasts and plagioclase grains, and have high Na2O, CaO, Sr and V, suggesting a coeval proximal volcanic source in Central West Junggar during the syn-rift stage. Middle Permian sandstones consist of trachyte and rhyolite clasts, and quartz and albite grains, and show a gradual increase of Th, U and SiO2, indicating an expansion of source areas to more distant Southern and Northern West Junggar during the post-rift stage. In the Lower Triassic, an abrupt increase in the percentages of quartz and K-feldspar, as well as the zircon U–Pb geochronology of granite-clast conglomerates (290–330 Ma), all indicate regional uplift and unroofing of Carboniferous–Permian granitic plutons in West Junggar during the tectonic inversion stage at the Permian-Triassic boundary. Various chemical weathering indices indicate cold and arid climate conditions during the early Permian, followed by a transition to warm and humid climatic conditions. Comprehensive analysis of petrography and geochemistry sheds a new light for studying the source-to-sink evolution of a rift basin, and has further implication for paleoclimate fluctuation and change.

Thermobarometry, vesicularity and microlite populations in pyroclastic density current deposits from the last 4500 years of activity at Galeras, Colombia

Vulcanian eruptions during the 19th and 20th Centuries at the Galeras volcano have produced small eruption columns and bomb fields around the active vent. Four pyroclastic density current (PDC) deposits from the early history of the currently active Galeras cone which have ages between 4500 and 2300 years before present have a much wider distribution. The first two (ML 1 and ML 2) were deposited from hot, dilute, pumice-rich pyroclastic density currents. Amphibole thermobarometry indicates that the magma for these eruptions tapped reservoirs between 5 and 28 km (ML 1) and 33–41 km (ML 2) below the crater. Debse, degassed magma formed a conduit plug which persisted for up to several weeks before the eruptions based on the thickness of breakdown rims around the amphibole. Amphibole-bearing pumice came from a reservoir 5–26 km below the crater and since it lacks breakdown rims it must have reached surface in <8 days. The vesicularity of the pumice indicates two phases of bubble nucleation and growth which coincides with growth of plagioclase and orthopyroxene microlites. The upper two layers (ML 3 and ML 4) are block and ash flows. ML3 shows significant hydrothermal alteration of the dense lithic clasts and has only minor vesicular scoria. The magma for the ML 3 eruption came from a reservoir 17–29 km below the crater and the presence of 20 μm thick breakdown rims on the amphibole implies that the degassing plug was stable for ∼20 days, though the degree of hydrothermal alteration of the clasts appears to require a significantly longer time. The uppermost layer (ML4) is relatively unaltered with a large proportion of pumice. Dense lithics indicate plug formation from magma that had its source at ∼17 km below the crater and remained stable during degassing for ∼20 days. The absence of amphibole from the pumice in ML 4 implies a distinct magma composition was emplaced after the plug.

Significance of silicate liquid immiscibility for the origin of young highly evolved lithic clasts in Chang’E-5 regolith

Highly evolved lithology distributes across the Moon sparsely but serves as a critical record of the extensive differentiation processes of lunar magmas. In contrast to the Apollo-returned highly evolved rocks that essentially formed before the end of the Nectarian period, silicic lithologies detected by remote sensing within the nearside Procellarum KREEP Terrane (PKT) have cratering model age as young as ∼2.5 Ga (Chevrel et al., 2009). The formation mechanism of the young silicic magmatism remains enigmatic. Here we present a detailed study of lithic clasts with highly evolved compositions from the northwestern PKT returned by Chang’E-5 mission. Two different types of highly evolved lithic clasts were recognized: (a) Type A clasts predominately consist of granophyric intergrowths of K-feldspar and quartz. They are highly depleted in incompatible elements (except for K, Rb, Cs, and Ba) and have a V-shaped REE pattern, which can be explained by silicate liquid immiscibility (SLI) following the fractionation of merrillite from a KREEP-like melt. The microtextural features of quartz in Type A clasts indicate that they could have crystallized through relatively slow cooling at temperature below 870 °C, supporting a shallow intrusive origin. The silicic intrusion exposed in the interior, rim, and ejecta of Aristarchus crater has a cratering model age of ∼2.5–3.7 Ga, which could be the source for Type A clasts; (b) Type B clast has little MgO, high incompatible element concentrations, and an REE pattern inclined to the right. Thermodynamic calculations indicate that Type B clast likely formed through SLI of the ∼25% residual melt of Em3 basalts in the Chang’E-5 landing region. This is consistent with the crystallization age of 2.57 ± 0.26 Ga for the zirconolite in Type B clast. The highly evolved samples from Chang’E-5 regolith provide new evidence that SLI may have played an important role in the young highly evolved intrusive bodies’ formation on the Moon. Furthermore, our thermodynamic modeling results show that compared to KREEP basalt, partial melting of quartz monzodiorite/monzogabbro at ∼930–1000 °C can produce melts with composition close to lunar granites and felsites. Thus, if a series of silicic volcanisms distributed mostly within the PKT was generated through this mechanism, quartz monzodiorite/monzogabbro may also widely distribute within the lunar nearside upper crust.

The Response of the Rivers of NW Greece to Late Quaternary Neotectonics, as Interpreted from Detrital Petrology

The modern drainage systems of the fold and thrust belt of the external Hellenide orogen of NW Greece are principally orogen-parallel. Late Quaternary changes in river courses have resulted from neotectonic deformation associated with the Katouna–Stamna fault and with footwall uplift in developing transverse grabens. This study assesses the impact of neotectonic deformation on river patterns and basin deposition. River sands show differences in modal abundance and varietal geochemistry of heavy minerals and fine sand lithic clasts, determined by scanning electron microscope, that allow identification of past river supply to raised fluvial terrace and beach deposits. In the past 200 ka, footwall uplift south of developing grabens at Lake Trichonis and the Amvrakikos Gulf promoted orogen-transverse flow, diverting the Arachthos-Louros rivers to the west, causing reversal of drainage to the north in the lower reach of the Acheloos River. A raised terrace gravel south of Preveza records the southwestward flow of a large paleo-Arachthos river, confirmed by sand petrology in beaches farther south on the Echinadon Sea coast. The use of varietal heavy minerals and lithic clasts is a rapid and powerful tool for tracking tectonically-induced changes in river patterns.