Clast Composition Research Articles

Shallow forearc mantle dynamics and geochemistry: New insights from IODP Expedition 366

The Mariana forearc is a unique setting on Earth where serpentinite mud volcanoes exhume clasts originating from depths of 15 km and more from the forearc mantle. These peridotite clasts are variably serpentinized by interaction with slab derived fluid, and provide a record of forearc mantle dynamics and changes in geochemistry with depth. During International Oceanic Discovery Program (IODP) Expedition 366, we recovered serpentinized ultramafic clasts contained within serpentinite muds of three different mud volcanoes located at increasing distance from the Mariana trench and at increasing depth to the slab/mantle interface: Yinazao (distance to the trench: 55 km / depth to the slab/mantle interface: 13 km), Fantangisña (62 km / 14 km) and Asùt Tesoru (72 km / 18 km). Four different types of ultramafic clasts were recovered: blue serpentinites, lizardite-serpentinites, antigorite/lizardite- and antigorite-serpentinites. Lizardite-serpentinites are primarily composed of orange serpentine, forming mesh and bastite textures. Raman and microprobe analyses revealed that these textures contain a mixture of Fe-rich brucite (XMg ~ 0.84) and lizardite/chrysotile. Antigorite/lizardite- and antigorite-serpentinites record the progressive recrystallization of mesh and bastite textures to antigorite, magnetite and pure Fe-poor brucite (XMg ~ 0.92). Oxygen isotope compositions of clasts and pore fluids showed that the transition from lizardite to antigorite is due to the increase in temperature from 200 °C to about 400 °C within the forearc area above the slab/mantle interface. Lizardite-, antigorite/lizardite- and antigorite-serpentinites displayed U-shaped chondrite normalized Rare Earth Element (REE) patterns and are characterized by high fluid mobile element concentrations (Cs, Li, Sr, As, Sb, B, Li) relative to abyssal peridotites and/or primitive mantle. The recrystallization of lizardite to antigorite is accompanied by a decrease in Cs, Li and Sr, and an increase in As and Sb concentrations in the bulk clasts, whereas B concentrations are relatively constant. Some clasts are overprinted by blue serpentine, often in association with sulfides. Most of these blue serpentinites were recovered at Yinazao and the uppermost units of Fantangisña and Asùt Tesoru suggesting alteration in the shallower portions of the forearc, possibly during exhumation of the clasts. This episode of alteration resulted in a flattening of REE spectra and an increase of Zn concentrations in serpentinites. Otherwise, no systematic changes of ultramafic clasts chemistry or mineralogy were observed with increasing depth to the slab. The samples document previously undescribed prograde metamorphic events in the shallow portions of the Mariana subduction zone, consistent with a continuous burial of the serpentinized forearc mantle during subduction. Similar processes, induced by the interaction with fluids released from the downgoing slab, likely occur in subduction zones worldwide. At greater depth, breakdown of brucite and antigorite will result in the massive transfer of fluids and fluid mobile elements, such as As, Sb and B, to the source of arc magmas.

Miocene fan delta conglomerates in the north-western part of the Danube Basin: provenance, paleoenvironment, paleotransport and depositional mechanisms

Abstract The Blatné Depression located in the NW part of the Danube Basin represents the northernmost sub-basins of the Pannonian Basin System. Its subsidence is associated with oblique collision of the Central Western Carpathians with the European platform, followed by the back-arc basin rifting stage in the Pannonian domain. The conglomerates recognized in the Cífer-2 well document the latest Burdigalian–early Langhian deposition in fan delta lobes situated above the footwall and hanging wall of a WSW–ENE trending fault system, the activity of which preceded the opening of the late Langhian–Serravallian accommodation space with a NE–SW direction. The provenance area of the “Cífer conglomerate” was linked to the Tatric Super-unit complexes. Similar rocks crop out in the southern part of the Malé Karpaty Mts. and are also present in the pre-Cenozoic basement of the Danube Basin. Documented extensive erosion of the crystalline basement and its sedimentary cover lasted until the early/middle Miocene boundary. The “Cífer conglomerate” has distinct clast composition. The basal part consists of poorly sorted conglomerate with sub-angular clasts of metamorphic rocks. Toward the overlying strata, the clasts consist of poorly sorted conglomerates with sub-rounded to well-rounded carbonates and granitoids. The uppermost part consists of poorly sorted conglomerates with sub-rounded to rounded clasts of carbonate, granitoid and metamorphic rock. Within the studied samples a transition from clast to matrix supported conglomerates was observed.

Geology and geochronology of Naruo large porphyry-breccia Cu deposit in the Duolong district, Tibet

The Duolong district is located in the south Qiangtang terrane of Tibet and is the most significant ore cluster within the Bangongco-Nujiang metallogenic belt. Duolong contains one giant, three large and two medium to small-sized porphyry (±epithermal ± breccia) copper deposits and several other mineralized porphyry bodies. All deposits are closely associated with early Cretaceous (123–115 Ma) intermediate-felsic intrusions. Naruo is a poorly studied porphyry-breccia copper deposit in the north of the Duolong district. Hydrothermal alteration surrounding the ore-bearing granodiorite at Naruo is characterized by an inner potassic zone and an outer propylitic zone, overlapped locally by minor phyllic and argillic alteration assemblages. A detailed paragenetic study has identified five distinct hydrothermal veins (M, A, B, C, D) within the porphyry system. Hydrothermal B veins are strongly related to copper mineralization. Strong propylitic alteration is also observed throughout the hydrothermal breccias identified at Naruo. Sandstone breccia, diorite-bearing breccia and granodiorite-bearing breccia were identified according to the distribution and composition of clasts. U-Pb zircon dating has determined the ages of the ore-bearing granodiorite (121.6 ± 1.3 Ma) and a barren intrusion (115.5 ± 1.1 Ma) within the porphyry system, diorite clasts (122.3 ± 0.9 Ma) and later diorite matrix (120.5 ± 1.0 Ma) in the hydrothermal breccia system, suggesting that with the exception of the late barren intrusion, they all belong to the same mineralizing event at Duolong. The geological and geochemical evidence presented in this study suggest that the porphyry and breccia systems may have originated from the same magma source, but are now spatially independent.

Triassic tectonic interactions between the Alxa Massif and Ordos Basin: Evidence from integrated provenance analyses on sandstones, North China

The Helanshan Tectonic Belt is situated among the Qilian Orogenic Belt to the southwest, the Alxa Massif to the west and the Ordos Block to the east. The Helanshan Tectonic Belt has received increasing attention since it was argued as the plate boundary separating the Alxa Massif from the Ordos Block, and hence Alxa Massif was isolated from the North China Craton during Triassic. The Middle to Upper Triassic strata in the northwestern Ordos and the Helanshan Tectonic Belt witnessed the tectonic evolutionary processes between the Alxa Massif and the Ordos Basin, hence are pivotal to understand the relationship between the Alxa Massif and the North China Craton. In this work, integrated paleocurrent orientation, gravel component, sandstone modal composition and detrital zircon U–Pb isotopic analyses were applied to trace the source area and reconstruct the source-to-sink relations between the Alxa Massif and Ordos Basin. The southeast orientated paleocurrent directions suggest detritus in the northwestern Ordos were mostly sourced from the northwest. Clastic compositions reveal a mixed orogeny provenance, including magmatic arc and continental block sources. Detrital zircons from four sandstones in the Helanshan Tectonic Belt yields four major LA-ICPMS U-Pb age groups of 2600–2200 Ma, 2000–1700 Ma, 480–400 Ma and 350–200 Ma, suggesting multiple-sourced provenance. Comparing to the magmatic records in the Alxa Massif and the Qilian Orogenic Belt, the Triassic detritus in the Helanshan Tectonic Belt were mainly from the Alxa Massif with additional supplements from the Qilian Orogenic Belt, which finally debouched to the lacustrine in the interior Ordos Basin to the southeast. Triassic basin evolution of the northwestern Ordos was further associated with post-collision in the Alxa Massif after the closure of the Paleo-Asian Ocean.

New biocenosis model of Vendian (Ediacaran) sedimentation basin of Podilia (Ukraine)

The aim of this study is to fully research all aspects of the distribution, development, conditions of burial and preservation of the Ediacaran biocomplex. Thiswork summarizes and extends all data on the unique Vendian invertebrates that are distributed in the natural and artificial outcrops of the Dniester River Basin within Podilia (Ukraine). One of the basic locations of the annual observation was a quarry of rubble stone production near the Dniester hydroelectric station-1, Novodnistrovsk city, which exposes a continuous section of the deposits of the Lomoziv, Yampil, Lyadova and Bernashivka Beds lying on a crystalline basement. This paper shows the outcomes of long-term fieldwork of the Upper Ediacaran which include deposits of the Mogyliv-Podilsky and Kanylivka Group. The researched section is characterized by its clastic composition and the absence of carbonate formations. The basic paleontological collection has more than two thousand specimens, for instance, the imprints of molluscous fauna, traces of their live activity, the remains of flora and fossils of a problematic nature. The most numerous and informative collection of these fossils is located in the stock of the Geological Museum of the Taras Shevchenko National University of Kyiv. The collection contains unique material, including a number of Ediacaran fossils described for the first time. On the whole within Podilia region, more than 100 species have been described in detail. The main areas of biota accumulation in the outcrops are associated with argillites, argillite-siltstones and their contact with sandstones. The best preservation of the imprints is detected in the boundary of facial transitions. Research has revealed that there is a decrease in the numerical and species composition of the molluscous biota, and the dynamic increase in evolution of burrowing organisms and plants within the Podilia Basin during the late Vendian. Such a phenomenon led to an environmental change, increase in oxygen and appearance of new groups of organisms that were subsequently displaced invertebrates. This occurred at the Precambrian/Cambrian transition, and in the geological literature is described as the «Cambrian explosion». Studies have found that the total number of taxonomic composition of the Eidacaran in Podilia is similar to the orictocoenosis of Southern Australia and the White Sea. Nevertheless, the Podilia biocomplex is more ancient than the Southern Australian and the White Sea, it is much younger than the Avallonian.

Mineralogical features of the clastic dykes of the Eastern Carpathians Skybova zone

We determined several areas with outcrops of clastic dikes which occur in the rocks of the Menilite suite of the Upper Paleogene period in the so-called Skybova zone [Ukr. Ски́ бова зо́на – the largest tectonic zone within the Carpathian folded structure. The word “skyba” derived from Polish, and is used in relation to nappe – Translator`s Note ] of the Eastern Carpathians. The objective of this article is to reveal the peculiarities of bedding, mineralogical composition and structural-texture peculiarities of the clastic dikes of the Sukyl, Stryi and Skhidnytsia river basins. During our research, we used the method of field structural-geological surveys, traditional method of laboratory analysis of mineralogical-petrographic composition of rocks in thin sections. As a result, we studied the conditions of bedding of clastic dikes, mineral composition and structural-texture peculiarities. We determined that the dikes are represented by aleuro-sandstone and aleurolite with quartz-carbonate cement. Aleurolite most often represents pre-selvage parts of dikes. Mineral grains are mostly formed by quartz of different degrees of roundness. In the selvages of the studied dikes, we observed a decrease in the sizes of mineral grains, enrichment of these parts of dikes by organic compound, increase in the content of carbonate minerals in the rock cement and numerous microdeformations of mineral grains. Also we determined an insignificant content of ore minerals in some studied plots. Additional analysis conducted for a polished sample which characterizes the vertical section of dike in the area of the river Sukyl allowed us to determine the structural signs in its selvages, indicating injection character of dikes` upward introduction to the bearing rocks. We studied the microdeformation of dikes` mineral grains, which are represented by veinles, microfaults and microshifts withclear mixing of their fragments. The obtained results indicate the formation of clastic dikes of the Skybova zone of the Eastern Carpathians in conditions of compression, when relatively flexible material of selvages of the dikes, represented by carbonates and organic compound, contributed to the introduction of the latter to the layer of flysch through the system of tectonic faults of north-west stretch.

Provenance of Ross Sea Drift in McMurdo Sound (Antarctica) and implications for middle-Quaternary to LGM glacial transport: New evidence from petrographic data

The provenance of Ross Sea Drift deposits from the McMurdo Sound region (Antarctica), ranging from middle Quaternary to a Last Glacial Maximum (LGM) age, has been investigated by means of petrographic techniques. A total of 19 bulk till samples from four areas was analyzed for three different granulometric fractions: pebble to cobble, granule, and coarse to very coarse sand grain size. Deposits were classified following the lithological composition of clasts and occurrence of different petrographic groups was evaluated for each sample. Clasts composition predominantly reflects source rocks cropping out in the region between Mackay and Koettlitz glaciers, with McMurdo Volcanic Group rocks being the most represented lithologies in the Royal Society Range foothills, while Granite Harbour Intrusive Complex rocks are more widespread in Taylor and Wright valleys. The lithological distribution of collected samples supports a distal provenance related to a grounded Ross Ice Sheet in Taylor Valley, while the specific distribution of volcanic lithologies in Royal Society Range foothills is evidence for a northward ice flow from Koettlitz Glacier catchment, thus supporting previous glaciological models of an expanded lobe during the LGM. In addition, middle-Quaternary Trilogy Drift composition from Wright Valley accounts for a local provenance, thus allowing the hypothesis of a thickened Wilson Piedmont Glacier rather than a grounded Ross Ice Sheet during past ice advances.

Sedimentation of Jurassic fan-delta wedges in the Xiahuayuan basin reflecting thrust-fault movements of the western Yanshan fold-and-thrust belt, China

Mesozoic thrusting within the Yanshan fold-and-thrust belt of North China resulted in a series of fault-bounded intramontane basins whose infill and evolution remain poorly understood. In particular, the bounding faults and adjacent sediment accumulations along the western segments of the belt are almost unstudied. A sedimentological and provenance analysis of the Lower Jurassic Xiahuayuan Formation and the Upper Jurassic Jiulongshan Formation have been mapped to show two distinctive clastic wedges: an early Jurassic wedge representing a mass-flow-dominated, Gilbert-type fan delta with a classic tripartite architecture, and an late Jurassic shoal-water fan delta without steeply inclined strata. The basinward migration of the fan-delta wedges, together with the analysis of their conglomerate clast compositions, paleocurrent data and detrital zircon U-Pb age spectra, strongly suggest that the northern-bounding Xuanhuan thrust fault controlled their growth during accumulation of the Jiulongshan Formation. Previous studies have suggested that the fan-delta wedge of the Xiahuayuan Formation was also syntectonic, related to movement on the Xuanhua thrust fault. Two stages of thrusting therefore exerted an influence on the formation and evolution of the Xiahuayuan basin during the early-late Jurassic.

Syn-sedimentary tectonics and facies analysis in a rift setting: Cretaceous Dalmiapuram Formation, Cauvery Basin, SE India

The Cretaceous (Albian–Cenomanian) Dalmiapuram Formation is one of the economically significant constituents in the hydrocarbon-producing Cauvery rift basin, SE India that opened up during the Late Jurassic–Early Cretaceous Gondwanaland fragmentation. The fossil-rich Dalmiapuram Formation, exposed at Ariyalur within the Pondicherry sub-basin of Cauvery Basin, rests in most places directly on the Archean basement and locally on the Lower Cretaceous (Barremian–Aptian) Basal Siliciclastic Formation. In the Dalmiapuram Formation, a facies association of tectonically-disturbed phase is sandwiched between two drastically quieter phases. The early syn-rift facies association (FA 1), records the first carbonate marine transgression within the basin, comprising a bar–lagoon system with occasionally storms affecting along the shore and a sheet-like non-recurrent biomicritic limestone bed on the shallow shelf that laterally grades into pyrite–glauconite-bearing dark-colored shale in the deeper shelf. Spectacular breccias together with varied kinds of mass-flow products comprise the syn-rift facies association (FA 2). While the breccias occur at the basin margin area, the latter extend in the deeper inland sea. Clast composition of the coarse clastics includes large, even block-sized limestone fragments and small fragments of granite and sandstone from the basement. Marl beds of quieter intervals between tectonic pulses occur in alternation with them. Faulted basal contact of the formation, and small grabens filled by multiple mass-flow packages bear the clear signature of the syntectonic activity localized contortions, slump folds, and pillow beds associated with mega slump/slide planes and joints, which corroborates this contention further. This phase of tectonic intervention is followed by another relatively quieter phase and accommodates the late syn-rift facies association (FA 3). A tidal bar–interbar shelf depositional system allowed a transgressive systems tract motif to grow eventually passing upwards into the Karai Shale Formation, whose contact with the Dalmiapuram Formation is gradational.

Crustal heat production and estimate of terrestrial heat flow in central East Antarctica, with implications for thermal input to the East Antarctic ice sheet

Abstract. Terrestrial heat flow is a critical first-order factor governing the thermal condition and, therefore, mechanical stability of Antarctic ice sheets, yet heat flow across Antarctica is poorly known. Previous estimates of terrestrial heat flow in East Antarctica come from inversion of seismic and magnetic geophysical data, by modeling temperature profiles in ice boreholes, and by calculation from heat production values reported for exposed bedrock. Although accurate estimates of surface heat flow are important as an input parameter for ice-sheet growth and stability models, there are no direct measurements of terrestrial heat flow in East Antarctica coupled to either subglacial sediment or bedrock. As has been done with bedrock exposed along coastal margins and in rare inland outcrops, valuable estimates of heat flow in central East Antarctica can be extrapolated from heat production determined by the geochemical composition of glacial rock clasts eroded from the continental interior. In this study, U, Th, and K concentrations in a suite of Proterozoic (1.2–2.0 Ga) granitoids sourced within the Byrd and Nimrod glacial drainages of central East Antarctica indicate average upper crustal heat production (Ho) of about 2.6 ± 1.9 µW m−3. Assuming typical mantle and lower crustal heat flux for stable continental shields, and a length scale for the distribution of heat production in the upper crust, the heat production values determined for individual samples yield estimates of surface heat flow (qo) ranging from 33 to 84 mW m−2 and an average of 48.0 ± 13.6 mW m−2. Estimates of heat production obtained for this suite of glacially sourced granitoids therefore indicate that the interior of the East Antarctic ice sheet is underlain in part by Proterozoic continental lithosphere with an average surface heat flow, providing constraints on both geodynamic history and ice-sheet stability. The ages and geothermal characteristics of the granites indicate that crust in central East Antarctica resembles that in the Proterozoic Arunta and Tennant Creek inliers of Australia but is dissimilar to other areas like the Central Australian Heat Flow Province that are characterized by anomalously high heat flow. Age variation within the sample suite indicates that central East Antarctic lithosphere is heterogeneous, yet the average heat production and heat flow of four age subgroups cluster around the group mean, indicating minor variation in the thermal contribution to the overlying ice sheet from upper crustal heat production. Despite these minor differences, ice-sheet models may favor a geologically realistic input of crustal heat flow represented by the distribution of ages and geothermal characteristics found in these glacial clasts.

Chemical variations within and between the clasts, and the matrix of the Abee enstatite chondrite suggest an impact-based differentiation mechanism

Abee is an enstatite chondrite breccia dominantly composed of kamacite, enstatite, silica, plagioclase, troilite and niningerite. Clasts are up to 220 mm long and vary in shape from angular to rounded. Some clasts are zoned with kamacite-enriched rims that follow the edge of the clast. Spatial compositional variations were examined in a small block to find out more about the petrological processes that produced this rock, particularly the relationship between the clasts, the matrix and the cores/rims of the zoned clasts. Compositional maps produced using a focussed-beam XRF were segmented into clasts and matrix, and rims and cores where possible. Compositions of most clasts, matrix and rim/cores define a simple, linear trend on simple variation diagrams. If it is assumed that all components were derived from an original homogeneous composition then the variation can be explained either by addition of kamacite or by loss of all other phases. Within this overall compositional variation the kamacite content generally increases as follows: matrix < large homogeneous clasts ≈ zoned clast cores < small homogeneous clasts ≈ zoned clast rims. Production of diversity by addition of kamacite to clasts and rim seems to require a complex history as the source cannot have been the current matrix. It is also difficult to produce the observed chemical variations and zoning by partial melting. However, differentiation by removal of all non-metallic phases may result from repeated impacts: Shock waves would deform kamacite whilst fracturing all other phases. The broken grains would then migrate towards the surface of the clasts where they would spall off into the matrix. This process would also lead to the observed rounding of some clasts. We propose that this shock-differentiation process be called ‘smithing’, as it resembles the ancient process of iron refining.

Magmatic processes revealed by anorthoclase textures and trace element modeling: The case of the Lajes Ignimbrite eruption (Terceira Island, Azores)

The Lajes Ignimbrite on Terceira Island (Azores) records the last major pyroclastic density current-forming eruption of Pico Alto Volcano that occurred ca. 21kyrs ago. This comenditic trachyte ignimbrite contains up to 30vol% of crystals, mostly anorthoclase. Geochemical investigation of the products collected throughout two key outcrops reveals that major element compositions are poorly variable, whereas trace elements show significant variability, pointing to the presence of a zoned magma reservoir. Thermometry and oxygen fugacity estimations yielded pre-eruptive temperatures of 850–900°C and ∆NNO from −2.4 to −1.8. Melt–alkali-feldspar hygrometer indicates magmatic H2O contents ranging from 5.8wt% in the upper part of the reservoir to 3.6wt% at the bottom, indicating that the magma reservoir (confined at ~4km depth) was mainly water-undersaturated before the eruption, except for the topmost portion. Two types of anorthoclase crystals were identified. Type 1 crystals show reverse to oscillatory zoning with An contents of 0.4–2.1mol% and Ba of 200–2000ppm. They formed in the middle/upper portion of the reservoir, where fractional crystallization processes dominated. Type 2 crystals, mainly present in the less evolved products, are characterized by patchy-zoned cores with large dissolution pockets surrounded by thick oscillatory-zoned rims and show a wide compositional range (An of 0.5–4.7mol% and Ba of 142–4824ppm). Their zoning patterns, together with whole-rock and glass compositions of the juvenile clasts, are consistent with the involvement of an anorthoclase-bearing cumulate from the bottom of the reservoir that underwent partial melting. Crystal dissolution was likely induced by the presence of a heat source at depth, without any mass transfer to the eruptible magma, as suggested by the lack of petrographic and chemical evidences of mixing between the resident comenditic trachyte and a mafic/intermediate magma. Thermal instability generated convective plumes that were responsible for the admittance of crystals from the cumulate level into the intermediate portions of the magma reservoir and possibly acted as trigger of the explosive eruption.

Linking tephrochronology and soil characteristics in the Sila and Nebrodi mountains, Italy

Recent studies have demonstrated that soils formed on pyroclastic ash deposits are much more common in the Mediterranean area than previously assumed. These soils are an important key to understanding past volcanic events and landscape evolution. Chronological information in soils of Quaternary volcanic events, however, remains still poorly understood in southern Italy. Using a multi-method forensic approach, we explore the origin and age of volcanic deposits (soils) in Sicily and Calabria. The geochemical signature of the soil was compared to the chemical fingerprint of the magmas of potential source areas of southern Italian volcanoes. The results indicate that the investigated soils on the Nebrodi (Sicily) and Sila (Calabria) mountains were both impacted by materials having a high-K calc-alkaline series volcanism. The Aeolian Islands (in particular Lipari and Vulcano) are the most likely source of origin, but contributions also from the Etna (particularly the Biancavilla ignimbrites and Plinian eruptions) occurred. Weathering and leaching processes, along with a potential contribution from the underlying non-volcanic bedrock, has altered the main chemical composition of soils, often precluding direct relation to potential source areas. Immobile elements and their ratios (e.g. the Nb/Y vs Zr/Ti plot) or trace elements (Co, Th) and rare earth elements (laser ablation ICP-MS analyses of glass particles, volcanic clasts and pumice-like materials) gave precious hints of the origin of the volcanic deposits. Radiocarbon dating of the H2O2 resistant soil organic fraction indicates a minimum age of 8–10ka of the soils. The weathering index WIP (weathering index according to Parker) and the chemical composition of volcanic glasses and clasts were tested as proxies for the age of the volcanic deposits and time for soil formation. The soils and landscape are characterised by multiple volcanic depositional phases for the last about 50ka in the Sila mountains and about 70ka or more in the Nebrodi mountains. Chemical-mineralogical analyses enabled the detection of deposition phases during the Pleistocene and also Holocene. The multi-method approach enabled the identification of potential source areas, provided a tentative age estimate of the start (and in part duration) of ash deposits and therefore improved our understanding of volcanic landscape evolution.

Provenance of Lower Paleogene Strata In the Huerfano Basin: Implications For Uplift of the Wet Mountains, Colorado, U.S.A.

Abstract: Sedimentary basins throughout the western interior of North America preserve a record of Late Cretaceous through latest Eocene sedimentation derived from flanking Laramide uplifts and Sevier hinterland. In northern and western basins, the strata contain a well-documented record of Laramide-style exhumation. However, the tectonic histories of more southerly basins, such as the Huerfano Basin studied herein, are comparatively poorly known despite being key for understanding the spatiotemporal evolution of Laramide tectonism. In this study we address this issue with a comprehensive analysis of provenance for the Poison Canyon, Cuchara, and Huerfano formations in the Huerfano Basin (south-central, Colorado, U.S.A.). As part of our provenance analysis, we characterized gravel clast composition, petrographic compositions of sandstone bodies (N = 31 thin sections), and U–Pb detrital-zircon age spectra (n = 848 age determinations) from fluvial sandstone units in each of the three formations. The results are used to construct a new unroofing and source history for the sediments in the basin that contradicts previous hypotheses. Diagnostic zircon peaks at 516–517 Ma, 1423–1430 Ma, and 1678–1687 Ma show that sediment delivered to the Huerfano Basin did not originate in the San Luis Highlands or the incipient Sangre de Cristo Mountains, but from the Precambrian crystalline core and associated Cambrian plutons of the Wet Mountains, which were exposed by the time Laramide deposition began in the basin. There are no detected provenance shifts upsection, indicating a largely stable or lithologically uniform sediment source from the Paleocene through at least ∼ 51 Ma. This suggests that the major changes recorded in the rock record were more likely related to variations in tectonic and climatic conditions rather than changes in lithology of the rocks being eroded.

Az Endrődi Formáció kőzettani és palinológiai vizsgálata a Hódmezővásárhely–I fúrásban (Makói-árok) — őskörnyezeti és diagenezis-történeti értékelés

Munkánkban a Hódmezővásárhely–I fúrás 35. és 40. magfúrási szakaszaiból (5167,0–5183,0 m, illetve 5468,0–5486,0 m) kiválasztott, az Endrődi Formációba sorolt kőzeteket (Tótkomlósi Tagozat, mészmárga és homokkő) vizsgáltuk. A minták általános jellemzője, hogy mikrites–mikropátos kalcitot, agyagásványokat, továbbá kőzetliszt–homok méretű, szögletes törmelékszemcséket (monokristályos és polikristályos kvarc, muszkovit, biotit, klorit; karbonát törmelék, metamorf kőzettörmelék) tartalmaznak. A polimikt, éretlen üledékanyag lokális forrást jelez, ami a környező aljzatmagaslatok kőzeteinek eróziójára hívja fel a figyelmet. A fúrás válogatott mintáin palinológiai vizsgálatok készültek az egyes magszakaszok biosztratigráfiai és őskörnyezeti értékelése céljából. A vizsgált mintákból két biozónát: az idősebb Spiniferites bentorii oblongus és a fiatalabb Spiniferites paradoxus Zónát lehetett kimutatni. A Spiniferitesbentorii oblongus Zónára jellemző dinociszta-együttes egy a parthoz közelebbi környezetet és/vagy nagyobb tápanyagbeáramlást jelez, míg a fiatalabb együttesben több olyan alak található, ami disztális környezetre, a vízszint meg növekedésére és/vagy a szárazföldi eredetű törmelékbehordódás csökkenésére utalhat. A membrános dinociszták jelenléte a felszíni vizek ingadozó sótartalmára és bizonyos dinoflagellaták esetén a holoplankton életmódra való áttérésre utal, amit a vízoszlopban bekövetkező ideiglenes oxigényszegény állapotok tehettek szükségessé. Mindkét zónaegyüttes regionális, az egész Pannon-medencére kiterjedő előfordulása alapján a planktonközösségekben lejátszódó regionális folyamatokra és a víztestek kommunikációjára lehet következtetni. A palinomorfák falának színe és megtartása a bete -metődés során bekövetkező jelentős hőmérsékleti hatásra, valamint az üledékes szerves anyag nagyfokú érettségére utal. Az intenzív diagenetikus átalakulási folyamatokat mind az ásványtani, mind a petrográfiai vizsgálatok meg erő sítették. A korai diagenezis során bakteriális szulfátredukcióra utaló pirit, majd vasmentes kalcitcement vált ki, amit Fe-dolomit/ankerit továbbnövekedési cement követett. A laza szemcseilleszkedés a mechanikai kompakció alárendelt szerepét jelzi, a vázszemcsék korai mechanikai átrendeződésével, rotációjával párhuzamosan a karbonátos cementáció a rendelkezésre álló pórustérfogatot szinte teljes egészében redukálta (a vizsgált kőzetek makro- és mikroporozitása elhanyagolható). A mély betemetődési diagenezis során elkülönített események a kémiai kompakció (szerves anyagos/pirites nyomási oldódási filmek megjelenése), az agyagásványok illitesedése, dolomithelyettesítés a kalcitcementben, valamint késői pirit megjelenése.

Provenance analysis reveals mountain uplift in the midsection of the Altyn Tagh Fault during the Middle Miocene

The Altyn Tagh Fault (ATF) defines the northern margin of the Tibetan Plateau; therefore, its tectonic history is key to understanding the plateau’s northward growth. However, our understanding of ATF tectonics is incomplete, owing in part to a lack of constraints in detailed basin evolution studies of this region. Approximately 1700 m of Middle Miocene – Pliocene clastic strata extracted from a section of the Yitunbulake Basin adjacent to the midsection of the ATF records the uplift of the Altyn Tagh Range. This paper reports 490 concordant detrital zircon U–Pb ages derived from this set of strata. In addition, paleocurrents and conglomerate clastic compositions were measured to determine the provenance of the basin. The dominant detrital zircon age populations within these sedimentary rocks are 260–240, 500–400, and 950–900 Ma. The 260–240 Ma component decreases sharply above the Lower (Xia) Youshashan (XYSS) Formation. Moreover, we performed (U–Th)/He dating on 260–240 Ma detrital zircons from the XYSS Formation to determine its source region. The results indicate that sandstones in this formation are most likely sourced immediately from plutonic rocks widely distributed in the Eastern Kunlun Mountains. The upward change in detrital zircon U–Pb age components in the section demonstrates that widespread surface uplift of the Akatengneng Mountains in the midsection of the ATF likely occurred after ∼16–15 Ma, which is synchronous with accelerated tectonic deformation along the ATF and a rapid increase in the sedimentation rate in the Qaidam Basin since the Middle Miocene.

A divergent heritage for complex organics in Isheyevo lithic clasts

Primitive meteorites are samples of asteroidal bodies that contain a high proportion of chemically complex organic matter (COM) including prebiotic molecules such as amino acids, which are thought to have been delivered to Earth via impacts during the early history of the Solar System. Thus, understanding the origin of COM, including their formation pathway(s) and environment(s), is critical to elucidate the origin of life on Earth as well as assessing the potential habitability of exoplanetary systems. The Isheyevo CH/CBb carbonaceous chondrite contains chondritic lithic clasts with variable enrichments in 15N believed to be of outer Solar System origin. Using transmission electron microscopy (TEM-EELS) and in situ isotope analyses (SIMS and NanoSIMS), we report on the structure of the organic matter as well as the bulk H and N isotope composition of Isheyevo lithic clasts. These data are complemented by electron microprobe analyses of the clast mineral chemistry and bulk Mg and Cr isotopes obtained by inductively coupled plasma and thermal ionization mass spectrometry, respectively (MC-ICPMS and TIMS). Weakly hydrated (A) clasts largely consist of Mg-rich anhydrous silicates with local hydrated veins composed of phyllosilicates, magnetite and globular and diffuse organic matter. Extensively hydrated clasts (H) are thoroughly hydrated and contain Fe-sulfides, sometimes clustered with organic matter, as well as magnetite and carbonates embedded in a phyllosilicate matrix. The A-clasts are characterized by a more 15N-rich bulk nitrogen isotope composition (δ15N=200–650‰) relative to H-clasts (δ15N=50–180‰) and contain extremely 15N-rich domains with δ15N<5000‰. The D/H ratios of the clasts are correlated with the degree of clast hydration and define two distinct populations, which we interpret as reflecting mixing between D-poor fluid(s) and distinct organic endmember components that are variably D-rich. High-resolution N isotope data of 15N-rich domains show that the lithic clast diffuse organic matter is typically more 15N-rich than globular organic matter. The correlated δ15N values and C/N ratios of nanoglobules require the existence of multiple organic components, in agreement with the H isotope data. The combined H and N isotope data suggest that the organic precursors of the lithic clasts are defined by an extremely 15N-poor (similar to solar) and D-rich component for H-clasts, and a moderately 15N-rich and D-rich component for A-clasts. In contrast, the composition of the putative fluids is inferred to include D-poor but moderately to extremely 15N-rich H- and N-bearing components. The variable 15N enrichments in H- and A-clasts are associated with structural differences in the N bonding environments of their diffuse organic matter, which are dominated by amine groups in H-clasts and nitrile functional groups in A-clasts. We suggest that the isotopically divergent organic precursors in Isheyevo clasts may be similar to organic moieties in carbonaceous chondrites (CI, CM, CR) and thermally recalcitrant organic compounds in ordinary chondrites, respectively. The altering fluids, which are inferred to cause the 15N enrichments observed in the clasts, may be the result of accretion of variable abundances of NH3 and HCN ices. Finally, using bulk Mg and Cr isotope composition of clasts, we speculate on the accretion regions of the various primitive chondrites and components and the origin of the Solar System’s N and H isotope variability.

Lithology, petrography and Cu occurrence of the Neoproterozoic glacial Mwale Formation at the Shanika syncline (Tenke Fungurume, Congo Copperbelt; Democratic Republic of Congo)

The Mwale Formation that constitutes the base of the Nguba Group in the Neoproterozoic Katanga Supergroup has recently attracted renewed interest for copper mineral exploration. We present new field observations combined with detailed logging and petrography of MWAS0001 drill hole at Shanika syncline in the Tenke Fungurume Mining District. Our study has enabled us to subdivide the Mwale Formation into 7 distinct sequences. This succession is host to glaciogenic, glaciomarine, glaciofluvial and glaciolacustrine deposits. Glaciomarine beds are typically a deposit by debris flow in deep water marine environment, induced by basin wide tectonics and glaciation influence. Glaciofluvial beds were deposited in shallow water, fluvial deltaic environment. The glaciolacustrine environment is indicated by dropstones occurring in the laminated mudstone and rhythmites with dispersed clasts observed in the siltstone and conglomerate. These beds are interlayered within the glaciogenic beds, and are characterised by variable clast composition (felsic, mafic and metamorphic). The clasts are very poorly sorted, angular, rounded to moderately rounded, faceted or striated, and supported in a sandy argillaceous or mud matrix.Two main episodes of sulphide mineralisation are distinguished in the Mwale Formation. The diagenetic episode consists of disseminated euhedral and framboidal pyrites. The hydrothermal episode is associated with Mg-metasomatism and characterised by low grade copper mineralisation that occurs (i) in veins filled with carbonate-chlorite and carbonate-quartz-chlorite-Cu sulphides, such as chalcocite, chalcopyrite and bornite, and (ii) as disseminated sulphides within the host rock. This second episode is late to post-orogenic and can be correlated with late brittle tectonics within the Lufilian arc. The other alteration types include silicification and potassic alteration; however, these alterations are not associated with mineralisation.

Interpreting provenance relations from sandstone detrital modes, southern Italy foreland region: Stratigraphic record of the Miocene tectonic evolution

The Southern Italy orogen preserves deep-marine turbitic clastic wedges that record the key tectonic events during structural growing over the Adria margin. The regional tectonic transition from thick-skinned Calabrian accretion and deformation (during Late Paleogene-to-middle Miocene) to thin-skinned Southern Apennines thrusting (since early-middle Miocene) is recorded by diverse contrasting petrofacies in uppermost Paleogene and Miocene sandstones of dominantly turbiditie deposits. Most of these sandstones reflect in time quartzolithic and quartzofeldspathic and arkosic petrofacies derived from growing and unroofing Calabrian terranes. Quartzose petrofacies mainly indicate provenance from cratonal African margin, during Langhian, and/or from lowland internal domains before its deformation, during the Cretaceous to Paleogene. Volcaniclastic sandstone petrofacies also testify active volcanism during the Late Paleogene to early Miocene. These variable compositions indicate strong palaeogeographic constraints for the central-western Mediterranean, during the Neogene, reflecting provenance relationships from differentiate source rocks. These include interplays between ophiolitiferous, uplifted continental shallow to deep crust terranes, volcanic and sedimentary (mostly carbonate) source rocks. Sandstone detrital modes provide an example of the close relations between clastic compositions and growing orogen in southern Italy and may contribute to unravel the geodynamic history of other major orogens.

Carboniferous History from Coarse Detritus of the Appalachian-Cahaba System: Conglomerate Clasts from the Upper Pottsville Formation, Cahaba Synclinorium, Alabama

AbstractMeasures of abundance of extraformational conglomerates and clast composition, taken together, can be used to unravel the unroofing history of an orogenic belt. This study develops a new approach in quantifying coarse detritus as a provenance indicator. Known as the “conglomerate measures” in the Cahaba synclinorium, the uppermost Pottsville Formation consists of conglomerates and subordinate sandstone, shale, and coal. These siliciclastic sediments were deposited during the Alleghenian orogeny primarily in braidplain-anastomosis environments in Alabama and Mississippi. The abundance of extraformational conglomerate suggests unroofing of active thrust sheets in the Alleghenian foreland basin, which can be used in deciphering the source of Alleghenian sediments in the southeastern United States. Conglomerate clasts in the upper Pottsville Formation consist mainly of sedimentary lithics (chert, sandstone, and mudstone) and metamorphic lithics (phyllite, schist, and quartzite), with minor volcanic an...