Proterozoic Sedimentary Rocks Research Articles

Caves, Karst Features and Speleological Heritage in Chapada Diamantina, Bahia, Brazil

Chapada Diamantina is among the best known and most visited landscapes in Brazil. Located in the state of Bahia, Northeast region of the country, it is characterized by mountains and plateaus that developed on Proterozoic sedimentary and metasedimentary rocks. Much of its territory is covered by carbonate and siliciclastic rocks, where relevant karst systems develop, marked by the occurrence of sinking streams, sinkholes, and caves with a great diversity of morphologies, speleothems, subterranean fauna, and paleontological and archaeological records. Relevant carbonate systems occur in Iraquara, such as the Lapa Doce, Torrinha, and Pratinha caves, which represent important tourist attractions. Also in these rocks, stand out the Brejões Cave, with a 106-m high entrance, and the Toca da Boa Vista, the largest cave in South America, extending across 114 km. Cultural manifestations are present in the prehistoric cave paintings at Santa Marta Shelter and recent religious pilgrimages at Mangabeiras Cave, in Ituaçu. In turn, siliciclastic karst systems are mainly in Serra do Sincorá. The Lapão and Castelo caves have expressive speleogens and speleothems, as well as the Torras Cave, in the Igatu region, ranked as the second largest in Brazil considering siliciclastic rocks.

Resource potential of the Proterozoic–Paleozoic Carrara depocentre, South Nicholson region, Australia: Insights from stratigraphic drilling

A comprehensive geochemical program was carried out on rock samples collected in the NDI Carrara 1 drill hole, the first stratigraphic test of the newly discovered Carrara Sub-basin located in the South Nicholson region of northern Australia. The drill hole recovered continuous core from 284 m to total depth at 1750 m and intersected approximately 1120 m of Proterozoic sedimentary rocks, unconformably overlain by 630 m of Cambrian Georgina Basin carbonate-rich rocks. Total organic carbon (TOC) contents from Rock-Eval pyrolysis highlight the potential for several thick black shales to be a source of petroleum for conventional and unconventional plays. Cambrian rocks contain an organic-rich section with TOC contents of up to 4.7 wt.% and excellent oil-generating potential. The Proterozoic section is overmature for oil generation but mature for gas generation, with potential for generating gas in carbonaceous mudstones showing TOC contents up to 5.5 wt.% between 680 and 725 m depth. A sustained release of methane (up to 2%) recorded during drilling from 1150 to 1500 m suggests potential for an unconventional gas system in the Proterozoic rocks from 950 to 1415 m depth, which exhibit favourable organic richness and thermal maturity. The Proterozoic rocks, which are comparable in age to the sediment-hosted deposits of the Century Mine, contain local occurrences of lead, zinc and copper sulfide minerals providing hints of mineralisation. The combined geochemical results offer the promise of a potential new resource province in northern Australia.

Crustal Mercury Addition Into the Giant Jinchuan Ni‐Cu Sulfide Deposit, China, and Its Geological Implications

AbstractMercury (Hg) isotopes have shown their power of tracing Hg pollution sources in ecosystems, but their potentials for petrogenetic tracing are yet to be explored. Here we conducted Hg isotope analysis for samples collected from major orebodies of the world‐class Jinchuan Ni‐Cu sulfide deposit, China. These samples show large variations of δ202Hg (−2.65 to +0.19‰) and Δ199Hg (−0.16 to +0.19‰). Some of the Δ199Hg values significantly deviate from current estimates on the primitive mantle (Δ199Hg: 0.0 ± 0.1‰, 2SD). The pronounced Hg mass‐independent fractionation (Hg‐MIF) signals, with significant positive (>0.1‰) and negative (<0.1‰) Δ199Hg values similar to marine sediments and terrestrial soils, respectively, suggests the addition of crustal materials into the Jinchuan deposit, via crustal assimilation during mantle‐derived magma ascending to the crust. These samples show δ34S values (−1.09 to +1.38‰) identical to that of the primitive mantle (0.0 ± 2.0‰), which may indicate a major sulfur source from the mantle. However, δ34S provides poor constraints on the sulfur source, and the early reported anomalous Δ33S values (+0.12 to +2.67‰) in the Jinchuan deposit support the involvement of external sulfur from Archean and Proterozoic sedimentary rocks during the formation of this deposit, similar to the case of Hg. This study shows the powerful use of Hg isotopes as a petrogenic tracer and highlights the importance of interaction between mantle‐derived magmas and crustal materials on the formation of the Jinchuan Cu‐Ni sulfide deposit.

Early Devonian sinistral shearing recorded by retrograde monazite-(Ce) in Oscar II Land, Svalbard

Abstract The Southwestern Basement Province of Svalbard extends northward from Sørkapp Land in the south to Oscar II Land. In the north, the Müllerneset Formation characterized by polymetamorphosed Proterozoic sedimentary rocks crops out. In this study we used an integrated tectonic and petrochronological approach to gain an insight into the structural and metamorphic evolution of the unit and surrounding basement. The Müllerneset Formation consists of two separate tec-tonic blocks. NNW-SSE trending retrograde foliation is associated with mineral and stretching lineation and kinematic indicators consistent with left-lateral to oblique sinistral shearing in the western block. The eastern block is characterized by the opposite sense of shear that was overturned during the Eurekan event as evidenced by unconformably overlaying Carboniferous sedimentary rocks. Conventional geothermobarometry yields the prograde peak pressure metamorphic conditions of 6.6 - 7.1 kbar at 480 - 520°C followed by peak temperature at 5.1 - 5.9 kbar and 530 - 560°C. Subsequent retrograde greenschist facies overprint is related to left-lateral NNW-SSE trending shearing. Tiny monazite occurs within foliation or overgrows allanite-(Ce), thus is interpreted as growth along a retrograde path. Th-U-total Pb dating of monazite-(Ce) provided an early Caledonian age (ca. 450 Ma) and younger population of ca. 410 ± 8 Ma. This age is consistent with previously reported 40Ar/39Ar cooling ages (410 ± 2 Ma) of muscovite supporting a retrograde growth of monazite. Petrochronological evidence combined with structural observations suggests that the Müllerneset Formation has been tectonically exhumed in the Early Devonian due to the NNW-SSE trending left-lateral shearing. Coeval folding and thrusting in the remaining basement of Oscar II Land to the east indicate a transpressional regime of the deformation in the Early Devonian. Similarly oriented contemporaneous tectonic zones within the Southwestern Basement Province of Svalbard may account for the same set of shear zones dispersing the Ordovician subduction complexes along western Spitsbergen.

Paragenesis of gold mineralization at the Kiyuk Lake Project, Kivalliq Region, Nunavut, Canada

ABSTRACT Exploration for gold in Nunavut has been primarily focused on Archean greenstone belts in the north and coastal regions of the territory, resulting in large areas of underexplored terrain in the south. The Kiyuk Lake property is located in the underexplored southwest corner of the Kivalliq Region of Nunavut within the Hearne domain of the ∼1.9 Ga western Churchill Province. The property is hosted by Proterozoic calc-silicate and clastic sedimentary units of the Hurwitz Group (<2.4–1.9 Ga) and the unconformably overlying Kiyuk Group (1.9–1.83 Ga). Gold mineralization in Proterozoic sedimentary rocks is rare in the Canadian Shield, so the Rusty Zone at Kiyuk Lake presents a unique opportunity to study the enigmatic gold mineralization hosted in such sedimentary rocks. Mineralization at the Rusty Zone is hosted by an immature lithic wacke cut by thin intermediate dikes that are associated with hydrothermal breccias composed of Fe-carbonate, calcite, calcic-amphibole, Fe-sulfide, Fe-oxide minerals, and gold. Textural and timing relationships suggest that the gold mineralization is post-sedimentary and syn- to post-intrusion of intermediate dikes. Stable isotope thermometry suggests that mineralization took place between 450 and 600 °C, and geochronological studies indicate that the intrusion and mineralization occurred before or about 1.83 Ga. Using basement breaching thrusts faults as conduits to the surface, over-pressurization along a later normal fault is thought to be the primary cause for the localized breccia pipe that controls gold mineralization. The hydrothermal fluids are postulated to be volatile-rich aqueous solutions exsolved from a source of cooling magmas at depth. Although sub-economic at present, the occurrence of high-grade gold in a Paleoproterozoic basin such as Kiyuk Lake could signal a new opportunity for exploration for gold in the Canadian Shield.

Structural, petrological, and tectonic constraints on the Loch Borralan and Loch Ailsh alkaline intrusions, Moine thrust zone, northwestern Scotland

During the Caledonian orogeny, the Moine thrust zone in northwestern Scotland (UK) emplaced Neoproterozoic Moine Supergroup rocks, metamorphosed during the Ordovician (Grampian) and Silurian (Scandian) orogenic periods, westward over the Laurentian passive margin in the northern highlands of Scotland. The Laurentian margin comprises Archean–Paleoproterozoic granulite and amphibolite facies basement (Scourian and Laxfordian complexes, Lewisian gneiss), Proterozoic sedimentary rocks (Stoer and Torridon Groups), and Cambrian–Ordovician passive-margin sediments. Four major thrusts, the Moine, Ben More, Glencoul, and Sole thrusts, are well exposed in the Assynt window. Two highly alkaline syenite intrusions crop out within the Moine thrust zone in the southern Assynt window. The Loch Ailsh and Loch Borralan intrusions range from ultramafic melanite-biotite pyroxenite and pseudoleucite-bearing biotite nepheline syenite (borolanite) to alkali-feldspar–bearing and quartz-bearing syenites. Within the thrust zone, syenites intrude up to the Ordovician Durness Group limestones and dolomites, forming a high-temperature contact metamorphic aureole with diopside-forsterite-phlogopite-brucite marbles exposed at Ledbeg quarry. Controversy remains as to whether the Loch Ailsh and Loch Borralan syenites were intruded prior to thrusting or intruded syn- or post-thrusting. Borolanites contain large white leucite crystals pseudomorphed by alkali feldspar, muscovite, and nepheline (pseudoleucite) that have been flattened and elongated during ductile shearing. The minerals pseudomorphing leucites show signs of ductile deformation indicating that high-temperature (~500 °C) deformation acted upon pseudomorphed leucite crystals that had previously undergone subsolidus breakdown. New detailed field mapping and structural and petrological observations are used to constrain the geological evolution of both the Loch Ailsh and the Loch Borralan intrusions and the chronology of the Moine thrust zone. The data supports the interpretation that both syenite bodies were intruded immediately prior to thrusting along the Moine, Ben More, and Borralan thrusts.

Fluoride Contamination in Groundwater, Around Bhopalpatnam Area, District-Bijapur, Chhattisgarh: Adverse Effect on Human Health

In India many cases of fluorosis (dental and skeletal) have been reported in Archaean and Proterozoic granitic and gneissic t errain from Andhra Pradesh, Rajasthan, Madhya Pradesh, and Chhattisgarh. The origin of hazardous fluoride is attributed to geological reasons. A systematic study is required to understand the behavior of fluoride in drinking water particularly in terms of hydrogeological settings, climatic conditions etc. The present study is an effort to assess hydrogeological study of groundwater in parts of Bhopalpatnam area, District-Bijapur, Chhattisgarh. The study is conducted to understand the fluoride contamination in groundwater and to infer the chemical parameters responsible for distribution of fluoride. The study area is underlain partly by crystalline basement and partly by Proterozoic sedimentary rocks (sandstone, shale and limestone). A total 57 water samples have been taken from dug cum bored wells from the study area in June 2015. The results of chemical analysis showed fluoride concentration from 0.12mg/l to 3.58mg/l. The fluoride bearing minerals in host rock interacted with groundwater and through chemical decomposition, dissociation, reactions dissolution fluoride concentration increased in groundwater. Chemical weathering with relatively high alkalinity favors high concentration of fluoride in Groundwater. Villagers have no option to drink high fluoride groundwater as a result they were badly suffered from dental and skeletal fluorosis.

Study on Groundwater Quality in Chungcheongnam-do

The purpose of this study was to document groundwater quality in Chungcheongnam-do. Samples were taken from Taean, Dangjin, Seocheon, Boryeong, Seosan, and Nonsan areas, and 48 water quality variables were analyzed in relation to applicable standards, including the amounts of naturally occurring radioactive materials(U and Rn). The results from testing 179 locations indicated that 128 were suitable and 51 were of unacceptable quality, in terms of drinking water quality standards. The nonconformity rate for nitrate nitrogen was 47.0%, while that for total coliforms was 24.2%. Heavy metals-such as Pb, Hg, Cd, and Cr-were detected in low concentrations at all points. Analysis of naturally occurring radioactive materials showed that U concentrations were within the water quality standard (0.03 mg/L) at all points. Rn concentrations were low in NW regions such as Taean, Dangjin, Seocheon, and Boryeong, where Proterozoic sedimentary rocks were distributed, but its concentrations in the Seosan and Nonsan areas, where granite rocks were widely distributed, required closer investigation, and it was found that the alternative maximum contaminant level (148 Bq/L) was exceeded in granite soils which originated from the Mesozoic Era. Key Words: Ground water, naturally occurring radioactive materials; radon, uranium

Paleomagnetism and Age Correlation of the Mesoproterozoic Rocks of the Udzha and Olenek Uplifts, Northeastern Siberian Platform

Abstract—This paper presents the results of paleomagnetic studies of the Proterozoic sedimentary and igneous rocks composing the structure of sections of the Olenek and Udzha uplifts. Carbonate rocks of the upper unit of Khaipakh formation have been studied within the Olenek uplift, and terrigenous and volcanic-sedimentary rocks of the Udzha and Unguokhtakh formations and the Early Mesoproterozoic igneous complex have been investigated within the Udzha uplift. Within the Olenek uplift, the carbonate rocks of the upper unit of the Khaipakh formation have been studied; within the Udzha uplift–terrigenous and volcanogenic-sedimentary rocks of the Udzha and Unguokhtakh formations, and the Early Mesoproterozoic magmatic complex. The results of the paleomagnetic study (1) indicate that the upper unit of Khaipakh formation of the Olenek uplift and the Udzha formation of the Udzha uplift have different sedimentation age, which contradicts the currently accepted correlation scheme of the Proterozoic sections in the northern Siberian platform; (2) support the existence of two stages of the Proterozoic magmatism in the territory of the Udzha uplift, with a more ancient stage having an age of ~1500 Ma according to the paleomagnetic data; (3) show that from ~1500 to 1110 Ma ago, the Siberian platform was located in the equatorial and subequatorial latitudes.

Multiple S Isotopes and S Isotope Heterogeneity at the East Eagle Ni-Cu-Platinum Group Element Deposit, Northern Michigan

Abstract The East Eagle Ni-Cu-platinum group element deposit is a conduit-type deposit located in northern Michigan, in close spatial proximity to the currently producing Eagle deposit. Massive and semimassive (net-textured) sulfide mineralization at East Eagle occurs approximately 800 m lower in the stratigraphic sequence than that at Eagle and only ~200 m above the contact between Proterozoic and Archean rocks. Although sulfide mineralogy and textural types are similar at the two occurrences, there are important differences in their S isotope systematics. Massive sulfide mineralization at East Eagle is characterized by a relatively narrow range of δ34S values from 1.5 to 3.2‰. Semimassive sulfides show a similar range from 2.1 to 3.8‰. In strong contrast to these values, those from disseminated sulfides that border the massive and semimassive mineralization define a much larger range from –4.3 to 22.8‰. The much more restricted range in δ34S values recorded in the massive and semimassive sulfide mineralization compared to that of the disseminated mineralization is thought to reflect isotopic exchange reactions in the conduit involving accumulated sulfide and pulses of magma containing S of mantle origin. The ∆33S values of all three major types of sulfide mineralization at East Eagle are near 0‰, with most values between –0.03 and 0.03‰. Unlike ∆33S values from semimassive sulfide mineralization at Eagle, the ∆33S values at East Eagle show no, or very limited, evidence for the involvement of S derived from Archean sedimentary rocks. The wide range in δ34S values recorded in the disseminated mineralization provides strong evidence that S from Proterozoic sedimentary host rocks was involved in the mineralization; in some cases, as much as 85% of the S may have been of external origin. In addition to the wide range in δ34S values, the disseminated mineralization is characterized by spatially heterogeneous δ34S values. Meter-scale S isotope variations, as well as variations in Pt and Pd tenor, are consistent with multiple inputs of magma, each characterized by distinct S isotope ratios. Heterogeneity of several per mill at the centimeter scale indicates that the degree of supercooling exceeded the S diffusivity, preserving small-scale S isotope variability inherited from the sedimentary country-rock source. Elongate, branching plagioclase grains in many of the gabbroic rocks that host the disseminated sulfide mineralization are consistent with a rapid second stage of cooling.

High-resolution bathymetry of the Alderney Race and its geological and sedimentological description (Raz Blanchard, northwest France)

ABSTRACT We present a high-resolution 1:15,000 bathymetric map (Main map) of Alderney Race located offshore of northwestern France, with the strongest currents in Europe. We use this map, underwater video transects and Shipek grabs to improve geological maps previously published. We distinguished Proterozoic crystalline rocks, Paleozoic and Cretaceous sedimentary rocks on the present-day sea floor. Some structures as faults and folds are also mapped. We identified a Quaternary cover made of pebbles, boulders and blocks interpreted as corestones resulting in differential erosion and alteration of the substratum. This cover is commonly encrusted by fixed fauna, such as bryozoans and barnacles. Finally, we describe the present-day mobile sediment cover characterized by sand patches and pebble dune fields (up to 10 m in height). Our videos show the presence of mobile fine-grained sediment patches under the resolution of our map lying between the cobble and pebble cover. We summarize our interpretations on a non-exhaustive geological-sedimentary map.

Rodinian granulites from southern Qiangtang terrane: Implications for tectonic evolution of the Tibetan Plateau

Bordered by the Longmu Co-Shuang Hu-Lancangjiang suture zone in the north and east, as well as the Bangong Nujiang suture zone in the south and west, the southern Qiangtang terrane is one of the least-studied blocks in the Tibetan region. The early tectonic evolution of the southern Qiangtang terrane has remained a controversy for a long time. Here we report granulites from the Tongka high-grade metamorphic complexes in the southern Qiangtang terrane. The mafic granulites occur as small lenses in the felsic granulites and leucogranites with peak mineral assemblage including garnet (core) + diopside + low An plagioclase + quartz. The retrograde assemblage is represented by garnet (rim) + pargasite + high An plagioclase + quartz. The fine-grained aggregates of feldspar + garnet + aluminosilicates + rutile around reddish-brown biotite relics in the felsic granulites are interpreted as products of partial melting of biotites. Thermobarometric estimates for the peak assemblages of the mafic rocks are P = 17.5 kbar and T = 811 °C, whereas the retrograde assemblages of the mafic rocks experienced decompression to P = 10.4 kbar, at T = 674 °C. Zircon texture and SIMS U-Pb data reveal that the felsic granulites were derived from Achaean to Proterozoic sedimentary rocks that underwent high-temperature metamorphism and transformation to paragneisses or granitoids at 1100 to 1000 Ma. During 950–900 Ma, the crystalline rocks were further buried deeply to be transformed into the felsic granulites. We therefore interpret the Tongka high-grade metamorphic complexes to be a portion of the Rodinian continental collision belt. Evidently some domains of the Rodinian continental crust were thickened during the Grenville events, similar to the more recent processes in the Himalaya and Tibetan plateau. The Tongka high-grade metamorphic complexes which form the basement of the southern Qiangtang terrane was subsequently disrupted and involved in the formation of the great Tibetan plateau during the Cenozoic times. Our work thus highlights the Precambrian history of the southern Qiangtang terrane.

Geology of Elu Inlet and Melville Sound, Nunavut, Arctic Canada

ABSTRACTWe present the results of helicopter- and field-based geological mapping of Elu Inlet and Melville Sound, Kitikmeot Region of Nunavut, Arctic Canada. The area includes a ∼150 km-wide belt of Proterozoic sedimentary rocks that unconformably overlie the Archean Slave Province of the Canadian Shield and are cross-cut by Neoproterozoic mafic rocks and covered by early Palaeozoic deposits. This work introduces an updated sedimentologic, stratigraphic, and structural framework for the area and is corroborated by geophysical analysis of natural radioactivity. Three Proterozoic sedimentary sequences have been identified, spanning in age from ∼1.9 to ∼1.2 Ga, and including fluvial–aeolian sandstone and shallow-marine carbonate rocks. Mass-spectrometric analyses identified above-baseline concentrations of uranium along the unconformities underlying the two oldest Proterozoic sequences. Proterozoic deposits display weak deformation, related to syn-orogenic foreland and intracratonic-sag stages of the Kilohigok and Elu basins, respectively.

Multiple S isotopes, zircon Hf isotopes, whole-rock Sr-Nd isotopes, and spatial variations of PGE tenors in the Jinchuan Ni-Cu-PGE deposit, NW China

Previous geochemical data for the Jinchuan Ni-Cu-(platinum-group elements, PGE) deposit, the single largest magmatic sulfide deposit in the world, are derived primarily from the upper parts of the deposit. This paper reports new PGE and S-Hf-Sr-Nd isotope data for the lower parts of the deposit that have become accessible for sampling by ongoing underground mining activity. New PGE data from this study, together with previous results, indicate that PGE tenors in the bulk sulfide ores of the deposit increase eastward, except for two fault-offset ore zones which occur together within the western part of the deposit. Generally, these two ore zones show depletions in IPGE (Ir, Ru, Rh) but not in PPGE (Pt, Pd) and Cu, and more fractionated olivine and Cr-spinel compositions than the rest of the deposit. These differences can be explained by a more evolved parental magma for the IPGE-depleted ore zones. The eastward increase of PGE tenors in the rest of the deposit can be explained by upgrading of preexisting sulfide liquid in a subhorizontal conduit by a new surge of magma moving through the conduit from west to east, which took place before the formation of the IPGE-depleted ore zones. The Jinchuan ultramafic rocks are characterized by elevated initial 87Sr/86Sr ratios from 0.7077 to 0.7093, negative e Nd values from −9.2 to −10.5, and zircon e Hf values from −4 to −7. These data indicate up to 20 % of crustal contamination in the Jinchuan magma. Four of nine multiple sulfur isotope analyses for the Jinchuan deposit show anomalous ∆33S values varying from 0.12 to 2.67 ‰. These results, together with elevated δ34S values (>2 ‰) for some of the samples analyzed previously by other researchers, indicate the involvement of external sulfur from Archean and Proterozoic sedimentary rocks. Modeling results based on our olivine data and magma compositions estimated previously by other researchers indicate that fractional crystallization did not play a major role in triggering sulfide saturation in the Jinchuan magma and that the parental magma experienced previous sulfide segregation during ascent or in staging chambers.

INDICATIONS OF LATERAL MOVEMENTS IN THE SOUTH-EAST MARGIN OF THE BALTIC SHIELD

The edge Vetreny Poyas in the south-east margin of the Baltic Shield corresponds mainly to the drop-shaped in plan massive of proterozoic volcanic and sedimentary rocks. The comparison of geologic and geomorphologic structure leads to the supposition of lateral neotectonic movements of massive alongside with the vertical ones. The mega-bend of archean rocks, having character of neotectonic activation, pushes the massive from the left side. In front of the massive there are the depression, which possibly marks the wedging crack; on the north of the massive there are indicators of left strike-slip. The valley of Onega River crossing the edge shows the signs of its uplift.

Late Paleozoic provenance shift in the south-central North China Craton: Implications for tectonic evolution and crustal growth

U–Pb geochronologic and Hf isotopic results of seven sandstones collected from Late Carboniferous through Early Triassic strata of the south-central part of the North China Craton record a dramatic provenance shift near the end of the Late Carboniferous. Detrital zircons from the Late Carboniferous sandstones are dominated by the Early Paleozoic components with positive εHf(t) values, implying the existence of a significant volume of juvenile crust at this age in the source regions. Moreover, there are also three minor peaks at ca. 2.5Ga, 1.87Ga and 1.1–0.9Ga. Based on our new data, in conjunction with existing zircon ages and Hf isotopic data in the North China Craton (NCC), Central China Orogenic Belt (CCOB) and Central Asian Orogenic Belt (CAOB), it can be concluded that Early Paleozoic and Neoproterozoic detritus in the south-central NCC were derived from the CCOB. Zircons with ages of 1.9–1.7Ga were derived from the NCC. However, the oldest components can't be distinguished, possibly from either the NCC or the CCOB, or both. In contrast, detrital zircons from the Permian and Triassic sandstones are characterized by three major groups of U–Pb ages (2.6–2.4Ga, 1.9–1.7Ga and Late Paleozoic ages). Specially, most of the Late Paleozoic zircons show negative εHf(t) values, similar to the igneous zircons from intrusive rocks of the Inner Mongolia Paleo-Uplift (IMPU), indicating that the Late Paleozoic detritus were derived from the northern part of the NCC. This provenance shift could be approximately constrained at the end of the Late Carboniferous and probably hints that tectonic uplift firstly occurred between the CCOB and the NCC as a result of the collision between the South and North Qinling microcontinental terranes, and then switched to the domain between the CAOB and the NCC. Additionally, on the basis of Lu–Hf isotopic data, we reveal the pre-Triassic crustal growth history for the NCC. In comparison among the three crustal growth curves obtained from modern river sands, our samples, and the Proterozoic sedimentary rocks, we realize that old components are apparently underestimated by zircons from the younger sedimentary rocks and modern river sands. Hence, cautions should be taken when using this method to investigate growth history of continental crust.

Lanthanides and highly mobile elements in sedimentary and metasedimentary rocks as indicators of the tectonic activity in the platform basement: An example of the Voronezh Crystalline Massif

The Eu/Eu*, Eu/Sm, and Ce/La ratios can serve as indicators of zones permeable to ascending fluid fluxes that mark time spans when the kinematics of faults in the basement changed (extension and compression phases). The Eu/Eu* ratio is more informative, the variations in the Eu/Sm ratio are correlated with transgressions in the territory of the anteclise, and the variations in the Ce/La ratio could be caused by both metasomatic processes and low-temperature hydrothermal solutions. In the Voronezh anteclise, whose sedimentary cover is relatively thin and provides no evidence of catagenetic processes, high As concentrations and Eu/Eu* ratios of sedimentary rocks can be utilized as indicators of deep zones of fluid generation centres. Comparable average Eu/Eu*, Eu/Sm, and Ce/La ratios in Proterozoic sedimentary rocks in the platform cover and metasediments of Proterozoic banded iron formations (BIF) confirm that the tectonic environments in which sedimentary units of various age were accumulated were similar.

Arumberia-type structures in the Upper Vendian of the Urals

Problematic arumberia-type structures are widespread in Upper Proterozoic sedimentary rocks deposited in depositional environments subject to periodic desiccation and fluctuating salinity. Here we report two new occurrences of arumberia-type structures in the Krutikha Member of the Upper Vendian Chernyi Kamen Formation on the western slope of the Central Urals (Us’va River) and the Zigan Formation of the Asha Group in the South Urals (new road Sterlitamak-Beloretsk). The results of the study of these structures significantly expand paleontological characteristics of the Upper Vendian non-marine rocks and allow us to re-examine the paleontological importance of the hastily forgotten group of arumberia-type organisms. We distinguished six varieties of arumberia-type structures that for the sake of convenience were given formal Latin names in binominal nomenclature although they are not biological species. Two species—Arumberia banski and A. vindhyanensis—were erected by previous researchers, whereas the A. beckeri, A. ollii, A. usvaensis, and A. multykensis varieties are recognized for the first time. Despite similarity to erosional structures on the bottom of turbidite beds, erosion does not explain the genesis of the entire spectrum of arumberia-type structures including those preserved on ripple marks, with evidence of soft-body deformation, or with ribbon and filamentous fabric replaced by clay minerals. The diversity of arumberia could be only a manifestation of living systems. The species of Arumberia are distinguished by their different biostratinomy, the distance between the main structural units, the preservation of the main structural units, and the presence of additional structures between the main structural units. Most likely, the diversity of arumberia reflects not only taphonomic, but also ontogenetic and phenotypic variation. The level of morphological complexity and biostratinomic features of arumberia apparently exceed the organization of microbial mats and represent a non-actualistic type of microbial communities. The occurrence in extremely shallow-water depositional setting suggests that arumberia had evolved an adaption to periodic desiccation and that arumberia-type organisms, along with microbial mats, had been an important factor of sediment biostabilization in the Late Vendian non-marine environments.

Crustal structure beneath the Sub-Himalayan fold–thrust belt, Kangra recess, northwest India, from seismic reflection profiling: Implications for Late Paleoproterozoic orogenesis and modern earthquake hazard

Most compressional orogens include salients and recesses along their strike, the age and origin of which can be hard to ascertain. In the Kangra recess in the trace of the Main Boundary Thrust (MBT), the largest such recess within the active Himalayan orogen, the Sub-Himalayan sedimentary fold-thrust belt increases in width to as much as 90 km (the Kangra Basin), but narrows to as little as 10 km in the adjoining Nahan salient of the MBT (the Subathu Basin) to the southeast. New seismic reflection profiling places the Himalayan décollement at 6–8 km depth above thin but reflective Meso- to Neoproterozoic Vindhyan (Lesser Himalayan Series-equivalent) strata. These data show that the Vindhyan sedimentary rocks are thinner in the Kangra recess than further southeast, allowing the hypothesis that the width of the Lesser Himalayan thrust belt, and the existence of the Kangra recess, could be related to the pre-deformation basin thickness. This hypothesis obviates the need for control of the Kangra recess by a lateral ramp in the Main Himalayan Thrust, so making it more likely that the Kangra segment could rupture as part of an earthquake far larger than the devastating 1905 M = 7.8 Kangra earthquake. Below the Proterozoic sedimentary rocks, our reflection data show a west–southwest-dipping reflective fabric spanning a 30 km-crustal thickness, which we infer corresponds to a widespread “Ulleri-Wangtu” orogenic event at c. 1850 Ma affecting a pre-Tethyan Indian continental margin, thickening the basement by c. 20%. The deepest 10 km of this ~ 50 km-thick crust shows a more horizontal, arguably younger, reflectivity, though the Moho is not clearly marked by strong reflectors.

Ages and Sources of Components of Zn-Pb, Cu, Precious Metal, and Platinum Group Element Deposits in the Goodsprings District, Clark County, Nevada

The Goodsprings district, Clark County, Nevada, includes zinc-dominant carbonate replacement deposits of probable late Paleozoic age, and lead-dominant carbonate replacement deposits, copper ± precious metal-platinum group element (PGE) deposits, and gold ± silver deposits that are spatially associated with Late Triassic porphyritic intrusions. The district encompasses ~500 km2 although the distribution of all deposits has been laterally condensed by late Mesozoic crustal contraction. Zinc, Pb, and Cu production from about 90 deposits was ~160,000 metric tons (t) (Zn > Pb >> Cu), 2.1 million ounces (Moz) Ag, 0.09 Moz Au, and small amounts of PGEs—Co, V, Hg, Sb, Ni, Mo, Mn, Ir, and U—were also recovered. Zinc-dominant carbonate replacement deposits (Zn > Pb; Ag ± Cu) resemble Mississippi Valley Type (MVT) Zn-Pb deposits in that they occur in karst and fault breccias in Mississippian limestone where the southern margin of the regional late Paleozoic foreland basin adjoins Proterozoic crystalline rocks of the craton. They consist of calcite, dolomite, sphalerite, and galena with variably positive S isotope compositions ( δ 34S values range from 2.5–13‰), and highly radiogenic Pb isotope compositions (206Pb/204Pb >19), typical of MVT deposits above crystalline Precambrian basement. These deposits may have formed when southward flow of saline fluids, derived from basinal and older sedimentary rocks, encountered thinner strata and pinch-outs against the craton, forcing fluid mixing and mineral precipitation in karst and fault breccias. Lead-dominant carbonate replacement deposits (Pb > Zn, Ag ± Cu ± Au) occur among other deposit types, often near porphyritic intrusions. They generally contain higher concentrations of precious metals than zinc-dominant deposits and relatively abundant iron oxides after pyrite. They share characteristics with copper ± precious metal-PGE and gold ± silver deposits including fine-grained quartz replacement of carbonate minerals in ore breccias and relatively low S and Pb isotope values ( δ 34S values vary from 0–~4‰; 206Pb/204Pb <18.5). Copper ± precious metal-PGE deposits (Cu, Co, Ag, Au, Pd, and Pt) consist of Cu carbonate minerals (after chalcocite and chalcopyrite) and fine-grained quartz that have replaced breccia clasts and margins of fissures in Paleozoic limestones and dolomites near porphyritic intrusions. Gold ± silver deposits occur along contacts and within small-volume stocks and dikes of feldspar porphyry, one textural variety of porphyritic intrusions. Lead isotope compositions of copper ± precious metal-PGE, gold ± silver, and lead-dominant carbonate replacement deposits are similar to those of Mojave crust plutons, indicating derivation of Pb from 1.7 Ga crystalline basement or from Late Proterozoic siliciclastic sedimentary rocks derived from 1.7 Ga crystalline basement. Four texturally and modally distinctive porphyritic intrusions are exposed largely in the central part of the district: feldspar quartz porphyry, plagioclase quartz porphyry, feldspar biotite quartz porphyry, and feldspar porphyry. Intrusions consist of 64 to 70 percent SiO2 and variable K2O/Na2O (0.14–5.33) that reflect proportions of K-feldspar and albite phenocrysts and megacrysts as well as partial alteration to K-mica; quartz and biotite phenocrysts are present in several subtypes. Albite may have formed during emplacement of magma in brine-saturated basinal strata, whereas hydrothermal alteration of matrix, phenocrystic, and megacrystic feldspar and biotite to K-mica, pyrite, and other hydrothermal minerals occurred during and after intrusion emplacement. Small volumes of garnet-diopside-quartz and retrograde epidote-mica-amphibole skarn have replaced carbonate rocks adjacent to one intrusion subtype (feldspar-quartz porphyry), but alteration of carbonate rocks at intrusion contacts elsewhere is inconspicuous. Uranium-lead ages of igneous zircons vary inconsistently from ~ 180 to 230 Ma and are too imprecise to distinguish age differences among intrusion subtypes; most ages are 210 to 225 Ma, yielding a mean of 217 ± 1 Ma. K-Ar and 40Ar/39Ar ages of magmatic (plagioclase, biotite) and hydrothermal (K-mica) minerals span a similar range (183–227 Ma), demonstrating broadly contemporaneous intrusion emplacement and hydrothermal alteration but allowing for multiple Late Triassic magmatic-hydrothermal events. Imprecision and range of isotopic ages may have resulted from burial beneath Mesozoic and Tertiary strata and multiple intrusion of magmas, causing thermal disturbance to Ar systems and Pb loss from zircons in intrusions. Separate late Paleozoic (zinc-dominant carbonate replacement deposits) and Late Triassic (all other deposits) mineralizing events are supported by form, distribution, and host rocks of metal deposits, by hydrothermal mineral assemblages, isotope compositions, metal abundances, and metal diversity, and by small intrusion volumes. These characteristics collectively distinguish the Goodsprings district from larger intrusion related carbonate replacement districts in the western United States. They can be used to evaluate proximity to unexposed porphyritic intrusions associated with PGE and gold ± silver mineralization.