Provenance Of Sandstones Research Articles

Provenance of northern Gondwana Lower Ordovician sandstones (Khabour Formation, northern Iraq) revealed by detrital zircon using LA‐ICP‐MS dating

We present new zircon U/Pb provenance data using laser ablation induced coupled plasma mass spectroscopy (LA‐ICP‐MS) for eight samples of mature quartz arenites and subarkosic sandstones of the Lower Ordovician Khabour Formation, northern Iraq, to establish their depositional age and provenance. The samples were collected from thin‐ to medium‐bedded sandstones along profiles of the Chalky Nasara and Ora sections. Most analysed detrital zircon analyses are concordant within 100 ± 10% and include a prevalence of Proterozoic over Archean ages. Collectively, the data can be divided into four main age groups: (a) Neoproterozoic ages, 570–1,000 Ma (58%); (b) Mesoproterozoic ages, 1,000–1,500 Ma (10%); (c) Palaeoproterozoic ages, 1,620–2,480 Ma (21%); and (d) Archean ages, 2,500–3,300 Ma (11%). The predominance of Cryogenian–Ediacaran ages (850–550 Ma) reflects major magmatic events associated with the assembly of northern Gondwana. The major age group at ~600 Ma likely represents the unroofing of late‐stage granitic rocks from the Arabian‐Nubian Shield. The lack of zircons younger than 490 Ma suggests that Lower Ordovician sandstones in northern Iraq were probably deposited on the distal shelf of the northern Gondwana passive margin and were not influenced by rifting and magmatism in northern Gondwana caused by the opening of Palaeo‐Tethys. Diagenetic xenotime overgrowths are common on detrital zircon grains, but radiometric dating of these was not possible.

Provenance, tectonic setting and source-area paleoweathering of the Upper Paleozoic sandstones in the northwestern Ordos Basin, China: evidence from whole-rock geochemistry

Provenance, tectonic setting and source-area paleoweathering of the Upper Paleozoic sandstones in the northwestern Ordos Basin, China: evidence from whole-rock geochemistry

Detrital zircon geochronology and provenance of the Middle to Late Jurassic Paradox Basin and Central Colorado trough: Paleogeographic implications for southwestern Laurentia

AbstractMiddle to Upper Jurassic strata in the Paradox Basin and Central Colorado trough (CCT; southwestern United States) record a pronounced change in sediment dispersal from dominantly aeolian deposition with an Appalachian source (Entrada Sandstone) to dominantly fluvial deposition with a source in the Mogollon and/or Sevier orogenic highlands (Salt Wash Member of the Morrison Formation). An enigmatic abundance of Cambrian (ca. 527–519 Ma) grains at this provenance transition in the CCT at Escalante Canyon, Colorado, was recently suggested to reflect a local sediment source from the Ancestral Front Range, despite previous interpretations that local basement uplifts were largely buried by Middle to Late Jurassic time.This study aims to delineate spatial and temporal patterns in provenance of these Jurassic sandstones containing Cambrian grains within the Paradox Basin and CCT using sandstone petrography, detrital zircon U-Pb geochronology, and detrital zircon trace elemental and rare-earth elemental (REE) geochemistry. We report 7887 new U-Pb detrital zircon analyses from 31 sandstone samples collected within seven transects in western Colorado and eastern Utah. Three clusters of zircon ages are consistently present (1.53–1.3 Ga, 1.3–0.9 Ga, and 500–300 Ma) that are interpreted to reflect sources associated with the Appalachian orogen in southeastern Laurentia (mid-continent, Grenville, Appalachian, and peri-Gondwanan terranes). Ca. 540–500 Ma zircon grains are anomalously abundant locally in the uppermost Entrada Sandstone and Wanakah Formation but are either lacking or present in small fractions in the overlying Salt Wash and Tidwell Members of the Morrison Formation. A comparison of zircon REE geochemistry between Cambrian detrital zircon and igneous zircon from potential sources shows that these 540–500 Ma detrital zircon are primarily magmatic. Although variability in both detrital and igneous REE concentrations precludes definitive identification of provenance, several considerations suggest that distal sources from the Cambrian granitic and rhyolitic provinces of the Southern Oklahoma aulacogen is also likely, in addition to a proximal source identified in the McClure Mountain syenite of the Wet Mountains, Colorado. The abundance of Cambrian grains in samples from the central CCT, particularly in the Entrada Sandstone and Wanakah Formation, suggests northwesterly sediment transport within the CCT, with sediment sourced from Ancestral Rocky Mountains uplifts of the southern Wet Mountains and/or Amarillo-Wichita Mountains in southwestern Oklahoma. The lack of Cambrian grains within the Paradox Basin suggests that the Uncompahgre uplift (southwestern Colorado) acted as a barrier to sediment transport from the CCT.

Deep- versus shallow-marine sandstone provenance in the mid-Carboniferous Clare Basin, western Ireland

In a source-to-sink sedimentary system, multiple processes have the potential to modify the sediment composition during sediment generation at the source, through transport, deposition and burial. To investigate these issues, a multi-proxy provenance study of deep-water and shallow-marine sandstones from the mid-Carboniferous Clare Basin was undertaken, utilizing zircon and apatite U–Pb geochronology, heavy mineral analysis (including apatite trace element data) and petrography. Data from the deep-water submarine fans show a similar provenance signal to the shallow-marine sandstones. Data from across the Clare Basin stratigraphy indicate that sands were probably and consistently derived from the south and SW, with a portion of the detritus being recycled from Old Red Sandstone basins to the south. The provenance signal, however, shows spatial and temporal variations across the basin that are explained by fluctuations in the amount of recycled sediments and are linked with the evolving Variscan Orogenic Belt. Heavy mineral data from both shallow-marine and deep-water sandstones suggest a basin configuration with a delta system feeding directly into the deep basin. Supplementary material: Figures S1–S4 and Tables S1–S8 are available at https://doi.org/10.6084/m9.figshare.c.5446739

Provenance of the Sawa Formation Sandstones, Vindhyan Super Group, Southeast Rajasthan, India

Integrated petrographical and geochemical analysis of Sawa Formation sandstones was analyzed to reconstruct their source area weathering, paleoclimate, tectonic setting and provenance conditions. Petrographically, quartz is dominant detrital mineral followed by feldspar, mica, rock fragments and heavy minerals. Sawa Formation sandstones have been classified as quartzarenite with subordinate sub-arkose and sub-litharenite type. Major oxide element abundances revealed the sandstones have high SiO2 concentration, high K2O/ Na2O ratio, which is consistent with the petrographic data. These sandstones were derived mainly from stable cratonic with minor collision suture and fold thrust belt source and deposited in rifted continental margin basin setting, reflecting high maturity of sediments and high stability of the source area. The CIA, CIW and PIA values of these sandstones indicate high intensity of weathering condition in the source area under warm and humid climate.

Tourmaline and rutile geochemistry in the Early–Middle Devonian sandstones of the Padeha Formation, Alborz Range, Northern Iran

The provenance of Devonian sandstones of the Padeha Formation (Fm.), Eastern Alborz in Iran, has been investigated by standard heavy‐mineral analysis and tourmaline and rutile geochemistry. Heavy‐mineral assemblage is dominated by the ultra‐stable tourmaline, zircon, and rutile, while unstable species are completely absent. The Padeha Fm. sandstones show a very high value of zircon‐tourmaline‐rutile index signalizing either strong weathering in source area(s) or their recycled origin in older Early Palaeozoic formations. Detrital tourmaline shows predominantly dravitic, lesser Mg‐foititic, and uvitic compositions and metasedimentary origin. Metapelitic source is also indicated by rutile geochemistry. Temperature estimates according to Zr‐in‐rutile thermometry show a wide range from 519 to 872°C and indicate the presence of low‐ to upper‐amphibolite and granulite facies metapelitic rocks. Based on chemical composition of detrital tourmaline and rutile, we inferred that the crystalline basement rocks of the Arabian–Nubian Shield were potential primary sources for the Padeha Fm. deposits. Shape of tourmaline and rutile as well as their microtexture surface features indicate long‐distance transport, storage, and recycled history.

Sedimentary environment and provenance of sandstones from the Qadir member in the Nayband Formation, Tabas block, east-central Iran

Qadir Member of Nayband Formation, located in East of Central Iran, has developed to a great extent. Investigation of the lithofacies and sedimentary environment, resulted in identification of the deltaic and marine deposits. Based on field evidence and facies features, Qadir Member consists of two lithofacies, including carbonate and siliciclastic facies. The siliciclastic facies were identified as having four sandstone facies including Sr, Sh, Sp, St, three fine-grained lithofacies, including FI, Fm, Fl (Sr) / Sr (FI) and one coal facies. Also, regarding the field, laboratory studies, and identification of lithofacies, the coastal plain, deltaic (including deltaic plain, proximal delta front, distal delta front, and prodelta) and open marine environments were identified for Qadir Member which is is under the impact of tidal currents. The chemical weathering index (71%) indicated semi-arid to semi-humid conditions and plotting the geochemical data showed the provenance of re-cycling and active continental margin and because of Chemical Index of Alteration, the weathering rate was found to be rather medium to high. The geochemical diagrams also showed a probable source of the intermediate igneous and sedimentary rocks. The active continental margin conditions for this deposit could suggest the Neotethys subduction under Iran’s plate and volcanic activity at the end of Triassic, which coincided with the early Cimmerian orogeny in Alborz and Central East Iranian Microcontinent.

Provenance and tectonic settings of the Eze-Aku Sandstone (Turonian) in Awajir and adjoining areas, Southern Benue Trough, Nigeria: evidence from petrography and geochemistry

Eighteen representative samples for petrographic (6) and geochemical (12) studies were collected from the Turonian (Eze-Aku Formation) sandstones outcropping within Awajir and adjoining areas in the northern section of the Southern Benue Trough. Sandstones of different textural variety underlie the study area: fine-, medium- and coarse-grain sandstones facies. Field study revealed an overall coarsening upward succession, ripple bedding surfaces, cross-stratification and bioturbation, which suggest prevalence of a shallow shelf with relict shoreline environmental settings. Petrographic study show that the sandstones are subarkosic to arkosic and deposited in a humid to semi-humid paleoclimatic condition. Polygenic (mixed) provenance source is inferred for the sandstones and the insignificant presence of sedimentary rock fragments in the framework constituents suggests the Precambrian Basement complex of southern Nigeria as the most likely source area. This result is consistent with trace element ratios such as Cr/Zr (< 0.6) and Cr/Th (0.3–15.7) as well as La/YbN versus CeN diagram which points all the sandstone facies to an intermediate Igneous provenance, unambiguously ruling out the chances of mafic igneous rocks being present in the source terrain. The most probable provenance for the sandstones is the continental Basement complex rocks of Obudu plateau and Oban massifs. The study showed that there was a mild influence of diagenetic alteration on the sandstone facies after deposition in an active continental margin-continental island arc setting.

Evidence from the U–Pb–Hf signatures of detrital zircons for a Baltican provenance for basal Old Red Sandstone successions, northern Scottish Caledonides

The provenance of Devonian Old Red Sandstone (ORS) continental successions in the northern Scottish Caledonides is poorly known: were they derived locally or from more distal sources? The integration of U–Pb and Hf isotope analyses in detrital zircon crystals reduces potential ambiguities arising from non-unique age populations and yields information on the crustal evolution of the source terranes. Samples of basal ORS successions yield zircon U–Pb age groupings of c. 1800–1500 and c. 1200–900 Ma, with minor Neoarchean, Tonian, Ediacaran and Ordovician contributions. SW Baltica provides the best match for detrital zircon ages and Hf isotopic signatures and much of the &gt;900 Ma zircon population was probably recycled from Neoproterozoic successions. ε Hf ( t ) values in c. 1800–1000 Ma grains reflect the assembly of Nuna, the development of a long-lived retreating subduction system along its margin and Grenville collisional orogenesis. These basal ORS successions were probably deposited within the same regional fluvial system as coeval sedimentary rocks in the Midland Valley, draining an area of positive relief in SW Baltica where continental convergence continued through the Early Devonian. Supplementary material : Isotopic data, statistical comparison of selected samples and TIMA heavy mineral data are available at https://doi.org/10.6084/m9.figshare.c.5301780

A Provenance Study of Upper Jurassic Hydrocarbon Source Rocks of the Flemish Pass Basin and Central Ridge, Offshore Newfoundland, Canada

A number of hydrocarbon discoveries have been made recently in the Flemish Pass Basin and Central Ridge, offshore Newfoundland, Canada, but there is only limited geological information available. The primary goal of this study was to determine the sedimentary provenance and paleodrainage patterns of mudstones and sandstones from the Upper Jurassic Rankin Formation, including the Upper and Lower Kimmeridgian Source Rock (organic-rich shale) members and Upper and Lower Tempest Sandstone Member reservoirs, in this area. A combination of heavy mineral analysis, whole-rock geochemistry and detrital zircon U-Pb geochronology was determined from cores and cuttings from four offshore wells in an attempt to decipher provenance. Detrital heavy minerals in 20 cuttings samples from the studied geologic units are dominated by either rutile + zircon + apatite ± chromite or rutile + apatite + tourmaline, with minor zircon, indicating diverse source lithologies. Whole rock Zr-Th-Sc trends suggest significant zircon recycling in both mudstones and sandstones. Detrital zircon U-Pb ages were determined in two mudstone and four sandstone samples from the four wells. Five major U-Pb age groups of grains were found: A Late Jurassic group that represents an unknown source of syn-sedimentary magmatism, a Permian–Carboniferous age group which is interpreted to be derived from Iberia, a Cambrian–Devonian group derived from the Central Mobile Belt of the Newfoundland–Ireland conjugate margin, and two older age groups (late Neoproterozoic and &gt;1 Ga) linked to Avalonia. The Iberian detritus is abundant in the Central Ridge and southern Flemish Pass region and units containing sizable populations of these grains are interpreted to be derived from the east whereas units lacking this population are interpreted to be sourced from the northeast and possibly also the west. The Upper Tempest Sandstone contains Mesozoic zircons, which constrain the depositional age of this unit to be no older than Late Tithonian.

Provenance of Neogene sandstones in western Taiwan traced with garnet geochemistry and zircon geochronology

AbstractIn this study, we use provenance analysis to shed light on the Neogene evolution of river drainage and sediment dispersal in eastern Asia as a consequence of the Himalayan orogeny and topographic rise of the Tibetan Plateau. As an attempt to envisage how sediment‐routing systems operated in the past, and to identify the ultimate source of siliciclastic detritus originally generated in mainland China and now incorporated in, and recycled from, the western Taiwan accretionary prism, we have used Raman spectroscopy of detrital garnet in modern river sands and upper Neogene sandstones, complemented by detrital‐zircon geochronology and by petrographic and heavy‐mineral analysis. Garnet grains are relatively abundant and largely represented by almandine with various percentages of pyrope molecules in Yangtze sand as in western Taiwan sandstones and modern river sand derived from them. Instead, they are rare and largely represented by grossular or andradite in the sand of the Pearl River and of coastal rivers of SE China facing the Taiwan Strait. This finding supports the result of detrital geochronology, which documents a sharp difference between U‐Pb age spectra of Pearl River and coastal SE China zircons (characterised by a Paleozoic‐Mesozoic triple peak) and Yangtze and western Taiwan zircons (characterised by prominent Neoproterozoic, Paleoproterozoic, and latest Archean clusters). The Pearl River and minor rivers facing the Taiwan Strait are thus ruled out as ultimate sources of upper Neogene sandstones exposed today along the western front of the Taiwan fold‐thrust belt. In the envisaged scenario, sand mostly supplied by the paleo‐Yangtze River was entrained for ~ca.1,000 km southward by longshore currents and deposited on the Chinese passive margin before being accreted along the front of the Taiwan orogen since ~6 Ma. Littoral sand drift represents a major factor of long‐distance sediment transport in modern shelves and needs to be taken into full account in source‐to‐sink studies and paleogeographic reconstructions.

Provenance of Carboniferous sandstones in the central and southern parts of the Pennine Basin, UK: evidence from detrital zircon ages

New U–Pb isotopic analyses of detrital zircon grains from Namurian and Westphalian sandstones in the central and southern parts of the Pennine Basin are combined with published analyses from the same region, to assess existing views on the nature and location of the source areas that supplied the clastic sediment. The study confirms that most sandstones were derived from distant areas to the north, west and south, and that a local source, in the Wales–Brabant High, also supplied sediment at times. The northern sources are thought to lie mainly in Laurentia (East Greenland), with some input from Baltica (Norway). Most sandstones entering from the west are thought to have been supplied from areas of Avalonian basement, with some components recycled from sediments that were themselves derived from the Caledonian belt that lay to the north. An exception is the Clifton Rock: its source is thought to lie entirely in the Irish Caledonides or in southern Scotland. Sandstones supplied from the south contain significant numbers of late Devonian and Carboniferous grains, indicating the inclusion of material eroded from the active Variscan orogenic belt in Europe. Northern provenance prevailed during Namurian and early Langsettian times, then alternated with western supply until the late Langsettian. Western input then dominated through most of Duckmantian times, until superseded in the late Duckmantian by supply from the Variscan orogen. The Woolley Edge Rock, now shown to be an isolated member of the northern group, entered the area just before the earliest sandstone of Variscan origin. Supplementary material: U–Pb data of detrital zircon is available at https://doi.org/10.6084/m9.figshare.c.5174702

Provenance, tectonic setting and source area-paleoweathering of sandstones of the Bahariya Formation in the Bahariya Oasis, Egypt: An implication to paleoclimate and paleogeography of the southern Neo-Tethys region during Early Cenomanian

The Lower Cenomanian Bahariya Formation forms the most prolific hydrocarbon reservoir in the Western Desert of Egypt, and represents a good example to illustrate the paleoclimatic conditions and paleogeographical evolution in the southern Neo-Tethys region during Early Cenomanian. It is also particularly important for its diverse vertebrate fauna including dipnoans, chelonians, crocodyliforms, squamates, plesiosaurs, decapod crustaceans and dinosaurs, which reflect sustained regional biostratigraphical and paleoenvironmental significance. In this study, a multidisciplinary approach of fieldwork, petrography and bulk-rock geochemistry of sandstones of the Bahariya Formation has been performed to constrain their provenance, tectonic setting, source area-paleoweathering and paleoclimatic conditions within the Neo-Tethyan realm. Petrographically, the studied sandstones are mainly of quartz-arenite type with subordinate sub-arkose and sublithic ones. Quartz types, trace and rare earth element concentrations and ratios indicate the sandstones were sourced from felsic granitic rocks with a rare contribution of felsic gneisses. The modal analysis reflects that the sandstones are mainly of cratonic interior and quartzose recycled tectonic provenance. The chondrite-normalized REE distribution pattern of the Bahariya sandstones are characterized by enriched LREE and flat HREE similar to those of UCC with negative Eu/Eu* anomalies. Major and trace elements of the sandstones suggest their deposition on a Neo-Tethys passive continental margin related to the Early Cretaceous rifting. The weathering indices (CIA, CIW, PIA and ICV) and the Al2O3-(CaO + Na2O)-K2O diagram suggest moderate to severe chemical weathering in the source area under semi-humid to humid climatic conditions. In conclusions, the Bahariya sandstones could be sourced by a fluvial reworking of moderately- to intensively-weathered Precambrian granites and gneisses of the surrounding Gebel Uweinat Massive (at the southwest of the study area), and were deposited in a low-lying basin (Bahariya area) of the Neo-Tethys passive continental margin. In a broad interest, results of this study could contribute in a reconstruction of the paleoclimatic conditions and paleogeographical evolution of the southern Neo-Tethys region during Early Cenomanian.

A Combined Petrographic-Geochemical Provenance and Tectonic Setting Study of Palaeozoic Rocks, in East Johor Basin, Peninsular Malaysia

DOI: 10.17014/ijog.8.1.11-24Several greywacke sandstones considered as Paleozoic rocks are found in three different formations, i.e. the Dohol, Linggiu, and Tanjung Leman Formations within the Palaeozoic East Johor Basin. The compositions of twenty-nine sandstone samples were identified using petrographical and geochemical methods to determine the provenance of sandstones as well as the tectonic setting of pre-and syn-sedimentation. Seven samples of them were examined using point counting method to obtain the mineralogical compositions. This petrographical point counting was done by plotting composition percentages to QFL and QmFLt triangular diagrams, The results showed a magmatic arc for Dohol Formation, a change from a magmatic to a recycled orogen for Linggiu Formation, and a recycled orogen for Tanjung Leman Formation. The recycled orogen tectonic setting of Linggiu and Tanjung Leman may have come from the underlying metamorphic and sedimentary rocks of Mersing and Murau Formations. Meanwhile, twenty-two samples were examined using a geochemical method by utilizing the ratio of K2O/Na2O and SiO2. The samples suggest a tectonic setting from both passive continental margin (PM) and active continental margin (ACM). Based on these findings, it is interpreted that the sedimentary rocks in East Johor were deposited in a subduction-related basin, such as fore-arc, magmatic arc, and back-arc.

Petrographic and geochemical constraints on petrofacies, provenance and tectonic setting of the upper cretaceous sandstones, Northern Bida Basin, north-central Nigeria

The petrographic and geochemical compositions of the Campanian-Maastrichtian siliciclastic sediments in the northern Bida Basin, North-central Nigeria were investigated with the aim to determine the petrofacies, their provenance and tectonic settings. The mineral composition of the samples selected from the 10 sub-facies in the study area is characterized by abundant quartz (predominantly of monocrystalline quartz) and minor feldspar, rock fragments and heavy minerals. The framework grains are angular, sub-angular to sub-rounded and well sorted with the quartz varieties exhibiting euhedral to subhedral, non-undulose to undulose characteristics. The modal composition reveals the sediments as quartzarenite to sublitharenite with minor sub-arkoses and also reflects felsic rocks derived within passive margin paleotectonics as provenance. Geochemical proxies obtained based on major, trace and rare earth elements data; Al2O3/TiO2, SiO2/Al2O3, K2O/Al2O3, La/Th, La/Co, Th/Co, La/Sc, Cr/Th, Zr/Nb and Zr/Th with chondrite-normalized REE patterns, light REE enrichment, heavy REE flat pattern and negative Eu anomalies revealed sediments derivation mainly from felsic source rocks. A higher Zr/Sc and Zr/Hf ratio with Th/Sc and Zr/Sc binary plot suggest considerable zircon enrichment in the source areas. Discrimination plots; log(K2O/Na2O) versus SiO2, TiO2 versus (Fe2O3+MgO), Al2O3/SiO2 versus (Fe2O3+MgO) and SiO2/20-(K2O+Na2O)-(TiO2+Fe2O3+MgO), La/Y versus Sc/Cr, La-Th-Sc, Th-Sc-Zr/10 of the analyzed sandstones suggest that source rocks may lie in the passive continental margin, before sediment transport and deposition in the basin by fluvial modes. This study suggests a passive paleotectonic setting for the Precambrian Basement Complex consisting of two igneous source materials from which the sediments are derived and supplied to the study area.

Diagenetic history and provenance of Devonian terrestrial sandstones at the margin of Gondwana: Padeha Formation, Eastern Alborz, Iran

• The northern margin of Gondwana in Iran rifted in the Devonian, forming a passive continental margin to the Paleotethys Ocean. • The Padeha sandstones were sourced by the late Neoproterozoic granitic gneisses of Iran. • Further mesodiagenesis was terminated by the Eocimmerian collision. The northern margin of Gondwana in Iran rifted in the Devonian, forming a passive continental margin to the Paleotethys Ocean, the details of which are obscured by later collision. A record of the early phase of opening of Paleotethys is preserved in the 600-m thick Padeha Formation, a Middle Devonian terrestrial rift basin succession. The sandstones are quartz arenite, sub-arkose and arkose and contain minimal detrital matrix (~1%). Bulk-rock geochemistry, according to major elements, suggests a source to the sandstones that was dominated by I-type granite, but also, based on trace elements, included small amounts of intermediate or mafic rocks. Low Zr and HREE contents suggest little or no sandstone in the source area and thus low abundance of fine-grained heavy minerals (<1%). The sandstones were sourced by the widespread granitic gneisses of central and northern Iran that formed at the northern margin of Gondwana in the late Neoproterozoic–Ediacarian. Diagenesis of the sandstones is dominated by compaction and fracturing of framework quartz without widespread stylolites in the sandstones, and cementation by silica, carbonates and Fe-oxides. Fractures within quartz grains are filled mostly by silica, but locally by carbonate and authigenic K-feldspar. Albitization of plagioclase, K-feldspar overgrowths and partial dissolution of detrital K-feldspar post-date silica cements and suggest temperatures between 70 and 120 °C. The particular diagenetic assemblage of altered K-feldspar and limited quartz stylolites was a consequence of a high geothermal gradient of ~70 °C/km at a burial depth of <1.5 km. Further mesodiagenesis was terminated by the Eocimmerian collision.

Detrital Zircon Provenance Analysis in the Central Asian Orogenic Belt of Central and Southeastern Mongolia—A Palaeotectonic Model for the Mongolian Collage

Our study is aimed at reconstructing the Palaeozoic–early Mesozoic plate tectonic development of the Central Asian Orogenic Belt in central and southeast Mongolia (Gobi). We use sandstone provenance signatures including laser ablation U-Pb ages of detrital zircons, their epsilon hafnium isotope signatures, and detrital framework grain analyses. We adopt a well-established terran subdivision of central and southeastern Mongolia. However, according to their affinity and tectonic assemblage we group them into three larger units consisting of continental basement, rift-passive continental margin and arc elements, respectively. These are in today’s coordinates: (i) in the north the late Cambrian collage from which the later Mongol-Okhotsk and the Central Mongolia-Erguna mountain ranges resulted, (ii) in the south a heterogeneous block from which the South Mongolia-Xin’gan and Inner Mongolia-Xilin belts developed, and (iii) in between we still distinguish the intra-oceanic volcanic arc of the Gurvansayhan terrane. We present a model for paleotectonic development for the period from Cambrian to Jurassic, which also integrates findings from the Central Asian Orogenic Belt in China and Russia. This mobilistic model implies an interplay of rift and drift processes, ocean formation, oceanic subduction, basin inversion, collision and suture formation in space and time. The final assemblage of the Central Asian Orogenic Belt occurred in Early Jurassic.

Provenance and tectonic setting of Paleogene sandstone in the center of the northern Qaidam Basin, China

The average thickness of Paleogene sandstones reaches about 3000 m or even 4000 m at the northern margin of the Qaidam Basin. However, the provenance of these sandstones has been uncertain; thus, more comprehensive research is needed. Integrated research was conducted on the provenance based on petrological characteristics, heavy mineral analysis, and U–Pb dating in the center of the northern Qaidam Basin. The results of lithofacies analysis show that the Paleogene sandstones were mainly derived from an active continental magmatic arc, subduction-accretionary or fold-thrust belt; The results of heavy mineral analysis show that the heavy mineral combinations in the Lenghu seventh area and Mabei area are consistent, mainly composed of zircon, garnet, magnetite, and leucosphenite. Moreover, GZi [garnet/garnet + zircon] and RZi [leucosphenite/(leucosphenite + zircon)] have good correlation with ZTR (the ZRT index refers to the proportions of three kinds of transparent heavy minerals in clastic rocks: zircon, rutile, and tourmaline). The zircon U–Pb results for the Paleogene sandstone in the northern Mabei area are consistent with the results of U–Pb dating in the middle of the South Qilian Mountains, which yielded the same results as river sand in the modern Yuka River. Based on three types of data, it is confirmed that the two areas, Lenghu seventh and Mabei, had the same sediment sources in the Paleogene, mainly from the middle of the South Qilian Mountains. The source rocks are mainly neutral - basic magmatic rocks and metamorphic rocks and the structure background is dominated by the magmatic island arc and the collision-thrust suture zone at the active continental margin.

The importance of trace element analyses in detrital Cr‐spinel provenance studies: An example from the Upper Triassic of the Barents Shelf

AbstractInvestigations of sandstone provenance often involve U–Pb dating and chemical/mineralogical investigations of detrital minerals that are stable in sediments. As most stable detrital minerals are from felsic–intermediate rocks, investigations of the only mafic–ultramafic mineral considered stable in sediments, chromian spinel (Cr‐spinel), can reveal contributions from mafic–ultramafic sources. Cr‐spinel chemical compositions are tied to petrogenesis, making it possible to identify the nature of, and differentiate between, potential sources. Earlier detrital Cr‐spinel studies have focused on major and minor element compositions, however, the advent of laser‐ablation analytical techniques now allow routine mineral trace element analyses. Here, we integrate major, minor and trace element compositions of detrital Cr‐spinel from sandstones with a well‐characterised provenance from the Triassic (Anisian to Early Norian) Snadd and De Geerdalen formations of the Barents Shelf. The analysed Cr‐spinel compositions are depleted in the major element cations Fe3+, Al and Mg and enriched in Cr and Fe2+. Relative to MORB chromite, the minor and trace element data show high concentrations of Zn, Co and Mn, low concentrations of Ni and Ga and variable concentrations of Ti, V and Sc. The major element compositions of the detrital Cr‐spinel are similar to ophiolite‐associated Cr‐spinel, while the trace element compositions indicate a more complex petrogenesis influenced by metamorphic alteration. The compositional variations between sample locations are small, suggesting similar source rocks for the detrital Cr‐spinel throughout the study area. The most likely sources of the Cr‐spinel grains are metamorphosed ophiolite complexes in the Uralian Orogen, in accordance with earlier provenance studies. The novel addition of trace element compositions to detrital Cr‐spinel studies adds significant source‐sensitive information.

Interpreting detrital modes and geochemistry of sandstones from the late Paleozoic Tepuel-Genoa Basin: Paleogeographic implications (Patagonia, Argentina)

The provenance of sandstones deposited in the late Paleozoic Tepuel-Genoa Basin is analyzed in this paper. Five sections were sampled in Esquel, Sierra de Tepuel, Sierra de Tecka, El Molle, and Río Genoa areas for petrographic and geochemical studies. The sandstones in the Tepuel-Genoa Basin are dominated by feldspathic litharenites and litharenites, showing lithic fragments of volcanic and sedimentary rocks in the Valle Chico Formation and medium-to high-grade metamorphic rock clasts in the rest of the units.Detrital modes of seventy-five sandstones samples from the Valle Chico, Pampa de Tepuel, Mojón de Hierro, and Río Genoa formations were counted and analyzed. Seven modal components have discriminant value for identifying provenance areas (Qm, Qi, Lv, Lmm-h, Lm-Lp, Lm, Qpm). These modal components allow identification of three petrofacies: 1. Quartzose-lithic (Qm69Lv2Lm29), 2. Quartzose (Qm89Lv4Lm7) and 3. Volcanic-sedimentary (Qm60Lv38Lm1). The quartzose-lithic petrofacies is mainly composed of monocrystalline quartz, medium- and high-grade metamorphic clasts and polycrystalline quartz with cataclastic texture, this assemblage is interpreted as being derived from the crystalline rocks that form the Deseado Massif. The quartzose petrofacies is composed of monocrystalline quartz with scarce contributions of metamorphic clasts and traces of volcanic fragments; the provenance area is ascribed to sedimentary terrains, which most likely covered part of the Deseado Massif. The volcanic-sedimentary petrofacies is comprised of volcanic (acidic and intermediate rocks) and sedimentary (sandstone and mudstone) clasts, with discrete amounts of quartz grains with idiomorph shapes and embayments. This assemblage may correspond to material supply from the Devonian-Early Carboniferous accretionary complex developed in Chile or the unroofing of the western volcanic arc located in the central part of Patagonia. The validity of the three defined petrofacies was evaluated using Principal Component Analysis and triangular compositional diagrams; both methods show good separation and lack of overlap between the three petrofacies. Major (Si, Al, Fe, Na, K) and trace-REE elements (Zr, Th, Sc, Hf) were used to improve the petrographic information. The relation SiO2 against K2O/Na2O indicates that the Pampa de Tepuel and the Mojón de Hierro formations correspond to a passive margin, while the Valle Chico and Río Genoa formations represent different types of active continental margins. The Th/Sc and Zr/Sc ratios and the Th-Hf-Co distributions indicate that the sandstones of the Tepuel Group were formed from rocks compatibles with the average composition of the upper continental crust.