Framework Petrography Research Articles

Revisiting the stratigraphical, sedimentological and provenance evolution of Lingshan Island, offshore of east China: Implications for the destruction of the north China craton

The Cretaceous strata of Lingshan Island, offshore of East China, are a key sedimentary archive for understanding the destruction of the North China Craton (NCC). However, there has been limited progress in characterizing its stratigraphical, sedimentological and provenance evolution in the context of the progressive lithospheric thinning and magmatism associated with the destruction of the NCC. We report field logging data, sandstone framework petrography, and detrital and volcanic zircon U–Pb geochronology data from the Cretaceous strata of Lingshan Island, and correlate these data with coeval sediments in the Jiaolai Basin and volcanic units in the East China. Our results indicate rapid deposition of the Laiyang and Qingshan groups from c. 124–123 Ma with an upward thickening and coarsening succession from the lacustrine turbidites of the Laiyang Group to the deltaic rocks of the Qingshan Group, accompanied by an increase in volcanic activity up-section. Sandstone petrology and detrital zircon U–Pb ages indicates that the source areas for the Laiyang and Qingshan Groups were syn-depositional volcanic rocks and plutonic rocks, with some contributions from the Yangtze Craton and Sulu terrane. Our compilation of detrital zircon U–Pb ages (n = 8513) from the Cretaceous strata of Lingshan island and the Jiaolai Basin in the hinterland implies provenance contributions from four different sources. The zircon Th/U ratios from this large dataset suggests that Cretaceous magmatic zircons formed in an extensional setting (Th/U ratios >1 but with significant variation). The Eu anomalies in magmatic zircons (n = 550) from the Jiaodong Peninsula indicate continuous lithospheric thinning in Eastern China since c. 130 Ma, leading to the destruction of the NCC. Based on all available data, Lingshan Island most likely was a rift basin during the Cretaceous.

Stratal evolution and provenance of a precambrian delta in a tectonically active terrane: The lower Signal Hill Group, Avalon Zone, Newfoundland

Sedimentologic and provenance studies of the syn-orogenic Ediacaran lower Signal Hill Group (Gibbett Hill and Quidi Vidi formations) in the Avalon Peninsula, Newfoundland, Canada, were conducted to test structural and depositional models related to the enigmatic late Ediacaran (ca. 575–550 Ma) Avalon orogenesis. Two facies associations corresponding to delta front and delta plain environments are identified from five stratigraphic sections. The presence of an unconformity between these facies near the location of a previously proposed thrust-related paleo-high and changes in sedimentary patterns reflecting shoreline regression support the inference of syn-sedimentary uplift and reveals coeval base level fall. Framework petrography, detrital geochronology, and detrital heavy mineral analysis indicate sediment sourcing from hinterlands of West Avalonian igneous and metamorphic basement. Changes in provenance between the delta front and delta plain facies coeval with regression of the Signal Hill delta suggest the thrusting of volcanic cover sequences over already exhumed plutonic sources and the exhumation of deeper/higher-grade metamorphic rocks in the hinterland. Detrital zircon U-Pb maximum depositional ages of the delta front and delta plain facies yield 557 ± 9 Ma and 556 ± 22 Ma, respectively, constraining this episode of West Avalonian hinterland exhumation, wedge-top foreland basin deformation, and forced regression to ca. 556 Ma. The regional significance of this late Ediacaran (ca. 565–538 Ma) foreland basin to tectonic models of West Avalonia’s transition from an arc setting to a Paleozoic rifted platform is not currently understood, but it may represent a retro-arc basin formed either as part of a coherent West Avalonian block overlying a subducted spreading ridge or on a subsidiary West Avalonian terrane prior to and during terrane collision preceding deposition of the Paleozoic overstep sequence.

Sedimentological Evidence for Pre‐Early Permian Continental Subduction in the Dabie Orogen, Central‐East China

AbstractHow to constrain the onset of continental subduction and prograde metamorphism in an orogen remains a fundamental question. The widespread Triassic ultrahigh‐pressure (UHP) metamorphic rocks in the Dabie orogen in central‐east China are generally attributed to continental subduction. The earliest Triassic peripheral basins (the Huangshi, Yueshan and Nanjing basins) around the Dabie orogen represent an ideal archive to reconstruct the early evolution of the orogen. Here we present a multidisciplinary provenance study on these Triassic strata, including framework petrography and heavy mineral analyses combined with U‐Pb age and trace‐element analyses of detrital zircon, rutile and apatite. The abundant metapelitic lithics and muscovite grains, a heavy mineral population dominated by metamorphic apatite, and a significant Permian (270–290 Ma) age peak from U‐Pb age spectra of detrital zircon, rutile and apatite imply an Early Permian medium‐high grade metamorphic source in the uppermost structural levels of the Dabie orogen. Our provenance data indicate that the onset of northward continental subduction of the South China Block commenced no later than the Early Permian (c. 290 Ma). This event is clearly earlier and distinct from the more widespread Triassic UHP metamorphism of the Dabie orogen, suggesting that continental subduction and mountain‐basin interaction were protracted processes (>55 Myr, c. 290–235 Ma). When combined with other geological evidence, our results show that the prolonged continental subduction is not always preceded by subduction of oceanic crust.

Early Jurassic initiation of the modern drainage pattern of the Dabie orogen (East China) revealed by a multi‐proxy provenance approach

AbstractThe timing of the initiation of the present‐day tectonic architecture and drainage systems in eastern China remains debated. This study presents a comprehensive provenance study of the Early Jurassic peripheral basins surrounding the Dabie orogen including framework petrography, heavy‐mineral analysis, single‐grain chronology and chemistry. Clasts of high‐grade schist, muscovite grains, rare gneissic fragments, abundant metamorphic garnet and phengite (Si > 3.3 pfu), combined with a main 216–256 Ma rutile U–Pb population found in these Early Jurassic sandstones, indicate a source from the Triassic (U)HP belt in the Dabie orogen. Sedimentary lithics and ultra‐stable heavy‐mineral assemblages indicate an additional source of recycled sedimentary rocks. Combined with the continuous shift of the youngest detrital rutile age population toward younger ages toward the north that mimics the pattern of metamorphic bedrock ages in the Dabie orogen, we infer that the present surface tectonic architecture and paleodrainage patterns of the Dabie orogen were established in the Early Jurassic. Thus, the Early Jurassic exhumation of the Dabie orogen marked the development of the watershed between Northern and Southern China, namely the Huai River and several principal tributary systems of the middle‐lower Yangtze River.

Provenance of modern sands from Baja California rivers (Mexico): petrographic constraints from light and heavy minerals

ABSTRACT We used high-resolution petrographic and dense-mineral data on modern sand to investigate erosion patterns of the El Rosario, San Fernando, and San Vicente river basins of Baja California (Mexico) to better understand the interrelationships between a complex magmatic arc terrane and surface processes. Modern sand composition of these three rivers reflects the nature of the source region, which lies in the central part of the Alisitos arc (Peninsular Ranges, Baja California, Mexico). The sand detrital modes correspond well with the main structural units drained by the El Rosario, San Fernando, and San Vicente rivers: 1) the Early Cretaceous oceanic arc of the Alisitos Group, 2) the Paleozoic to Mesozoic continental-margin metasedimentary rocks, 3) the Cretaceous plutons, 4) the Upper Cretaceous to Tertiary sedimentary rocks, and 5) the Tertiary volcanics. The modern sand of the San Vicente, San Fernando, and El Rosario rivers is fed chiefly from erosion of a magmatic arc and consists mostly of minor feldspatho-lithic (Fl) to quartzo-litho-feldspathic (qFL) sand and dominant quartzo-feldspatho-lithic (qLF) and litho-feldspatho-quartzose (lQF) sand. Framework petrography also suggests a progressive increase in quartz, K-feldspar, sedimentary and metamorphic lithic fragments, and a decrease in volcanic lithic fragments. Sand, in the Lv field, microlitic (Lvmi), felsitic (Lvf) and lathwork (Lvl) types, and trace amounts of vitric grains (Lvv), such as pumice particles. The andesitic volcanic province of the Alisitos arc sheds quartz-poor sand containing mainly microlitic lithic fragments and plagioclase, whereas sand derived from more felsic rhyolites and rhyodacitic and trachyandesitic products contains largely felsitic volcanic lithics and minor lathwork lithics are mainly derived from subordinate basalts. The abundance of intrusive rock fragments and volcanic and sedimentary lithics of the sampled river sands faithfully represents the relative abundance of a heterogeneous bedrock exposure consisting of sedimentary and metasedimentary rocks, as well as volcanic, plutonic, and medium- to high-grade metamorphic rocks in each drainage basin. Transparent heavy-mineral assemblages including major amounts of amphibole, pyroxene, epidote, titanite, zircon, and minor amounts of staurolite, rutile, actinolite, tourmaline, garnet, kyanite, andalusite, sillimanite, and apatite are in good agreement with a mixed provenance characterized mainly by magmatic, primarily volcanic (andesite, rhyolite, and basalt) and secondarily plutonic (granitoid rocks) and metamorphic source rocks. Some labile species such as hornblende and pyroxene grains show mainly corroded to etched morphologies due to dissolution processes and by chemical weathering processes occurring in a paleo and current semiarid climate. The Zircon+Tourmaline+Rutile index of the heavy-mineral modes, coupled with their subrounded to rounded grain surface texture, indicates recycling from the sedimentary source rocks. Heavy-mineral abundance and weathering textures in the San Fernando and San Vincente river sands match predominantly volcanic bedrock lithologies, while the El Rosario river sands match sedimentary and metasedimentary source rocks.

Transcontinental retroarc sediment routing controlled by subduction geometry and climate change (Central and Southern Andes, Argentina)

AbstractCentral Argentina from the Pampean flat‐slab segment to northern Patagonia (27°–41°S) represents a classic example of a broken retroarc basin with strong tectonic and climatic control on fluvial sediment transport. Combined with previous research focused on coastal sediments, this actualistic provenance study uses framework petrography and heavy‐mineral data to trace multistep dispersal of volcaniclastic detritus first eastwards across central Argentina for up to ca. 1,500 km and next northwards for another 760 km along the Atlantic coast. Although detritus generated in the Andes is largely derived from mesosilicic volcanic rocks of the cordillera, its compositional signatures reflect different tectono‐stratigraphic levels of the orogen uplifted along strike in response to varying subduction geometry as well as different character and crystallization condition of arc magmas through time and space. River sand, thus, changes from feldspatho‐litho‐quartzose or litho‐feldspatho‐quartzose in the north, where sedimentary detritus is more common, to mostly quartzo‐feldspatho‐lithic in the centre and to feldspatho‐lithic in the south, where volcanic detritus is dominant. The transparent‐heavy‐mineral suite changes markedly from amphibole ≫ clinopyroxene > orthopyroxene in the north, to amphibole ≈ clinopyroxene ≈ orthopyroxene in the centre and to orthopyroxene ≥ clinopyroxene ≫ amphibole in the south. In the presently dry climate, fluvial discharge is drastically reduced to the point that even the Desaguadero trunk river has become endorheic and orogenic detritus is dumped in the retroarc basin, reworked by winds and temporarily accumulated in dune fields. During the Quaternary, instead, much larger amounts of water were released by melting of the Cordilleran ice sheet or during pluvial events. The sediment‐laden waters of the Desaguadero and Colorado rivers then rushed from the tract of the Andes with greatest topographic and structural elevation, fostering alluvial fans inland and flowing in much larger valleys than today towards the Atlantic Ocean. Sand and gravel supply to the coast was high enough not only to promote rapid progradation of large deltaic lobes but also to feed a cell of littoral sediment transport extending as far north as the Río de la Plata estuary.

Influencing Factors on Petrography Interpretations in Provenance Research—A Case-Study Review

The use of framework petrography is a common initial step in provenance research of sand and sandstone. The data tend to be interpreted based on the three main components quartz, feldspar, and lithic fragments. Surprisingly often, this is done without taking other influencing factors than the tectonic setting of the catchment and/or the surroundings of the depositional basin into account. Based on a database of 14 studies with approximately 900 petrographic data points from sand and sandstone, this study demonstrates quantitative effects on the apparent composition resulting from both geological and non-geological biases. The study illustrates sandstone-classification differences based on different specifications of the three end-members quartz, feldspar, and lithic or rock fragments, how the point-counting method can affect the apparent petrographic composition of sandstone, how sorting and facies bias may be differentiated from a climate or provenance signal, and how bias due to diagenetic effects can be minimised. In conclusion, both geological and non-geological biases should be considered for provenance studies that include petrographic data.

Submarine topography-related spatial variability of the southern Taiwan Strait sands (East Asia)

The Taiwan Strait serves as a link between the East China Sea and South China Sea in East Asia. Complex ocean dynamics, huge sediment inputs and distinct tectonic, climatic and bedrock lithological settings of the two sides of the strait make it ideal for sediment source-to-sink studying. While mud sediments in the strait have been well investigated, sand composition and provenance remain understudied. Here, we present framework petrography and heavy mineral data of sands from the southern Taiwan Strait and the adjacent representative rivers to characterize sand provenance and depositional mechanisms. As expected, the SE China river sands are dominated by quartz and feldspar, whereas sands from the westward-flowing mountainous rivers in Taiwan are rich in lithic fragments and heavy minerals of metamorphic origin. The southern Taiwan Strait sands show significant spatial variations in composition and texture of the framework grains and heavy minerals. Framework grain-based provenance modeling results show that sands in the southwest margin of Taiwan Strait (water depth of 30–60 m) are mainly supplied by SE China rivers. Taiwan mountainous rivers made prominent contributions to the central-western Taiwan Strait (40–60 m) and the south of Taiwan Shoal (below 50 m), both of which are far away from the Taiwan island (ca. 100–300 km away). Furthermore, sands from the Taiwan Shoal (20–30 m) show extremely high compositional maturity and are mainly composed of coarse, rounded quartz. These sands, previously proposed as relict sediments, have been intensely altered by modern high-energy hydrodynamic conditions and can also be interpreted as palimpsest sediments. These results demonstrate that modern river-derived sands are eventually deposited in relatively deep-water regions in the strait, rather than the shallow regions (Taiwan Shoal). We propose that the sand composition and distribution are closely related to the submarine topography of the Taiwan Strait. Combining previous mud belt investigations, we suggest that sands and muds tend to have different fates in shallow continental shelves with complex climate, ocean current and seafloor landform conditions. This study also highlights the importance of both modern and relict sands in the strait and our findings are important to better understanding of shelf sedimentary systems with huge river-sediment-input and high wave/tidal-current-energy.

Sediment provenance and tidal current-driven recycling of Yellow River detritus in the Bohai Sea, China

A detailed sediment-provenance study is presented on the modern Bohai Sea, China, the innermost gulf of the Yellow Sea, using framework petrography, heavy-mineral and grain-size analyses. A series of subaqueous river deltas, characteristic of multisource, is distinguished along the coastal zone. First-cycle fluviodeltaic sediments are attributed principally to three large source areas: the Loess Plateau, the Yanshan highlands, and the Horqin sandland. Coastal sands along eastern Liaodong Bay are produced by weathering and physical erosion of near-source Mesozoic granitoid rocks during Quaternary lowstands. Apart from subaqueous deltas and coastal sands, sediment provenance is only attributed to two end-member mixing with various proportions between recycled Holocene Yellow River sediments and ancient fluvial sediments of the Liaohe river system, even though detrital sources are multiple along the coast. Relative contributions are quantified on a ternary diagram of heavy-mineral compositions, using the proportion of relative distances between a given mixed area and the two end-member deltas. The eastern Bohai flood-tidal delta, characterized by abundant garnet and ilmenite, is regarded as a large repository of ancient Liaohe sediments, which had been intermittently accumulated during Quaternary lowstands and reworked during multiple transgressions. As a secondary sediment source detached from the present-day Liaohe River delta, it is remobilized and involved in the modern sedimentation. A complete tidal current-dominated depositional pattern is proposed throughout the Bohai Sea to explain sediment accumulation and recycling. We suggest that dominant ebb tidal currents, prevailing in the southern Bohai Strait, are a primary driver carrying fine-grained Yellow River sediments eastward to the Yellow Sea. In contrast, the recycling of Yellow River sediments is driven by flood tidal currents, prevailing in the northern Bohai Strait. The internal recycling process in the Bohai Sea builds the sand sheet and its terminal lobe, i.e., the eastern Bohai mud belt, whereas the external recycling process that involves the depocenters of Yellow River sediments in the outside North Yellow Sea builds the sand ridges and its terminal lobe, i.e., the quartz-rich area. This study improves our understanding on the Yellow River dispersal system. It also provides a typical example that demonstrates how ancient alluvial sediments accumulated during eustatic lowstands are reactivated and join the modern sedimentation processes.

Provenance and tectonic setting of the Jurassic Huayacocotla Formation and Alamitos Sandstone, Central Mexico

We present a modified model for the paleogeographic evolution of Mexico during Early and Late Jurassic time that is constrained by the tectonic setting and the weathering conditions of the Early Jurassic Huayacocotla Formation and Late Jurassic Alamitos Sandstone basins in state San Luis Potosí in central Mexico. Framework petrography constrains feldspato-quartzose sandstone (mean of Q68F22L10) and litho-quartzose (mean of Q75F6L19) sandstone compositions for the two units, respectively. The abundant lithic fragments are totally dominated by volcanic fragments. Quartz cathodoluminescence colours and textures from the Alamitos Sandstone supports a large input of volcanic material, but also indicates the presence of metamorphic quartz. Similarly, the geochemical composition is more mafic for the Huayacocotla Formation (Th/Sc: ˜0.6 and Cr/Th: ˜10) than for the Alamitos Sandstone (Th/Sc: ˜1.1 and Cr/Th: ˜48). Also the weathering conditions were less intense during the Early (CIA: ˜60, PIA: ˜61) than the Late Jurassic (CIA ˜85, PIA ˜97). Well preserved lithic fragments and feldspar grains, particularly in the Huayacocotla Formation, indicate that weathering indeed was minor for this unit. We interpret the difference between the two units as a combined result of climate change and tectonic setting. During the Early Jurassic, transport of volcanic detritus probably dominated from the active Nazas arc in the west. Later, additional sources from the metamorphic basement of Mexico were included. During Late Jurassic time strike-slip faulting related to the opening of the Gulf of Mexico may have re-directed the sediment-transport systems. Finally, the degree of weathering was affected by drastic climatic change from arid to humid tropical conditions during the Middle to Upper Jurassic, possibly related to the first incursions of Gulf of Mexico marine environments linked to the rotation of the Yucatan block.

Origin of deep-sea clastics of the Magura Basin (Eocene Makovica sandstones in the Outer Western Carpathians) with constraints of framework petrography, heavy mineral analysis and zircon geochronology

Petrographic examination, heavy mineral analysis and detrital zircon U-Pb dating were performed on the Eocene siliciclastic rocks in the Rača Unit of the Outer Western Carpathians in order to reveal their origin and establish the development of the Magura Basin during the Eocene. The medium- to fine-grained sublitharenites and quartzarenites were mainly derived from extra-basinal sources, and the deposits predominantly contain minerals from metamorphic rocks. The terrigenous material was derived from low- to medium-grade metapelites and granitoids. The sedimentation was also controlled by a sediment supply from the mafic source. The basic and metabasic rocks contain pyrope-rich garnets and Cr-spinels. Palaeo-currents document that the sedimentary material was supplied from the South-East. The first detrital zircon U-Pb ages confirm zircon-producing events occurring in the Proterozoic from approximately 2200 to 590 Ma; but predominantly in the Paleozoic between 550 and 60 Ma. The palaeocurrent indicators, petrographic data, heavy mineral spectra and zircon geochronology strongly suggest that the Tisza Mega-Unit Variscan crystalline basement erosion with accompanying sedimentary cover supplied the Magura Basin from the South. The Mecsek Zone is also suggested to support the Villáni-Bihor and part of the Békes-Codru zones in supplying the Magura Basin during the Eocene to Oligocene. The Eocene transport of significant detrital material to the Magura Basin is also related to erosion of the Marmarosh Massif Proterozoic–Ordovician low- to medium-grade crystalline basement. Therefore, it is most likely that Magura Basin sedimentation was dominated by supply from the sub-ophiolitic Fore-Marmarosh Suture Zone of the Eastern Carpathians.

Provenance of the Gondwana sediments, Palar Basin, Southern India

Palar Basin is considered as one of the pericratonic rift basins of East Coast of India. An integrated petrography, clay mineralogy, and heavy mineral studies of sandstone and shale from the Palar Basin South India, Tamil Nadu, have been carried out to decipher their provenance, palaeoclimate, and tectonic setting. The mineralogical make-up of the clastic rocks is largely composed of quartz followed by feldspar, rock fragments with minor amounts of chlorite, glauconite, zircon, garnet, and opaque. Palar sandstones are coarse to medium-grained and mineralogically immature (poorly sorted and few are moderately sorted). The detrital quartz grains consist of well rounded and rounded quartz, monocrystalline quartz with uniform or straight extinction, and polycrystalline grains with five crystals of straight to slightly curved intercrystalline boundaries. Few of the monocrystalline quartz contain inclusions of sillimanite, rutile, and zircon needles and low content of plagioclase and k-feldspar. These petrographic analyses of the sandstone suggest derivation from metamorphic, igneous, and reworked sediments of different grades which infer that the recycling and the clasts were subjected to both long and short transport distances. The recycled orogen provenance suggests that the sandstone has been derived predominantly from low-lying granite and gneissic sources. The framework petrography exhibits (a) higher percentage of quartz, (b) predominance of monocrystalline grains, (c) feldspar affinity, and (d) paucity of rock fragments, and low F/R ratio suggests that the sediments deposited were in a passive continental margin tectonic setting. The presence of euhedral, angular, and subrounded grains of zircon, rutile with reddish and dark boundaries, the high and moderate ZTR Index (zircon-tourmaline-rutile) and the ratio of RuZi (rutile/zircon) and GZi (garnet/zircon) low values reveal that the Palar Basin sediments were sourced from the combination of metamorphic and igneous (granite and gneisses) rock types. The presence of high amount of rock derived clay (illite, chlorite) is predominant than soil derived (kaolinite, smectite) clay minerals. The high content of illite indicates the source of the clay minerals from pre-existing rocks of granite and gneisses, subjected to physical weathering over chemical weathering in a temperate climate (hot/humid) with moderate hydrolysis.

Reduced sediment supply in a fast eroding landscape? A multi-proxy sediment budget of the upper Rhône basin, Central Alps

Alpine water and sediment supply influence the sediment budget of many important European fluvial systems such as the Rhine, Rhône and Po rivers. In the light of human induced climate change and landscape modification, it becomes increasingly important to understand the mechanisms of sediment production and supply in Alpine sediment systems. This study aims to investigate the modern sediment budget of the upper Rhône basin, one of the largest Alpine intramontane watersheds, located in the Central Alps of southwestern Switzerland. Major areas of sediment generation are fingerprinted by framework petrography, heavy mineral concentrations and bulk geochemistry. The relative contributions of the three major sources to the sediment of the trunk Rhône river are identified by compositional mixing modelling. Concentrations of the terrestrial cosmogenic nuclide 10Be measured in quartz separated from fluvial sediments provide spatially averaged denudation rates for selected tributary basins. Results from sediment fingerprinting and mixing modelling suggest that tributaries located in the North and the East of the catchment are generating most of the sediment transported by the Rhône river to its primary sedimentary sink in Lake Geneva. Despite having some of the highest denudation rates within the basin, tributaries located in the southern area of the Rhône basin are relatively underrepresented in the sediment budget of the Rhône river. These tributaries are severely affected by human activities, for example through sediment mining as well as water and sediment abstraction in large hydropower reservoirs. Together, these processes reduce the basin-wide sediment discharge by about 50%, thereby explaining most of the observed compositional pattern. In addition, there is evidence suggesting that large amounts of glaciogenic sediments are currently supplied by retreating glaciers. Glaciogenic material with its low 10Be concentrations can lead to a significant overestimation of denudation rates and thus limit the applicability of cosmogenic nuclide analysis in such glaciated settings.

Provenance and tectonic setting of the Upper Palaeozoic sandstones in western Inner Mongolia (the Shalazhashan and Solonker belts), China: insights from detrital zircon U–Pb ages and Hf isotopes

AbstractThe Solonker and Shalazhashan belts are hotly debated tectonic units of the Central Asian Orogenic Belt (CAOB), because they may either represent a Permian or Triassic suture zone of the CAOB, or a rifting zone overprinted on an Early Palaeozoic orogen. Provenance analysis of the Upper Palaeozoic sandstones in these belts may provide useful constraints on this issue. This study collected six sandstone samples from three study areas: the Mandula area of the Solonker Belt, the Quagan Qulu area of the Shalazhashan Belt but close to the Alxa block, and the Enger Us area of the Shalazhashan Belt, for framework petrography, zircon morphology, U–Pb and Lu–Hf isotopic analyses. Framework petrography reveals that the Mandula and Enger Us area samples contain high proportions of volcanic fragments, whereas the samples from the Quagan Qulu area include not only volcanic fragments but also significant amounts of biotite and muscovite. The detrital zircons of the Mandula area and the Enger Us area yield two main age groups: (i) 260–330 Ma, with dominant εHf(t) values of –5 to +12; and (ii) 420–550 Ma, with dominant εHf(t) values of –9 to +9, suggesting that Early Palaeozoic arc-related magmatic rocks and Late Palaeozoic syn-depositional volcanic rocks are the main source rocks. The detrital zircons of the Quagan Qulu area have one main age group of 420–500 Ma and some grains of 0.9–1.1 Ga, 1.4–1.5 Ga, 1.8–1.9 Ga and ~ 2.5 Ga, which derive from the northern margin of the Alxa block. The lithological and fossil assemblages of the Upper Palaeozoic sandstones suggest shallow-marine to deep-water depositional environments and a northward-deepening transition. Based on the zircon spectra, sedimentary environment analysis and previous studies, we argue that the Solonker Belt and the Shalazhashan Belt of the CAOB are in extensional basins of a fore-arc or rifting setting.

Evolution of the northern Albertine Rift reflected in the provenance of synrift sediments (Nkondo-Kaiso area, Uganda)

Rift sediments are important archives for the evolution of the East African Rift System. We present a source-to-sink study of the Nkondo-Kaiso area in the northern Albertine Rift from a ∼200 m thick late Miocene to early Pleistocene sediment succession. The multi-proxy provenance analysis includes framework petrography, heavy mineral studies and single grain studies of garnet and rutile. Mineral textures and provenance signatures indicate two major stages. Sediment of Stage 1 (late Miocene - late Pliocene; ∼6.5–2.6 Ma) is less mature with quartz contents of 58–81%, K-feldspar of 9–15%, plagioclase of 4–15%, and rock fragments of 1–9%. Heavy mineral spectra are dominated by epidote and amphibole with minor abundances of zircon, sillimanite and garnet. Garnet is almandine-rich and can be grouped according to grossular contents (<10% and >10%). Rutile exhibits a wide range of Nb and Cr concentrations, most of them typical for a metapelitic origin. Zr-in-rutile formation temperatures range between ∼570 and 940 °C. Garnet and rutile geochemistry mainly correspond to amphibolite-to granulite-facies igneous and metasedimentary rocks, which exist in the Mesoarchean Karuma Group and the Neoarchean granitoid gneiss of the North Uganda Terrane. Both are part of the adjacent eastern rift flank of the Albertine Rift. A slight change of the heavy mineral composition at ∼4.5 Ma can be correlated with the onset of the synrift stage ∼0.5–1.0 Ma later than in the southern Albertine Rift. Sediment of Stage 2 (early Pleistocene ∼2.6–1.0 Ma) shows a higher quartz content of 82–93%, and lower contents of K-feldspar of 5–11%, plagioclase of 1–7%, and rock fragments of 1–2%. Stable heavy minerals (ZTR index: 19–63) and epidote dominate with minor amphibole and garnet. Rutile and garnet chemical compositions remain largely unchanged to Stage 1 pointing to the same primary source. Obviously, Pleistocene sediment was mainly recycled from sedimentary rocks of the Neoproterozoic Bunyoro Group, which originate from identical Archean rock assemblages. Ongoing river incision reactivated the primary Archean source in the upper part of Stage 2. In conclusion, Miocene to Pleistocene sediment of the Nkondo-Kaiso region is supplied from local sources of the rift flank and the adjacent Ugandan plateau. Tectonic pulses at ∼4.5 Ma, ∼2.6 Ma, and ∼1.5 Ma led to river incision and moderate expansion of drainage basins towards the east. These pulses are roughly coincident with other parts of the EARS but also show regional time lag and delayed response of the source-to-sink system.

Palaeoenvironment and provenance in the early Cape Basin of southwest Gondwana: sedimentology of the Lower Ordovician Piekenierskloof Formation, Cape Supergroup, South Africa

The lowermost unit of the Table Mountain Group (Cape Supergroup), the Ordovician Piekenierskloof Formation is a siliciclastic succession that formed during the initial stages of the Cape Basin development in southwest Gondwana. This contemporary sedimentological re-evaluation of the depositional history and provenance of the Piekenierskloof Formation provides new insights into the palaeoenvironment and tectonic setting of the early Cape Basin. Outcrop-based sedimentary facies analysis revealed distinctive depositional features, dominated by large trough cross-bedding, which suggest a shallow, perennial, sand-bed braided fluvial style with bedload transportation in roughly 1 to 2.5 m deep and relatively wide channels. This fluvial style was possibly influenced by the global absence of substrate stabilizing terrestrial flora in pre-Devonian rivers. Based on an integrated approach of clast count, framework petrography and palaeocurrent studies, the provenance analysis show that the source rocks of the Piekenierskloof Formation were likely situated in source areas characterized by two main rock types: (1) a dominant low metamorphic rank metasedimentary rock suite with parent rocks of variable grain-size, and (2) minor plutonic rocks. The data also suggest that the parent rocks were locally intruded by quartz veins and/or pegmatites. Consistent palaeoflow to the southeast and east further indicates that these source areas were located to the northwest and west of the clastic sediment depocentres in the Cape Basin of southwest Gondwana in the Early Ordovician. Accessible outcrops of the Piekenierskloof Formation are mostly laterally limited and sparsely distributed, which hinder stratigraphic correlations, and therefore inferences of tectonic activity during the sedimentation in the Early Ordovician cannot be convincingly made. For a better understanding of the Early Palaeozoic evolution of the Cape Basin in southwest Gondwana, systematic outcrop studies acquiring high-resolution digital imagery using unmanned aerial vehicles (UAVs) and terrestrial laser scanning, coupled with subsurface facies analysis should be undertaken. The Piekenierskloof Formation and the rest of the Table Mountain Group, with their exceptionally extensive, but rather inaccessible cliff faces, are excellent candidates for such high-resolution digital-based studies.

Detrital zircon U–Pb ages and Hf isotopes of Permo-Carboniferous sandstones in central Inner Mongolia, China: Implications for provenance and tectonic evolution of the southeastern Central Asian Orogenic Belt

The tectonic setting of the southeastern Central Asian Orogenic Belt (CAOB) during the Late Paleozoic has been debated for many years. Provenance analysis of Permo-Carboniferous sedimentary rocks can effectively address this issue. In this study, eight sandstone samples were collected for zircon U–Pb and Lu–Hf isotopic analyses combined with petrographic analysis. Framework petrography and zircon morphology suggest that the samples were from recycled orogen of an igneous origin. Carboniferous rocks, with a significant age peak at 432Ma and εHf (t) values of −9.0 to 13.6, were mainly derived from Early to Mid-Paleozoic magmatic rocks and deposited in a piedmont zone, namely, the margin of an inland sea. Permian rocks, mostly with age peaks at 445Ma and/or 280Ma and εHf (t) values of −25.2 to 11.4, dominantly originated from a pre-existing Early to Mid-Paleozoic magmatic arc and Late Paleozoic igneous rocks. These rocks formed in restricted basins of the piedmont and intermountain zones. Based on zircon spectral discrimination, sedimentary environmental analysis, and previous studies, this study supports the interpretation that the southeastern CAOB entered stages of extension and rifting during the Late Paleozoic. In the end, this study proposes a tectonic-paleogeographic reconstruction to explain the tectonic evolution of the southeastern CAOB and the exhumation–transportation–deposition processes between the basins and ranges developed in this orogen.

Provenance of the Middle Permian Zhesi Formation in central Inner Mongolia, northern China: constraints from petrography, geochemistry and detrital zircon U-Pb geochronology

The exceptionally thick Middle Permian Zhesi Formation is considered key to understanding the late Palaeozoic tectonic setting of the North China–Mongolia segment of the Central Asian Orogenic Belt, yet its sedimentary environment and provenance remain ambiguous. An integrated approach incorporating detailed field observation and measurement, framework petrography, whole-rock geochemistry and detrital zircon U–Pb geochronology is applied here to investigate this problem. The framework petrography and whole-rock geochemical characteristics jointly suggest that the Zhesi Formation was derived primarily from felsic upper continental crust, with the source rocks undergoing intermediate weathering and short-distance transportation. Furthermore, the source rocks were composed of granites/granitoids that occurred in a transitional recycled orogen. LA–ICP-MS U–Pb detrital zircon data from sandstone samples show two main age groups of 480–410 and 290–265 Ma. Accordingly, we deduce that the dominant provenance of the Zhesi Formation was northerly early to mid-Palaeozoic orogenic belt, late Palaeozoic granites/granitoids and volcanics, with a possible contribution from the Hunshandake Block. The subsiding depositional environment of this succession is in response to the Middle Permian extensional tectonic setting of the orogenic belt. Copyright © 2015 John Wiley & Sons, Ltd.

Provenance of Paleocene–Eocene red beds from NE Iraq: constraints from framework petrography

AbstractThe red-bed deposits in northern Iraq are situated in an active foreland basin adjacent to the Zagros Orogenic Belt, bound to the north by the Iranian plate thrust over the edge of the Arabian plate. The red-bed successions are composed of alternating red and brown silty mudstones, purplish red calcareous siltstone, fine- to coarse-grained pebbly sandstone and conglomerate. The red beds in the current study can be divided into four parts showing a trend of upward coarsening with fine-grained deposits at the top. A detailed petrographic study was carried out on the sandstone units. The clastic rocks consist mainly of calcite cemented litharenite with rock fragments (volcanic, metamorphic and sedimentary), quartz and minor feldspar. The petrographic components reflect the tectonic system in the source area, laterally ranging from a mixed orogenic and magmatic arc in Mawat–Chwarta area to recycled orogenic material rich in sedimentary rock fragments in the Qandel area. The Cretaceous–Palaeogene foreland basin of northern Iraq formed to the southwest of the Zagros Suture Zone and the Sanandaj–Sirjan Zone of western Iran. During Palaeogene time deposition of the red beds was caused by renewed shortening in the thrust sheets overlying the Arabian margin with uplift of radiolarites (Qulqula Formation), resulting in an influx of radiolarian debris in addition to continuing ophiolitic detritus. Mixed sources, including metamorphic, volcanic and sedimentary terranes, were present during deposition of the upper part of the red beds.

Provenance of Tertiary sandstone in the northern Qaidam basin, northeastern Tibetan Plateau: Integration of framework petrography, heavy mineral analysis and mineral chemistry

An exceptionally thick Cenozoic sedimentary succession has developed in the Qaidam basin of the northeastern Tibetan Plateau. The provenance remains enigmatic; thus, more precise investigations are needed. An integrated study of sandstone framework petrography, heavy mineral analysis and mineral chemistry was adopted to perform provenance analysis of the Tertiary sandstones in the northern Qaidam basin.No individual method exists that can provide comprehensive provenance interpretations on spatial and temporal variations. Based on three types of data, three depositional areas can be distinguished. Sandstones of Area A exhibit relatively high abundances of quartz, garnet and zircon, as well as relatively high textural maturity, implying long-distance sources. Multi-composition garnets and tourmalines reveal derivations of metasedimentary rocks and intermediate-acidic igneous rocks. Sandstones of Area B are rich in metamorphic lithic fragments, epidote and garnet. A dominance of Fe-rich garnets with low Mg, low Mn and variable Ca contents and dravites demonstrates predominant derivation of metasedimentary rocks. Therefore, the North Qaidam and South Qilian terranes are potential source areas for these two depositional areas. Additionally, high metamorphic heavy mineral abundances in the upper formations imply increasing contributions of these two metamorphic belts during the Tertiary tectonic uplift. However, sandstones of Area C are characterized by relatively high abundances of feldspar, igneous heavy minerals and high-Fe+Mn garnet, which suggest a main source of igneous rocks. The Altun and Qilian Mountains are potential source regions. Furthermore, increasing amounts of feldspar and igneous heavy minerals in the upper formations indicate a significant presence of igneous parent rocks, which are most likely a response to the multi-stage uplift events in the Altun Mountains since the early Eocene.