| 1. |
- Abadi, Mehrdad Sardar, et al.
(författare)
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A comment on overlooked storm sensitivity of the carbonate factory recorded in the Mississippian Mobarak Formation (Alborz Mountains, Iran)
- 2022
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Ingår i: Geological Journal. - : John Wiley & Sons. - 0072-1050 .- 1099-1034. ; 57:10, s. 4388-4392
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- New interpretations of depositional palaeoenvironments in the Mississippian (Lower Carboniferous) Mobarak Formation (Alborz Mountains, Iran) suggest a significant and persistent influence of storms. This deviates from previous conclusions that these deposits recorded mounds, patch reefs, and extensive lagoons deposited under stagnant environmental conditions. We here clarify and discuss the origin and nature of this misconception by explaining "unexpected" observations that are informed by outdated interpretations of the depositional environment of the Mobarak Formation. This evaluation offers the context required for appropriately interpreting and correlating Mississippian depositional records across the Alborz Basin.
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| 2. |
- Appelquist, Karin, 1979, et al.
(författare)
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Character and origin of variably deformed granitoids in central southern Sweden: implications from geochemistry and Nd isotopes
- 2011
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Ingår i: Geological Journal. - : Wiley. ; 46:6, s. 597-618
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Tidskriftsartikel (refereegranskat)abstract
- We present major and trace element data for eighteen 1.71–1.66 Ga granitoid samples, and Sm–Nd whole‐rock isotope data for eleven of these samples, in a transect across the border between the Transscandinavian Igneous Belt (TIB) and the Eastern Segment in central southern Sweden. The geochemistry of the granitoids varies from alkalic to alkali‐calcic and peraluminous in the east to predominantly calc‐alkaline and metaluminous in the west. Rocks in the west also have lower SiO2 contents. Trace element signatures favour formation in an active continental margin setting. Nd isotope data are completely overlapping along the transect and initial εNd values are mildly depleted in the range +0.3 to +2.6. The combined data suggest that the magmas were derived mainly from juvenile, pre‐existing crust, increasingly mafic and less alkaline towards the west.
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| 3. |
- Johansson, Åke, et al.
(författare)
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Petrogenesis and geotectonic setting of early Svecofennian arc cumulates in the Roslagen area, east-central Sweden
- 2012
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Ingår i: Geological Journal. - : Wiley. - 0072-1050 .- 1099-1034. ; 47:6, s. 557-593
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Tidskriftsartikel (refereegranskat)abstract
- Several intrusions of ultrabasic to basic composition occur in the Roslagen area of east-central Sweden in close spatial and temporal association with the surrounding 1.90-1.87Ga old early orogenic Svecofennian granitoids. An imprecise Sm-Nd WR errorchron yields an age of 1895±71Ma. In spite of the penetrative deformation in the granitoids, the basic-ultrabasic rocks mostly appear undeformed and largely preserve magmatic textures with plagioclase, olivine (in some rock types), orthopyroxene and clinopyroxene, and amphibole as major constituents. The plagioclase is typically very anorthitic (ca. An 90). The Roslagen intrusions range in composition from primitive to evolved (Mg# 80 to 49) but contain only 40-50wt% SiO 2. Many samples are highly elevated in Al 2O 3 (up to 30wt%), CaO (up to 16wt%) and Sr (up to 800ppm), with strongly positive Eu and Sr anomalies, in line with being plagioclase cumulates. Although masked by cumulus effects, the relative trace element contents indicate a volcanic arc signature. The initial Nd isotope composition is homogeneously 'mildly depleted', with ε Nd of +0.3 to +1.1, and the initial Sr isotope composition 'mildly enriched', with ε Sr of +8 to +15. Non-cumulus rocks with small Eu and Sr anomalies can be used to deduce the composition of the parental magma. This LILE- and LREE-enriched and HFSE-depleted high-alumina basalt magma, with Mg# of ca. 50-60 and Ca# of ca. 80, most likely formed by partial melting of mantle material, enriched by fluids in a subduction environment, at 1.9Ga. The cumulate rocks apparently crystallized from a somewhat more evolved water-rich magma with Mg# of ca. 40. Crystallization was followed by the development of late-magmatic to post-magmatic coronas between olivine and plagioclase in the presence of H 2O-rich fluids. The subduction-related setting would make these intrusions Palaeoproterozoic counterparts of Alaskan-type ultramafic intrusions, but they differ from those in being plagioclase enriched, possibly reflecting different levels of exposure.
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| 4. |
- Morad, Sadoon, et al.
(författare)
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Hydrothermal alteration of plagioclase in granitic rocks from Proterozoic basement of SE Sweden
- 2010
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Ingår i: Geological Journal. - : Wiley. - 0072-1050 .- 1099-1034. ; 45:1, s. 105-116
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Tidskriftsartikel (refereegranskat)abstract
- Petrographic examinations and electron microprobe analyses of Proterozoic granitic rocks, SE Sweden aimed to characterize and unravel the mechanisms and conditions of plagioclase alterations. These alterations include saussuritization, albitization and replacement of plagioclase by K-feldspar. The hydrothermal alterations, which are inferred to have occurred at ca. 250-400°C, resulted in concomitant formation of Alrich titanite, epidote, calcite, pumpellyite, prehnite and iron oxides. Replacement of plagioclase by K-feldspar occurs in red-stained zones, which have developed close to thin fractures owing to the precipitation of tiny Fe-oxide pigment particles within the altered plagioclase, whereas saussuritized plagioclase has less systematic spatial relationships to these fractures. Albitization of plagioclase occurred in rocks that are poor in biotite compared to rocks that suffered extensive saussuritization. The chemical and textural characterization of various types of plagioclase alterations allows elucidation of the granitic hydrothermal systems. Features of feldspar alteration in the granitic rocks are similar to those encountered in feldspathic sandstones and should hence be considered in studies on diagenetic changes of siliciclastic successions during basin evolution.
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| 5. |
- Peel, John S., et al.
(författare)
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An association of problematic corals, crinoids and parasites from the Sholeshook Limestone Formation (Ordovician) of Wales
- 2016
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Ingår i: Geological Journal. - : Wiley. - 0072-1050 .- 1099-1034. ; 51:2, s. 212-222
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Tidskriftsartikel (refereegranskat)abstract
- Coralla of the solitary coral Talfania calicula gen. et sp. nov. from the Upper Ordovician (Ashgill Series; Katian Stage) of Llanddowror, South Wales, UK, are often coiled around crinoid columnals, suggesting a premortem association between some of the corals and living crinoids. Irregularities within the deepest part of the open calice imply infestation of T. calicula by parasitic worms. Talfania calicula is distinguished from contemporaneous rugose corals by its lack of septa within the calice and its systematic position within Zoantharia is unresolved. Pitted calical grooves are interpreted as attachment scars of desmocytes connecting the soft tissues to the exoskeleton. Coral and crinoid remains in the assemblage are bored by postmortem microendoliths.
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| 6. |
- Rao, C.V. Dharma, et al.
(författare)
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New constraints on the metamorphic evolution of the Eastern Ghats Belt, India, based on relict composite inclusions in garnet from ultrahigh-temperature sapphirine granulites
- 2011
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Ingår i: Geological Journal. - : Wiley. - 0072-1050 .- 1099-1034. ; 46:2-3, s. 240-262
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Tidskriftsartikel (refereegranskat)abstract
- The sapphirine granulites from Gangaraju Madugula, Eastern Ghats Belt (EGB), India preserve a rich variety of mineral assemblages and unique isolated and composite mineral inclusions within garnet that provide robust evidence for extreme crustal metamorphism at ultrahigh temperature (UHT) conditions (>900°C). Diagnostic UHT assemblages in these rocks include sapphirine + quartz, spinel + quartz and high alumina orthopyroxene + sillimanite + quartz. The stability of spinel + quartz, sapphirine + quartz and orthopyroxene + sillimanite + quartz assemblages provides evidence for temperatures exceeding 960°C at moderate pressures. The mineral association of garnet–orthopyroxene is indicative of a subsequent high P–UHT metamorphic event as indicated by the high alumina contents of orthopyroxene (>10 wt% Al2O3) coexisting with garnet. Peak P–T conditions of ∼970°C and 9.5 kbars are calculated from conventional garnet–orthopyroxene geothermobarometry. Calculated isochemical sections constructed in the model system Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–Fe2O3 (NCKFMASHTO) for the sapphirine granulites and garnet–orthopyroxene granulites adequately predict phase relationships that are consistent with those observed in the rocks. An evaluation of the assemblages and textures and P–T estimates indicate a three-stage evolution of the sapphirine granulites and associated garnet–orthopyroxene granulites: (1) inclusion assemblages with sapphirine, spinel and quartz on the low-pressure prograde path (M1 stage); (2) a peak UHT assemblage of porphyroblastic garnet–orthopyroxene (M2 stage) and (3) a retrogression that resulted in orthopyroxene–cordierite intergrowths and biotite rims on Grt (M3 stage). The sapphirine granulites and associated garnet–orthopyroxene granulites indicate that they grew during the prograde and retrograde stage. The thermo-barometric estimates from mineral compositions and the complimentary isochemical sections approached from bulk rock compositions allow tighter constraints to be placed on the P–T evolution of this sector of the EGB.
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| 7. |
- Yousefi, Fazilat, et al.
(författare)
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Petrology, petrogenesis, and geochronology review of the Cenozoic adakitic rocks of northeast Iran : Implications for evolution of the northern branch of Neo‐Tethys
- 2021
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Ingår i: Geological Journal. - : John Wiley & Sons. - 0072-1050 .- 1099-1034. ; 56:1, s. 298-315
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Tidskriftsartikel (refereegranskat)abstract
- Cenozoic adakitic rocks of the northern part of the Central Iran Structural Zone (CISZ) are among the notable geological features of the terrains in northeast Iran, so a comprehensive comparison of several of these adakitic sequences is presented. This lithogeochemical analysis is constrained to examining adakitic magmatism of the three magmatic belts within the CISZ, which from southeast to northeast and from oldest to youngest are as follows: (a) south of Shahrood‐Damghan, (b) north‐northwest of Sabzevar‐Neyshabour, and (c) south of Qouchan and west of Esfarayen. Radiogenic isotope analysis using Rb–Sr and Sm–Nd methods show that the adakitic rocks associated with Qouchan‐Esfarayen magmatism have 0.512581 to 0.51288 initial 143Nd/144Nd and 0.703903 to 0.705627 initial 87Sr/86Sr, with εNd −0.86 to 4.98. Adakitic rocks in south to southeast Shahrood have 0.512775 to 0.512893 initial 143Nd/144Nd and 0.703746 to 0.705314 initial 87Sr/88Sr, with εNd 3.69 to 6.0, and adakites emplaced into the Sabzevar ophiolite have 0.512846 to 0.512911 initial 143Nd/144Nd and 0.70379 to 0.705019 initial 87Sr/86Sr contents with εNd of 5.26 to 6.54. Isotopic initial ratios of Nd and Sr support an origin involving partial melting of the subducting oceanic lithosphere of the northern branch of Neo‐Tethys and the associated suprasubduction mantle wedge in producing these adakitic rocks.
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| 8. |
- Zhang, Wen, et al.
(författare)
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Recognition of a Devonian‐early Mississippian plutonic belt in the eastern Beishan area, Northwest China, and its tectonic implications
- 2018
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Ingår i: Geological Journal. - : Wiley. - 0072-1050 .- 1099-1034. ; 53:3, s. 803-819
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Tidskriftsartikel (refereegranskat)abstract
- The Beishan area, located in the southernmost part of the Central Asia Orogenic Belt, is crucial for understanding the tectonic evolution associated with the closure of the Paleo‐Asian Ocean. One intermediate and two granitic plutons from the eastern Beishan area between Mingshui–Shibanjing–Xiaohuangshan (MSX) and Niujuanzi–Xichangjing (NX) ophiolitic belts, including Tongchangkou gabbroic diorite, Northern Tongchangkou and Sandaomingshui plutons, are dated at 426 ± 3, 408 ± 2, and 365 ± 2 Ma by SIMS U–Pb zircon analyses. The Middle Silurian Tongchangkou gabbroic diorites with medium‐K calc‐alkaline metaluminous characteristics represent volcanic arc rocks. The Early Devonian Northern Tongchangkou pluton, a highly evolved calc‐alkaline mylonitic monzogranite with low εNd(t), −3.5 and −2.4, and relatively low initial 87Sr/86Sr (0.707095 and 0.707249), was mainly derived from Mesoproterozoic mafic to intermediate igneous protolith and shows both volcanic arc and postcollisional characteristics. The Late Devonian Sandaomingshui pluton, a calc‐alkaline granite with slightly positive εNd(t), 0.6 and 0.9, and low (87Sr/86Sr)t, 0.705543 and 0.705851, is likely from a more depleted source and represents a volcanic arc granite. Combined with previous studies of Late Paleozoic granites, we find that the widely distributed Permian granites in Central Asia Orogenic Belt are absent between MSX and NX ophiolitic belts. Given the regional geology, we conclude that the back‐arc basin represented by the NX ophiolitic belt closed during Early Devonian and afterward, flat subduction of the oceanic basin represented by the MSX ophiolitic belt occurred. It also indicates that the oceanic crust was still being produced in the Paleo‐Asian Ocean during the early Carboniferous.
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| 9. |
- Friberg, M, et al.
(författare)
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Structure of the middle Urals, east of the Main Uralian Fault
- 1998
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Ingår i: GEOLOGICAL JOURNAL. - : JOHN WILEY & SONS LTD. - 0072-1050. ; 33:1, s. 37-48
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- In the Middle Urals, volcanic-are and back-are basin rocks of Ordovician to Devonian age occur in the Tagil Synform. These outboard terranes were thrust westwards in the late Carboniferous onto continental margin associations of late Proterozoic and Palae
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| 10. |
- Joy, Sojen, et al.
(författare)
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Depositional history and provenance of cratonic “Purana” basins in southern India : A multipronged geochronology approach to the Proterozoic Kaladgi and Bhima basins
- 2019
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Ingår i: Geological Journal. - : Wiley. - 0072-1050. ; 54:5, s. 2957-2979
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Tidskriftsartikel (refereegranskat)abstract
- Peninsular India is a collage of Archaean cratonic domains separated by Proterozoic mobile belts. A number of cratonic basins, known as “Purana basins” in the Indian literature, formed in different parts of the Indian Peninsula during extensional tectonic events, from Paleoproterozoic through Neoproterozoic times. In this contribution, we present a diversity of new geochronological data for different units within the Kaladgi and the Bhima basins, which overlie the western and eastern Dharwar cratons, respectively. The new geochronology data are discussed in terms of depositional history and provenance of these poorly understood Proterozoic intracratonic basins. For the Kaladgi Group, a U–Pb baddeleyite age of 1,861 ± 4 Ma obtained for a dolerite dyke intruding the Yendigere Formation is used to constrain the minimum age of deposition of the lower Kaladgi Group. This result demonstrates that this part of the succession is comparable in age to the Papaghni Group of the Cuddapah Basin, heralding onset of Purana sedimentation at ~1,900 Ma. The detrital zircon populations from the clastic rocks of the Kaladgi and Bhima basins show unique and distinct age patterns indicating different source of sediments for these two basins. Palaeocurrent analysis indicates a change in provenance from south or southeast to west or northwest between the Kaladgi and Bhima clastic sedimentation. New U–Th–Pb and Rb–Sr radiometric dates of limestones and glauconite-bearing sandstones of the Bhima Group (Bhima Basin) and the Badami Group (Kaladgi Basin) indicate deposition at around 800–900 Ma, suggesting contemporaneity for the two successions. Thus, the unconformity between the Kaladgi Group and the overlying Badami Group represents a time gap of up to 1,000 Myr. These new results demonstrate the complex multistage burial and unroofing history of the Archaean Dharwar Craton throughout the Proterozoic, with important implications for exploration of metal deposits and diamonds in Peninsular India.
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| 11. |
- Land, J. S., et al.
(författare)
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Origin of red beds and paleosols in the Palaeoproterozoic Transvaal and Olifansthoek Supergroups of South Africa: provenance versus metasomatic controls
- 2018
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Ingår i: Geological Journal. - : Wiley. - 0072-1050. ; 53:1, s. 191-202
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Tidskriftsartikel (refereegranskat)abstract
- The Palaeoproterozoic Transvaal and Olifantshoek Supergroups of South Africa contain some of the earliest hematite-rich sedimentary rocks (red-beds) and paleosols on record. The origin of these rocks has been variously attributed to surface processes under an oxygenated atmosphere that post-dated the ca. 2.3Ga Great Oxidation Event (GOE). Interpretations of their geochemical signatures, however, have been inconclusive with respect to the causes of the apparent K-enrichment that these rocks record. Here, we re-visit the basal Mapedi Formation of the Olifantshoek Supergroup and the unconformably underlying Drakenstein palaeo-weathering profile that develops against the Ongeluk Formation of the upper Transvaal Supergroup, and present new petrographic and geochemical data in an attempt to constrain the burial metasomatic history of these rocks. Apart from the strong hematitic nature and K-metasomatic overprint seen in both the Mapedi Formation and Ongeluk paleosol, a curious and hitherto unexplored enrichment in high-field strength elements (HFSEs: Ti, Nb, Y, Zr, REE, etc.) by several orders of magnitude higher than average shale characterizes the lower part of the Mapedi Formation as examined here. We show that such enrichments cannot be explained by normal source-to sink weathering processes, unless an unlikely provenance of special geochemical composition (i.e. alkali igneous rocks) is to be invoked. We conclude that the HFSE enrichment, K-metasomatism and evidently transgressive Fe-oxidation effects in the Mapedi shales can only be accounted for via post-depositional fluid-rock interaction, possibly involving F-bearing diagenetic brines. This opens the distinct possibility that such fluids may have also been implicated in alteration processes, enhanced Fe mobility and development of epigenetic hematitic iron-ores as seen at the Transvaal-Olifantshoek unconformity on regional scales. Copyright (c) 2017 John Wiley & Sons, Ltd.
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| 12. |
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| 13. |
- Torres Sánchez, Sonia Alejandra, et al.
(författare)
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Magmatic source and metamorphic grade of metavolcanic rocks from the Granjeno Schist : Was northeastern Mexico a part of Pangaea?
- 2016
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Ingår i: Geological Journal. - : Wiley. - 0072-1050. ; 51:6, s. 845-863
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Tidskriftsartikel (refereegranskat)abstract
- The geochemistry of the metavolcanic rocks from the Granjeno Schist in northeastern Mexico indicates an origin in different tectonic environments: mid-ocean ridge and ocean island. High ratios of Hf/Th and Th/Nb (4.4-14 and 0.08-0.15), low ratios of LaN/YbN and LaN/SmN (0.74-1.7 and 0.60-1.4) and depleted LREE patterns in metabasalt display mid-ocean ridge characteristics. In contrast, the pattern of trace-element ratios and REEs in metabasalt and metapillow lava 60km to the west indicates a magma source with ocean-island basalt characteristics. Both areas were metamorphosed during the Late Carboniferous (300±4Ma). Estimated metamorphic conditions deduced from white mica and chlorite compositions, distinguish greenschist facies (350°C and 4kbar) for the mid-ocean ridge basalt, and prehnite-pumpellyite facies (250°C and 2.5kbar) for the ocean-island-type basalt. This metamorphism took place at an active continental margin during Pennsylvanian time. Our new tectonic model, which differs from earlier models, suggests that the origin of the Granjeno Schist is related to a subduction zone located at the western margin of Pangaea, active after Laurentia-Gondwana collision.
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| 14. |
- Westerlund, Joakim, et al.
(författare)
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Can panel data really improve the predictability of the monetary exchange rate model?
- 2007
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Ingår i: Journal of Forecasting. - : Wiley. - 1099-131X .- 0277-6693. ; 26:5, s. 365-383
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Tidskriftsartikel (refereegranskat)abstract
- A common explanation for the inability of the monetary model to beat the random walk in forecasting future exchange rates is that conventional time series tests may have low power, and that panel data should generate more powerful tests. This paper provides an extensive evaluation of this power argument to the use of panel data in the forecasting context. In particular, by using simulations it is shown that although pooling of the individual prediction tests can lead to substantial power gains, pooling only the parameters of the forecasting equation, as has been suggested in the previous literature, does not seem to generate more powerful tests. The simulation results are illustrated through an empirical application. Copyright (C) 2007 John Wiley & Sons, Ltd.
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