The Lower Silurian Osmundsberg K-bentonite. Part II: mineralogy, geochemistry, chemostratigraphy and tectonomagmatic significance

1998 ◽  
Vol 135 (1) ◽  
pp. 15-26 ◽  
Author(s):  
WARREN D. HUFF ◽  
STIG M. BERGSTRÖM ◽  
DENNIS R. KOLATA ◽  
HEPING SUN
Keyword(s):  
Melt Inclusions ◽  
Tectonic Setting ◽  
Analytical Data ◽  
Clay Fraction ◽  
Parental Magma ◽  
Margin Setting ◽  
Lower Silurian ◽  
Regional Correlation ◽  
Tectonically Active ◽  
Chemical Fingerprinting

The Lower Silurian Osmundsberg K-bentonite is a widespread ash bed that occurs throughout Baltoscandia and parts of northern Europe. This paper describes its characteristics at its type locality in the Province of Dalarna, Sweden. It contains mineralogical and chemical characteristics that permit its regional correlation in sections elsewhere in Sweden as well as Norway, Estonia, Denmark and Great Britain. The <2 μm clay fraction of the Osmundsberg bed contains abundant kaolinite in addition to randomly ordered (RO) illite/smectite (I/S). Modelling of the X-ray diffraction tracings showed the I/S consists of 18% illite and 82% smectite. The high smectite and kaolinite content is indicative of a history with minimal burial temperatures. Analytical data from both pristine melt inclusions in primary quartz grains as well as whole rock samples can be used to constrain both the parental magma composition and the probable tectonic setting of the source volcanoes. The parental ash was dacitic to rhyolitic in composition and originated in a tectonically active collision margin setting.Whole rock chemical fingerprinting of coeval beds elsewhere in Baltoscandia produced a pronounced clustering of these samples in the Osmundsberg field of the discriminant analysis diagram. This, together with well-constrained biostratigraphic and lithostratigraphic data, provides the basis for regional correlation and supports the conclusion that the Osmundsberg K-bentonite is one of the most extensive fallout ash beds in the early Phanerozoic. The source volcano probably lay to the west of Baltica as part of the subduction complex associated with the closure of Iapetus.

scholarly journals Parental magma of the Skaergaard intrusion: constraints from melt inclusions in primitive troctolite blocks and FG-1 dykes

2009 ◽  
Vol 159 (1) ◽  
pp. 61-79 ◽  
Author(s):  
Jakob K. Jakobsen ◽  
Christian Tegner ◽  
C. Kent Brooks ◽  
Adam J. R. Kent ◽  
Charles E. Lesher ◽  
...  
Keyword(s):  
Melt Inclusions ◽  
Parental Magma ◽  
Skaergaard Intrusion

scholarly journals Origin of alkali-rich volcanic and alkali-poor intrusive carbonatites from a common parental magma

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Ivan F. Chayka ◽  
Vadim S. Kamenetsky ◽  
Nikolay V. Vladykin ◽  
Alkiviadis Kontonikas-Charos ◽  
Ilya R. Prokopyev ◽  
...  
Keyword(s):  
Empirical Evidence ◽  
Fractional Crystallization ◽  
Melt Inclusions ◽  
Parental Magma ◽  
Progressive Increase ◽  
Topical Problem ◽  
Oldoinyo Lengai ◽  
Southern Siberia ◽  
Magmatic Stage ◽  
Common Parent

AbstractThe discrepancy between Na-rich compositions of modern carbonatitic lavas (Oldoinyo Lengai volcano) and alkali-poor ancient carbonatites remains a topical problem in petrology. Although both are supposedly considered to originate via fractional crystallization of a “common parent” alkali-bearing Ca-carbonatitic magma, there is a significant compositional gap between the Oldoinyo Lengai carbonatites and all other natural compositions reported (including melt inclusions in carbonatitic minerals). In an attempt to resolve this, we investigate the petrogenesis of Ca-carbonatites from two occurrences (Guli, Northern Siberia and Tagna, Southern Siberia), focusing on mineral textures and alkali-rich multiphase primary inclusions hosted within apatite and magnetite. Apatite-hosted inclusions are interpreted as trapped melts at an early magmatic stage, whereas inclusions in magnetite represent proxies for the intercumulus environment. Melts obtained by heating and quenching the inclusions, show a progressive increase in alkali concentrations transitioning from moderately alkaline Ca-carbonatites through to the “calcite CaCO3 + melt = nyerereite (Na,K)2Ca2(CO3)3” peritectic, and finally towards Oldoinyo Lengai lava compositions. These results give novel empirical evidence supporting the view that Na-carbonatitic melts, similar to those of the Oldoinyo Lengai, may form via fractionation of a moderately alkaline Ca-carbonatitic melt, and therefore provide the “missing piece” in the puzzle of the Na-carbonatite’s origin. In addition, we conclude that the compositions of the Guli and Tagna carbonatites had alkali-rich primary magmatic compositions, but were subsequently altered by replacement of alkaline assemblages by calcite and dolomite.

Neoproterozoic Amdo and Jiayuqiao microblocks in the Tibetan Plateau: Implications for Rodinia reconstruction

2020 ◽  
Author(s):  
Yiming Liu ◽  
Yuhua Wang ◽  
Sanzhong Li ◽  
M. Santosh ◽  
Runhua Guo ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
South China ◽  
Tectonic Setting ◽  
Parental Magma ◽  
Tibet Plateau ◽  
Geochemical Data ◽  
The Tibetan Plateau ◽  
South China Craton ◽  
Neoproterozoic Magmatism ◽  
T Values

The Tibetan Plateau is composed of several microblocks, the tectonic affinity and paleogeographic correlations of which remain enigmatic. We investigated the Amdo and Jiayuqiao microblocks in central Tibet Plateau with a view to understand their tectonic setting and paleogeographic position within the Neoproterozoic supercontinent Rodinia. We present zircon U-Pb and Lu-Hf isotope, and whole-rock geochemical data on Neoproterozoic granitic gneisses from these microblocks. Zircon grains from the Jiayuqiao granitic gneiss yielded an age of 857 ± 9 Ma with variable εHf(t) values (−8.9 to 4.0). The Amdo granitic gneisses yielded ages of 893 ± 5 Ma, 807 ± 5 Ma, and 767 ± 11 Ma, with εHf(t) values in the range of −4.9 to 3.5. Geochemically, the granitoids belong to high-K calc-alkaline series, with the protolith derived from partial melting of ancient crustal components. The ascending parental magma of the Amdo granitoids experienced significant mantle contamination as compared to the less contaminated magmas that generated the Jiayuqiao intrusions. In contrast to the Lhasa, Himalaya, South China, and Tarim blocks, we suggest that the Amdo and Jiayuqiao microblocks probably formed a unified block during the Neoproterozoic and were located adjacent to the southwestern part of South China craton. The Neoproterozoic magmatism was probably associated with the subduction of the peripheral ocean under the South China craton and the delamination of lithospheric mantle beneath the Jiangnan orogen.

Geochemistry and zircon U–Pb–Hf isotopes of the Mante Aobao granite porphyry at East Ujimqin Banner, Inner Mongolia: implications for petrogenesis and tectonic setting

2019 ◽  
Vol 157 (7) ◽  
pp. 1068-1086
Author(s):  
Fei Hu ◽  
Wei Huang ◽  
Zeli Yang ◽  
Simon A. Wilde ◽  
Harald Furnes ◽  
...  
Keyword(s):  
Inner Mongolia ◽  
Saturation Index ◽  
Tectonic Setting ◽  
Active Continental Margin ◽  
Late Ordovician ◽  
Granite Porphyry ◽  
Hf Isotopes ◽  
Margin Setting ◽  
Juvenile Crust ◽  
Early Palaeozoic

AbstractWe present detailed petrography, geochemistry and zircon U–Pb–Hf isotopes of the Mante Aobao granite porphyry in East Ujimqin Banner, Inner Mongolia, with the aim of determining its age and petrogenesis, important for understanding the early Palaeozoic tectonic evolution of the Xing’an–Mongolian Orogenic Belt. The Mante Aobao granite porphyry consists of plagioclase, quartz and minor biotite, but without amphibole. Zircon U–Pb analyses yield ages of 450 ± 1 Ma and 445 ± 2 Ma for the granite porphyry, indicating that it formed during Late Ordovician time. The granite porphyry is metaluminous to slightly peraluminous (aluminous saturation index A/CNK = 0.98–1.11) with high SiO2, K2O and Na2O concentrations and differentiation index (DI = 85–90). Chondrite-normalized rare earth element (REE) patterns display enrichment of light REEs (LREEs) with high ratios of (La/Yb)N and negative Eu anomalies. In the mantle-normalized multi-element variation diagrams, all samples are characterized by depletions of high-field-strength elements (HFSEs; Nb, Ta and Ti) and enrichments of large-ion lithophiles (LILEs; Rb, Th, U and K). These geochemical features indicate that the granite porphyry is a highly fractionated I-type granite and formed in a subduction-related setting. Zircon grains have positive εHf(t) values of +9.2 to +11.2, and TDM2(Hf) ages of 691–821 Ma, suggesting that the granite porphyry was generated by partial melting of Neoproterozoic juvenile crust with involvement of fractional crystallization during magmatic evolution. It is likely that underplating of mantle-derived magmas during Late Ordovician time provided the necessary heat to partially melt this juvenile crust. Combined with the regional geological data, we infer that the Mante Aobao granite porphyry was emplaced in an active continental margin setting that was probably related to the northwards subduction of the Paleo-Asian Plate beneath the South Mongolian Terrane along the Sonid Zuoqi–Xilinhot axis.

Soil genesis on hypersaline tidal flats (apicum ecosystem) in a tropical semi-arid estuary (Ceará, Brazil)

Soil Research ◽  
2014 ◽  
Vol 52 (2) ◽  
pp. 140 ◽  
Author(s):  
A. G. B. M. Albuquerque ◽  
T. O. Ferreira ◽  
G. N. Nóbrega ◽  
R. E. Romero ◽  
V. S. Souza Júnior ◽  
...  
Keyword(s):  
Tidal Flat ◽  
Coastal Wetland ◽  
Anthropogenic Activities ◽  
Analytical Data ◽  
Clay Fraction ◽  
Tidal Flats ◽  
Brazilian Coast ◽  
The North ◽  
North Eastern ◽  
Semi Arid

Wetland soils, especially those under a semi-arid climate, are among the least studied soils in the tropics. The hypersaline tidal flats on the north-eastern Brazilian coast, locally named apicum, are coastal wetland ecosystems in the peripheral portions of semi-arid estuaries. Despite their great ecological importance, they have been highly impacted by anthropogenic activities. Morphological and analytical data of six soil profiles, representative of the different coastal compartments (mangroves, apicum and coastal tablelands) of the north-eastern Brazilian coast, were examined to better understand the pedogenesis of apicum soils. The hypersaline tidal flat soils were classified as Typic Fluvaquents and Typic Sulfaquents with the following main characteristics: predominance of sand fraction (62–77%); presence of high-activity clays (>24 cmolc kg–1 clay); clay fraction comprising kaolinite, illite, smectite and an interstratified smectite/illite; exchangeable complex dominated by Na+ (ESP ≥15%); elevated levels of salinity (electrical conductivity, EC 25–44 dS m–1); alkaline pH values (7.5–9.5). The sandy texture and quartz-dominated composition of the hypersaline, tidal flat soils indicate a pedogenesis associated with the superficial addition of mineral material. This upbuilding process would have lowered the watertable (relatively to the ground level) and decreased the flooding frequency by the tides, favouring salinisation and solonisation processes at the hypersaline tidal flats. Furthermore, the still-existing hydromorphism would have promoted the maintenance of gleisation and sulfidisation. The presence of pyrite on the hyper-saline tidal flat soils further corroborates the formation of apicum soils from/over buried mangroves.

scholarly journals Relationships between Alluvial Facies/Depositional Environments, Detrital Zircon U-Pb Geochronology, and Bulk-Rock Geochemistry in the Cretaceous Neungju Basin (Southwest Korea)

Minerals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1023
Author(s):  
Hyojong Lee ◽  
Min Gyu Kwon ◽  
Seungwon Shin ◽  
Hyeongseong Cho ◽  
Jong-Sun Kim ◽  
...  
Keyword(s):  
Continental Margin ◽  
Detrital Zircon ◽  
Tectonic Setting ◽  
Active Continental Margin ◽  
Depositional Environments ◽  
Source Rocks ◽  
Bulk Rock ◽  
Zircon Age ◽  
Margin Setting ◽  
Weathering Intensity

Zircon U-Pb geochronology and bulk-rock geochemistry analyses were carried out to investigate their relationship with depositional environments of the non-marine Neungju Basin sediments in South Korea. The Neungju Basin was formed in an active continental margin setting during the Late Cretaceous with associated volcanism. Detrital zircon age distributions of the Neungju Basin reveal that the source rocks surrounding the basin supplied sediments into the basin from all directions, making different zircon age populations according to the depositional environments. Mudstone geochemistry with support of detrital zircon U-Pb age data reveals how the heterogeneity affects the geochemical characteristics of tectonic setting and weathering intensity. The sediments in the proximal (alluvial fan to sandflat) and distal (playa lake) environments differ compositionally because sediment mixing occurred exclusively in the distal environment. The proximal deposits show a passive margin signature, reflecting their derivation from the adjacent metamorphic and granitic basement rocks. The distal deposits properly indicate an active continental margin setting due to the additional supply of reworked volcaniclastic sediments. The proximal deposits indicate a minor degree of chemical weathering corresponding to fossil and sedimentological records of the basin, whereas the distal deposits show lower weathering intensity by reworking of unaltered volcaniclastic detritus from unstable volcanic and volcaniclastic terranes. Overall, this study highlights that compositional data obtained from a specific location and depositional environments may not describe the overall characteristic of the basin.

scholarly journals Petrology, Geochronology and Geochemistry of Late Triassic Alkaline Rocks of the Bailinchuan District in Liaodong Peninsula, Northeast China

Minerals ◽  
2018 ◽  
Vol 8 (11) ◽  
pp. 528
Author(s):  
Xihui Cheng ◽  
Jiuhua Xu ◽  
Hao Wei ◽  
Fuquan Yang ◽  
Hui Zhang ◽  
...  
Keyword(s):  
Mantle Source ◽  
Lithospheric Mantle ◽  
Tectonic Setting ◽  
Parental Magma ◽  
Late Triassic ◽  
Geochemical Data ◽  
Geodynamic Setting ◽  
Growth Zoning ◽  
Geochemical Studies ◽  
Alkaline Complexes

The Bailinchuan alkaline syenite (BAS) is located in the easternmost part of the Triassic alkaline magmatic belt along the northern North China Craton (NCC). Based on a detailed study of the zircon U–Pb age, petrological, and geochemical data of the complex, the characteristics of the magmas system, petrogenesis and the nature of mantle source provide new constraints on the origin and tectonic setting of the Triassic alkaline belt. The BAS is composed of alkaline syenite and/or aegirine-nepheline syenite, with zircon U–Pb age of 226–229 Ma. Aegirine, Na-rich augite, biotite, orthoclase, and nepheline are the major minerals. Most of the zircons selected for the analysis show fine-scale to weak oscillatory growth zoning in CL images, suggesting a magmatic origin. Mineralogy, petrology and geochemical studies show that the parental magma of the BAS is SiO2-undersaturated, potassic, and is characterized by high contents of CaO, Fe2O3, K2O, Na2O. The BAS originated from a phlogopite-rich, enriched lithospheric mantle source in a garnet-stable area. The occurrence of the BAS, together with many other alkaline complexes of similar ages (235–209 Ma) in the northern NCC during the Late Triassic implies that the lithospheric mantle beneath the northern NCC was previously metasomatized by melts/fluids. Bailinchuan Late Triassic syenites were formed in a post-collisional extensional setting, which provides time constraints on the major geodynamic setting at the northern NCC.

Tectonic setting and origin of the Proterozoic rapakivi granites of southeastern Fennoscandia

1992 ◽  
Vol 83 (1-2) ◽  
pp. 165-171 ◽  
Author(s):  
Ilmari Haapala ◽  
O. Tapani Rämö
Keyword(s):  
Tectonic Setting ◽  
Parental Magma ◽  
Transitional Zone ◽  
Isotopic Evolution ◽  
Domal Structure ◽  
Deep Seismic Soundings ◽  
Mafic Magmas ◽  
Thin Crust ◽  
High Level ◽  
Dyke Swarms

ABSTRACTThe 1·65–1·54 Ga rapakivi granites of southeastern Fennoscandia represent the silicic members of a bimodal magmatic association in which the mafic members are tholeiitic diabase dykes and minor gabbroic-anorthositic bodies. They are metaluminous to slightly peraluminous A-type granites and occur as high-level batholiths and stocks in an E-W-trending belt extending from Soviet Karelia to southwestern Finland. The Soviet Karelian granites were emplaced into the contact zone between Archaean craton and Svecofennian juvenile 1·9Ga-old crust, while the Finnish granites were intruded into the Svecofennian crust. Deep seismic soundings show that the rapakivi granites and the contemporaneous, mainly WNW or NW-trending diabase dyke swarms are situated in a zone of relatively thin crust. Below the Wiborg Batholith there exists a domal structure in the lithosphere in which a transitional zone (mafic underplate) occurs between the crust and the mantle.The Nd isotopic evolution of the rapakivi granites (εNd(T) −3·1—−0·2) corresponds to the evolution of the 1·9Ga-old Svecofennian crust, as do their Pb isotopic compositions. This implies that the Finnish granites represent anatectic melts of the Svecofennian crust. In contrast, the Soviet Karelian granites show isotopic composition indicative of substantial incorporation of Archaean lower crust material. Petrochemical modelling of one of the Finnish batholiths shows that its parental magma could have been generated by c. 20% melting of a granodioritic source and that fractional crystallisation was important during the subsequent evolution of this magma.The rapakivi granites are redefined as A-type granites that show the rapakivi texture at least in larger batholiths. The field, geochemical, and seismic data indicate that the classical Finnish rapakivi granites were generated in an anorogenic extensional regime by partial melting of the lower/middle crust. The melting, and possibly also the extensional tectonics, were related to upwellings of hot mantle material which led to intrusion of mafic magmas at the base and into the crust.

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