scholarly journals Geochronology of the so-called South Bulgarian granitoids – a review (1836–2000)

2017 ◽  
Vol 46 (2) ◽  
pp. 40
Author(s):  
Vasil Arnaudov
Keyword(s):  
Quantitative Methods ◽  
Lead Isotope ◽  
Lead Isotopes ◽  
Volcanic Rocks ◽  
The South ◽  
Granitoid Magmatism ◽  
Basic Model ◽  
Ore Minerals ◽  
Geochemical Studies ◽  
Metamorphic Complexes

This review treats the concepts concerning the age of granitoid magmatism in southern Bulgaria and considers the age assessments of the large granite intrusions in the metamorphic complexes known as “South Bulgarian granites”. In terms of the available contributions, this analysis encloses a long period, from 1836, the time of Ami Boué, the first geologist who visited Bulgarian land, to 2000. The review discusses both ideas and geochronological data on a large time-span, from the Archean to the “Tertiary”. The emphasis is on the progress of Bulgarian researchers’ views that had been made prior to the first pioneering attempts at radiological determinations (i.e., using He and Pb quantitative methods), and especially after the advent of modern equipment for radioisotope dating, based on various isotope systems (e.g., K-Ar, U-Th-Pb, Rb-Sr) and mathematical models of lead isotopes (Pb-Pb) following the basic model of “plumbotectonics” and the fission track method. The bulk of radioisotope data (more than 300 dates on feldspar and 500 dates on galena and other ore minerals) have been made by using the Pb-Pb method, which was introduced by Blagoy Amov and improved by the same worker via his “dynamic model of a continuous lead-isotope evolution” in the Earth’s crust. From 1969, when pegmatites that are genetically linked to granite intrusions of southern Bulgaria were dated as “Tertiary”, until 2000, all of the above-mentioned methods were tested. These methods confirmed the “Tertiary” ages of the granitoids of the Rhodope Massif and their difference in age from the Hercynian granitoids of the Srednogorie Zone. Owing to this, two groups of granitoids of dissimilar ages, previously referred to as “South Bulgarian granites”, were determined. This distinction was corroborated by varieties of mineralogical, petrological and geochemical studies, which were carried out by collaborators from the Department of Geochemistry of the Geological Institute. The “magical boundary”, defined by Acad. Strashimir Dimitrov and followed by the majority of Bulgarian geologists, that “the South Bulgarian granites are pre-Mesozoic in age, since fragments of them are present in the Permian–Triassic conglomerates of the Lozen Mountain” has been overcome, mainly due to the results of geochemical studies. Also, the absence of Archean and Proterozoic metamorphism in the Rhodope Massif has been revealed by U-Th-Pb and Pb/Pb radiogeochronological investigations. The analysis of available mineralogical, geochemical and radiogeochronological data, supported by the ages of the migmatites from Ardino area (63–32 Ma), allowed to assume that both migmatized gneisses and the South Bulgarian granites of the Rila and Rhodope Mountains, as well as the volcanic rocks and associated intrusions and ore mineralizations, were a product of a single and prolonged stage of the Alpine activation of the Rhodope crystalline complex that started during the Cretaceous.

Lead- and strontium-isotope geochemistry of Paleozoic Sicker Group and Jurassic Bonanza Group volcanic rocks and Island Intrusions, Vancouver Island, British Columbia

1989 ◽  
Vol 26 (5) ◽  
pp. 894-907 ◽  
Author(s):  
Anne Andrew ◽  
Colin I. Godwin
Keyword(s):  
Lead Isotope ◽  
Isotope Geochemistry ◽  
Lead Isotopes ◽  
Volcanic Rocks ◽  
Isotope Ratios ◽  
Ore Deposits ◽  
Island Arc ◽  
Lead Isotope Ratios ◽  
Rock Suite ◽  
Isotope Analyses

Whole-rock and galena lead-isotope analyses have been obtained from the Sicker Group Paleozoic island-arc volcanic package and from a Jurassic island-arc represented by the Bonanza Group volcanics and Island Intrusions. Galena lead-isotope analyses from the volcanogenic ore deposits at the Buttle Lake mining camp in the Sicker Group provide estimates of the initial lead ratios for the Sicker Group. Lead-isotope signatures are uniform within each of the major orebodies, but the Myra orebody is less radiogenic than the older H–W orebody. This has major significance in terms of ore genesis for these important deposits.There are significant differences in isotopic composition between the Sicker Group and Devonian island-arc type rocks in the Shasta district, California, which rules out direct correlations between the rock units of these two areas. Relatively high initial values of 207Pb/204Pb (> 15.56) and 208Pb/204Pb (> 38.00) suggest that large quantities of crustal lead must have been involved in the formation of the Sicker Group volcanic rocks. Thus it is proposed that the trench related to the Paleozoic island arc had a substantial input of continental detritus and may have lain near a continent.The Jurassic island arc is characterized by low 207Pb/204Pb ratios (< 15.59), suggesting a more primitive arc environment than for the Paleozoic arc. Bonanza Group volcanic rocks contain lead that is less radiogenic than lead in the Island Intrusions. Present and initial lead-isotope ratios of both the Bonanza Group volcanics and Island intrusions follow the same trend, supporting the hypothesis that they are comagmatic. Lead isotopes from a galena vein within the Island Copper porphyry deposit plot with the initial ratios for Bonanza Group volcanics and Island Intrusions. This confirms the hypothesis that this mineralization is related to the Jurassic island-arc volcanic event.Initial lead-isotope ratios for the Jurassic rock suite form a linear array on both 207Pb/204Pb versus 206Pb/204Pb and 208Pb/204Pb versus 206Pb/204Pb plots. If interpreted as due to isotopic mixing, the more radiogenic end member has a composition that is lower in 207Pb/204Pb and higher in 206Pb/204Pb than typical upper continental crust. Assimilation of Sicker Group material during the emplacement of the Jurassic arc can explain the mixing trend.

scholarly journals THE FIRST EVIDENCE OF LATE DEVONIAN GRANITOID MAGMATISM IN THE NORTHEASTERN FLANK OF THE SOUTH MONGOLIA–KHINGAN OROGENIC BELT

2021 ◽  
pp. 65-76
Author(s):  
Y.V. Smirnov ◽  
◽  
A.A. Sorokin ◽  
N.M. Kudryashov ◽  
◽  
...  
Keyword(s):  
Continental Margin ◽  
Orogenic Belt ◽  
Late Devonian ◽  
The South ◽  
Granitoid Magmatism ◽  
Margin Setting ◽  
Low Concentrations ◽  
History Of ◽  
Northeastern Flank ◽  
Geochemical Studies

The results of geochemical, U-Pb geochronological, Sm-Nd isotopic-geochemical studies of granites of the Medvedka Massif in the northern part of the Nora–Sukhotino terrane are presented. It has been found that these granites are of 378 ± 3 Ma in age. It was shown that these granites are characterized by the presence of ferruginous silicates, high iron index (FeO*/(FeO*+MgO)), low concentrations of Al2O3, CaO, MgO, high contents of Nb, Ga, Y, deficiency of Sr, Eu, positive values of εNd(t) (+3.0...+4.1), and high values of the ratio Y/Nb. In total, this indicates that the granites of the Medvedka massif are related to A2-type granites. The Late Devonian hastingsite-biotite granites of the Medvedka Massif most likely reflect evidence of the transform continental margin setting in the history of the formation of the South Mongolian – Khingan orogenic belt.

Mafic igneous rocks and mineralisation in the Palaeoproterozoic Ketilidian orogen, South-East Greenland: project SUPRASYD 1996

1997 ◽  
pp. 66-74
Author(s):  
Henrik Stendal ◽  
Wulf Mueller ◽  
Nicolai Birkedal ◽  
Esben I. Hansen ◽  
Claus Østergaard
Keyword(s):  
Mineral Exploration ◽  
Volcanic Rocks ◽  
Shear Zones ◽  
Field Work ◽  
Igneous Rocks ◽  
Border Zone ◽  
The South ◽  
East Greenland ◽  
North West ◽  
Arc Setting

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Stendal, H., Mueller, W., Birkedal, N., Hansen, E. I., & Østergaard, C. (1997). Mafic igneous rocks and mineralisation in the Palaeoproterozoic Ketilidian orogen, South-East Greenland: project SUPRASYD 1996. Geology of Greenland Survey Bulletin, 176, 66-74. https://doi.org/10.34194/ggub.v176.5064 _______________ The multidisciplinary SUPRASYD project (1992–96) focused on a regional investigation of the Palaeoproterozoic Ketilidian orogenic belt which crosses the southern tip of Greenland. Apart from a broad range of geological and structural studies (Nielsen et al., 1993; Garde & Schønwandt, 1994, 1995; Garde et al., 1997), the project included a mineral resource evaluation of the supracrustal sequences associated with the Ketilidian orogen (e.g. Mosher, 1995). The Ketilidian orogen of southern Greenland can be divided from north-west to south-east into: (1) a border zone in which the crystalline rocks of the Archaean craton are unconformably overlain by Ketilidian supracrustal rocks; (2) a major polyphase pluton, referred to as the Julianehåb batholith; and (3) extensive areas of Ketilidian supracrustal rocks, divided into psammitic and pelitic rocks with subordinate interstratified mafic volcanic rocks (Fig. 1). The Julianehåb batholith is viewed as emplaced in a magmatic arc setting; the supracrustal sequences south of the batholith have been interpreted as either (1) deposited in an intra-arc and fore-arc basin (Chadwick & Garde, 1996), or (2) deposited in a back-arc or intra-arc setting (Stendal & Swager, 1995; Swager, 1995). Both possibilities are plausible and infer subduction-related processes. Regional compilations of geological, geochemical and geophysical data for southern Greenland have been presented by Thorning et al. (1994). Mosher (1995) has recently reviewed the mineral exploration potential of the region. The commercial company Nunaoil A/S has been engaged in gold prospecting in South Greenland since 1990 (e.g. Gowen et al., 1993). A principal goal of the SUPRASYD project was to test the mineral potential of the Ketilidian supracrustal sequences and define the gold potential in the shear zones in the Julianehåb batholith. Previous work has substantiated a gold potential in amphibolitic rocks in the south-west coastal areas (Gowen et al., 1993.), and in the amphibolitic rocks of the Kutseq area (Swager et al., 1995). Field work in 1996 was focused on prospective gold-bearing sites in mafic rocks in South-East Greenland. Three M.Sc. students mapped showings under the supervision of the H. S., while an area on the south side of Kangerluluk fjord was mapped by H. S. and W. M. (Fig. 4).

MODELING THE SOUTH ATLANTIC OCEAN FROM MEDIUM TO HIGH RESOLUTION

2014 ◽  
Vol 31 (2) ◽  
Author(s):  
Mariela Gabioux ◽  
Vladimir Santos da Costa ◽  
Joao Marcos Azevedo Correia de Souza ◽  
Bruna Faria de Oliveira ◽  
Afonso De Moraes Paiva
Keyword(s):  
High Resolution ◽  
Atlantic Ocean ◽  
Large Scale ◽  
South Atlantic ◽  
Surface Relaxation ◽  
The South ◽  
Small Surface ◽  
Basic Model ◽  
Basic Set ◽  
Set Up

Results of the basic model configuration of the REMO project, a Brazilian approach towards operational oceanography, are discussed. This configuration consists basically of a high-resolution eddy-resolving, 1/12 degree model for the Metarea V, nested in a medium-resolution eddy-permitting, 1/4 degree model of the Atlantic Ocean. These simulations performed with HYCOM model, aim for: a) creating a basic set-up for implementation of assimilation techniques leading to ocean prediction; b) the development of hydrodynamics bases for environmental studies; c) providing boundary conditions for regional domains with increased resolution. The 1/4 degree simulation was able to simulate realistic equatorial and south Atlantic large scale circulation, both the wind-driven and the thermohaline components. The high resolution simulation was able to generate mesoscale and represent well the variability pattern within the Metarea V domain. The BC mean transport values were well represented in the southwestern region (between Vitória-Trinidade sea mount and 29S), in contrast to higher latitudes (higher than 30S) where it was slightly underestimated. Important issues for the simulation of the South Atlantic with high resolution are discussed, like the ideal place for boundaries, improvements in the bathymetric representation and the control of bias SST, by the introducing of a small surface relaxation. In order to make a preliminary assessment of the model behavior when submitted to data assimilation, the Cooper & Haines (1996) method was used to extrapolate SSH anomalies fields to deeper layers every 7 days, with encouraging results.

The Late Cretaceous magmatic arc of the south Aegean: Geodynamic implications from petrological and geochemical studies of granitoids from Anafi island (Cyclades – Greece)

2021 ◽  
pp. 1-24
Author(s):  
Petros Koutsovitis ◽  
Konstantinos Soukis ◽  
Panagiotis Voudouris ◽  
Stylianos Lozios ◽  
Theodoros Ntaflos ◽  
...  
Keyword(s):  
Late Cretaceous ◽  
The South ◽  
Magmatic Arc ◽  
Geochemical Studies

Mineralization of the South Pennine Orefield, UK—A Review

2016 ◽  
Vol 61 (1) ◽  
pp. 55-86 ◽  
Author(s):  
T.D. Ford ◽  
N.E. Worley
Keyword(s):  
Wall Rock ◽  
Hydraulic Gradient ◽  
Mississippi Valley ◽  
The South ◽  
The North ◽  
East Midlands ◽  
Ore Minerals ◽  
Placer Deposits ◽  
Fractured Limestone ◽  
Host Rocks

This review of the South Pennine Orefield (SPO) draws together the findings from many years of underground field observations and petrographical study. Mineralization is of the Mississippi Valley-type (MVT) and is concentrated within an area of some 200 km2, mainly along the eastern margins of a large inlier, the Derbyshire High, in Carboniferous platform carbonate host rocks. The inlier covers some 390 km2, forms an up-dip promontory of a larger structure, the East Midlands Shelf, and is surrounded by shales and sandstones of the Millstone Grit and Pennine Coal Measures groups. Mineralization probably began during the late Westphalian (Moscovian, Mid Pennsylvanian), when subsidence due to thermal sag resulted in the limestone being buried to depths of c. 4 km beneath younger strata. A palaeohydraulic reconstruction is presented from analysis of mineralized palaeokarst features, which are interpreted as representing hypogenic or deep-seated karst formed by the interstratal circulation of hydrothermal water in a mostly confined hydrodynamic setting. It is reasoned that Variscan inversion of N–S faults to the east of the SPO resulted in erosion of Namurian and Westphalian (Upper Mississippian–Middle Pennsylvanian) rocks and created a hydraulic gradient inclined towards the south-west. Acidic F-Ba-Pb-Zn enriched fluid evolved in the Namurian basinal rocks and migrated into fractured limestone. The resultant wall-rock dissolution along existing wrench faults led to the formation of a maze of stratiform mineral deposits (flats) and more irregular spongework-shaped structures (pipes). The presence of hydrocarbon accumulations in the limestones and evidence from fluid inclusions indicates that the mineralizing fluids were chloride/fluoride-rich and compositionally typical of oilfield brine. Isotope evidence demonstrates a sulphate evaporite source of sulphur, mainly from the Chadian (Visean, Middle Mississippian) Middleton Anhydrite Formation. By the late Cenozoic, karstification of exposed carbonate rocks began and the current pattern of epigenic karst drainage started to develop as the regional hydraulic gradient reversed, assuming its present eastward inclined attitude. The mineralized hypogenic karst was overprinted by later drainage systems as the hydraulic gradient changed, and placer deposits were formed from the erosion of existing mineralization. This was accompanied by circulation of meteoric water and resulted in the supergene weathering of the sulphide ore minerals. Eastward underflow of meteoric groundwater also exploited the same mineralization flow paths. There is evidence that pre-mineralization hypogenic karst was also significant in the formation of orebodies in the North Pennine Orefield and the Halkyn–Minera Orefield of NE Wales.

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