Borislav Kamenov | Sofia University "St. Kliment Ohridski" (original) (raw)
Papers by Borislav Kamenov
Antarctic Science, Jun 1, 1989
World geomorphological landscapes, 2022
Island, the second largest in the archipelago of the
Abstract. Late Cenozoic mafic alkaline volcanic rocks occur throughout the entire Pacific coast o... more Abstract. Late Cenozoic mafic alkaline volcanic rocks occur throughout the entire Pacific coast of West Antarctica, including in some of the islands adjacent or within the Bransfield Strait. Amongst them, Livingston Island is the least well-known, particularly in respect to mineralogy, petrology and geochemistry of the sparse manifestations of this type rocks, known as Inott Point Formation. The petrographic and geoche-mical aspects of old and new-discovered outcrops of primitive volcanic rocks are described. The new chemi-cal analyses specify the nomenclature as low-Ti undersaturated olivine basalts mainly, and hawaiites rarely. Comparisons with the trace element characteristics of the similar rocks from the islands Greenwich, Penguin, Deception and Bridgemen revealed common features: high LILE/HFSE ratios (e.g. Ba/Zr 1.4-2.2; Ba/Nb 42-67; Rb/Nb 2.7-4; Ce/Nb 2.5-10; Th/Nb 0.25- 0.90; K/Zr 39-67 etc.). These ratios are opposite to the low LILE/HFSE ratios in the alkalic provinces in...
New petrographical data, including rock-forming mineralogy are presented for the Late Cretaceous ... more New petrographical data, including rock-forming mineralogy are presented for the Late Cretaceous Malko Turnovo pluton, outcropped in the Strandja Mountain. Four intrusive phases are distinguished: I. Basic rocks (pyroxenite, gabbro-pyroxenite, gabbro, monzogabbro); II. Monzonitoids (monzodiorite, quartz- monzodiorite, monzonite, quartz-monzonite); III. Quartz-syenites; IV. Porphyry rocks (quartz-diorite porphyrite, granodiorite porphyrite, quartz-monzonite porphyrite, quartz-syenite porphyry). A typical for monzonitoid transitional alkaline series trend is revealed from the new modal analyses. The essential features of the main rock-forming minerals are described in an attempt to deduce the typomorphic peculiarities of the ore-magmatic system. Plagioclase feldspars span much of the crystallization history of the pluton. Three magmatic plagioclase generations have been recognized. The calcic cores Pl I range in composition An56-An51. Pl II consists of repeated fine-scale oscillations...
Geological Society, London, Special Publications, 2002
Single zircons from several porphyry dykes bracketing the time of formation of the Elatsite porph... more Single zircons from several porphyry dykes bracketing the time of formation of the Elatsite porphyry Cu-Au deposit (Bulgaria) were dated by high-precision U-Pb isotope analysis, using thermal ionization mass spectrometry (TIMS). On the basis of cross-cutting relationships, and the mineralogy and geochemistry of igneous and altered rocks, five dyke units are distinguished. The earliest porphyry dyke is associated with, and overprinted by, the main stage of ore-related veining and potassic alteration. U-Pb analyses of zircons yield a mean 206Pb/238U age of 92.1 ± 0.3 Ma, interpreted to reflect the time of intrusion. Zircons of the latest ore forming dyke, crosscutting the main stage veins but still associated with minor potassic alteration and veining, give an intrusion age of 91.84 ± 0.3 Ma. Thus, ore mineralization is confined by individually dated igneous events, indicating that the entire time span for the ore-forming magmatism and high temperature hydrothermal activity extended o...
Late Cenozoic mafic alkaline volcanic rocks occur through-out the entire Pacific coast of West An... more Late Cenozoic mafic alkaline volcanic rocks occur through-out the entire Pacific coast of West Antarctica, including some of the islands adjacent or within the Bransfield Strait. Amongst them, Livingston Island is the least well-known, particularly in respect to mineralogy, petrology and geochemistry of the scarce manifestations of this type rocks, known as Inott Point Formation. This contribution presents new major element and trace element data from old and new-discovered outcrops in Livingston Island and compares them geochemically with simi-lar rocks from the island Greenwich situated in South Shet-land Islands arc and with Quaternary basalts in the islands Penguin, Deception and Bridgeman, within the back-arc rift basin Bransfield Strait. Alkaline basalts from the provinces in
Occupying the core of a large dome-like structure of high metamorphic rocks in Southeastern Bulga... more Occupying the core of a large dome-like structure of high metamorphic rocks in Southeastern Bulgaria, the Sakar granitoid batholith has been an object of conflicting interpretations for a long time. Lots of contradictory speculations about its structure, emplacement age and significance for regional correlations have been raised in our literature. Considered as Caledonian, Hercynian, Late Jurassic or even Early Cretaceous in age, the batholith still evokes professional curiosity. On the basis of extensive re-mapping and a large set of laboratory analyses carried out by 1987, we presented quite a while ago some brief information concerning the petrographical units, structural peculiarities, emplacement mechanism and geochemistry of the rocks in an extended abstract (Vergilov et al., 1986). A paper devoted to petrology and geochemistry of the pluton was accepted for publication (Kamenov et al., 2010), but the principle conclusions and results of our work are still not familiar to our ...
Based on a new sample set and extensive re-mapping an attempt is made to elucidate the field rela... more Based on a new sample set and extensive re-mapping an attempt is made to elucidate the field relations, mineral composition, nomenclature, geochemical features, magmatic and postmagmatic evolution, and to find new evidence for geodynamic reconstructions of the Sakar batholith. The dome-like batholith is emplaced into high-grade metamorphic rocks of still unclear age. It is covered by Permian and Triassic sedimentary rocks. The batholith is composed of the following granitoid units: equigranular in the inner parts, porphyroid with large microcline megacrysts in the outer parts, and small aplitoid bodies. Large xenoliths of gneisses and orthoamphibolites occur in the marginal parts of the batholith. The modal petrographic species are quartz-monzodiorite, quartz-monzonite, granodiorite, granite, quartz-syenite and leucogranite. The main rock-forming minerals are separated from artificial heavy concentrates and studied optically, chemically, by X-ray and IR-analysis. No characteristic d...
Geochem., Mineral., …, 2007
Magmatic rocks of Late Cretaceous age from the Central Srednogorie, Bulgaria show marked variatio... more Magmatic rocks of Late Cretaceous age from the Central Srednogorie, Bulgaria show marked variations in its geochemistry. The present study is focused on the common features in the magma evolution paths of several ore-magmatic systems: Elatsite, Chelopech, Medet, Assarel, Elshitsa and Capitan Dimitrievo considered as links of a petrological across-arc transect. The whole range of SiO 2 is large (40-73%). The evolution from intermediate to more basic stages is a common characteristic for most of the centers, but it is complicated by fractional differentiation and mixing of magmas. High-K calc-alkaline to shoshonitic series predominate, calc-alkaline being only in the middle of the transect. The geochemical peculiarities are typical for an enriched mantle source and indicate a subduction-related volcanic-arc setting. Melting degrees are estimated as small for both ends of the transect and higher for the central parts. The magmatic activity started at the northern end of the transect at 92.1 Ma, gradually became younger and finished at the border to the Rhodopes massif at 78 Ma. The 87 Sr/ 86 Sr ratios (0.704-0.706), suggest melts generated in a mantle source, modified by the addition of crustal materials. Pb-isotope analyses and ε-Hf values show an increase of the radiogenic component from North to South. The subduction slab retreat model is applied to explain the trenchward migration of the magmatic activity along the transect length.
1 Sofia University “St. K. Ohridski”, 1000 Sofia, Bulgaria, e-mail: kamenov@gea.uni-sofia.bg; 2 B... more 1 Sofia University “St. K. Ohridski”, 1000 Sofia, Bulgaria, e-mail: kamenov@gea.uni-sofia.bg; 2 Bulgarian Academy of Sciences, Geological Institute, 1113 Sofia, Bulgaria 3 Earth Science Section of the University of Geneva, 1211 Geneva, Switzerland 4 Bulgarian Academy of Sciences, Central Laboratory of Mineralogy and Crystallography, 1113 Sofia, Bulgaria 5 Institute of Isotope Geology and Mineral Resources, ETH, 8092 Zurich, Switzerland 6 University of Mining and Geology “St. Ivan Rilski”, 1700 Sofia, Bulgaria
ABSTRACT The Oman-Fakya pluton is a complex I type calc-alkaline body of Late Cretaceous age offe... more ABSTRACT The Oman-Fakya pluton is a complex I type calc-alkaline body of Late Cretaceous age offering a wide variety of rocks of intermediate composition between gabbro and more evolved magmas. The relationship between these rock types suggests that they are of different origin than it was supposed before. New pieces of evidence emerging from recent remapping, as well as from the mineralogical and chemical investigations point to a modified genetic view. The new observations show that magma mixing and mingling have taken place with the creation of a range of hybrid rocks with compositions between gabbroic and quartz-syenitic end-members. The mineralogical features of the rock-forming mafic minerals clinopyroxene, biotite and amphibole have been examined to establish some facets of their crystallization history. These features (normal and reverse zonings, incompatible assemblages, mineral relics in disequilibrium with host magmas ect.) are interpreted as signs for an open system evolution of the crystallizing magmas. The several crystal populations with a complex history indicate rapid changes in crystallization environment, most likely due to convective transport between crystallizing boundary layers and new basic magma pulses. The clinopyroxene is of diopside species and its chemistry bears traces of disturbed by the input of new basic magma crystallization. Biotite compositions seem to be result of contaminated magma of higher alkalinity theoretically favourable for generation of rich in Cu and Au fluids. Amphiboles present in the pluton are assigned to wide nomenclature divisions. Normal and reverse zonings are observed and regular changes in their composition are explained by an increasing of the activity of Si and of alkalies, as well as by pressure, temperature and degree of polymerization dependencies. The main coupled substitution mechanisms are of tschermakite and edenite types and Ti-tschermakite one is of minor importance. Polybaric crystallization and mixing of contrasting magmas are reprinted on the chemical composition of the amphiboles. All amphiboles fall within the field of granitoids crystallized at high f O2 . Thermal, chemical and mechanical interactions as principal types of exchange between coexisting magmas produced probably the appearant and hidden heterogeneities present in the mafic assemblage. It is believed that the revealed typomorphic features of the mafic mineral assemblage in the Oman-Fakya pluton are result of the complex succession and repetition of exchanges and partial chemical equilibration and every attempt to model the evolution of the magmatic system should comply with the conclusions extracted from the mafic minerals of the pluton.
Late Cenozoic mafic alkaline volcanic rocks occur throughout the entire Pacific coast of West Ant... more Late Cenozoic mafic alkaline volcanic rocks occur throughout the entire Pacific coast of West Antarctica, including in some of the islands adjacent or within the Bransfield Strait. Amongst them, Livingston Island is the least well-known, particularly in respect to mineralogy, petrology and geochemistry of the sparse manifestations of this type rocks, known as Inott Point Formation. The petrographic and geochemical aspects of old and new-discovered outcrops of primitive volcanic rocks are described. The new chemical analyses specify the nomenclature as low-Ti undersaturated olivine basalts mainly, and hawaiites rarely. Comparisons with the trace element characteristics of the similar rocks from the islands Greenwich, Penguin, Deception and Bridgemen revealed common features: high LILE/HFSE ratios (e.g. Ba/Zr 1.4-2.2; Ba/Nb 42-67; Rb/Nb 2.7-4; Ce/Nb 2.5-10; Th/Nb 0.25-0.90; K/Zr 39-67 etc.). These ratios are opposite to the low LILE/HFSE ratios in the alkalic provinces in Antarctic Peninsula (AP) and in Marie Byrd Land (MBL). The generally low absolute abundances of HFSE in all within and around the Bransfield Strait alkaline basalts and the high Zr/Nb (19-43) and Sr/Nb (>100) ratios are in contrast to such ratios in AP and MBL exposures. Higher degree of melting and variable interaction with the continental lithosphere is probably responsible for the geochemical differences with the alkaline basalts from the other provinces in West Antarctica. The regional geochemical LILE differences between MBL and AP substantiate the conclusion that they were derived from different source regions. Alkaline basalts from cratonic flood basalts in Patagonia and from the Atlantic Ocean island Ascension were used for correlation and their geochemistry is similar to plume-related MBL basalts. In spite of the extensional setting in the back-arc rift of Bransfield Strait, the studied alkaline basalts bear most of arc trace element signatures. New subdivision of the alkaline basalt provinces in West Antarctica is proposed. To the AP province, known to be derived from MORB-source asthenosphere in slab-window setting and to the MBL one, related to a deep mantle plume, we may add another one specific province, namely Bransfield Strait extensional one with alkaline basalts bearing traces of a lithospheric contamination and subduction-related geochemical signature.
ABSTRACT Borislav K. Kamenov. THE VARSHILO PLUTON IN STRANDJA – NEW MINERALOGICAL AND GEOCHEMICAL... more ABSTRACT Borislav K. Kamenov. THE VARSHILO PLUTON IN STRANDJA – NEW MINERALOGICAL AND GEOCHEMICAL DATA SUPPORTING ITS PETROLOGICAL EVOLUTION Initial studies of the Varshilo pluton exposed in Strandja Mountain concluded that magmas followed different petrochemical trends – an iron-enrichment with little silica enrichment until the final stages of crystallization and a high silica-enrichment one. The new presented mineral and geochemical data confirm the old speculations with more convincingness. The vast cumulative set of modal and chemical analyses worked out the following rock units within the pluton: I – pyroxenites, II – gabbro, III – gabbrodiorites, IV – monzodiorites and quartz-monzodiorites, V – quartz-diorites, VI – granodiorites, VII – aplites. The essential features of the main rock-forming minerals are present and they are consistent with the differentiation of two parental magmas – basic and intermediate. Textural and chemical evidences support the magma-mingling and magma-mixing phenomena. The extent of the fractionation, magma-mixing and fluid influences are figured out of the geochemical plots and general mass balance calculations. REE and MORB-normalized patterns support the island-arc geodynamic setting and subduction-related origin of the Varshilo magma. The main mechanisms of the magmatic evolution are modeled successfully by general mixing calculations – fractional crystallization, magma mixing, cumulative segregation and fluid involvement. The observed geochemical variations of the trace elements are modeled almost perfectly using published partition coefficients for coexisting minerals and liquids in the pluton. It was established that LIL-elements Rb, La, Ce, Sm, Yb, Th and U had been introduced in amounts exceeding the necessary ones if only fractional crystallization would be realized. Magma-fluid relations and crystallization in an open system in the magma chambers are offered in the interpretations. The proposed model fits well into the revealed three geochemical trends of the magma evolution: I – cumulative trend of imperfect mineral separation leading to pyroxenite at the end of the process; II – tholeiitic trend of iron-enrichment in the basic magma units; III – calc-alkaline trend in the intermediate magmas. The hybrid origin of the rock unit IV (quartz-monzodiorites and monzodiorites) was grounded more confidently. The new results could be stimulating for rising new ideas about this key-case complex multiphase Upper Cretaceous pluton in Bulgaria.
New petrological data, including rock-forming mineralogy and geochemistry are presented for a Lat... more New petrological data, including rock-forming mineralogy and geochemistry are presented for a Late Cretaceous ring-like pluton Izgrev, exposed in Strandja Mountain, Southeastern Bulgaria. The multi-phased pluton is a part of the volcano-plutonic Papya structure. Four intrusive phases are distinguished: (1) gabbro-pyroxenite, (2) monzogabbro-monzodiorite-diorite, (3) quartz-diorite-granodiorite, (4) aplite. A lot of petrographical modal varieties are separated into each one of the magmatic phases. Postplutonic dykes accompany the plutonic rocks. They are assigned to gabbro-porphyrite, monzogabbroporphyrite, monzodiorite-porphyrite, quartz-monzonite porphyry, diorite porphyrite, and granodiorite porphyry. The essential features of the main rock-forming minerals are present. Some field, textural and structural criteria suggest magma-mingling and magma-mixing phenomena, but crystal fractionation seems to have been the predominant rock-forming process. High-K calc-alkaline series prevail, the diversities to the tholeiitic, calc-alkaline and shoshonitic series being also available. Typical geochemical fingerprints of subduction-related affinity (LILE enrichment, HFSE depletion, compared to LREE) in MORB-normalized trace-element patterns are discussed. REE geochemical peculiarities are the clues to the idea of an enriched mantle source and they also indicate an island-arc magmatic setting. Trace-element ratios are used to reveal that the rock varieties have been controlled by the mixed mantle-crust source of the parental magmas. It appears that the crustal contamination and sediment input into the magma source had been inessential, but the fluid influx out of the altered oceanic crust had exerted much more influence on the source. Mixing of contrast magmas on the background of the extended fractional crystallization is proposed as a principal reason for the petrological evolution (MFC process) in the pluton. The geochemical correlation with analogical plutons from Eastern Srednogorie zone confirmed the petrological conclusions. The new results could serve as a basis of new ideas and models for the magmatic development in the Eastern segment of the Srednogorie island-arc magmatic system.
Antarctic Science, Jun 1, 1989
World geomorphological landscapes, 2022
Island, the second largest in the archipelago of the
Abstract. Late Cenozoic mafic alkaline volcanic rocks occur throughout the entire Pacific coast o... more Abstract. Late Cenozoic mafic alkaline volcanic rocks occur throughout the entire Pacific coast of West Antarctica, including in some of the islands adjacent or within the Bransfield Strait. Amongst them, Livingston Island is the least well-known, particularly in respect to mineralogy, petrology and geochemistry of the sparse manifestations of this type rocks, known as Inott Point Formation. The petrographic and geoche-mical aspects of old and new-discovered outcrops of primitive volcanic rocks are described. The new chemi-cal analyses specify the nomenclature as low-Ti undersaturated olivine basalts mainly, and hawaiites rarely. Comparisons with the trace element characteristics of the similar rocks from the islands Greenwich, Penguin, Deception and Bridgemen revealed common features: high LILE/HFSE ratios (e.g. Ba/Zr 1.4-2.2; Ba/Nb 42-67; Rb/Nb 2.7-4; Ce/Nb 2.5-10; Th/Nb 0.25- 0.90; K/Zr 39-67 etc.). These ratios are opposite to the low LILE/HFSE ratios in the alkalic provinces in...
New petrographical data, including rock-forming mineralogy are presented for the Late Cretaceous ... more New petrographical data, including rock-forming mineralogy are presented for the Late Cretaceous Malko Turnovo pluton, outcropped in the Strandja Mountain. Four intrusive phases are distinguished: I. Basic rocks (pyroxenite, gabbro-pyroxenite, gabbro, monzogabbro); II. Monzonitoids (monzodiorite, quartz- monzodiorite, monzonite, quartz-monzonite); III. Quartz-syenites; IV. Porphyry rocks (quartz-diorite porphyrite, granodiorite porphyrite, quartz-monzonite porphyrite, quartz-syenite porphyry). A typical for monzonitoid transitional alkaline series trend is revealed from the new modal analyses. The essential features of the main rock-forming minerals are described in an attempt to deduce the typomorphic peculiarities of the ore-magmatic system. Plagioclase feldspars span much of the crystallization history of the pluton. Three magmatic plagioclase generations have been recognized. The calcic cores Pl I range in composition An56-An51. Pl II consists of repeated fine-scale oscillations...
Geological Society, London, Special Publications, 2002
Single zircons from several porphyry dykes bracketing the time of formation of the Elatsite porph... more Single zircons from several porphyry dykes bracketing the time of formation of the Elatsite porphyry Cu-Au deposit (Bulgaria) were dated by high-precision U-Pb isotope analysis, using thermal ionization mass spectrometry (TIMS). On the basis of cross-cutting relationships, and the mineralogy and geochemistry of igneous and altered rocks, five dyke units are distinguished. The earliest porphyry dyke is associated with, and overprinted by, the main stage of ore-related veining and potassic alteration. U-Pb analyses of zircons yield a mean 206Pb/238U age of 92.1 ± 0.3 Ma, interpreted to reflect the time of intrusion. Zircons of the latest ore forming dyke, crosscutting the main stage veins but still associated with minor potassic alteration and veining, give an intrusion age of 91.84 ± 0.3 Ma. Thus, ore mineralization is confined by individually dated igneous events, indicating that the entire time span for the ore-forming magmatism and high temperature hydrothermal activity extended o...
Late Cenozoic mafic alkaline volcanic rocks occur through-out the entire Pacific coast of West An... more Late Cenozoic mafic alkaline volcanic rocks occur through-out the entire Pacific coast of West Antarctica, including some of the islands adjacent or within the Bransfield Strait. Amongst them, Livingston Island is the least well-known, particularly in respect to mineralogy, petrology and geochemistry of the scarce manifestations of this type rocks, known as Inott Point Formation. This contribution presents new major element and trace element data from old and new-discovered outcrops in Livingston Island and compares them geochemically with simi-lar rocks from the island Greenwich situated in South Shet-land Islands arc and with Quaternary basalts in the islands Penguin, Deception and Bridgeman, within the back-arc rift basin Bransfield Strait. Alkaline basalts from the provinces in
Occupying the core of a large dome-like structure of high metamorphic rocks in Southeastern Bulga... more Occupying the core of a large dome-like structure of high metamorphic rocks in Southeastern Bulgaria, the Sakar granitoid batholith has been an object of conflicting interpretations for a long time. Lots of contradictory speculations about its structure, emplacement age and significance for regional correlations have been raised in our literature. Considered as Caledonian, Hercynian, Late Jurassic or even Early Cretaceous in age, the batholith still evokes professional curiosity. On the basis of extensive re-mapping and a large set of laboratory analyses carried out by 1987, we presented quite a while ago some brief information concerning the petrographical units, structural peculiarities, emplacement mechanism and geochemistry of the rocks in an extended abstract (Vergilov et al., 1986). A paper devoted to petrology and geochemistry of the pluton was accepted for publication (Kamenov et al., 2010), but the principle conclusions and results of our work are still not familiar to our ...
Based on a new sample set and extensive re-mapping an attempt is made to elucidate the field rela... more Based on a new sample set and extensive re-mapping an attempt is made to elucidate the field relations, mineral composition, nomenclature, geochemical features, magmatic and postmagmatic evolution, and to find new evidence for geodynamic reconstructions of the Sakar batholith. The dome-like batholith is emplaced into high-grade metamorphic rocks of still unclear age. It is covered by Permian and Triassic sedimentary rocks. The batholith is composed of the following granitoid units: equigranular in the inner parts, porphyroid with large microcline megacrysts in the outer parts, and small aplitoid bodies. Large xenoliths of gneisses and orthoamphibolites occur in the marginal parts of the batholith. The modal petrographic species are quartz-monzodiorite, quartz-monzonite, granodiorite, granite, quartz-syenite and leucogranite. The main rock-forming minerals are separated from artificial heavy concentrates and studied optically, chemically, by X-ray and IR-analysis. No characteristic d...
Geochem., Mineral., …, 2007
Magmatic rocks of Late Cretaceous age from the Central Srednogorie, Bulgaria show marked variatio... more Magmatic rocks of Late Cretaceous age from the Central Srednogorie, Bulgaria show marked variations in its geochemistry. The present study is focused on the common features in the magma evolution paths of several ore-magmatic systems: Elatsite, Chelopech, Medet, Assarel, Elshitsa and Capitan Dimitrievo considered as links of a petrological across-arc transect. The whole range of SiO 2 is large (40-73%). The evolution from intermediate to more basic stages is a common characteristic for most of the centers, but it is complicated by fractional differentiation and mixing of magmas. High-K calc-alkaline to shoshonitic series predominate, calc-alkaline being only in the middle of the transect. The geochemical peculiarities are typical for an enriched mantle source and indicate a subduction-related volcanic-arc setting. Melting degrees are estimated as small for both ends of the transect and higher for the central parts. The magmatic activity started at the northern end of the transect at 92.1 Ma, gradually became younger and finished at the border to the Rhodopes massif at 78 Ma. The 87 Sr/ 86 Sr ratios (0.704-0.706), suggest melts generated in a mantle source, modified by the addition of crustal materials. Pb-isotope analyses and ε-Hf values show an increase of the radiogenic component from North to South. The subduction slab retreat model is applied to explain the trenchward migration of the magmatic activity along the transect length.
1 Sofia University “St. K. Ohridski”, 1000 Sofia, Bulgaria, e-mail: kamenov@gea.uni-sofia.bg; 2 B... more 1 Sofia University “St. K. Ohridski”, 1000 Sofia, Bulgaria, e-mail: kamenov@gea.uni-sofia.bg; 2 Bulgarian Academy of Sciences, Geological Institute, 1113 Sofia, Bulgaria 3 Earth Science Section of the University of Geneva, 1211 Geneva, Switzerland 4 Bulgarian Academy of Sciences, Central Laboratory of Mineralogy and Crystallography, 1113 Sofia, Bulgaria 5 Institute of Isotope Geology and Mineral Resources, ETH, 8092 Zurich, Switzerland 6 University of Mining and Geology “St. Ivan Rilski”, 1700 Sofia, Bulgaria
ABSTRACT The Oman-Fakya pluton is a complex I type calc-alkaline body of Late Cretaceous age offe... more ABSTRACT The Oman-Fakya pluton is a complex I type calc-alkaline body of Late Cretaceous age offering a wide variety of rocks of intermediate composition between gabbro and more evolved magmas. The relationship between these rock types suggests that they are of different origin than it was supposed before. New pieces of evidence emerging from recent remapping, as well as from the mineralogical and chemical investigations point to a modified genetic view. The new observations show that magma mixing and mingling have taken place with the creation of a range of hybrid rocks with compositions between gabbroic and quartz-syenitic end-members. The mineralogical features of the rock-forming mafic minerals clinopyroxene, biotite and amphibole have been examined to establish some facets of their crystallization history. These features (normal and reverse zonings, incompatible assemblages, mineral relics in disequilibrium with host magmas ect.) are interpreted as signs for an open system evolution of the crystallizing magmas. The several crystal populations with a complex history indicate rapid changes in crystallization environment, most likely due to convective transport between crystallizing boundary layers and new basic magma pulses. The clinopyroxene is of diopside species and its chemistry bears traces of disturbed by the input of new basic magma crystallization. Biotite compositions seem to be result of contaminated magma of higher alkalinity theoretically favourable for generation of rich in Cu and Au fluids. Amphiboles present in the pluton are assigned to wide nomenclature divisions. Normal and reverse zonings are observed and regular changes in their composition are explained by an increasing of the activity of Si and of alkalies, as well as by pressure, temperature and degree of polymerization dependencies. The main coupled substitution mechanisms are of tschermakite and edenite types and Ti-tschermakite one is of minor importance. Polybaric crystallization and mixing of contrasting magmas are reprinted on the chemical composition of the amphiboles. All amphiboles fall within the field of granitoids crystallized at high f O2 . Thermal, chemical and mechanical interactions as principal types of exchange between coexisting magmas produced probably the appearant and hidden heterogeneities present in the mafic assemblage. It is believed that the revealed typomorphic features of the mafic mineral assemblage in the Oman-Fakya pluton are result of the complex succession and repetition of exchanges and partial chemical equilibration and every attempt to model the evolution of the magmatic system should comply with the conclusions extracted from the mafic minerals of the pluton.
Late Cenozoic mafic alkaline volcanic rocks occur throughout the entire Pacific coast of West Ant... more Late Cenozoic mafic alkaline volcanic rocks occur throughout the entire Pacific coast of West Antarctica, including in some of the islands adjacent or within the Bransfield Strait. Amongst them, Livingston Island is the least well-known, particularly in respect to mineralogy, petrology and geochemistry of the sparse manifestations of this type rocks, known as Inott Point Formation. The petrographic and geochemical aspects of old and new-discovered outcrops of primitive volcanic rocks are described. The new chemical analyses specify the nomenclature as low-Ti undersaturated olivine basalts mainly, and hawaiites rarely. Comparisons with the trace element characteristics of the similar rocks from the islands Greenwich, Penguin, Deception and Bridgemen revealed common features: high LILE/HFSE ratios (e.g. Ba/Zr 1.4-2.2; Ba/Nb 42-67; Rb/Nb 2.7-4; Ce/Nb 2.5-10; Th/Nb 0.25-0.90; K/Zr 39-67 etc.). These ratios are opposite to the low LILE/HFSE ratios in the alkalic provinces in Antarctic Peninsula (AP) and in Marie Byrd Land (MBL). The generally low absolute abundances of HFSE in all within and around the Bransfield Strait alkaline basalts and the high Zr/Nb (19-43) and Sr/Nb (>100) ratios are in contrast to such ratios in AP and MBL exposures. Higher degree of melting and variable interaction with the continental lithosphere is probably responsible for the geochemical differences with the alkaline basalts from the other provinces in West Antarctica. The regional geochemical LILE differences between MBL and AP substantiate the conclusion that they were derived from different source regions. Alkaline basalts from cratonic flood basalts in Patagonia and from the Atlantic Ocean island Ascension were used for correlation and their geochemistry is similar to plume-related MBL basalts. In spite of the extensional setting in the back-arc rift of Bransfield Strait, the studied alkaline basalts bear most of arc trace element signatures. New subdivision of the alkaline basalt provinces in West Antarctica is proposed. To the AP province, known to be derived from MORB-source asthenosphere in slab-window setting and to the MBL one, related to a deep mantle plume, we may add another one specific province, namely Bransfield Strait extensional one with alkaline basalts bearing traces of a lithospheric contamination and subduction-related geochemical signature.
ABSTRACT Borislav K. Kamenov. THE VARSHILO PLUTON IN STRANDJA – NEW MINERALOGICAL AND GEOCHEMICAL... more ABSTRACT Borislav K. Kamenov. THE VARSHILO PLUTON IN STRANDJA – NEW MINERALOGICAL AND GEOCHEMICAL DATA SUPPORTING ITS PETROLOGICAL EVOLUTION Initial studies of the Varshilo pluton exposed in Strandja Mountain concluded that magmas followed different petrochemical trends – an iron-enrichment with little silica enrichment until the final stages of crystallization and a high silica-enrichment one. The new presented mineral and geochemical data confirm the old speculations with more convincingness. The vast cumulative set of modal and chemical analyses worked out the following rock units within the pluton: I – pyroxenites, II – gabbro, III – gabbrodiorites, IV – monzodiorites and quartz-monzodiorites, V – quartz-diorites, VI – granodiorites, VII – aplites. The essential features of the main rock-forming minerals are present and they are consistent with the differentiation of two parental magmas – basic and intermediate. Textural and chemical evidences support the magma-mingling and magma-mixing phenomena. The extent of the fractionation, magma-mixing and fluid influences are figured out of the geochemical plots and general mass balance calculations. REE and MORB-normalized patterns support the island-arc geodynamic setting and subduction-related origin of the Varshilo magma. The main mechanisms of the magmatic evolution are modeled successfully by general mixing calculations – fractional crystallization, magma mixing, cumulative segregation and fluid involvement. The observed geochemical variations of the trace elements are modeled almost perfectly using published partition coefficients for coexisting minerals and liquids in the pluton. It was established that LIL-elements Rb, La, Ce, Sm, Yb, Th and U had been introduced in amounts exceeding the necessary ones if only fractional crystallization would be realized. Magma-fluid relations and crystallization in an open system in the magma chambers are offered in the interpretations. The proposed model fits well into the revealed three geochemical trends of the magma evolution: I – cumulative trend of imperfect mineral separation leading to pyroxenite at the end of the process; II – tholeiitic trend of iron-enrichment in the basic magma units; III – calc-alkaline trend in the intermediate magmas. The hybrid origin of the rock unit IV (quartz-monzodiorites and monzodiorites) was grounded more confidently. The new results could be stimulating for rising new ideas about this key-case complex multiphase Upper Cretaceous pluton in Bulgaria.
New petrological data, including rock-forming mineralogy and geochemistry are presented for a Lat... more New petrological data, including rock-forming mineralogy and geochemistry are presented for a Late Cretaceous ring-like pluton Izgrev, exposed in Strandja Mountain, Southeastern Bulgaria. The multi-phased pluton is a part of the volcano-plutonic Papya structure. Four intrusive phases are distinguished: (1) gabbro-pyroxenite, (2) monzogabbro-monzodiorite-diorite, (3) quartz-diorite-granodiorite, (4) aplite. A lot of petrographical modal varieties are separated into each one of the magmatic phases. Postplutonic dykes accompany the plutonic rocks. They are assigned to gabbro-porphyrite, monzogabbroporphyrite, monzodiorite-porphyrite, quartz-monzonite porphyry, diorite porphyrite, and granodiorite porphyry. The essential features of the main rock-forming minerals are present. Some field, textural and structural criteria suggest magma-mingling and magma-mixing phenomena, but crystal fractionation seems to have been the predominant rock-forming process. High-K calc-alkaline series prevail, the diversities to the tholeiitic, calc-alkaline and shoshonitic series being also available. Typical geochemical fingerprints of subduction-related affinity (LILE enrichment, HFSE depletion, compared to LREE) in MORB-normalized trace-element patterns are discussed. REE geochemical peculiarities are the clues to the idea of an enriched mantle source and they also indicate an island-arc magmatic setting. Trace-element ratios are used to reveal that the rock varieties have been controlled by the mixed mantle-crust source of the parental magmas. It appears that the crustal contamination and sediment input into the magma source had been inessential, but the fluid influx out of the altered oceanic crust had exerted much more influence on the source. Mixing of contrast magmas on the background of the extended fractional crystallization is proposed as a principal reason for the petrological evolution (MFC process) in the pluton. The geochemical correlation with analogical plutons from Eastern Srednogorie zone confirmed the petrological conclusions. The new results could serve as a basis of new ideas and models for the magmatic development in the Eastern segment of the Srednogorie island-arc magmatic system.