Papers by jaroslav dostal
Minerals, May 2, 2022
The Meguma terrane is a unique unit of the Northern Appalachians as it is only identified in Nova... more The Meguma terrane is a unique unit of the Northern Appalachians as it is only identified in Nova Scotia. It was thrust over the Avalon terrane during the Early Devonian Acadian Orogeny. The Avalon and Meguma terranes are exotic to North America and likely originated along the margin of Gondwana. The precise relationship between the terranes is uncertain and very little is known about the basement rocks of each terrane. Hosted within the Late Devonian lamprophyric Popes Harbour dyke of the Meguma terrane are xenoliths of meta-sedimentary and meta-igneous rocks that are from the basement of the Avalon terrane. The xenoliths offer a glimpse into the nature of the lower crust of the Northern Appalachians. In this study, we present in situ zircon U-Pb age dates from a rare dioritic xenolith in order to assess its origin. The results show that the majority of zircons ages are between ~580 Ma and ~616 Ma with smaller groups at 750-630 Ma, ~2100 Ma, and <570 Ma. The zircon 206 Pb/ 238 U weighted-mean age of the rock is 603 ± 5.3 Ma and contemporaneous, with granitic intrusions of the Avalon terrane located within the Antigonish and Cobequid highlands of Nova Scotia. The diorite is compositionally similar to granitoids from an active continental margin. The discovery of Early Paleoproterozoic (~2100 Ma) zircons and the absence of Late Paleoproterozoic (1900( -1700 Ma) Ma) and Mesoproterozoic (1600-1000 Ma) zircons suggests that the parental magma either encounters only Early Paleoproterozoic and Late Neoproterozoic rocks during emplacement or is derived by the melting of Paleoproterozoic rocks and/or the melting and mixing of Paleoproterozoic and Late Neoproterozoic rocks. Therefore, it is possible that Paleoproterozoic rocks may exist within the basement of the Avalon terrane.
Eocene Volcanic Complex from Central British Columbia: The Role of Fractional Crystallization during the Magmatic Evolution
Lithosphere
The Challis-Kamloops belt of south-central British Columbia is a regionally extensive (>65,000... more The Challis-Kamloops belt of south-central British Columbia is a regionally extensive (>65,000 km2) magmatic province that erupted within the North American Cordillera during the Eocene (55-45 Ma). The inland volcanic belt runs parallel to the coast, and the rocks were emplaced mainly within extensional basins indicating volcanism was attributed to rift-related decompressional melting. The rocks include both calc-alkaline and tholeiitic mafic and intermediate types (i.e., low-Fe, medium-Fe, and high-Fe suites). Voluminous volcanic units (Buck Creek, Goosly Lake, Swans Lake) of the Buck Creek volcanic complex (~3,000 km2 in area) within the Nechako plateau erupted within 1-2 million years and show significant internal chemical variability. All rock types have similar Sr-Nd isotopic (87Sr/86Sri=0.70435-0.70487; εNdt=+2.6-+4.0) ratios indicating they originated from the same sub-Cordilleran mantle source. Petrological modeling using the most primitive rocks of the Buck Creek, Goosly...
Upper Triassic Takla Group volcanic rocks, Stikine Terrane, north-central British Columbia: geochemistry, petrogenesis, and tectonic implications
Canadian Journal of Earth Sciences, 1999
The Upper Triassic Takla Group volcano-sedimentary assemblage is part of the Stikine Terrane of t... more The Upper Triassic Takla Group volcano-sedimentary assemblage is part of the Stikine Terrane of the Intermontane Belt in the Canadian Cordillera and covers an area of more than 30 000 km2 in a belt up to 50 km wide and more than 800 km long. In the McConnell Creek area of north-central British Columbia, the assemblage consists of plagioclase-clinopyroxene-phyric, dominantly basaltic to andesitic flows and pyroclastic rocks, interlayered with volcanogenic sedimentary rocks. Compositionally, the volcanic rocks are intermediate between tholeiitic and calc-alkaline. Their mantle-normalized trace element patterns are characterized by a moderate large-ion lithophile element enrichment and Nb and Ti depletion, suggesting that magmatism occurred in a volcanic-arc setting. Flat, heavy rare earth element chondrite-normalized patterns with (La/Yb)n ratios from 2 to 4.5 suggest that the parent magma was produced by mantle melting in the spinel stability field. The low Sr isotopic ratios (87Sr/8...
Geochemistry of the Cretaceous alkali basaltic rocks of the central part of the Western Carpathians (Slovakia)
Rare Metal Deposits Associated with Alkaline/Peralkaline Igneous Rocks
Rare Earth and Critical Elements in Ore Deposits
Approximately 20,000 thousand years ago, during the last glacial maximum, continental ice sheets ... more Approximately 20,000 thousand years ago, during the last glacial maximum, continental ice sheets up to one kilometer thick covered the province of Nova Scotia. The advancing ice sheets removed large amounts of material from the tops of gold bearing anticlines and deposited that material in the form of glacial till. A recent discovery of an old adit in a well consolidated till deposit down ice of the Tangier gold district led to a previous investigation of the economic potential of the Tangier site. As a result of the work done in Tangier, a sluicing project was carried out in the summer of 2005 to evaluate three different sites in three different gold districts of Nova Scotia: Moose River, Lake Catcha, and Kemptville. Sampling methodology includes the sluicing of one bulk till sample from each site with a Long-Tom sluice. A separate head grade and tailings sample was taken and analyzed with bottle roll cyanidation with AAS finish from each site. The head sample was split to determine grain size concentrations of Au. Sluice concentrates were further concentrated with a Wifley Table for analysis with a scanning electron microscope. Final grade calculations will be worked back to establish a gold value per metric tonne.
In island arcs, the latest stage of subduction-related processes is commonly followed by an exten... more In island arcs, the latest stage of subduction-related processes is commonly followed by an extensional tectonic regime. The Stikine terrane of the Canadian Cordillera records one such transition in the rocks of the Early to Middle Jurassic upper Hazelton Group, in northwestern British Columbia. These rocks are host to the world-class Eskay Creek volcanogenic massive sulphide (VMS) deposit. Recent targeted studies of the upper Hazelton Group have documented a number of characteristics which confi rm that the upper Hazelton Group represents a shift from arc building during the Early Jurassic to an extensional environment during the late Early to Middle Jurassic. These characteristics include 1) the presence of original rift bounding faults; 2) unconformities that are associated with rift fi lling conglomerates, including one that grades into more distal facies argillite; 3) a shift in the geochemical signature of mainly intermediate Early Jurassic calc-alkaline volcanic rocks to Midd...
The Hazelton Group comprises the youngest pre-accretionary rocks of the Stikine terrane in NW Bri... more The Hazelton Group comprises the youngest pre-accretionary rocks of the Stikine terrane in NW British Columbia. The group is dominated by several successions of Early to Middle Jurassic subaerial and submarine calc-alkaline island-arc volcanic and sedimentary rocks. One of them, the Salmon River Formation (SRF), which represents a brief period of volcanic activity at the boundary between the Aalenian and Bajocian, is compositionally distinct. The SRF is host to three economic VMS deposits, including the world class Eskay Creek Ag-Au and base metal deposit, as well as over 60 other VMS prospects. The Formation is preserved as several fault-bounded erosional remnants or separate sub-basins along a 200 km belt. The ba-
Late Devonian syenitic intrusion from southeastern Alaska: Petrogenesis, tectonic implications, and rare metal metallogeny
Lithos, 2021
Abstract The Late Devonian Corner Bay pluton is a part of the Sitkoh alkaline plutonic complex on... more Abstract The Late Devonian Corner Bay pluton is a part of the Sitkoh alkaline plutonic complex on the Chichagof Island, southeastern Alaska, which is located in the Alexander terrane of the North American Cordillera. The intrusion, about 12 km long and 4 km wide, is composed predominantly of amphibole-biotite-bearing syenitic/ monzonitic rocks with minor alkaline gabbros and has a U Pb zircon age of ~367 Ma interpreted as the crystallization age of the pluton. The rocks are metaluminous and have silica contents ranging from 47 to 63 wt% with a silica gap at 52–58 wt% and have high contents of alkalis, typical of shoshonitic rocks. They are rich in large-ion-lithophile elements (including Rb, Sr, Ba, U) and their isotopic composition is characterized by relatively uniform ƐNd(t) values (+3.4 to +3.6), Neoproterozoic Nd depleted mantle model ages (650–700 Ma) and initial 87Sr/86Sr ratios (~0.704). The rocks were generated by fractional crystallization of alkali basaltic magma formed by partial melting of an amphibole-phlogopite-bearing peridotite of the sub-arc lithospheric mantle. The mantle-source underwent a Neoproterozoic metasomatic enrichment event and does not show a contribution from juvenile Devonian mantle indicating that rifting associated with the magma emplacement was of limited extent as it did not replace the old lithospheric mantle. Several geothermobarometers document emplacement of the parental magma at mid-crustal levels (8.5–10 kb) and polybaric crystallization from ~1200 °C to solidus. Crystallization of amphibole took place at ~880-980 °C and 2.4–5.5 kb. Subsequently the rocks underwent recrystallization (feldspars: 170 Ma – 40Ar/39Ar age) and re-equilibration (biotite: 129 Ma (40Ar/39Ar) at ~600-650 °C and 2 kb). Zircon, rutile and apatite saturation temperatures provide consistent results (~800 °C). The intrusion is a part of a metallogenic province of rare metals, which stretched across the islands in the southeastern most part of Alaska.
Some new data for chrysoberyl from Marsikov, northern Moravia, Czechoslovakia
General principles of neutron activation analysis
Trace element geochemistry of paleozoic amphibolites from S. W. Spain
Mineralogy and Petrology, 1979
ABSTRACT
Lithos, 1977
Rare-earth element abundances of calc-alkaline andesitic rocks from southern Peru ,how that these... more Rare-earth element abundances of calc-alkaline andesitic rocks from southern Peru ,how that these rocks cannot be produced by a single stage process. The high content of LILE, particularly LREE requires their derivation from a source already enriched in ~hese elements and having a distinctly fractionated REE pattern. It is suggested that ascending hydrous fluids, released from the subducted c~:eanic lithosphere, enriched the upper manHe in LILE by zone refining. The partial melting of such an enriched upper raantle, follo~ed by fractional crystallization, could produce andesitic rocks. REE data indlcetc that shosl-.o-. nitic rocks from southern Peru can be derived from an unfractionated garnet-bearing peridotite by a low degree of partial melting.
Lithos, 1976
The U content of major rock-forming minerals in a suite of calc-alkaline volcamc rocks from Sardi... more The U content of major rock-forming minerals in a suite of calc-alkaline volcamc rocks from Sardinia is very low and their partition coefficient of U (D c =CS/C l') is smaller than 0.1. The values of D U of the mineral phases decrease from basalt to dacite and, in all rocks, the bulk of U and K is present in the groundmass. The apparent close association between K and U in basic and intermediate rocks probably reflects the fact that most of their rock-forming minerals are relatively 'inert' with respect to both of these elements.
Journal of Volcanology and Geothermal Research, 1978
The Upper Tertiary to Quaternary volcanic complex of Kouh-e-Shahsavaran in southeastern Iran is c... more The Upper Tertiary to Quaternary volcanic complex of Kouh-e-Shahsavaran in southeastern Iran is composed of calc-alkaline rocks of island arc type (high-alumina basalts, basic andesites, andesites and dacites) even though it was emplaced on the continental basement. The volcanic rocks of the complex are genetically related and were probably derived by low-pressure fractional crystallization of high-A] basalts. The anomalously high content of Sr in some rocks probably reflects an accumulation of plagioclase. The trace element data are consistent with the origin of the parental magma by partial melting of an "enriched" upper mantle peridotite.
Journal of Volcanology and Geothermal Research, 1979
The chemical variations in the continental-margin andesitic suite from northwestern Sardinia are ... more The chemical variations in the continental-margin andesitic suite from northwestern Sardinia are compatible with a mechanism involving both fractional crystallization and contamination. Contamination is probably related to interaction with ignimbrites formed by crustal anatexis, which are spatially and temporally associated with andesitic rocks. A similar process may have also affected other calc-alkaline andesitic suites such as those of New Zealand and southern Peru where the contents of lithophile elements and the Sr isotope ratios appear to be related to the composition of associated ignimbrites.
Journal of Volcanology and Geothermal Research, 1981
Quaternary volcanic rocks of Stromboli (Italy) can be divided into older calc-alkaline and younge... more Quaternary volcanic rocks of Stromboli (Italy) can be divided into older calc-alkaline and younger shoshonitic series. The SiO 2 contents of the rocks range from 50% to 61% but the majority of them are basalts. The rocks show systematic variations in chemical composition which correlate with the volcanic stratigraphy, such that, at a given SiO 2 content, K and other incompatible elements such as REE increase with decreasing age. In addition, the La/Yb ratio increases while the K/Rb, K/Ba, Zr/Ce and Zr/Nb ratios decrease towards the top of the volcanic pile. On the other hand, the abundances of transition elements, V, Co, Sc and Zn, like most major elements are broadly similar in comparable rocks of different ages. It is suggested that the parent magmas were derived by partial melting from upper mantle peridotite enriched in incompatible elements by fluids released from the descending oceanic lithosphere. The temporal chemical variations may probably be related to the lengths of time during which fluids were in contact with the upper mantle source.
Partitioning of transition elements between clinopyroxene and garnet
Earth and Planetary Science Letters, 1980
ABSTRACT
Earth and Planetary Science Letters, 1978
REE abundances in gabbros and peridotites from Site 334 of DSDP Leg 37 show that these rocks are ... more REE abundances in gabbros and peridotites from Site 334 of DSDP Leg 37 show that these rocks are cumulates produced by fractional crystallization of a primitive oceanic tholeiite magma. They may be part of a layered oceanic complex. The REE distributions in the residual liquids left after such a fractionation are similar to those of incompatible element-depleted oceanic tholeiites. The REE data indicate that the basalts which overlie the gabbro-peridorite complex, are not genetically related to plutonic rocks.
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Papers by jaroslav dostal