Geologiska Föreningen i Stockholm Förhandlingar, 1982
... The lower part of the Seve-Koli Nappe Complex is composed of the Seve nappes, con-sisting of ... more ... The lower part of the Seve-Koli Nappe Complex is composed of the Seve nappes, con-sisting of schists, gneisses and metabasic ... 3B) with partially sharp and partially more gradational contacts towards the surrounding gneisses and metabasites occur in the upper part of the ...
Geologiska Föreningen i Stockholm Förhandlingar, 1980
... They were prepared by standard methods involving HF-HC10, dissolution plus HCl ca-tion exchan... more ... They were prepared by standard methods involving HF-HC10, dissolution plus HCl ca-tion exchange. The 87Sr/soSr ratios were deter-mined on an AVCO 901-A mass spectro-meter. The ratios are normalized to a value of s6Sr/8SSr =O. 1194. ...
Monazite in melt-producing, poly-metamorphic terranes can grow, dissolve or reprecipitate at diff... more Monazite in melt-producing, poly-metamorphic terranes can grow, dissolve or reprecipitate at different stages during orogenic evolution particularly in hot, slowly cooling orogens such as the Svecofennian. Owing to the high heat flow in such orogens, small variations in pressure, temperature or deformation intensity may promote a mineral reaction. Monazite in diatexites and leucogranites from two Svecofennian domains yields older, coeval and younger U-Pb SIMS and EMP ages than zircon from the same rock. As zircon precipitated during the melt-bearing stage, its U-Pb ages reflect the timing of peak metamorphism, which is associated with partial melting and leucogranite formation. In one of the domains, the Granite and Diatexite Belt, zircon ages range between 1.87 and 1.86 Ga, whereas monazite yields two distinct double peaks at 1.87-1.86 and 1.82-1.80 Ga. The younger double peak is related to monazite growth or reprecipitation during subsolidus conditions associated with deformation along late-orogenic shear zones. Magmatic monazite in leucogranite records systematic variations in composition and age during growth that can be directly linked to Th/U ratios and preferential growth sites of zircon, reflecting the transition from melt to melt crystallisation of the magma. In the adjacent Ljusdal Domain, peak metamorphism in amphibolite facies occurred at 1.83-1.82 Ga as given by both zircon and monazite chronology. Pre-partial melting, 1.85 Ga contact metamorphic monazite is preserved, in spite of the high-grade overprint. By combining structural analysis, petrography and monazite and zircon geochronology, a metamorphic terrane boundary has been identified. It is concluded that the boundary formed by crustal shortening accommodated by major thrusting.
Deeply buried 1.5 Ga Polish anorthosites, accessible only by bore holes, reveal diagnostic featur... more Deeply buried 1.5 Ga Polish anorthosites, accessible only by bore holes, reveal diagnostic features of some massif-type anorthosites (polybarism, jotunitic parent magma), diapirically emplaced in the mid crust together with the rapakivi granites of the EW-trending Mazury complex, intruded along a major crustal discontinuity. Geochemical modelling and isotope data corroborate recent experimental work on the basaltic system in dry conditions: the source rock of the parental magma is a gabbronorite, necessarily lying in the lower crust. Since no Archaean crust is known in the region, high initial 188 Os ⁄ 187 Os ratios for sulphide-oxide isochrons and negative e Nd values are best accounted for by melting a 2.0 Ga mafic crust.
ABSTRACT Metasediments intruded by 1.90-1.87 Ga old plutonic rocks form the oldest major Proteroz... more ABSTRACT Metasediments intruded by 1.90-1.87 Ga old plutonic rocks form the oldest major Proterozoic crustal component in the Svecofennian Domain of the Baltic (Fennoscandian) Shield. Their NdTDM model ages and conventional multigrain zircon UPb ages between 2.4 and 2.1 Ga have previously been interpreted either as mixing ages between ∼ 1.9 Ga old juvenile materials and a minor Archaean component, or as actual rock and protolith ages. To resolve the ensuing controversy, 120 individual detrital zircons from Svecofennian metasediments in Sweden and Finland were analysed using the SHRIMP ion microprobe.The oldest materials in this array are a 3.44 Ga old zircon from the Tampere Schist Belt in Finland and a 3.32 Ga old crystal from southeastern Sweden. About 30% of the analysed crystals are 2.97-2.60 Ga old, while ∼ 65% have ages between 2.12 and 1.88 Ga. Thus there is no evidence of 2.6-2.1 Ga old protoliths, but the age range of the Proterozoic zircons indicates that a major area of 2.1-1.9 Ga old crust was in erosional position 1.9 Ga ago. This implies that the formation of Palaeoproterozoic crust in the Baltic Shield or its one-time close neighbourhood must have commenced 100–200 Ma earlier than hitherto assumed.In conjunction with previously obtained isotopic data, the youngest detritus ages of the present study constrain the age of Svecofennian sedimentation. It can also be concluded that the Archaean zircons found in quartzites from southern Sweden may have been derived from source areas to the southwest of the central-Svecofennian marine depositional basin, the so-called Bothnian Basin, separating southern Sweden from the Archaean craton in the northeastern part of the Shield.
We present U–Pb age data for detrital zircons from dike-intruded Neoproterozoic sedimentary rocks... more We present U–Pb age data for detrital zircons from dike-intruded Neoproterozoic sedimentary rocks of the Caledonian Middle Allochthon in central Sweden and Norway.Detrital zircons from 11 samples from the Särv, Sætra and upper Leksdal nappes (informally referred to as the Särv nappes) are clustered within ca. 0.9–1.75Ga, but display a bimodal distribution with major ca. 1.45–1.75Ga and ca. 0.9–1.2Ga components.
Whole-rock and mineral samples from the Jabal al Wask and Jabal Ess ophiolites, northwestern Saud... more Whole-rock and mineral samples from the Jabal al Wask and Jabal Ess ophiolites, northwestern Saudi Arabia, yield Sm-Nd isochron ages of 743+24 Ma and 782±38 Ma, respectively. These formation ages, which provide maximum limits for possible obduction ages, are in broad but not precise agreement with the previously known geologic history of the Arabian Shield. They indicate that the ophiolitic
Deeply buried 1.5 Ga Polish anorthosites, accessible only by bore holes, reveal diagnostic featur... more Deeply buried 1.5 Ga Polish anorthosites, accessible only by bore holes, reveal diagnostic features of some massif-type anorthosites (polybarism, jotunitic parent magma), diapirically emplaced in the mid crust together with the rapakivi granites of the EW-trending Mazury complex, intruded along a major crustal discontinuity. Geochemical modelling and isotope data corroborate recent experimental work on the basaltic system in dry conditions: the source rock of the parental magma is a gabbronorite, necessarily lying in the lower crust. Since no Archaean crust is known in the region, high initial 188 Os ⁄ 187 Os ratios for sulphide-oxide isochrons and negative e Nd values are best accounted for by melting a 2.0 Ga mafic crust.
... Gyr. Most zircons are 1.9-2.0 Gyr old suggesting that a major, still unknown early Proterozoi... more ... Gyr. Most zircons are 1.9-2.0 Gyr old suggesting that a major, still unknown early Proterozoic terrain older than 1.9 Ga supplied detritus to the early orogenic Svecofennian turbidites. These ... results. Terra Nova, 3,175-179 INTRODUCTION ...
The Precambrian basement in the western part of the East European Craton (EEC) consists of a seri... more The Precambrian basement in the western part of the East European Craton (EEC) consists of a series of arcuate tectonic belts metamorphosed in amphibolite and granulite facies. These are separated from each other by crustal discontinuities generally trending NNE±SSW. In conjunction with previously published Sm±Nd and U±Pb isotopic data, the results reported now show that the basement between the Baltic and Ukrainian Shields is Palaeoproterozoic in age. It was formed between 2.1 and 1.8 Ga ago.
Before the deposition of a Proterozoic cover and the repeated Proterozoic reworking of the older ... more Before the deposition of a Proterozoic cover and the repeated Proterozoic reworking of the older rocks, the presently exposed Archaean areas in northern Sweden formed part of a coherent craton. In the present study, we have used Sm-Nd isotopic analyses of Proterozoic granitoids and metavolcanics to delineate the Archaean palaeoboundary. In a regional context, the transition from strongly negative 6(Nd(t))
ABSTRACT SmNd data are presented for basic rocks and metagreywackes from the early Proterozoic B... more ABSTRACT SmNd data are presented for basic rocks and metagreywackes from the early Proterozoic Bothnian basin in central Sweden. The basic rocks include synsedimentary metabasalts, early orogenic intrusions, and anorogenic dolerites, covering the age range 1.9-1.2 Ga. The samples thus span the entire period from the early part of the Svecokarelian thermo-tectonic episode to the time when this region of the Baltic Shield had been a stable craton for about 0.4 Ga. All these samples have slightly positive ϵNd-values, up to +2 for synorogenic rocks and up to +3.5 for anorogenic dolerites. If these values are representative for the contemporaneous mantle, they suggest a less depleted character for this mantle than that shown for several other Proterozoic shield areas. Three metagreywacke samples have ϵNd-values of −2.4 to −3.1 indicating a significant influx of detrital older crustal material into the Bothnian basin.
Whole rock Sm-Nd isotope dating of the Garhwal and Bhowali mafic volcanics of the Kumaun Lesser H... more Whole rock Sm-Nd isotope dating of the Garhwal and Bhowali mafic volcanics of the Kumaun Lesser Himalayan sector yield an age of 2.51±0.08 Ga and an initial e Nd =5.1±0.5. This age and initial e Nd are the same as that of the Rampur-Mandi volcanics, which occur to the west in the Lesser Himalayas. In addition to confirming the widespread presence of the Late Archaean crustal elements in the Himalayas, these data constrain the age of the oldest rifting event and deposition of supracrustal sediments in the Himalayas and set at rest the long standing controversy about the age and inter-relationship of these mafic volcanics. Despite their present-day disparate occurrence as a result of the post-eruption deformation, the area covered by these mafic volcanics is large enough to classify them as flood basalts, the Rampur flood basalt (RFB) province. Rift-related volcanism of the same age is known from the contiguous Aravalli region of the NW Indian Shield. The orientation of the rifts in the two regions suggests the possibility of a mantle plume setting for the RFB.
The UThPb isotopic systematics of zircons from six sanukitoid intrusions in the Karelian Craton... more The UThPb isotopic systematics of zircons from six sanukitoid intrusions in the Karelian Craton has been investigated, using the secondary ion mass spectrometer (SIMS). Our results show that Karelian sanukitoids formed between 2745 and 2705 Ma ago and that ...
The Paleoproterozoic Bothnian Basin in central Sweden and south-central Finland is dominated by a... more The Paleoproterozoic Bothnian Basin in central Sweden and south-central Finland is dominated by a 10 km thick sequence of metasediments, mainly metaturbidites. These have been intruded by granitoids, which have traditionally been classified as early, late and postorogenic relative to the c. 1.9-l .8 Ga Svecofennian Orogeny. The early erogenic granitoids are part of a calcalkaline suite ranging in composition from ultramafic to granitic, while the late erogenic granitoids mainly are purely granitic and associated with abundant pegmatites. The postorogenic group forms large massifs of mainly granitic composition, and associated pegmatites are rare.
Geologiska Föreningen i Stockholm Förhandlingar, 1982
... The lower part of the Seve-Koli Nappe Complex is composed of the Seve nappes, con-sisting of ... more ... The lower part of the Seve-Koli Nappe Complex is composed of the Seve nappes, con-sisting of schists, gneisses and metabasic ... 3B) with partially sharp and partially more gradational contacts towards the surrounding gneisses and metabasites occur in the upper part of the ...
Geologiska Föreningen i Stockholm Förhandlingar, 1980
... They were prepared by standard methods involving HF-HC10, dissolution plus HCl ca-tion exchan... more ... They were prepared by standard methods involving HF-HC10, dissolution plus HCl ca-tion exchange. The 87Sr/soSr ratios were deter-mined on an AVCO 901-A mass spectro-meter. The ratios are normalized to a value of s6Sr/8SSr =O. 1194. ...
Monazite in melt-producing, poly-metamorphic terranes can grow, dissolve or reprecipitate at diff... more Monazite in melt-producing, poly-metamorphic terranes can grow, dissolve or reprecipitate at different stages during orogenic evolution particularly in hot, slowly cooling orogens such as the Svecofennian. Owing to the high heat flow in such orogens, small variations in pressure, temperature or deformation intensity may promote a mineral reaction. Monazite in diatexites and leucogranites from two Svecofennian domains yields older, coeval and younger U-Pb SIMS and EMP ages than zircon from the same rock. As zircon precipitated during the melt-bearing stage, its U-Pb ages reflect the timing of peak metamorphism, which is associated with partial melting and leucogranite formation. In one of the domains, the Granite and Diatexite Belt, zircon ages range between 1.87 and 1.86 Ga, whereas monazite yields two distinct double peaks at 1.87-1.86 and 1.82-1.80 Ga. The younger double peak is related to monazite growth or reprecipitation during subsolidus conditions associated with deformation along late-orogenic shear zones. Magmatic monazite in leucogranite records systematic variations in composition and age during growth that can be directly linked to Th/U ratios and preferential growth sites of zircon, reflecting the transition from melt to melt crystallisation of the magma. In the adjacent Ljusdal Domain, peak metamorphism in amphibolite facies occurred at 1.83-1.82 Ga as given by both zircon and monazite chronology. Pre-partial melting, 1.85 Ga contact metamorphic monazite is preserved, in spite of the high-grade overprint. By combining structural analysis, petrography and monazite and zircon geochronology, a metamorphic terrane boundary has been identified. It is concluded that the boundary formed by crustal shortening accommodated by major thrusting.
Deeply buried 1.5 Ga Polish anorthosites, accessible only by bore holes, reveal diagnostic featur... more Deeply buried 1.5 Ga Polish anorthosites, accessible only by bore holes, reveal diagnostic features of some massif-type anorthosites (polybarism, jotunitic parent magma), diapirically emplaced in the mid crust together with the rapakivi granites of the EW-trending Mazury complex, intruded along a major crustal discontinuity. Geochemical modelling and isotope data corroborate recent experimental work on the basaltic system in dry conditions: the source rock of the parental magma is a gabbronorite, necessarily lying in the lower crust. Since no Archaean crust is known in the region, high initial 188 Os ⁄ 187 Os ratios for sulphide-oxide isochrons and negative e Nd values are best accounted for by melting a 2.0 Ga mafic crust.
ABSTRACT Metasediments intruded by 1.90-1.87 Ga old plutonic rocks form the oldest major Proteroz... more ABSTRACT Metasediments intruded by 1.90-1.87 Ga old plutonic rocks form the oldest major Proterozoic crustal component in the Svecofennian Domain of the Baltic (Fennoscandian) Shield. Their NdTDM model ages and conventional multigrain zircon UPb ages between 2.4 and 2.1 Ga have previously been interpreted either as mixing ages between ∼ 1.9 Ga old juvenile materials and a minor Archaean component, or as actual rock and protolith ages. To resolve the ensuing controversy, 120 individual detrital zircons from Svecofennian metasediments in Sweden and Finland were analysed using the SHRIMP ion microprobe.The oldest materials in this array are a 3.44 Ga old zircon from the Tampere Schist Belt in Finland and a 3.32 Ga old crystal from southeastern Sweden. About 30% of the analysed crystals are 2.97-2.60 Ga old, while ∼ 65% have ages between 2.12 and 1.88 Ga. Thus there is no evidence of 2.6-2.1 Ga old protoliths, but the age range of the Proterozoic zircons indicates that a major area of 2.1-1.9 Ga old crust was in erosional position 1.9 Ga ago. This implies that the formation of Palaeoproterozoic crust in the Baltic Shield or its one-time close neighbourhood must have commenced 100–200 Ma earlier than hitherto assumed.In conjunction with previously obtained isotopic data, the youngest detritus ages of the present study constrain the age of Svecofennian sedimentation. It can also be concluded that the Archaean zircons found in quartzites from southern Sweden may have been derived from source areas to the southwest of the central-Svecofennian marine depositional basin, the so-called Bothnian Basin, separating southern Sweden from the Archaean craton in the northeastern part of the Shield.
We present U–Pb age data for detrital zircons from dike-intruded Neoproterozoic sedimentary rocks... more We present U–Pb age data for detrital zircons from dike-intruded Neoproterozoic sedimentary rocks of the Caledonian Middle Allochthon in central Sweden and Norway.Detrital zircons from 11 samples from the Särv, Sætra and upper Leksdal nappes (informally referred to as the Särv nappes) are clustered within ca. 0.9–1.75Ga, but display a bimodal distribution with major ca. 1.45–1.75Ga and ca. 0.9–1.2Ga components.
Whole-rock and mineral samples from the Jabal al Wask and Jabal Ess ophiolites, northwestern Saud... more Whole-rock and mineral samples from the Jabal al Wask and Jabal Ess ophiolites, northwestern Saudi Arabia, yield Sm-Nd isochron ages of 743+24 Ma and 782±38 Ma, respectively. These formation ages, which provide maximum limits for possible obduction ages, are in broad but not precise agreement with the previously known geologic history of the Arabian Shield. They indicate that the ophiolitic
Deeply buried 1.5 Ga Polish anorthosites, accessible only by bore holes, reveal diagnostic featur... more Deeply buried 1.5 Ga Polish anorthosites, accessible only by bore holes, reveal diagnostic features of some massif-type anorthosites (polybarism, jotunitic parent magma), diapirically emplaced in the mid crust together with the rapakivi granites of the EW-trending Mazury complex, intruded along a major crustal discontinuity. Geochemical modelling and isotope data corroborate recent experimental work on the basaltic system in dry conditions: the source rock of the parental magma is a gabbronorite, necessarily lying in the lower crust. Since no Archaean crust is known in the region, high initial 188 Os ⁄ 187 Os ratios for sulphide-oxide isochrons and negative e Nd values are best accounted for by melting a 2.0 Ga mafic crust.
... Gyr. Most zircons are 1.9-2.0 Gyr old suggesting that a major, still unknown early Proterozoi... more ... Gyr. Most zircons are 1.9-2.0 Gyr old suggesting that a major, still unknown early Proterozoic terrain older than 1.9 Ga supplied detritus to the early orogenic Svecofennian turbidites. These ... results. Terra Nova, 3,175-179 INTRODUCTION ...
The Precambrian basement in the western part of the East European Craton (EEC) consists of a seri... more The Precambrian basement in the western part of the East European Craton (EEC) consists of a series of arcuate tectonic belts metamorphosed in amphibolite and granulite facies. These are separated from each other by crustal discontinuities generally trending NNE±SSW. In conjunction with previously published Sm±Nd and U±Pb isotopic data, the results reported now show that the basement between the Baltic and Ukrainian Shields is Palaeoproterozoic in age. It was formed between 2.1 and 1.8 Ga ago.
Before the deposition of a Proterozoic cover and the repeated Proterozoic reworking of the older ... more Before the deposition of a Proterozoic cover and the repeated Proterozoic reworking of the older rocks, the presently exposed Archaean areas in northern Sweden formed part of a coherent craton. In the present study, we have used Sm-Nd isotopic analyses of Proterozoic granitoids and metavolcanics to delineate the Archaean palaeoboundary. In a regional context, the transition from strongly negative 6(Nd(t))
ABSTRACT SmNd data are presented for basic rocks and metagreywackes from the early Proterozoic B... more ABSTRACT SmNd data are presented for basic rocks and metagreywackes from the early Proterozoic Bothnian basin in central Sweden. The basic rocks include synsedimentary metabasalts, early orogenic intrusions, and anorogenic dolerites, covering the age range 1.9-1.2 Ga. The samples thus span the entire period from the early part of the Svecokarelian thermo-tectonic episode to the time when this region of the Baltic Shield had been a stable craton for about 0.4 Ga. All these samples have slightly positive ϵNd-values, up to +2 for synorogenic rocks and up to +3.5 for anorogenic dolerites. If these values are representative for the contemporaneous mantle, they suggest a less depleted character for this mantle than that shown for several other Proterozoic shield areas. Three metagreywacke samples have ϵNd-values of −2.4 to −3.1 indicating a significant influx of detrital older crustal material into the Bothnian basin.
Whole rock Sm-Nd isotope dating of the Garhwal and Bhowali mafic volcanics of the Kumaun Lesser H... more Whole rock Sm-Nd isotope dating of the Garhwal and Bhowali mafic volcanics of the Kumaun Lesser Himalayan sector yield an age of 2.51±0.08 Ga and an initial e Nd =5.1±0.5. This age and initial e Nd are the same as that of the Rampur-Mandi volcanics, which occur to the west in the Lesser Himalayas. In addition to confirming the widespread presence of the Late Archaean crustal elements in the Himalayas, these data constrain the age of the oldest rifting event and deposition of supracrustal sediments in the Himalayas and set at rest the long standing controversy about the age and inter-relationship of these mafic volcanics. Despite their present-day disparate occurrence as a result of the post-eruption deformation, the area covered by these mafic volcanics is large enough to classify them as flood basalts, the Rampur flood basalt (RFB) province. Rift-related volcanism of the same age is known from the contiguous Aravalli region of the NW Indian Shield. The orientation of the rifts in the two regions suggests the possibility of a mantle plume setting for the RFB.
The UThPb isotopic systematics of zircons from six sanukitoid intrusions in the Karelian Craton... more The UThPb isotopic systematics of zircons from six sanukitoid intrusions in the Karelian Craton has been investigated, using the secondary ion mass spectrometer (SIMS). Our results show that Karelian sanukitoids formed between 2745 and 2705 Ma ago and that ...
The Paleoproterozoic Bothnian Basin in central Sweden and south-central Finland is dominated by a... more The Paleoproterozoic Bothnian Basin in central Sweden and south-central Finland is dominated by a 10 km thick sequence of metasediments, mainly metaturbidites. These have been intruded by granitoids, which have traditionally been classified as early, late and postorogenic relative to the c. 1.9-l .8 Ga Svecofennian Orogeny. The early erogenic granitoids are part of a calcalkaline suite ranging in composition from ultramafic to granitic, while the late erogenic granitoids mainly are purely granitic and associated with abundant pegmatites. The postorogenic group forms large massifs of mainly granitic composition, and associated pegmatites are rare.
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