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Laurence Page - One of the best experts on this subject based on the ideXlab platform.
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Ar-40/Ar-39 hornblende geochronology from the Forsmark area in central Sweden : constraints on late Svecofennian cooling, Ductile Deformation and exhumation
Precambrian Research, 2008Co-Authors: Tobias Hermansson, Michael B. Stephens, Laurence PageAbstract:At Forsmark, ca. 120 km north of Stockholm in central Sweden, Ductile high-strain belts with WNW to NW trend anastomose around tectonic lenses with an inferred lower degree of Ductile strain. Previous studies of Ductile Deformation zones with WNW to NW trend, elsewhere in the western part of the Svecofennian orogen in central Sweden, have yielded estimates for the timing of at least one phase of discrete Ductile Deformation that fall in the time interval 1.82-1.78 Ga. Most of these ages were determined by the U/Pb dating of titanite and, for this reason, provide no information on the thermal evolution. In this paper, we make use of Ar-40/Ar-39 hornblende geochronology to address late Svecofennian cooling, Ductile Deformation and exhumation. The data demonstrate the presence of three Ar-40/Ar-39 hornblende age generations. All ages have been adjusted to take account of ca. 1% systematic bias between Ar-40/Ar-39 and U/Pb ages recently reported in the literature. The oldest age, ca. 1.87 Ga, and the intermediate age generation, 1.85-1.84 Ga, are spatially restricted to the tectonic lenses. By contrast, the youngest age generation, 1.83-1.81 Ga, occurs both within the tectonic lenses and the enveloping high-strain belts. one explanation for the structurally controlled age distribution involves regional cooling beneath the closure temperature for argon isotopic mobility around or above 500 degrees C by 1.84 Ga, as represented in the oldest and intermediate age generations, followed by resetting of the argon isotope system in hornblende between 1.83 and 1.81 Ga, as represented in the youngest age generation. This resetting occurred in response to retrograde, lower amphibolite- to upper greenschist-facies Deformation along discrete high-strain zones within the broader high-strain belts and was associated with regional exhumation. An alternative explanation involves no resetting of the ages. Instead, it is suggested that a period of slow cooling of hornblendes with slightly different closure temperatures, from ca. 1.87 to 1.82 Ga, may have caused the age variation observed within the tectonic lenses, whereas locally maintained higher temperatures, due to activity along the discrete high-strain zones, can explain the consistently younger ages in the broad, enveloping high-strain belts. In this explanation, an increase in cooling rate, in response to regional exhumation, finally closed the argon isotope system in hornblende throughout the area at 1.83-1.81 Ga. It is suggested that the regional exhumation at 1.83-1.81 Ga, which is included in both explanations, is related to far-field effects of the Deformation that ended an accretionary tectonic cycle in adjacent tectonic domains. (c) 2008 Elsevier B.V. All rights reserved. (Less)
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ar 40 ar 39 hornblende geochronology from the forsmark area in central sweden constraints on late svecofennian cooling Ductile Deformation and exhumation
Precambrian Research, 2008Co-Authors: Tobias Hermansson, Michael B. Stephens, Laurence PageAbstract:At Forsmark, ca. 120 km north of Stockholm in central Sweden, Ductile high-strain belts with WNW to NW trend anastomose around tectonic lenses with an inferred lower degree of Ductile strain. Previous studies of Ductile Deformation zones with WNW to NW trend, elsewhere in the western part of the Svecofennian orogen in central Sweden, have yielded estimates for the timing of at least one phase of discrete Ductile Deformation that fall in the time interval 1.82-1.78 Ga. Most of these ages were determined by the U/Pb dating of titanite and, for this reason, provide no information on the thermal evolution. In this paper, we make use of Ar-40/Ar-39 hornblende geochronology to address late Svecofennian cooling, Ductile Deformation and exhumation. The data demonstrate the presence of three Ar-40/Ar-39 hornblende age generations. All ages have been adjusted to take account of ca. 1% systematic bias between Ar-40/Ar-39 and U/Pb ages recently reported in the literature. The oldest age, ca. 1.87 Ga, and the intermediate age generation, 1.85-1.84 Ga, are spatially restricted to the tectonic lenses. By contrast, the youngest age generation, 1.83-1.81 Ga, occurs both within the tectonic lenses and the enveloping high-strain belts. one explanation for the structurally controlled age distribution involves regional cooling beneath the closure temperature for argon isotopic mobility around or above 500 degrees C by 1.84 Ga, as represented in the oldest and intermediate age generations, followed by resetting of the argon isotope system in hornblende between 1.83 and 1.81 Ga, as represented in the youngest age generation. This resetting occurred in response to retrograde, lower amphibolite- to upper greenschist-facies Deformation along discrete high-strain zones within the broader high-strain belts and was associated with regional exhumation. An alternative explanation involves no resetting of the ages. Instead, it is suggested that a period of slow cooling of hornblendes with slightly different closure temperatures, from ca. 1.87 to 1.82 Ga, may have caused the age variation observed within the tectonic lenses, whereas locally maintained higher temperatures, due to activity along the discrete high-strain zones, can explain the consistently younger ages in the broad, enveloping high-strain belts. In this explanation, an increase in cooling rate, in response to regional exhumation, finally closed the argon isotope system in hornblende throughout the area at 1.83-1.81 Ga. It is suggested that the regional exhumation at 1.83-1.81 Ga, which is included in both explanations, is related to far-field effects of the Deformation that ended an accretionary tectonic cycle in adjacent tectonic domains. (c) 2008 Elsevier B.V. All rights reserved. (Less)
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penetrative Ductile Deformation and amphibolite facies metamorphism prior to 1851 ma in the western part of the svecofennian orogen fennoscandian shield
Precambrian Research, 2007Co-Authors: Tobias Hermansson, Michael B. Stephens, Jenny Andersson, Fernando Corfu, Laurence PageAbstract:The Svecofennian orogen in the Fennosandian Shield consists of several Palaeoproterozoic meta-igneous provinces that generally young progressively southwards and westwards. The understanding of the tectonic evolution of these different provinces is linked to the ability to constrain the timing of Ductile Deformation and metamorphism within them. In the western part of the orogen, in central Sweden, Ductile Deformation and metamorphism is conventionally thought to have occurred after 1.85 Ga and mainly around 1.82-1.80 Ga. At Forsmark in central Sweden, we have dated two undeformed granite dykes that cross-cut the tectonic fabric in their host rocks to 1851 +/- 15 and 1855 +/- 6 Ma, respectively. Since the former shows an unequivocal field relationship with respect to the tectonic fabric, we establish that penetrative Ductile Deformation under amphibolite-facies metamorphic conditions occurred prior to 1851 +/- 5 Ma. This U-Pb zircon minimum age for the timing of Ductile Deformation is supported by a U-Pb titanite age of 1844 +/- 4 Ma. These data as well as the field relationships at Forsmark indicate that an early phase of penetrative Deformation and metamorphism affected the Svecofennian bedrock in the western part of the Fennoscandian Shield and was overprinted, after 1851 +/- 5 Ma, by spatially more confined Deformational events. In conjunction with earlier results, our data help to establish the presence of tectonic domains with contrasting tectonothermal histories in the western part of the Svecofennian orogen. (c) 2006 Elsevier B.V. All rights reserved. (Less)
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Penetrative Ductile Deformation and amphibolite-facies metamorphism prior to 1851 Ma in the western part of the Svecofennian orogen, Fennoscandian Shield
Precambrian Research, 2007Co-Authors: Tobias Hermansson, Michael B. Stephens, Jenny Andersson, Fernando Corfu, Laurence PageAbstract:Abstract The Svecofennian orogen in the Fennosandian Shield consists of several Palaeoproterozoic meta-igneous provinces that generally young progressively southwards and westwards. The understanding of the tectonic evolution of these different provinces is linked to the ability to constrain the timing of Ductile Deformation and metamorphism within them. In the western part of the orogen, in central Sweden, Ductile Deformation and metamorphism is conventionally thought to have occurred after 1.85 Ga and mainly around 1.82–1.80 Ga. At Forsmark in central Sweden, we have dated two undeformed granite dykes that cross-cut the tectonic fabric in their host rocks to 1851 ± 5 and 1855 ± 6 Ma, respectively. Since the former shows an unequivocal field relationship with respect to the tectonic fabric, we establish that penetrative Ductile Deformation under amphibolite-facies metamorphic conditions occurred prior to 1851 ± 5 Ma. This U–Pb zircon minimum age for the timing of Ductile Deformation is supported by a U–Pb titanite age of 1844 ± 4 Ma. These data as well as the field relationships at Forsmark indicate that an early phase of penetrative Deformation and metamorphism affected the Svecofennian bedrock in the western part of the Fennoscandian Shield and was overprinted, after 1851 ± 5 Ma, by spatially more confined Deformational events. In conjunction with earlier results, our data help to establish the presence of tectonic domains with contrasting tectonothermal histories in the western part of the Svecofennian orogen.
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Penetrative Ductile Deformation and amphibolite-facies metamorphism prior to 1851Ma in the western part of the Svecofennian orogen, Fennoscandian Shield
Precambrian Research, 2007Co-Authors: Tobias Hermansson, Michael B. Stephens, Jenny Andersson, Fernando Corfu, Laurence PageAbstract:The Svecofennian orogen in the Fennosandian Shield consists of several Palaeoproterozoic meta-igneous provinces that generally young progressively southwards and westwards. The understanding of the tectonic evolution of these different provinces is linked to the ability to constrain the timing of Ductile Deformation and metamorphism within them. In the western part of the orogen, in central Sweden, Ductile Deformation and metamorphism is conventionally thought to have occurred after 1.85 Ga and mainly around 1.82-1.80 Ga. At Forsmark in central Sweden, we have dated two undeformed granite dykes that cross-cut the tectonic fabric in their host rocks to 1851 +/- 15 and 1855 +/- 6 Ma, respectively. Since the former shows an unequivocal field relationship with respect to the tectonic fabric, we establish that penetrative Ductile Deformation under amphibolite-facies metamorphic conditions occurred prior to 1851 +/- 5 Ma. This U-Pb zircon minimum age for the timing of Ductile Deformation is supported by a U-Pb titanite age of 1844 +/- 4 Ma. These data as well as the field relationships at Forsmark indicate that an early phase of penetrative Deformation and metamorphism affected the Svecofennian bedrock in the western part of the Fennoscandian Shield and was overprinted, after 1851 +/- 5 Ma, by spatially more confined Deformational events. In conjunction with earlier results, our data help to establish the presence of tectonic domains with contrasting tectonothermal histories in the western part of the Svecofennian orogen. (c) 2006 Elsevier B.V. All rights reserved
Tobias Hermansson - One of the best experts on this subject based on the ideXlab platform.
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Ar-40/Ar-39 hornblende geochronology from the Forsmark area in central Sweden : constraints on late Svecofennian cooling, Ductile Deformation and exhumation
Precambrian Research, 2008Co-Authors: Tobias Hermansson, Michael B. Stephens, Laurence PageAbstract:At Forsmark, ca. 120 km north of Stockholm in central Sweden, Ductile high-strain belts with WNW to NW trend anastomose around tectonic lenses with an inferred lower degree of Ductile strain. Previous studies of Ductile Deformation zones with WNW to NW trend, elsewhere in the western part of the Svecofennian orogen in central Sweden, have yielded estimates for the timing of at least one phase of discrete Ductile Deformation that fall in the time interval 1.82-1.78 Ga. Most of these ages were determined by the U/Pb dating of titanite and, for this reason, provide no information on the thermal evolution. In this paper, we make use of Ar-40/Ar-39 hornblende geochronology to address late Svecofennian cooling, Ductile Deformation and exhumation. The data demonstrate the presence of three Ar-40/Ar-39 hornblende age generations. All ages have been adjusted to take account of ca. 1% systematic bias between Ar-40/Ar-39 and U/Pb ages recently reported in the literature. The oldest age, ca. 1.87 Ga, and the intermediate age generation, 1.85-1.84 Ga, are spatially restricted to the tectonic lenses. By contrast, the youngest age generation, 1.83-1.81 Ga, occurs both within the tectonic lenses and the enveloping high-strain belts. one explanation for the structurally controlled age distribution involves regional cooling beneath the closure temperature for argon isotopic mobility around or above 500 degrees C by 1.84 Ga, as represented in the oldest and intermediate age generations, followed by resetting of the argon isotope system in hornblende between 1.83 and 1.81 Ga, as represented in the youngest age generation. This resetting occurred in response to retrograde, lower amphibolite- to upper greenschist-facies Deformation along discrete high-strain zones within the broader high-strain belts and was associated with regional exhumation. An alternative explanation involves no resetting of the ages. Instead, it is suggested that a period of slow cooling of hornblendes with slightly different closure temperatures, from ca. 1.87 to 1.82 Ga, may have caused the age variation observed within the tectonic lenses, whereas locally maintained higher temperatures, due to activity along the discrete high-strain zones, can explain the consistently younger ages in the broad, enveloping high-strain belts. In this explanation, an increase in cooling rate, in response to regional exhumation, finally closed the argon isotope system in hornblende throughout the area at 1.83-1.81 Ga. It is suggested that the regional exhumation at 1.83-1.81 Ga, which is included in both explanations, is related to far-field effects of the Deformation that ended an accretionary tectonic cycle in adjacent tectonic domains. (c) 2008 Elsevier B.V. All rights reserved. (Less)
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ar 40 ar 39 hornblende geochronology from the forsmark area in central sweden constraints on late svecofennian cooling Ductile Deformation and exhumation
Precambrian Research, 2008Co-Authors: Tobias Hermansson, Michael B. Stephens, Laurence PageAbstract:At Forsmark, ca. 120 km north of Stockholm in central Sweden, Ductile high-strain belts with WNW to NW trend anastomose around tectonic lenses with an inferred lower degree of Ductile strain. Previous studies of Ductile Deformation zones with WNW to NW trend, elsewhere in the western part of the Svecofennian orogen in central Sweden, have yielded estimates for the timing of at least one phase of discrete Ductile Deformation that fall in the time interval 1.82-1.78 Ga. Most of these ages were determined by the U/Pb dating of titanite and, for this reason, provide no information on the thermal evolution. In this paper, we make use of Ar-40/Ar-39 hornblende geochronology to address late Svecofennian cooling, Ductile Deformation and exhumation. The data demonstrate the presence of three Ar-40/Ar-39 hornblende age generations. All ages have been adjusted to take account of ca. 1% systematic bias between Ar-40/Ar-39 and U/Pb ages recently reported in the literature. The oldest age, ca. 1.87 Ga, and the intermediate age generation, 1.85-1.84 Ga, are spatially restricted to the tectonic lenses. By contrast, the youngest age generation, 1.83-1.81 Ga, occurs both within the tectonic lenses and the enveloping high-strain belts. one explanation for the structurally controlled age distribution involves regional cooling beneath the closure temperature for argon isotopic mobility around or above 500 degrees C by 1.84 Ga, as represented in the oldest and intermediate age generations, followed by resetting of the argon isotope system in hornblende between 1.83 and 1.81 Ga, as represented in the youngest age generation. This resetting occurred in response to retrograde, lower amphibolite- to upper greenschist-facies Deformation along discrete high-strain zones within the broader high-strain belts and was associated with regional exhumation. An alternative explanation involves no resetting of the ages. Instead, it is suggested that a period of slow cooling of hornblendes with slightly different closure temperatures, from ca. 1.87 to 1.82 Ga, may have caused the age variation observed within the tectonic lenses, whereas locally maintained higher temperatures, due to activity along the discrete high-strain zones, can explain the consistently younger ages in the broad, enveloping high-strain belts. In this explanation, an increase in cooling rate, in response to regional exhumation, finally closed the argon isotope system in hornblende throughout the area at 1.83-1.81 Ga. It is suggested that the regional exhumation at 1.83-1.81 Ga, which is included in both explanations, is related to far-field effects of the Deformation that ended an accretionary tectonic cycle in adjacent tectonic domains. (c) 2008 Elsevier B.V. All rights reserved. (Less)
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40Ar/39Ar hornblende geochronology from the Forsmark area in central Sweden: Constraints on late Svecofennian cooling, Ductile Deformation and exhumation
Precambrian Research, 2008Co-Authors: Tobias Hermansson, Michael B. Stephens, Laurence M. PageAbstract:At Forsmark, ca. 120 km north of Stockholm in central Sweden, Ductile high-strain belts with WNW to NW trend anastomose around tectonic lenses with an inferred lower degree of Ductile strain. Previous studies of Ductile Deformation zones with WNW to NW trend, elsewhere in the western part of the Svecofennian orogen in central Sweden, have yielded estimates for the timing of at least one phase of discrete Ductile Deformation that fall in the time interval 1.82-1.78 Ga. Most of these ages were determined by the U/Pb dating of titanite and, for this reason, provide no information on the thermal evolution. In this paper, we make use of Ar-40/Ar-39 hornblende geochronology to address late Svecofennian cooling, Ductile Deformation and exhumation. The data demonstrate the presence of three Ar-40/Ar-39 hornblende age generations. All ages have been adjusted to take account of ca. 1% systematic bias between Ar-40/Ar-39 and U/Pb ages recently reported in the literature. The oldest age, ca. 1.87 Ga, and the intermediate age generation, 1.85-1.84 Ga, are spatially restricted to the tectonic lenses. By contrast, the youngest age generation, 1.83-1.81 Ga, occurs both within the tectonic lenses and the enveloping high-strain belts. one explanation for the structurally controlled age distribution involves regional cooling beneath the closure temperature for argon isotopic mobility around or above 500 degrees C by 1.84 Ga, as represented in the oldest and intermediate age generations, followed by resetting of the argon isotope system in hornblende between 1.83 and 1.81 Ga, as represented in the youngest age generation. This resetting occurred in response to retrograde, lower amphibolite- to upper greenschist-facies Deformation along discrete high-strain zones within the broader high-strain belts and was associated with regional exhumation. An alternative explanation involves no resetting of the ages. Instead, it is suggested that a period of slow cooling of hornblendes with slightly different closure temperatures, from ca. 1.87 to 1.82 Ga, may have caused the age variation observed within the tectonic lenses, whereas locally maintained higher temperatures, due to activity along the discrete high-strain zones, can explain the consistently younger ages in the broad, enveloping high-strain belts. In this explanation, an increase in cooling rate, in response to regional exhumation, finally closed the argon isotope system in hornblende throughout the area at 1.83-1.81 Ga. It is suggested that the regional exhumation at 1.83-1.81 Ga, which is included in both explanations, is related to far-field effects of the Deformation that ended an accretionary tectonic cycle in adjacent tectonic domains. (c) 2008 Elsevier B.V. All rights reserved
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penetrative Ductile Deformation and amphibolite facies metamorphism prior to 1851 ma in the western part of the svecofennian orogen fennoscandian shield
Precambrian Research, 2007Co-Authors: Tobias Hermansson, Michael B. Stephens, Jenny Andersson, Fernando Corfu, Laurence PageAbstract:The Svecofennian orogen in the Fennosandian Shield consists of several Palaeoproterozoic meta-igneous provinces that generally young progressively southwards and westwards. The understanding of the tectonic evolution of these different provinces is linked to the ability to constrain the timing of Ductile Deformation and metamorphism within them. In the western part of the orogen, in central Sweden, Ductile Deformation and metamorphism is conventionally thought to have occurred after 1.85 Ga and mainly around 1.82-1.80 Ga. At Forsmark in central Sweden, we have dated two undeformed granite dykes that cross-cut the tectonic fabric in their host rocks to 1851 +/- 15 and 1855 +/- 6 Ma, respectively. Since the former shows an unequivocal field relationship with respect to the tectonic fabric, we establish that penetrative Ductile Deformation under amphibolite-facies metamorphic conditions occurred prior to 1851 +/- 5 Ma. This U-Pb zircon minimum age for the timing of Ductile Deformation is supported by a U-Pb titanite age of 1844 +/- 4 Ma. These data as well as the field relationships at Forsmark indicate that an early phase of penetrative Deformation and metamorphism affected the Svecofennian bedrock in the western part of the Fennoscandian Shield and was overprinted, after 1851 +/- 5 Ma, by spatially more confined Deformational events. In conjunction with earlier results, our data help to establish the presence of tectonic domains with contrasting tectonothermal histories in the western part of the Svecofennian orogen. (c) 2006 Elsevier B.V. All rights reserved. (Less)
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Penetrative Ductile Deformation and amphibolite-facies metamorphism prior to 1851 Ma in the western part of the Svecofennian orogen, Fennoscandian Shield
Precambrian Research, 2007Co-Authors: Tobias Hermansson, Michael B. Stephens, Jenny Andersson, Fernando Corfu, Laurence PageAbstract:Abstract The Svecofennian orogen in the Fennosandian Shield consists of several Palaeoproterozoic meta-igneous provinces that generally young progressively southwards and westwards. The understanding of the tectonic evolution of these different provinces is linked to the ability to constrain the timing of Ductile Deformation and metamorphism within them. In the western part of the orogen, in central Sweden, Ductile Deformation and metamorphism is conventionally thought to have occurred after 1.85 Ga and mainly around 1.82–1.80 Ga. At Forsmark in central Sweden, we have dated two undeformed granite dykes that cross-cut the tectonic fabric in their host rocks to 1851 ± 5 and 1855 ± 6 Ma, respectively. Since the former shows an unequivocal field relationship with respect to the tectonic fabric, we establish that penetrative Ductile Deformation under amphibolite-facies metamorphic conditions occurred prior to 1851 ± 5 Ma. This U–Pb zircon minimum age for the timing of Ductile Deformation is supported by a U–Pb titanite age of 1844 ± 4 Ma. These data as well as the field relationships at Forsmark indicate that an early phase of penetrative Deformation and metamorphism affected the Svecofennian bedrock in the western part of the Fennoscandian Shield and was overprinted, after 1851 ± 5 Ma, by spatially more confined Deformational events. In conjunction with earlier results, our data help to establish the presence of tectonic domains with contrasting tectonothermal histories in the western part of the Svecofennian orogen.
Michael B. Stephens - One of the best experts on this subject based on the ideXlab platform.
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Ar-40/Ar-39 hornblende geochronology from the Forsmark area in central Sweden : constraints on late Svecofennian cooling, Ductile Deformation and exhumation
Precambrian Research, 2008Co-Authors: Tobias Hermansson, Michael B. Stephens, Laurence PageAbstract:At Forsmark, ca. 120 km north of Stockholm in central Sweden, Ductile high-strain belts with WNW to NW trend anastomose around tectonic lenses with an inferred lower degree of Ductile strain. Previous studies of Ductile Deformation zones with WNW to NW trend, elsewhere in the western part of the Svecofennian orogen in central Sweden, have yielded estimates for the timing of at least one phase of discrete Ductile Deformation that fall in the time interval 1.82-1.78 Ga. Most of these ages were determined by the U/Pb dating of titanite and, for this reason, provide no information on the thermal evolution. In this paper, we make use of Ar-40/Ar-39 hornblende geochronology to address late Svecofennian cooling, Ductile Deformation and exhumation. The data demonstrate the presence of three Ar-40/Ar-39 hornblende age generations. All ages have been adjusted to take account of ca. 1% systematic bias between Ar-40/Ar-39 and U/Pb ages recently reported in the literature. The oldest age, ca. 1.87 Ga, and the intermediate age generation, 1.85-1.84 Ga, are spatially restricted to the tectonic lenses. By contrast, the youngest age generation, 1.83-1.81 Ga, occurs both within the tectonic lenses and the enveloping high-strain belts. one explanation for the structurally controlled age distribution involves regional cooling beneath the closure temperature for argon isotopic mobility around or above 500 degrees C by 1.84 Ga, as represented in the oldest and intermediate age generations, followed by resetting of the argon isotope system in hornblende between 1.83 and 1.81 Ga, as represented in the youngest age generation. This resetting occurred in response to retrograde, lower amphibolite- to upper greenschist-facies Deformation along discrete high-strain zones within the broader high-strain belts and was associated with regional exhumation. An alternative explanation involves no resetting of the ages. Instead, it is suggested that a period of slow cooling of hornblendes with slightly different closure temperatures, from ca. 1.87 to 1.82 Ga, may have caused the age variation observed within the tectonic lenses, whereas locally maintained higher temperatures, due to activity along the discrete high-strain zones, can explain the consistently younger ages in the broad, enveloping high-strain belts. In this explanation, an increase in cooling rate, in response to regional exhumation, finally closed the argon isotope system in hornblende throughout the area at 1.83-1.81 Ga. It is suggested that the regional exhumation at 1.83-1.81 Ga, which is included in both explanations, is related to far-field effects of the Deformation that ended an accretionary tectonic cycle in adjacent tectonic domains. (c) 2008 Elsevier B.V. All rights reserved. (Less)
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ar 40 ar 39 hornblende geochronology from the forsmark area in central sweden constraints on late svecofennian cooling Ductile Deformation and exhumation
Precambrian Research, 2008Co-Authors: Tobias Hermansson, Michael B. Stephens, Laurence PageAbstract:At Forsmark, ca. 120 km north of Stockholm in central Sweden, Ductile high-strain belts with WNW to NW trend anastomose around tectonic lenses with an inferred lower degree of Ductile strain. Previous studies of Ductile Deformation zones with WNW to NW trend, elsewhere in the western part of the Svecofennian orogen in central Sweden, have yielded estimates for the timing of at least one phase of discrete Ductile Deformation that fall in the time interval 1.82-1.78 Ga. Most of these ages were determined by the U/Pb dating of titanite and, for this reason, provide no information on the thermal evolution. In this paper, we make use of Ar-40/Ar-39 hornblende geochronology to address late Svecofennian cooling, Ductile Deformation and exhumation. The data demonstrate the presence of three Ar-40/Ar-39 hornblende age generations. All ages have been adjusted to take account of ca. 1% systematic bias between Ar-40/Ar-39 and U/Pb ages recently reported in the literature. The oldest age, ca. 1.87 Ga, and the intermediate age generation, 1.85-1.84 Ga, are spatially restricted to the tectonic lenses. By contrast, the youngest age generation, 1.83-1.81 Ga, occurs both within the tectonic lenses and the enveloping high-strain belts. one explanation for the structurally controlled age distribution involves regional cooling beneath the closure temperature for argon isotopic mobility around or above 500 degrees C by 1.84 Ga, as represented in the oldest and intermediate age generations, followed by resetting of the argon isotope system in hornblende between 1.83 and 1.81 Ga, as represented in the youngest age generation. This resetting occurred in response to retrograde, lower amphibolite- to upper greenschist-facies Deformation along discrete high-strain zones within the broader high-strain belts and was associated with regional exhumation. An alternative explanation involves no resetting of the ages. Instead, it is suggested that a period of slow cooling of hornblendes with slightly different closure temperatures, from ca. 1.87 to 1.82 Ga, may have caused the age variation observed within the tectonic lenses, whereas locally maintained higher temperatures, due to activity along the discrete high-strain zones, can explain the consistently younger ages in the broad, enveloping high-strain belts. In this explanation, an increase in cooling rate, in response to regional exhumation, finally closed the argon isotope system in hornblende throughout the area at 1.83-1.81 Ga. It is suggested that the regional exhumation at 1.83-1.81 Ga, which is included in both explanations, is related to far-field effects of the Deformation that ended an accretionary tectonic cycle in adjacent tectonic domains. (c) 2008 Elsevier B.V. All rights reserved. (Less)
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40Ar/39Ar hornblende geochronology from the Forsmark area in central Sweden: Constraints on late Svecofennian cooling, Ductile Deformation and exhumation
Precambrian Research, 2008Co-Authors: Tobias Hermansson, Michael B. Stephens, Laurence M. PageAbstract:At Forsmark, ca. 120 km north of Stockholm in central Sweden, Ductile high-strain belts with WNW to NW trend anastomose around tectonic lenses with an inferred lower degree of Ductile strain. Previous studies of Ductile Deformation zones with WNW to NW trend, elsewhere in the western part of the Svecofennian orogen in central Sweden, have yielded estimates for the timing of at least one phase of discrete Ductile Deformation that fall in the time interval 1.82-1.78 Ga. Most of these ages were determined by the U/Pb dating of titanite and, for this reason, provide no information on the thermal evolution. In this paper, we make use of Ar-40/Ar-39 hornblende geochronology to address late Svecofennian cooling, Ductile Deformation and exhumation. The data demonstrate the presence of three Ar-40/Ar-39 hornblende age generations. All ages have been adjusted to take account of ca. 1% systematic bias between Ar-40/Ar-39 and U/Pb ages recently reported in the literature. The oldest age, ca. 1.87 Ga, and the intermediate age generation, 1.85-1.84 Ga, are spatially restricted to the tectonic lenses. By contrast, the youngest age generation, 1.83-1.81 Ga, occurs both within the tectonic lenses and the enveloping high-strain belts. one explanation for the structurally controlled age distribution involves regional cooling beneath the closure temperature for argon isotopic mobility around or above 500 degrees C by 1.84 Ga, as represented in the oldest and intermediate age generations, followed by resetting of the argon isotope system in hornblende between 1.83 and 1.81 Ga, as represented in the youngest age generation. This resetting occurred in response to retrograde, lower amphibolite- to upper greenschist-facies Deformation along discrete high-strain zones within the broader high-strain belts and was associated with regional exhumation. An alternative explanation involves no resetting of the ages. Instead, it is suggested that a period of slow cooling of hornblendes with slightly different closure temperatures, from ca. 1.87 to 1.82 Ga, may have caused the age variation observed within the tectonic lenses, whereas locally maintained higher temperatures, due to activity along the discrete high-strain zones, can explain the consistently younger ages in the broad, enveloping high-strain belts. In this explanation, an increase in cooling rate, in response to regional exhumation, finally closed the argon isotope system in hornblende throughout the area at 1.83-1.81 Ga. It is suggested that the regional exhumation at 1.83-1.81 Ga, which is included in both explanations, is related to far-field effects of the Deformation that ended an accretionary tectonic cycle in adjacent tectonic domains. (c) 2008 Elsevier B.V. All rights reserved
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penetrative Ductile Deformation and amphibolite facies metamorphism prior to 1851 ma in the western part of the svecofennian orogen fennoscandian shield
Precambrian Research, 2007Co-Authors: Tobias Hermansson, Michael B. Stephens, Jenny Andersson, Fernando Corfu, Laurence PageAbstract:The Svecofennian orogen in the Fennosandian Shield consists of several Palaeoproterozoic meta-igneous provinces that generally young progressively southwards and westwards. The understanding of the tectonic evolution of these different provinces is linked to the ability to constrain the timing of Ductile Deformation and metamorphism within them. In the western part of the orogen, in central Sweden, Ductile Deformation and metamorphism is conventionally thought to have occurred after 1.85 Ga and mainly around 1.82-1.80 Ga. At Forsmark in central Sweden, we have dated two undeformed granite dykes that cross-cut the tectonic fabric in their host rocks to 1851 +/- 15 and 1855 +/- 6 Ma, respectively. Since the former shows an unequivocal field relationship with respect to the tectonic fabric, we establish that penetrative Ductile Deformation under amphibolite-facies metamorphic conditions occurred prior to 1851 +/- 5 Ma. This U-Pb zircon minimum age for the timing of Ductile Deformation is supported by a U-Pb titanite age of 1844 +/- 4 Ma. These data as well as the field relationships at Forsmark indicate that an early phase of penetrative Deformation and metamorphism affected the Svecofennian bedrock in the western part of the Fennoscandian Shield and was overprinted, after 1851 +/- 5 Ma, by spatially more confined Deformational events. In conjunction with earlier results, our data help to establish the presence of tectonic domains with contrasting tectonothermal histories in the western part of the Svecofennian orogen. (c) 2006 Elsevier B.V. All rights reserved. (Less)
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Penetrative Ductile Deformation and amphibolite-facies metamorphism prior to 1851 Ma in the western part of the Svecofennian orogen, Fennoscandian Shield
Precambrian Research, 2007Co-Authors: Tobias Hermansson, Michael B. Stephens, Jenny Andersson, Fernando Corfu, Laurence PageAbstract:Abstract The Svecofennian orogen in the Fennosandian Shield consists of several Palaeoproterozoic meta-igneous provinces that generally young progressively southwards and westwards. The understanding of the tectonic evolution of these different provinces is linked to the ability to constrain the timing of Ductile Deformation and metamorphism within them. In the western part of the orogen, in central Sweden, Ductile Deformation and metamorphism is conventionally thought to have occurred after 1.85 Ga and mainly around 1.82–1.80 Ga. At Forsmark in central Sweden, we have dated two undeformed granite dykes that cross-cut the tectonic fabric in their host rocks to 1851 ± 5 and 1855 ± 6 Ma, respectively. Since the former shows an unequivocal field relationship with respect to the tectonic fabric, we establish that penetrative Ductile Deformation under amphibolite-facies metamorphic conditions occurred prior to 1851 ± 5 Ma. This U–Pb zircon minimum age for the timing of Ductile Deformation is supported by a U–Pb titanite age of 1844 ± 4 Ma. These data as well as the field relationships at Forsmark indicate that an early phase of penetrative Deformation and metamorphism affected the Svecofennian bedrock in the western part of the Fennoscandian Shield and was overprinted, after 1851 ± 5 Ma, by spatially more confined Deformational events. In conjunction with earlier results, our data help to establish the presence of tectonic domains with contrasting tectonothermal histories in the western part of the Svecofennian orogen.
Jun You - One of the best experts on this subject based on the ideXlab platform.
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Cu and Mo re-enrichment during Ductile Deformation: A case study of the Yuleken porphyry Cu deposit, Eastern Junggar, NW China
Journal of Asian Earth Sciences, 2018Co-Authors: Tao Hong, Jun YouAbstract:Abstract Porphyry Cu deposits can be strongly deformed during subsequent tectonic evolution. To date, research pertaining to the Deformation and the enrichment of mineralization in porphyry deposits has suffered from a paucity of proof. Here, we describe the diagnostic petrologic and geochemical signatures of the Yuleken porphyry Cu deposit from stages of metallogenic overprinting. The rocks studied in this work are from Deformation-metallogenic structures that have (1) a distinguished metallogenic and tectonic evolution, (2) a three-layer, spatial, Deformation-metallogenic structure, (3) distinguishably different fluid components within protomylonite, mylonite, and ultramylonite zones, and (4) variational geochemical characteristics of coexisting chalcopyrite and magnetite. Integrated sulfide and oxide mineral investigations pertaining to the mineral Deformation and the trace element variation of the minerals chalcopyrite and magnetite in the Yuleken porphyry Cu deposit indicated that Cu and Mo can be enriched during Ductile Deformation through physical (analogous geochemical characteristics of chalcopyrite from different stages) and chemical migrations. The elemental variation of magnetite (magnetites from deformed stages have higher contents of Ti, V, Co, Mn, and Ga than those from other stages) and the variation of the fluid components within the protomylonite, mylonite, and ultramylonite zones reveal that the migration and precipitation of Cu, Mo, and Fe were influenced by oxygen fugacity, fluid components, and temperature variation. In conclusion, the arc-related porphyry deposits were able to become involved in the Ductile Deformation zone, inducing areas of Cu and Mo enrichment in theory. Units subjected to Ductile Deformation may have great potential for porphyry Cu (-Mo) deposit formation under the influence of magmatism.
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element migration of pyrites during Ductile Deformation of the yuleken porphyry cu deposit nw china
Ore Geology Reviews, 2017Co-Authors: Tao Hong, Jun Gao, Stephen G Peters, Mingjian Cao, Peng Xiang, Jun YouAbstract:Abstract The strongly deformed Yuleken porphyry Cu deposit (YPCD) occurs in the Kalaxiangar porphyry Cu belt (KPCB), which occupies the central area of the Central Asian Orogenic Belt (CAOB) between the Sawu’er island arc and the Altay Terrane in northern Xinjiang. The YPCD is one of several typical subduction-related deposits in the KPCB, which has undergone syn-collisional and post-collisional metallogenic overprinting. The YPCD is characterized by three pyrite-forming stages, namely a hydrothermal stage A (Py I), a syn-Ductile Deformation stage B (Py II) characterized by Cu-Au enrichment, and a fracture-filling stage C (Py III). In this study, we conducted systematic petrographic and geochemical studies of pyrites and coexist biotite, which formed during different stages, in order to constrain the physicochemical conditions of the ore formation. Euhedral, fragmented Py I has low Pb and high Te and Se concentration and Ni contents are low with Co/Ni ratios mostly between 1 and 10 (average 9.00). Py I is further characterized by enrichments of Bi, As, Ni, Cu, Te and Se in the core relative to the rim domains. Anhedral round Py II has moderate Co and Ni contents with high Co/Ni ratios >10 (average 95.2), and average contents of 46.5 ppm Pb and 5.80 ppm Te. Py II is further characterized by decreasing Bi, Cu, Pb, Zn, Ag, Te, Mo, Sb and Au contents from the rim to the core domains. Annealed Py III has the lowest Co content of all pyrite types with Co/Ni ratios mostly
Tao Hong - One of the best experts on this subject based on the ideXlab platform.
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Cu and Mo re-enrichment during Ductile Deformation: A case study of the Yuleken porphyry Cu deposit, Eastern Junggar, NW China
Journal of Asian Earth Sciences, 2018Co-Authors: Tao Hong, Jun YouAbstract:Abstract Porphyry Cu deposits can be strongly deformed during subsequent tectonic evolution. To date, research pertaining to the Deformation and the enrichment of mineralization in porphyry deposits has suffered from a paucity of proof. Here, we describe the diagnostic petrologic and geochemical signatures of the Yuleken porphyry Cu deposit from stages of metallogenic overprinting. The rocks studied in this work are from Deformation-metallogenic structures that have (1) a distinguished metallogenic and tectonic evolution, (2) a three-layer, spatial, Deformation-metallogenic structure, (3) distinguishably different fluid components within protomylonite, mylonite, and ultramylonite zones, and (4) variational geochemical characteristics of coexisting chalcopyrite and magnetite. Integrated sulfide and oxide mineral investigations pertaining to the mineral Deformation and the trace element variation of the minerals chalcopyrite and magnetite in the Yuleken porphyry Cu deposit indicated that Cu and Mo can be enriched during Ductile Deformation through physical (analogous geochemical characteristics of chalcopyrite from different stages) and chemical migrations. The elemental variation of magnetite (magnetites from deformed stages have higher contents of Ti, V, Co, Mn, and Ga than those from other stages) and the variation of the fluid components within the protomylonite, mylonite, and ultramylonite zones reveal that the migration and precipitation of Cu, Mo, and Fe were influenced by oxygen fugacity, fluid components, and temperature variation. In conclusion, the arc-related porphyry deposits were able to become involved in the Ductile Deformation zone, inducing areas of Cu and Mo enrichment in theory. Units subjected to Ductile Deformation may have great potential for porphyry Cu (-Mo) deposit formation under the influence of magmatism.
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element migration of pyrites during Ductile Deformation of the yuleken porphyry cu deposit nw china
Ore Geology Reviews, 2017Co-Authors: Tao Hong, Jun Gao, Stephen G Peters, Mingjian Cao, Peng Xiang, Jun YouAbstract:Abstract The strongly deformed Yuleken porphyry Cu deposit (YPCD) occurs in the Kalaxiangar porphyry Cu belt (KPCB), which occupies the central area of the Central Asian Orogenic Belt (CAOB) between the Sawu’er island arc and the Altay Terrane in northern Xinjiang. The YPCD is one of several typical subduction-related deposits in the KPCB, which has undergone syn-collisional and post-collisional metallogenic overprinting. The YPCD is characterized by three pyrite-forming stages, namely a hydrothermal stage A (Py I), a syn-Ductile Deformation stage B (Py II) characterized by Cu-Au enrichment, and a fracture-filling stage C (Py III). In this study, we conducted systematic petrographic and geochemical studies of pyrites and coexist biotite, which formed during different stages, in order to constrain the physicochemical conditions of the ore formation. Euhedral, fragmented Py I has low Pb and high Te and Se concentration and Ni contents are low with Co/Ni ratios mostly between 1 and 10 (average 9.00). Py I is further characterized by enrichments of Bi, As, Ni, Cu, Te and Se in the core relative to the rim domains. Anhedral round Py II has moderate Co and Ni contents with high Co/Ni ratios >10 (average 95.2), and average contents of 46.5 ppm Pb and 5.80 ppm Te. Py II is further characterized by decreasing Bi, Cu, Pb, Zn, Ag, Te, Mo, Sb and Au contents from the rim to the core domains. Annealed Py III has the lowest Co content of all pyrite types with Co/Ni ratios mostly
