TY - JOUR
T1 - Neoproterozoic to Cenozoic magmatism in the central part of the Bohemian Massif (Czech Republic)
T2 - Isotopic tracking of the evolution of the mantle through the Variscan orogeny
AU - Dostal, Jaroslav
AU - Murphy, J. Brendan
AU - Shellnutt, J. Gregory
AU - Ulrych, Jaromír
AU - Fediuk, Ferry
N1 - Funding Information:
We thank Drs. Nelson Eby, John Greenough and Václav Kachlík for their constructive reviews. JD and JBM acknowledge the continuing support of NSERC , Canada, and Randy Corney for technical assistance. This research was also supported by the institutional project RVO 67985831 of the Institute of Geology of the Czech Academy of Sciences to JU and by MOST (Taiwan) grant 106-2116-M-003-007 to JGS.
Funding Information:
We thank Drs. Nelson Eby, John Greenough and Václav Kachlík for their constructive reviews. JD and JBM acknowledge the continuing support of NSERC, Canada, and Randy Corney for technical assistance. This research was also supported by the institutional project RVO 67985831 of the Institute of Geology of the Czech Academy of Sciences to JU and by MOST (Taiwan) grant 106-2116-M-003-007 to JGS.
Publisher Copyright:
© 2018
PY - 2019/2
Y1 - 2019/2
N2 - The evolution of the mantle source beneath the Teplá-Barrandian (TBB) and the adjacent southern part of the Saxo-Thuringian (S-STB) and northern part of the Moldanubian (N-MB) blocks of the Bohemian Massif (Czech Republic) is tracked from the Late Neoproterozoic to the Cenozoic in order to examine the coupling between the crust and underlying continental lithospheric mantle (CLM) during the Late Paleozoic Variscan orogeny. In the TBB, Late Neoproterozoic mafic rocks have highly radiogenic Nd but moderately radiogenic Sr isotopes and were derived from a spinel peridotite mantle. These within-plate rocks were emplaced in an intra-oceanic back-arc basin. Early Paleozoic (Ordovician to Early Devonian) mafic rocks are rift/extension-related, enriched in LREE and Nb relative to HREE and were probably derived from a garnet peridotite mantle source. Compared to Neoproterozoic basalts, their Ɛ Nd (t) values are slightly lower but T DM model ages are indistinguishable suggesting derivation from a deeper portion of the same mantle source. Thus, the weak deformation and low-grade metamorphism associated with the Cadomian orogeny did not significantly decouple the crust from the underlying mantle source beneath the TBB. Early Paleozoic rift-related mafic rocks of the S-STB and N-MB have comparable isotopic signatures indicating a similar mantle source. Late Paleozoic mafic magmatism occurred during the extensional collapse phase of the Variscan orogen, in the aftermath of the collision between Gondwana and Laurussia. The TBB and S-STB basaltic rocks are within-plate, and transitional between alkaline and tholeiitic compositions but show a relative depletion of Nb. Their isotopic characteristics contrast with older basalts in that they have negative Ɛ Nd (t) values, high initial 87 Sr/ 86 Sr ratios and older T DM model ages (1050 to 1300 Ma). Late Paleozoic mantle-derived potassic-ultrapotassic magmas occurring as lamprophyre dikes and small volume high Mg–K intrusions in N-MB, S-STB and TBB have similar isotopic characteristics suggesting that all these Late Paleozoic rocks were derived from an old CLM contaminated by fluids or silicic melts derived from subducted Precambrian crustal material or alternatively, the region was underthrust by Gondwanan mantle during the Variscan collision. Cenozoic volcanic rocks in the Bohemian Massif are local representatives of the regionally extensive Cenozoic European volcanic province. The rocks are within-plate, alkaline basalts enriched in LREE and Nb and were derived from garnet peridotite mantle. They are significantly more juvenile than Carboniferous-Early Permian mafic rocks, with higher Ɛ Nd (t) values (typically +3 to +5), lower initial 87 Sr/ 86 Sr ratios and significantly younger T DM age. These data suggest significant input from upwelling asthenospheric mantle, implying that at least a part of the Permian CLM mantle was re-fertilized.
AB - The evolution of the mantle source beneath the Teplá-Barrandian (TBB) and the adjacent southern part of the Saxo-Thuringian (S-STB) and northern part of the Moldanubian (N-MB) blocks of the Bohemian Massif (Czech Republic) is tracked from the Late Neoproterozoic to the Cenozoic in order to examine the coupling between the crust and underlying continental lithospheric mantle (CLM) during the Late Paleozoic Variscan orogeny. In the TBB, Late Neoproterozoic mafic rocks have highly radiogenic Nd but moderately radiogenic Sr isotopes and were derived from a spinel peridotite mantle. These within-plate rocks were emplaced in an intra-oceanic back-arc basin. Early Paleozoic (Ordovician to Early Devonian) mafic rocks are rift/extension-related, enriched in LREE and Nb relative to HREE and were probably derived from a garnet peridotite mantle source. Compared to Neoproterozoic basalts, their Ɛ Nd (t) values are slightly lower but T DM model ages are indistinguishable suggesting derivation from a deeper portion of the same mantle source. Thus, the weak deformation and low-grade metamorphism associated with the Cadomian orogeny did not significantly decouple the crust from the underlying mantle source beneath the TBB. Early Paleozoic rift-related mafic rocks of the S-STB and N-MB have comparable isotopic signatures indicating a similar mantle source. Late Paleozoic mafic magmatism occurred during the extensional collapse phase of the Variscan orogen, in the aftermath of the collision between Gondwana and Laurussia. The TBB and S-STB basaltic rocks are within-plate, and transitional between alkaline and tholeiitic compositions but show a relative depletion of Nb. Their isotopic characteristics contrast with older basalts in that they have negative Ɛ Nd (t) values, high initial 87 Sr/ 86 Sr ratios and older T DM model ages (1050 to 1300 Ma). Late Paleozoic mantle-derived potassic-ultrapotassic magmas occurring as lamprophyre dikes and small volume high Mg–K intrusions in N-MB, S-STB and TBB have similar isotopic characteristics suggesting that all these Late Paleozoic rocks were derived from an old CLM contaminated by fluids or silicic melts derived from subducted Precambrian crustal material or alternatively, the region was underthrust by Gondwanan mantle during the Variscan collision. Cenozoic volcanic rocks in the Bohemian Massif are local representatives of the regionally extensive Cenozoic European volcanic province. The rocks are within-plate, alkaline basalts enriched in LREE and Nb and were derived from garnet peridotite mantle. They are significantly more juvenile than Carboniferous-Early Permian mafic rocks, with higher Ɛ Nd (t) values (typically +3 to +5), lower initial 87 Sr/ 86 Sr ratios and significantly younger T DM age. These data suggest significant input from upwelling asthenospheric mantle, implying that at least a part of the Permian CLM mantle was re-fertilized.
KW - Bohemian Massif
KW - continental lithospheric mantle
KW - crust
KW - Nd and Sr isotopes
KW - rift/extension-related mafic igneous rocks
KW - Variscan orogeny
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U2 - 10.1016/j.lithos.2018.12.028
DO - 10.1016/j.lithos.2018.12.028
M3 - Article
AN - SCOPUS:85059682678
SN - 0024-4937
VL - 326-327
SP - 358
EP - 369
JO - Lithos
JF - Lithos
ER -