The Experts below are selected from a list of 3294 Experts worldwide ranked by ideXlab platform
Michel Faure - One of the best experts on this subject based on the ideXlab platform.
-
early paleozoic or early middle triassic collision between the south china and indochina blocks the controversy resolved structural insights from the kon tum massif central vietnam
Journal of Asian Earth Sciences, 2018Co-Authors: Michel Faure, Van Vuong Nguyen, Luong Thi Thu Hoai, Claude LepvrierAbstract:Abstract In Central Vietnam, the Kontum massif is subdivided from North to South into: (i) Kham Duc, (ii) Ngoc Linh, (iii) Kan Nack complexes. The Kham Duc complex consists of metapelite, metapsammite, paragneiss, metagabbro, amphibolite, serpentinized ultramafic, and orthogneiss blocks. The southern part of this complex experienced an Early Paleozoic crustal melting event responsible for Migmatites and anatectic granites. The Ngoc Linh complex, the largest one, is formed by metatexite and granitoid enclosing blocks of eclogite, high pressure (HP) granulite, orthogneiss, metagabbro, amphibolite, granodiorite, and Migmatite. The Kan Nack complex is formed by Migmatites with (ultra) high temperature (U)HT granulite, charnockites and enderbites. The three metamorphic complexes are intruded by per-aluminous granite, and subordinate mafic plutons. In spite of local variations, the foliation of the Ngoc Linh complex defines a bulk domal structure, and the stretching lineation consistently trends NW-SE. The NW-SE lineation is also observed in the tectonically overlying the Kan Nack complex. The Ngoc Linh and Kan Nack complexes are interpreted here as parts of a metamorphic core complex (MCC), or “Ngoc Linh MCC”, exhumed by a top-to-the-NW detachment fault. Along the northern margin of the Ngoc Linh MCC, upright folds with E-W striking axes, and E-W stretching lineation deform the foliation. These structures are developed in a transpressive regime coeval with the activity of plurikilometer-scale dextral strike-slip faults. Zircon and monazite U/Pb radiometric datings document a 250–240 Ma age for the crustal melting, and the top-to-the-NW ductile shearing coeval with the formation of the Ngoc Linh MCC. This extensional tectonics is followed by a dextral strike-slip faulting, at ca 240–230 Ma, before the emplacement of the two-mica granitic plutons at ca 240–224 Ma. Furthermore in the Ngoc Linh and Kan Nack complexes, zircon and monazite yield U-Pb Early Paleozoic ages. In the Kham Duc complex, a ca 460 Ma MP/MT, garnet-biotite-staurolite-kyanite metamorphism, followed by Migmatites at ca 450 Ma, is also recognized. The 420–400 Ma age of the Dai Loc plutonic suite, and the 450–425 Ma age of the Dien Binh calc-alkaline granodiorite document an Early Paleozoic event. The Early Paleozoic mafic and ultramafic masses of the Hiep Duc complex are ophiolites included into a metasedimentary matrix. Thus, the Kham Duc complex is interpreted as a tectonic melange formed during a collisional orogeny that subsequently underwent crustal melting giving rise to the Migmatites. A part of the Early Paleozoic rocks are enclosed as xenoliths in the Triassic Migmatite of the Ngoc Linh MCC. These petrologic, structural, and chronological features allow us to propose the following geodynamic evolution for the Kontum massif. During the Early Paleozoic, a continental collision, which was accommodated by a north-directed subduction of a southern block (S. Vietnam, or Viet-Cambodia block) below a northern block (N. Vietnam or Viet-Lao block), occurred along the Tam Ky-Phuoc Son suture. During the Early Triassic, at ca 250–245 Ma, the S. Vietnam block experienced a crustal melting giving rise to the Ngoc Linh MCC that reworked the Early Paleozoic orogen. Lastly, during the Middle Triassic, the dextral faulting superimposed upon the Ngoc Linh Migmatite. The geodynamic significance of the Kontum massif is discussed in the general framework of Indochina- South China relationships. The Early Paleozoic collision in Vietnam is viewed as the driving force responsible for the development of the intracontinental orogeny of S. China. In order to account for the important heat flow required for the formation of UHT metamorphic rocks, a possible interaction between the SCB-Indochina collision, and the Emeishan mantle plume is proposed.
-
middle carboniferous intracontinental subduction in the outer zone of the variscan belt montagne noire axial zone french massif central multimethod geochronological approach of polyphase metamorphism
Geological Society London Special Publications, 2014Co-Authors: Michel Faure, Alain Cocherie, Philippe Rossi, Julien Gache, Chloe Esnault, Catherine Guerrot, Lin Wei, Li QiuliAbstract:In the migmatitic dome of the Montagne Noire Axial Zone (Variscan French Massif Central), mafic eclogites yield zircon and rutile U-Pb SHRIMP and SIMS ages around 315-308 Ma. These "young" dates, obtained in two different laboratories, do not comply with the geological constraints available for the study area that suggest an older age of the high pressure-low temperature (M1) metamorphism. Nevertheless, the Sm/Nd age of the same rock at ca 358 Ma appears in better agreement with the geological constraints, and thus might reflect the age of the HP event. Similar 357-352 Ma monazite U-Th-Pbtot ages are obtained from relict grains in the Axial Zone kinzigites that represent restites enclosed in Migmatites. Fur thermore, monazite grains from biotite-garnet-staurolite micaschists from the outer dome envelope, and Axial Zone kinzigites, yield U-Th-Pbtot ages ranging between 340 and 320 Ma. These dates are in good agreement with previously documented zircon and monazite ages from the Migmatite and anatectic granites that represent a high temperature-low pressure (M2) event. The significance of the zircon and rutile ages in the eclogites is discussed in terms of hydrothermal circulations. A crustal scale model involving a North-directed intracontinental subduction, responsible for the high pressure34 low temperature (M1) metamorphism, and coeval with km-scale S-vergent recumbent folds in the Palaeozoic non-metamorphic cover, is followed by the high temperature-low pressure (M2) event, which is coeval with the development of the Axial Zone migmatitic dome, and upright folding in the Palaeozoic non-metamorphic series.
-
The emplacement of the granite-Migmatite dome of the Montagne Noire Axial Zone (French Massif Central): new insights from AMS and petro-structural studies
2007Co-Authors: Nicolas Charles, Michel Faure, Yan ChenAbstract:In the southern French Massif Central, the Montagne Noire Axial Zone is a NE-SW elongated granitic-migmatitic dome surrounded by recumbently folded Palaeozoic sedimentary series with a southern vergence. The Axial Zone is composed of micaschist and augen gneiss, cordierite Migmatite, and anatectic Laouzas granite from edge to centre, respectively. Syn- to late kinematic granitoids intrude the dome. Anisotropy Magnetic Susceptibility (AMS) study (135 sites and almost 830 cores) and petro-structural studies have been carried out on anatectic cordierite/garnet granites and Migmatites. Thermomagnetic experiments indicate that biotite is the main carrier of the AMS fabric. The attitude of the magnetic foliation complies with the preferred orientation of biotite, schlierens, enclaves and host-rock septa in granite and with migmatitic foliation. The AMS foliation confirms the shape of the Axial Zone inferred from the migmatitic and gneissic envelopes. The southward dipping foliation recognized in both flanks is in agreement with an asymmetric dome, overturned to the North. Conversely, the magnetic linear fabric exhibits a contrasted pattern with a dominant NE-SW trend, and also a N-S one. The different models invoked to account for the tectonic setting of the Montagne Noire Axial Zone will be discussed on the basis of these new AMS results as well as petro-structural observations.
-
Exhumation tectonics of the ultrahigh-pressure metamorphic rocks in the Qinling orogen in east China: New petrological-structural-radiometric insights from the Shandong Peninsula
Tectonics, 2003Co-Authors: Michel Faure, Wei Lin, Patrick Monié, Nicole Le Breton, Stéphane Poussineau, Dominique Panis, Etienne DelouleAbstract:In eastern China, the Sulu area is recognized as the eastern extension of the Qinling-Dabie Belt, which is famous for its ultrahigh-pressure (UHP) metamorphism. Although numerous petrologic and geochemical works are available, structural data are still rare. This paper provides the first extensive study of bulk geometry and kinematic analysis of the Shandong Peninsula. The study area is divided into three tectonic areas by Cretaceous faults, namely, a southern UHP belt or Sulu area, a northern Migmatite area, and an eastern eclogite and Migmatite area or Weihai area. Conversely to the deeply entrenched idea that the later area belongs to the North China Belt, and the two others to the South China Block (SCB), we argue that all three areas are parts of the SCB. Structural, petrologic, 40Ar/39Ar, and U/Pb data comply with this new interpretation. In the North Shandong area, mafic granulites enclosed as blocks within gneissic Migmatites do not significantly differ from the Sulu and Weihai eclogites which also experienced a granulite facies overprint before migmatization. The circa 210–200 Ma age of the main ductile deformation is related to an extensional event during the Triassic (or Indosinian) orogeny. This date corresponds to the temperature climax, but the time of the pressure peak, i.e., the real age of the UHP metamorphism is discussed.
Li Qiuli - One of the best experts on this subject based on the ideXlab platform.
-
middle carboniferous intracontinental subduction in the outer zone of the variscan belt montagne noire axial zone french massif central multimethod geochronological approach of polyphase metamorphism
Geological Society London Special Publications, 2014Co-Authors: Michel Faure, Alain Cocherie, Philippe Rossi, Julien Gache, Chloe Esnault, Catherine Guerrot, Lin Wei, Li QiuliAbstract:In the migmatitic dome of the Montagne Noire Axial Zone (Variscan French Massif Central), mafic eclogites yield zircon and rutile U-Pb SHRIMP and SIMS ages around 315-308 Ma. These "young" dates, obtained in two different laboratories, do not comply with the geological constraints available for the study area that suggest an older age of the high pressure-low temperature (M1) metamorphism. Nevertheless, the Sm/Nd age of the same rock at ca 358 Ma appears in better agreement with the geological constraints, and thus might reflect the age of the HP event. Similar 357-352 Ma monazite U-Th-Pbtot ages are obtained from relict grains in the Axial Zone kinzigites that represent restites enclosed in Migmatites. Fur thermore, monazite grains from biotite-garnet-staurolite micaschists from the outer dome envelope, and Axial Zone kinzigites, yield U-Th-Pbtot ages ranging between 340 and 320 Ma. These dates are in good agreement with previously documented zircon and monazite ages from the Migmatite and anatectic granites that represent a high temperature-low pressure (M2) event. The significance of the zircon and rutile ages in the eclogites is discussed in terms of hydrothermal circulations. A crustal scale model involving a North-directed intracontinental subduction, responsible for the high pressure34 low temperature (M1) metamorphism, and coeval with km-scale S-vergent recumbent folds in the Palaeozoic non-metamorphic cover, is followed by the high temperature-low pressure (M2) event, which is coeval with the development of the Axial Zone migmatitic dome, and upright folding in the Palaeozoic non-metamorphic series.
Andrea Giuliani - One of the best experts on this subject based on the ideXlab platform.
-
isotopic disequilibrium in migmatitic hornfels of the gennargentu igneous complex sardinia italy records the formation of low 87sr 86sr melts from a mica rich source
Journal of Petrology, 2018Co-Authors: Mario Gaeta, Andrea Giuliani, Tommaso Di Rocco, Vanni Tecchiato, Cristina Perinelli, Vs KamenetskyAbstract:Isotopic disequilibrium is increasingly recognized as a common feature of magmatic systems, but the details of the mechanism(s) underpinning the development of isotopic disequilibrium during partial melting processes are not fully understood. Partial melting of mica-rich lithologies may be predicted to generate melts enriched in radiogenic Sr compared to the bulk protolith compositions due to the typically high Rb/Sr ratio coupled with low melting temperature of mica in crustal rocks. Here we report a puzzling case study where the Sr-isotope composition of the melt fraction (leucosome) of partially molten metapelites (Migmatites) is instead less radiogenic than the restitic component (melanosome). The examined Migmatites fringe (∼50 m wide zone) a low-pressure (≤200 MPa), high-temperature (∼1050 °C) quartz-dioritic intrusion, which was emplaced in the Gennargentu Igneous Complex (Sardinia, Italy) at 306 ± 26 Ma (bulk-rock Rb/Sr dating). The Migmatites derive from anatexis of the muscovite-rich metapelitic wall-rocks. They include a quartzo-feldspathic leucosome and a melanosome containing cordierite, K-feldspar, plagioclase, biotite, Fe-Ti oxide minerals and both corundum and hercynite. The leucosome has a less radiogenic Sr and more radiogenic Nd isotope composition than the melanosome (87Sr/86Sr (306 Ma) = 0.71068 and 0.71536; eNd(306 Ma) = -6.4 and -9.2, respectively), with bulk Migmatite samples having intermediate compositions. The significantly lower content of mica in the Migmatites compared to the protolith indicates that muscovite and, to a lesser extent, biotite largely contributed to melt formation. However, the leucosome volume (∼50%) estimated through mass balance calculations is considerably higher than the amount of melt (≤10 vol.%) generally produced by mica-dehydration melting in the crust, suggesting that partial melting was enhanced by an external hydrous fluid. The O-isotope composition of the Migmatites is lower than the typical metapelite values (>10‰) but overlaps with the δ18O range of the quartz-diorites (8.8-9.9‰), suggesting that such a hydrous fluid was released from the quartz-dioritic intrusion. We put forward a model whereby the anatexis temperature conditions (T < 800 °C) favored the preservation of isotopic disequilibrium of micas and plagioclase in the protolith. In this context, the leucosome formed by the preferential melting of less radiogenic plagioclase rather than more radiogenic micas. The melt was then efficiently separated from the melanosome containing restitic biotite and "peritectic K-feldspar and magnetite" derived from mica breakdown. During the anatectic process the quartz-diorite provided not only the heat budget, but also the fluid amount responsible for (i) the hydration of the pelitic country rock, (ii) the increase of melt fraction, and (iii) the higher mobility of anatectic magma.
Claude Lepvrier - One of the best experts on this subject based on the ideXlab platform.
-
early paleozoic or early middle triassic collision between the south china and indochina blocks the controversy resolved structural insights from the kon tum massif central vietnam
Journal of Asian Earth Sciences, 2018Co-Authors: Michel Faure, Van Vuong Nguyen, Luong Thi Thu Hoai, Claude LepvrierAbstract:Abstract In Central Vietnam, the Kontum massif is subdivided from North to South into: (i) Kham Duc, (ii) Ngoc Linh, (iii) Kan Nack complexes. The Kham Duc complex consists of metapelite, metapsammite, paragneiss, metagabbro, amphibolite, serpentinized ultramafic, and orthogneiss blocks. The southern part of this complex experienced an Early Paleozoic crustal melting event responsible for Migmatites and anatectic granites. The Ngoc Linh complex, the largest one, is formed by metatexite and granitoid enclosing blocks of eclogite, high pressure (HP) granulite, orthogneiss, metagabbro, amphibolite, granodiorite, and Migmatite. The Kan Nack complex is formed by Migmatites with (ultra) high temperature (U)HT granulite, charnockites and enderbites. The three metamorphic complexes are intruded by per-aluminous granite, and subordinate mafic plutons. In spite of local variations, the foliation of the Ngoc Linh complex defines a bulk domal structure, and the stretching lineation consistently trends NW-SE. The NW-SE lineation is also observed in the tectonically overlying the Kan Nack complex. The Ngoc Linh and Kan Nack complexes are interpreted here as parts of a metamorphic core complex (MCC), or “Ngoc Linh MCC”, exhumed by a top-to-the-NW detachment fault. Along the northern margin of the Ngoc Linh MCC, upright folds with E-W striking axes, and E-W stretching lineation deform the foliation. These structures are developed in a transpressive regime coeval with the activity of plurikilometer-scale dextral strike-slip faults. Zircon and monazite U/Pb radiometric datings document a 250–240 Ma age for the crustal melting, and the top-to-the-NW ductile shearing coeval with the formation of the Ngoc Linh MCC. This extensional tectonics is followed by a dextral strike-slip faulting, at ca 240–230 Ma, before the emplacement of the two-mica granitic plutons at ca 240–224 Ma. Furthermore in the Ngoc Linh and Kan Nack complexes, zircon and monazite yield U-Pb Early Paleozoic ages. In the Kham Duc complex, a ca 460 Ma MP/MT, garnet-biotite-staurolite-kyanite metamorphism, followed by Migmatites at ca 450 Ma, is also recognized. The 420–400 Ma age of the Dai Loc plutonic suite, and the 450–425 Ma age of the Dien Binh calc-alkaline granodiorite document an Early Paleozoic event. The Early Paleozoic mafic and ultramafic masses of the Hiep Duc complex are ophiolites included into a metasedimentary matrix. Thus, the Kham Duc complex is interpreted as a tectonic melange formed during a collisional orogeny that subsequently underwent crustal melting giving rise to the Migmatites. A part of the Early Paleozoic rocks are enclosed as xenoliths in the Triassic Migmatite of the Ngoc Linh MCC. These petrologic, structural, and chronological features allow us to propose the following geodynamic evolution for the Kontum massif. During the Early Paleozoic, a continental collision, which was accommodated by a north-directed subduction of a southern block (S. Vietnam, or Viet-Cambodia block) below a northern block (N. Vietnam or Viet-Lao block), occurred along the Tam Ky-Phuoc Son suture. During the Early Triassic, at ca 250–245 Ma, the S. Vietnam block experienced a crustal melting giving rise to the Ngoc Linh MCC that reworked the Early Paleozoic orogen. Lastly, during the Middle Triassic, the dextral faulting superimposed upon the Ngoc Linh Migmatite. The geodynamic significance of the Kontum massif is discussed in the general framework of Indochina- South China relationships. The Early Paleozoic collision in Vietnam is viewed as the driving force responsible for the development of the intracontinental orogeny of S. China. In order to account for the important heat flow required for the formation of UHT metamorphic rocks, a possible interaction between the SCB-Indochina collision, and the Emeishan mantle plume is proposed.
Seth C Kruckenberg - One of the best experts on this subject based on the ideXlab platform.
-
crustal scale convection and diapiric upwelling of a partially molten orogenic root naxos dome greece
Tectonophysics, 2018Co-Authors: Olivier Vanderhaeghe, Seth C Kruckenberg, Muriel Gerbault, Laure Martin, Stephanie Duchene, Etienne DelouleAbstract:Abstract The goal of this paper is to use the structural, metamorphic and geochronological record from the migmatitic core of the Naxos dome (Greece) and its associated subdomes to address the internal dynamics of a partially molten orogenic root. U-Pb ages from ca. 24 to 16 Ma and textures of zircon in the Migmatites suggest successive dissolution and precipitation cycles with a period of 1 to 2 Ma, interpreted as the timescale of convective instabilities in a ca. 20 km thick partially molten layer. Dimensional analysis indicates that convection of this root requires a viscosity lower than 1018 Pa·s, consistent with viscosity values expected for partially molten felsic rocks. Structural analysis and U-Pb geochronology of deformed granitic dikes rooting in the Migmatites record the subsequent development of the Naxos dome by diapirism from ca. 16 to 13 Ma. The size of the first order Migmatite dome on Naxos (5 × 12 km) requires that the unstable layer at the onset of diapirism was 5 to 10 km thick and presented a moderate viscosity contrast with its envelope. From this analysis we propose that the Naxos Migmatite dome documents a two stage dynamic evolution for the partially molten root of the Aegean belt characterized by (1) crustal scale convection for at least 8 Ma and (2) diapirism for about 3 Ma during progressive thinning of the collapsing orogenic crust.
-
cretaceous partial melting deformation and exhumation of the potters pond Migmatite domain west central idaho
Lithosphere, 2017Co-Authors: William J Montz, Seth C KruckenbergAbstract:The Potters Pond Migmatite domain (PPMD) is a heterogeneous zone of Migmatites located ∼10 km southwest of Cascade, Idaho, within the western Idaho shear zone (WISZ). The PPMD is the only known exposure of Migmatites within the WISZ over its ∼300 km length, occurring where the shear zone orientation changes from 024° south to 005° north of the Migmatite domain. Structural mapping within the PPMD has identified multiple generations of Migmatite with varied structural fabrics. Leucosome layers were sampled from distinct Migmatite localities and morphologies (e.g., metatexite and diatexite) to determine the timing and duration of partial melting in the PPMD. U-Pb age determinations of zircon by means of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) document two periods of protracted Migmatite crystallization during the Early and Late Cretaceous. Early Cretaceous (ca. 145–128 Ma) Migmatite crystallization ages are coeval with the collision and suturing of oceanic terranes of the Blue Mountains province with North America and the formation of the Salmon River suture zone (SRSZ). Migmatite crystallization ages from ca. 104–90 Ma are associated with Late Cretaceous dextral transpression in the WISZ. Field observations and geochronology of crosscutting leucosome relationships are interpreted to record deep crustal deformation and anatexis associated with formation of the SRSZ, subsequently overprinted by solid-state deformation and renewed anatexis during the evolution of the WISZ. These data are the first direct evidence of the synmetamorphic fabric related to the SRSZ east of the initial Sr 0.706 isopleth and indicate that the WISZ is a temporally distinct overprinting structure.
-
flow of partially molten crust and the internal dynamics of a Migmatite dome naxos greece
Tectonics, 2011Co-Authors: Seth C Kruckenberg, Christian Teyssier, Olivier Vanderhaeghe, E C Ferre, Donna L WhitneyAbstract:[1] Migmatite domes are common in metamorphic core complexes. Dome Migmatites deform in the partially molten or magmatic state and commonly record complex form surfaces, folds, and fabrics while units mantling the dome display a simpler geometry, typically formed by transposition during crustal extension. We use field observations and magnetic fabrics in the Naxos dome (Greece) to quantify the complex flow of anatectic crust beneath an extensional detachment system. The internal structure of the Naxos dome is characterized by second-order domes (subdomes), pinched synforms, and curved lineation trajectories, which suggest that buoyancy-driven flow participated in dome evolution. Subdomes broadly occur within two compartments that are separated by a steep, N-S oriented, high-strain zone. This pattern has been recognized in domes formed by polydiapirism and in models of isostasy-dominated flow. The preferred model involves a combination of buoyancy- and isostasy-driven processes: the Naxos dome may have been generated by regional N-S extension that triggered convergent flow of partially molten crust at depth and the upwelling of anatectic Migmatites within the dome. This pattern is complicated by gravitational instabilities and/or overturning of the high melt fraction crust leading to the growth of subdomes. As the Migmatites within the Naxos dome reached a higher structural level, they were affected by regional top-to-the-NNE kinematics of the detachment system. Dome formation therefore occurred by a combination of coeval and coupled processes: upper crustal extension, deep crust contraction during convergent flow of anatectic crust, diapirism and/or density-driven crustal convection forming subdomes, and north directed detachment kinematics.
-
paleocene eocene Migmatite crystallization extension and exhumation in the hinterland of the northern cordillera okanogan dome washington usa
Geological Society of America Bulletin, 2008Co-Authors: Seth C Kruckenberg, Donna L Whitney, Christian Teyssier, Mark C Fanning, James W DunlapAbstract:The Okanogan gneiss dome, Washington, is located in the hinterland of the North American Cordillera and is part of a chain of metamorphic core complexes containing gneiss and Migmatite domes exhumed during Eocene extension of thickened crust. U-Pb sensitive high-resolution ion microprobe (SHRIMP) analyses of zircon, monazite, and titanite, and 40 Ar39 Ar analyses of biotite from Migmatites exposed in the footwall of the Okanogan detachment, coupled with a detailed structural analysis, document the timing and duration of Migmatite crystallization and indicate coeval crystallization, extensional deformation, and exhumation of the dome. Okanogan Migmatites are folded and deformed, and preserve successive generations of leucosomes generated by synkinematic anatexis. Analyses of Migmatite samples from a highmelt fraction subdome near Stowe Mountain suggest that the Okanogan dome records a history of Migmatite crystallization spanning at least 12 m.y., as indicated by 206 Pb/