Three Pan-African hypersthene-bearing monzogranitic and quartz–monzonitic plutons from the Easter... more Three Pan-African hypersthene-bearing monzogranitic and quartz–monzonitic plutons from the Eastern terrane of Nigeria have been investigated in detail. New major, trace and REE data, used to constrain their origen and nature, indicate that they display chemical features of ferro-potassic trans-alkaline affinity. Further trace element discrimination suggests (i) production of calc-alkaline medium-K diorite magmas by partial melting of fluid-metasomatised mantle wedge
Serpentinized peridotites from the Betic-Rif Arc constitute the largest exposure of subcontinenta... more Serpentinized peridotites from the Betic-Rif Arc constitute the largest exposure of subcontinental mantle. Exhumation of these large peridotitic bodies is still controversial and therefore extensive structural studies as well as paleomagnetic studies have been carried out. However, the origen of the magnetic susceptibility and magnetic remanence as well as the timing of NRM acquisition have not been established yet. A
Since the 1970s, ferromagnetic minerals were believed to be absent in the Earth’s mantle and, eve... more Since the 1970s, ferromagnetic minerals were believed to be absent in the Earth’s mantle and, even if present, the temperatures were considered too high for such phases to carry magnetic remanence. However, new experimental data, measurements on mantle xenoliths and an improved understanding of long-wavelength features in aeromagnetic data require that the magnetization of the mantle be revisited. In this Review, we examine mantle magnetism through the xenolith record, evaluate the latest experimental advances, assess detection methods of deep-seated mantle sources and identify salient, unsolved questions about magnetic sources in the Earth’s mantle. Critically, magnetic data on a worldwide collection of mantle xenoliths have revealed that pure magnetite is common in the uppermost mantle (<150 km), particularly in subduction zones and cratons. Furthermore, experiments on haematite and its polymorphs suggest that they could carry a magnetic remanence down to ~600 km, for example, in cold, subducted slabs. Finally, modern spectral analysis of aeromagnetic data confirms that a magnetized layer is present below the crust–mantle boundary in multiple tectonic settings. Future work needs to explore the magnetic minerals in the deepest available mantle xenoliths (150–660 km), in conjunction with experiments on mantle materials at pressures corresponding to these depths. Although it was assumed for decades that the Earth’s mantle could not be magnetic, recent evidence suggests that parts of the upper mantle have magnetic remanence. This Review critically revisits mantle magnetism, discusses recent magnetic data and identifies unresolved questions about the sources of this magnetism. The old view of a globally non-magnetic mantle should be revisited. Some iron oxides are stable and carry a magnetic remanence down to 660 km. Magnetite is ubiquitous in upper mantle xenoliths. New spectral methods show that some magnetic sources lie within the mantle. Low-geotherm regions are prime locations for mantle magnetic sources. The old view of a globally non-magnetic mantle should be revisited. Some iron oxides are stable and carry a magnetic remanence down to 660 km. Magnetite is ubiquitous in upper mantle xenoliths. New spectral methods show that some magnetic sources lie within the mantle. Low-geotherm regions are prime locations for mantle magnetic sources.
The objectives for Expedition 352 were to drill through the entire volcanic sequence of the Bonin... more The objectives for Expedition 352 were to drill through the entire volcanic sequence of the Bonin fore arc to 1. Obtain a high-fidelity record of magmatic evolution during subduction initiation and early arc development, 2. Test the hypothesis that fore-arc basalt lies beneath boninite and understand chemical gradients within these units and across the transition, 3. Use drilling results to understand how mantle melting processes evolve during and after subduction initiation, and 4. Test the hypothesis that the fore-arc lithosphere created during subduction initiation is the birthplace of suprasubduction zone (SSZ) ophiolites. Expedition 352 successfully cored 1.22 km of igneous basement and 0.46 km of over-lying sediment, providing diverse, stratigraphically controlled suites of fore-arc basalts (FAB) and boninite related to seafloor spreading and earliest arc development. FAB were recovered at the two deeper water sites (U1440 and U1441) and boninites at the two sites (U1439 and U...
Journal of Geophysical Research: Solid Earth, 2003
Page 1. Magnetic susceptibility anisotropy: A new petrofabric tool in migmatites Eric C. Ferré,1 ... more Page 1. Magnetic susceptibility anisotropy: A new petrofabric tool in migmatites Eric C. Ferré,1 Christian Teyssier,2 Mike Jackson,3 James W. Thill,3 and Emma SG Rainey2 Received 25 January 2002; revised 15 August 2002 ...
The Havre 2012 deep-sea rhyolite eruption went unobserved and was initially recognised from a mas... more The Havre 2012 deep-sea rhyolite eruption went unobserved and was initially recognised from a massive pumice raft at the sea surface. Havre pumices are predominantly white or grey, however pink pumice is common in the raft. In subaerial explosive eruptions, pink pumice is understood to result from high-temperature atmospheric iron-oxidation. The presence of pink pumice questions the effusive eruption model for the Havre raft. Here we report results from X-ray Absorption Near Edge Structure spectroscopy, magnetic measurements, TEM imaging and glass chemistry that collectively show the colour results from increasing amounts of magnetite nanolites in the raft pumice glass oxidizing to hematite. This suggests a short-lived but powerful explosive eruption phase penetrated the water column allowing hot pyroclasts to oxidise in air. Our results therefore challenge the known depth limits for explosive eruptions in the marine realm and suggest pink pumice can be an indicator of magnetite nan...
International Ocean Discovery Program (IODP) Expedition 352 recovered a high-fidelity record of v... more International Ocean Discovery Program (IODP) Expedition 352 recovered a high-fidelity record of volcanism related to subduction initiation in the Bonin fore-arc. Two sites (U1440 and U1441) located in deep water nearer to the trench recovered basalts and related rocks; two sites (U1439 and U1442) located in shallower water further from the trench recovered boninites and related rocks. Drilling in both areas ended in dolerites inferred to be sheeted intrusive rocks. The basalts apparently erupted immediately after subduction initiation and have compositions similar to those of the most depleted basalts generated by rapid sea-floor spreading at mid-ocean ridges, with little or no slab input. Subsequent melting to generate boninites involved more depleted mantle and hotter and deeper subducted components as subduction progressed and volcanism migrated away from the trench. This volcanic sequence is akin to that recorded by many ophiolites, supporting a direct link between subduction initiation, fore-arc spreading and ophiolite genesis.
We welcome Kletetschka's comment as an opportunity to clarify certain aspects of our contribution... more We welcome Kletetschka's comment as an opportunity to clarify certain aspects of our contribution. This comment also gives us a chance to cite important references that we had unfortunately neglected to mention.
Many migmatites represent crystallized partially molten crust and therefore record the mechanisms... more Many migmatites represent crystallized partially molten crust and therefore record the mechanisms and pathways of orogenic crustal flow. Field and microstructural methods may be insufficient to characterize the planar and linear elements of rock fabric in migmatites due to obscured flow fabrics or protracted deformation. In the Naxos dome (Greece), we test the anisotropy of magnetic susceptibility (AMS) as a tool for recovering mineral fabric symmetry and the kinematic axes of flow in migmatites. Measurements of 155 migmatite samples yield dominantly low values (<300 × 10 −6 [SI]) of bulk magnetic susceptibility (K m) consistent with biotite being the dominant carrier of the AMS. Higher values of K m , thermomagnetic, hysteresis, and microstructural data, however, suggest a ferromagnetic contribution from magnetite in a subset of samples (N = 15). Using electron backscatter diffraction (EBSD) analysis, we establish the correspondence of the biotite subfabric with the AMS and structural fabric of the Naxos migmatites. EBSD data from biotite suggests that magnetic lineation in these dominantly paramagnetic migmatites arises from a zone axis orientation of biotite crystals organized about the direction of viscoplastic flow. Over a range of spatial scales, migmatitic foliation and magnetic foliation are well correlated. The magnetic lineation recovered by AMS displays a coherent organization despite the heterogeneous structure and composition of the Naxos migmatites. These data suggest that the apparent complexity of migmatites masks a simpler flow regime controlled by bulk viscoplastic flow. Furthermore, our study demonstrates the utility of the AMS method for studying the dynamics of partially molten orogenic crust.
Journal of Geophysical Research: Solid Earth, 2012
ABSTRACT We investigate the petrographic, geochemical and magnetic properties of fault pseudotach... more ABSTRACT We investigate the petrographic, geochemical and magnetic properties of fault pseudotachylytes formed by frictional melting in granitic rocks from Southern California, the Italian Alps and Kyushyu, Japan. The main magnetic remanence carriers are mixtures of grain sizes of fine grained magnetite. These ferrimagnetic grains record a stable, multicomponent magnetization that consists of one or more of the following: coseismic thermal remanent magnetization, coseismic lightning isothermal remanent magnetization and post-seismic chemical remanent magnetization. Fault pseudotachylytes from the three localities display contrasting magnetic properties, which suggests that oxygen fugacity and host rock composition ultimately control the magnetic assemblage.
Geological Society, London, Special Publications, 2005
In metamorphic core complexes two types of detachments develop, coupled by flow of partially molt... more In metamorphic core complexes two types of detachments develop, coupled by flow of partially molten crust: a channel detachment and a rolling-hinge detachment. The channel detachment, on the hinterland side of the orogen, represents the long-lived interface that separates the partially molten crust flowing in a channel from the rigid upper crustal lid. On the foreland side of the core complex, a rolling-hinge detachment develops. This detachment dips toward the foreland, probably affects the whole crust, and its geometry is governed by strain localization at the critical interface between cold foreland and hot hinterland. Activation of the rolling-hinge detachment drives rapid decompression and melting, leading to the diapiric rise of migmatite domes in the footwall of the detachment. A kinematic hinge (switch in sense of shear) separates the two types of detachments. Structural, metamorphic and geo/thermochronological studies in the Shuswap core complex (North American Cordillera),...
Our knowledge of the petrology and seismic properties of the subcontinental mantle is deduced mos... more Our knowledge of the petrology and seismic properties of the subcontinental mantle is deduced mostly from three sources: (i) large scale seismic anisotropy investigations; (ii) non-oriented mantle xenoliths and (iii) rare peridotite bodies such as the Ronda massif. These three sources provide information at different scales, from grain size (xenoliths and peridotitic bodies) to tens of kilometers (seismology). Xenoliths exhibit
Paleomagnetic and rock magnetic analysis was conducted on a complex fault propagation fold train ... more Paleomagnetic and rock magnetic analysis was conducted on a complex fault propagation fold train in Kananaskis Country, Alberta to compliment an ongoing study of orogenic remagnetiztions in the thin-skinned, fold and thrust belt (NW Montana and SW Alberta). The complex structure is composed of an asymmetrical anticline to the west and chevron syncline to the east, with both folds plunging
ABSTRACT Migmatites constitute a rheologically complex, two-phase system for which the determinat... more ABSTRACT Migmatites constitute a rheologically complex, two-phase system for which the determination of kinematic axes has proven problematic. As a consequence, field and microstructural methods may be insufficient to characterize the planar and linear elements of rock fabric. Migmatites deform in the partially molten state and acquire complex form surfaces, folds, and fabrics while the surrounding rocks commonly display a simpler geometry. The Naxos dome, Greece, provides opportunities to establish new methods for characterizing flow in the partially molten crust. We use the anisotropy of magnetic susceptibility (AMS) in the Naxos migmatites as a tool capable of recovering mineral fabric symmetry and the kinematic axes of flow in heterogeneous migmatites. Measurements of 155 samples yield dominantly low values of bulk magnetic susceptibility (Km&lt; 300 x 10-6 [SI]), consistent with biotite being the dominant carrier of the AMS. Over a range of spatial scales, migmatitic foliation and magnetic foliation are well correlated. The magnetic lineation recovered by AMS displays a coherent organization despite the heterogeneous structure and composition of the Naxos migmatites. These data suggest that the apparent complexity of migmatites masks a simpler flow regime controlled by bulk viscoplastic flow. The internal dynamics in the flowing partially molten crust are therefore revealed by the combination of AMS and structural analysis in the Naxos dome migmatites. The first-order geometry of the migmatitic core of the dome broadly consists of two compartments that are separated by a steep, N-S oriented, high-strain zone, a pattern that has been recognized in models of isostasy-driven flow. The internal structure of the dome displays second-order subdomes and pinched synforms of variable orientations, with curved lineation trajectories, which suggest that buoyancy-driven flow participated in dome evolution. Our preferred model emphasizes a combination of isostasy- and buoyancy-driven processes: The first-order dome may have been generated by opening of an elongate zone of extension in the upper crust that triggered convergent flow of partially molten crust at depth and transposition of planar and linear fabrics into a general N-S direction. However, this pattern is complicated locally by convection of the high melt fraction crust. As subdomes reached shallower levels, they were overturned by the top-to-the-NNE kinematics of the detachment system. Formation of the Naxos dome therefore occurred by coeval and coupled upper crustal extension, deep crust contraction and upward convergent flow of partially molten crust, convection within subdomes, and north-directed detachment kinematics. This study demonstrates the utility of the AMS method for tectonic studies involving the dynamics of partially molten orogenic crust and illustrates the bulk flow behavior of migmatites over a range of spatial scales.
Three Pan-African hypersthene-bearing monzogranitic and quartz–monzonitic plutons from the Easter... more Three Pan-African hypersthene-bearing monzogranitic and quartz–monzonitic plutons from the Eastern terrane of Nigeria have been investigated in detail. New major, trace and REE data, used to constrain their origen and nature, indicate that they display chemical features of ferro-potassic trans-alkaline affinity. Further trace element discrimination suggests (i) production of calc-alkaline medium-K diorite magmas by partial melting of fluid-metasomatised mantle wedge
Serpentinized peridotites from the Betic-Rif Arc constitute the largest exposure of subcontinenta... more Serpentinized peridotites from the Betic-Rif Arc constitute the largest exposure of subcontinental mantle. Exhumation of these large peridotitic bodies is still controversial and therefore extensive structural studies as well as paleomagnetic studies have been carried out. However, the origen of the magnetic susceptibility and magnetic remanence as well as the timing of NRM acquisition have not been established yet. A
Since the 1970s, ferromagnetic minerals were believed to be absent in the Earth’s mantle and, eve... more Since the 1970s, ferromagnetic minerals were believed to be absent in the Earth’s mantle and, even if present, the temperatures were considered too high for such phases to carry magnetic remanence. However, new experimental data, measurements on mantle xenoliths and an improved understanding of long-wavelength features in aeromagnetic data require that the magnetization of the mantle be revisited. In this Review, we examine mantle magnetism through the xenolith record, evaluate the latest experimental advances, assess detection methods of deep-seated mantle sources and identify salient, unsolved questions about magnetic sources in the Earth’s mantle. Critically, magnetic data on a worldwide collection of mantle xenoliths have revealed that pure magnetite is common in the uppermost mantle (<150 km), particularly in subduction zones and cratons. Furthermore, experiments on haematite and its polymorphs suggest that they could carry a magnetic remanence down to ~600 km, for example, in cold, subducted slabs. Finally, modern spectral analysis of aeromagnetic data confirms that a magnetized layer is present below the crust–mantle boundary in multiple tectonic settings. Future work needs to explore the magnetic minerals in the deepest available mantle xenoliths (150–660 km), in conjunction with experiments on mantle materials at pressures corresponding to these depths. Although it was assumed for decades that the Earth’s mantle could not be magnetic, recent evidence suggests that parts of the upper mantle have magnetic remanence. This Review critically revisits mantle magnetism, discusses recent magnetic data and identifies unresolved questions about the sources of this magnetism. The old view of a globally non-magnetic mantle should be revisited. Some iron oxides are stable and carry a magnetic remanence down to 660 km. Magnetite is ubiquitous in upper mantle xenoliths. New spectral methods show that some magnetic sources lie within the mantle. Low-geotherm regions are prime locations for mantle magnetic sources. The old view of a globally non-magnetic mantle should be revisited. Some iron oxides are stable and carry a magnetic remanence down to 660 km. Magnetite is ubiquitous in upper mantle xenoliths. New spectral methods show that some magnetic sources lie within the mantle. Low-geotherm regions are prime locations for mantle magnetic sources.
The objectives for Expedition 352 were to drill through the entire volcanic sequence of the Bonin... more The objectives for Expedition 352 were to drill through the entire volcanic sequence of the Bonin fore arc to 1. Obtain a high-fidelity record of magmatic evolution during subduction initiation and early arc development, 2. Test the hypothesis that fore-arc basalt lies beneath boninite and understand chemical gradients within these units and across the transition, 3. Use drilling results to understand how mantle melting processes evolve during and after subduction initiation, and 4. Test the hypothesis that the fore-arc lithosphere created during subduction initiation is the birthplace of suprasubduction zone (SSZ) ophiolites. Expedition 352 successfully cored 1.22 km of igneous basement and 0.46 km of over-lying sediment, providing diverse, stratigraphically controlled suites of fore-arc basalts (FAB) and boninite related to seafloor spreading and earliest arc development. FAB were recovered at the two deeper water sites (U1440 and U1441) and boninites at the two sites (U1439 and U...
Journal of Geophysical Research: Solid Earth, 2003
Page 1. Magnetic susceptibility anisotropy: A new petrofabric tool in migmatites Eric C. Ferré,1 ... more Page 1. Magnetic susceptibility anisotropy: A new petrofabric tool in migmatites Eric C. Ferré,1 Christian Teyssier,2 Mike Jackson,3 James W. Thill,3 and Emma SG Rainey2 Received 25 January 2002; revised 15 August 2002 ...
The Havre 2012 deep-sea rhyolite eruption went unobserved and was initially recognised from a mas... more The Havre 2012 deep-sea rhyolite eruption went unobserved and was initially recognised from a massive pumice raft at the sea surface. Havre pumices are predominantly white or grey, however pink pumice is common in the raft. In subaerial explosive eruptions, pink pumice is understood to result from high-temperature atmospheric iron-oxidation. The presence of pink pumice questions the effusive eruption model for the Havre raft. Here we report results from X-ray Absorption Near Edge Structure spectroscopy, magnetic measurements, TEM imaging and glass chemistry that collectively show the colour results from increasing amounts of magnetite nanolites in the raft pumice glass oxidizing to hematite. This suggests a short-lived but powerful explosive eruption phase penetrated the water column allowing hot pyroclasts to oxidise in air. Our results therefore challenge the known depth limits for explosive eruptions in the marine realm and suggest pink pumice can be an indicator of magnetite nan...
International Ocean Discovery Program (IODP) Expedition 352 recovered a high-fidelity record of v... more International Ocean Discovery Program (IODP) Expedition 352 recovered a high-fidelity record of volcanism related to subduction initiation in the Bonin fore-arc. Two sites (U1440 and U1441) located in deep water nearer to the trench recovered basalts and related rocks; two sites (U1439 and U1442) located in shallower water further from the trench recovered boninites and related rocks. Drilling in both areas ended in dolerites inferred to be sheeted intrusive rocks. The basalts apparently erupted immediately after subduction initiation and have compositions similar to those of the most depleted basalts generated by rapid sea-floor spreading at mid-ocean ridges, with little or no slab input. Subsequent melting to generate boninites involved more depleted mantle and hotter and deeper subducted components as subduction progressed and volcanism migrated away from the trench. This volcanic sequence is akin to that recorded by many ophiolites, supporting a direct link between subduction initiation, fore-arc spreading and ophiolite genesis.
We welcome Kletetschka's comment as an opportunity to clarify certain aspects of our contribution... more We welcome Kletetschka's comment as an opportunity to clarify certain aspects of our contribution. This comment also gives us a chance to cite important references that we had unfortunately neglected to mention.
Many migmatites represent crystallized partially molten crust and therefore record the mechanisms... more Many migmatites represent crystallized partially molten crust and therefore record the mechanisms and pathways of orogenic crustal flow. Field and microstructural methods may be insufficient to characterize the planar and linear elements of rock fabric in migmatites due to obscured flow fabrics or protracted deformation. In the Naxos dome (Greece), we test the anisotropy of magnetic susceptibility (AMS) as a tool for recovering mineral fabric symmetry and the kinematic axes of flow in migmatites. Measurements of 155 migmatite samples yield dominantly low values (<300 × 10 −6 [SI]) of bulk magnetic susceptibility (K m) consistent with biotite being the dominant carrier of the AMS. Higher values of K m , thermomagnetic, hysteresis, and microstructural data, however, suggest a ferromagnetic contribution from magnetite in a subset of samples (N = 15). Using electron backscatter diffraction (EBSD) analysis, we establish the correspondence of the biotite subfabric with the AMS and structural fabric of the Naxos migmatites. EBSD data from biotite suggests that magnetic lineation in these dominantly paramagnetic migmatites arises from a zone axis orientation of biotite crystals organized about the direction of viscoplastic flow. Over a range of spatial scales, migmatitic foliation and magnetic foliation are well correlated. The magnetic lineation recovered by AMS displays a coherent organization despite the heterogeneous structure and composition of the Naxos migmatites. These data suggest that the apparent complexity of migmatites masks a simpler flow regime controlled by bulk viscoplastic flow. Furthermore, our study demonstrates the utility of the AMS method for studying the dynamics of partially molten orogenic crust.
Journal of Geophysical Research: Solid Earth, 2012
ABSTRACT We investigate the petrographic, geochemical and magnetic properties of fault pseudotach... more ABSTRACT We investigate the petrographic, geochemical and magnetic properties of fault pseudotachylytes formed by frictional melting in granitic rocks from Southern California, the Italian Alps and Kyushyu, Japan. The main magnetic remanence carriers are mixtures of grain sizes of fine grained magnetite. These ferrimagnetic grains record a stable, multicomponent magnetization that consists of one or more of the following: coseismic thermal remanent magnetization, coseismic lightning isothermal remanent magnetization and post-seismic chemical remanent magnetization. Fault pseudotachylytes from the three localities display contrasting magnetic properties, which suggests that oxygen fugacity and host rock composition ultimately control the magnetic assemblage.
Geological Society, London, Special Publications, 2005
In metamorphic core complexes two types of detachments develop, coupled by flow of partially molt... more In metamorphic core complexes two types of detachments develop, coupled by flow of partially molten crust: a channel detachment and a rolling-hinge detachment. The channel detachment, on the hinterland side of the orogen, represents the long-lived interface that separates the partially molten crust flowing in a channel from the rigid upper crustal lid. On the foreland side of the core complex, a rolling-hinge detachment develops. This detachment dips toward the foreland, probably affects the whole crust, and its geometry is governed by strain localization at the critical interface between cold foreland and hot hinterland. Activation of the rolling-hinge detachment drives rapid decompression and melting, leading to the diapiric rise of migmatite domes in the footwall of the detachment. A kinematic hinge (switch in sense of shear) separates the two types of detachments. Structural, metamorphic and geo/thermochronological studies in the Shuswap core complex (North American Cordillera),...
Our knowledge of the petrology and seismic properties of the subcontinental mantle is deduced mos... more Our knowledge of the petrology and seismic properties of the subcontinental mantle is deduced mostly from three sources: (i) large scale seismic anisotropy investigations; (ii) non-oriented mantle xenoliths and (iii) rare peridotite bodies such as the Ronda massif. These three sources provide information at different scales, from grain size (xenoliths and peridotitic bodies) to tens of kilometers (seismology). Xenoliths exhibit
Paleomagnetic and rock magnetic analysis was conducted on a complex fault propagation fold train ... more Paleomagnetic and rock magnetic analysis was conducted on a complex fault propagation fold train in Kananaskis Country, Alberta to compliment an ongoing study of orogenic remagnetiztions in the thin-skinned, fold and thrust belt (NW Montana and SW Alberta). The complex structure is composed of an asymmetrical anticline to the west and chevron syncline to the east, with both folds plunging
ABSTRACT Migmatites constitute a rheologically complex, two-phase system for which the determinat... more ABSTRACT Migmatites constitute a rheologically complex, two-phase system for which the determination of kinematic axes has proven problematic. As a consequence, field and microstructural methods may be insufficient to characterize the planar and linear elements of rock fabric. Migmatites deform in the partially molten state and acquire complex form surfaces, folds, and fabrics while the surrounding rocks commonly display a simpler geometry. The Naxos dome, Greece, provides opportunities to establish new methods for characterizing flow in the partially molten crust. We use the anisotropy of magnetic susceptibility (AMS) in the Naxos migmatites as a tool capable of recovering mineral fabric symmetry and the kinematic axes of flow in heterogeneous migmatites. Measurements of 155 samples yield dominantly low values of bulk magnetic susceptibility (Km&lt; 300 x 10-6 [SI]), consistent with biotite being the dominant carrier of the AMS. Over a range of spatial scales, migmatitic foliation and magnetic foliation are well correlated. The magnetic lineation recovered by AMS displays a coherent organization despite the heterogeneous structure and composition of the Naxos migmatites. These data suggest that the apparent complexity of migmatites masks a simpler flow regime controlled by bulk viscoplastic flow. The internal dynamics in the flowing partially molten crust are therefore revealed by the combination of AMS and structural analysis in the Naxos dome migmatites. The first-order geometry of the migmatitic core of the dome broadly consists of two compartments that are separated by a steep, N-S oriented, high-strain zone, a pattern that has been recognized in models of isostasy-driven flow. The internal structure of the dome displays second-order subdomes and pinched synforms of variable orientations, with curved lineation trajectories, which suggest that buoyancy-driven flow participated in dome evolution. Our preferred model emphasizes a combination of isostasy- and buoyancy-driven processes: The first-order dome may have been generated by opening of an elongate zone of extension in the upper crust that triggered convergent flow of partially molten crust at depth and transposition of planar and linear fabrics into a general N-S direction. However, this pattern is complicated locally by convection of the high melt fraction crust. As subdomes reached shallower levels, they were overturned by the top-to-the-NNE kinematics of the detachment system. Formation of the Naxos dome therefore occurred by coeval and coupled upper crustal extension, deep crust contraction and upward convergent flow of partially molten crust, convection within subdomes, and north-directed detachment kinematics. This study demonstrates the utility of the AMS method for tectonic studies involving the dynamics of partially molten orogenic crust and illustrates the bulk flow behavior of migmatites over a range of spatial scales.
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