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M. Santosh - One of the best experts on this subject based on the ideXlab platform.
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Gold metallogeny associated with craton destruction: A geophysical perspective from the North China Craton
Ore Geology Reviews, 2016Co-Authors: M. Santosh, Qiong-yan YangAbstract:Abstract Currently ranking as the largest producer of gold in the world, China's gold reserves are spread over 200 major gold deposits and several minor deposits. A large part of these belong to the late Mesozoic gold deposits in the North China Craton (NCC) that occur along craton margins, as well as within the cratonic interior in reactivated paleo sutures, and show a close spatio-temporal relationship with zones of lithospheric thinning and craton destruction. Here we integrate and evaluate geophysical information from the NCC through an analysis of receiver function and tomography that suggest Mantle Upwelling accompanied by lower crustal or lithospheric delamination. Our results identify that the major gold belts in the NCC are largely located above zones of Mantle Upwelling and craton destruction. The faults and paleo sutures provided the pathways for migration of ore-bearing fluids, with the granitoids offering favorable conditions for gold deposition.
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Mantle Upwelling during Permian to Triassic in the northern margin of the North China Craton: Constraints from southern Inner Mongolia
Journal of Asian Earth Sciences, 2014Co-Authors: Zhou Zhang, Hong-fu Zhang, Ji'an Shao, Ji-feng Ying, Yue-heng Yang, M. SantoshAbstract:Abstract The nothern margin of the North China Craton (NCC) preseves the tectonic imprints of early Paleozoic to Triassic tectonic processes. Here we investigate the geochronology, geochemistry, zircon hafnium and whole rock Nd isotope data on a suite of magmatic rocks from the Ningcheng pyroxenite–gabbro–diorite complex and the Jiwangyingzi Formation in the Inner Mongolia region of the northern NCC. The zircon U–Pb dating identifies multiple stages of mafic to intermediate magmatism from Early Permian (298 ± 4 Ma) to Middle Triassic (219 ± 1 Ma) in this area and their hafnium isotopes display diverse Mantle sources. An integration of field observations, geochronology and elemental and isotopic geochemistry indicates a complex petrogenetic history for the magmatic suite. The Ningcheng pyroxenite–gabbro–diorite complex is a product of multiple pulses of magmas with crystal fractionation, hybridization and assimilation, with the involvement of melts derived from lithospheric Mantle and even the asthenosphere. Our data reveal an increasing involvement of Mantle component from Late Permian to Triassic. The features of progressive Mantle Upwelling correlate with tectonic processes associated with the closure of Paleo-Asian Ocean and subsequent post collisional extension, resulting in active magmatism from Carboniferous to Triassic in this region.
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magmatism and metallogeny associated with Mantle Upwelling zircon u pb and lu hf constraints from the gold mineralized jinchang granite ne china
Ore Geology Reviews, 2013Co-Authors: M. Santosh, Hua-feng Zhang, Jia-jun Liu, Chun-rong Diwu, Hong ZhangAbstract:Abstract The Jinchang gold deposit is located in the easternmost portion of the Central Asian Orogenic Belt (CAOB), and represents one of the major gold districts in eastern Jilin–Heilongjiang provinces of China. The gold ore bodies are hosted mainly in altered Mesozoic granitoids, breccia pipes and ring and radial faults. Gold mineralization consists of alteration (stockwork in hydrothermally altered granites), breccia, and quartz-sulfide vein-types. Alteration assemblages around the alteration-style ore body show a vertical sequence of potassic, phyllic, and propylitic zones. In this study, we present U–Pb and Lu–Hf isotope data on zircons derived from mineralized granophyric granite, biotite monzogranite, granodiorite, and granite porphyry, and sericite Rb–Sr ages from the Jinchang gold deposit. The results show 206Pb/238U ages of 201 ± 3 Ma (MSWD = 1.1), 203 ± 4 Ma (MSWD = 1.4), 201 ± 5 Ma (MSWD = 2.1), and 110 ± 3 Ma (MSWD = 1.6), respectively. Sericite from the gold-mineralized phyllic-altered granodiorite and granite porphyry returns Rb–Sr isochron ages of 110 ± 4 Ma (MSWD = 1.04) and 107 ± 5 Ma (MSWD = 0.91), respectively. Our new data indicate that the gold mineralization at Jinchang took place at ca. 110 Ma and was temporally related to intrusion of the granite porphyry. Zircon e Hf (200 Ma) values of the ca. 200 Ma granites vary from − 4.8 to + 8.1, with TCDM model ages of 727–1535 Ma, reflecting their derivation mainly by partial melting of juvenile Proterozoic crust. The gold-bearing 110 Ma granite porphyry returns e Hf (110 Ma) values in the range of − 1.6 to + 9.8, with TCDM model ages of 542–1069 Ma, suggesting partial melts of juvenile Proterozoic crust with notable input of Mantle components as compared to the ca. 200 Ma granites. Compiled oxygen (δ18OSMOW = − 0.7–10.1) and hydrogen (δDSMOW = − 99 to − 70) stable isotopic values of quartz from ores indicate that the ore-forming fluids were predominantly exsolved from magmas with minor amount of meteoric water in quartz-sulfide veins at the late stage. The Hf isotope data from the granite porphyry, integrated with the results from previous data on S and Pb isotopic composition of ores, constrain the source of ore-forming components as lower crust with discernible Mantle inputs and wall rock assimilation. Our results have implications bearing on the widespread magmatism and metallogenic event during the Early Cretaceous time in East China, and link them to Mantle Upwelling that contributed both heat and volatiles for crustal melting and scavenging of metals which in turn were concentrated in upper crustal levels through exsolution for the magmas.
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Magmatism and metallogeny associated with Mantle Upwelling: Zircon U–Pb and Lu–Hf constraints from the gold-mineralized Jinchang granite, NE China
Ore Geology Reviews, 2013Co-Authors: Hua-feng Zhang, M. Santosh, Jia-jun Liu, Chun-rong Diwu, Hong ZhangAbstract:Abstract The Jinchang gold deposit is located in the easternmost portion of the Central Asian Orogenic Belt (CAOB), and represents one of the major gold districts in eastern Jilin–Heilongjiang provinces of China. The gold ore bodies are hosted mainly in altered Mesozoic granitoids, breccia pipes and ring and radial faults. Gold mineralization consists of alteration (stockwork in hydrothermally altered granites), breccia, and quartz-sulfide vein-types. Alteration assemblages around the alteration-style ore body show a vertical sequence of potassic, phyllic, and propylitic zones. In this study, we present U–Pb and Lu–Hf isotope data on zircons derived from mineralized granophyric granite, biotite monzogranite, granodiorite, and granite porphyry, and sericite Rb–Sr ages from the Jinchang gold deposit. The results show 206Pb/238U ages of 201 ± 3 Ma (MSWD = 1.1), 203 ± 4 Ma (MSWD = 1.4), 201 ± 5 Ma (MSWD = 2.1), and 110 ± 3 Ma (MSWD = 1.6), respectively. Sericite from the gold-mineralized phyllic-altered granodiorite and granite porphyry returns Rb–Sr isochron ages of 110 ± 4 Ma (MSWD = 1.04) and 107 ± 5 Ma (MSWD = 0.91), respectively. Our new data indicate that the gold mineralization at Jinchang took place at ca. 110 Ma and was temporally related to intrusion of the granite porphyry. Zircon e Hf (200 Ma) values of the ca. 200 Ma granites vary from − 4.8 to + 8.1, with TCDM model ages of 727–1535 Ma, reflecting their derivation mainly by partial melting of juvenile Proterozoic crust. The gold-bearing 110 Ma granite porphyry returns e Hf (110 Ma) values in the range of − 1.6 to + 9.8, with TCDM model ages of 542–1069 Ma, suggesting partial melts of juvenile Proterozoic crust with notable input of Mantle components as compared to the ca. 200 Ma granites. Compiled oxygen (δ18OSMOW = − 0.7–10.1) and hydrogen (δDSMOW = − 99 to − 70) stable isotopic values of quartz from ores indicate that the ore-forming fluids were predominantly exsolved from magmas with minor amount of meteoric water in quartz-sulfide veins at the late stage. The Hf isotope data from the granite porphyry, integrated with the results from previous data on S and Pb isotopic composition of ores, constrain the source of ore-forming components as lower crust with discernible Mantle inputs and wall rock assimilation. Our results have implications bearing on the widespread magmatism and metallogenic event during the Early Cretaceous time in East China, and link them to Mantle Upwelling that contributed both heat and volatiles for crustal melting and scavenging of metals which in turn were concentrated in upper crustal levels through exsolution for the magmas.
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Guangtoushan granites and their enclaves: Implications for Triassic Mantle Upwelling in the northern margin of the North China Craton
Lithos, 2012Co-Authors: Zhou Zhang, Hong-fu Zhang, Ji'an Shao, Ji-feng Ying, Yue-heng Yang, M. SantoshAbstract:Abstract Mineral electron microprobe, bulk rock major, trace elements and Nd isotopes, and zircon U–Pb and Hf isotopic data are reported for granites and dioritic enclaves from the Guangtoushan granitic complex in the northern margin of the North China Craton. The zircon U–Pb dating identifies two stages of magmatism. The early stage enclave and host granite have identical ages (250 ± 2 Ma) and similar bulk rock Nd isotopes (eNd(t) = − 11.5 to − 12.2) as well as similar zircon Hf isotopes (eHf(t) = − 13.3 to − 17.4). However, although the late stage enclave (206 ± 2 Ma), host granite (208 ± 1 Ma) and leucogranite (207 ± 3 Ma) display comparable ages, but exhibit distinct isotopic features: the granite displays moderate bulk rock Nd isotopic value (eNd(t) = − 8.3) and zircon eHf(t) from − 2.6 to − 10.4; the enclave shows least negative bulk rock eNd(t) of − 3.9 and zircon eHf(t) from 0 to − 5.4; and the leucogranite possesses more pronounced negative bulk rock Nd (eNd(t) = − 17.2) and zircon Hf isotopic compositions (eHf(t) = − 6.2 to − 19.0). An integration of field observations, geochronology, geochemistry and zircon Hf isotopic data points to a complex petrogenetic history, where the early stage enclave–granite pair is a product of the early crystallization of felsic magmas that evolved from a mafic magma, whereas the late stage enclave and granite were derived by magma mixing. The late stage leucogranite is considered as a product of remelting of Phanerozoic igneous rocks within this region. The Guangtoushan granitic complex offers robust evidence for a gradual Mantle Upwelling during Triassic in the northern margin of the North China Craton.
E. M. Parmentier - One of the best experts on this subject based on the ideXlab platform.
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Mantle Upwelling and melting beneath slow spreading centers: effects of variable rheology and melt productivity
Earth and Planetary Science Letters, 2001Co-Authors: Gaël Choblet, E. M. ParmentierAbstract:Abstract We examine the effects of non-uniform rheology and melting models on the 3D structure of Mantle Upwelling beneath spreading centers. Our numerical models identify a range of conditions for which 3D Upwelling can be considered as a possible mechanism for magmatic segmentation of slow spreading ridges. In a highly viscous shallow region due to dehydration of the solid by melt extraction, flow results essentially from the plate spreading. This contrasts with a deeper, buoyant, low viscosity region, where melt is present but Upwelling solid is not yet dehydrated, and where both solid and melt flows acquire their 3D nature. The thickness of this buoyant region, depending mainly on the temperature interval between the wet and dry solidi, results in a specific characteristic length scale for the Upwelling. Smaller segmentation wavelengths occur for smaller values of this thickness. In contrast to isoviscous models where minimum segmentation wavelengths were large (>150 km), minimum wavelengths obtained in models with non-uniform rheology and melt production (40–70 km) are comparable to smallest observed segment lengths. A single wavelength may be preferred for a given set of parameters, but such a preferred wavelength is difficult to achieve because a range of initially prescribed wavelengths can persist for long times. The persistence of 3D solutions for tens of millions of years of model time indicate that segment lengths observed at slow mid-ocean ridges may be inherited from the initial stages of spreading.
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Buoyant Mantle Upwelling and crustal production at oceanic spreading centers: On‐axis segmentation and off‐axis melting
Journal of Geophysical Research: Solid Earth, 1997Co-Authors: Kopal Barnouin-jha, E. M. Parmentier, David SparksAbstract:Numerical experiments are used to examine the effect of buoyant Mantle flow on melt generation near spreading centers. Buoyancy results from (1) the depletion of residual Mantle in Fe relative to Mg (Mantle-depletion buoyancy), (2) the presence of low-density melt (melt-retention buoyancy), and (3) thermal expansion (thermal buoyancy). Thermal buoyancy drives off-axis convective rolls that develop closer to the spreading axis at slower spreading rates. Melt-retention buoyancy drives focused Upwelling into isolated melting centers. With increasing spreading rate, the amplitude of on-axis crustal segmentation decreases, the melting region being essentially two-dimensional at full spreading rates greater than 100 km/m.y. These numerical experiments predict centers of Mantle Upwelling that are more widely spaced than the actual wavelength of inferred crustal thickness variations. This discrepancy indicates that short wavelength segmentation of slow spreading centers requires some process not included in our models of Mantle flow. At fast spreading rates, when the lithosphere is thinner, melt-retention buoyancy gives rise to isolated, focused centers of off-axis Upwelling and melt production. Off-axis melting centers begin to form at about 300 km from the axis, with a characteristic along-axis spacing of 200 km. Successive off-axis melting centers are shifted along axis, so that crustal thickness far from the axis is increased at a 100 km wavelength.
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buoyant Mantle Upwelling and crustal production at oceanic spreading centers on axis segmentation and off axis melting
Journal of Geophysical Research, 1997Co-Authors: Kopal Barnouinjha, E. M. Parmentier, David SparksAbstract:Numerical experiments are used to examine the effect of buoyant Mantle flow on melt generation near spreading centers. Buoyancy results from (1) the depletion of residual Mantle in Fe relative to Mg (Mantle-depletion buoyancy), (2) the presence of low-density melt (melt-retention buoyancy), and (3) thermal expansion (thermal buoyancy). Thermal buoyancy drives off-axis convective rolls that develop closer to the spreading axis at slower spreading rates. Melt-retention buoyancy drives focused Upwelling into isolated melting centers. With increasing spreading rate, the amplitude of on-axis crustal segmentation decreases, the melting region being essentially two-dimensional at full spreading rates greater than 100 km/m.y. These numerical experiments predict centers of Mantle Upwelling that are more widely spaced than the actual wavelength of inferred crustal thickness variations. This discrepancy indicates that short wavelength segmentation of slow spreading centers requires some process not included in our models of Mantle flow. At fast spreading rates, when the lithosphere is thinner, melt-retention buoyancy gives rise to isolated, focused centers of off-axis Upwelling and melt production. Off-axis melting centers begin to form at about 300 km from the axis, with a characteristic along-axis spacing of 200 km. Successive off-axis melting centers are shifted along axis, so that crustal thickness far from the axis is increased at a 100 km wavelength.
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Crenulated seafloor: Evidence for spreading-rate dependent structure of Mantle Upwelling and melting beneath a mid-oceanic spreading center
Earth and Planetary Science Letters, 1995Co-Authors: Jason Phipps Morgan, E. M. ParmentierAbstract:Abstract The availability of dense GEOSAT-GM satellite altimetry data south of 30°S [1] provides the first opportunity to compare at ∼ 25 km resolution seafloor generated at ridges spreading with a wide range of spreading rates. The axis of the slow-spreading Southwest Indian Ridge as well as the seafloor that it has generated has a distinctly crenulated appearance. This crenulated seafloor shows regularly spaced gravity lineations in the spreading direction, crenulations that record stationary centers of Mantle Upwelling over the life of the Southwest Indian Ridge. A similar pattern of crenulation is seen along sections of the slow-spreading northern Mid-Atlantic Ridge, but along the faster (intermediate) spreading southern Mid-Atlantic Ridge, while regularly spaced highs are apparent along sections of the spreading axis, stationary crenulation does not persist off the axis. This pattern implies that the faster spreading southern Mid-Atlantic Ridge has variable centers of time-dependent Upwelling that migrate along the ridge. Crenulations are not visible near the axis of the fast-spreading Pacific-Antarctic Ridge. Crenulation amplitudes decrease strongly with increasing spreading rate. The absence of crenulation at high spreading rate could be due to a 3D/2D transition in flow structure or the effect of mechanisms to redistribute crust along axis. While crenulations are not ubiquitous, even at slowly spreading ridges, where they exist they provide a time record to observe the characteristics of mid-ocean ridge Upwelling, melting and melt migration not only beneath active spreading centers but through a much longer spreading history.
David Sparks - One of the best experts on this subject based on the ideXlab platform.
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Three‐dimensional Mantle Upwelling, melt generation, and melt migration beneath segment slow spreading ridges
Journal of Geophysical Research: Solid Earth, 1997Co-Authors: Laura S. Magde, David SparksAbstract:In contrast to the along-axis uniformity observed at the East Pacific Rise (EPR), crustal accretion at the Mid-Atlantic Ridge (MAR) appears to be a highly complex and heterogeneous process. Besides spreading rate, one of the first-order differences between the EPR and the MAR is the much higher degree of ridge segmentation observed in the Atlantic. Circular lows in the Mantle Bouguer anomaly (MBA bull's-eyes) are common at centers of spreading segments of the MAR, suggesting crustal thickness variations of up to 4 km along individual segments. We use a three-dimensional numerical model of Mantle flow to examine the effect of ridge segmentation on Mantle Upwelling and the resulting overall crustal production and along-axis variations in crustal thickness. Mantle flow in our model is driven by both buoyant forces and segmented plate spreading. Various asthenospheric viscosity structures, plate spreading geometries, and Mantle potential temperatures are explored. We find that a combination of buoyant Mantle flow and three-dimensional melt migration can reproduce crustal thickness variations similar to those inferred from gravity. Buoyant flow gives rise to variations in Upwelling velocity at along-axis wavelengths greater than 150 km but does not contribute to short-wavelength variations. However, three-dimensional melt migration may greatly enhance crustal thickness variations along all segments, independent of the wavelength of buoyant Upwelling. We present an idealized model, in which melt first rises vertically and then flows along the base of the lithosphere toward the ridge axis, that easily produces crustal thickness variations greater than 4 km. The models also predict that the average crustal thickness should decrease with increasing amount of segmentation and decreasing spreading rate. Therefore the thinner, more heterogeneous crust observed at the MAR may result from the combined effects of slower spreading rate and more pervasive ridge segmentation.
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three dimensional Mantle Upwelling melt generation and melt migration beneath segment slow spreading ridges
Journal of Geophysical Research, 1997Co-Authors: Laura S. Magde, David SparksAbstract:In contrast to the along-axis uniformity observed at the East Pacific Rise (EPR), crustal accretion at the Mid-Atlantic Ridge (MAR) appears to be a highly complex and heterogeneous process. Besides spreading rate, one of the first-order differences between the EPR and the MAR is the much higher degree of ridge segmentation observed in the Atlantic. Circular lows in the Mantle Bouguer anomaly (MBA bull's-eyes) are common at centers of spreading segments of the MAR, suggesting crustal thickness variations of up to 4 km along individual segments. We use a three-dimensional numerical model of Mantle flow to examine the effect of ridge segmentation on Mantle Upwelling and the resulting overall crustal production and along-axis variations in crustal thickness. Mantle flow in our model is driven by both buoyant forces and segmented plate spreading. Various asthenospheric viscosity structures, plate spreading geometries, and Mantle potential temperatures are explored. We find that a combination of buoyant Mantle flow and three-dimensional melt migration can reproduce crustal thickness variations similar to those inferred from gravity. Buoyant flow gives rise to variations in Upwelling velocity at along-axis wavelengths greater than 150 km but does not contribute to short-wavelength variations. However, three-dimensional melt migration may greatly enhance crustal thickness variations along all segments, independent of the wavelength of buoyant Upwelling. We present an idealized model, in which melt first rises vertically and then flows along the base of the lithosphere toward the ridge axis, that easily produces crustal thickness variations greater than 4 km. The models also predict that the average crustal thickness should decrease with increasing amount of segmentation and decreasing spreading rate. Therefore the thinner, more heterogeneous crust observed at the MAR may result from the combined effects of slower spreading rate and more pervasive ridge segmentation.
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Buoyant Mantle Upwelling and crustal production at oceanic spreading centers: On‐axis segmentation and off‐axis melting
Journal of Geophysical Research: Solid Earth, 1997Co-Authors: Kopal Barnouin-jha, E. M. Parmentier, David SparksAbstract:Numerical experiments are used to examine the effect of buoyant Mantle flow on melt generation near spreading centers. Buoyancy results from (1) the depletion of residual Mantle in Fe relative to Mg (Mantle-depletion buoyancy), (2) the presence of low-density melt (melt-retention buoyancy), and (3) thermal expansion (thermal buoyancy). Thermal buoyancy drives off-axis convective rolls that develop closer to the spreading axis at slower spreading rates. Melt-retention buoyancy drives focused Upwelling into isolated melting centers. With increasing spreading rate, the amplitude of on-axis crustal segmentation decreases, the melting region being essentially two-dimensional at full spreading rates greater than 100 km/m.y. These numerical experiments predict centers of Mantle Upwelling that are more widely spaced than the actual wavelength of inferred crustal thickness variations. This discrepancy indicates that short wavelength segmentation of slow spreading centers requires some process not included in our models of Mantle flow. At fast spreading rates, when the lithosphere is thinner, melt-retention buoyancy gives rise to isolated, focused centers of off-axis Upwelling and melt production. Off-axis melting centers begin to form at about 300 km from the axis, with a characteristic along-axis spacing of 200 km. Successive off-axis melting centers are shifted along axis, so that crustal thickness far from the axis is increased at a 100 km wavelength.
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buoyant Mantle Upwelling and crustal production at oceanic spreading centers on axis segmentation and off axis melting
Journal of Geophysical Research, 1997Co-Authors: Kopal Barnouinjha, E. M. Parmentier, David SparksAbstract:Numerical experiments are used to examine the effect of buoyant Mantle flow on melt generation near spreading centers. Buoyancy results from (1) the depletion of residual Mantle in Fe relative to Mg (Mantle-depletion buoyancy), (2) the presence of low-density melt (melt-retention buoyancy), and (3) thermal expansion (thermal buoyancy). Thermal buoyancy drives off-axis convective rolls that develop closer to the spreading axis at slower spreading rates. Melt-retention buoyancy drives focused Upwelling into isolated melting centers. With increasing spreading rate, the amplitude of on-axis crustal segmentation decreases, the melting region being essentially two-dimensional at full spreading rates greater than 100 km/m.y. These numerical experiments predict centers of Mantle Upwelling that are more widely spaced than the actual wavelength of inferred crustal thickness variations. This discrepancy indicates that short wavelength segmentation of slow spreading centers requires some process not included in our models of Mantle flow. At fast spreading rates, when the lithosphere is thinner, melt-retention buoyancy gives rise to isolated, focused centers of off-axis Upwelling and melt production. Off-axis melting centers begin to form at about 300 km from the axis, with a characteristic along-axis spacing of 200 km. Successive off-axis melting centers are shifted along axis, so that crustal thickness far from the axis is increased at a 100 km wavelength.
Junmeng Zhao - One of the best experts on this subject based on the ideXlab platform.
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Crustal and upper Mantle velocity structure beneath central Tibet by P-wave teleseismic tomography
Geophysical Journal International, 2012Co-Authors: Heng Zhang, Junmeng ZhaoAbstract:SUMMARY A detailed 3-D P-wave velocity model beneath central Tibet was obtained using 26 741 arrival times from 1025 teleseismic events recorded by the portable stations of the Hi-CLIMB project. In the crustal correction, we consider both vertical and lateral velocity variations. Our teleseismic P-wave tomography result reveals that the Indian lithospheric Mantle underthrusts no further than 32.5°N. In addition, the presence of low velocity anomalies under the Indus-Tsangpo suture suggests that subduction is not a simple and continuous process. We suggest that the delamination of Indian Mantle lithosphere induces Mantle Upwelling beneath the rifts, which in turn created cracks or a break in the subducted plate. Moreover, the formation of active rifts near the profile is related to the Mantle Upwelling.
Kristoffer T. Walker - One of the best experts on this subject based on the ideXlab platform.
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Shear‐wave splitting around the Eifel hotspot: evidence for a Mantle Upwelling
Geophysical Journal International, 2005Co-Authors: Kristoffer T. Walker, Götz Bokelmann, Simon L. Klemperer, G. BockAbstract:SUMMARY We present the results of a shear-wave splitting analysis across the Eifel hotspot in westcentral Europe. Our data set includes 18 permanent European broadband stations and 102 temporary Eifel broadband and short-period stations. We observe variations in splitting at most permanent stations, but are not able to model them reliably with unique dipping-axis or two-layer anisotropy models. We prefer instead a single-layer model with a horizontal fast axis to approximate the first-order anisotropy, which varies smoothly between stations. We observe a first-order parabolic pattern in fast polarization azimuth around the hotspot, which suggests that a lattice preferred orientation (LPO) of olivine fast axes exists in the asthenosphere as a result of the interaction between the slowly WSW-moving Eurasian plate and a Mantle Upwelling beneath the Eifel volcanic fields. The minority of the variation not explained by this model correlates with rapid lateral changes in splitting, and is interpreted as a result of additional anisotropy and/or the effects of dynamic recrystallization associated with LPO development in the region of corner flow near the conduit. Our parabolic asthenospheric flow (PAF) interpretation is consistent with Eifel geological, tomographic, receiver function, global absolute plate motion, electrical conductivity anisotropy, and geochemical studies, as well as with splitting studies in the Great Basin and around Hawaii. We suggest that the Eifel Upwelling is sporadic, and a result of a low excess Upwelling temperature and/or varying crustal stresses that periodically shift and facilitate eruption. The PAF pattern we observe neither suggests nor rules out anisotropy in the conduit associated with a wet Eifel Upwelling. We use our optimum PA F model parameters to calculate a Eurasian plate speed of 12 km Ma −1 ,w hich is consistent with the recent HS3-NUVEL1A speed of 19 ± 14 km Ma −1 .
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shear wave splitting around the eifel hotspot evidence for a Mantle Upwelling
Geophysical Journal International, 2005Co-Authors: Kristoffer T. Walker, Götz Bokelmann, Simon L. Klemperer, G. BockAbstract:SUMMARY We present the results of a shear-wave splitting analysis across the Eifel hotspot in westcentral Europe. Our data set includes 18 permanent European broadband stations and 102 temporary Eifel broadband and short-period stations. We observe variations in splitting at most permanent stations, but are not able to model them reliably with unique dipping-axis or two-layer anisotropy models. We prefer instead a single-layer model with a horizontal fast axis to approximate the first-order anisotropy, which varies smoothly between stations. We observe a first-order parabolic pattern in fast polarization azimuth around the hotspot, which suggests that a lattice preferred orientation (LPO) of olivine fast axes exists in the asthenosphere as a result of the interaction between the slowly WSW-moving Eurasian plate and a Mantle Upwelling beneath the Eifel volcanic fields. The minority of the variation not explained by this model correlates with rapid lateral changes in splitting, and is interpreted as a result of additional anisotropy and/or the effects of dynamic recrystallization associated with LPO development in the region of corner flow near the conduit. Our parabolic asthenospheric flow (PAF) interpretation is consistent with Eifel geological, tomographic, receiver function, global absolute plate motion, electrical conductivity anisotropy, and geochemical studies, as well as with splitting studies in the Great Basin and around Hawaii. We suggest that the Eifel Upwelling is sporadic, and a result of a low excess Upwelling temperature and/or varying crustal stresses that periodically shift and facilitate eruption. The PAF pattern we observe neither suggests nor rules out anisotropy in the conduit associated with a wet Eifel Upwelling. We use our optimum PA F model parameters to calculate a Eurasian plate speed of 12 km Ma −1 ,w hich is consistent with the recent HS3-NUVEL1A speed of 19 ± 14 km Ma −1 .