Phase and group velocities and Q of mantle Love and Rayleigh waves of the first two modes and their azimuthal dependences for the 1963 Kurile Islands earthquake

Phase and group velocities and Q of mantle Love and Rayleigh waves from the 1963 Kurile Islands earthquake (M_w = 8.5) were determined over 37 great circle paths by a time variable filtering technique, in a period range 100–500 s for the fundamental modes and 100–275 s for the first higher modes. The preliminary reference Earth model (PREM) explains reasonably well the average dispersion results for the fundamental Love and Rayleigh waves. There exists a small, but significant inconsistency between the observation and the model for the first higher Love and Rayleigh waves. The Q structure of PREM is inconsistent with the observation for the fundamental Love waves, but explains other observations reasonably well. The dispersion of each mode shows a clear azimuthal dependence from which the four azimuthal windows were established. The phase and group velocity measurements for each window were, in general, shown to be mutually consistent. The azimuthal variations are largest for the first higher Rayleigh waves, indicating strong lateral heterogeneity in the structure of the low velocity zone. The first of the four windows is characterized by the largest fraction of Precambrian shields and the second window by the largest fraction of normal oceans. A comparison of these two windows may give some insight into deep lateral heterogeneity between continents and oceans. The observed phase and group velocities of the first window are systematically higher than those of the second window for the fundamental Love and Rayleigh waves at periods up to 400 s, and for the first higher Love and Rayleigh waves up to 175 s. Their differences are greatest for the first higher Rayleigh waves and least for the fundamental Rayleigh waves. Although the fundamental Rayleigh waves show the least velocity differences, their persistence up to a period of longer than 300 s is in striking contrast with some of the pure path phase velocities derived earlier for continents and oceans. A set of models for continents and oceans. PEM-C and PEM-O are not consistent with our observation. The third azimuthal window is characterized by trench-marginal seas and the fourth window by mountainous areas, typically the Asian high plateaus from northern China to the Middle East through Tibet. A comparison of these two windows gives some information about deep structural differences between subduction zones and continental collision zones, both belonging to plate convergence zones. For the fundamental and the first higher Love waves, the phase and group velocities for the third window are markedly low, whereas those for the fourth window are somewhat comparable to those for the second window. Slow Rayleigh waves are evident for two windows, with the fourth window apparently being the slowest for the fundamental Rayleigh above 200 s and for the first higher Rayleigh. For the fundamental Rayleigh waves, the third window is very slow below 200 s, but becomes progressively fast as the period increases and tends to be the fastest window around 400 s, suggesting a deep seated high velocity anomaly beneath trench-marginal seas. The dispersion characteristics of the fourth window indicate a thick high velocity lid with an extensive low velocity zone beneath it. The shield-like lithosphere, coupled with an extensive low velocity zone, may be a characteristic feature of continental collision zones. The particle motion of the fundamental Love waves was found not to be purely transverse to a great-circle connecting the epicenter to a station. The departure from the purely transverse motion is systematic among different periods, different G arrivals (G₂, G₃,…) and different stations, which may be interpreted as being due to lateral refraction.     

A Microstructural sequence of quartz schists in central Shikoku, south-west Japan

This paper describes a microstructural sequence of quartz schists (metamorphosed chert) in the Asemi river region of the Sambagawa metamorphic terrain in central Shikoku, southwest Japan. The Asemi river region is divided into three areas on the basis of characteristics of microstructures of quartz schists observed under the optical microscope: areas I, II and III, in ascending order of metamorphic grade. Microstructures in area I consist of finer, equant, equidimensional and polygonal quartz grains free from internal deformation features. Microstructures in area II are characterized by oblate or elliptical grains with remarkable undulatory extinction surrounded by serrated grain boundaries. Microstructures in area III consist mainly of coarser and equant grains without distinct internal deformation features.The formation conditions of these microstructures are discussed in the light of recent experimental results.     

Elastic properties of garnet solid-solution series

The elastic constants of sixteen garnet specimens of wide variety in chemical composition are accurately determined by means of the rectangular parallelpiped resonance method. The dependence of the elastic properties on chemical composition is analyzed using the present data and those for seven garnets investigated by other authors. The property X_i of a garnet solid solution i is given by a linear addition law in terms of the mole fraction n_ij of component j; X_i = Σn_ijX_j where the X_j's are the properties of the end-members j (j = pyrope, almandine, spessartine, grossular and andradite). The X_j's are determined for density ρ, bulk modulus K, and shear moduli C_s = (C₁₁ ? C₁₂)/2 and C₄₄. No systematic deviation is observed from the linear addition law for the elastic moduli nor for other quantities such as the elastic wave velocities. The extrapolated elastic moduli (Mbar) of the end-members are:

     

85.

Recognition of conjugate solid-type and liquid-type relationship among the oceanic basalts,with respect to REE     

Masuda  A.  Shimokawa  T.  Jibiki  H.  Nagawa  T. 《Contributions to Mineralogy and Petrology》1974,48(4):265-274

The REE abundances and their chondrite-normalized pattern lead one to consider that the basalt from the Caroline ridge area southeast of the Marianas Arc and the one from the Puerto Rico Trench happen to be equivalent to conjugate liquid-type and solid-type materials, respectively, reflecting an equilibrium of a 20% partial melting. This line of interpretation enables us not only to assess the REE abundances in the original solid-type material (M), but also to estimate the corresponding values in the product (¯L) of a very small (say, less than 1 %) extent of a partial melting. It is also found that the relative REE abundances in a basalt from directly east of the Marianas Trench are quite the same as those thus estimated. Alternatively, it is possible to interpret this basalt as representing the residual liquid left after the primary fractional differentiation of the mantle.It is suggested that the straight-type bulk partition coefficients, the absence of the apparent europium anomaly, and the higher pressure are closely associated.     

86.

Evolution of lunar materials in light of the abundance variation of oxyphile trace elements     

Akimasa Masuda  Noboru Nakamura 《Contributions to Mineralogy and Petrology》1970,29(1):11-27

Based on the lunar data on lanthanides, U, Th, Ba, and Sr, the partition coefficients for fractional solidification were estimated for these elements. The resultant values suggest the removal of solids with perhaps pyroxenic composition. The partition coefficient for europium can be judged to be normal as divalent europium dominantly present in the melt. When we go back following the trend of fractionation of abundances, we can reach the stage where there is no europium anomaly and where the thorium concentration level is chondritic. It can be imagined that the material corresponding to this stage was the directly original lunar material system. As a possibility, a zone melting is thought to be a possible process for the derivation of that material from chondritic material. The chondrite-normalized lanthanide patterns for silicate materials of two stony-irons appear to provide us with an intriguing clue to this problem.     

87.

Temperature coefficients of elastic constants of single crystal MgO between 80 and 1,300 K     

Yoshio Sumino  Orson L. Anderson  Isao Suzuki 《Physics and Chemistry of Minerals》1983,9(1):38-47

Elastic constants of single crystal MgO have been measured by the rectangular parallelepiped resonance (RPR) method at temperatures between 80 and 1,300 K. Elastic constants C _ij (Mbar=10³ kbar) and their temperature coefficients (kbar/K) are: $$\begin{gathered} {\text{ }}C_{{\text{11}}} {\text{ }}C_{{\text{12}}} {\text{ }}C_{{\text{44}}} {\text{ }}K_s {\text{ }}C_s \hfill \\ C_{ij} {\text{ 300 K 2}}{\text{.966 0}}{\text{.959 1}}{\text{.562 1}}{\text{.628 1}}{\text{.004}} \hfill \\ \partial C_{ij} {\text{/}}\partial T{\text{100 K }} - {\text{0}}{\text{.259 0}}{\text{.013 }} - {\text{0}}{\text{.072 }} - {\text{0}}{\text{.078 }} - {\text{0}}{\text{.136}} \hfill \\ {\text{ 300K }} - {\text{0}}{\text{.596 0}}{\text{.068 }} - {\text{0}}{\text{.122 }} - {\text{0}}{\text{.153 }} - {\text{0}}{\text{.332}} \hfill \\ {\text{ 800 K }} - {\text{0}}{\text{.619 0}}{\text{.009 }} - {\text{0}}{\text{.152 }} - {\text{0}}{\text{.200 }} - {\text{0}}{\text{.314}} \hfill \\ {\text{ 1,300 K }} - {\text{0}}{\text{.598 0}}{\text{.036 }} - {\text{0}}{\text{.130 }} - {\text{0}}{\text{.223 }} - {\text{0}}{\text{.218}} \hfill \\ \end{gathered} $$ By combining the present results with the previous data on the thermal expansivity and specific heat, the thermodynamic properties of magnesium oxide are presented and discussed. The elastic parameters of MgO at very high temperatures in the earth's lower mantle are also clarified.     

88.

PP-P differential traveltime measurement with crustal correction     

Masayuki Obayashi  Daisuke Suetsugu  Yoshio Fukao 《Geophysical Journal International》2004,157(3):1152-1162

     

89.

Trace element characteristics of the fluid liberated from amphibolite-facies slab: Inference from the metamorphic sole beneath the Oman ophiolite and implication for boninite genesis   总被引：3，自引：0，他引：3  

Tsuyoshi Ishikawa  Shiori Fujisawa  Kazuya Nagaishi  Toshiaki Masuda 《Earth and Planetary Science Letters》2005,240(2):355-377

Major and trace element compositions of amphibolites and quartzose rocks in the 230-m-thick metamorphic sole underlying the mantle section of the Oman ophiolite in Wadi Tayin area were determined to investigate the chemical characteristics of the hydrous fluid released from subducted amphiboltie-facies slab. The fluid-immobile element compositions indicate that protoliths of these rocks are mid-ocean ridge basalt-like tholeiite and deep-sea chert, which is consistent with the idea that these rocks represent Tethyan oceanic crust overridden during the early, intraoceanic thrusting stage of the Oman ophiolite emplacement. The rare-earth element (REE) and high field-strength element concentrations of the amphibolites show limited variations, within a factor of two except for a few evolved samples, throughout transect of the sole. On the other hand, concentrations of fluid-mobile elements, especially B, Rb, K and Ba, in amphibolites are highly elevated in upper 30 m of the sole (> 600 °C in peak metamorphic temperature), suggesting the equilibration with evolved, B-Rb-K-Ba-rich fluids during prograde metamorphism. The comparison with amphibolites in the lower 150 m (500 to 550 °C) demonstrates that the trace element spectra of the fluids equilibrated with the high-level amphibolites may vary as a function of metamorphic temperature. The fluids are characterized by striking enrichments of B, Rb, K and Ba and moderate to minor enrichments of Sr, Li, Be and Pb. At higher temperature (up to 700 °C), the fluids become considerably enriched in light REE and Nb in addition to the above elements. The estimated trace element spectra of the fluids do not coincide with the compositions of basalts from matured intra-oceanic arcs, but satisfactorily explain the characteristics of the low-Pb andesites and boninites found in the Oman ophiolite. Compositional similarity between the boninites of Oman and other localities suggests that the fluids estimated here well represent the amphibolite-derived fluids involved in the magmatism of immatured, hot, shallow subduction zones.     

90.

Caledonide development offshore–onshore Svalbard based on ocean bottom seismometer, conventional seismic, and potential field data     

Asbjrn Johan Breivik  Rolf Mjelde  Paul Grogan  Hideki Shimamura  Yoshio Murai  Yuichi Nishimura 《Tectonophysics》2005,401(1-2):79-117

The western Barents Sea and the Svalbard archipelago share a common history of Caledonian basement formation and subsequent sedimentary deposition. Rock formations from the period are accessible to field study on Svalbard, but studies of the near offshore areas rely on seismic data and shallowdrilling. Offshore mapping is reliable down to the Permian sequence, but multichannel reflection seismic data do not give a coherent picture of older stratigraphy. A survey of 10 Ocean Bottom Seismometer profiles was collected around Svalbard in 1998. Results show a highly variable thickness of pre-Permian sedimentary strata, and a heterogeneous crystalline crust tied to candidates for continental sutures or major thrust zones. The data shown in this paper establish that the observed gravity in some parts of the platform can be directly related to velocity variations in the crystalline crust, but not necessarily to basement or Moho depth. The results from three new models are incorporated with a previously published profile, to produce depth-to-basement and -Moho maps south of Svalbard. There is a 14 km deep basement located approximately below the gently structured Upper Paleozoic Sørkapp Basin, bordered by a 7 km deep basement high to the west, and 7–9 km depths to the north. Continental Moho-depth range from 28 to 35 km, the thickest crust is found near the island of Hopen, and in a NNW trending narrow crustal root located between 19°E and 20°E, the latter is interpreted as a relic of westward dipping Caledonian continental collision or major thrusting. There is also a basement high on this trend. Across this zone, there is an eastward increase in the V_P, V_P/V_S ratio, and density, indicating a change towards a more mafic average crustal composition. The northward basement/Moho trend projects onto the Billefjorden Fault Zone (BFZ) on Spitsbergen. The eastern side of the BFZ correlates closely with coincident linear positive gravity and magnetic anomalies on western Ny Friesland, apparently originating from an antiform with high-grade metamorphic Caledonian terrane. A double linear magnetic anomaly appears on the BFZ trend south of Spitsbergen, sub-parallel to and located 10–50 km west of the crustal root. Based on this correlation, it is proposed that the suture or major thrust zone seen south of Svalbard correlates to the BFZ. The preservation of the relationship between the crustal suture, the crustal root, and upper mantle reflectivity, challenges the large-offset, post-collision sinistral transcurrent movement on the BFZ and other trends proposed in the literature. In particular, neither the wide-angle seismic data, nor conventional deep seismic reflection data south of Svalbard show clear signs of major lateral offsets, as seen in similar data around the British Isles.     

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	Almandine	Pyrope	Spessartine	Grossular	Andradite
$\text{K}$	1.779 ± 0.008	1.730 ± 0.009	1.742 ± 0.009	1.691 ± 0.008	1.379 ± 0.017
$\text{C}{}_{\mathrm{<mtext>s</mtext>}}$	0.981 ± 0.004	0.925 ± 0.004	0.964 ± 0.004	1.106 ± 0.004	0.979 ± 0.007
$\text{C}{}_{\mathrm{<mtext>44</mtext>}}$	0.958 ± 0.005	0.919 ± 0.005	0.937 ± 0.005	1.017 ± 0.006	0.827 ± 0.010

Recognition of conjugate solid-type and liquid-type relationship among the oceanic basalts,with respect to REE

The REE abundances and their chondrite-normalized pattern lead one to consider that the basalt from the Caroline ridge area southeast of the Marianas Arc and the one from the Puerto Rico Trench happen to be equivalent to conjugate liquid-type and solid-type materials, respectively, reflecting an equilibrium of a 20% partial melting. This line of interpretation enables us not only to assess the REE abundances in the original solid-type material (M), but also to estimate the corresponding values in the product (¯L) of a very small (say, less than 1 %) extent of a partial melting. It is also found that the relative REE abundances in a basalt from directly east of the Marianas Trench are quite the same as those thus estimated. Alternatively, it is possible to interpret this basalt as representing the residual liquid left after the primary fractional differentiation of the mantle.It is suggested that the straight-type bulk partition coefficients, the absence of the apparent europium anomaly, and the higher pressure are closely associated.     

Evolution of lunar materials in light of the abundance variation of oxyphile trace elements

Based on the lunar data on lanthanides, U, Th, Ba, and Sr, the partition coefficients for fractional solidification were estimated for these elements. The resultant values suggest the removal of solids with perhaps pyroxenic composition. The partition coefficient for europium can be judged to be normal as divalent europium dominantly present in the melt. When we go back following the trend of fractionation of abundances, we can reach the stage where there is no europium anomaly and where the thorium concentration level is chondritic. It can be imagined that the material corresponding to this stage was the directly original lunar material system. As a possibility, a zone melting is thought to be a possible process for the derivation of that material from chondritic material. The chondrite-normalized lanthanide patterns for silicate materials of two stony-irons appear to provide us with an intriguing clue to this problem.     

Temperature coefficients of elastic constants of single crystal MgO between 80 and 1,300 K

Elastic constants of single crystal MgO have been measured by the rectangular parallelepiped resonance (RPR) method at temperatures between 80 and 1,300 K. Elastic constants C _ij (Mbar=10³ kbar) and their temperature coefficients (kbar/K) are: $$\begin{gathered} {\text{ }}C_{{\text{11}}} {\text{ }}C_{{\text{12}}} {\text{ }}C_{{\text{44}}} {\text{ }}K_s {\text{ }}C_s \hfill \\ C_{ij} {\text{ 300 K 2}}{\text{.966 0}}{\text{.959 1}}{\text{.562 1}}{\text{.628 1}}{\text{.004}} \hfill \\ \partial C_{ij} {\text{/}}\partial T{\text{100 K }} - {\text{0}}{\text{.259 0}}{\text{.013 }} - {\text{0}}{\text{.072 }} - {\text{0}}{\text{.078 }} - {\text{0}}{\text{.136}} \hfill \\ {\text{ 300K }} - {\text{0}}{\text{.596 0}}{\text{.068 }} - {\text{0}}{\text{.122 }} - {\text{0}}{\text{.153 }} - {\text{0}}{\text{.332}} \hfill \\ {\text{ 800 K }} - {\text{0}}{\text{.619 0}}{\text{.009 }} - {\text{0}}{\text{.152 }} - {\text{0}}{\text{.200 }} - {\text{0}}{\text{.314}} \hfill \\ {\text{ 1,300 K }} - {\text{0}}{\text{.598 0}}{\text{.036 }} - {\text{0}}{\text{.130 }} - {\text{0}}{\text{.223 }} - {\text{0}}{\text{.218}} \hfill \\ \end{gathered} $$ By combining the present results with the previous data on the thermal expansivity and specific heat, the thermodynamic properties of magnesium oxide are presented and discussed. The elastic parameters of MgO at very high temperatures in the earth's lower mantle are also clarified.     

Trace element characteristics of the fluid liberated from amphibolite-facies slab: Inference from the metamorphic sole beneath the Oman ophiolite and implication for boninite genesis

Major and trace element compositions of amphibolites and quartzose rocks in the 230-m-thick metamorphic sole underlying the mantle section of the Oman ophiolite in Wadi Tayin area were determined to investigate the chemical characteristics of the hydrous fluid released from subducted amphiboltie-facies slab. The fluid-immobile element compositions indicate that protoliths of these rocks are mid-ocean ridge basalt-like tholeiite and deep-sea chert, which is consistent with the idea that these rocks represent Tethyan oceanic crust overridden during the early, intraoceanic thrusting stage of the Oman ophiolite emplacement. The rare-earth element (REE) and high field-strength element concentrations of the amphibolites show limited variations, within a factor of two except for a few evolved samples, throughout transect of the sole. On the other hand, concentrations of fluid-mobile elements, especially B, Rb, K and Ba, in amphibolites are highly elevated in upper 30 m of the sole (> 600 °C in peak metamorphic temperature), suggesting the equilibration with evolved, B-Rb-K-Ba-rich fluids during prograde metamorphism. The comparison with amphibolites in the lower 150 m (500 to 550 °C) demonstrates that the trace element spectra of the fluids equilibrated with the high-level amphibolites may vary as a function of metamorphic temperature. The fluids are characterized by striking enrichments of B, Rb, K and Ba and moderate to minor enrichments of Sr, Li, Be and Pb. At higher temperature (up to 700 °C), the fluids become considerably enriched in light REE and Nb in addition to the above elements. The estimated trace element spectra of the fluids do not coincide with the compositions of basalts from matured intra-oceanic arcs, but satisfactorily explain the characteristics of the low-Pb andesites and boninites found in the Oman ophiolite. Compositional similarity between the boninites of Oman and other localities suggests that the fluids estimated here well represent the amphibolite-derived fluids involved in the magmatism of immatured, hot, shallow subduction zones.     

Caledonide development offshore–onshore Svalbard based on ocean bottom seismometer, conventional seismic, and potential field data

The western Barents Sea and the Svalbard archipelago share a common history of Caledonian basement formation and subsequent sedimentary deposition. Rock formations from the period are accessible to field study on Svalbard, but studies of the near offshore areas rely on seismic data and shallowdrilling. Offshore mapping is reliable down to the Permian sequence, but multichannel reflection seismic data do not give a coherent picture of older stratigraphy. A survey of 10 Ocean Bottom Seismometer profiles was collected around Svalbard in 1998. Results show a highly variable thickness of pre-Permian sedimentary strata, and a heterogeneous crystalline crust tied to candidates for continental sutures or major thrust zones. The data shown in this paper establish that the observed gravity in some parts of the platform can be directly related to velocity variations in the crystalline crust, but not necessarily to basement or Moho depth. The results from three new models are incorporated with a previously published profile, to produce depth-to-basement and -Moho maps south of Svalbard. There is a 14 km deep basement located approximately below the gently structured Upper Paleozoic Sørkapp Basin, bordered by a 7 km deep basement high to the west, and 7–9 km depths to the north. Continental Moho-depth range from 28 to 35 km, the thickest crust is found near the island of Hopen, and in a NNW trending narrow crustal root located between 19°E and 20°E, the latter is interpreted as a relic of westward dipping Caledonian continental collision or major thrusting. There is also a basement high on this trend. Across this zone, there is an eastward increase in the V_P, V_P/V_S ratio, and density, indicating a change towards a more mafic average crustal composition. The northward basement/Moho trend projects onto the Billefjorden Fault Zone (BFZ) on Spitsbergen. The eastern side of the BFZ correlates closely with coincident linear positive gravity and magnetic anomalies on western Ny Friesland, apparently originating from an antiform with high-grade metamorphic Caledonian terrane. A double linear magnetic anomaly appears on the BFZ trend south of Spitsbergen, sub-parallel to and located 10–50 km west of the crustal root. Based on this correlation, it is proposed that the suture or major thrust zone seen south of Svalbard correlates to the BFZ. The preservation of the relationship between the crustal suture, the crustal root, and upper mantle reflectivity, challenges the large-offset, post-collision sinistral transcurrent movement on the BFZ and other trends proposed in the literature. In particular, neither the wide-angle seismic data, nor conventional deep seismic reflection data south of Svalbard show clear signs of major lateral offsets, as seen in similar data around the British Isles.