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L. E. Levin 《Geotectonics》2006,40(5):357-366
The lithosphere and asthenosphere make up a common geodynamic system but are characterized by different physical parameters. The former has a temperature of 1200–1300°C, a density of 3.3 g/cm3, and a viscosity of 1022 poise, while the latter has a density of 3.23 g/cm3, a viscosity in the range 1021-1018–19 poise, and a temperature from 1200–1300°C to 1600–1700°C. The asthenosphere is distinguished by a great variability of its physical state in the lateral and vertical directions. This circumstance necessitates the recognition of the different types of the asthenosphere: seismic (LVZ zone), electrical, thermal, and seismological. The structure and the physical state of the thermal asthenosphere is considered in this paper on the basis of P-T parameters. Its state normally fits viscous Newtonian liquid beneath the continents and provides partial (5–20%) melting in spreading zones and along continental margins. No partial melting is detected beneath the main portion of the continents. The interaction between the asthenosphere and lithosphere is characterized by spatiotemporal migration of partial melting zones and asthenosphere upwelling, and such interaction determines the entire range of geodynamic processes from spreading and rifting to collision and vertical motions of different senses. 相似文献
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Thomas A. Vogel Timothy P. Flood Lina C. Patino Melissa S. Wilmot Raymond Patrick R. Maximo Carmencita B. Arpa Carlo A. Arcilla James A. Stimac 《Contributions to Mineralogy and Petrology》2006,151(3):267-281
Silicic volcanic deposits (>65 wt% SiO2), which occur as domes, lavas and pyroclastic deposits, are relatively abundant in the Macolod Corridor, SW Luzon, Philippines.
At Makiling stratovolcano, silicic domes occur along the margins of the volcano and are chemically similar to the silicic
lavas that comprise part of the volcano. Pyroclastic flows are associated with the Laguna de Bay Caldera and these are chemically
distinct from the domes and lavas at Makiling stratovolcano. As a whole, samples from the Laguna de Bay Caldera contain lower
concentrations of MgO and higher concentrations of Fe2O3(t) than the samples from domes and lavas. The Laguna de Bay samples are more enriched in incompatible trace elements. The silicic
rocks from the domes, Makiling Volcano and Laguna de Bay Caldera all contain high alkalis and high K2O/Na2O ratios. Melting experiments of primitive basalts and andesites demonstrate that it is difficult to produce high K2O/Na2O silicic magmas by fractional crystallization or partial melting of a low K2O/Na2O source. However, recent melting experiments (Sisson et al., Contrib Mineral Petrol 148:635–661, 2005) demonstrate that extreme
fractional crystallization or partial melting of K-rich basalts can produce these silicic magmas. Our model for the generation
of the silicic magmas in the Macolod Corridor requires partial melting of mantle-derived, evolved, moderate to K-rich, crystallized
calc-alkaline magmas that ponded and crystallized in the mid-crust. Major and trace element variations, along with oxygen
isotopes and ages of the deposits, are consistent with this model.
Electronic Supplementary Material Supplementary material is available for this article at 相似文献
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The tectonic evolution of the Por’ya Guba segment of the White Sea Rift System began in the late Paleoproterozoic, i.e., soon
after completion of the Svecofennian collision. The fracture system that controlled localization of the lamproite dike complex
was formed under conditions of horizontal compression combined with shear. Subsequently, this system predetermined the location
of a rift-graben segment that formed as a result of simple shear. The reactivation of the rift system in the Middle Paleozoic
proceeded in two stages. The first stage, when strike-slip movements along previously formed faults predominated, resulted
in formation of quartz-carbonate veins bearing base-metal mineralization. The veins that filled the shear fractures opened
owing to local reorientation of the stress field. The second stage fitted the transtension conditions, and the Late Devonian
alkaline ultramafic dikes of this stage introded into the already existing fracture system, which was oriented at a roughly
right angle to the predominant stress orientation. 相似文献
990.