نتایج جستجو برای: lava rock
تعداد نتایج: 41494 فیلتر نتایج به سال:
The Figuera Lava, the oldest stratigraphic unit now recognized in northeastern Puerto Rico, and the overlying Fajardo Formation are redescribed and the name Figuera redefined and reinstated for formal use. Previously, lower Tertiary strata some distance from the type areas of the Figuera and Fajardo were correlated with the units by reconnaissance. Recent detailed mapping and paleontology now p...
Point-counted modes, representative mineral analyses, and whole-rock majorand trace-element compositions determined by X-ray fluorescence spectroscopy and inductively coupled plasma mass spectroscopy (ICP-MS) are presented for 11 samples of the hornblende^andesite block-lava flows erupted from Volca¤n de Colima in 1991 and 1998^1999. New ICP-MS trace-element data are also presented for 37 andes...
چکیده ندارد.
Amazonian The youngest of the geologic epochs on Mars identified through geoiogic mapping of superposition relations, and the area! density of impact craters. caldera An irregular collapse feature formed over the evacuated magma chamber within a volcano. central volcano Emplacement of volcanic materials from a centralized source vent rather than along a distributed line of vents, composite volc...
The Isua greenstone belt (Fig. 1) contains the oldest known, relatively well preserved, metavolcanic and metasedimentary rocks on Earth. The rocks are all deformed and many were substantially altered by metasomatism, but both the deformation and metasomatism were heterogeneous. Transitional stages can be seen from relatively well preserved primary volcanic and sedimentary structures to schists ...
Shallow-level sill emplacement can uplift Earth’s surface via forced folding, providing insight into the location and size of potential volcanic eruptions. Linking the structure and dynamics of ground deformation to sill intrusion is thus critical in volcanic hazard assessment. This is challenging, however, because (1) active intrusions cannot be directly observed, meaning that we rely on trans...
One of the key issues in forecasting volcanic eruptions is to detect signals that can track the propagation of dykes towards the surface. Continuous monitoring of active volcanoes helps significantly in achieving this goal. The seismic data presented here are unique, as they document surface faulting processes close (tens to a few hundred meters) to their source, namely the dyke tip. They origi...
[l] The SHARAD instrument on the Mars Reconnaissance Orbiter detects subsurface interfaces beneath lava flow fields northwest of Ascraeus Mons. The interfaces occur in two locations; a northern flow that originates south of Alba Patera, and a southern flow that originates at the rift zone between Ascraeus and Pavonis Montes. The northern flow has permittivity values, estimated from the time del...
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