SATELLITE Pictures

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Summary

The Permian marks an important, yet poorly understood, tectonic transition in the Tian Shan region of northwestern China between Devonian-Carboniferous continental amalgamation and recurrent Mesozoic-Cenozoic intracontinental orogenic reactivation. The Turpan-Hami basin accommodated up to 3000 m sediment and is ideally positioned to provide constraints on this transition. New stratigraphic data and mapping indicate that extension dominated Early Permian tectonics in the region, whereas flexural, foreland subsidence controlled Late Permian basin evolution.

Lower Permian strata in the northwestern Turpan-Hami basin consist of coarse-grained debris flow and alluvial fan deposits interbedded with mafic to intermediate volcanic sills and flows. In contrast, Lower Permian rocks in the north-central and northeastern Turpan-Hami basin unconformably overlie an Upper Carboniferous volcanic arc sequence. These Lower Permian strata include possible shallow marine carbonate, and thick volcanic and volcaniclastic rocks which are in turn followed by littoral to profundal lacustrine facies. Following a regional Lower-Upper Permian unconformity, regional sedimentation patterns record the development of a more integrated sedimentary basin. The Upper Permian is entirely nonmarine and can be correlated along the west-east depositional strike of the basin. The lower Upper Permian consists of a broad belt of braided fluvial deposits shed northward. This is followed by fluctuating littoral-profundal lacustrine and associated fluvial facies. The uppermost Permian is characterized by shallow lake-plain and fluvial environments.

Location map of the Junggar and Turpan-Hami basins, showing maximum known extent of Upper Permian lake deposits.
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Organic-rich Upper Permian oil shales of the Lucaogou Formation, southern Junggar basin (photo: Alan Carroll).
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Geologic map and satellite image of the Taoshuyuan fault, southern Bogdashan. The Taoshuyuan fault is interpreted to be a reactivated Early Permian normal fault (Wartes et al., in press).
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Geologic setting

The volcanic necks exposed in the Rio Puerco drainage lie within the Jemez Lineament, a prominent N50E alignment of Cenozoic volcanic fields ( [ برای مشاهده لینک ، با نام کاربری خود وارد شوید یا ثبت نام کنید ] ). This volcanic alignment appears to follow the trend of a Precambrian province boundary in the subsurface (Karlstrom & Humphreys, 1998), although there is little to no fault expression of this feature at the surface. In the area of the Rio Puerco valley (RPV), the lineament marks the location of the Transition Zone that separates the Colorado Plateau from the extended lithosphere of the Rio Grande rift and Basin and Range province (Baldridge et al., 1991; Perry et al., 1987, 1988, 1990).

The Puerco necks occur on the east flank of the ~3-1.5 Ma Mt. Taylor volcanic field (Hunt, 1937; Perry et al., 1990) between Mesa Chivato on the west and Mesa Prieta on the east ( [ برای مشاهده لینک ، با نام کاربری خود وارد شوید یا ثبت نام کنید ] ). The necks are broadly confined to the Rio Puerco fault zone, a NNE-trending belt of Laramide faults that were reactivated during Rio Grande rifting (Hallett, 1992; Slack et al., 1996). Although few of the necks are directly associated with individual faults, the confinement of the necks to this zone suggests that the fault network facilitated magma transport to the surface.

Geophysical studies in the region show a change in crustal thickness from 40-45 km beneath the Colorado Plateau to ~30-35 km beneath the Transition Zone and under the Rio Grande rift (Hendricks & Plescia, 1991; Keller et al., 1998; Nishimura et al., 1997; Parsons et al., 1996; Rosca et al., 2000; Snelson et al., 1998; Zandt et al., 1995). Lithospheric thicknesses are estimated to be around 90 km below the plateau, and thinner beneath the rift (e.g., Davis, 1991). Heat flow is elevated within the rift and the Jemez Lineament with respect to values from the Colorado Plateau, reflecting both Cenozoic magmatic activity and extensional thinning of the lithosphere (Eggleston & Reiter, 1984). Deep seismic reflection data across the Jemez Lineament to the east of the Rio Grande rift show a strongly reflecting, south-dipping ramp through the crust that has been interpreted to be the trace of a ca. 1.6 Ga paleo-subduction zone (Magnani et al., 2001).

Considerable debate exists concerning the role that remnants of the Mesozoic Farallon slab (e.g., Humphreys, 1995; van der Lee & Nolet, 1997; Bunge & Grand, 2000) might have played at depth beneath and adjacent to the Colorado Plateau. Helmstaedt & Schulze (1991) argued that subduction of the Farallon plate produced an inverted metamorphic gradient in the mantle beneath the Colorado Plateau and also caused hydration of the overlying mantle. Smith (1995) has documented extensive hydration of mantle xenoliths at anomalously low temperatures beneath the Plateau, but argues that available data cannot distinguish between Proterozoic processes, hydration during Laramide flat-slab subduction, or percolation of fluids down from the overlying crust. The high present-day topography in the western U.S. requires support via mantle buoyancy, and thus cold mantle must have been replaced by warm mantle following Farallon subduction (e.g., Humphreys; 1995; Karlstrom & Humphreys, 1998; Bunge & Grand, 2000).

Isotopic studies in alkali basalts throughout the western U.S. show that there is a good correlation between tectonic setting and mantle source region for the basalts. For example, Nd isotopic studies of alkali basalts from the southern Basin and Range province show extraction from depleted asthenosphere (eNd=+7 to +8), whereas basalts from relatively unextended areas (Colorado Plateau; Great Plains) were generally derived from enriched mantle (eNd=0 to +2; Perry et al., 1987; but note Lee et al., 2001, Re-Os data indicating depleted root). The Transition Zone between the Colorado Plateau and the Basin and Range records a mixed source region with eNd= +3 to +6.

Basalts from the Mt. Taylor (Perry et al., 1990) and Rio Puerco (Hallett, 1994) volcanic fields generally have relatively high eNd (+3.5 to +5) and low 87Sr/86Sr (<0.7041). These values are consistent with those from Transition Zone rocks in Arizona, and not surprisingly lie between the Colorado Plateau and Rio Grande rift values (Baldridge et al., 1991; Duncker et al., 1991; Johnson & Thompson, 1991; McMillan et al., 2000). These data suggest that the mantle beneath the Rio Puerco region has been partially modified by extension and asthenospheric upwelling.

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Satellite photo mosaic of Kachchh Mainland. The active fault traces identified along Kachchh Mainland Fault Zone
and along Katroll Hill Fault Zone have been shown enclosed in the area marked in yellow.

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Alborz Mountains

The Alborz Mountain range separates the Iranian plateau from the Caspian Sea. In contrast to the dry plateau the north side of the mountains and the coastal plains are humid and green. In the foreground the Sefid River crosses through the mountains and enters into the Caspian Sea near the city of Rasht.

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تو سایت زیر شما فقط کافیه فلش پلیر ( آخرین ورزنش ) رو نصب کرده باشین
بعد با دادن مختصات هرجای دنیا رو که میخوای نگا کن

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اینم مال ناساست

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[amiraha9097]

nasa world win را از كجا ميشود گرفت؟

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بفرما عزیز جان

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