FGF signaling controls somite boundary position and regulates segmentation clock control of spatiotemporal Hox gene activation

AbstractVertebrate segmentation requires a molecular oscillator, the segmentation clock, acting in presomitic mesoderm (PSM) cells to set the pace at which segmental boundaries are laid down. However, the signals that position each boundary remain unclear. Here, we report that FGF8 which is expressed in the posterior PSM, generates a moving wavefront at which level both segment boundary position and axial identity become determined. Furthermore, by manipulating boundary position in the chick embryo, we show that Hox gene expression is maintained in the appropriately numbered somite rather than at an absolute axial position. These results implicate FGF8 in ensuring tight coordination of the segmentation process and spatiotemporal Hox gene activation

Opacified fibrous thermal insulation

Lightweight, opacified, glass fiber batting for high temperature insulation in cryogenic tanks has lower apparent thermal conductivity than untreated insulations. Decrease results from impeding the transmission of radiant energy without increasing the solid conductance of the material

The Origin and Evolution of the Southern Snake Range Decollement, East Central Nevada

Regional and local stratigraphic, metamorphic, and structural constraints permit reconstruction of the southern Snake Range extensional deformational system in east central Nevada. The dominant structure of the range, the southern Snake Range décollement (SSRD), operated during Oligocene and Miocene extensional deformation to exhume a footwall of multiply deformed metasedimentary and plutonic rocks. Intrusion of three plutons (∼160 Ma, 79.1 ± 0.5 Ma, and 36 ± 1 Ma, respectively) and development of two cleavages preceded the onset of extensional deformation. Plastic deformation of lower plate metasedimentary rocks accompanied the early phases of regional extension and produced bedding-parallel grain shape foliations and WNW trending stretching lineations. These fabrics parallel the SSRD even in low-strain domains, suggesting that a significant component of pure shear strain probably accompanied noncoaxial deformation associated with motion on the SSRD, consistent with other lines of evidence. Meanwhile, hanging wall rocks were greatly extended by at least two generations of tilt block-style normal faults soling into the SSRD, with the earlier faults antithetic to the SSRD and the later faults dipping in the same direction as the SSRD. A retrodeformed regional cross-section sequence illustrates plausible alternative schemes for reconstructing the southern Snake Range extensional system. In one scheme, the SSRD forms as a crustal scale stretching shear zone separating an upper plate that extends on steeply inclined normal faults from a lower plate that stretches by penetrative flow. In the other, lower plate deformation incorporates a component of coaxial stretching, but the SSRD also functions as a conventional shear zone accommodating through-going displacement between opposing plates. In either case, as tectonic unroofing proceeds, differential isostatic unloading induces the SSRD to rotate to steeper dips as it migrates into the frictional sliding regime, thus enabling it to remain active as a brittle normal fault until it finally rotates to its present shallow inclination. In either scenario, cross-section constraints suggest that total extension accommodated by the SSRD was probably between 8 km and 24 km

Quartzite Fabric Transition in a Cordilleran Metamorphic Core Complex

Photomicrographs 143A-143F record fabric variations in quartzite with increasing structural depth in a \u3e 1 km thick, amphibolite-facies, normal-sense shear zone in the East Humboldt metamorphic core complex, Nevada (Figure 143.1). This shear zone and the overlying detachment system unroofed an infrastructure of high-grade, migmatitic gneiss during Oligocene to early Miocene extension (Dallmeyer and others, 1986; Wright and Snoke, 1993; McGrew and Snee, 1994). Thermobarometric constraints from near the base of the mylonitic zone record deformation conditions of 550°- 620°C and 300-400 MPa (Hurlow and others, 1991). Sample WBC6 (l43A and 143B) characterizes the mylonitic zone, whereas sample 8706-1 (143C and 143D) is transitional in nature, and sample 8727-3 (143E and 143F) represents the infrastructure (Figure 143.1). These three samples record a decreasing contribution from simple shear strain and an actual reversal in shear sense at the deepest structural levels. Inferred variations in quartz deformation mechanisms probably reflect decreasing strain rate and increasing temperature with depth beneath the detachment. We argue that the East Humboldt Range shear system represents a fundamental boundary between an upper crust deforming primarily by rigid block translation and a deeper crust deforming by regional-scale ductile flow

Evaluation of liquid methane storage and transfer problems in supersonic aircraft

Evaluation of liquid methane storage and transfer problems for future supersonic aircraft cryogenic fuel requirement

Geologic Map of the Welcome Quadrangle and an Adjacent Part of the Wells Quadrangle, Elko County, Nevada

Located in central Elko County, the Welcome and adjacent part of the Wells quadrangles expose a remarkable array of critical relationships for understanding the geologic history of the State of Nevada and the interior of the southwestern U.S. Cordillera. Covering the northern end of the East Humboldt Range and adjacent Clover Valley and Clover Hill, this map includes the northern terminus of the Ruby Mountains-East Humboldt Range metamorphic core complex. The oldest rocks in the State of Nevada (the gneiss complex of Angel Lake), and Nevada’s only exposures of Archean rock, form the core of a multikilometer scale, southward-closing recumbent foldnappe, the Winchell Lake nappe (WLN). Although intensely metamorphosed and profoundly ductilely attenuated, the WLN folds a series of pre-metamorphic thrust allochthons that collectively form an essentially complete sequence of Paleoproterozoic to Mississippian metasedimentary rocks. The WLN transported what may be Nevada’s most deeply exhumed rocks, with peak pressures ranging to 10 kb, peak temperatures in excess of 750 ºC, and widespread partial melting and stromatic migmatization, all related to Late Cretaceous to Paleocene tectonism. Overprinting the metamorphic core is a WNW-directed kilometer-scale shear zone that, together with the detachment fault that forms its roof, accommodated tens of kilometers of extensional displacement in mid- to late Cenozoic time, diachronously exhuming the terrain from mid-crustal depths by late Miocene time. In addition, the high-grade rocks are extensively intruded by one of the Nevada’s most diverse suites of magmatic rocks, ranging in age from Archean to Miocene and in composition from mafic to felsic. On the west flank of Clover Hill, a westdipping detachment-fault system separates the highgrade metamorphic core from an overlying plexus of brittlely deformed, partly correlative but lower grade to non-metamorphosed Paleozoic rocks. In turn, a sequence of partly syntectonic volcanic and sedimentary rocks ranging in age from Eocene to Miocene structurally overlie the fault-bounded Paleozoic units. The Cenozoic sequence includes late Eocene and Oligocene ignimbrites and volcaniclastic rocks, Miocene sedimentary rocks and megabreccias, a Miocene rhyolite complex, and younger sedimentary rocks and vitric tuffs. The presence of the most distal northeasterly exposure of a key Oligocene volcanic marker, the 29 Ma tuff of Campbell Creek, suggests that a broad, low-relief (unfaulted) terrain was dissected by paleovalleys that extended at least 200 km to the west. Bracketed between the tuff of Campbell Creek and a 15.5 Ma tuffaceous sandstone at the base of the Miocene Humboldt Formation is a proximal sedimentary sequence known as the sedimentary sequence of Clover Creek that includes conglomerate, sedimentary breccia, sandstone, and megabreccia as well as intercalations of fossiliferous lacustrine strata. The megabreccias consist of unmetamorphosed mid- Paleozoic rocks (chiefly Upper Devonian Guilmette Formation) interpreted as rock-avalanche deposits shed from evolving normal-fault scarps inferred to have bounded the basin to the east. Disconformably overlying the sedimentary sequence of Clover Creek is a thick sequence of Miocene Humboldt Formation that is tilted steeply down against the detachment fault system, documenting large-scale displacement on the detachment system extending to at least as young ca. 9 Ma. Finally, bounding the range today on both east and west are large, normal-fault systems that were active in Quaternary time, including the Clover Hill fault, which may represent a southerly extension of the blind fault that caused the 2008 Mw 6.0 Wells earthquake

Grand Tour-Part 2: Petrogenesis and Thermal Evolution of Deep Continental-Crust: The Record from the East Humboldt Range, Nevada

The northern part of the East Humboldt Range, Nevada, provides a rare opportunity to explore the petrogenetic environment of deep levels in the middle crust during both large-scale Mesozoic contraction and Cenozoic regional extension. On this segment of the field trip, we will explore evidence bearing on the character of the metamorphic and magmatic history of this terrane, and attempt to link these constraints to the rheology and tectonic evolution of the middle crust during the Mesozoic and Cenozoic