Nevadaplano

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volcanic eruptions distributed ignimbrites
over the plateau and down the valleys draining it.

During the Miocene, changes in the tectonic regime may have caused a collapse and dismemberment of the Nevadaplano. Tectonic extension gave rise to the Basin and Range province and separated the Sierra Nevada-Great Valley block from the Nevadaplano, forming today's landscape.

Research history

The existence of the Nevadaplano was proposed in 2004 by DeCelles

high plateau of South America.[3] It is also known as the "Great Basin Altiplano".[4] Unlike the present-day Andean Altiplano and Tibetan plateau, the Nevadaplano was dismembered during the Cenozoic and thus its structure and evolution are poorly understood.[5]

Geologic history

The Nevadaplano probably formed as part of either the

Laramide Orogeny[6] when volcanism shifted far to the east.[11] The exact geologic evolution and character of the Nevadaplano is controversial, however,[12] as is the notion that it was a geologically stable environment.[13]

The Nevadaplano underwent

slab rollback decreased the tectonic forces. At that time, volcanic activity swept southwestward,[10] away from the volcanoes of central Nevada to the Sierra.[14] This may have been accompanied by uplift[15][16] that would have continued when the Yellowstone hotspot developed in the Miocene.[17] The plateau overrode the heat source of the East Pacific Rise
about 28 million years ago.

By far the most significant stage of extension was the later[18] episode of east–west extension and northwestward shearing,[1] which was underway by 16-17 million years ago[19] and continues to a lesser extent today. That extension probably caused the high plateau to lose elevation. The heat flow from the Yellowstone hotspot is one mechanism that has could have caused the collapse process.[17] Also during the Miocene, the Sierra Nevada-Great Valley block separated from the Nevadaplano and was tilted to the west along the Sierra Escarpment,[20] beheading a number of westward-going drainages in the process.[19] Former drainages of the Nevadaplano were buried by volcanic rocks and disrupted by tectonic processes.[21] Farther east, the dismemberment of the drainages may have created suitable environments for the evolution of sucker fish.[22]

Miocene extension also created the well-known

plate boundary between the Pacific Plate and the North American Plate. Presently, relic surfaces around the Middle Fork Feather River valley[23] and the high elevations of the northern Basin and Range may be considered remnants of the Nevadaplano.[17]

The Nevadaplano during its existence

The Nevadaplano was located in present-day

high plateau consisting of a peneplain[1] and reached a width of 400–500 kilometres (250–310 mi).[27] Isotope analysis indicates that the Nevadaplano stood at high elevations,[1] probably higher than[28] or comparable to the then-Sierra Nevada. The elevation of the Nevadaplano exceeded 3 kilometres (1.9 mi),[18] but the exact value is controversial,[12] as is whether it was flat or featured rugged topography.[29] There is evidence of basins at its western margin,[30] although the relief of the Nevadaplano is debated and was probably less than that of the Altiplano.[31]

The Nevadaplano probably drained to

internal basins such as the Elko[32] and Uinta Basins,[33] the Western Interior Seaway[34] and westward to the Pacific Ocean.[6] A drainage divide extended from the Mogollon Highlands in the south through the Kingman Uplift into the Nevadaplano.[34] There is some uncertainty in the drainage directions across the Nevadaplano, with some evidence interpreted as indicating that drainage divides shifted over time[25] and that the divide between Nevada and Idaho was offset along a Neoproterozoic lineament.[35] Among the reconstructed drainages are the Tyee and Princeton Rivers from what is present-day north-central Idaho to present-day Oregon and northern California, the Idaho River also from present-day north-central Idaho to the Green River basin and the California River from present-day southernmost California to the Uinta Basin.[36] The northernmost among these rivers may have formed the northern boundary of the Nevadaplano.[37]

Some

normal faulting took place within the Nevadaplano, along with the exposure of core complexes, and generated isolated basins.[38] This may have created regional basins in the late Cretaceous similar to those that lie in the present-day Altiplano-Puna region, and which include the Sheep Pass Formation basin[39] and the long-lived Elko Basin.[40] Lake sediments and volcanic rocks accumulated in these basins. The formation of these basins may have been an early stage of the collapse of the Nevadaplano.[41]

Geographical and geological boundaries

West of the Nevadaplano stood the Sierra Nevada, which was volcanically active[1] until 80 million years ago[42] and featured exposed batholiths from former volcanism. Its exact elevation at the time is unclear, with alternate models proposing either that it had already reached a height similar to today's Sierra Nevada or that it rose to present-day height in the Miocene and Pliocene.[12] Alternatively, the Luning-Fencemaker fold-and-thrust belt may have formed the western boundary.[43]

It probably did not constitute a

placer gold deposits of California,[3] as part of intense westward sediment transport.[51] On the eastern side, the proto-Platte and proto-Arkansas Rivers drained the Nevadaplano.[52]

Remnants of the

closed plateau.[57] To the south, the California River may have separated the Nevadaplano from an analogous high plateau to the south, called "Mexicoplano"[58] or "Arizonaplano".[59] The Colorado Plateau was either to the east of the Nevadaplano[9] or else formed an integral part of the plateau.[18] The San Juan Mountains region may have formed its own upland, the "Colorado-plano".[60]

Geology

Color image with a white background of an ignimbrite
Ignimbrites were scattered across some areas of the Nevadaplano

During the Miocene, volcanic activity covered the Nevadaplano with

lava flows and volcanic sediments.[1] In central Nevada and western Utah, at least 71[61] calderas located at high elevation erupted ignimbrites which propagated for over 200 kilometres (120 mi) westward and across former valleys in the Sierra Nevada,[20] filling them in during the process.[61] In particular, the 28.9 million year old[24] Campbell Creek tuff covered an area of 55,000 square kilometres (21,000 sq mi) and propagated far east and west of its source area.[62]

The underlying

sialic composition and reached thicknesses of 45–65 kilometres (28–40 mi).[1] It consisted of metamorphic rocks[1] that are now exposed as metamorphic core complexes such as in the Pequop Mountains of Nevada,[63] as well as plutonic rocks including batholiths.[64]

Ecosystems and climate

Based on the fossils found in the

giant sequoias may have migrated from or through the Nevadaplano to California[68][69] when the climate cooled during the Oligocene, founding the temperate forest communities of California.[70]

Evidence suggests that lakes and

diatomites were emplaced in.[76]

References

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Sources

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