Q. 41: Why do you conclude that the Sierra batholith must have been molten during the Flood?

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CPT Q. #41 – 101 Q&A on Catastrophic Plate Tectonics

Question: 41. Why do you conclude that the Sierra batholith must have been molten during the Flood?

Response: Geological investigations of the rocks of the Sierra Nevada over the past fifty years [ed. — i.e., since the mid-20th century] have revealed that the granitic rocks that form what is called the Sierra Nevada Batholith crystallized a few kilometers beneath the surface from molten magma that had risen from below and had ponded as hundreds to thousands of individual pancake-shaped plutons at the shallower depths. Careful and extensive radioisotope dating indicates these plutons were emplaced during the Mesozoic, mostly during the Cretaceous, which implies that the melting and cooling took place during the Flood.

Let me quote the beginning three paragraphs from an article entitled, “The Sierra Nevada Batholith as exposed in the Yosemite Valley area and western foothills of the Sierra Nevada,” by Marty Giaramita from California State University, Stanislaus, which provides a good summary description of the rocks of the Sierra Nevada Batholith in the region around Yosemite National Park:

The terrane of Yosemite National Park is characterized by abundant light-colored and less common dark-colored rocks that crystallized slowly from molten rock kilometers beneath the Earth’s surface. The present exposure of these relatively coarse-grained rocks is the result of uplift and removal of the overlying rock by erosive agents such as rivers and glaciers long after their intrusion into the crust due to tectonic-plate conversion during Mesozoic time.

Igneous rocks are those that crystallized from melt. They are broadly subdivided into volcanic (extrusive) rocks, if they were erupted on the surface and hence rapidly cooled, and plutonic (intrusive) rocks, if they crystallized slowly at depth beneath the Earth’s surface and cooled slowly. Although volcanic rocks are present in the Sierra Nevada Mountains (and we will drive through some en route to Yosemite), the predominant rock type in the region of Yosemite National Park is plutonic. Exposed bodies of plutonic rock are referred to as plutons that are further subdivided on the basis of their shape. A stock is a roughly equidimensional pluton; a dike is a fracture filled with plutonic rock. A batholith is a large composite of many individual plutons.

The intrusive rocks of the Yosemite Region are part of the Sierra Nevada Batholith consisting of hundreds of individual plutons intruded from the Triassic through the Cretaceous periods (See the geologic map of Yosemite Valley below). Most geologists now agree that the batholith owes its existence to the process of tectonic-plate convergence during which melting occurred as a consequence of subduction of oceanic lithosphere (the rigid crust and upper part of the mantle) beneath the margin of the North American continent during Mesozoic time. A present-day analogue for this process is the subduction of the Nazca oceanic plate beneath the western margin of the South American continent.

Below is a photo of some granitic rock typical of that which comprises the entire batholith:

Half Dome granodiorite in Yosemite National Park near Vernal Fall (source)

Below is a geological map of the Yosemite area that shows the extent of the individual plutons which can be distinguished by their distinctive chemical compositions and mineralogies. Most of these plutonic rocks are of Cretaceous (K) age. Most of the Quaternary (Q) rocks are associated with the glacial processes of the Ice Age. This map provides a representative sampling of the geological character of the entire batholith.

Portion of Geologic Map of Yosemite National Park and Vicinity, California, U.S. Geologic Survey Miscellaneous Investigations Series Map I-1874 by N. King Huber, Paul C. Bateman, and Clyde Wahrhaftig, published in 1989. Complete map is available from the U.S. Geological Survey, browse graphic.

Explanation of Symbols

The massive volume of granitic magma was generated via subduction of the Farallon Plate beneath the western edge of North America and likely involved the melting of a significant volume of sediments entrained by the subducting slab. As I noted in my answer to question 30:

The belt of Mesozoic-Tertiary plutonic rocks extending from Alaska to Antarctica, forming much of the mountain belt known as the American Cordillera, was produced by this subduction-caused melting beneath the western margins of these continents. The maps below display the main sites of this plutonic emplacement of new crustal material. Isostatic adjustment in these belts has resulted in the mountains we see there today.

“Major plutons of the North American Cordillera (left) and of the South American Cordillera (right), principal segments of a continuous Mesozoic-Tertiary belt from the Aleutians to Antarctica. Reproduced from Winter, An Introduction to Igneous and Metamorphic Petrology” 1

Let me here emphasize that not only was the Sierra Nevada Batholith generated by upwelling granitic magma during the Flood, but all the batholiths shown in the figure above were produced by the same subduction-driven process during the Flood.

Footnotes

  1. J. D. Winter, An Introduction to Igneous and Metamorphic Petrology, Prentice Hall, 2001.↩︎