Geology of the North Half of the White Mountain Quadrangle, California-Nevada. Petrography of the North Half of the White Mountain Quadrangle, California-Nevada. Stratigraphy and Faunal Relationships of Pliocene Beds of San Diego Age in the Vicinity of Las Llajas Canyon, Simi Valley, California

Citation

Anderson, George Harold (1933) Geology of the North Half of the White Mountain Quadrangle, California-Nevada. Petrography of the North Half of the White Mountain Quadrangle, California-Nevada. Stratigraphy and Faunal Relationships of Pliocene Beds of San Diego Age in the Vicinity of Las Llajas Canyon, Simi Valley, California. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/GWZS-9815. https://resolver.caltech.edu/CaltechETD:etd-05022006-163249

Abstract

Geology of the north half of the White Mountain Quadrangle, California-Nevada:

The White Mountain range, the principal topographic unit of the White Mountain Quadrangle, is an up-faulted block between two relatively depressed areas. It differs from the ordinary basin range block in that it is a tilted horst. The marginal faults of the horst are of unusual complexity.

Physiographically, the range is in the late youthful or early mature stage of the arid cycle of erosion. Glaciation has complicated to some degree the normal development of the cycle. Renewal of uplift by faulting appears to have taken place in recent times.

Upon the crest of the range are remnants of land surfaces of low relief, formed, probably, by erosion before the block faulting which uplifted the range. These surfaces are designated herein as the "Pellisier Erosion Surface" and the "Sub-summit Oldland". It is probable that both were formed in the same cycle of erosion.

The core of the range is a granite batholith, intrusive into Cambrian or pre-Cambrian sedimentary rocks, chiefly calcareous and argillaceous in composition. For this ancient sedimentary series the name "McNett Formation" is proposed. It is non-fossiferous but on the basis of its lithology it is considered to be the equivalent of a thick series of dolomites and "green knotted schists" which Turner described as underlying the lowest fossiliferous Cambrian in the Silver Peak Quadrangle.

The contacts of the intrusive and the ancient sediments are everywhere characterized by intense contact metamorphism. This is described in some detail in the section on petrography.

Overlying the older rocks is a volcanic series of Tertiary age. These are chiefly rhyolites with some andesites. They include flows and pyroclastics. Vertebrate remains discovered in playa deposits closely associated with the extrusive rocks indicate that the latter were accumulated in part during the upper Miocene and lower Pliocene.

The most recent igneous rocks in the area are Quaternaty basalts which cover much of the northers part of the quadrangle.

In the petrography section of this thesis, separately paged and indexed, are to be found descriptions and discussions of certain types of alteration affecting the rocks of the batholith on an enormous scale. These alterations, believed to be of hydrothermal origin, include the albitization of the potash feldspars and the development of a replacement texture closely resembling cataclastic texture but distinguished from the latter by its corrosive pattern and by the formation accompanying it of a large number of minerals not present in the original rock.

Petrography of the north half of the White Mountains Quadrangle California-Nevada:

The igneous rocks of the north half of the White Mountain Quadrangle consist of a group of closely related intrusives, probably of Jurassic Age, and a Tertiary-Quaternary series of extrusives. The former, chiefly granitic in composition, compose the White Mountain batholith which intrudes calcareous and argillaceous rocks of early Cambrian or pre-Cambrian Age. The batholith is surrounded by a wide zone of intense contact metamorphism.

The volcanic series may be subdivided into two groups. The earlier, whose accumulation probably occupied much of the middle and later Tertiary, is predominately siliceous in composition. The later, for the most part Quaternary in age, consists of basic andesites and basalts.

In the following thesis all of these groups of rocks, including the contact metamorphics, are described in detail. Especial attention is paid to certain compositional and textural peculiarities exhibited by the intrusives. These peculiarities are highly significant, not only in the history of these particular rocks, but also in respect the general problem of the genesis of sodic and alkaline types. They are the result of replacement processes which appear to have been active on an enormous scale through the batholithic mass at a time considerably later than at least the outer parts of the magma. They involved the introduction of large quantities of material, especially sodium and silica and possibly also iron and magnesium from some source outside the field tion. The results are evident in the wholesale albitization of the potash feldspars, formation of secondary minerals including quartz, sericite, chlorite, epidote, biotite and hornblende and in the development of a texture here designated pseudo-cataclastic texture which closely resembles true cataclastic texture but is distinguishable from the latter by criteria set forth below.

Stratigraphy and faunal relationships of Pliocene beds of San Diego age in the vicinity of Las Llajas Canyon, Simi Valley, California:

The results of a careful search of the literature for material bearing upon replacement processes in igneous rocks are set forth in the thesis. Various theories which may account for the phenomena are critically discussed.

Overlying the Modelo Formation of Upper Miocene age north of Simi Valley is a series of arenaceous beds of marine origin whose stratigraphy and faunal relationships have heretofore been in doubt. At the suggestion of Dr. W. P. Woodring, then Professor of Invertebrate Paleontology at the California Institute of Technology, I undertook to study some of these beds as part of my preparation for the degree of Doctor of Philosophy. The following report covers in particular the section exposed from Las Llajas Canyon west to about two miles beyond Tapo Canyon.

Thesis Files