Santa Lucia Range Research Articles

Relations of Granitic and Gabbroic Rocks, Northern Santa Lucia Range, California

The plutonic rocks of the northern Santa Lucia Range arc calc-alkaline and consist of hornblende gabbro, tonalite-granodiorite, and quartz monzonite of probable Cretaceous age. They were emplaced as concordant plutons during regional folding and metamorphism at temperatures above 650° C and at depths of 15 to 20 km. The country rocks consist predominantly of quartzofeldspathic meta-sedimentary rocks (Sur series) of probable Paleozoic age. The earliest major intrusions were of hornblende gabbro and leucocratic quartz monzonite. These formed homogeneous, mappable plutons and heterogeneous mixtures of gabbro and quartz monzonite with locally abundant hybrid rock. Tonahte-granodionte plutons were emplaced next and locally intruded the heterogeneous gabbro-quartz monzonite terrane. The last major intrusions were of quartz monzonite. Contacts between quartz monzonite and hornblende gabbro vary Irom sharp to gradational, and hybrid rocks are locally developed. Most contact relations indicate that gabbro was solid when quartz monzonite magma intruded it. Structural evidence of the broad contemporaneity of quartz monzonitic and gabbroic magmas allows the possibility that some mixing of magmas furthered the development of hybrid rocks and gradational contacts. Tonalite-granodiorite plutons emplaced somewhat later may have formed by hybridization of gabbro and quartz monzonite.

Pre-Cenozoic Tectonic History of the Salinian Block, Western California

The Salinian block is the elongate segment of the California Coast Ranges that lies between the Sur-Nacimiento and San Andreas fault zones. Known basement rocks within this block consist of Cretaceous and older granitic and high-grade metamorphic rocks that contrast sharply with Franciscan Group rocks of overlapping age east of the San Andreas and west of the Sur-Nacimiento fault zones. The metamorphic rocks of the Salinian block (often termed Sur series) are probably in part Paleozoic in age and appear to have been derived from a relatively shallow-water shelf-type sequence of psammitic rocks with subordinate calcareous and pelitic rocks. A graphite- and pyrite-bearing unit, mapped for more than 20 mi in the northern Santa Lucia Range, defines two sets of folds. Mineral lineations and mesoscopic folds indicate that major folding about northeast-trending axes occurred prior to prominant folding about north-northwest-trending axes. Assuming approximately 300 mi of post-Cretaceous right slip along the San Andreas fault, the metamorphic rocks of the Salinian block are tentatively correlated with similar Paleozoic and, perhaps in part, Precambrian rocks of the Mojave Desert and southwestern Tehachapi Mountains. The age of the early northeast-trending folds is unknown, but they may be a southwestward extension of Paleozoic tectonic and stratigraphic trends that head from Nevada into southern California. The north-northwest-trending folds are in part Cretaceous as indicated by the syntectonic emplacement of Cretaceous granitic rocks.

Faulting in the Burro Mountain Area, California Coast Ranges, and Its Relation to the Nacimiento Fault

Research Article| April 01, 1970 Faulting in the Burro Mountain Area, California Coast Ranges, and Its Relation to the Nacimiento Fault ROBERT A LONEY ROBERT A LONEY U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar Author and Article Information ROBERT A LONEY U.S. Geological Survey, Menlo Park, California 94025 Publisher: Geological Society of America Received: 29 Sep 1969 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1970, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1970) 81 (4): 1249–1254. https://doi.org/10.1130/0016-7606(1970)81[1249:FITBMA]2.0.CO;2 Article history Received: 29 Sep 1969 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation ROBERT A LONEY; Faulting in the Burro Mountain Area, California Coast Ranges, and Its Relation to the Nacimiento Fault. GSA Bulletin 1970;; 81 (4): 1249–1254. doi: https://doi.org/10.1130/0016-7606(1970)81[1249:FITBMA]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The northwest-striking Nacimiento fault, in the southern Coast Ranges of California, has generally been regarded as the boundary between two major structural blocks: the Nacimiento block to the southwest, in which the basement rocks belong to the Franciscan Formation (Upper Jurassic to Upper Cretaceous), and the Salinian block to the northeast, in which the basement rocks are granitic and high-grade metamorphic. It has been found, however, that in the Burro Mountain area of the southern Santa Lucia Range, the “Nacimiento” fault of Jennings (1959) is nearly vertical and is within the Nacimiento block. In this area, the Franciscan Formation crops out northeast of the “Nacimiento” fault through windows in an older, low-angle thrust fault that brings the Asuncion Group of Taliaferro (1943) (Upper Cretaceous) over the Franciscan Formation. The fault boundary between the Nacimiento and the Salinian blocks must therefore lie farther to the northeast, where it may be buried beneath the Asuncion Group and younger strata. This conclusion is supported by Hanna's recent aeromagnetic work (1969). This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Tectonic Emplacement of the Burro Mountain Ultramafic Body, Santa Lucia Range, California

The Burro Mountain body is a crudely equidimensional block of unusually fresh ultramafic rock. This block, along with numerous smaller and more elongate serpentinite bodies, has been emplaced in a highly sheared Franciscan terrane immediately west of the Nacimiento fault. This fault separates two major structural units: (1) on the east, a 40- by 300-mile block with basement of granitic rock, schists and gneisses, and (2) on the west, a 10- by 100-mile tract of Franciscan Formation. Within the Burro Mountain body the primary rock types and their approximate percentages are: peridotite (65), dunite (35), and pseudopyroxenite (<1). Variations among these lithologic types produce a well-defined internal structure, the two major elements of which are: (1) pervasive compositional layering whose attitude throughout the body varies little from N. 5° W., 80° E., and (2) superimposed discordant structures which may cut the earlier layering at any angle. The first set is thought to have been formed by metamorphic differentiation associated with internal deformation, the second set by metasomatic replacement, possibly a succeeding phase of the earlier metamorphic differentiation. Serpentinization is nearly complete at the margins but progressively decreases toward the center of the body. Contact metasomatism, related to Serpentinization, is responsible for the sporadic presence of rodingites around the margins. An arm-like extension of the main body and linear trains of serpentinite bodies extending for miles parallel to the regional structure may represent previous marginal material sheared out during emplacement. The tectonic nature of the emplacement is demonstrated by the discordance of internal versus regional structure, discrepancy of metamorphic grade between ultramafic and country rock, extreme marginal shearing, lack of igneous contacts, and association with other tectonic inclusions. Several lines of evidence suggest a subcrustal origin for the primary ultramafic rock.

Provenance and Paleocurrents of the Paso Robles Formation, California

A provenance and paleocurrent study of the middle and upper Pliocene continental Paso Robles Formation in the Salinas Valley area, California, adds to the knowledge of the late Cenozoic geologic history of the California Coast Ranges. The geographical distribution of heavy minerals and pebbles in the Paso Robles Formation and in streams presently draining proposed source areas leads to the same conclusions as do measurements of foreset beds, pebble imbrication, and channels in the formation. Uplift in the Santa Lucia and La Panza ranges initiated Paso Robles deposition in early Pliocene time. The paleodrainage was southeastward from the Santa Lucia Range and northward from the La Panza Range, continuing across the present site of the Temblor Range and into a marine basin at the present site of the southern San Joaquin Valley. The Salinas River was a relatively unimportant stream during Paso Robles deposition. Near the end of the Pliocene, uplift in the Temblor Range and southwestward tilting of the Gabilan Mesa brought about the end of Paso Robles deposition by defeating the southeast-flowing drainage and creating the conditions for its capture by the modern Salinas River. Lithologic differences between juxtaposed beds of the Paso Robles Formation on either side of the San Andreas fault suggest that about 25 miles of right-lateral movement has occurred since deposition of the formation.

Structural Evolution of Santa Lucia Range, California: ABSTRACT

The rocks of the Santa Lucia Range are divisible into a bedrock complex and a superjacent series, separated by a major unconformity which represents early Late Cretaceous deformation (Santa Lucia orogeny). Decollement tectonics, involving gravity sliding of the Franciscan rocks over carbonate rocks of the Gabilan mesa, played an important role in the deformation of the bedrock complex during Late Jurassic and middle Cretaceous times (Hsu, 1965). The superjacent rocks were deformed by wrench faulting, and by folding during several Cenozoic orogenic episodes. Thrust faults have been observed in wrench-fault zones. Local changes from wrench to thrust faulting are related to slight changes in the magnitude of the vertical and horizontal principal stresses. These thrusts sho ld not be confused with the decollement tectonics which affected only the bedrock complex. The Franciscan-Recent succession of the region is illustrated and discussed. The stratigraphy of the superjacent sediments is based on the work of previous investigators. The stratigraphy of the bedrock complex is based mainly on the writer's structural interpretations. Although the Franciscan rocks were deformed during late Mesozoic and denuded during early Tertiary, they furnished very little debris to the Cretaceous and early Tertiary sedimentary formations of California. End_Page 648------------------------------ Nevertheless, large volumes of Franciscan debris must have been removed from the Santa Lucia Range before the Miocene transgression. This debris probably was transported west and deposited as thick early Tertiary clastic sequences in offshore basins. End_of_Article - Last_Page 649------------

Analyses of Pliocene-Pleistocene Deformation and Stresses in Northern Santa Lucia Range, California

The Pliocene-Pleistocene orogeny that formed Santa Lucia Range folded its granitic and metamorphic basement as well as the overlying sedimentary rocks, which were 1−2½ miles thick in the area studied. The folds tend to flatten up-section from the basement and to become disharmonic high in the sedimentary sequence. Most are cut by reverse faults that also tend to die out up-section. Both folds and faults trend roughly parallel to basement foliations, which are older than latest Cretaceous. The folds are broad and open over granitic plutons and more closely spaced and tight (locally isoclinal) over metamorphic rocks. Within belts of metamorphic rocks lie the major reverse faults, which dip in the same direction as the metamorphic foliations. The deformation was thus directed appreciably by older rock units and structures. Basement folding involved some flexure of foliated rocks, but the principal mechanism was a gross flowage due to piecemeal slip on pre-existing fractures. In the more deformed sectors, minor faults lie about 1 foot apart and have an average displacement of 6 inches. Groove directions on 1500 minor faults measured in 43 subareas indicate systematic movement patterns. Analyzed on equal-area nets, the patterns are so like that predicted for ideal shear within a fractured-rock body that their σ 1 orientations can be approximated. These orientations are roughly accordant to petrofabric compression axes determined from calcite {0112} lamellae in 19 marbles and 26 sandstones. Most of the 81σ 1 orientations trend about normal to nearby fold axes and traces of reverse faults, while σ 2 orientations are parallel to these features and roughly horizontal. The vertical angles between σ 1 orientations and the reverse faults measure about 30 degrees. The average of all the σ 1 orientations in the basement is a line plunging 30° N. 30° E. The range trends N. 40° W. The basement rocks of the range were shortened about 12 per cent in a direction roughly normal to the range. Despite the pronounced ordering of folds along older structures, the range itself extends in nearly a straight line across major divisions of the California basement. These relationships indicate that the range was produced by deep-seated deformation, possibly a northeast-to-southwest flowage under the crust. The σ 1 orientations in the upper sandstones typically plunge parallel to bedding. This and the occurrence of disharmonic folds high in the section indicate that basement shortening caused the upper part of the sedimentary sequence to buckle more or less independently of the basement.

Charnockitic rocks of Santa Lucia Range, California

Charnockitic rocks of Santa Lucia Range, California

Geology and Exploration for Oil in the Huasna District, San Luis Obispo County: ABSTRACT

The Huasna district, an area of approximately 100 square miles, lies at the southern end of the Santa Lucia Range in the California Coast Range province about 12 miles northeast of the town of Santa Maria. Geologically it consists of a synclinal basin filled with Miocene sediments and interbedded volcanics. The basin is roughly limited on the east and west by two nearly parallel faults. On or near these boundaries Miocene strata are found in fault or depositional contact with Franciscan rocks on the west and Cretaceous sediments on the east. Anticlines have formed on the flanks of the major syncline. Middle and upper Miocene (Monterey) shales and sands crop out along the eastern flank of the syncline. Basinward they are overlain by 2,000 feet of Santa Margarita sands and shales. Wells drilled within the deeper portion of the basin penetrate 4,000-6,500 feet of brown cherty and siliceous shales and dark brown calcareous shales representing all the foraminiferal stages from upper Mohnian to Relizian. Shows of tarry oil occur throughout this interval both in outcrop and in wells, probably accounting for many of the shows of oil recorded by early tests in the district. At and throughout the basal portion of this predominantly shale section volcanic interbeds of tuff, agglomerate and ashy sands of middle and lower Miocene (Saucesian ?) age are encountered. Incomplete records on earlier wells and lack of deep stratigraphic penetration in more than one well near the center of the basin lead to some conjecture as to the nature and distribution of lower Miocene sediments. Thirty-five wells have been drilled in the Huasna district since 1898. Two or three wells have produced a small amount of oil. The Barneberg No. 2, drilled on the Tar Springs anticline, has produced 11,400 barrels of 16 degrees A.P.I. oil, which appears to have come from near the Santa Margarita-Monterey gradational contact and from within the underlying locally fractured shales. Recent wells drilled nearby failed to develop production. The possibilities of stratigraphic traps at depth within the basin and of better structural position on some of the asymmetric anticlines are indicated as being the objectives of future exploration in the district. End_of_Article - Last_Page 2630------------

Santa Maria Region: ABSTRACT

The Santa Maria province is a roughly triangular area in the California coastal belt which is bounded on the west by the Pacific Ocean, on the south by the Santa Ynez Mountains, and on the north and northeast by the Santa Lucia Range. The province consists of several more or less isolated structural basins with similar sedimentary histories and related types of objective zones and traps. Many types of rocks underlie the zones of present and prospective production. The term, basement, as used in this paper, refers to rocks older than Eocene that consist of Jurassic metamorphics and basic intrusives and Cretaceous and Jurassic sediments that have undergone various degrees of alteration. The Santa Maria province has an area of 2,126 square miles, of which 1,824 square miles are underlain by objective sediments. The volume of unaltered sediments is estimated at 1,112 cubic miles and the maximum depth to basement rocks is approximately 16,000 feet. About 400 exploratory wells have been drilled in the province, resulting in the discovery of 14 productive areas with a cumulative production to December 31, 1949, of slightly more than 300 million barrels of oil. Production is largely from Miocene sands, shales, and cherts. Significant amounts of oil have been produced from lower Pliocene sands and in one area from fractured sandstones of Jurassic age. This Jurassic production is considered to have migrated from overlapping Miocene beds. End_Page 2383------------------------------ Prospective sediments range in age from Eocene to Pliocene. They are marine, with the exception of minor amounts of lower Miocene non-marine beds near basement highs and a veneer of upper Pliocene and Pleistocene continental beds in the central portion of the province. Commercial oil production comes from anticlinal closures and stratigraphic and fault traps. It is probable that substantial undiscovered reserves of heavy crude exist in this province, and that lighter oils may be found in parts of the stratigraphic section or in areas not before subjected to intensive search. Stratigraphic and structural studies may well be expected to yield important discoveries. End_of_Article - Last_Page 2384------------

Cretaceous and Paleocene of Santa Lucia Range, California

Cretaceous and Paleocene of Santa Lucia Range, California

Volcanic Tuffs of Santa Lucia Range and Miocene Paleogeography of Salinas Valley, California: GEOLOGICAL NOTES

Volcanic Tuffs of Santa Lucia Range and Miocene Paleogeography of Salinas Valley, California: GEOLOGICAL NOTES

Some coast migrations, Santa Lucia range, California

Introductory Note The following article presents observations made during a trip from Monterey to San Luis Obispo along the intervening Coast ranges. I was accompanied by Doctor H. W. Fairbanks, in whose articles many of the facts herein presented have already been published,* and I am indebted to him not only for pointing out the most interesting and significant phenomena of the region, but also for helpful discussion of their interpretation. Professor A. C. Lawson* has described the geology of Carmelo bay just south of Monterey, a district which adjoins on the north that herein referred to and which includes the Santa Lucia granite, the youngest member of the Coast complex hereafter defined. My observations are in general in accord with those made by Lawson at Carmelo bay and by Fairbanks farther south. The present Scene Point Sur, a prominence of the California coast, lies 24 miles south of . . .