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The Smartville Intrusive Complex, Sierra Nevada, California: the Core of a Rifted Volcanic Arc

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The Smartville Intrusive Complex, Sierra Nevada, California: the Core of a Rifted Volcanic Arc The Smartville intrusive complex, Sierra Nevada, California: The core of a rifted volcanic arc HOWARD W^DAY } department of Geology, University of California, Davis, California 95616 ABSTRACT the intrusion of the sheeted dike complex. western and southern Smartville complex Clasts of plutonic and hypabyssal rocks re- were deformed prior to the intrusion of the The Smartville complex is a Jurassic vol- sembling the younger intrusives, however, dike complex. canic and plutonic arc in the northwestern occur locally in some of the youngest volcani- Sierra Nevada that was deformed during the clastic rocks, suggesting that shallow pluton- INTRODUCTION Late Jurassic Nevadan "orogeny." We inter- ism and volcanism could be broadly coeval. pret the Smartville intrusive complex to have Early Nevadan thrust faults juxtapose vol- The Smartville complex is a Late Jurassic se- formed during the incipient rifting of an ac- canic and older plutonic rocks of the Smart- quence of volcanic, hypabyssal, and plutonic tive volcanic arc. This interpretation is sup- ville complex and Mesozoic(?) chert-argillite rocks that forms the westernmost of the four ported by the close relationship between broken formation to the east. The younger main fault-bounded lithotectonic belts of the volcanism and plutonism and by the close as- plutons and the dike complex in the Smart- northern Sierra Nevada (Fig. 1). The relation- sociation between sheeted dikes and the ville are deformed by steep, late Nevadan ship of these belts to each other and the tectonic younger plutonic rocks. Further support is faults and do not intrude chert-argillite evolution of the northern Sierra Nevada has found in the similarities that exist between the broken formation. The youngest granodiorite been controversial (Moores, 1970, 1972; Smartville complex and modern arcs that plutons in the area truncate Nevadan faults, Schweickert and Cowan, 1975; Davis and oth- developed on oceanic crust, either at a con- intrude the chert-argillite formation, and ap- ers, 1978; Saleeby, 1981; Schweickert, 1981; tinental margin or in the ocean basins. pear to be unrelated to the Smartville Day and others, 1985). Two schools of thought Smartville volcanic rocks consist of a lower complex. have emerged to explain the distribution of unit of tholeiitic submarine flows and pil- The Smartville volcanic arc underwent Middle to Upper Jurassic volcanic rocks that lowed flows that grades upward into an pre-Nevadan intra-arc extension. The sheeted occur in the western, central, and eastern belts of upper unit of calc-alkaline pyroclastic and dike complex is the primary manifestation of the Sierra Nevada and in parts of the Klamath volcaniclastic deposits. Intrusive rocks in- the rifting event. The elongate shapes of the Mountains. Some workers (Davis and others, clude older units of metamorphosed gabbro younger plutons, which are coeval with the 1978; Burchfiel and Davis, 1981; Saleeby, 1981, and massive diabase, which are intruded by a dike complex, reflect extensional control on 1982; Harper and Wright, 1984) have inter- unit of 100% mafic and felsic, sheeted and their emplacement. Volcanic rocks in the preted the arc rocks in these areas as the prod- unsheeted dikes. Biotite-hornblende tonalite and granophyric hornblende tonalite plutons are coeval with the dike complex, and both rock types occur locally as dikes within the 120° LEGEND dike unit. Continuously and reversely zoned 111! EASTERN BELT (FBI gabbro-diorite plutons are also coeval with the dike complex. Granodiorite plutons are FEATHER RIVER CFB) PERIDOTITE BELT the youngest intrusive unit and may be re- lated to the Sierra Nevada batholith. :: | CENTRAL BELT CCD] Relative age relations suggest that the BRB BALD ROCK BATHOLITH Smartville complex formed in a single volcanic-plutonic system of pre-Nevadan age. SNB SIERRA NEVADA BATHOLITH The dike complex intrudes and is intruded by YRP YUBA RIVERS PLUTON both the tonalite and zoned gabbro-diorite WESTERN BELT plutons. Both the upper and lower volcanic o 10 20 KM SMARTVILLE COMPLEX units are intruded by all of the plutonic and Ijll Intrusive Rocks (SI] hypabyssal units and were deformed prior to cAiiuùivy nouKb v.ovj *Present address: M.S. SN4, National Aeronautics Figure 1. Sketch of the northern Sierra Nevada, showing the location of the Smartville and Space Administration, Johnson Space Center, complex and the study area. Belt nomenclature after Day and others (1985) and Schweickert Houston, Texas 77058. (1981). Geological Society of America Bulletin, v. 99, p. 779-791, 14 figs., 2 tables, December 1987. 779 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/99/6/779/3998436/i0016-7606-99-6-779.pdf by guest on 27 September 2021 780 BEARD AND DAY ucts of a single subduction system developed plutonic complex. Volcanic rocks were de- of metagabbro (mgb, Fig. 2) and metamor- during Late Jurassic oblique convergence at the formed prior to the intrusion of plutons, which phosed massive diabase (md, Fig. 2). These are continental margin. Other workers (Moores, were emplaced at the same time as a sheeted intruded by a sheeted dike complex (sdc) and a 1970, 1972; Schweickert and Cowan, 1975; dike complex. Both volcanic and plutonic rocks series of tonalité (bht), granophyric tonalité (gt), Schweickert, 1981; Day and others, 1985) be- were deformed by Nevadan-age faults. The only gabbro-diorite (gb), and granodiorite (grd) plu- lieve that the Smi.rtville complex is not related demonstrably post-Nevadan igneous rocks in tons. Each of these intrusive lithologies will be to Jurassic volcanic rocks in the eastern belt and the area studied are some small granodiorite discussed in the next section. that more than one Late Jurassic subduction plutons. These, and some larger plutons outside Direct evidence for the nature of the base- zone is representee! in northern California. the study area, may represent the onset of mag- ment on which the Smartville complex was con- Moores and Day (1984) and Day and others matism related to the Sierra Nevada batholith. structed is lacking, but basement probably (1985) correlated volcanic and plutonic rocks in includes older ophiolitic rocks. Serpentinite and the central belt with the Smartville complex and THE SMARTVILLE COMPLEX metagabbro of unknown age occur along the argued that the volcanic rocks are in tectonic Grass Valley-Wolf Creek fault zone and are in- contact with chei t-argillite broken formation The Smartville complex (Fig. 1) consists of truded by massive diabase similar to that of the and mélange in the central belt. They have pro- Upper Jurassic volcanic, plutonic, and hypabys- Smartville complex intrusive core (Tuminas, posed that the Smartville complex was thrust sal rocks. Volcanic rocks occur in a broad belt in 1983). In addition, volcano-plutonic complexes over the central belt and subsequently deformed the western and southern Smartville complex in the central belt that have been correlated with by steep folds and faults during the Late Jurassic and in a narrow region along the eastern bound- the Smartville complex have ophiolitic base- Nevadan orogeny. ary of the complex. The plutonic and hypabyssal ment (Day and others, 1985; Tuminas, 1983; The origin of the Smartville complex itself has rocks occur in an elongate, north-northwest- Murphy and Moores, 1985). also been the subject of considerable discussion. trending intrusive complex in the eastern and Early workers (Lindgren and Turner, 1895; Hie- central Smartville complex (Fig. 1). The com- Age of the Smartville Complex tanen, 1951, 1973, 1976; Compton, 1955; plex is bounded on the north and east by the Big Clark, 1960, 1964) interpreted the volcanic and Bend-Grass Valley-Wolf Creek fault zone (Hie- Isotopic ages for the Smartville complex are hypabyssal greenstones of the Smartville as a tanen, 1977; Tuminas, 1983; Day and others, similar to those of other rocks in the western belt Triassic or Jurassic volcanic terrane that was 1985). On the west, the complex is overlain un- (Saleeby, 1981, 1982). Available U-Pb ages metamorphosed, deformed, and subsequently conformably by Cretaceous and younger sedi- from zircon include those for (1) upper volcanic intruded by a series of post-kinematic plutons. mentary rocks in the Great Valley. Although it unit (Bloomer Hill Formation), northern Smart- The plutonic and volcanic rocks were generally seems clear that the Smartville complex corre- ville complex: 159 Ma (Saleeby, 1981); (2) pla- considered unrelated. More recently, the upper lates with western belt rocks farther south, the giogranite (called "granophyric tonalité" in this part of an ophiolite pseudo-stratigraphy (gabbro, detailed correlation of those rocks with the report) associated with the Smartville sheeted sheeted dikes, pillowed flows) was recognized Smartville complex is uncertain. dike complex: 160 Ma (McJunkin and others, within the Smartville complex, leading to its in- The volcanic rocks of the Smartville complex 1979), 159 Ma (Saleeby and Moores, 1979), terpretation as an ophiolite (Moores, 1975; SV (Fig. 1) were not examined in detail for this 163 Ma (Saleeby and Moores, 1984); (3) the Cady, 1975; Xenophontos and Bond, 1978). study. Earlier workers (Xenophontos and Bond, Yuba Rivers pluton, a synorogenic tonalité that These workers recognized that the ophiolitic 1978; Buer, 1979; Menzies and others, 1980; intrudes and is deformed by faults in the Grass rocks are overlain ty a thick section of interme- Xenophontos, 1984) recognized two major vol- Valley-Wolf
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