Van Buer, N.J. and Miller, E.L., 2010, the Sahwave Batholith, NW

Downloaded from lithosphere.gsapubs.org on October 28, 2010 Lithosphere Sahwave Batholith, NW Nevada: Cretaceous arc flare-up in a basinal terrane Nicholas J. Van Buer and Elizabeth L. Miller Lithosphere 2010;2;423-446 doi: 10.1130/L105.1 Email alerting services click www.gsapubs.org/cgi/alerts to receive free e-mail alerts when new articles cite this article Subscribe click www.gsapubs.org/subscriptions/ to subscribe to Lithosphere Permission request click http://www.geosociety.org/pubs/copyrt.htm#gsa to contact GSA Copyright not claimed on content prepared wholly by U.S. government employees within scope of their employment. Individual scientists are hereby granted permission, without fees or further requests to GSA, to use a single figure, a single table, and/or a brief paragraph of text in subsequent works and to make unlimited copies of items in GSA's journals for noncommercial use in classrooms to further education and science. This file may not be posted to any Web site, but authors may post the abstracts only of their articles on their own or their organization's Web site providing the posting includes a reference to the article's full citation. GSA provides this and other forums for the presentation of diverse opinions and positions by scientists worldwide, regardless of their race, citizenship, gender, religion, or political viewpoint. Opinions presented in this publication do not reflect official positions of the Society. Notes © 2010 Geological Society of America Downloaded from lithosphere.gsapubs.org on October 28, 2010 RESEARCH Sahwave Batholith, NW Nevada: Cretaceous arc fl are-up in a basinal terrane Nicholas J. Van Buer1 and Elizabeth L. Miller1 1DEPARTMENT OF GEOLOGICAL AND ENVIRONMENTAL SCIENCES, STANFORD UNIVERSITY, 450 SERRA MALL, BLDG. 320, STANFORD, CALIFORNIA 94305-2115, USA ABSTRACT Detailed mapping and sensitive high-resolution ion microprobe (SHRIMP) U-Pb geochronology centered around the Nightingale and Sah- wave Ranges, ~100 km northeast of Reno, Nevada, reveal that most of the Mesozoic basement in this area is composed of predominantly granodiorite-composition plutonic rocks intruded ca. 110–88.5 Ma. These rocks are similar in age, petrology, and composition to the mid- Cretaceous eastern part of the Sierra Nevada Batholith, and are likely related. The youngest plutonic rocks, ca. 93–88.5 Ma, form a large, compositionally zoned intrusive suite, referred to as the Sahwave intrusive suite. This suite is composed of a set of nested, inward-younging intrusions, varying between mafi c, equigranular granodiorite around the periphery to more felsic, K-feldspar–megacrystic granodiorite in the center. The Sahwave intrusive suite is coeval with the Cathedral Range intrusive event along the crest of the Sierra Nevada, including the Tuolumne intrusive suite. The geochemistry and petrology of this intrusion also support similar magma genesis and emplacement. Intrusions of the Cathedral Range intrusive event in the Sierra Nevada were emplaced along the margin of North American continental crust, whereas the Sahwave intrusive suite was intruded into a thick package of basinal metasedimentary rocks that were likely underlain by 87 86 ε transitional crust. More primitive initial Sr/ Sr and Nd values (ca. 0.7047 and –0.2, respectively) refl ect this difference. In light of this likely fundamental difference in lower-crustal character, other factors, possibly related to subducted, water-rich material, must be responsible for creating similar melting conditions among the series of large intrusions that represent the last magmatic fl are-up of the Cretaceous arc. LITHOSPHERE; v. 2; no. 6; p. 423–446; Data Repository 2010289. doi: 10.1130/L105.1 INTRODUCTION cially scoured Sierra Nevada, the Sahwave and istry. Comparison of data between these intru- Nightingale Ranges, about an hour NE of Reno, sive suites allows us to evaluate whether the The Mesozoic Sierra Nevada Batholith pre- Nevada, form a broad, uplifted horst block of Sierra Nevada Batholith should be considered to serves an extensive record of continental-margin Mesozoic basement that is well suited for inves- extend into the NW Basin and Range (Fig. 1). arc magmatism that serves as a classic, world- tigating the relationship between plutonic rocks Furthermore, differences between these regions wide model, especially for high-intrusive-fl ux in the NW Basin and Range and in the Sierra of high intrusive fl ux may have important impli- magmatism. Previously, however, only recon- Nevada (Figs. 1 and 2). Detailed mapping in the cations for arc fl are-up models. naissance-level studies (e.g., Smith et al., 1971; Sahwave and Nightingale Ranges, combined Barton et al., 1988; Van Buer et al., 2009) have with reconnaissance of the surrounding areas, REGIONAL GEOLOGIC SETTING explored the possibility that this batholith might was used to identify distinct intrusive units for extend past the Sierra Nevada mountains into the further quantitative study. Most of the intrusive Subduction-related arc magmatism in the NW Basin and Range Province (Fig. 1), where units in this area were identifi ed as belonging Cordillera began in the Triassic and continued Mesozoic relationships are obscured by Ceno- to a single, very large, roughly concentrically episodically into the Late Cretaceous (and into zoic volcanism and basin development related zoned intrusive suite, emplaced at ca. 90 Ma, the Paleocene north of the Snake River Plain to extensional faulting. Consequently, many referred to here as the Sahwave intrusive suite and in southern Arizona; Fig. 1). The resulting published fi gures depicting the Sierra Nevada (Fig. 2). Zoned intrusive suites of approximately batholithic belt has been variably disrupted by Batholith are truncated against the edge of the the same age in the Sierra Nevada, such as the Cenozoic extension and translation and now Basin and Range or the Nevada border (e.g., Tuolumne intrusive suite, have received detailed forms several distinct segments, including the Tikoff and de Saint Blanquat, 1997; DeGraaff- geochronological, mineralogical, geochemical, Idaho Batholith, the Sierra Nevada Batholith, Surpless et al., 2002; Lackey et al., 2005), and and structural study due to vigorous and ongo- and the Peninsular Ranges Batholith (Fig. 1). the Sierra Nevada Batholith is often considered ing debate about their petrogenesis and emplace- The fi nal episode of magmatism in California to be restricted to the mountains it was named ment (e.g., Bateman, 1992; Coleman et al., 2004; and Nevada spanned ca. 120–85 Ma, and was for. However, boundaries as recent as the Neo- Žák and Paterson, 2005; Hirt, 2007; Gray et al., particularly voluminous during the latter half gene limit of Basin and Range extension (dotted 2008), and therefore provide an excellent data of this period (e.g., Barton et al., 1988; Ducea, line, Fig. 1), which defi nes the eastern scarp of set for comparison with the Sahwave intrusive 2001). In most of the U.S. Cordillera, the Creta- the Sierra Nevada, would seem to rather arbi- suite. As the fi rst report of its kind in this region, ceous batholith exhibits a regular younging pat- trarily delimit the much older Mesozoic Sierra this paper attempts to set forth several types of tern from west to east that is generally mirrored Nevada Batholith. Although Mesozoic outcrops basic data, from map data and rock descriptions by geochemical trends from more mafi c to more in the Basin and Range are less continuous and to modal mineralogy, U-Pb geochronology, and felsic (e.g., Evernden and Kistler, 1970; Hynd- more deeply weathered than those in the gla- major- and trace-element, and isotope geochem- man, 1983; Silver et al., 1979). LITHOSPHEREFor permission to| Volumecopy, contact 2 | Number [email protected] 6 | www.gsapubs.org | © 2010 Geological Society of America 423 Downloaded from lithosphere.gsapubs.org on October 28, 2010 VAN BUER AND MILLER 126° W 124° W 122° W 120° W 118° W 116° W 114° W 112° W 110° W 42° N ORORORO MarginalMaM rggini ala Idaho Batholith IDIDIDD 87 86 CACACACA terranes Sr/ Srr ==0 00.706.7.70. 6 S n in 44° N Figure 1. Plutons of the Mesozoic KlKlamathammatth ake Pla Riivve r magmatic arc (white) are most 40° N RRaRangeangn e NVNVNV prominently exposed in the Idaho Batholith, the Sierra Nevada Batho- lith, and the Peninsular Ranges arareareaa ooff Study Batholith. The Sierra Nevada Batho- FigFig.i ..2 2 42° N W a l k e r L a n e area lith was emplaced across the bound- Sierra Nevada Batholith ary between the continental litho- a 38° N LFTB UTUTUT sphere of cratonal North America l B a s i n and a variety of marginal terranes k a n d that have oceanic- or transitional- e R a n g e 40° N affi nity lithosphere, as defi ned by the r 87 86 initial Sr/ Sr = 0.706 line (dashed line; from Farmer and DePaolo, 36° N NorthNorth 1983). The main part of the Basin L and Range Province is outlined by a a dotted line. The Walker Lane accom- AmericanAmericican n 38° N modates right-lateral shear near the e AZAZAZ western boundary of the Basin and N cratoncratono Range (Wesnousky, 2005). The Lun- 34° N ing-Fencemaker thrust belt (LFTB) is developed in Mesozoic basinal sequences (Oldow, 1984). Distribu- 36° N tion of Mesozoic intrusions is modi- fi ed from King and Beikman (1974). Peninsular 32° N Ranges 500 km Batholith 34° N 122° W 120° W 118° W 116° W114° W 112° W 110° W 108° W One of the most distinctive features of the boundary between North American continental Peak Group east of the main locus of Cretaceous Sierra Nevada Batholith is the series of large, crust and oceanic terranes to the west, as approx- magmatism (Silberling and Wallace, 1969), but compositionally zoned intrusions of the Cathe- imated by the initial 87Sr/86Sr = 0.706 line (Fig.

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