Evidence for past ocean-continent convergence zones has been preserved in metamorphic

Transcription

1 Tectonic implications of geochronology and geochemistry from metasedimentary and metavolcanic units in the Iron Mountain Pendant, central Sierra Nevada, California Brittany Gelbach Senior Thesis Advisor: Scott Paterson Date to Submit: Spring 2011 Abstract Evidence for past ocean-continent convergence zones has been preserved in metamorphic rock pendants along ancient plate contacts. One example of this preservation lies in the Sierra Nevada region of California. In the Mesozoic Era, the Sierra Nevada region underwent several tectonic events due to a convergence between the Pacific Plate and the North American continental margin. This collision brought exotic marine rock units in contact with the North American units and also caused wide-spread magmatism throughout the region. In 2009, members of the undergraduate team research program at the University of Southern California chose to examine the Iron Mountain pendant in order to determine which tectonic blocks are present there and to establish the ages of certain rock units. Within the pendant, there are metavolcanic, volcaniclastic, metasedimentary, and hypabyssal plutonic rocks. Geochemistry and thin section analyses allowed us to confirm these rock descriptions and provide additional information regarding the units as well. ICP-MS, U/Pb zircon dating has established that an overlying volcanic unit resembling dacite is approximately m.y., a package of marine metasedimentary phyllites, schists, and quartzites have a minimum peak age of about 140 m.y., and an older package of mature quartzites, and phyllites with Precambrian zircon populations has peaks at 1100, 1400, 1770, and 2700 m.y. that closely resemble miogeoclinal rocks elsewhere. We have interpreted the data to conclude that the pendant does contain a portion of the miogeoclinal Snow Lake Block unit as well as a Jurassic overlap sequence which are both overlain by Cretaceous volcanics. Ductile shear zones were observed in the area and may separate the Jurassic overlap from the miogeoclinal unit. The observations above add support to the hypotheses that the Snow Lake Block extends throughout the central and southern Sierra Nevada and that a Jurassic overlap sequence is present in these areas as well. Also, we believe the overlying Cretaceous volcanics in the Iron Mountain pendant represent the westernmost exposure recognized to date from the belt of Cretaceous volcanic preserved along the central axis of the Sierra.

2 Introduction During the Mesozoic Era, the Sierra Nevada was dominated by continental arc magmatism in response to the eastward subduction of the Pacific plate beneath the California continental margin. Arc magmatism and volcanism occurred intermittently in this region from 250 Ma to 85 Ma. At times oblique subduction continued to drive transpressive deformation of the arc leading to faulting and lateral displacement of arc pieces (Saleeby, 1981). Extensive previous studies are beginning to establish the nature of pre-mesozoic basement terranes through and onto which the arc was constructed (Saleeby, 1981; Nokleberg, 1983; Lahren and Schweickert, 1989). From west to east, proposed basement terranes include (1) exotic ocean terranes (ophiolites, mafic volcanics, and ocean sediments) west of a major boundary known as the Sierran Foothills Suture; (2) the Shoo Fly Complex, (3) the Snow Lake Block, (4) the Roberts Mountain allochton-el Paso terrane (see Figure 1), and (5) the North American passive margin. The Shoo Fly Complex potentially is comprised of Cambrian to Ordovician quartzites, phyllites, and chert (Memeti et al., 2010). Ediacaran fossils were recently found in this unit, which suggests the Shoo Fly may not be from North America, an idea which has been gaining popularity (Lindsley-Griffin, 2008). The fossil find has also emphasized that the boundary between the Shoo Fly Complex and the next unit to the east, the Snow Lake Block, may be of fundamental importance and record a large amount of displacement. The Snow Lake Block is a unit of passive margin sediments representing shallow water strata. Previously, the Snow Lake Block was referred to as the Kings Sequence, which was described as a collection of metasedimentary rocks and few volcanic rocks seen in various outcrops from the Strawberry Mine roof pendant in the north to the Isabella roof pendant in the south (Nokleberg, 1983). Common rocks seen in the Kings Sequence include quartzite, marble, andalusite-bearing- hornfels, and schists as well as various volcanic rock types (Bateman, 1992). Lastly, the Roberts-Mountain allochton-el Paso terrane represents deep water oceanic rocks which may or may not be resting on a continental basement. Remnants of the Roberts Mountain allochthon include chert, siliceous argillite, and slate (Greene et al. 1997; Stevens and Greene, 1999; Memeti et al., 2010).

3 Figure 1: Map overview showing the relations between the Shoo Fly Complex, the Snow Lake Block, and the Roberts Mountain allochton-el Paso terrane. It is clear that the Snow Lake Block is out of place since it is surrounded on either side by eugeoclinal rocks: the displaced Shoo Fly Complex and other oceanic rocks to the west and the Roberts Mountain allochton-el Paso terrane to the east. Lahren and Schweickert (1989) proposed that a strike-slip fault, called the Mojave-Snow Lake fault, moved the Snow Lake Block approximately 400 km from the Mojave desert region to its present location. They correlated the Snow Lake unit with the rocks of the Mojave region based on a comparison of a Mesozoic overlap sequence at each location, the recording of the Independence dike swarm in both rock units, and also because of structural similarities between the units (Lahren and Schweickert, 1989). More recently, however, the Mojave has been called into question as the possible origin for the Snow Lake Block. In 2008, Memeti and Mueller found an ammonoid fossil in the overlap sequence present at the Snow Lake pendant. Mueller also discovered a rock layer with several fossils which, along with the ammonoid fossil, were determined to be marine invertebrates that likely lived on and above the sea floor (Memeti et al., 2010). Although the two overlap sequences may have appeared similar at first, the Snow Lake cover sequence looks marine in origin while the cover sequence near Victorville is non-marine. This, in addition to zircon age comparisons done by Memeti et al. (2010), leads to the conclusion that the two areas are not linked. Without a solid correlation, new efforts to find the origin

4 of the Snow Lake fault may be spent looking at the regions just to the east or perhaps northeast of the present location. It appears that a piece of the North American margin, closer to Idaho, may be missing and could be the first clue to solving this enigma (Scott Paterson, University of Southern California, 2011, personal commun.). The focus of this paper will be in the vicinity of the Sierran Foothills Suture, specifically an area called Iron Mountain. Iron Mountain is a metamorphic pendant that lies near the contact between the Shoo Fly Complex and the Snow Lake Block (see Figure 2). The research at Iron Mountain presented in this paper began as part of a study done by the Undergraduate Team Research (UTR) program of the Earth Sciences department at the University of Southern California in June A group of four undergraduates along with advisor Scott Paterson and teaching assistant Vali Memeti, set out to answer a number of questions regarding the metamorphic pendant. First, we wanted to determine if there were miogeoclinal rocks, resembling the Snow Lake Block, present in the pendant or if the metasedimentary rocks were more characteristic of the Shoo Fly Complex. Second, we wanted to determine if a Jurassic overlap sequence existed in this area. Third, we wanted to confirm the age of the metavolcanic rocks in the pendant since previous maps were in disagreement and suggested ages ranging from Paleozoic to Cretaceous (Huber et al., 1989; Peck, 1980; Peck, 2002). And finally, we wanted to determine if there was any evidence of a major tectonic boundary in this region. In searching for the above information, we came to three conclusions regarding the metamorphic pendant: (1) there are miogeoclinal rocks present at Iron Mountain that fit nicely into the Snow Lake Block, (2) the metavolcanic rocks are of Late Cretaceous age and formed around the peak magmatic age for the Sierra Nevada region, and (3) there is also a marine Jurassic overlap on top of the Paleozoic unit which is similar to the overlap sequence seen in most pendants in the Sierra Nevada. It remains unclear if there is a major tectonic boundary in this pendant. Presented in this paper are the thin section analysis, the geochemistry data, and the geochronology results that led to those conclusions.

5 Figure 2: Map showing the location of the Iron Mountain pendant. Geologic Setting Below our geologic map of Iron Mountain and accompanying cross section from the June 2009 UTR program along with recent data from Zhang (Tao Zhang, University of Southern California, 2011, personal commun.) is presented (Figures 3 and 4). The rock types we observed can be divided into three categories: metavolcanic, metasedimentary, and plutonic rocks. The metavolcanic unit included volcanic breccias, some with very large fragments, tuffs, and also lithic and accretionary lapilli. Our observations agreed with previous work done by Huber, Bateman, and Wahrhaftig who described the unit as Cretaceous metavolcanic rock largely formed from pyroclastic rocks and lesser lava flows and includes tuff and tuff breccias (Huber et al., 1989). Other maps have defined the rocks as being mostly gray metarhyodacite tuff from the lower Cretaceous containing dark lapilli as well as altered phenocrysts of plagioclase, quartz, and hornblende in a fine-grained groundmass (Peck, 2002). We observed the accretionary lapilli and altered phenocrysts in our mapping area as well. The metasedimentary units of the Iron Mountain pendant were suggested to be derived from sandstone, siltstone, shale, limestone, and conglomerate and were speculated to be of Jurassic age

6 (Huber et al., 1989). Other maps also agreed that the sediments were pre-cretaceous and included biotite schist, gray metaquartzite, and some argillite (Peck, 2002). We did observe these rock types in the pendant and concluded that the metasedimentary unit in the central part of our mapping area may be of miogeoclinal origin and not the Jurassic overlap sequence. This unit was characterized largely by quartzites while the Jurassic metasedimentary unit in the east was dominated more by thin, grey metasiltstones and metashales. Lastly, the above units are intruded by plutonic bodies at Iron Mountain including granite, granodiorite, and tonalite. To the west of the large, main plutonic body at Iron Mountain is the 102 Ma El Capitan Granite and the Ma Bass Lake Tonalite (Huber et al., 1989; Peck, 2002). The El Capitan Granite is a coarse-grained, light colored biotite granite and biotite granodiorite that is often porphyritic with phenocrysts of potassium feldspar and quartz grains (Huber et al., 1989). The Bass Lake Tonalite is comprised mostly of medium-grained tonalite and calcic granodiorite with mafic inclusions (Peck, 2002; Lackey, oral commun., 2010). The large pluton in the middle we have identified as the Granodiorite of Iron Creek. Previous mapping has described this unit as mediumgrained granodiorite with some granite with an age of about 110 Ma (Peck, 2002). Other maps considered part of what we have called the Granodiorite of Iron Creek to be the Granite porphyry of Star Lakes, a light colored granite porphyry, quartz monzonite, and sodic granodiorite with an age of about 108 Ma (Peck, 2002). This pluton is displayed on our geologic map as a smaller section just to the north of the Granodiorite of Iron Creek (Figure 3). To the east we have three main plutonic units all of Cretaceous age. The Granodiorite of Grizzly Creek is a mafic granodiorite and tonalite. The Granite of Shuteye Peak is a light-colored leucogranite and biotite granite which shows signs of shearing, something we observed in the field as well (Peck, 1980). The Granodiorite of Ostrander Lake unit contains hornblende-biotite granodiorite and also biotite granite (Huber et al, 1989). Overall, our new geologic mapping placed these intrusive igneous rocks in the same or similar locations as previous works with some minor differences. The most significant being that our Granodiorite of Iron Creek extends further west and is the dominant plutonic unit in the area rather than the Granite porphyry of Star Lakes as seen on Peck s 2002 Yosemite Quadrangle map. Huber et al. (1989), on the other hand, did not identify the Granodiorite of Iron Creek as its own unit; the

7 Granite porphyry of Star Lakes covered that entire area (Huber et al., 1989). Some field photos of the units mentioned above can be seen in Figure 5. Figure 3: Geologic map of Iron Mountain. Figure 4: Cross section of Iron Mountain.

8 Petrological Study Figure 5: In the volcanic rocks we observed large breccias fragments (photos A and B) as well as accretionary lapilli (C) which indicate that a large volcanic eruption must have taken place in the area. From the miogeoclinal unit, we have an image of a quartzite (D). From the Jurassic metasedimentary unit to the east, we have an image of a thin, grey siltstone (E).

9 Fifteen thin sections were made from rock samples collected in the Iron Mountain region. These samples help to describe four rock units present in the area: the Cretaceous metavolcanic units in the western and central part of the map, the quartz rich schist found in the westernmost metasedimentary units, the quartzite believed to be of passive margin origin located in the center of the map, and also the marine Jurassic metasedimentary rocks further east. Representative thin sections from each of these areas will be described below moving from west to east across the Iron Mountain area. GS-3 is the thin section sample from the metavolcanic unit on the western edge of the map (Figure 6). The rock is a dacite and includes quartz (85%), biotite (10%), and hornblende (5%). The thin section shows a fine grained quartz matrix with larger phenocrysts of biotite and hornblende. For the most part, the biotite appears to be growing around the hornblende. There has been some recrystallization of the matrix but there is very little internal deformation as indicated by the lack of crystal alignment. However, our field observations indicated that these volcanic layers were steeply dipping and thus are deformed but are not strongly, internally strained.

10 Figure 6: These are all thin section photos from the metavolcanic rock sample GS-3. The first three show biotite crystals in a fine grained matrix along with larger quartz clasts. The last photo shows a quartz grain breaking down. YM-12 is the thin section sample representing the quartz rich schist (Figure 7). The main mineral components are quartz (90%) and muscovite (10%) with some traces of sericite. This rock has been strongly deformed. There is evidence of shearing visible under the microscope and it is clear that the fine grained opaques are lined up rather well in planar zones which may be associated with fluid flow. The finer grain sizes seen in some deformation zones may be present because of the presence of recrystallized mudstone or slate that broke up within the rock.

11 Figure 7: These are thin section photos from the metasedimentary rock YM-12. The photo to the left shows the fine grained quartz mica matrix. The photo on the right shows the fine grained shearing. HE-8 is an example of an almost pure quartzite believed to be of miogeoclinal origin (Figure 8). The minerals present include quartz (96%), biotite (2%), and either chlorite, epidote, or actinolite (2%). Although it is unclear what the last mineral is, it is apparent that biotite grade metamorphism occurred followed by a lower grade metamorphism. The quartz in this sample has been recyrstallized as suggested by triple junctions of 120 and the lack of round edges. Figure 8: These are thin section photos from a quartzite rock labeled HE-8. The rock is mostly quartz with some biotite. RG-6 is a quartz biotite schist sample from the Jurassic sedimentary units on the eastern edge of the mapped region (Figure 9). The quartz and mica matrix, including muscovite and biotite, accounts for eighty-five percent (85%) of the thin section while the other fifteen percent (15%) is composed of beautiful, radial chlorite porphyroblasts. The radial chlorite crystals that overgrow the

12 main foliation suggest that the rock was not actively deforming during final retrograde cooling. This sample appears to have reached biotite grade before the final cooling began. Figure 9: These are thin section photos from the metasedimentary rock RG-6. The radial chlorite clasts are embedded in a quartz mica matrix. Geochronology We conducted U-Pb zircon dating on two metasedimentary rocks and one metavolcanic sample using the laser-ablation-multicollector-inductively coupled plasma-mass spectrometer (LA- MC-ICP-MS) at the Arizona LaserChron Center, Tucson, Arizona. Standard mineral separation and mounting preparation techniques were used to separate and process the zircons (Arizona LaserChron Center, 2010). We randomly selected 100 zircon grains from each of the metasedimentary rocks and 25 from the metavolcanic sample. Zircons with inclusions or fractures were avoided. The youngest significant peak for HE-8, our quartzite sample we believe to be of miogeoclinal origin (Figure 10) is around 1100 Ma meaning the rock cannot be older than this age. The most distinctive peak is about 1770 Ma but there are others at 1400 Ma and 2700 Ma. The peaks from sample HE-8 nicely match peaks exhibited by other miogeoclinal rocks in the central and southern Sierra Nevada (Figure 9). Namely, they have peaks around 2700 Ma, 1770 Ma, 1400 Ma, and 1100 Ma. We thus interpret the rock to be approximately Ordovician in age, based on comparison to stratigraphic characteristic and zircon population in other Ordovician rocks in the Snow Lake Block (Fig. 10), with the Precambrian zircons derived from the North American craton.

13 Figure 10: Geochronology plots showing the results for sample HE-8 and also a comparison to other miogeoclinal rocks in the Sierra Nevada. The thin, grey metasiltstone, FD-2, exhibited several peaks as well, the youngest being around 144 Ma meaning the rock is likely of Late Jurassic age. Other peaks were at 1440 Ma, 1770 Ma, and 2700 Ma (Figure 11). These results are similar to other Jurassic cover sequence rocks present in the central and southern Sierra Nevada (Figure 11).

14 Figure 11: Geochronology plot of sample FD-2 and a comparison to other metasedimentary units in the central and southern Sierra Nevada. Zircons from the metavolcanic sample, GS-3 show a range between 90 and 110 Ma with a peak age around 103 Ma. We interpret the peak as the likely eruption age (~ Ma), the younger zircon ages as reflecting minor Pb loss, and the zircons with slightly older ages as antecrystic zircons inherited from older parts of the magma plumbing system (e.g., Miller et al., 2007). Our age matches well with other volcanic rock samples from the central and southern Sierra Nevada supporting the interpretation that a belt of Cretaceous volcanics and plutonic units formed

15 along the central axis of the Sierra (Figure 12). To our knowledge these volcanics in the Iron Mountain region form the westernmost exposures of this Cretaceous belt known to date. Figure 12: Geochronology plot showing the peak age for our volcanic sample, GS-3, and also a comparison of other Sierra Nevada samples. Geochemistry Our only present geochemistry samples at Iron Mountain are four samples from the Cretaceous volcanic units. We chose to do geochemistry on these samples in order to confirm our classification of the types of volcanic rocks present in the unit and also to get a more in-depth look at

16 the composition of the samples. YM-4 and GS-3 are from the western side of Iron Mountain while MN-9 and HE-4 are from the central area. Geochemistry on these volcanic samples was obtained from the Washington State University GeoAnalytical Lab which has a ThermoARL Advant XP+ sequential X-ray fluorescence spectrometer. Elements analyzed on this spectrometer include the ten major and minor elements of most rocks in addition to nineteen trace elements. Also used was the Agilent 7700 ICP-MS, a quadrupole mass spectrometer, which is used to analyze REE in the rock samples (GeoAnalytical Lab Equipment, 2011). Our samples covered a fairly large range of silica content from about 55 to 70 wt%. The range of alkali elements was fairly small, from 2 to 4.2 wt%. On the TAS diagram, our samples fall into a range of basaltic trachy-andesite, andesite, dacite, to rhyolite (Figure 13). Because the samples span a wide range of compositions, it suggests that they cover a significant amount of the evolutionary history of the magma. The basaltic rocks are less evolved and can provide information regarding the earliest phases of the magmatism. The rhyolitic rocks can tell more about the final stages of the magma evolution. These rock types are in agreement with what we observed in the field and in thin section. According to the AFM diagram, our samples form a calc-alkaline trend (Figure 14). The calc-alkaline series generally includes rocks like basalt, andesite, dacite, and rhyolite but not silica-undersaturated rocks. Calc-alkaline rocks are generally found in volcanic arcs on continental crust, which makes sense regarding the tectonic history of the Sierra Nevada region. Our last classification plot, the Shand diagram, places most of our samples in the metaluminous category and one sample in the peraluminous area (Figure 14). This means that there is more aluminum than sodium and potassium combined but not more than sodium, potassium, and calcium combined and that one peraluminous sample has more aluminum more than the combination of the three alkalic elements. This also matches with what we observed in the field and in thin section since we did see some micas in our volcanic rocks. GS-3 is the one sample that was placed in the peraluminous category, meaning it has even higher concentrations of aluminum. Under thin section, GS-3 does contain some muscovite (common for high aluminum rocks) therefore supporting this plot made from geochemical data.

17 Figure 13: TAS diagram showing the rock types of our volcanic samples. The volcanic samples span a wide range of volcanic rock types from basalt trachy-andesite to rhyolite. Figure 14: AFM diagram and A/CNK-A/NK plot showing the series type and aluminum content. Our samples fell mostly in the calc-alkaline series and were mostly metaluminous. Next, we looked at the Harker diagrams (Figure 15) showing the composition of the volcanic rocks as crystallization of the magma occurred. The x-axis goes from mafic to felsic so that changes can be seen over the evolutionary history of the magma, from the early stages to the later ones. These plots show that the magma has been fractionated because certain elements are proportionally increasing while others are decreasing depending on compatibility. FeOt, Al O, MgO, and CaO are generally decreasing over time. They are compatible elements that like to go to solid phase as crystallization starts. P O and TiO also exhibit a decreasing trend which makes sense as apatite and sphene crystallize out early as well. Na O and K O, on the other hand, are incompatible elements and usually go to solid phase later, which is why their weight percent increases.

18 Figure 15: Compatible and incompatible element plots showing that the magma has been fractionated since some elements are increasing and others are decreasing depending on compatibility. Lastly, we have a rare earth element plot (Figure 16) and a trace element plot (Figure 17). The REE plot shows that the volcanic samples generally follow the same trend and could be derived from the same magma source. The negative europium anomaly signifies the crystallization of plagioclase in the magma. Because it appears that two samples do not have this anomaly, at least not as pronounced, they may be from a different origin or may have fractionated differently. The trace element plot shows again that the samples follow the same general trend signifying that they could be from the same source. They all have a phosphorus depletion from apatite formation and a titanium depletion from sphene formation. Figure 16: Rare earth element plot showing that the volcanic samples mostly follow the same trend and could be derived from the same magma source.

19 Figure 17: Trace element plot showing similar trend for all volcanic samples. Discussion and Conclusions Based on our mapping, thin section analysis, geochronology data, and geochemistry we have come to three main conclusions. First is that we have identified a quartzite dominated rock unit with zircon populations that nicely match the Ordovician miogeoclinal units in the Snow Lake Block in the Sierra Nevada. This supports the hypothesis that the Snow Lake Block extends throughout much of the central and southern Sierra Nevada. We also identified a second sedimentary unit that has characteristics and a zircon age population that nicely match an early Jurassic marine overlap sequence seen elsewhere in the Sierra Nevada. There must be an unconformity or fault in between this unit and the miogeoclinal rocks mentioned above. We did observe some areas of shearing between these two units, which may provide more information regarding the separation of the rock types. But much of this boundary is intruded by younger plutons and thus difficult to examine. Our claim for the presence of the Jurassic Overlap Sequence was supported by thin section analysis, which showed that the rock could be a phyllite rock and geochronology, which suggested that the age was Late Jurassic. We were able to establish a Cretaceous age for the metavolcanic rocks in the Iron Mountain pendant. Geochemistry allowed us to provide more detailed information about the formation of these volcanics. The volcanics range in composition but the ones we observed were mostly rhyolite or dacite. We believe that Iron Mountain is one of the westernmost exposures know of to date of a belt of Cretaceous volcanics along the central axis of the Sierra Nevada. These Cretaceous rocks were

20 all deformed meaning that Cretaceous or younger deformation occurred in this pendant. Our observations were supported by field observations, thin section analysis, and geochemistry data and the Cretaceous age was confirmed by U-Pb zircon dating. It is still unclear if there is a major tectonic boundary in the Iron Mountain pendant. Most of the units in the pendant nicely match the geology of the Snow Lake Block as defined by Memeti, et al. (2010). We would thus infer that the major proposed fault between the Snow Lake and Shoo Fly complexes lies immediately west of this pendant and is now intruded out by Cretacous plutons. More field work and data collection needs to be done to provide evidence for its existence and also to provide further support for the ideas in this paper. Acknowledgements Special thanks to Scott Paterson, thesis advisor and supervisor of the USC June 2009 Undergraduate Team Research program. Also thanks to the other June 2009 UTR participants Emily Van Guilder, Ryan Stanley, Jonathan Chang, and Vali Memeti and to Tao Zhang for assistance on the Iron Mountain studies. Funding was provided by the USC Provost s Office.

21 References Arizona LaserChron Center, 2010, Arizona LaserChron Center, University of Arizona: (accessed April 2011). Bateman, P.C., 1992, Plutonism in the Central Part of the Sierra Nevada Batholith, California: U.S. Geological Survey Professional Paper 1483, 186 p. GeoAnalytical Lab Equipment, 2011, GeoAnalytical Lab, Washington State University: (accessed April 2011). Huber, N.K., Bateman, P.C., and Wahrhaftig, C., 1989, Geologic Map of Yosemite National Park and Vicinity, California: U.S. Geological Survey Miscellaneous Investigations Series Map I-1874, scale 1:125,000. Lahren, M.M., Schweickert, R.A., 1989, Proterozoic and Lower Cambrian passive margin rocks of Snow Lake pendant, Yosemite-Emigrant Wilderness, Sierra Nevada, California: Evidence for major Early Cretaceous dextral translation: Geology, v.17, p , doi: / (1989)017<0156:PALCMR>2.3.CO;2. Lindsley-Griffin, N., Griffin, J.R., and Farmer, J.D., 2008, Paleogeographic significance of Ediacaran cyclomedusoids within the Antelope Mountain Quartzite, Yreka subterrane, eastern Klamath Mountains, California: Geological Society of America Special Paper 442, p.1-37, doi: / (01). Memeti, V., Gehrels, G.E., Paterson, S.R., Thompson, J.M., Mueller, R.M., and Pignotta, G.S., 2010, Evaluating the Mojave-Snow Lake fault hypothesis and origins of central Sierran metasedimnetary pendant strata using detrital zircon provenance analyses: Lithosphere, v.2, p , doi: /l58.1. Nokleberg, W.J., 1983, Wallrocks of the Central Sierra Nevada Batholith, California: A Collage of Accreted Tectono-Stratigraphic Terranes: U.S. Geological Survey Professional Paper 1255, 28 p. Peck, D.L., 1980, Geologic Map of the Merced Peak Quadrangle, Central Sierra Nevada, California: U.S. Geological Survey Geologic Quadrangle Map, Survey GQ-1531, scale 1:62,500. Peck, D.L., 2002, Geologic Map of the Yosemite Quadrangle, Central Sierra Nevada, California: U.S. Geological Survey Investigation Series Map I-2751, scale 1:62,500. Saleeby, J.B., 1981, Ocean floor accretion and volcanoplutonic arc evolution of the Mesozoic Sierra Nevada, in Ernst, W.G., ed., The geotectonic development of California (Rubey Volume 1): Englewood Cliffs, N.J., Prentice-Hall, p