CalCal PolyPoly -- PomonaPomona GeologyGeology ClubClub SpringSpring 20032003 FFieldield TTriprip BigBig SurSur David R. Jessey Randal E. Burns Leianna L. Michalka Danielle M. Wall ACKNOWLEDGEMENT The authors of this field guide would like to express their appreciation and sincere thanks to the Peninsula Geologic Society, the California Geological Survey and Caltrans. Without their excellent publications this guide would not have been possible. We apologize for any errors made through exclusion or addition of trip field stops. For more detailed descriptions please see the following: Zatkin, Robert (ed.), 2000, Salinia/Nacimiento Amalgamated Terrane Big Sur Coast, Central California, Peninsula Geological Society Spring Field Trip 2000 Guidebook, 214 p. Wills, C.J., Manson, M.W., Brown, K.D., Davenport, C.W. and Domrose, C.J., 2001, LANDSLIDES IN THE HIGHWAY 1 CORRIDOR: GEOLOGY AND SLOPE STABILITY ALONG THE BIG SUR COAST, California Department of Conservation Division of Mines & Geology, 43 p. 0 122 0 00' 122 0 45' 121 30 Qal Peninsula Geological Society Qal G a b i Qt la Field Trip to Salina/Nacimento 1 n R S a A n L Big Sur Coast, Central California I g N qd A e S R Qt IV E Salinas R S a lin a s Qs V Qal 101 a Qs Monterey Qc lle Qt Qp y pgm Tm Qm Seaside pgm EXPLANATION Qt Chualar Qp Qt UNCONSOLIDATED Tm pgm SEDIMENTS Qp Carmel Qal sur Qs Qal Alluvium qd CARMEL RIVER Tm Qal Point sur Qs Dune Sand Tm Lobos pgm 0 S 0 36 30 ie ' r 36 30' pgm ra Qt Quaternary non-marine d CARMEL e S terrace deposits VALLEY a Qal lin a Qt Pleistocene non-marine Tm pgm s Qc 1 Tm Tula qd rcit Qp Plio-Pleistocene non-marine qd os F ault Qm Pleistocene marine Terrace sur sur deposits qd Tm COVER ROCKS pgm qd Tm Monterey Formation, mostly qm pgm qm pgm marine biogenic and sur pgm clastic sediments middle to qdp sur qd late Miocene in age. Tm qm sur sp qm FRANCISCAN SUBDUCTION Qs fs Tm qm Tm sp COMPLEX J-K Point Sur K sur qd sur sp qm fs Graywacke, deep-sea trench K sur sur deposits fc Qm K qm fc Deep-ocean bedded radiolarian cherts fs sp qm 0 fc qm 36 15' P 0 a 36 15' c Sheared serpentine derived from i K sur sp fi qdp oceanic depleted harzburgite. c sur qm O qm c FOREARC SEDIMENTS J-K e 28 a qm K Great Valley forearc turbidite n qm sediments qdp sur sur NEVADAN ISLAND ARC INTRUSIVE ARC ROCK K (78 -150 Ma age of arc) S u r ISLAND ARC BASEMENT T qm Porphyritic grandiorite of Monterey h ru K Sur Series or Sur Complex st sur K pgm Quartz monzonite quartzofeldspathic schist, marble granofels, and gneiss. Protolith qdp pg Porphyritic grandiorite age is Precambrian 1.7 Ga and the qd Quartz diorite metamorphic age is 78 to 100 Ma. qdp sur sur qdp Quartz -poor quartz diorite fs (some are recrystallized tonalites 0 10 20 km fs qdp containing granulite facies 0 5 10 miles Lucia 0 garnet + opx , Compton's charnockite) 0 36 00' SCALE 36 00' 122 0 00' 122 0 45' 1 Cross Section Location CROSS SECTION OF THE SOUTHERN COAST RANGES AND SAN JOAQUIN VALLEY in California FROM OFFSHORE OF POINT SUR TO MADERA, CALIFORNIA S an A nd re as F au lt G R E D ia A Macera bl T o B San Gregorio-Hosgri Fault R an ge V A G L ab Sa L Monterey Sa ila n E R nt an n An a R Y ge Lu an dr ea ci ge A a s F au lt Su ult r-N aci ck Fa mie Garlo nto Fa Pacfic Ocean ult 0 200 km Scale Western edge of former Coast Range Jurassic-Cretaceous subduction zone San Andreas Thrust A for Point Sur area Fault Zone Sur-Nacimiento B Santa Lucia Sierra de Gabilan Madera Fault Zone Salinas KM4 Range Salinas Valley Range Panoche Hills San Joaquin Valley 4 KM PACIFIC OCEAN Point Sur Diablo Range Sea Level 0 0 -4 2.0 -4 Franciscan Subduction Complex -8 Jkf Middle to Late Jurassic -8 Franciscan Subduction Complex magmatic underplating of west facing -12 -12 Jkf “infant arc” Sierra Nevada Jkf -16 MORB stalled underplate -16 -20 ? Sierra Nevada Basement -20 -24 -24 -28 Mantle MORB stalled underplate -28 -32 -32 -36 -36 -40 -40 110 100 90 80 70 60 50 40 30 20 10 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 KM EXPLANATION Nevadan Island Arc Quaternary & Pleistocene Tonalite Intrusive granites 78 - 100 Ma Slow spreading initiates partial melting in the mantle ~ 165 Ma Tertiary sediments Sur Series continental basement 1.7 Ga Fore Arc Great Valley Dikes Cretaceous-Jurassic sediments Great Valley Ophiolite slow spreading underplating of Sierran Basement Sierra Nevada Basement Coast Range ophiolite generated above suprasuduction zone Cretaceous-Jurassic Mid ocean ridge basalt MORB Franciscan subduction complex, Mantle, depleted harzburgite Cretaceous-Jurassic Big Sur Field Trip Road log and Field Guide D. Jessey, R. Burns, L. Michalka and D. Wall Mileage Description 0.0 San Simeon Creek Campground – Turn right (north on Highway 1). 3.0 Turnoff to Hearst Castle. 8.7 Piedras Blancas Lighthouse Road – STOP 1. At this stop marine terraces, uplifted by motion along the San Simeon fault, are a common feature of the landscape. The San Simeon fault, which may be an onshore segment of the Hosgri fault, is a multistrand break; it cuts and displaces late Pleistocene marine terraces and Holocene dune sands near San Simeon Point. Although faulted shoreline-angle geometry and the correlation of wave-cut platforms across this fault are subject to some uncertainty, Weber (1983) suggested a horizontal right-slip component of about 0.5 cm/yr. Earthquake focal mechanisms along the San Simeon fault indicate a dip of 55° E and nearly equal components of reverse and strike slip. Right-oblique slip at a rate of about 0.5 cm/yr on the Hosgri fault is indicated by earthquake focal mechanisms, sea-floor scarps, the distribution of late Quaternary wave-cut platforms, and faulted seismic-reflection horizons of late Cenozoic age. 16.3 Northern extent of San Simeon terraces. We have now crossed the San Simeon fault and entered the more rugged terrain characteristic of the central California coast. The rocks underlying this portion of the coastline are part of the Sur-Obispo terrain; more commonly termed the Franciscan after the type section north of San Francisco. Most likely we are stopped at the traffic light so you may have the opportunity to quickly examine the rocks. The Franciscan is a “classic” mélange sequence (see our discussion elsewhere in this field guide) with tectonically dismembered slices of ophiolite. However, the exposures north of Cambria are limited and not as striking as the Coast Range Ophiolite (CRO) at Point Sal to the south (Vandenberg AFB) or along the Smith River to the north (Josephine Ophiolite). Remember from GSC 111 that ophiolite consist of three components; layered ultramafics and gabbro, pillow basalt and deep water sediments. The latter are the most common along this portion of the central California coast. Where present, the igneous components tend to be so heavily serpentinized that it is difficult to recognize the protolith. The reason for the signal light is to enable Caltrans to control traffic flow while they repair this portion of the road from a winter landslide. You will realize by the end of this field trip that those portions of the highway traversing Franciscan rocks are far more landslide prone than other parts of the highway. 17.6 Town of Ragged Point. 18.0 Striking beds of interlayered black shale and white chert typical of the deep water sediments associated with ophiolite sequences. 19.1 Monterey County line. 19.7 Leianna’s lunch: note the undigested salami. 21.3 Salmon Creek. 24.5 Nathaniel Owens Memorial Redwood - the fortunes of this protected area took a dramatic turn for the worse after Leianna claimed to be attacked by a giant flying insect and proceeded to decimate the local wildlife population with a rock hammer. 26.6 More bedded chert. 28.8 The metropolis of Gorda. 32.1 Jade Cove – STOP 2. Park as close as possible to the Jade Cove Beach sign, cross over the fence and follow the well-worn trail to the beach. Jade Cove is a portion of the ophiolite sequence that was subjected to high pressure/low temperature (blueschist facies) metamorphism, often with plate subduction and accretion along a convergent margin. Slickensides are present on the rocks along the trail below the marine terrace. On the beach, there are blue and green schists, fibrous to asbestiform serpentine, graywackes, and nephrite jade from which the name of the cove is derived. Pure nephrite is usually white, but the presence of impurities results in a variety of shades of green, from lightly tinted, nearly transparent, to a rich, dark green. Underwater, jade is fairly easy to distinguish from other rocks by its characteristic, almost luminescent color. Jade is hard and cannot be scratched by a rock hammer, while the softer, and more common, serpentine is easily scratched. Small pebbles of jade may be found in the gravel beds, particularly near Cave Rock and the north point of the cove. Jade hunters don’t need to be divers as many small jade pebbles can be found in tide pools between the boulders, and in areas of coarser gravel.