Landscape Evolution at an Active Plate Margin - Biological Science ...

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ed it could be caused by assimilation of crustal rocks when the basaltic magma rose to shallow depth and became gravitationally stable. Heat from the ponded magma would melt the surrounding rocks increasing oxygen fugacity and changing the composition of the mama through assimilation, thus accounting for the significant compositional variation between the various Owens Valley basalt fields. Evidence for this hypothesis comes from isotopes. Figure 1-17 is an εNd diagram for the Coso and Big Pine fields. Coso basalts lie wholly within the mantle array, suggesting Coso magmas were extracted from the mantle and extruded quickly after only limited interaction with the crust. Big Pine basalts, however, lie largely outside the mantle array and along an evolutionary trend (Zindler and Hart, 1986) requiring crustal contamination (Zindler and Hart, 1986). For Owens Valley basalt fields this contamination occurred when ponded basaltic magma assimilated crustal rocks. Proceed southwest to Tinemaha Creek Campground. 203.7 (0.6) Turn around at the intersection of Tinemaha Road and Fuller Road. RETRACE to Griffith Road. Red Mountain is the large volcanic cone to the west-southwest and the cinder cone of Crater Mountain is to the north. 205.3 (1.6) TURN LEFT on Griffith Road from Tinemaha Road. The view northwest at 10:00 is of a small red cinder cone with black basalt flows from Crater Mountain (elev. 6055’) to the northwest. 205.7 (0.4) Join Fish Springs Road. Proceed north. The scarp of the Inyo/Owens/Fish Creek fault at the base of Crater Mountain is at 10:00. 207.0 (1.3) Fish Springs hatchery on the left is the largest in Owens Valley. 207.6 (0.6) PULL TO THE RIGHT and PARK. STOP 1-8. Fish Springs Fault Scarp. Two scarps are exposed along the east face of Crater Mountain. Looking to the west, the Owens Valley fault (OVF) scarp is visible as an east-facing scarp. This part of the fault defines a 12 mile long segment of the OVF extending from the northwest side of the Poverty Hills to a termination north of Big Pine and referred to as the Big Pine segment. Almost due west of the stop is a tephra cone that is cut on its west side by the fault. Following with the eye northward from the cone, the scarp is first seen to cut alluvial fan material and then to cut basalt of Crater Mountain. The scarp cuts west D. R. Jessey and R. E. Reynolds of a hill composed of basalt just north of the alluvial fan materials. Another scarp is developed on the east side of the hill. On the north side of the hill, the faults on either side of the hill merge. The portion of the Big Pine fault segment between the Poverty Hills and the point where the two faults merge is referred to as the Fish Springs fault. From study of the tephra cone offset, Martel (1989) demonstrated that the Fish Springs fault is an eastside down dip slip fault with no strike-slip component. This poses a problem to the transpressional uplift model for the Poverty Hills. Without a rightlateral component of slip on the Fish Springs fault, there is no geometric reason for uplift of the western Poverty Hills. Beanland and Clark (1994) proposed that the Big Pine segment contains a large strike-slip component north of the Fish Springs fault. As evidence, they listed the possible right-lateral offset of two hills along the fault at Crater Mountain, offset of a line of tree stumps near Big Pine, and offset of a stream channel north of Big Pine. Examination of each of these features suggests that the evidence is weak. The possible offset of the hills is questioned because it is not clear how the hills formed. They are localized in an unusual area of the fault, where the fault contains a graben structure. Until the origin of the hills is understood, it is arguable that the hills have been offset horizontally. The line of tree stumps is irregular and it is not clear the trees were not planted in a pattern that today suggests the possibility of right lateral offset. Furthermore, it is not even clear that the trees pre-date the most recent fault rupture. Finally, it is not clear that the proposed offset stream channels were ever directly adjacent to another. In order to explain the lack of a strike-slip displacement on the Fish Springs fault, they suggested that strike-slip motion and dip-slip motion is partitioned at the latitude of the Fish Springs fault with dip-slip movement occurring on the Fish Springs fault and strike-slip movement occurring on the eastern fault. This suggestion is speculative in that there is no evidence for strike-slip displacement on the eastern fault. As an alternative in light of the weak evidence for strike-slip displacement on the Big Pine segment it is proposed that the entire Big Pine segment is a pure dip slip fault. We will consider evidence for this possibility at the next stop. Return to vehicles. Proceed north. 26 2009 Desert Symposium
Figure 1-18. Upper—view to the north of the Big Pine fault segment near the town of Big Pine. Lower—view to the north of the Lone Pine fault east of the town of Lone Pine. The Lone Pine fault ruptured in 1872 and still has a steep, well-developed free face, whereas the Big Pine fault scarp is strongly degraded and does not contain a free face anywhere along its length. The lack of a free-face in the Big Pine fault is evidence that the fault did not rupture in 1872. [K. M. Bishop photos] 207.9 (0.3) Stop at southbound Hwy 395. Watch for traffic, cross southbound lanes, and TURN LEFT on northbound 395. 210.9 (3.0) Continue past a right turn to Steward Lane. Prepare for left turn onto Big Pine Dump Road. 211.2 (0.3) TURN LEFT on Big Pine Dump Road. 211.5 (0.3) PARK at waste transfer station. WALK up the gated dirt road to the Big Pine fault scarp. STOP 1-9. Big Pine Fault Scarp. The current paradigm for this segment is that the fault last ruptured in 1872 and that it contains a predominant strike-slip component and a lesser dip slip component. The purpose of this stop is to examine the surface trace of the Owens Valley fault and consider evidence for the following two concepts: 1) the Big Pine segment did not rupture in 1872, and 2) the Big Pine segment’s kinematics is pure dip slip. 2009 Desert Symposium Landscape evolutuion at an active plate margin: field trip Two lines of evidence suggest that the fault did not rupture in 1872. First, rock varnish is ubiquitously developed on rocks exposed in the fault scarp, as best seen in the basalt of Crater Mountain. Rock varnish takes approximately 2000 years to develop sufficiently to be visually discernible. If the Big Pine segment ruptured in 1872, then a zone of unvarnished rock disrupted by the fault movement should be present, but it is not. A second line of evidence is the state of fault scarp degradation where the fault cuts fanglomeratic deposits. Along its entire length, the maximum scarp gradient is no greater than approximately 30 degrees, the angle of repose for loose, sandy material. Nowhere is a “free face” (steep exposure of in-situ material cut by the fault) present. Wallace (1978) studied fault scarp degradation rates and suggests that in the Great Basin, free faces persist in fault scarps on the order of a couple thousand years following rupture. The lack of a free face anywhere along the Big Pine fault segment thus argues against 1872 rupture. This notion is well-illustrated by comparing the Lone Pine fault scarp, where a free face in fanglomerate created by 1872 rupture is still well-formed, and the Big Pine fault scarp, with its lack of a free face (Fig. 1-18). Directly west of the Big Pine dump transfer station, the Big Pine fault cuts basalt to form a 150 foot wide graben. The west side of the graben is defined by two parallel east-facing scarps. The westernmost of the two faults is crossed by the channel of an intermittent stream. Channel erosion has developed in both the upthrown and downthrown fault blocks. There is no horizontal offset of the channel across the fault. It may be possible that the channel has been eroded since the last fault displacement. If so, the lack of horizontal offset offers no evidence of a horizontal component of offset. However, the scarp reaches 12 feet in height, which suggests it was created by multiple displacements. Given that the channel is incised approximately 6 feet into the downthrown fault block, it seems unlikely that the channel has been formed only since the last fault rupture. Approximately 0.3 mile north of the incised stream along the main fault scarp is a line of boulders marking the edge of an ancient debris flow. This line of boulders crosses the fault scarp and is displaced downward across the scarp. There is no horizontal offset of the debris flow edge. This provides a second piece of evidence arguing against a horizontal component of displacement for the Big Pine fault. 27
Page 1 and 2: Landscape Evolution at an Active Pl
Page 3 and 4: Table of contents Landscape evoluti
Page 5 and 6: Evaluation of minor and trace eleme
Page 7 and 8: Landscape evolution at an active pl
Page 9 and 10: 25.3 (0.2) Continue past Osdick Rd.
Page 11 and 12: and Wesnousky, 1994). Reported rate
Page 13 and 14: into six units which range in age f
Page 15 and 16: Nevada & California railroad were u
Page 17 and 18: een built to meet the growing deman
Page 19 and 20: Figure 1-10. Offset drainages of Lo
Page 21 and 22: tary and metavolcanic units are lar
Page 23 and 24: Landscape evolutuion at an active p
Page 25: the Independence fault is dip-slip,
Page 29 and 30: 2009 Desert Symposium Landscape evo
Page 31 and 32: eruption of the Long Valley caldera
Page 33 and 34: Figure 2-2. Collapsed aqueduct pipe
Page 35 and 36: 63.7 (0.4) PARK at turnout. STOP 2-
Page 37 and 38: Sierra Nevada fault system has offs
Page 39 and 40: Landscape evolutuion at an active p
Page 41 and 42: (Cleveland, 1962). The rhyolite has
Page 43 and 44: ahead on the left. 95.6 (1.2) Stop
Page 45 and 46: ay. The big 40m dish is now used by
Page 47 and 48: cupied in 1865, and finally abandon
Page 49 and 50: Figure 3-6. Independence dikes. [S.
Page 51 and 52: which has significant concentration
Page 53 and 54: The Pliocene (Blancan NALMA) Coso F
Page 55 and 56: Current Research in the Pleistocene
Page 57 and 58: Quaternary data and references: A c
Page 59 and 60: and volume, p. 26-35. Smith, G. I.,
Page 61 and 62: Stolzite and jixianite from Darwin,
Page 63 and 64: (112) (Palache, et al., 1951). The
Page 65 and 66: ing gold and silver deposits. From
Page 67 and 68: the United States. Several small de
Page 69 and 70: at the base of the Lost Burro were
Page 71 and 72: silver-lead ore and is the one exce
Page 73 and 74: Significance of the Independence Di
Page 75 and 76: Independence Dike Swarm Figure 2: C
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40 km of displacement was too low.
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dominant northwest strike. Dikes wi
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Moore, J.G., 1963, Geology of the M
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summarizes the formations you will
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The Perdido Formation conformably r
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note the spheroidal weathering patt
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Lower Cambrian-Precambrian stratigr
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lus. Six to ten species of echinode
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The Olancha Dunes, Owens Valley, Ca
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Triassic ammonoids from Union Wash,
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Archaeocyathids from Westgard Pass,
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Basaltic volcanism in the southern
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Basaltic volcanism in the southern
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oxene, whereas Pleistocene basalt i
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in much slower rates of displacemen
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Vegetation of the Owens Valley and
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cone and limber pine woodlands and
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Figure 21. The alpine zone of the W
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The rush from the Kern River mines
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The rush from the Kern River mnes i
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2009 Desert Symposium The rush from
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mining company; and A. K. Warner an
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chinery and the castings for a smel
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Advertisement for the Hobard and Re
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November 1864, a series of lines be
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When the geologist W. A. Goodyear v
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Montgomery City Alan Hensher, 593 C
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The Blue Chert Mine: an epithermal
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2009 Desert Symposium The Blue Cher
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2009 Desert Symposium The Blue Cher
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Tectonic implications of basaltic v
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The Goler Club Figure 2. Outcrop ma
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closest relatives were early Paleoc
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The Goler Club Figure 8. Goler Club
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prospecting, Baum wandered over to
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ejonian age (Thewissen 1990; Lofgre
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Fish Creek rhythmites and aperiodic
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We analyzed each of the three rhyth
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Figure 10. Threshold rhythmite prod
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Holocene slip rate and tectonic rol
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Figure 2. Camelops sp. (camel) meta
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moist, brush- and grass-covered, fr
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Recent records of fossil fish from
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geal arches are similar to S. b. sn
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elatives seen in Pliocene and early
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Jennings, C.W. 1958, Geologic map o
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Competing mesquite and creosote dun
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Figure 9. Sheetwash area near the w
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The Oak Crrek mudflow of July 12, 2
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Photo 8. Deeply incised channel of
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than the north fork because of the
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mass contents of Gram negatives (sa
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to different uses. I do not suggest
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Geochronology and paleoenvironment
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Reproductive ecology of female Sono
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Garbage production is the other sid
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ties and preparation for use of som
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