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- Creator:
- Gebauer, Samantha
- Description:
- The exhumed root of the Triassic to Early Cretaceous continental arc in Fiordland, New Zealand preserves a record of deep crustal arc processes during and following high‐flux magmatism from c. 124‐115 Ma. We present new LASS-ICP-MS and SHRIMP‐RG 206Pb/238U dates, as well as Ti-in-zircon and Zr-in-titanite temperatures for metamorphic zircon and titanite in order to (1) reconstruct the thermal history of northern Fiordland, and (2) illuminate spatio‐temporal patterns in arc root metamorphism. Samples were collected over ~50 km along an arc‐parallel transect from George Sound ( ~8 kbar) to Milford Sound (~16 kbar) in order to understand the thermal evolution of the arc as a function of paleocrustal depth. Rims that grew on zircon in samples from the Arthur River Complex indicate that Early Cretaceous metamorphism initiated at 134.9 ± 3.1 Ma (T = 720°C) and lasted until 126.5 ± 2.7 Ma (T = 700 °C). Subsequent granulite‐facies metamorphic zircon growth occurred from 121.3 ± 1.6 to 116.0 ± 2.3 Ma in Bligh and George Sounds at 830-700°C. These dates and temperatures overlap with existing garnet Sm‐Nd dates from the Pembroke granulite (Milford Sound) and likely reflect heating associated with deep crustal emplacement of the Western Fiordland Orthogneiss from c. 125‐115 Ma during the final stages of Median Batholith magmatism. Titanite LASS chronology of metasedimentary rocks shows complex spatio‐temporal patterns that reveal multiple pulses of titanite growth and/or recrystallization. East of Sutherland Sound, titanites yield a date of 120.6 ± 4.4 Ma and a Zr‐in‐titanite temperature of 765°C, which is similar to metamorphic zircon results in the region. At George Sound, titanites yield a date of 112.0 ± 2.4 Ma and a temperature of 760°C which overlaps with values reported in central Fiordland from Caswell to Breaksea Sounds. Younger dates of 104.8 ± 1.6 and 94.0 ± 2.3 Ma also occur in Bligh and George Sounds, and yield temperatures of 930 and 840°C, respectively. These dates and temperatures indicate that titanite growth and/or recrystallization occurred during multiple pulses of lower crustal heating which we speculate may have resulted from either lithospheric thinning related to extension and/or episodic foundering of a high‐density arc root produced during the arc flare‐up event.
- Resource Type:
- Thesis
- Campus Tesim:
- Northridge
- Department:
- Geological Sciences
2. Geomorphic Response to Accelerated Sediment Transport and Erosion in Tectonically Active Streams.
- Creator:
- Dirgo, Dannon
- Description:
- Drainage basins and their network of streams affected by past and ongoing tectonic activity may be characterized by high gradients, re-directed (offset) channels and sediment loads that reflect hydrologically discontinuous transport and deposition processes. Further, watersheds that experience profound anthropomorphic changes such as removal of trees and generations of unregulated grazing, have resulted in hillslope and streamside instability owing to a decline of native riparian, arboreal, understory, and forb species. This study describes and evaluates patterns of sediment erosion, transport and deposition in the 126 km2 San Emigdio watershed in Kern County, California. Using an Unmanned Aerial Vehicle (UAV) in conjunction with an RTK GPS base station and rover along a 4 km reach, a series of high resolution (2 cm) images, a georeferenced orthomosaic, and digital terrain model (DTM) were generated to provide a baseline for sediment accumulation, bank erosion, and longitudinal profile changes over time. Channel cross sections and the longitudinal profile were surveyed with a total station and georeferenced with the UAV generated data. Results showed that while there were active hotspots of channel bank erosion at knickpoints which appear to be fault-controlled, there was also significant bank instability and addition of sediment into the active channel along the entire reach even under very low flow conditions. These processes combine to load sediment in the channel that apparently can be removed only by high discharge events. With increasing precipitation variability in the region during the past half century, punctuated by periods of drought, storage of sediment in the channel and its potential to be transported beyond the watershed into neighboring agricultural land suggests that continued measurement of channel and bank erosion and sediment transport and deposition is critical.
- Resource Type:
- Thesis
- Campus Tesim:
- Northridge
- Department:
- Geography and Environmental Studies
- Creator:
- Vilkas, Marius
- Description:
- The western Tarim Basin contains the sedimentary record of the adjacent Tian Shan and Pamir orogens. Diverse basement lithologies and mixing of sources here complicates the sedimentary signature of orogenic growth. To understand the southern Tian Shan foreland response to tectonic changes, we present new U/Pb detrital zircon (DZ) data and sandstone compositions from 9 samples collected within a ~4 km-thick, Miocene to Quaternary stratigraphic section to establish a paleogeographic reconstruction of the Southwestern Tian Shan, Eastern Pamir, and the Northern Tarim Basin during the Late Cenozoic. Bulk petrographic analysis of the nine sandstones reveals a recycled orogen signature for the section, with dominant sedimentary-metamorphic lithic compositions that exhibit little to no stratigraphic or depositional trends. Although the present position of this stratigraphic section implies the strata resulted from Miocene present uplift and erosion of the Tian Shan, the DZ data reveal a different history with a strong Pamir signal in the middle Miocene. Overall, three distinctive DZ spectra are observed that represent a change from dominantly Pamir sourced sediment at 14.3 Ma to exclusively Tian Shan sourced by 1.5 Ma. The apparent influx of Pamir sourced grains decreases up-section, except for the eolian strata at 11.5 Ma that contain anomalous DZ peak ages at ca. 12 Ma and 100 Ma, which are unique to the Pamir and must have been blown in from the southwest. Although it is difficult to completely distinguish Paleozoic DZ age-populations between the Pamir and Tian Shan, the presence of Cenozoic, Cretaceous, and Triassic grains in the lower part our section are distinctively Pamir sourced, revealing that sediment from the Pamir was actively being deposited in the Tian Shan Foreland from ~14 Ma until at least 7.6 Ma. Samples from 5.8, 3.6, and 1.5 Ma do not have any DZ peaks <200 Ma, suggesting a lack of Pamir influence. Our study reveals the complicated provenance signal from the amalgamated Tian Shan - Pamir foreland, highlighting the complexity and importance of resolving provenance from mixed, heterogeneous sources in intracontinental basin settings.
- Resource Type:
- Thesis
- Campus Tesim:
- Northridge
- Department:
- Geological Sciences
- Creator:
- Farley, Kathleen A., Saleeby, Z., Saleeby, J., and Cecil, M. Robinson
- Description:
- Thermomechanical models of mantle lithosphere removal from beneath the southern Sierra Nevada region, California (USA), predict a complex spatiotemporal pattern of vertical surface displacements. We evaluate these models by using (U-Th)/He thermochronometry, together with other paleothermometry estimates, to investigate such topographic transients. We target Tertiary strata from the Kern arch, a crescent-shaped active uplift located in the southeastern San Joaquin Basin, along the western flank of the southern Sierra Nevada. Kern arch stratigraphy provides a unique record of subsidence and exhumation in a sensitive region immediately adjacent to the delaminating mantle lithosphere at depth. Detrital apatite (U-Th)/He ages from Oligocene-Miocene sandstones collected in Kern arch well cores indicate postdepositional heating to temperatures beyond those corresponding with their present burial depths. When integrated with available geologic and stratigraphic constraints, temperature-time modeling of thermochronometric data suggests partial He loss from apatites at temperatures of 70-90 °C, followed by exhumation to present burial temperatures of 35-60 °C since ca. 6 Ma. By constraining the late Cenozoic geothermal gradient to ?25 °C/km, our results imply 1.0-1.6 km of rapid (?0.4 mm/yr) subsidence and sedimentation, and then subsequent uplift and exhumation of southeastern San Joaquin Basin strata in latest Miocene-Quaternary time. Stratigraphic and geomorphic relations further constrain the principal burial episode to ca. 2.5 Ma or later, and exhumation to ca. 1 Ma or later. Subtle differences in the maximum temperatures achieved in various wells may reflect differing degrees of tectonic subsidence and sedimentation as a function of growth faulting and distance from the range front. Our results are consistent with estimates of surface subsidence and uplift from Sierran delamination models, which predict a minimum of ?0.7 km of tectonic subsidence in regions retaining mantle lithosphere adjacent to the area of delamination, and a minimum of ?0.8 km of rock uplift in regions where delamination occurred recently. We attribute the marked pulse of tectonic subsidence in the San Joaquin Basin to viscous coupling between the lower crust and a downwelling mass in the delaminating slab. The ensuing episode of exhumation is interpreted to result from the northwestward peeling back of the slab and the associated replacement of dense lithosphere with buoyant asthenosphere that drove rapid rock and surface uplift.
- Resource Type:
- Article
- Identifier:
- 1553-040X
- Campus Tesim:
- Northridge
- Creator:
- Kylander-Clark, Andrew, Stowell, Harold H., Shen, R., Schwartz, Joshua J., Hacker, Bradley, Tulloch, Andy, Klepeis, Keith A., Lin, Z.X., Ren, Y.J., Deng, W.Y., Sheng, Donna, Coble, Matthew, Xing, D.Y., and Sheng, L.
- Description:
- The exhumed Fiordland sector of Zealandia offers a deep-crustal view into the life cycle of a Cordilleran-type orogen from final magmatic construction to extensional orogenic collapse. We integrate U-Pb thermochronologic data from metamorphic zircon and titanite with structural observations from >2000 km2 of central Fiordland to document the tempo and thermal evolution of the lower crust during the tectonic transition from arc construction and crustal thickening to crustal thinning and extensional collapse. Data reveal that garnet granulite facies metamorphism and partial melting in the lower crust partially overlapped with crustal thickening and batholith construction during emplacement of the Western Fiordland Orthogneiss (WFO) from 118 to 115 Ma. Metamorphic zircons in metasedimentary rocks yield 206Pb/238U (sensitive high-resolution ion microprobe-reverse geometry) dates of 116.3-112.0 Ma. Titanite laser ablation split stream inductively coupled plasma-mass spectrometry chronology from the same rocks yielded complex results, with relict Paleozoic 206Pb/238U dates preserved at the margins of the WFO. Within extensional shear zones that developed in the thermal aureole of the WFO, titanite dates range from 116.2 to 107.6 Ma and have zirconium-in-titanite temperatures of ∼900-750 °C. A minor population of metamorphic zircon rims and titanites in the Doubtful Sound region yield younger dates of 105.6-102.3 Ma with corresponding temperatures of 740-730 °C. Many samples record Cretaceous overdispersed dates with 5-10 m.y. ranges. Core-rim traverses and grain maps show complex chemical and temporal variations that cannot easily be attributed to thermally activated volume diffusion or simple core-rim crystallization. We interpret these Cretaceous titanites not as cooling ages, but rather as recording protracted growth and/or crystallization or recrystallization in response to fluid flow, deformation, and/or metamorphic reactions during the transition from garnet granulite to upper amphibolite facies metamorphism.We propose a thermotectonic model that integrates our results with structural observations. Our data reveal a clear tectonic break at 108-106 Ma that marks a change in processes deep within the arc. Prior to this break, arc construction processes dominated and involved (1) emplacement of mafic to intermediate magmas of the Malaspina and Misty plutons from 118 to 115 Ma, (2) contractional deformation at the roof of the Misty pluton in the Caswell Sound fold-thrust belt from 117 to 113 Ma, and (3) eclogite to garnet granulite facies metamorphism and partial melting over >8 m.y. from 116 to 108 Ma. These processes were accompanied by complex patterns of lower crustal flow involving both horizontal and vertical displacements. After this interval, extensional orogenic collapse initiated along upper amphibolite facies shear zones in the Doubtful Sound shear zone at 108-106 Ma. Zircon and titanite growth and/or crystallization or recrystallization at this time clearly link upper amphibolite facies metamorphism to mylonitic fabrics in shear zones. Our observations are significant in that they reveal the persistence of a hot and weak lower crust for ≥15 m.y. following arc magmatism in central Fiordland. We propose that the existence of a thermally weakened lower crust within the Median Batholith was a key factor in controlling the transition from crustal thickening to crustal thinning and extensional orogenic collapse of the Zealandia Cordillera.
- Resource Type:
- Article
- Identifier:
- 1553-040X
- Campus Tesim:
- Northridge
- Creator:
- Gehrels, George E., Marsaglia, Kathleen M., Barth, Andrew P., Koch, Lauren G., Lessard, Sarah J., Stephenson, Erin J., Hawley, John A., Rivas, Donato A., Yaspelkis III, Benedict B., Pedrick, Jane N., Nourse, Jonathan A., Grove, Marty, Britton, Steven L., and Jacobson, Carl E.
- Description:
- During the Late Cretaceous to early Cenozoic, southern California was impacted by two anomalous tectonic events: (1) underplating of the oceanic Pelona-Orocopia-Rand schists beneath North American arc crust and craton; and (2) removal of the western margin of the arc and inner part of the forearc basin along the Nacimiento fault. The Pelona-Orocopia-Rand schists crop out along a belt extending from the southern Sierra Nevada to southwestern Arizona. Protolith and emplacement ages decrease from >90 Ma in the northwest to <60 Ma in the southeast. Detrital zircon U-Pb ages imply that meta-sandstones in the older schists originated primarily from the western belt of the Sierran-Peninsular Ranges arc. Younger units were apparently derived by erosion of progressively more inboard regions, including the southwestern edge of the North American craton. The oldest Pelona-Orocopia-Rand schists overlap in age and provenance with the youngest part of the Catalina Schist of the southern California inner continental borderland, suggesting that the two units are broadly correlative. The Pelona-Orocopia-Rand-Catalina schists, in turn, share a common provenance with forearc sequences of southern California and the associated Salinian and Nacimiento blocks of the central Coast Ranges. This observation is most readily explained if the schists were derived from trench sediments complementary to the forearc basin. The schists and forearc units are inferred to record an evolution from normal subduction prior to the early Late Cretaceous to flat subduction extending into the early Cenozoic. The transition from outboard to inboard sediment sources appears to have coincided with removal of arc and forearc terranes along the Nacimiento fault, which most likely involved either thrusting or sinistral strike slip. The strike-slip interpretation has not been widely accepted but can be understood in terms of tectonic escape driven by subduction of an aseismic ridge, and it provides a compelling explanation for the progressively younger ages of the Pelona-Orocopia-Rand schists from northwest to southeast.
- Resource Type:
- Article
- Identifier:
- 0016-7606, 1943-2674
- Campus Tesim:
- Northridge
- Creator:
- Macy, Kyle
- Description:
- The Yorba Linda Trend is a proposed NE-SW alignment of earthquakes near the western edge of the Los Angeles Basin in southern California first described by Egill Hauksson in the early 1990s (Hauksson, 1990). Most earthquakes in this area exhibit a strike-slip mechanism, but they do not fall on or near any mapped fault traces. More recent events and earthquake sequences have occurred within the boundaries of the Yorba Linda Trend since its conception: the 2002 Yorba Linda and 2008 Chino Hills earthquakes. These two sequences may now be considered part of this trend. Both of these sequences have a northeast-southwest striking orientation. The 2014 La Habra earthquake sequence located nearby follows a parallel orientation. The largest events of each of these sequences all exhibit a strike slip or oblique mechanism. The aftershock sequences, combined with the mechanisms, suggest previously unmapped left-lateral strike-slip faults may be responsible, but their exact geometry is unclear. Bookshelf faulting within the Chino Hills, potentially produced by the tectonic movement of the Whittier Fault and the Chino Fault may provide an explanation to the origin of some of these earthquakes. Because a majority of these earthquakes are small, they are poorly located. Seismic relocation using waveform cross-correlation allows for these small events to be relocated with a relatively high accuracy and for possible fault structures to be revealed. In this study, we utilized the GISMO cross correlation MATLAB toolbox (Thompson & Reyes, 2018) to determine correlation values and lag times of similar earthquakes in order to improve the arrival time measurements of the P- and S-waves of these earthquakes. We then entered these improved arrival times in the GrowClust relative relocation algorithm (Trugman & Shearer, 2017). In this relocation procedure, we used three 1-D velocity models: the IASP91 velocity model (Kennett & Engdahl, 1991), the smoothed southern California velocity model (Shao et al., 2012), and the Los Angeles Basin velocity model determined from the 1987 Whittier Narrows Earthquake (Hauksson et al., 2008) under a 0.2 sec RMS differential travel time residual, as well as a 0.6 sec differential travel time residual to successfully relocate earthquakes in the region of the YLT from 1989 to 2018. Each of the results for the six relocation attempts reveals two distinct clusters of earthquakes that are relatively planar centered around the 2008 Chino Hills Earthquake and the 2002 Yorba Linda Earthquakes. A noticeable gap is present between these two sequences. Relocation of the 2014 La Habra Sequence has aligned these earthquakes to form a northwest dipping planar structure, with many events clustered around the Coyote Hills Fault System. Other clusters of seismicity that were revealed by the GrowClust relocation show a system of earthquakes within the Los Angeles Basin just north of the Peralta Hills and El Modeno Faults, which may be anthropogenically induced by oil extraction within the Richfield Oil Field. None of the relocation results show a clear through-going planar structure connecting the Yorba Linda and Chino Hills Sequences. In addition, we do not see any seismicity trends that imply the presence of bookshelf faulting that connect the two sequences. The Yorba Linda Sequence may be situated along a high angle fault structure to the Whittier Fault. The orientation of this fault structure in combination with the focal mechanisms is indicative of a left-lateral strike slip fault. The Chino Hills Sequence is situated along a similarly oriented fault. Relocations of the La Habra Sequence consistently reveal that these events are oriented along a northeast-southwest striking fault, beginning at the Whittier Fault and extending towards the Coyote Hills Fault System. This orientation, in combination with the focal mechanisms of this sequence, would imply the existence of a steeply dipping or near vertical left-lateral strike-slip fault.
- Resource Type:
- Graduate project
- Campus Tesim:
- Pomona
- Department:
- Geological Sciences
8. The Stanislaus Group in a Beheaded Drainage: Tectonics at the Margin of the Sierra Nevada Microplate
- Creator:
- Schubert, Rosalie, Power
- Description:
- West of Bridgeport Valley near the Sierra Nevada crest, the Little Walker Caldera erupted Late Miocene Stanislaus Group lavas (Table Mountain Formation) and ignimbrites (Eureka Valley Tuff). Remnants of these rocks are now distributed from the western Sierra Nevada foothills across the range and into the Walker Lane. This wide distribution is attributed to the lavas flowing down paleochannels, and provides an excellent marker for post-emplacement deformation in the region. Priest (1978) documented a thick section of these lavas along Flatiron Ridge and other peaks surrounding Buckeye Canyon, including four members in stratigraphic order: Lower, Large Plagioclase, Two-Pyroxene, and Upper Member. 40Ar/39Ar geochronology indicates these Table Mountain Formation Lavas erupted from 10.4-9.5 Ma. Lithologically similar lavas have been identified near Rancheria Mountain, geochemical and paleomagnetic data support this correlation. The lavas flowed down a now-beheaded late Miocene drainage, supporting a westward shift of the Sierra Nevada crest since the Late Miocene.
- Resource Type:
- Thesis
- Campus Tesim:
- Fresno
- Department:
- Earth and Environmental Sciences