Tectonic geomorphology of the Chukchi borderland: constraint for tectonic reconstruction models

Thesis (M.S.) University of Alaska Fairbanks, 2009"The Chukchi Borderland is a region of extended continental crust within the Amerasia Basin and is bounded on one side by oceanic crust of the Canada Basin. Because of its central location within the basin, tectonic models for the reconstruction of the Arctic Ocean, must include the Chukchi Borderland although there is no consensus about its pre-rift location or kinematic development. In recent years bathymetric data have been collected that can offer constraint on the tectonic evolution of the Amerasia Basin by providing details about the geomorphology of the intra-basinal ridges allowing comparison of bathymetric features to those in other ocean basins. Bathymetric information in conjunction with multi-channel seismic and chirp sub-bottom profiler data show the location and strike of inferred faults used to determine rift directions which then provide constraint on tectonic reconstructions. The central Amerasia Basin, which includes the Chukchi Borderland, Mendeleev Ridge and south central Alpha Ridge, has experienced significant extension in generally the same direction and probably during one event. This type of plate boundary scale extension requires the development of accommodation faulting or transfer zones that facilitate the amalgamation of long fault segments. Features consistent with this type of faulting are observed throughout the Chukchi Borderland. There is no evidence of compression along the Northwind Ridge nor is there any indication of a strike-slip boundary within the Northern Chukchi Borderland as some tectonic models suggest. Whichever model is preferred, the geomorphology of the intra-basinal ridges must be taken into account and used as constraint for the reconstruction of the Amerasia Basin"--Leaf iii1. Introduction -- 1.1. Overview -- 1.2. Amerasia Basin provinces -- 1.3. Bathymetry and tectonic reconstructions -- 1.3.1. Early ideas -- 1.3.2. Heezan and Ewing -- 1.3.3. Plate tectonics and Cold War data -- 1.3.4. New data, new methods -- 2. Method -- 2.1. Bathymetric comparisons -- 2.1.1. Healy data -- 2.1.2. Seismic reflection -- 2.2. Geomorphic considerations -- 2.2.1. Landslides -- 2.2.2. Slope gullies -- 2.2.3. Pockmarks -- 2.2.4. Fault scarps -- 3. Observations -- 3.1. Amerasia basin -- 3.1.1. Subduction in the Arctic -- 3.1.2. High Arctic large igneous province (HALIP) -- 3.1.3. Dredged rock samples, 2008 -- 3.1.4. Radiating dyke swarm -- 3.2. Amerasia basin summary -- 3.2.1. Extension on Alpha and Mendeleev ridges -- 4. Chukchi borderland -- 4.1. Chukchi borderland bathymetric analogue -- 4.1.2. Northern Chukchi borderland and Nautilus basin -- 4.2. Northwind ridge -- 4.2.1. Northwind escarpment -- 4.3. Boundaries of major Northwind Fault Block -- 4.3.1. Hanna Canyon -- 4.3.2. Sags and Listric slump faulting -- 4.4. Compression in the borderland? -- 4.4.1. Seismic evidence for extension -- 4.5. Northwind basin -- 4.6. The Chukchi Plateau -- 5. Plate boundary scale rifting in the Chukchi borderland -- 5.1. Transfer zones -- 5.1.1. Central Chukchi rift -- 5.1.2. Remnant accommodation zones -- 6. Summary and conclusions -- References cited

Satellite Water Column Data for Hydrography

Optical-band satellite images selected for satellite-derived bathymetry (SDB) analysis require clear water with low turbidity. As a result, image selection processes exclude images with excess turbidity regardless of cause. Images with water-column turbidity contain valuable information. Under certain conditions, vortex patterns in navigable waters are present in satellite imagery. Although vortex-induced turbidity excludes these images from SDB processing, the presence and shape of these vortices contain information relevant to hydrography. In this observational study, we use two case studies to describe vortex patterns and environmental conditions leading to their formation and then explore novel hydrographic survey applications of these phenomena.Las imágenes satelitales de banda óptica seleccionadas para el análisis debatimetría derivada de satélites (SDB) requieren agua clara con una baja turbidez.Como resultado, los procesos de selección de imágenes excluyen las imágenescon exceso de turbidez, independientemente de la causa.Las imágenes con turbidez en la columna de agua contienen información valiosa.En determinadas condiciones, los patrones de vórtices en aguas navegables estánpresentes en las imágenes satelitales. Aunque la turbidez inducida por losvórtices excluye estas imágenes del procesado SDB, la presencia y la forma deestos vórtices contienen información relevante para la hidrografía. En este estudiode observación, utilizamos dos estudios de casos para describir los patrones delos vórtices y las condiciones ambientales que llevan a su formación y luegoexploramos nuevas aplicaciones de estos fenómenos a los levantamientoshidrográficos.Les images satellitaires en bande optique sélectionnées pour l'analyse de labathymétrie dérivée par satellite (SDB) nécessitent une eau claire et de faibleturbidité. Par conséquent, les processus de sélection d'images excluent les imagesprésentant une turbidité excessive, quelle qu'en soit la cause.Les images qui montrent la turbidité dans la colonne d'eau contiennent desinformations précieuses. Dans certaines conditions, les images satellitairesmontrent des tourbillons dans les eaux navigables. Bien que la turbidité induite parles tourbillons exclue ces images du traitement SDB, la présence et la forme deces tourbillons contiennent des informations pertinentes pour l'hydrographie. Danscette étude basée sur l'observation, nous utilisons deux études de cas pour décrireles configurations des tourbillons et les conditions environnementales qui ontconduit à leur formation, puis nous explorons de nouvelles applications de cesphénomènes pour les levés hydrographiques

The Caledonian suture in the high Arctic? New Data from the Chukchi Borderland, Amerasia Basin

The Chukchi Borderland (CB) is a bathymetric high in the Arctic Ocean that is extended by N-S and E-W striking faults. Based on sediment cores of talus slope fragments at the base of the Northwind Ridge (NWR), basement of the CB was previously interpreted as a Paleozoic platform sequence comparable to passive margin strata of western Laurentia (Grantz et al., 1998). The discovery of Silurian (~430 Ma) orthogneiss dredged from a fault scarp in the central CB suggests instead that the CB is a displaced fragment of the Caledonian orogen (Brumley et al., 2008). U-Pb geochronology of zircon suites from rocks dredged from the NWR and central CB fault scarps help resolve the make-up of the CB basement. Samples from the central CB are believed to represent the country rocks of the previously dated Silurian orthogneiss. They consist mostly of paragneiss and lesser orthogneiss intruded by leucosomal segregations, all deformed and metamorphosed to amphibolite facies with assemblages Qtz Kfs Plag Bt Grt ± Ms ± Chl (retrograde) with accessory zircon, sphene and apatite. The abundance of Kfs Plag Bt in paragneiss samples suggest a volcanogenic sediment protolith. Dynamic recrystallization of quartz by grain-boundary migration and recrystallization/myrmekite development along the edges of feldspar crystals suggest final deformation at temperatures of ~450 C. U-Pb geochronology of zircon from an orthogneiss sample from the central CB yields an age of 499.2 ± 0.9 Ma with late Neoproterozoic (600 Ma) and Mesoproterozoic - early Paleoproterozoic (1100-1700 Ma) grains. Detrital zircon geochronology from four paragneiss samples show a broad range of ages between 480-650 Ma with a dominant age peak ~500 Ma. Lesser, mostly discordant, Mesoproterozoic and Paleoproterozoic zircons are also present. The paragneiss sampled represent an arc-proximal sediment intruded by Silurian granitoids. Dredge samples from the NWR consist of deformed and metamorphosed calcareous sandstones, low-grade phyllites and highly altered but undeformed basalts. Low-grade (sub to greenschist facies) deformation is indicated by pressure solution cleavage in phyllites and minor recrystallization of quartz in sandstones. Detrital zircons from a silty phyllite from the NWR display age peaks of 1070-1170, 1600-2000 and 2300-3000 Ma. These peaks are known to be characteristic of sediments deposited along the northern passive margin of Laurentia, developed as the result of the breakup of Rodinia in the Late Precambrian and existing as a passive margin until the onset of the Caledonian orogeny. The contrasting rock types and geochronology from this study of dredged bedrock from the CB suggest the juxtaposition of a Cambro-Ordovician volcanic arc terrane intruded by Silurian granitoids with sedimentary rocks representing the northern margin of Laurentia, thus providing a more accurate geologic tie point of the Chukchi Borderland back to the region of Pearya, Lomonosov Ridge and Svalbard. This new data argues against previous interpretations of the CB as part of the Proterozoic to Jurassic passive margin of western Laurentia (Grantz et al. 1998) as well as the restoration of CB to the Chukotka margin of Russia (Lawver et al. 2011)

Petrography and U-Pb zircon geochronology of Caledonian age orthogneisses dredged from the Chukchi Borderland, Arctic Ocean

The Caledonian orogenic belt developed in the Ordovician to Devonian affecting northern Europe, Greenland and Arctic Canada. Caledonian deformational trends continue into the Arctic region disappearing at the rifted margin of the Arctic Ocean. Syn-orogenic magmatism in the Barents region date deformation of Grenvillian basement during the Caledonian event to be between about 450-410 Ma (Johansson et al., 2005; Gee et al., 2006; Gee and Tebenkov, 2004). Over 500 kilos of metamorphic rock was dredged from outcrops in the central Chukchi Borderland in 2009 (HLY0905) that included amphibolites and orthogneisses metamorphosed to amphibolite facies continuing to deform under greenschist conditions. Zircons were separated from two orthogneiss samples from this dredge, and single grain zircon U-Pb ages were determined by SHRIMP analysis be 428 Ma ± 3.4 for both samples (N=60). One sample had several zircon grains with distinct igneous cores that ranged in age from about 850-1000 Ma. Grenville age plutons (1000-910 Ma) that were later involved in Caledonian deformation and intruded by 450-410 Ma aged plutons are found on western and eastern Svalbard (Johansson et al., 2005), eastern Greenland, and the Pearya Terrane of northern Ellesmere Island (Trettin,1986, 1992). The Franklinian basement of Arctic Alaska and Canada do not share these Grenvillian ages (Trentin et al, 1987). This suggests that the inherited zircon cores in the Chukchi Borderland orthogneisses were derived, at least in part, from an older Grenvillian basement like that of Pearya, Svalbard and parts of Greenland and later intruded by Caledonian aged granites

Dredged Bedrock Samples from the Amerasia Basin, Arctic Ocean

Between 2008-2012, as part of the U.S. Extended Continental Shelf project in the Amerasia Basin, Arctic Ocean, 17 dredges were successfully collected sampling the first rock outcrops in the Chukchi Borderland and surrounding regions for the purpose of describing the geologic nature of the bathymetric features in this area. Multiple lines of evidence indicate that the specimens were collected from submarine rock exposures and were not samples of ice rafted debris, common in the ice covered waters of the Arctic Ocean. Using the USCGC Healy, each dredge was collected along very steep slopes (\u3e35 degrees) measured with high resolution multibeam swath bathymety data. Each haul yielded samples of similar lithologies and identical metamorphic grade with manganese crusts on the surfaces exposed to seawater and fresh surfaces where the rocks were broken from outcrop. High tension pulls on the dredge line also indicated sampling of bedrock exposures. Dredged samples from a normal fault scarp in the central Chukchi Borderland consisted of Silurian (c. 430 Ma) orthogneisses that intruded older (c. 487-500 Ma) gabbros and luecogranties that were all metamorphosed to amphibolite grade (Brumley et al., 2011). Samples from the northern Northwind Ridge consisted of metasediments (greenschist facies) interpreted to have been deposited in a proximal arc setting with detrital zircon U-Pb age peaks at 434, 980 Ma with lesser peaks between 500-600, 1100-2000 Ma, and rare 2800 Ma grains (Brumley et al, 2010). Other dredges in the region of the Northwind Ridge yielded deformed and metamorphosed calcareous sandstones and low-grade phyllites (O\u27Brien et al., 2013). Taken together these rocks indicate a relationship to the Pearya Terrane of northern Ellesmere Island and S.W. Svalbard that were thought to represent a Cambro-Ordovician volcanic arc terrane that was involved in Caledonian orogenesis (Brumley et al., 2011). These findings constrain plate tectonic reconstruction models and bring into question long held ideas that the Chukchi Borderland was made up of an undeformed platformal sequence that was part of the Laurentian passive margin from Proterozoic through Jurassic time (e.g. Grantz et al., 1998). Dredges collected along fault scarps that border the edges of the Nautilus Basin yielded undeformed but highly altered volcaniclastic rocks that were deposited in a shallow water setting and contain primary potassium feldspar phenocrysts that are not associated with mafic magmas. Also in this region, several dredges contained undeformed Late Cretaceous (112, 88-80 Ma) basalts (Andronikov et al., 2008; Mukasa et al., 2009) interpreted to have been derived from a continental lithospheric source similar to continental flood basalts from other regions (Mukasa et al., 2009). These dredged rock samples not only have implications for the Extended Continental Shelf projects of Arctic nations, but add greatly to the body of geologic information about the history of the Arctic Ocean and provide the first ground truth as to the nature of the bathymetric features within the Amerasia Basin

First bedrock samples dredged from submarine outcrops in the Chukchi Borderland, Arctic Ocean

The Chukchi Borderland, a prominent bathymetric feature within the Arctic Ocean, has been interpreted as a fragment of an undeformed continental platform sequence rifted from the passive margin of Arctic Canada. Dredges collected for the U.S. Extended Continental Shelf project aboard the icebreaker U.S. Coast Guard Cutter Healy (cruise number HLY0905) recovered hundreds of kilograms of broken crystalline basement lithologies consisting of mylonitically deformed biotite-bearing amphibolite, garnet-bearing feldspathic gneiss, and augen-bearing orthogneiss from the Chukchi Borderland. Metamorphic zircon within the amphibolite and associated leucogranitic seams within these rocks yielded U-Pb zircon ages between ca. 480 and 530 Ma. Garnet-bearing feldspathic gneisses contain variably discordant Mesoproterozoic zircon, ca. 600 Ma igneous zircon, and ca. 485–505 Ma metamorphic overgrowths. While we interpret these gneisses as deformed and metamorphosed granitoids, they could, instead, have a very immature sedimentary protolith. The youngest rocks sampled were K-feldspar augen orthogneisses that yield ca. 430 Ma zircon crystallization ages. Whole-rock geochemistry and Sr-Nd isotopic data indicate that the orthogneisses are I-type calc-alkaline granitoids. All of the basement rocks including the orthogneisses are variably metamorphosed and mylonitized. Collectively, the U-Pb age, geochemistry, and fabric of the dredged Chukchi Borderland basement samples indicate that they represent Neoproterozoic–Ordovician orogenic crust and Silurian arc batholithic rocks. This geologic origin is inconsistent with the Neoproterozoic to early Paleozoic passive margin history of western Arctic Canada to which the Chukchi Borderland has been previously correlated. We alternatively propose that the basement of the Chukchi Borderland is related to the peri-Laurentian composite terranes of Pearya and western Svalbard that have similar geologic histories

Petrography and U-pb, Detrital Zircon Geochronology of Metasedimentary Strata Dredged from the Chukchi Borderland, Amerasia Basin, Arctic Ocean

In 2008-2009, twelve dredges were taken aboard the USCGC Healy from outcrops along the Alpha Ridge, Northern Chukchi Borderland, Northwind Ridge and the Chukchi Plateau in the Arctic Ocean as part of the U.S. Extended Continental Shelf Project. To ensure sampling of outcrop, steep bathymetric slopes (\u3e40°) with little mud cover were identified with multibeam sonar and targeted for dredging. The first dredge from Alpha Ridge yielded volcaniclastic sedimentary rocks deposited from a phreatomagmatic eruption in shallow water