The Caucasus is a land corridor between the Black and Caspian seas, linking Africa to Northern Eurasia, and is considered a migratory route for Neanderthals and Anatomically Modern Humans (AMH). Numerous cave sites in Armenia, Azerbaijan, Georgia and southwestern Russia indicate that Neanderthals and AMH occupied the region, but poor chronological control meant that the precise timing of the occupations was unknown. This work involved identifying and geochemically characterising volcanic ash layers (tephra) in archaeological cave and open air sites spanning approximately 125 ka to 30 ka to generate a tephrostratigraphic framework. This framework was used to correlate the sites and assess the synchronicity of Neanderthal and AMH occupation across the region. Tephra investigations were also carried out on a core (M72/5-25-GC1) from the southeast Black Sea (that spans the last ~ 60 ka), with the aim of linking the archaeological sites to this palaeoenvironmental archive, to investigate the impact changes in climate had on the archaeology in the region. Eleven of the archaeological sites investigated (Gubs rock shelter and Weasel Cave in Russia; Ortvale Klde, Ortvale Cave, Sakajia and Undo Cave in Georgia; Aghitue 3, Lusakert 1, Fantan and Kagasi in Armenia; and Azokh Cave in Azerbaijan) had tephra, 30 cryptotephras and 8 visible layers, preserved. Twenty-two tephra layers were identified in the Black Sea core, with distinct periods of frequent volcanic activity separated by long periods, up to 9 ka, of seemingly volcanic quiescence in the region. The glass chemistry of the tephra found in the archaeological sites and the core, determined using a wavelength-dispersive electron microprobe, was used to characterise and correlate the units between the sedimentary sequences. Although some widespread tephra from the major Mediterranean sources (3.6 ka Minoan eruption from Santorini, Greece and the ~39 ka Campanian Ignimbrite super eruption from Campi Flegrei, Italy) were identified in the Black Sea core, none of the archaeological sites contained Mediterranean tephra. Most of the tephra layers in the archaeological sites investigated and the Black Sea core are from sources in the Caucasus and Turkey. The limited information on the volcanic history and compositional data of these sources in the region does not allow most of the units to be correlated to particular eruptions or volcanoes. However, some of the cryptotephra units have been correlated to eruptions from Nemrut, Acigöl and Erciyes Dagi volcanoes in Turkey. Unfortunately, there are no tephra layers that are common to the Black Sea core and any of the archaeological sites, prohibiting direct correlation of the sites to this detailed palaeoenvironmental record. However, the ~30 ka Nemrut Formation (NF) eruption from Nemrut volcano, Turkey, is found in the Lake Van palaeoenvironmental record and in two of the archaeological sites. This allows the archaeological sites to be correlated to each other and palaeoclimate information can also be imported into these sites. More detailed characterisation of the proximal deposits may allow more units to be correlated to eruptions and will enable these distal records to be used to further constrain the tempo of explosive volcanic activity in the region. A few compositionally distinct tephra layers were found and a suite of new radiocarbon dates were obtained at various sites, allowing archaeological occupations to be dated and the synchronicity between sites to be assessed. A distinct rhyolitic tephra correlates a layer with an Upper Palaeolithic stone technology, associated with AMH, in Azokh Cave (Azerbaijan) to a layer in Sakajia cave (Georgia) that contains Neanderthal remains. This is clear evidence that AMH and Neanderthals were in the region (within 600 km) at the same time. Other sites have also been correlated with tephra. A dacitic tephra correlates a unit with an Upper Palaeolithic lithic and bone tool techno-complex in Ortvale Klde (Georgia) to a unit with a Middle Palaeolithic lithic assemblage in Lusakert 1 (Armenia). The Middle Paleolithic tool assemblage in Lusakert 1 is clearly different from the Upper Paleolithic assemblage that is clearly associated with AMH in Ortvale Klde, but it is not clear whether the other assemblage is associated with Neanderthals, archaic modern humans or AMH. This correlation between different lithic assemblages clearly indicates that there were different groups, with different technologies, occupying the region at the same time. The NF tephra is also found shallower in the sequences at both Lusakert 1 and Ortvale Klde. This time marker shows that the Middle Paleolithic assemblage is still being used in Lusakert 1 at ~30 ka, indicating that a less diverse stone techno-complex was used for a prolonged period of time in central Armenia. There does not appear to be any direct relationship between occupation in the region and the climate at the time, implying that this had little effect on the archaeological story in the region. A new radiocarbon based age model that combines new dates with published data for the sites within the Caucasus shows temporal overlap between AMH and Neanderthals in the region. This confirms the tephra correlations and clearly indicates both species co-existed in the Caucasus. The new radiocarbon data also suggest that AMH arrived in the region earlier than previously thought, at ~50-44 ka cal BP. The arrival of AMH in the Caucasus is now temporally similar to other early AMH sites in northern Eurasia.

No description available.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Science, 1979. / Microfiche copy available in Archives and Science. / Bibliography: leaf 93. / by Carolyn Alexandria Morrow. / M.S.

The Dinner Creek Tuff is a mid-Miocene rhyolitic to dacitic ignimbrite, consisting of four cooling units with 40Ar/39Ar ages 16--15 Ma. Previous geologists have suspected that the source of the tuff is located in northwestern Malheur County, eastern Oregon. This broad area is called the Dinner Creek Tuff Eruptive Center. This thesis summarizes field work, XRF/ICP-MS geochemistry, thin section petrography, and SEM feldspar analysis from the summers of 2015 and 2016. The main purpose of this study is to identify sources for the Dinner Creek Tuff units within the Dinner Creek Tuff Eruptive Center. The secondary purpose is to map lava flows that pre-date and post-date the Dinner Creek Tuff, and correlate them with regionally extensive volcanic units. Two volcanic centers related to the Dinner Creek Tuff were identified. The southern volcanic center, centered at Castle Rock, is a caldera and source of the Dinner Creek Tuff unit 1 (DIT1). Rheomorphic, densely welded DIT1 is over 300 m thick along the east side of Castle Rock. The northwestern margin of the caldera has been uplifted along faults, showing vertically foliated tuff dikes and associated mega-breccia deposits. Up to 200 m of incipiently welded tuffs, and fluvial volcanoclastic sediments were deposited on the caldera floor, which has been uplifted due to resurgence and regional extension, creating the complex structural relationships between the volcanic units. The northern volcanic center is located at Ironside Mountain, where densely welded rheomorphic Dinner Creek Tuff unit 2 (DIT2) is exposed in outcrops over 600 m thick. The top of the DIT2 consists of glassy, moderately welded tuff. Sources for the DIT2 are tuff dikes along the south and western flanks of Ironside Mountain. The thick deposits of DIT2 at Ironside Mountain indicate that the mountain is an uplifted caldera, herein named the Ironside Mountain caldera. Uplift may have been due to resurgence, but it is most likely due to normal faulting along the Border Fault, a major regional normal fault that strikes across the northern margin of the caldera. Pre-Dinner Creek Tuff lava flows occur throughout the study area, and can be correlated with the Strawberry Volcanics and the Basalt of Malheur Gorge. A distinct lava flow, herein called the Ring Butte trachy-basalt occurs within the center of the study area, and is distinct from regional lava flows. Following the eruptions of the Dinner Creek Tuff units 1 & 2, aphyric basaltic-andesite and icelandite intrude into, and overlie the intra-caldera tuffs and caldera floor sediments at both calderas. These aphyric lavas are similar in appearance and stratigraphic position with the regionally extensive Hunter Creek basalt. Porphyritic olivine basalt overlies the aphyric Hunter Creek basalt at the Castle Rock caldera. This porphyritic lava is similar in appearance and major/trace element geochemistry to the regional Tim's Peak basalt.

Large-volume silicic ignimbrites erupt from reservoirs that vary in composition, temperature, volatile content and crystallinity. The 9.7 Ma Devine Canyon Tuff (DCT) of eastern Oregon is a large-volume (>250 km3), compositionally zoned and variably welded ignimbrite. The ignimbrite exhibits heterogeneous trace element compositions, variable volatile content and crystallinity. These observations were utilized in the investigation into the generation, accumulation and evolution of the magmas composing the DCT. Building off previous research, pumices were selected from the range of trace element compositions and analyzed with respect to crystallinity, mineral abundances and assemblages. The DCT displays a gradational trace element enrichment and decrease in crystallinity from least evolved, dacite, at ~22% crystals to most evolved high-silica rhyolite at 3% crystals. Two distinct mineral populations of feldspar and clinopyroxene were identified in previous work, one belonging to the rhyolitic magma and the other to the dacitic magma. Volatile content derived from melt inclusion Fourier Transform Infrared (FTIR) spectrometer analysis revealed an increase in water content from 1.2 to 3.7 wt.% in the most evolved rhyolite. The DCT exhibits low and variable δ18O signatures, 4.52‰ to 5.76‰ , based on δ18O values measured on quartz and sanidine. Low δ18O signatures of all DCT rhyolites suggest the incorporation of hydrothermally altered crust into the melt. Furthermore, quartz phenocrysts from all high-silica rhyolite groups display dark oscillatory zoned cores and Ti-rich bright rims. These data provide insight into how these magmas were generated and subsequently stored in the crust. Commonalities of petrographic and compositional features among rhyolites, especially the zoning characteristics of quartz phenocrysts, exclude the possibility of storage and evolution in multiple reservoirs. Envisioning a scenario where all magmas are stored within a single reservoir prior to eruption and assuming rhyolites A and D are the product of partial melting. The mixing of A and D rhyolites produced rhyolite B, and subsequent mixing of intermediate rhyolite B and end-member rhyolite D generated rhyolite C. However, some trace element inconsistencies, between mixing model and observed intermediate rhyolites suggest a secondary process. Post mixing, rhyolites B and C require some modification by fractional crystallization to account for LREE and other inconsistencies between mixed models and observed rhyolites. Finally, the origin of the dacite is likely through mixing of group D rhyolite and an intrusive fractionated basalt, which could have led to the eruption of the Devine Canyon Tuff.

The study of the subsurface flow and distribution of water is critical to the evaluation of the unsaturated zone for a potential geologic high-level radioactive waste repository. This site is located at Yucca Mountain, Nevada in the northern Mojave Desert. and was chosen on the basis of its low precipitation, deep unsaturated zone, and layered volcanic rocks providing the potential for natural hydraulic barriers to reduce the downward percolation of water through the waste storage area. The detailed characterization of hydrologic properties is necessary to evaluate the mechanisms responsible for the distribution and flow of water in the unsaturated zone. Analyses in this study have provided detailed hydrogeologic units with unique hydrologic properties and hydraulic parameters. Porosity was determined to be a useful physical property for predicting hydraulic parameters, as it relates to the largescale deterministic processes that created the volcanic rocks. The detailed property dataset, along with field measurements of moisture status, temperature, and chemistry, were used to evaluate the potential for lateral diversion in the rocks above the potential repository. It was determined that lateral diversion is a small-scale process in this natural system. On the basis of analyses performed in this study, it is suggested that large-scale diversion is not likely to occur at this site. This mechanism should not, therefore, be relied upon to perform as a natural hydraulic barrier to flow reducing percolation through the unsaturated zone. / Graduation date: 2002

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No description available.

Geological evidence suggests large-scale continental extension during the breakup of the eastern Gondwana margin was the predominant force controlling rifting of New Caledonia from the eastern Gondwana margin and formation of the Tasman Sea in the Late Cretaceous. Tectonic models suggest slab-rollback forces elongated and thinned the crustal lithosphere detaching crustal fragments from the Gondwana margin. Current tectonic models lack detailed timing and placement of this crustal detachment with respect to New Caledonia based on lack of evidence (rocks). An isotope and paleomagnetic study was carried out on a bi-modal assemblage of volcanic rock exposed on the southwest side of New Caledonia in the Nouméa Basin. U/Pb isotope ages of zircon grains found within siliceous volcanic rock in the Nouméa Basin provide temporal evidence that volcanism persisted both before and after the breakup of the eastern Gondwana Continent (100-90 Ma) in the Late Cretaceous. Four isotope ages >97 Ma and a series (11 samples) ranging from 91-76 Ma constrain the siliceous volcanism of the Nouméa Basin to the Late Cretaceous. A paleomagnetic inquiry utilizing statistics of both McFadden/Reid and Fisher carried out on 16 Nouméa Basin siliceous and mafic in situ formations place the oldest volcanic units found within the Nouméa Basin at 650 S latitude as New Caledonia began to separate from Gondwana (~100 Ma). The data suggests a well-developed arc signature in the region, which persisted for at least 15 Ma in the Late Cretaceous. Compared to current tectonic models of the southwest Pacific Region from the Late Cretaceous to Eocene, our data suggests New Caledonia was further south on the eastern Gondwana supercontinent prior to rifting in the Late Cretaceous than current models. / Geologic background -- Tectonic setting -- Methods -- Sampling -- Results -- Discussion. / Department of Geological Sciences

The purpose of this study is to investigate the origin, source characteristics, evolution petrogenesis and emplacement mechanisms of Beypazari-Oymaaga&ccedil / granitoids. These granitoids are intruded into a metamorphic basement and nonconformably overlain by Neogene clastic rocks. Field work, petrographical and geochemical studies are carried out to determine the petrologic features and tectonic setting of the granitoid body. The Beypazari-Oymaaga&ccedil / pluton is a composite pluton with its host batholith, enclaves, aplite dykes and a pegmatite. The batholith is generally composed of quartz, K-feldspar, plagioclase and hornblende. Field observations and petrographic investigations indicate that the host batholith has granodiorite composition and shows distinct differences in the abundances of quartz, amphibole minerals (e.g., hornblende) and of enclaves. The samples taken from TavuktaSi Tepe contain relatively less amphibole and enclaves but more quartz. Compared with them, samples from the rest of the batholith have relatively abundant amphibole, K-feldspar megacrysts, and enclaves but less quartz. Enclaves derived from magma mixing/mingling processes are dioritic in composition. Geochemical data obtained from whole rock analyses show that the pluton is shallowly emplaced and has calc-alkaline, metaluminous to peraluminous chemistry. It is characterized by enrichments in LIL and LREE, especially in K, Rb and Th. Although, there is a distinct petrographic variation in the batholith, the geochemical characteristics are uniform throughout the pluton. The Oymaaga&ccedil / Granitoids which have I-type identity are typical representatives of magmatic arc environment. The present study suggests that the possible source of magma is the upper crust and can be compared with the coeval volcanism in Galatean Volcanic Arc.