Subalklaine Volcanism in the Eastern Basin and Range Province: Examples from the Miocene McCullough Range Volcanic Field and the Pliocene to Holocene Black Rock Desert Volcanic Field

This dissertation is composed of three papers that apply geologic mapping, whole rock geochemical and isotopic analysis, and mineral chemistry to describe two large, long-lived (~6 million years), and compositionally heterogeneous volcanic fields and posit sources of the rock types present in each. These fields are the McCullough Range in southern Nevada, which was a locus of volcanic activity from ~19 - 12 Ma and the Black Rock Desert volcanic field in west-central Utah, which began forming at ~6 Ma and is still active today, with the most recent eruption occurring ~720 years ago. Chapter Two is composed of a paper summarizing the physical and chemical properties of the Black Rock Desert (BRD) and Markagunt Plateau (MP) volcanic fields in Utah. Both the BRD and MP volcanic fields have been active for about 6 million years and are composed of similar rock types. In the last 2.5 million years, volcanoes in both the BRD and MP fields erupted tholeiitic basalts and calc-alkaline intermediate rocks. Comparing and contrasting the chemical attributes of the two volcanic fields led to the conclusion that despite differences in the amount of crustal extension, subalkaline rocks in both volcanic fields are both common and share common petrogenetic histories. Chapter Three is a detailed study of a subfield of the BRD volcanic field: the ca. 2.7 - 2.1 Ma Twin Peaks volcanic field. The paper presents the results of detailed mapping and extensive sampling, and utilizes both whole rock and mineral chemistry to propose a basic petrogenetic model for the formation and evolution of the Twin Peaks caldera. Two major conclusions came from this study: 1) the Twin Peaks caldera was produced in a similar fashion to the 1912 Novarupta-Katmai eruption in Alaska, in that the earliest eruptions, including those that formed the Twin Peaks caldera, occurred ~10 km west of the actual location of the caldera itself. 2) The range in compositions and order of eruptions for the first episode was the product of partially emptying a zoned magma chamber with rhyolite at the top and basalt at the bottom of the erupted portion. Chapter Four is focused on the lower to middle Miocene strata of the McCullough Range volcanic field. Located along the western margin of the northern Colorado River extensional corridor (NCREC), the McCullough Range volcanic field has two attributes which make it ideally suited for detailed geochemical study: 1) it was active prior to and during large magnitude extension in the central Basin and Range Province; and, 2) it is tilted but not as highly extended or altered as volcanic fields within the NCREC itself. The major findings of this study include the discovery of the pre-extensional Enigma stratovolcano. The Enigma Volcano is comprised of a chemically enriched lower portion and of a calc-alkaline upper portion. Detailed mapping and chemistry suggested that volcanic rocks formed during early magmatic activity in the NCREC obtained their chemical enrichments (high volatiles, P, Zr, Sr, Ba, and LREE) from partial melting of a melt-metasomatized and subduction-modified sub-continental lithospheric mantle. In contrast to the early activity, later pre-extensional NCREC volcanism, typified by the upper Enigma Volcano, was the typical calc-alkaline intermediate composition associated with the early phases of extensional activity in the rest of the BRP

Using cryptotephra to link Neanderthal and AMH Middle Paleolithic sites in NW Italy.

Establishing robust and reliable chronologies at archaeological sites is essential for understanding the sequence and timing of past events. At Middle and Upper Paleolithic sites like Arma Veirana and Riparo Bombrini, robust chronologies are especially important for answering questions regarding the Middle-to-Upper Paleolithic transition in Europe. Arma Veirana is located in the Ligurian pre-Alps of northwest Italy and Riparo Bombrini is located along the Mediterranean coast, about 80 km away. Both sites have deposits that overlap in age and contain cultural industries attributed to Neanderthals and anatomically modern humans (AMH). Stratigraphic evidence suggests that Neanderthals may have been present at Arma Veirana while AMHs were present at Riparo Bombrini, making it an ideal area to understand the interactions and dynamics of these two species during a key transitional phase. Cryptotephra, also known as microscopic volcanic ash, were recently identified at Arma Veirana in a stratigraphic unit known as the Black Mousterian (BM). AMS radiocarbon dates of charcoal samples collected in the BM, range from 43,781 to 43,121 (68.2%) cal. Yr. BP. Because these dates are close to the measurement limit of radiocarbon, the presence of cryptotephra provides a way to test these existing dates as well as establish a precise isochron to correlate with other sites. Major element chemistry obtained by electron microprobe indicate that the shards found in the BM layers are high silica rhyolite (>75 wt. %) with FeO < 1 wt.%. Trace elements by LA-ICP-MS show depletions in Ba, Sr, and Eu and an enrichment in Th, U and Pb. Both major and trace chemistries show unique geochemical signatures and are rare for volcanoes in the central Mediterranean region. The source volcano is currently unknown; however, this unique chemistry eliminates volcanoes from Iceland, North America, Canaries or Azores, and Aeolian Islands. Potential source volcanoes are located in Turkey (Acigol Dagi Volcano), the Carpathian Mountains (Ciomadul Volcano) and Greece (Nisryos volcano and Santorini Caldera). To test the hypothesis that Neanderthals were displaced from the coast when modern humans arrived in the region, I will take cryptotephra samples at Riparo Bombrini in the summer of 2018 with the goal of directly linking both sites. Identifying the same cryptotephra horizon at Riparo Bombrini will provide an unprecedented temporal correlation between the two sites. This will lead to a better understanding of Neanderthal and AMH interactions during the Middle to Upper Paleolithic transition in Europe

Humans thrived in South Africa through the Toba eruption about 74,000 years ago.

Approximately 74 thousand years ago (ka), the Toba caldera erupted in Sumatra. Since the magnitude of this eruption was first established, its effects on climate, environment and humans have been debated. Here we describe the discovery of microscopic glass shards characteristic of the Youngest Toba Tuff-ashfall from the Toba eruption-in two archaeological sites on the south coast of South Africa, a region in which there is evidence for early human behavioural complexity. An independently derived dating model supports a date of approximately 74 ka for the sediments containing the Youngest Toba Tuff glass shards. By defining the input of shards at both sites, which are located nine kilometres apart, we are able to establish a close temporal correlation between them. Our high-resolution excavation and sampling technique enable exact comparisons between the input of Youngest Toba Tuff glass shards and the evidence for human occupation. Humans in this region thrived through the Toba event and the ensuing full glacial conditions, perhaps as a combined result of the uniquely rich resource base of the region and fully evolved modern human adaptation