Little Ice Age (LIA) deposits are recognized on Mt. Tbielsen, southern Oregon Cascades (43° 9' N, 122° 3' W), based on particle morphology and relative position. The initial advance, Lathrop 1, created a sharp-crested moraine and a protalus rampart within 200 m of the headwall. The retreat of the glacier and recent ice movement, Lathrop 2, is recognized by the deformation of the moraine and a mantle of "protalus till" creating a polygenetic "push-deformation'' moraine. Both the moraine and the protalus rampart have sparse vegetation, no lichens, and a lightly weathered Cox/C soil. This sequence is correlative with LIA Phase 1 and Phase 2 on Mt. Jefferson, central Oregon Cascades, and is broadly correlated with LIA deposits throughout the Cascades, Sierra Nevada, and Rocky Mountains. There is no evidence for pre-LIA deposits at Mt. Thielsen. The ELA on Lathrop Glacier (2450 m) is lower than ELAs on nearby glaciers. The glacier probably exists because of its preferential topographic position and extensive debris cover; thus, if annual snowfall decreases the glacier will persist longer than a similar sized bare ice glacier. Conversely, a growing protalus rampart may indicate an increase in annual snowfall but not necessarily a decrease in annual temperatures. The lack of older Neoglacial deposits on Mt. Thielsen may be a result of insufficient snowfall to maintain or advance the Lathrop Glacier. As such, the LIA may represent a period when climatic conditions were more severe than at any other time in the Neoglacial. Boulder size, shape, and orientation proved useful for classifying geomorphic features and assessing the relative ages of slopes. However, soils are the best method for correlating deposits in the cirque with other locations. Soils beyond the moraine are developed in Mazama ash and have moderately developed Bw horizons, depth to weathering over 70 cm, and Harden's PDI for B horizons of 2.10-3.64. Soils are Typic Vitricryands.

published_or_final_version / abstract / Earth Sciences / Doctoral / Doctor of Philosophy

published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy

published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy

The Trans-North China Orogen (TNCO) has been recognized as a continent-continent collisional belt along which the Eastern and Western Blocks amalgamated to form the North China Craton. However, controversy has surrounded the timing and tectonic processes involved in the collision between the two blocks, ranging from the westward-directed subduction with final collision at ~2.5 Ga, through the west-dipping subduction with two collisional events at ~2.1 Ga and ~1.85 Ga, to the eastward-directed subduction with final collision at ~1.85 Ga. This project aims to present detailed lithostratigraphic, geochronological and isotopic data for the low-grade supracrustal successions in the TNCO to examine current models and to establish a reasonable scenario for the tectonic evolution of the TNCO in the Paleoproterozoic. The low-grade supracrustal successions include the Hutuo and Yejishan Groups in the middle sector of the TNCO and the Songjiashan, Lower Zhongtiao, Upper Zhongtiao, Danshanshi and Songshan Groups in the southern sector. Lithostratigraphic data indicate that the Songjiashan, Lower Zhongtiao Groups and lower parts of the Hutuo and Yejishan Groups are composed of metaclastic rocks, carbonates and metavolcanic rocks, interpreted as back-arc basin deposits, whereas the Upper Zhongtiao, Danshanshi, Songshan Groups and the upper parts of the Hutuo and Yejishan Groups consist only of metaconglomerates and metasandstones, interpreted as foreland basin deposits. To constrain the provenance and maximum depositional ages for these low-grade supracrustal successions, the LA-MC-ICP-MS technique was applied to analyze U-Pb and Hf isotopic compositions for detrital zircons from them. For the Hutuo and Yejishan Groups, we found major age peaks at ~2.5 and ~2.2 Ga and minor amounts of 2.8-2.6 Ga detrital zircons, which are consistent with ages of the lithological units in the middle sector of the TNCO. On the other hand, for the Songjiashan, Lower Zhongtiao, Upper Zhongtiao, Danshanshi and Songshan Groups, detrital zircons from them have the major age population of 2.85-1.95 Ma and the minor age population of 3.6-3.1 Ga, of which the former is comparable with ages of the lithological units in the southern sector of the TNCO and the latter was derived from the Paleoarchean and Mesoarchean crust of the Eastern Block. The maximum depositional ages of the low-grade supracrustal successions have also been well constrained in this study. For the back-arc basin deposits, their maximum depositional ages were constrained between ~2.15 and ~2.10 Ga. For the foreland basin deposits, the presence of ~1.85 Ga detrital zircons indicates that they were deposited after this time. Taken together, we present a brief scenario for the evolution of the sedimentary basins in the TNCO. At 2.15-2.10 Ga, a series of back-arc basins developed behind an “Andean-type” arc that were subsequently incorporated into the TNCO during the collision of the Eastern and Western Blocks. At ~1.85 Ga, the two blocks collided along the TNCO, resulting in the crustal thickening followed by rapid exhumation/uplift, which shifted the back-arc basins to foreland basins. Such a shift in the late Paleoproterozoic supports the model that the collision between the Eastern and Western Blocks occurred at ~1.85 Ga. / published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy

A study of a poorly understood limestone unit was conducted to contribute temporal information necessary to unraveling a series of cryptic events for a complex geologic region containing economically important natural resources. Secondary objectives included understanding the environment of deposition and regional influences. Biostratigraphic and sedimentologic information observed from the Uitoé Limestone went to reconstructing the paleoenvironment, constraining the age of deposition and indicating the paleogeographic faunal associations. Facies associations indicate a middle ramp depositional setting common in many location in the Tethys Sea. Paleogeographic associations for the microflora and fauna indicate a Tethyan signature present but a lack of Australian influence. A combination of planktic and benthic foraminiferal assemblages for the region constrain the age of the Uitoé Limestone between the middle of the Lutetian and the Early Bartonian. / Department of Geological Sciences

Thesis (M.S.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 87-95). Also available on the World Wide Web.

Thesis (Ph. D.)--Rutgers University, 2007. / "Graduate Program in Geological Sciences." Includes bibliographical references (p. 219-232).

M.Sc. / The ca. 800 km2 Tete Complex of NW Mozambique is located at the eastern end of the 830 ±30 Ma Zambezi Belt, near the transition zone into the Neoproterozoic Mozambique Belt. The Complex is located just south of the Sanangoe Shear Zone where Mesozoic and Late Palaeozoic cover rocks obscure much of the region. Country rocks immediately in contact with the Tete Complex include amphibolitic gneiss, graphite-bearing marble, calcsilicate gneiss, muscovite and biotite schist and quartzite of the Chidue Group. The Tete Complex may have been intrusive into the Chidue Group, although there is evidence inferring tectonic emplacement. Those few contact exposures that exist are equivocal. Some of the rocks within the Tete Complex have been affected by metamorphism up to amphibolite grade, although large proportions of the rocks retain pristine magmatic mineralogy and texture. The Tete Complex contains mafic, ultramafic and anorthositic rocks, dolerite dykes and minor Fe-Ti oxide-rich rocks that occur as rubble. Pyroxenite occurs as thin (<1-2 m), cumulate layers within gabbroic rocks. Most exposed anorthositic rocks occur in the Nyangoma area in the eastern part of the Tete Complex. The anorthosites and leucotroctolites are massive, coarse grained (2-3 cm), and contain plagioclase (An47-An57) megacrysts up to 10 cm in length, interstitial olivine (Fo59-Fobs) and orthopyroxene (En59- En75, mean A1203 = 1.84 wt.%) rimmed by clinopyroxene (mean = Wo 46En38Fs i6), pyrite and Fe-Ti oxides. Secondary biotite, iddingsite, epidote and green spinet are present. The stable coexistence of olivine and plagioclase limits the depth of emplacement to <7-8 kbar, or <20- 25 km; a relatively shallow level of emplacement is favored by the generally fine grain size of the gabbroic and doleritic rocks. Compositions of coexisting plagioclase and mafic silicates (orthopyroxene and olivine) are similar to those of massif-type anorthosites. Previously unmapped meta-anorthosite occurs along the western and northern margin (within the Sanangoe Shear Zone) of the Tete Complex and has been metamorphosed to amphibolite grade. The rock contains plagioclase (An38-An39), with the more Ab-rich compositions related to the formation of garnet (mean = A1m67GrotsPYI6Sp2). Metamorphic orthopyroxene (Enso-En53), clinopyroxene (mean = Wo37En38Fs25), mizzonitic scapolite (Me63), amphibole, biotite and apatite are present. High Cl contents in amphibole, scapolite and biotite (e.g., up to 4.7 wt. % in amphibole), suggest that a Cl-rich metamorphic fluid infiltrated the western margin of the Tete Complex. Olivine melagabbro from the north-central part of the Tete Complex contains plagioclase (An70-An26), olivine (Fo82-Fos4) and clinopyroxene (mean = WanEn1Fs0.2, mean A1203 = 2.56 wt. %), with primitive compositions compared to those in Nyangoma anorthositic rocks and pyroxenites. Pyroxenites are modally dominated by clinopyroxene (mean = Wo46-48En36-39Fsi3-18) with accessory interstitial plagioclases (Ano-An45) and discrete and exsolved orthopyroxenes (En 56-En75). Clinopyroxenes with high A1203 contents up to 9 wt. % are similar to high-Al pyroxene megacrysts. One sample of pyroxenite contains orthopyroxene (En56-En60) and plagioclase (An40-An45) with more evolved compositions compared to those in Nyangoma anorthositic rocks and olivine melagabbro. Normal Fe4- and Na-enrichment trends accompanying fractionation from magmas that may be common to the Nyangoma anorthositic rocks, pyroxenites and olivine melagabbro, are associated with an increase in Al relative to Cr along a line of nearly constant relative Ti content. Gabbro contains olivine and plagioclase crystals that are commonly zoned, thus ranging widely in composition (Fool -Fos°, Anss-Ans2)• Clinopyroxene (mean = Wo36En47Fsi6) constitutes ca. 34 modal % of gabbro. New whole-rock (Nyangoma anorthosite and leucotroctolite) and mineral (plagioclase, clinopyroxene and orthopyroxene) Sm-Nd isotopic data yields ages between 975 ±33 Ma and 1041 ±131 Ma. The igneous crystallization age of the anorthositic rocks is estimated at 1025 ±79 Ma (9-point whole-rock regression). Rb-Sr isotopic compositions for whole-rock samples reveal no meaningful age relationships. Initial Nd isotopic compositions (calculated at 1.0 Ga) correspond to E Nd values between +3.5 and +4.5 (mean = +4.1) with Is, = 0.70276 — 0.70288 (mean = 0.70282), both inferring magmatic derivation from a depleted mantle source, possibly with little or no contamination by Archaean crustal components. TDM model ages range between 1074 and 1280 Ma (mean = 1148 Ma). There is a striking similarity between the Tete Complex anorthosites and those of SW Madagascar in terms of Nd isotopic compositions and the nature of country rocks; in both regions the anorthosites were emplaced either magmatically or tectonically into shelf-type supracrustal metasediments (marbles, quartzites, graphitic schists, etc.). Anorthosites intruded similar country rocks in Draining Maud Land, eastern Antarctica. Although anorthosites from Mozambique and Madagascar share a common depleted mantle signature with little or no contamination by Archaean crustal components, a direct stratigraphic correlation between these two areas (and possibly eastern Antarctica), awaits further geological and geochronological data.

Ph.D. (Geology) / The successions of the Cape- and Karoo Supergroups preserve an integrated history of sedimentation along the paleo-Pacific margin of Gondwana from the Paleozoic to the Early Mesozoic. The Cape- and Karoo Supergroups have been well studied with regard to stratigraphy, sedimentary facies and depositional environment. However, the nature and location of their source regions, especially for the changeover from deposition within an Atlantic-type continental margin basin for the successions of the Cape Supergroup to an Andean-type continental foreland basin for some of the units of the Karoo Supergroup, remains poorly understood. In order to shed light on the nature of these source regions, a comprehensive U-Pb detrital zircon study of the successions of the Cape- and lower Karoo Supergroups was launched. A representative number of samples from the upper and lower successions of the Table Mountain- Bokkeveld- and Witteberg Groups of the Cape Supergroup as well as the Dwyka and Ecca Groups of the Karoo Supergroup were collected throughout the western, southwestern and southern Cape region. A few samples of the Dwyka Group were also collected within the more eastern outcrop regions of the succession located in Kwazulu-Natal. The sedimentary rocks of the Natal Group and Msikaba Formation have long been regarded as coeval with the Cape Supergroup. Similar to the successions of the Cape- and Karoo Supergroups, very little is known about their sedimentary source regions. Also, their relative age of sedimentation remains poorly constrained. The U-Pb detrital zircon study of the successions of the Cape- and lower Karoo Supergroups was thus extended so as to include the successions of the Natal Group and Msikaba Formation. The detrital zircon age populations of the successions of the Natal Group and Msikaba Formation would not only improve the present understanding with regards to the sedimentary source regions to these units but would also facilitate the evaluation of possible correlations between these units and the stratigraphic units of the Cape Supergroup. Samples of both the lower Durban Formation and the upper Mariannhill Formation of the Natal Group and the Msikaba Formation (which is presently regarded as being part of the Cape Supergroup) were therefore collected within their respective outcrop regions in the Kwazulu-Natal area. The similarities in litho- and bio-stratigraphy between the successions of the Cape- and Karoo Supergroups and those of the Ordovician to Early Permian successions of the Ventania System and the Ordovician to Silurian successions of the Tandilia System in Argentina have long been recognized. Although the detrital zircon populations of some of the formations within these Systems have been evaluated in the past, it is yet to be determined whether these successions and those of the Cape- and lower Karoo Supergroups have certain source regions in common. In order to facilitate such a comparison, samples of selected units of the Ventania System were therefore collected near Sierra de la Ventania, while a sample of the Balcarce Formation of the Tandilia System was obtained near Mar del Plata. The detrital zircon age populations of the successions of the Ventania and Tandilia Systems were also further evaluated in the light of establishing or confirming a time-correlation between these formations and those of the Cape- and lower Karoo Supergroups. U-Pb age determination of the detrital zircons population of the samples was conducted by means of Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS). Although LA-ICP-MS is a routine, well-established technique where the U-Pb age determination of detrital zircons is concerned, it was yet to be established at the centralized analytical facility of the University of Johannesburg, SPECTRUM, using the instrumentation currently available (i.e. 213nm Nd:YAG laser coupled to Quadrupole-based ICP-MS). The U-Pb age determination of detrital zircons was therefore preceded by a fair amount of instrument optimization and method development. Well studied shortcomings of U-Pb detrital zircon dating by LA-ICP-MS such as laser induced elemental fractionation, mass discrimination effects and as well as the possible occurrence of minor common-Pb needs were addressed and corrected for. The detrital zircon populations of successions in the Cape Supergroup have a distinct major Neoproterozoic to Early Cambrian age component, which can be attributed to an input of detritus from successions related to the Pan-African Orogeny in South Africa, such as the Gariep- and Saldania Belts located towards the north of the Cape Basin. A substantial amount of Mesoproterozoic detrital zircon grains is also present in all the samples from the successions of the Cape Supergroup. These grains of Mesoproterozoic age were probably derived from the Namaqua-Natal Metamorphic Province, which is also regarded as the source of some minor amounts of Paleoproterozoic detrital zircon grains. The near absence of Archean grains from the detrital zircon populations of the successions of the Cape Supergroup is notable, and is thought to be due to the Namaqua-Natal Metamorphic Province acting as a geomorphological barrier at the time of their deposition. The minor Paleozoic (Ordovician to Carboniferous) detrital zircon populations in the samples from the formations of the Cape Supergroup increase progressively upwards through the succession. ....