Thesis (Ph.D.)--University of Melbourne, School of Earth Sciences, 2007. / Typescript. Includes bibliographical references (leaves 211-240).

Thesis (Ph.D.(Geology))--University of Pretoria, 2008. / Includes summary and abstracts in English. Includes bibliographical references and index.

No description available.

Η Ρόδος είναι το μεγαλύτερο σε έκταση νησί των Δωδεκανήσων και το πλέον απομακρυσμένο από την ηπειρωτική Ελλάδα. Παρουσιάζει σημαντικό γεωλογικό ενδιαφέρον αφού αποτελεί το ανατολικό όριο του νησιωτικού τόξου του Αιγαίου, το οποίο εκτείνεται από την Πελοπόννησο ως τη Μικρά Ασία συμπεριλαμβάνοντας επίσης τα νησιά Κύθηρα – Αντικύθυρα – Κρήτη – Κάσο - Κάρπαθο και συνδέει τις Ελληνίδες με τις Ταυρίδες οροσειρές. / Rhodes is the largest island of the Dodecanese and the farthest from the mainland of Greece. Presents important geological interest as it constitutes the eastern boundary of the Aegean island arc, which extends from the Peloponnese to Asia Minor also including the islands Kythira - Antikythyra - Crete - Kaso - Karpathos and connects the Greeks with the Taurid mountain ranges.

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

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

Cretaceous continental extension was accommodated by the development of the Paparoa Metamorphic Core Complex, resulting in the separation of New Zealand from Gondwana. High grade (Lower Plate) and low grade (Upper Plate) rocks are separated by the Ohika and Pike Detachment Faults. The two detachment faults have distinctly different histories, with greater exhumation along the Pike Detachment Fault. The onset of crustal extension is proposed to have commenced along the Pike Detachment Fault at 116.2 ± 5.9 Ma (Rb/Sr dating). Both geochemical and geochronological approaches are adopted for this thesis, through the in situ analysis of oxygen and hafnium isotope ratios, trace metals and U-Pb content. Chemical changes are tracked during the petrogenesis of the Buckland Granite, with mafic replenishment observed in the later stages of crystallisation. Crystallisation temperatures of the Buckland Granite are calculated using zircon saturation thermometry, with an average Ti-in-zircon temperature of 697℃ (upper-amphibolite facies). Inherited zircons in Lower Plate rocks show distinct age peaks at c. 1000, 600 and 300 Ma, illustrating the incorporation of heterogeneous local crust (Greenland Group and Karamea Batholith). Model ages (TDM) are calculated for inherited zircons of the Lower Plate rocks, which record the time at which magma bodies (zircon host rocks) were extracted from the mantle. Maximum and minimum model ages for the Buckland Granite average at 3410 Ma and 2969 Ma, with the maximum TDM value of 3410 Ma coinciding with the proposed major crustal formation event of the Gondwana supercontinent at c. 3.4-3.5 Ga. Two distinct U-Pb zircon age peaks are observed in the Buckland Granite at 102.4 ± 0.7 and 110.3 ± 0.9 Ma. The 110.3 ± 0.9 Ma age is interpreted as the crystallisation age of the pluton, while the 102.4 ± 0.7 is proposed to represent a younger thermal (magmatic?) event associated with the 101-102 Ma Stitts Tuff.

I determined the source parameters of 53 moderate-sized earthquakes in the region of the Eastern Himalayan Syntaxis through the joint inversion of regional and teleseismic distance long-period body waves. The average rates of deformation are determined by summing the moment tensors from both recent and historic earthquakes. Strike-slip movement on the Sagaing fault terminates in the north (just south of the syntaxis), where thrusting (northeast convergence) and crustal thickening are predominant. Slip vectors for thrust mechanisms in the Eastern Himalaya in general are not orthogonal to the Himalayan mountain front but show an oblique component of slip. A combination of thrust and strike-slip faulting (Molnar and Deng, 1984) for the great 1950 Assam earthquake is consistent with the rates of underthrusting in the entire Himalaya and the rate of spreading in Tibet (assuming that a 1950-type earthquake recurs every 400 years). An estimated 4-21 mm/yr of right-lateral motion between southeast Asia and the Burma subplate is absorbed within the zone of distributed shear between the Sagaing and Red River faults. A component of westward motion (3-7 mm/yr) of the western boundary of the distributed shear zone may cause some of the late Cenozoic compression and folding in the northern Indoburman Ranges. Distributed shear and clockwise rotation of blocks is also occurring in Yunnan north of the Red River Fault. The inversion of 130 regional distancewaveforms for average crustal thickness and upper mantle Pn velocity indicates an increase in Pn velocity, coincident with increase in crustal thickness, of about 0.20 km/s beneath the Tibetan Plateau. Impulsive Pn arrivals from paths that cross the Tibetan Plateau can be modeled with a positive upper mantle velocity gradient, indicating an upper mantle lid approximately 100-km-thick beneath southern Tibet. This "shield-like" structure supports a model in which Indian continental lithosphere has underthrust Tibet. The crustal shortening within Tibet 8 mm/yr is thus viewed as an upper crustal phenomenon in which the faults do not penetrate the deep crust or upper Mantle. The forces generated by the thick crust in Tibet may partly cause the strike-slip faulting and east-west convergence in Sichuan and the movement of upper crustal blocks in Yunnan.

Rates of latest Quaternary slip obtained from stream terraces and glacial moraines displaced by faults of the Alpine shear system vary with space and time. Field measurements yield displacement values for faulted geomorphic surfaces, while the rate of thickening of weathering rinds and changes in soil properties, calibrated at sites of known age, yield age estimates. Precisions are 5-20% from weathering rinds and 15-50% from soil data. The oldest surfaces examined have ages of 15-20 ka and right-lateral fault displacements up to 400-600 m. Latest Quaternary lateral-slip rates are 20-45 mm/yr across the Alpine fault in the Southern Alps. To the northeast slip is distributed across a system of faults in Marlborough. The main faults of this shear system--the Wairau, Awatere, Clarence, Hope, and Porters Pass--have latest Quaternary rates of 5-10, 7-10, 7-9, 20-40, and 4-5 mm/yr respectively. Each fault has undergone a substantial decrease in lateral slip in the last 3-5 ka. Long-term rates of horizontal slip across the Australian-Pacific plate boundary--the Alpine shear system in most of the South Island--are 35-50 mm/yr parallel and 8-25 mm/yr normal. Sums of fault-slip rates exceed these plate motions for the early-middle Holocene, but late Holocene fault-slip rates are less than half the long-term average. Rates of geodetic strain and seismic moment release over the last 50-100 yr approximate the long-period rates in Marlborough but are only half in the Southern Alps. The best explanations of these variabilities are that the proportion of plate-boundary motion accommodated by fault slip changes, or that the rate of motion across the plate boundary varies, perhaps over 5 ka intervals. The first hypothesis is not consistent with the early Holocene rates exceeding the long-term average, but the second hypothesis implies that the last 50-100 yr is a period of renewed high tectonic activity. The second hypothesis is more consistent with the data, and the last 15-20 ka may be the time interval necessary to average out shorter, 5 ka episodic variations in plate-boundary motions.

The western margin of South America between 30ºS and 36ºS is seismically active. While the largest magnitude earthquakes are the interplate subduction zone events, the historically most devastating earthquakes have been the moderate-to-large magnitude earthquakes with depths < 35 km in the Andean back-arc. This region is characterized by accreted terranes later reactivated during Mesozoic extensional processes. Crustal seismicity in the back-arc is related to the thin-skinned Precordillera (PC) fold-thrust belt and the thick-skinned Sierras Pampeanas (SP) basement-cored uplifts overlying the flat slab segment. South of 33ºS, the active volcanic arc above the normally dipping subducted plate is also seismically active at crustal depths. In this study we combined historical and regional broadband seismic data to characterize moderate-to-large earthquakes and the crustal structure in this region. We have digitized and modeled teleseismic records of the 1944 and 1952 San Juan, Argentina PC earthquakes. Both events have shallow source depths, short duration of the source time functions with a thrusting focal solution for the 1944 (Mw 7.0) earthquake and a major strike-slip component in the 1952 (Mw 6.8) earthquake solution. By modeling regional broadband waveforms collected during the CHile-ARgentina Geophysical Experiment (CHARGE) during 2000 and 2002 we constrained the seismic moment tensor and improved focal depths for 27 crustal (3.5 < Mw < 5.1) earthquakes. We found predominantly thrust-fault focal mechanisms and focal depths of 10-26 km for earthquakes over the flat slab region; the eastern SP and active arc have earthquakes with strike-slip focal mechanisms and shallower depths. We used these same earthquakes to determine the crustal structure using raypaths that sample different geologic terranes. Our results indicate high Vp, low Vs for the northern Cordillera, PC and western SP thicker crust; low Vp, low Vs and a thinner crust beneath the arc (south of 33°S) consistent with a mafic composition and partial melt. The eastern SP basement shows low Vp, low Vs and thinner crust consistent with a more quartz-rich composition. These differences have an important control on the present day Andean earthquake deformation and the high seismic hazard posed in this region.