Thesis (M. Phil.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 106-131) Also available in print.

Thesis (M. Phil.)--University of Hong Kong, 2002. / Includes bibliographical references (leaves.

Thesis (Ph. D.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 203-224). Also available on the World Wide Web.

Detailed mapping and structural analysis along the base of the Semail ophiolite thrust sheet in the northern Oman mountains has revealed a distinct and separate thrust sheet between the underlying marine sediments of the Hawasina Complex, and the overlying 12 km+ thick Semail ophiolite. This thrust sheet is termed the Haybi complex, and consists of sub-ophiolitic metamorphic rocks and serpentinite, alkaline and tholeiitic basalts (the Haybi volcanics), associated with mountain-sized "Exotic" limestones and an Upper Cretaceous sedimentary melange. The rocks of the Haybi complex are bounded by major thrust planes, the Semail thrust above and the Haybi thrust beneath, which truncate all schistosities, fold axes, imbricate thrust and associated features. The Haybi volcanics are mainly Triassic in age and form a substrate to or enclose large, isolated blOCKS of Permian or Triassic "Exotic" limestones, Although they have been considerably disrupted and imbricated during south-westward emplacement, intact sequences show that the lower part is composed mainly of alkaline pyroclastics and lavas, including ankaramites, nephelinites and trachytes, whereas the upper part is predominantly tholeiitic pillow lavas and breccias. Late sills of alkali pyroxenite, wehrlite and kaersutite gabbro intrude the tholeiitic volcanics in a few localities and have been dated as Turonian (Upper Cretaceous). Geochemical studies, particularly of "immobile" elements show that the lower volcanics and the late sills are strongly alkaline with high Ti, p, Zr and Nb contents, low ^Y/Nb ratios and steep LREE enriched rare earth patterns. They are typical "within-plate" alkaline magmas characteristic of continental rift zones and some ocean islands. Two types of tholeiites are recognised: a relative (to MORB) trace-element enriched "transitional" type which probably farmed in a transitional within-plate tectonic setting and a "depleted" type with the characteristics of islandarc tholeiites. The uppermost Haybi arc lavas are probably Middle Cretaceous in age (from radiolaria in interbedded cherts) and may be related to the initiation of a subduction zone in the Cretaceous. prior to ophiolite formation and emplacement. Metamorphic rocks showing an inverted metamorphic zonation from upper amphibolite facies immediately beneath the peridotite to greenschist facies at lower levels, outcrop discontinuously along the base of the Semail ophiolite thrust sheet. These metamorphic rocks show polyphase deformation, mylonitic fabrics, and have been disrupted. folded and imbricated, and in places form tectonic inclusions in a serpentinite melange. In the more intact sequences, garnet-clinopyroxene amphibolites, with rare hornblende and clinopyroxene-bearing marbles and banded quartzites occur at the higher levels whilst a wide range of meta-sedimentary and metabasaltic rOCKS occur in the greenschist facies. "Immobile" element and REE geochemistry supports field assumptions that the amphibolites were derived mainly from Haybi "transitional" (or MORS-type) volcanics. Protoliths of the meta-sediments include "Exotic" limestones, Mn-rich cherts and argillaceous turbidites probably derived from the Hawasina Complex. Low glaucophane content of amphiboles and low jadeite content of clinopyroxenes suggest relatively low pressures of crystallisation. The distribution coefficient K_D for coexisting garnet and clinopyroxene suggests a temperature range of 670^o to 750^oC, the upper limit of the amphibolite facies. Residual heat from the recently-formed ophiolite provided the dominant heat source for metamorphism during the Turonian-Cenomanian (Upper Cretaceous) although frictional heating during thrusting could have supplemented this. Ophiolite emplacement in Oman is thought to be essentially a two-stage process. During initial displacement, high-temperature metamorphism occurred along the base of the fractured ophiolite forming the metamorphic sheet and successive tectonic slices were incorporated onto the base of the ophiolite, presumably by underthrusting. The metamorphism probably occurred along a shallowdipping subduction zone (dipping north-east) which was initiated during the formation of the Haybi arc lavas in the Middle Cretaceous. Final emplacement of the Semail ophiolite by gravity sliding or spreading was facilitated by a thin decollement layer of basal serpentinite along the Semail thrust plane which truncates all underlying structures. Since continent-continent collision has not occurred in this area of Tethys, the Oman ophiolite remains largely undeformed unlike the ophiolites along the Zagros suture zone of Iran or the Indus-Tsangpo suture zone in the Himalayas.

The Eastern Limassol Forest Complex (ELFC) lies at the southern margin of the Troodos ophiolite, Cyprus, and preserves a Penrose-type stratigraphy with a 4km-thick crustal sequence. The ELFC is separated from the main part of the Troodos Massif by an east-west trending fault zone, the Arakapas Fault Belt, which earlier studies suggest formed the northern wall of an oceanic transform fault. Transform-related structures are identifiable in the northern part of the ELFC, and volcaniclastic turbiditic sediments intercalated with lava flows attest to the existence of a bathymetric depression coincident with the fault zone. A southern boundary to the transform fault zone is recognised within the ELFC, with the abrupt disappearance of interlava sediments and E-W trending structures. Crust to the south of the boundary was generated at an 'Anti-Troodos' ridge axis. A width of c.5km is implied for the transform. The accretionary geometry of the ELFC has been extensively modified by postvolcanic tectonism. Sustained extension oblique to the trend of the transform has resulted in the reactivation of transform-related structures as normal faults, which have been rotated 'falling domino' style, together with the greater part of the axis sequence crust, above a decollement horizon located near to the petrological Moho. Extensional strain was preferentially accommodated in the transform-tectonised north of the ELFC. In the south, NW-striking normal faults are more steeply dipping, and block tilting is less extreme. Mesostructural data suggest that these normal faults have been reactivated as oblique dextral strike-slip faults and, with subsidiary NE-trending structures, are responsible for clockwise block rotations about steeply plunging axes. The timing of the deformation is constrained with respect to the overlying pelagic sediments, which suggest that the extension continued from the Turonian (i.e. almost immediately after ophiolite formation) to the late Campanian, and that the strike-slip reactivation occurred in late Campanian to early Maastrictian times. Palaeomagnetic studies have shown that Cyprus experienced a 90· anticlockwise rotation, which commenced in the Campanian-Maastrichtian interval, and it is argued that the late dextral strike-slip movements in the southern ELFC reflect deformation close to the margin of the rotating Cyprus microplate. The extensional reactivation of the transform in the Turonian-Campanian may correspond to an anticlockwise torque applied to the Troodos ocean floor prior to actual rotation. The rotation of Cyprus is thought to have been a consequence of the collision of the Arabian continental promontory to the east with an intra-oceanic subduction zone (above which Troodos was created) in the Upper Cretaceous.

Remote sensing techniques are being used increasingly to address volcanological problems. This thesis is concerned with the interpretation of multispectral infrared data of volcanic thermal features. Data from the two short wavelength infrared (SWIR) bands of the Landsat Thematic Mapper (TM) are used to constrain sizes and temperatures of subpixel resolution hot spots. Analysis of a 1989 TM scene of Lonquimay volcano suggests a cooling from 250 to 170°C of the crust of an active lava flow down 1.5 km of its length. Estimates of the summed radiative and convective heat losses from the flow top fall from 6 to 3 MW per 30 x 30 m pixel downflow. Thermal data were collected at volcanoes in Chile, Nicaragua and Italy to test assumptions explicit in such calculations. These surveys suggest that SWIR emission from fumarole fields is dominated by that from the interior walls of vents, and that surface temperatures around fumarole vents are lower than those of typical active lava bodies. The relative response of the two SWIR sensors of the TM is sensitive to such differences and therefore provides a basis for the interpretation of thennal anomalies known only from satellite data. Comparison of measurements in the two SWIR bands is petfonned with fourteen TM scenes recorded between 1984 and 1991, of a persistent hot spot at Lascar volcano, Chile. Evolution of the thennal source is charted by comparing the summed spectral radiance in each of the SWIR bands. Thus it appears that Lascar has experienced at least two periods of lava dome growth punctuated by the explosive eruptions of 1986 and 1990. Infrared sensors to be deployed on forthcoming remote sensing platfonns, including the Japanese Earth Resources Satellite and NASA's Earth Observing System, promise to constrain thennal emissions from volcanoes more effectively than possible with existing orbital systems. These investigations will improve understanding of the physical processes that influence the emplacement of lavas, as well as the potential for detecting eruption precursors and evaluating volcanic hazards.

Heat transfer in active volcanoes was investigated in this thesis. A general model of a crater lake system was developed that takes inputs of lake temperature, volume, chemical content, and meteorological conditions, and outputs the mass, energy, and chemical flows to and from the lake. The model was applied to lakes at Pods (Costa Rica) and Ruapehu (New Zealand), yielding volcanic power outputs of -102-103 MW, and heat fluxes of -102-104 W m-2. Heat is added to the lakes by hot brine and steam, derived from lake seepage and magmatic gas. The heat source is magma crystallising, cooling, and degassing. Background heat inputs are maintained by hydrothermal infiltration of magma, releasing latent and specific heat. Infiltration of the conductive boundary layer surrounding magma was modelled. The permeability created by contractive cooling was equated with the permeability required for two-phase convection to transport heat away from the boundary. Infiltration rates of -1-100 m a-1 (metres/year), into conductive layers -30-0.3 m thick, creating permeabilities of _10-10-10-14m 2, will provide the required heat flux. Cracking temperatures of magma depend upon infiltration rate, ranging from hydrothermal system temperatures at slow rates, to magma temperatures at the fastest rates. Predicted maximum rates are -300 m a-1 for near-surface magma, and -800 m a-1 for magma at -1-3 km depth. Measured S02 fluxes at Pods, and calculated influxes of HCl to both lakes imply that degassed magma volumes (-0.004-0.08 km3 a-i) are much larger than likely intrusions. A new model was developed of small, vesiculating intrusions that circulate magma due to the density increase associated with gas loss. Dense, degassed magma descends, whilst buoyant, volatile-rich magma rises from a deep source. Pipe-like intrusions of radius -5 m, tapping magma volumes >-0.05 km3, can produce the gas fluxes needed. Intrusions of this type probably occurred in 1980/81 and 1986 at Pods, and in 1968,1971,1975,1977,1981 and 1985 at Ruapehu, and were followed by intermittent eruptions and degassing. This degassing mechanism probably occurs at many volcanoes where high gas fluxes are observed, but no evidence exists for large, shallow intrusions. A model of compressible fluid flow in a rough fumarole conduit, with conductive heat loss to the surroundings, allows fumarole temperatures to be used to estimate the depth of their magma source. This also indicates shallow magma was emplaced at Pods in 1980/81 and 1986. In summary, heat transfer is achieved by a combination of intermittent gas release from minor shallow intrusions, together with infiltration of deeper magma. Infiltration is one mechanism for providing fractures allowing the release of gas from shallow intrusions, and circulation probably ceases due to freezing caused by infiltration.

The Himalaya provide the most significant example of present-day orogenesis and consequently have been extensively studied to gain an understanding of the principle controls on the response of the crust to continental collision. However, our understanding of the prograde metamorphic evolution of the orogen remains poor. This thesis builds on recent advances in the study of PTt paths, using garnet chronometry, to better constrain the thennobarometric evolution of the Garhwal section of the Indian Himalaya. Results show that the metamorphic core of the Garhwal Himalaya - the High Himalayan Crystalline Series (HHCS) - records a complex, continuous prograde thermal history from initial burial -10 Ma after continental collision at -50 Ma, up to cooling and exhumation at 20-16 Ma BP. PT paths obtained from garnets indicate that prograde metamorphism occurred during crustal thickening and "peak" thermobarometric estimates show that the presently exposed HHCS records temperatures of -700 °C throughout the section accompanied by a decrease in pressures from --13 kbar at the base to -6 kbar at the top. However, chronometric information shows that reorganisation of the orogenic wedge resulted in the juxtaposition of rocks which attained different PT conditions at different times and places during orogenesis. Additionally, temperatures were sufficient in the early stages of orogenesis for the development of small leucogranitic bodies to form by fluid-present melting. The HHCS in Garhwal, therefore, cannot be considered as a single coherent crustal slice. Furthermore, the continued reorganisation of the orogen since collision also means the heat generation within the overthickened orogenic wedge is sufficient for anatexis of the crust to form the well-studied melts intruding the upper levels of the HHCS. However, interpretation of the results is complicated by the isotopic systematics involved in garnet chronometry and by the role of small inclusions with high concentrations of the critical elements of- Nd, Pb, Sr. The systematics of the Sm-Nd system in garnet has been investigated by a comparison of concentrations obtained insitu by LA-ICP-MS with those obtained by isotope dilution. Results show that while such inclusions can pose a problem to chronometry, their effects can be identified and constrained. In the course of such work data was obtained on the trace-element zonation in garnet, which acts as a monitor of the chemical evolution of the rock. While the controls on such zonation are still poorly understood the data presented here emphasise the importance of fractionation of the chemical system from which the garnet grows by both accessory minerals and by garnet itself. Furthermore, different minerals fractionate distinctly different elements this can be recognised in the trace-element zonation preserved in garnet.

The Dam Feliciano Belt is a Pan-African mobile belt from the Ribeira orogen of southern Brazil. A detailed field and geochemical traverse along the BR392 road section between Pelotas and Cacapava do SuI identifies two major tectonic domains; the Pelotas Batholith and the Santana Metamorphic Belt, striking NNE-SSW parallel to the major foliation of the belts. The two belts are separated by a Triassic basin with flat lying red beds and interbedded andesites and rhyolites. The Santana Metamorphic Belt is a NW-verging fold belt with a metamorphosed shelf sequence of quartzites, marbles and graphitic schists and a polydeformed Lower Proterozic gneissic basement deformed during the Pan-African orogeny. Detailed mapping recognized four phases of deformation in the basement gneisses, three of which are recorded in the basement schists and cover sequence. There is also evidence of late NE-verging thrusting post-dating the formation unmetamorphosed Paleozoic sediments. Late extension caused NW-SE and NE-SW normal faulting. Metamorphism occurred contemporaneously with D2 and 03, and PT conditions for peak: metamorphism have been calculated as 8.6Kb and 60QOCwithin the basement schists corresponding to garnet growth during D3 deformation. Three phases of granite intrusion are recognized in the Santana Metamorphic Belt The Santana Granite (8oom.y.) represents the first phase intruding the basement and it is folded by 02 and 03. The Campinas Granite (Soom.y.) has a 03 foliation and the Cacapava Granite (474m.y.) is post-tectonic and intrudes the NW portion of the Santana Metamorphic Belt The Pelotas Batholith is almost entirely composed of granitoids of Pan-African age (600- 4S0m.y.). Both D2 and D3 are recognized in the batholith. A two fold subdivision based on geoc~emical and field criteria distinguishes the following categories of granitoid; foliated granitoids and unfoliated granites.

<p> In the Roberts Mountains of north-central Nevada, several large masses of the autochthonous carbonate succession overlie the highly deformed siliciclastic succession of the Roberts Mountains allochthon (RMA). These carbonate masses, or tectonic erratics, were plucked from the underlying autochthon and carried in the base of the upper plate of the post-Antler Orogeny Henderson thrust as it ramped structurally upwards and eastwards. Kinematic indicators in the form of folds and fractures within the carbonate masses at Henderson Summit, Vinini Creek, Mineral Hill, and Lone Mountain show a general eastward stress direction. Intense brecciation is observed in the lower parts of the carbonate masses and in the immediately underlying siliciclastic strata of the RMA. Based on observations and kinematic evidence, the carbonate masses at Henderson Summit, Vinini Creek, Mineral Hill, and Lone Mountain are interpreted to be tectonic erratics, which in turn further supports and extends the tectonic erratic hypothesis.</p><p>