No description available.

In this thesis I use a multi-disciplinary approach to investigate two areas of active mountain-building within the Alpine-Himalayan belt: the Altai range in western Mongolia, and the Zagros mountains in southern Iran. I begin by studying a clustered earthquake sequence that struck a previously unrecognised fault zone in the NW Altai mountains in 2003. By combining seismology and field observations with satellite radar interferometry (InSAR), I attempt to unravel the detailed history of faulting in time and space. Differences between body-wave and InSAR-based models prevent me from matching individual seismic events with individual fault segments, and I explore the cause of these discrepancies. In the following two chapters, I establish late Quaternary slip-rates on major right-lateral and thrust faults in the eastern part of the Altai. In particular, I explore the use of in situ-produced cosmogenic Be-10 and Optically Stimulated Luminescence (OSL) for dating offset alluvial fans and river terraces. My results suggest that faulting has migrated toward the eastern margin of the range from the high, interior Altai, presumably in response to stresses introduced by topography. In the final, main chapter, I investigate a link between buried reverse faulting and surface folding in the Zagros Simply Folded Belt. Using surface displacements measured with InSAR, I show that a major anticline on Qeshm Island was uplifted during an earthquake in 2005. However, the pattern of uplift is discordant with the growth of neighbouring folds, preventing us from establishing a simple connection between faulting and folding. All in all, my work demonstrates the importance of using several techniques in parallel when studying regions of active continental deformation.

The Yarlung (India-Asia) suture zone in southern Tibet records Middle Jurassic—Late Cretaceous development of the Lhasa terrane (Eurasian) convergent margin and subsequent India-Asia collision beginning in Paleocene time. This dissertation reports data from field-based geologic investigation of the Yarlung suture zone in the Lopu Range and Lazi Regions, ~600 and ~300 km west of the city of Lhasa, respectively. Field data were combined with new geochronology (detrital and igneous zircon U-Pb, garnet Lu-Hf), thermochronology (white mica Ar-Ar and zircon U-Th/He), and metamorphic petrology data to develop a tectonic model involving multiple episodes of shallow underthrusting, rollback, and breakoff of both oceanic and continental lithosphere. Switches between extensional and contractional deformation along the Yarlung suture zone appear to be controlled by changes in subduction dynamics. If this tectonic model is representative, then the tectonic process of inter-continental collision is responsible for much larger magnitudes of crustal recycling that previously thought. A hornblende-plagioclase-epidote paragneiss block in ophiolitic mélange, deposited during Middle Jurassic time, records Late Jurassic or Early Cretaceous subduction initiation along the Eurasian margin followed by Early Cretaceous forearc extension. Detrital zircons from Xigaze forearc basin strata deposited unconformably atop ophiolitic mélange produced a maximum depositional age of 97 ± 1 Ma, providing a minimum age for establishment of an arc-forearc-trench convergent margin along the southern Lhasa terrane. Metasedimentary rocks that were originally deposited along the Indian passive margin were subducted beneath the Lhasa terrane to upper-mantle depths, reaching high-pressure (HP), low-temperature conditions (≥1.4 GPa at T≤600 °C). Garnet Lu-Hf geochronology indicates that prograde metamorphism of the Indian metasedimentary rocks was ongoing at 40.4 ± 1.4 Ma while white mica Ar-Ar thermochronology indicates exhumation to mid-crustal depths between 39-34 Ma. Gangdese arc magmatism persisted after the onset of India-Asia collision, producing plutons that intruded sedimentary-matrix mélange of the southern Lhasa terrane subduction-accretion complex between 49-37 Ma. These data suggest steep subduction or southward trench retreat immediately prior to shutdown of arc magmatism along the Yarlung suture zone (37 Ma), shortly after the onset of high-pressure rock exhumation. We interpret that these data record a Paleocene—Eocene episode of southward rollback, breakoff, and underthrusting. During Oligocene—Miocene time, nonmarine strata were deposited along the Yarlung suture zone immediately prior to shortening across a system of out-of-sequence, top-north reverse faults. Based on our data and previous work, we interpret that sedimentation was driven by a second episode of rollback and breakoff of Indian continental lithosphere, whereas subsequent contractional deformation was driven by renewed shallow subduction. Compilation of regional thermochronological data and interpretation of seismic reflection data from previous investigations suggests that the top-north reverse faults comprise a foreland-dipping passive roof duplex above the leading edge of a structurally deeper, hinterland-dipping duplex beneath the southern Lhasa terrane. The Yarlung suture zone switched from north-south contraction to east-west extension by ~16 Ma based on a crosscutting relationship between a leucogranitic dike and a normal fault related to a larger horst structure in the Lopu Range region. Tectonic exhumation in the footwall block of the horst drove cooling through zircon (U-Th)/He closure temperature (~180 °C) between 12-6 Ma.

Thesis advisor: Ethan F. Baxter / Spiral garnets are well-documented metamorphic microstructures that have been observed in orogens throughout the world. The preferred orientation of spiral garnet axes has been proposed (Bell and Johnson, 1989) to record and preserve information about the timing, rate, and orientation of the tectonic-scale processes. Using the model of Be Spiral garnets are well-documented metamorphic microstructures that have been observed in orogens throughout the world. The preferred orientation of spiral garnet axes has been proposed (Bell and Johnson, 1989) to record and preserve information about the timing, rate, and orientation of the tectonic-scale processes. Using the model of Bell and Johnson (1989), Aerden et al. (2013) proposed a link between the preferred orientation of spiral garnets and changes in relative plate motion between Iberia and Africa. The goal of this thesis is to this relationship by absolutely dating, eight samples from the Betic-Rif arc with measurable spiral axis orientations were chosen for Sm-Nd garnet geochronology. Chapter one is a detailed literature review of prior work on the formation and interpretation of spiral garnets. In chapter two we present 11 bulk Sm-Nd garnet ages from eight samples, these ages range from 35.6 ± 2.8 to 13.62 ± 0.69 Ma. The results from the obtained bulk garnet ages reveal a more complex relationship between FIA orientations and plate motion that originally hypothesized in Aerden et al. (2013). Large-scale rigid block rotations that postdate garnet growth may have influenced the current orientation of FIA from the western Betic-Rif. In chapter three, zoned geochronology was conducted on a single sample from the Nevado-Filabride Complex. This study revealed spiral garnet formation occurring on a rapid timescale, just 〖0.45〗_(-0.32)^(+0.51) Myr. While other zoned garnet studies have shown similar rapid growth in subduction zone setting (Dragovic et al., 2012), this is the first such documentation of such rapid growth from a garnet hosting spiral inclusion trails in a regional metamorphic setting. We calculated strain rates considering different genetic models for the spiral inclusion trails either by garnet rotation in simple shear, or by episodic overgrowth of suborthogonal crenulation cleavages due to switching stress axes. In both cases a similar fast strain rate of ca. 10-13 s-1 was obtained, which is an order of magnitude faster than typical regional strain rates and faster than previous spiral garnet studies regardless of the method used to calculate strain-rate. / Thesis (MS) — Boston College, 2019. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

This is an integrated study of the stratigraphy, deformation, magmatism, and metamorphism in the vicinity of the Ida and Palmenhorst Domes, an area in the southwestern Central Zone of the Damara Orogen, Namibia. The principal aim is to understand the timing of tectonic events through high-precision U-Pb dating of structurally constrained intrusions and anatectic rocks, and link these tectonic events across the Damara Orogen and Pan-African Orogeny. A secondary aim is to compare the Central Zone and Damara Orogen to other collisional orogens. The stratigraphy of the study area is similar to that noted elsewhere in the Central Zone, but the mapped distribution of lithologies differs slightly from previous work. Specifically, Damara Supergroup rocks have been found infolded with the Abbabis Complex, and the stratigraphic positions of certain units in have been locally reclassified. The mapped distribution of lithologies suggests a Type-2 fold interference pattern across the study area. This Type-2 fold interference is confirmed by structural analysis. A D2 deformation event formed strongly S- to SE-verging km-scale recumbent to shallow NW-dipping folds with smaller-scale parasitic folds. The long limbs of these folds are extended, and a number of shear zones are found on these extending limbs, as well as near the contact between the Abbabis Complex and the Damara Supergroup. NE-SW extension is associated with the late stages of D2, and forms a conjugate set of shear bands and a shallow NE-plunging mineral stretching lineation. This D2 event was overprinted by upright to steeply WNW-dipping km-scale D3 folds to form the domes in the study area. Mesoscale fold interference structures are rare, but D2 structures are shown to be consistently reoriented by D3 structures. D3 deformation does not have a strong vergence, and mesoscale D3 folds are rare. D2 and D3 were preceded by a D1 fabric forming event locally observed as rootless isoclinal intrafolial folds, and followed by brittle deformation. The Ida Dome is a fairly simple domal structure formed by the km-scale interference between a shallow NNW-dipping D2 anticline and an upright to steeply WNW-dipping D3 anticline. East of the Ida Dome, NE-trending D3 structures predominate, but are seen to overprint earlier D2 structures. The Palmenhorst Dome is a larger area where Damara Supergroup rocks have been infolded into the Abbabis Complex during D2 deformation. These isoclinal, N- to NW-dipping D2 folds have been refolded by upright D3 folds to form a Type-2 fold interference pattern. D2 structures along the southern margin of the Palmenhorst Dome dip steeply towards the south, in contrast to D2 structures elsewhere. This is interpreted to be the result of a lower-intensity km-scale D2 fold. The orogen-parallel extension and orogen-perpendicular recumbent folding that took place during D2 cannot be explained by previous structural models for the Central Zone and a new model is suggested where these structures form as the result of coeval irrotational NE-SW extension and S- to SE-verging simple shear during extensional collapse of the orogen. A number of intrusive rock types are found in the study area and have been dated using SHRIMP U-Pb. Amphibolite dykes have a chemical affinity to mafic rocks of the Goas Suite, and are suggested to be either pre-Damaran or early Damaran intrusives as they cut the gneisses of the Abbabis Complex, and are affected by D2. They have been dated at 2026.9 ± 2.3 Ma (zircon) or 557.2 ± 7.4 Ma (zircon) with metamorphic overgrowths in this sample giving 520 ± 6.9 Ma. Red, potassic granites emplaced near the contact with the Abbabis Complex and Damara Supergroup contain a D2 gneissic fabric and give ages of 536 ± 7.2 Ma (monazite), and zircons have lower intercept ages of 539 ± 17 Ma and upper intercept ages of 1013 ± 21 Ma. Grey granites are abundant in the study area, and form a continuum from dark grey granites (which are tonalitic to dioritic in composition and contain hornblende and abundant biotite) to light grey granites (which are leucogranitic and contain abundant K-feldspar and minor biotite). These grey granites show a fractionation trend from dark to light varieties, and cross-cutting relationships indicate that the lighter variety is younger than the darker variety. The grey granites show syn-D2 structural relationships and contain a fabric subparallel to the S2 fabric, and which is more pronounced in the darker varieties. They show similarities with granites described by earlier workers, and two samples have been dated at 519.1 ± 4.2 Ma and 520.4 ± 4.2 Ma (zircon). A variety of sheeted granites are found – quartz-feldspar-magnetite pegmatitic granites are associated with grey granites, occur axial-planar to F2 folds, and have metamict zircons which are dated at 530-525 Ma. Garnet (± cordierite) granites are leucocratic, have garnet poikiloblasts, are emplaced axial planar to F2 folds and are also folded and boudinaged by D2. They are associated with pelitic units in the Damara Supergroup and are dated at 520.3 ± 4.6 Ma (zircon) and 514.1 ± 3.1 Ma (monazite). Uraniferous leucogranites found are similar to those widely described in the Central Zone, but metamict zircons give imprecise ages of between 515 and 506 Ma. Pink pegmatitic leucogranites comprise pink perthitic feldspar and milky quartz, are emplaced into more brittle structures and gives an age of 434.4 ± 2 Ma (zircon). Almost all granites analysed appear to be crustal-melt granitoids, with the exception of the darker grey granites, which show a calc-alkaline affinity. No Salem-type granites are found in the study area. In addition, SHRIMP U-Pb analyses of zircons from three Abbabis Complex gneisses give ages of 2056 +11/-10 Ma, 2044 +32/-27 Ma and 2044 +17/-14 Ma, and titanites from an amphibolite sample give ages of 493.4 ± 6.4 Ma. Two anatectic leucosomes from D2 shear zones and shear bands give zircon ages of 511 ± 18 Ma and 508.4 ± 8.7 Ma in spite of high-U zircons. Lu-Hf data on zircons from an Abbabis Complex gneiss gives model ages of ca. 3 Ga, whilst similar data for a grey granite gives a model age of ca. 2 Ga. Zircons from the Abbabis Complex gneiss have variable O-isotopic values, whilst the grey granite gives O-isotopic values of ca. 7‰. These geochonological and isotopic data show that the Abbabis Complex is part of the Congo Craton, and that some amphibolites are pre-Damaran, whilst others may be related to the Goas Intrusive Suite, and represent a phase of early Damaran magmatism. In contrast to the chronology previously presented for the Central Zone, M1 in the study area appears to have occurred at 535-540 Ma, with M2 coeval with D2 deformation at 510-520 Ma. Elsewhere in the Central Zone, NW-verging D2 deformation is dated at 540-560 Ma, and the Central Zone appears to have a diachronous tectonometamorphic evolution along strike. It is suggested here that this represents the preservation of two separate tectonic events in the Central Zone at different crustal levels, one at 540-560 Ma and the other at 520-510 Ma. D3 deformation is suggested to have taken place at 508 Ma, immediately after D2 extension. The Central Zone began to cool following D2, and the 495 Ma titanite age reflects this cooling. Isotopic evidence from this and other studies shows that Damaran granitoids (with 1.5-2.2 Ga model ages) cannot be derived from the Abbabis Complex (with 3 Ga model ages) but must come from an alternative source, suggested here to be Kalahari Craton material subducted below the Congo Craton. Textural studies of a number of pelitic samples indicate syn-D2 low-pressure, high-temperature metamorphism. Differences in observed assemblages between various sample types are due to compositional differences, and samples appear to have reached similar conditions across the study area. Mineral compositional profiles show no prograde zoning, indicating mineral re-equilibration. Orthopyroxene is locally observed, suggesting lower-granulite conditions. This is confirmed by pseudosection modelling of a number of samples, which gives peak conditions of 750-850 °C and 4.5-5 kbar. This modelling shows lower-granulite facies conditions with higher temperatures than previous estimates based on mineral compositional geothermometers, which are affected by re-equilibration. These conditions are sufficiently high for fluid-absent biotite breakdown to form the voluminous anatectic leucosomes and granitoids in the southwestern Central Zone. Pseudosection modelling and phase relationships indicates a low-pressure (ca. 4 kbar) clockwise heating path, with slight decompression at the thermal peak. All metamorphism noted is 520-510 Ma M2 metamorphism, and no petrographic evidence exists for earlier 540-535 M1 metamorphism. This cryptic M1 is suggested to be related to the emplacement of the Goas Intrusive Suite and Salem-type granites early in the orogenic history, whilst M2 may be related to thermal relaxation following crustal thickening early in the orogenic history, but requires an additional heat source. The difference in ages for deformation and metamorphism between the study area and elsewhere in the lower grade portions of the Central Zone is suggested to be related to the preservation of different portions of the orogenic history in different areas. The results of this study together with previous work details a multi-stage evolution for the Central Zone involving subduction, continent-continent collision, crustal thickening, slab breakoff, magmatism, granulite-facies metamorphism and exhumation of the mid-crust. This multistage evolution explains the multiple ages for deformation and metamorphism in the Central Zone. NW-folding and thrusting documented in the Karibib area at 560-540 Ma is related to an early phase of crustal thickening owing to continent-continent collision following a brief period of subduction. Slab breakoff led to asthenospheric upwelling and heating of the lower crust, and produced the Goas Intrusive Suite and Salem-type granites, as well as providing heat for 540-535 Ma M1 metamorphism and the melting of the crust to produce anatectic red granites. SE-verging deformation, extension and granulite facies metamorphism recorded in this study is related to orogenic collapse following crustal thickening, and the heat source for low-P, high-T metamorphism may be highly radiogenic crust that was thickened , which is suggested to be either burial of crust enriched in heat-producing elements, or asthenospheric upwelling owing to delamination of the Congo Craton lithospheric mantle or asthenospheric upwelling owing to the position of the southwestern Central Zone on a major orocline. The events recorded for the Central Zone have been correlated across the entire Damara Orogen, and the timing of events can be correlated along strike into the Zambezi Belt. Events in the Kaoko Belt appear to predate those in the Damara Belt, which appears to also show a similar collisional timing to the Gariep Belt. It is therefore proposed that the Gariep and Damara Belts formed part of a younger orogenic episode to that which formed the Kaoko and Dom Feliciano orogenic belts. The Damara Belt shows similarities to both Alpine-style and Himalayan-style orogens. An evaluation is provided of a channel flow model for the Central Zone, but there are currently insufficient data for the Damara Belt to confirm or repudiate this model. Nonetheless, this study has identified a more complex tectonic history for the Central Zone than previously, with chronological and lithogeochemical evidence for two episodes of deformation and metamorphism that have been linked to the collisional history of the entire Damara Belt and have been correlated with events in other Pan-African belts.

A study has been made of two deposits of Fe-Cu-Zn sulphide ores, from Gr¢sli and Eiker, in the Proterozoic Kongsberg Series of South Norway. The ores are located at the junction of acid-intermediate supracrustals and amphibolitized gabbros. The supracrustals underwent Upper Amphibolite facies metamorphism of Svecofennian age (1600 to 1500 m.y.B.P.) and were then intruded by the gabbros which underwent subsequent Sveconorwegian (1200 to 1000 m.y.B.P.) metamorphism at ~lid-Amphiboli te facies grade. The ore bodies were originally part of the supracrustal sequence, which was deposited as a volcano-sedimentary succession (with some hydrothermally altc:ced equivalents), similar to the KuroKo-type c1r.'posits of Japan. The ores have thus undergone both phases of h5[;h grade regional metamorphism. At Gr¢sli, the ores were partially incorporated in the gabbros prior to the later (Sveconorwegian) metar.lorphism, during which extensive shearing occurred throughout the ores at Eiker. The cores of the gabbroic intrusions retained original igneous mineralogies and textures, with progressive amphibolitization towards the peripheries. A subsequent Epidote-Amphibolite and later Greenschist facies grade overprint produced varying retrograde assemblages in the silicate rocks. Under Greenschist facies conditions, rejuvenation of the Sveconorwegian shear (at Eiker) caused brittle faulting, while fluid activity (at both Gr¢sli and Eiker) caused the formation of chloriteact ino.li te-carbo!)a.te assemblages around some of the ore bodies. Renobilisation of ~he ore material itself was minimal. Studies of R00thermometry and geobarometry indicate that the ore deposits were re-equilibrated during the Epidote-Ampllj boli te facies overprinting.

This thesis presents the results of structural analyses and detailed field mapping from a region near Adams Burn in central Fiordland, New Zealand. The region preserves assemblages of metasedimentary and metaigneous rocks deposited, intruded, and ultimately metamorphosed and deformed during the growth of a Gondwana-margin continental arc from Cambrian-Early Cretaceous. Evidence of arc growth is preserved in the Late Devonian-Early Cretaceous Median Batholith, a belt of intrusive rock whose growth culminated with the emplacement of the Western Fiordland Orthogneiss (WFO) into the middle-lower crust of the margin. Following this magmatic flare-up, the margin experienced Late Cretaceous extensional orogenic collapse and rifting. During the Late Tertiary, the margin records oblique convergence that preceded the Alpine fault. The history of arc growth and record of changing tectonic and deformational regimes makes the area ideal for study of structural reactivation during multiple cycles of magmatism, metamorphism and deformation, including during a mid-lower crust magma flare-up. Structural and lithologic mapping, structural analyses, and cross-cutting relationships between superposed structures and three intrusions were used to bracket the relative timing of four tectonic events (D1-D4), spanning the Paleozoic to the Tertiary. The oldest event (D1) created a composite fabric in the metasedimentary and metaigneous rocks of the Irene Complex and Jaquiery granitoid gneiss prior to emplacement of the Carboniferous Cozette pluton. S1 foliation development, set the stage for structural reactivation during the second phase of deformation (D2), where S1 was folded and reactivated via intra-arc shearing. These second-phase structures were coeval with the emplacement of the Misty pluton, (part of WFO in central Fiordland), and record crustal thickening and deformation involving a kinematically partitioned style of transpression. Arc-normal displacements were localized into the rocks of the Irene Complex. Oblique displacements were localized along the Misty-Cozette plutonic contact, forming a ≥1 km-wide, upper amphibolite-facies gneissic shear zone that records sinistral-reverse offset. Second-phase structures are cross-cut by widespread leucocratic pegmatite dikes. S2 in the Cozette and Misty plutons is reactivated by localized, ≤10 m-thick, greenschist-facies (ultra)mylonitic shear zones that record sinistral-normal offsets. S3/L3 shear zones and lithologic contacts were then reactivated by two episodes of Tertiary, fourth-phase faulting compatible with Alpine faulting, everywhere truncating the pegmatite dikes. Early faults accommodated shortening normal to the Alpine fault, and were obliquely reactivated by a younger population of faults during dextral transpression. My results show that structural reactivation occurred repeatedly after D1, and that structural inheritance played a key role in the geometry, distribution, and kinematics of younger deformation events throughout the arc's history. The sheeted emplacement of the Misty pluton was accompanied, and possibly facilitated, by a system of partitioned transpression during Early Cretaceous crustal thickening and arc magmatism. These results show that transpression helped accommodate and move magma through the middle and lower crust during the flare-up. This conclusion is important for the study of continental arcs globally, as evidence of deformation during high-flux magmatism at lower crustal depths (~40 km) is rarely preserved and exhumed to the surface.

We analyzed detrital zircons in Lower-Middle Pennsylvanian strata collected from seven sandstones in the Forest City Basin and seven sandstones in the Illinois Basin. In these basins, Lower-Middle Pennsylvanian strata unconformably overlie Mississippian and Devonian strata and reflect a renewed influx of detritus after a significant depositional hiatus. In the total combined dataset (n=3,106), U-Pb ages of approximately 66% of zircons match ages interpreted to be derived from the Appalachian region, including Grenville (1.3-1.0 Ga), Pan-African (530-620 Ma and 750 Ma), Taconic (440-490 Ma), Acadian (350-420 Ma), and Alleghenian (330-270 Ma) ages. Subordinate populations of grains consist of Granite-Rhyolite (1300 -1500 Ma), Yavapai and Mazatzal Terrane (1600- 1800 Ma), Penokean and Trans-Hudson orogens (1800-1900 Ma), and Superior Province (>2.0 Ga) ages. Proportions of grains matching Appalachian sources increased in the Illinois Basin from ~46% to ~79% between our stratigraphically lowest and highest samples, respectively. The Forest City Basin exhibited a similar upsection increase in Appalachian derived grains, which increased from ~52% in our stratigraphically lowest sample to ~70% in our stratigraphically highest sample. Proportions of grains from northern sources (the Canadian Shield and Penokean Province) diminished upsection as these source areas and recycled sediments containing associated grains become covered with Appalachian-derived sediments. Overall, these shifts are interpreted to reflect an increased flux of Alleghenian erosional detritus across the Laurentian craton as a result of the overfilling of the Appalachian foreland region. These results supplement our understanding of the stratigraphic and provenance records left by fluvially dominated large-scale sedimentation events that occur during the formation of supercontinents.

The Australian-Pacific plate boundary is an uncomplicated structure along most of its length in the South Island, New Zealand. In South Westland, south of the Arawata River, however, several terranes converge onto the Alpine fault. Inherent anisotropies arising from the position of pre-existing fault structures, lithological contacts and rheological heterogeneities within these give rise to an atypically diffuse and complex zone, the overall geometry of which resembles a regional scale transpressive flower structure. The flower structure is a broad deformation zone 60 km in length extending approximately 7 km from the Alpine fault to its eastern limit, the Dun Mountain Ophiolite Belt. Integral parts of the structure are the Hollyford Fault System and the Livingstone Fault System. The area is characterised by an array of left-stepping, subparallel faults with an average 060� strike linked by 020� striking structures. All fault traces offset Quaternary features. Fractions of the total interplate slip are partitioned across the reactivated structures. Additionally, kinematic indicators reveal partitioning of strike-slip and oblique/dip-slip deformation across the related secondary fault zones. The behaviour of the plate boundary zone in South Westland is fundamentally controlled by reactivation of the Hollyford Fault System and the Livingstone Fault System which partition slip away from the Alpine fault. As a consequence, the eastward transferral of slip onto the curved geometry of the converging fault systems has ultimately created a left-stepping contractional regime, the equivalent of a restraining bend in the plate boundary zone. The competent Dun Mountain Ophiolite Belt controls the geometry and evolution of the reactivated structures. It also acts as an indenter and imposes additional boundary conditions adding to the shortening component in the region and the onset of complex transpressional strain patterns. The geometry and kinematics of the flower structure in the upper crust is mimicked in the ductile mid to lower crust. Upper greenschist facies mylonites reveal a complex fold pattern developed in response to contemporaneous non-coaxial and coaxial deformation. The folding formed during a continuation of deformation associated with mylonitisation at depths within the fault system. The fact that strain localisation and transpressive strain patterns in the brittle crust continue into the ductile zones suggests there is a feedback relationship between the two regimes. The reactivation of pre-existing structures and the influence of rheological factors are considered as first order factors controlling strain partitioning in the plate boundary zone. Recognition of local strain partitioning is important for assessing slip rates and earthquake recurrence. Similarly, the faults extend down below the seismogenic zone so that interaction of the different structures with each other may produce changes in fault behaviour which affects earthquake nucleation. Although the Alpine fault is a major structure in the South Island of New Zealand with over 400 km of dextral movement, the reactivated structures still exert a degree of control locally on the structure and kinematics of the plate boundary zone. Reactivation of inherent fault structures has important implications for the initiation of plate boundary faults and the alteration of the plate boundary geometry with evolving deformation.

Graduation date: 1985