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Alpine Fault (alpine + fault)
Selected AbstractsRole of fluids in the metamorphism of the Alpine Fault Zone, New ZealandJOURNAL OF METAMORPHIC GEOLOGY, Issue 1 2001J. K. Vry Abstract Models of fluid/rock interaction in and adjacent to the Alpine Fault in the Hokitika area, South Island, New Zealand, were investigated using hydrogen and other stable isotope studies, together with field and petrographic observations. All analysed samples from the study area have similar whole-rock ,D values (,DWR = ,56 to ,30,, average = ,45,, n = 20), irrespective of rock type, degree of chloritization, location along the fault, or across-strike distance from the fault in the garnet zone. The green, chlorite-rich fault rocks, which probably formed from Australian Plate precursors, record nearly isothermal fluid/rock interaction with a schist-derived metamorphic fluid at high temperatures near 450,500°C (,D of water in equilibrium with the green fault rocks (,DH2O, green) ,,,18,; ,D of water in equilibrium with the greyschists and greyschist-derived mylonites (,DH2O, grey) , ,19, at 500°C; ,DH2O, green , ,17,; ,DH2O, grey , ,14, at 450°C). There is no indication of an influx of a meteoric or mantle-derived fluid in the Alpine Fault Zone in the study area. The Alpine Fault Zone at the surface shows little evidence of late-stage retrogression or veining, which might be attributed to down-temperature fluid flow. It is probable that prograde metamorphism in the root zone of the Southern Alps releases metamorphic fluids that at some region rise vertically rather than following the trace of the Alpine Fault up to the surface, owing to the combined effects of the fault, the disturbed isotherms under the Southern Alps, and the brittle,ductile transition. Such fluids could mix with meteoric fluids to deposit quartz-rich, possibly gold-bearing veins in the region c. 5,10 km back from the fault trace. These results and interpretations are consistent with interpretations of magnetotelluric data obtained in the South Island GeopHysical Transects (SIGHT) programme. [source] Frontal accretion and thrust wedge evolution under very oblique plate convergence: Fiordland Basin, New ZealandBASIN RESEARCH, Issue 4 2002P. M. Barnes ABSTRACT A thrust wedge with unusual geometry has developed under very oblique (50,60°) convergence between the Pacific and Australian Plates, along the 240-km length of the Fiordland margin, New Zealand. The narrow (25 km-wide) wedge comprises three overlapping components, lying west of the offshore section of the Alpine Fault, and straddles a change of > 30° in the regional strike of the plate boundary. Swath bathymetry, marine seismic reflection profiles, and dated samples together reveal the stratigraphy, structure, and evolution of the wedge and the underthrusting, continental, Caswell High (Australian Plate). Lateral variations in the composition and structure of the accretionary wedge, and the depth of the décollement thrust, result partly from variations in crustal structure and basement relief of the underthrust plate, and from associated variations in the thickness of turbidites available for frontal accretion. In the southern Fiordland Basin the underthrust plate is undergoing flexural uplift and extension, and a thick turbidite section is available for accretion. Along-strike, a structurally elevated portion of the underthrust plate is very obliquely colliding with the central part of the accretionary wedge, the turbidite section available for accretion is condensed, and structural inversion occurs in the underthrust plate. ,Growth of the thrust wedge is inferred to have commenced in the Pliocene prior to 3 ± 1 Ma, but much of the wedge developed in the Quaternary. The spatial distribution of thrusting has varied through time, with most late Quaternary shortening occurring on structures within 10 km of the right-stepping deformation front. Estimates of the magnitude and rates of deformation indicate that the wedge accommodates a significant component of the oblique convergence between the Pacific and Australian Plates. Shortening of up to 7.3 ± 1.4 km and 9.1 ± 1.8 km within the southern and central parts of the wedge, respectively, represent about 5,15% of the total 70,140 km of shortening predicted across the plate boundary since 6.4 Ma, and about 10,30% since 3 Ma. Late Quaternary shortening rates of the order of 1,5 mm yr,1, estimated across both the northern and southern parts of the wedge, represent about 10,50 and 5,21% of the total NUVEL-1 A shortening across the plate boundary at these respective latitudes, implying that most shortening is occurring onshore. Furthermore, possible oblique-slip thrusting within the wedge may be accommodating boundary-parallel displacement of 0,6 mm yr,1, representing 0,17% of the total predicted within the plate boundary. [source] A complex, young subduction zone imaged by three-dimensional seismic velocity, Fiordland, New ZealandGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2001Donna Eberhart-Phillips Summary The Fiordland subduction zone, where subduction developed in the late Miocene, has been imaged with P and S,P arrival-time data from 311 earthquakes in a simultaneous inversion for hypocentres and 3-D VP and VP/VS models. The three-month microearthquake survey, recorded with 24 portable seismographs, provides excellent coverage, and, since earthquakes to depths of 130 km are included, parts of the model are well-resolved to depths of 100 km. The crustal features are generally consistent with geology. The low velocity in the upper 10 km is associated with the Te Anau and Waiau basins. The Western Fiordland Orthogneiss is associated with a prominent feature from near-surface to over 40 km depth, which includes the residue from the basaltic source rocks. It is defined by high VP (7.4 km s,1 at 15 km depth) and slightly low VP/VS, and has distinct boundaries on its southern and eastern margins. Adjacent to the deepest earthquakes, there is high-velocity Pacific mantle below 80 km depth, inferred to be the mantle expression of ongoing shortening since the early Miocene. As the subducting slab moves down and northeast, it is hindered by the high-velocity body and bends to near-vertical. Bending is accommodated by distributed fracturing evidenced by high VP/VS and persistent deep earthquake activity. Buckling of the subducted plate pushes up the Western Fiordland Orthogneiss. In the transition to the Alpine fault in northern Fiordland, a prominent low-velocity crustal root is consistent with ductile thickening in combination with downwarp of the subducted plate. [source] Disentangling causes of disjunction on the South Island of New Zealand: the Alpine fault hypothesis of vicariance revisitedBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 3 2007MARTIN HAASE Many elements of the flora and fauna of New Zealand's South Island show disjunct distributions with conspecific populations or closely-related species that occur in the north-west and south separated by a central gap. Three events have been implicated to account for this pattern: Pleistocene glaciations, Pliocene mountain building, or displacement along the Alpine fault, the border of the Pacific and Australian plates stretching diagonally across the South Island from south-west to north-east that formed during the Miocene. Disjunct distributions of species level taxa are probably too young to be due to Alpine fault vicariance. It has therefore been suggested that the biogeographical impact of the Alpine fault, if any, should be apparent on deeper phylogenetic levels. We tested this hypothesis by reconstructing the phylogenetic relationships of the hydrobiid gastropods of New Zealand based on mitochondrial DNA fragments of cytochrome oxidase subunit I (CO I) and 16S rDNA. The creno- and stygobiont species of this family are typically poor dispersers. Therefore, ancient patterns of distribution may be conserved. The phylogenetic reconstructions were in accordance with the Alpine fault hypothesis uniting genera occurring on either side of the fault. Divergence estimates based on a molecular clock of CO I indicated splits predating the Pliocene uplift of the Alps. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 91, 361,374. [source] | ||||||||||