摘要:

Detailed geological mapping, petrography, geochemistry, and geochronological studies in the Hohonu Batholith, North Westland, have identified 10 granitoid plutons emplaced during three intrusive episodes. The earliest episode is represented by a single dated Paleozoic pluton, Summit Granite (new) (381.2 ± 7.3 Ma), which is correlated with a discrete pulse of Mid—Late Devonian plutonism recognised in the Karamea Batholith. The undated Mount Graham Granite (new) is also likely to be Paleozoic, based on chemical and petrographic characteristics.

ISSN:0028-8306    

DOI:10.1080/00288306.1997.9514736

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The Upper Hutt Basin is one of three onshore Quaternary basins in the Wellington region, New Zealand. This northeast‐trending basin is bounded along its northwest margin by the predominantly strike‐slip Wellington Fault, northwest of which upthrown Torlesse Terrane basement rocks crop out. Quaternary sediment filling the basin rests unconformably on the basement rocks, onlapping the sloping basement surface at the east side of the basin. Interpretation of the seismic and gravity data indicates a total sediment thickness of c. 360–480 m in the main Upper Hutt Basin and 225 m in the Witako Basin. Gravity modelling indicates a dip of c. 60° to the northwest for the Wellington Fault, and has defined a basement high within the basin, which is the subsurface continuation of a NNE‐trending topographic spur. The basement high separates a sub‐basin, the Witako Basin, from the main Upper Hutt Basin. A drillhole near the basement high penetrated interbedded 10–50 m thick gravel and silt/peat units and reached basement at 204 m. Other drillholes indicate that this stratigraphy, at least in the upper 80 m, is consistent in the southwest area of the basin. There are few constraints on the chronology of the sequence in the basin, but a unit of silt and peat between 51.5 and 68 m depth in one drillhole yielded cool climate pollen assemblages and is of early Last Glacial age (50–80 ka).

ISSN:0028-8306    

DOI:10.1080/00288306.1997.9514737

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The Early Permian Plato volcanics consist of mafic volcanogenic sediments and synvolcanic mafic intrusions, intruded in the Mesozoic by calc‐alkaline plutons. The Plato volcanics have high and variable background Cu contents of 50–110 ppm, and mafic intrusion backgrounds can be >200 ppm. Neighbouring belts and calc‐alkaline Mesozoic intrusions have typical background Cu contents of 10–50 ppm. Mineralogical changes during prehnite‐pumpellyite to lower greenschist facies metamorphism of the Plato volcanics and their synvolcanic intrusives have been partially controlled by fluid access along brittle faults and fractures associated with late Mesozoic fault zones. Rock alteration is dominated by epidote, actinolite, chlorite, and hematite, with prehnite and locally andradite in lower grade rocks. Epidote (up to 90 modal percent), with minor chlorite and hematite, dominates the alteration assemblage on some fracture margins. Epidote cannot accommodate more than c. 10 ppm Cu, so oxidative metamorphism and pidotisation release Cu from mafic rocks. The Cu migrates locally (metre scale) and concentrates in fault zones as chalcopyrite veins up to 1 m long. Surficial alteration remobilises Cu to form brochantite‐limonite‐calcite coatings under cliff overhangs. The described Cu anomalies are not economically significant due to lack of kilometre‐scale Cu mobility.

ISSN:0028-8306    

DOI:10.1080/00288306.1997.9514738

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Fissure veins containing adularia, bladed calcite, quartz, and chlorite occur in fractures in schist immediately west of the mountain crest in the Southern Alps, an active collisional mountain range. The vein minerals contain primary fluid inclusions which homogenise between 240 and 260°C. The fluids have low dissolved salt content (<2 wt% NaCl equivalent) and low CO2content (<1 wt%). Fluid inclusions in adularia show physical (co‐existing liquid and vapour) and chemical (variable CO2contents) evidence for boiling during entrapment. The mineral assemblage is similar to that seen in boiling zones of modern geothermal systems. Boiling occurred at 500 ± 150 m below topographic surface, or c. 1 km above sea level, and fluid temperature was higher than rock temperature. In contrast, fluids trapped in the same rock sequence at 300–350°C at 6–10 km under lithostatic and hydrostatic fluid pressure were approximately the same temperature as host rock and define part of a conductive thermal anomaly. The boiling zone developed due to topography‐driven two‐dimensional circulation of meteoric water into the uplift‐induced conductive anomaly, followed by rapid buoyant rise of heated and partially isotopically exchanged water to shallow levels under hydrostatic fluid pressure.

ISSN:0028-8306    

DOI:10.1080/00288306.1997.9514739

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A NNE—NE trending strip, 3–8 km wide, extending from the Freshwater valley across Mt Rakeahua, Table Hill, and Mt Allen to the northern end of the Tin Range was mapped at a scale of 1:12 500 to locate and investigate the boundary between the Median Tectonic Zone (MTZ) and Western Province on Stewart Island.

ISSN:0028-8306    

DOI:10.1080/00288306.1997.9514740

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Data from the new Taranaki Volcano‐Seismic Network provide the first detailed information on microseismicity in the vicinity of Egmont Volcano (Mt Taranaki) and central Taranaki. During the period January 1994 to March 1995, 133 earthquakes were located within a 40 x 40 km area centred on Egmont Volcano. Earthquake magnitudes varied from 1.5 to 3.4, with five events being of magnitude 3 or greater. Most earthquakes were located in the northwest of the study area, with a distinct cluster of earthquakes occurring c. 12 km WNW of the summit of Egmont Volcano. Levels of seismicity were low in the remainder of the area and occurred throughout the crust, with depths ranging to just over 30 km.

ISSN:0028-8306    

DOI:10.1080/00288306.1997.9514741

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

This paper describes the application to New Zealand data of two algorithms recently made available through the IASPEI software programme. These are the M8 algorithm, which has the objective of identifying times and regions of heightened probability of the occurrence of a large damaging earthquake, and the Lin‐Lin algorithm, which has the objective of identifying linear causal relationships between one sequence of events and another. The M8 algorithm is applied to the New Zealand events listed in the NEIC catalogue, and to shallow, deep, and combined events listed in the New Zealand local catalogue. The most notable feature of the M8 analysis is the generation of TIPS (times of increased probability) for 1993 onward, for central New Zealand regions from both the New Zealand and NEIC catalogues. No short‐term linear causal relationships between New Zealand deep and shallow earthquakes are detected by the Lin‐Lin algorithm.

ISSN:0028-8306    

DOI:10.1080/00288306.1997.9514742

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Sixteen unconformities, some with correlative conformities, are recognised within the Late Cretaceous‐Tertiary transgressive‐regressive sediments of coastal Otago. These provide the basis for stratigraphic division and correlation with seismic reflectors in the offshore age‐equivalent sediments of the Great South Basin. The ages of the unconformities/conformities are constrained mainly by dinoflagellate biostratigraphy, but foraminiferal biostrati‐graphy is important for the Oligocene—Miocene. In terms of current biozone‐stage correlation, the 16 unconformities comprise the following: two intra‐Haumurian (Late Cretaceous) unconformities, one at the K/T boundary, three intra‐Teurian (Paleocene) unconformities, two of early Waipawan age, two of late Mangaorapan — early Heretaungan age, a late Heretaungan unconformity, a late Porangan ‐ early Bortonian unconformity, a late Bortonian unconformity (a total of seven Eocene unconformities), a late Runangan ‐ early Whaingaroan unconformity, a late Whaingaroan unconformity (both Oligocene), and a mid‐Waitakian (Miocene) unconformity. Other, early—mid‐Cretaceous unconformities are inferred from offshore seismic profiles. Six unconformities/correlative conformities in onland Otago provide the basis for recognising four informal alloformations.

ISSN:0028-8306    

DOI:10.1080/00288306.1997.9514743

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Coastal exposures of four lithified pyroclastic units at Pigeon Bay on Banks Peninsula in Canterbury, New Zealand, record flank explosive activity at the Miocene Akaroa volcano. These eroded units are the surface expression of lateral dike injections of hawaiite magma from a central conduit beneath the Akaroa lava shield. The form of the deposits was severely modified by erosion before burial within the volcanic pile and during exhumation. Four lithofacies are proposed, based on the size and shape of clasts and inferred degree of welding: (1) ash‐rich deposits; (2) non‐flattened scoria deposits; (3) mixed scoria deposits; and (4) densely welded scoria deposits. Spatial relationships between lithofacies, steep primary dips, and rapid changes in thickness and grainsize of the beds enable us to infer that the deposits are the eroded remnants of Hawaiian and Strombolian cones. Within the deposits, variations in clast shape and size reflect subtle variations in the processes of fragmentation, in turn controlled by the size and rise rate of bursting gas bubbles. Different degrees of welding reflect local variation in accumulation rates and clast temperature on deposition (in turn partially dependent on residence time in the vent, distance from vent to point of deposition, and clast size).

ISSN:0028-8306    

DOI:10.1080/00288306.1997.9514744

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

ISSN:0028-8306    

DOI:10.1080/00288306.1997.9514745

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor