scholarly journals The Horizontal Kinematics of the North Island of New Zealand

2021 ◽  
Author(s):  
◽  
Bryan Arthur Sissons
Keyword(s):  
Indian Plate ◽  
Taupo Volcanic Zone ◽  
Plate Boundaries ◽  
Advantages And Disadvantages ◽  
Spreading Axis ◽  
The North ◽  
Central Plate ◽  
Back Arc ◽  
Geodetic Strain ◽  
Shear Belt

<p>The advantages and disadvantages of the 'displacement' approach and the 'strain' approach to the analysis of repeated geodetic surveys for crustal deformation are discussed and two methods of geodetic strain analysis are described in detail. Repeated geodetic surveys in the central North Island show i) secular widening of the Taupo Volcanic Zone (TVZ) at 7 mm y-1 without significant transcurrent motion ii) north-south dextral motion at 14 mm y-1 and east-west narrowing at 4 mm y-1 across the northern end of the North Island Shear Belt iii) 3.1 m extension at 135' across a 15 km-wide region north of Lake Taupo, and adjacent zones of compressive rebound all associated with the 1922 Taupo Earthquakes. From the epicentral distribution and horizontal strain pattern a 15 km-square fault dipping 40' and striking parallel to the TVZ is inferred for the 1922 earthquakes. The seismic moment, 1.3 x 10 26 dyne cm, and the stress drop, 134 bars, are abnormally high for the TVZ. Widening of the TVZ is considered to be back-arc spreading. The spreading axis is postulated to extend northeast into the Havre Trough via a north-south dextral transform; and southwest into the Waverley Fault Zone and Waimea Depression via the sinistral reverse Raetihi Transform. Deformation of the North Island is not homogeneous. Fault zones are idealized as line plate boundaries and four plates -Indian, Central, Kermadec and Pacific - are postulated to account for the deformation. The Indian-Pacific macroplate pole is adopted and non-unique positions and rotation rates for the remaining poles are determined from geodetic strain data and the geometry of plate interactions. The Central Plate is moving away from the Indian Plate at the back-arc spreading axis; the Kermadec Plate is moving dextrally with respect to the Central Plate at the North Island Shear Belt which accommodates most of the transcurrent component of motion between the Indian and Pacific plates in the North Island and gives almost pure subduction of the Pacific Plate under the Kermadec Plate at the Hikurangi Margin.</p>

scholarly journals The Horizontal Kinematics of the North Island of New Zealand

2021 ◽  
Author(s):  
◽  
Bryan Arthur Sissons
Keyword(s):  
Indian Plate ◽  
Taupo Volcanic Zone ◽  
Plate Boundaries ◽  
Advantages And Disadvantages ◽  
Spreading Axis ◽  
The North ◽  
Central Plate ◽  
Back Arc ◽  
Geodetic Strain ◽  
Shear Belt

<p>The advantages and disadvantages of the 'displacement' approach and the 'strain' approach to the analysis of repeated geodetic surveys for crustal deformation are discussed and two methods of geodetic strain analysis are described in detail. Repeated geodetic surveys in the central North Island show i) secular widening of the Taupo Volcanic Zone (TVZ) at 7 mm y-1 without significant transcurrent motion ii) north-south dextral motion at 14 mm y-1 and east-west narrowing at 4 mm y-1 across the northern end of the North Island Shear Belt iii) 3.1 m extension at 135' across a 15 km-wide region north of Lake Taupo, and adjacent zones of compressive rebound all associated with the 1922 Taupo Earthquakes. From the epicentral distribution and horizontal strain pattern a 15 km-square fault dipping 40' and striking parallel to the TVZ is inferred for the 1922 earthquakes. The seismic moment, 1.3 x 10 26 dyne cm, and the stress drop, 134 bars, are abnormally high for the TVZ. Widening of the TVZ is considered to be back-arc spreading. The spreading axis is postulated to extend northeast into the Havre Trough via a north-south dextral transform; and southwest into the Waverley Fault Zone and Waimea Depression via the sinistral reverse Raetihi Transform. Deformation of the North Island is not homogeneous. Fault zones are idealized as line plate boundaries and four plates -Indian, Central, Kermadec and Pacific - are postulated to account for the deformation. The Indian-Pacific macroplate pole is adopted and non-unique positions and rotation rates for the remaining poles are determined from geodetic strain data and the geometry of plate interactions. The Central Plate is moving away from the Indian Plate at the back-arc spreading axis; the Kermadec Plate is moving dextrally with respect to the Central Plate at the North Island Shear Belt which accommodates most of the transcurrent component of motion between the Indian and Pacific plates in the North Island and gives almost pure subduction of the Pacific Plate under the Kermadec Plate at the Hikurangi Margin.</p>

The Thirty-Ninth Thomas Lowe Gray Lecture: Offshore Drilling, with Particular Reference to the North Sea and the ‘Sea Quest’

1966 ◽  
Vol 181 (1) ◽  
pp. 848-875 ◽  
Author(s):  
R. G. S. Avery
Keyword(s):  
North Sea ◽  
Essential Factor ◽  
Safety Equipment ◽  
Offshore Drilling ◽  
Advantages And Disadvantages ◽  
The North ◽  
Drilling Equipment ◽  
Sea Bed ◽  
Weight Problems ◽  
The North Sea

The origins of offshore drilling work and the development of structures used at sea are traced. Comparison of the various types illustrates the advantages and disadvantages of each. Tables show the numbers in operation, being built, and the apparent liability of each type to damage. Typical bore-hole structures are illustrated, the need for undersea well-heads explained and their development into a sea-bed completion is discussed. Much more research is necessary before this can be considered a practical proposition. The design of drilling barge equipment is compared with typical land rigs and the development of drilling equipment, including the sophisticated electric drive and turbo-drill, discussed. Rigs in various types of barge are compared. Fire precautions and other safety equipment are described. The problems associated with control by the driller lead to complications of motive power layout. The lecture describes in some detail the design of the semi-submersible drilling barge Sea Quest, illustrates the weight problems and their effect on floating stability and indicates the need for management decisions on the degree of resistance to damage. This is measured by the variable deck load of drilling equipment that can be held on board and the degree of weather deterioration that can be tolerated before disengaging the drill from the hole. The need for, and extent of, diving is discussed, with some comparison between diving vehicles. Weather too is an essential factor of work in the North Sea and both pre-surveys and day-to-day reporting are described.

Volatiles in submarine volcanic rocks from the spreading axis of the East Scotia Sea back-arc basin

1980 ◽  
Vol 47 (2) ◽  
pp. 272-278 ◽  
Author(s):  
David W. Muenow ◽  
Norman W.K. Liu ◽  
Michael O. Garcia ◽  
Andrew D. Saunders
Keyword(s):  
Volcanic Rocks ◽  
Scotia Sea ◽  
Spreading Axis ◽  
Back Arc

Understanding pre- and syn-orogenic tectonic evolution in western Himalaya through age and petrogenesis of Palaeozoic and Cenozoic granites from upper structural levels of Bhagirathi Valley, NW India

2021 ◽  
pp. 1-27
Author(s):  
Aranya Sen ◽  
Koushik Sen ◽  
Amitava Chatterjee ◽  
Shubham Choudhary ◽  
Alosree Dey
Keyword(s):  
Inductively Coupled Plasma ◽  
Age Distribution ◽  
Normal Fault ◽  
Western Himalaya ◽  
Indian Plate ◽  
Low Grade ◽  
Inductively Coupled ◽  
The North ◽  
Plasma Mass Spectrometry ◽  
Structural Levels

Abstract The Himalaya is characterized by the presence of both pre-Himalayan Palaeozoic and syn-Himalayan Cenozoic granitic bodies, which can help unravel the pre- to syn-collisional geodynamics of this orogen. In the Bhagirathi Valley of Western Himalaya, such granites and the Tethyan Himalayan Sequence (THS) hosting them are bound to the south by the top-to-the-N extensional Jhala Normal Fault (JNF) and low-grade metapelite of the THS to its north. The THS is intruded by a set of leucocratic dykes concordant to the JNF. Zircon U–Pb laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) geochronology of the THS and one leucocratic dyke reveals that the two rocks have a strikingly similar age distribution, with a common and most prominent age peak at ~1000 Ma. To the north of the THS lies Bhaironghati Granite, a Palaeozoic two-mica granite, which shows a crystallization age of 512.28 ± 1.58 Ma. Our geochemical analysis indicates that it is a product of pre-Himalayan Palaeozoic magmatism owing to extensional tectonics in a back-arc or rift setting following the assembly of Gondwana (500–530 Ma). The Cenozoic Gangotri Leucogranite lies to the north of Bhaironghati Granite, and U–Pb dating of zircon from this leucogranite gives a crystallization age of 21.73 ± 0.11 Ma. Our geochemical studies suggest that the Gangotri Leucogranite is a product of muscovite-dehydration melting of the lower crust owing to flexural bending in relation to steepening of the subducted Indian plate. The leucocratic dykes are highly refracted parts of the Gangotri Leucogranite that migrated and emplaced along extensional fault zones related to the JNF and scavenged zircon from the host THS during crystallization.

scholarly journals Mapping Stress and Structure From Subducting Slab to Magmatic Rift: Crustal Seismic Anisotropy of the North Island, New Zealand

2020 ◽  
Author(s):  
Finnigan Illsley-Kemp ◽  
Martha Savage ◽  
Colin Wilson ◽  
S Bannister
Keyword(s):  
New Zealand ◽  
Stress Field ◽  
Large Scale ◽  
Seismic Anisotropy ◽  
Taupo Volcanic Zone ◽  
Volcanic Zone ◽  
The North ◽  
Magma Reservoirs ◽  
Tectonic Forces ◽  
Subducting Slab

© 2019. American Geophysical Union. All Rights Reserved. We use crustal seismic anisotropy measurements in the North Island, New Zealand, to examine structures and stress within the Taupō Volcanic Zone, the Taranaki Volcanic Lineament, the subducting Hikurangi slab, and the Hikurangi forearc. Results in the Taranaki region are consistent with NW-SE oriented extension yet suggest that the Taranaki volcanic lineament may be controlled by a deep-rooted, inherited crustal structure. In the central Taupō Volcanic Zone anisotropy fast orientations are predominantly controlled by continental rifting. However at Taupō and Okataina volcanoes, fast orientations are highly variable and radial to the calderas suggesting the influence of magma reservoirs in the seismogenic crust (≤15 km depth). The subducting Hikurangi slab has a predominant trench-parallel fast orientation, reflecting the pervasive presence of plate-bending faults, yet changing orientations at depths ≥120 km beneath the central North Island may be relics from previous subduction configurations. Finally, results from the southern Hikurangi forearc show that the orientation of stresses there is consistent with those in the underlying subducting slab. In contrast, the northern Hikurangi forearc is pervasively fractured and is undergoing E-W compression, oblique to the stress field in the subducting slab. The north-south variation in fore-arc stress is likely related to differing subduction-interface coupling. Across the varying tectonic regimes of the North Island our study highlights that large-scale tectonic forces tend to dictate the orientation of stress and structures within the crust, although more localized features (plate coupling, magma reservoirs, and inherited crustal structures) can strongly influence surface magmatism and the crustal stress field.

The Making of the Himalaya, Karakoram, and Tibetan Plateau

2013 ◽  
Author(s):  
Mike Searle
Keyword(s):  
Tibetan Plateau ◽  
Plate Boundary ◽  
Indian Plate ◽  
North West ◽  
Geological Interpretation ◽  
Mountain Ranges ◽  
The Road ◽  
The North ◽  
On The Road ◽  
The Himalaya

My quest to figure out how the great mountain ranges of Asia, the Himalaya, Karakoram, and Tibetan Plateau were formed has thus far lasted over thirty years from my first glimpse of those wonderful snowy mountains of the Kulu Himalaya in India, peering out of that swaying Indian bus on the road to Manali. It has taken me on a journey from the Hindu Kush and Pamir Ranges along the North-West Frontier of Pakistan with Afghanistan through the Karakoram and along the Himalaya across India, Nepal, Sikkim, and Bhutan and, of course, the great high plateau of Tibet. During the latter decade I have extended these studies eastwards throughout South East Asia and followed the Indian plate boundary all the way east to the Andaman Islands, Sumatra, and Java in Indonesia. There were, of course, numerous geologists who had ventured into the great ranges over the previous hundred years or more and whose findings are scattered throughout the archives of the Survey of India. These were largely descriptive and provided invaluable ground-truth for the surge in models that were proposed to explain the Himalaya and Tibet. When I first started working in the Himalaya there were very few field constraints and only a handful of pioneering geologists had actually made any geological maps. The notable few included Rashid Khan Tahirkheli in Kohistan, D. N. Wadia in parts of the Indian Himalaya, Ardito Desio in the Karakoram, Augusto Gansser in India and Bhutan, Pierre Bordet in Makalu, Michel Colchen, Patrick LeFort, and Arnaud Pêcher in central Nepal. Maps are the starting point for any geological interpretation and mapping should always remain the most important building block for geology. I was extremely lucky that about the time I started working in the Himalaya enormous advances in almost all aspects of geology were happening at a rapid pace. It was the perfect time to start a large project trying to work out all the various geological processes that were in play in forming the great mountain ranges of Asia. Satellite technology suddenly opened up a whole new picture of the Earth from the early Landsat images to the new Google Earth images.

Origin of grain-coating chlorite by smectite transformation: an example from Miocene sandstones, North Sumatra back-arc basin, Indonesia

Clay Minerals ◽  
1994 ◽  
Vol 29 (4) ◽  
pp. 681-692 ◽  
Author(s):  
B. Humphreys ◽  
S. J. Kemp ◽  
G. K. Lott ◽  
Bermanto ◽  
D.A. Dharmayanti ◽  
...  
Keyword(s):  
Geothermal Gradient ◽  
Upper Miocene ◽  
The North ◽  
Direct Precipitation ◽  
Back Arc ◽  
North Sumatra ◽  
Textural Evidence ◽  
High Geothermal Gradient

AbstractGrain-coating chlorite cements commonly occur within sandstones of late Middle and Upper Miocene age deposited in the North Sumatra back-arc basin. Chlorites from the Lower Keutapang Member contain Ca (maximum 0.75 wt% oxide) and show textural evidence for direct precipitation on grains. However, crystals are subhedral, showing curved faces and often ragged edges, and show a tendency to merge together. In overlying beds of the Upper Keutapang Member, grain-coating chlorite-smectite (20% smectite) cements display an identical morphology but are more siliceous, have a lower octahedral occupancy and contain higher total (Na + Ca + K). It is proposed that chlorite cements in the Keutapang Formation originated as smectite-rich cement rims whose initial precipitation was related to the breakdown of volcanic detritus in the sediments. Transformation to chlorite occurred subsequently during burial, facilitated by a high geothermal gradient in the back-arc basin.

scholarly journals Crustal deformation rates in Kashmir valley and adjoining regions from continuous GPS measurements from 2008 to 2019

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Sridevi Jade ◽  
Ramees R. Mir ◽  
Chiranjeevi G. Vivek ◽  
T. S. Shrungeshwara ◽  
I. A. Parvez ◽  
...  
Keyword(s):  
Dislocation Model ◽  
Seismic Gap ◽  
Extension Rate ◽  
Kashmir Valley ◽  
Low Velocity ◽  
The North ◽  
Geodetic Strain Rate ◽  
Gps Velocities ◽  
Continuous Gps ◽  
Geodetic Strain

Abstract We present GPS velocities in Kashmir valley and adjoining regions from continuous Global Positioning System (cGPS) network during 2008 to 2019. Results indicate total arc normal shortening rates of ~ 14 mm/year across this transect of Himalaya that is comparable to the rates of ~ 10 to 20 mm/year reported else-where in the 2500 km Himalaya Arc. For the first time in Himalayas, arc-parallel extension rate of ~ 7 mm/year was recorded in the Kashmir valley, pointing to oblique deformation. Inverse modeling of the contemporary deformation rates in Kashmir valley indicate oblique slip of ~ 16 mm/year along the decollement with locking depth of ~ 15 km and width of ~ 145 km. This result is consistent with the recorded micro-seismicity and low velocity layer at a depth of 12 to 16 km beneath the Kashmir valley obtained from collocated broadband seismic network. Geodetic strain rates are consistent with the dislocation model and micro-seismic activity, with high strain accumulation (~ 7e−08 maximum compression) to the north of Kashmir valley and south of Zanskar ranges. Assuming the stored energy was fully released during 1555 earthquake, high geodetic strain rate since then and observed micro-seismicity point to probable future large earthquakes of Mw ~ 7.7 in Kashmir seismic gap.

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