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Keywords = Otago Schist

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9 pages, 6129 KiB  
Article
A Morphological and Size-Based Study of the Changes of Iron Sulfides in the Caples and Torlesse Terranes (Otago Schist, New Zealand) during Prograde Metamorphic Evolution
by Victor Cardenes, Raúl Merinero, Álvaro Rubio-Ordoñez, Veerle Cnudde, Javier García-Guinea and Iain K. Pitcairn
Minerals 2020, 10(5), 459; https://doi.org/10.3390/min10050459 - 19 May 2020
Viewed by 2297
Abstract
It is widely accepted that metamorphism induces a remobilization of iron sulfides, sweeping away original ones while creating new ones. This paper analyzes size distributions of iron sulfides in several samples from the Caples and Torlesse terranes from the Otago Schist (New Zealand) [...] Read more.
It is widely accepted that metamorphism induces a remobilization of iron sulfides, sweeping away original ones while creating new ones. This paper analyzes size distributions of iron sulfides in several samples from the Caples and Torlesse terranes from the Otago Schist (New Zealand) using high-resolution X-ray computed tomography, which allows all iron sulfides larger than the resolution at which X-ray scans were performed to be characterized. Framboids and clusters of framboids are common in unmetamorphosed samples, but disappear in greenschist/amphibolite facies samples, where iron sulfides have anhedral habits. By contrast, the size and standard deviation of the new iron sulfides both remain within the same range. The results illuminate the evolution of iron sulfides throughout metamorphism, proposing boundaries for the metamorphic processes based on the shape of these iron sulfides. Full article
(This article belongs to the Section Mineral Deposits)
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21 pages, 5841 KiB  
Article
Far-Field Deformation Resulting from Rheologic Differences Interacting with Tectonic Stresses: An Example from the Pacific/Australian Plate Boundary in Southern New Zealand
by Phaedra Upton, Dave Craw and Rachel Walcott
Geosciences 2014, 4(3), 93-113; https://doi.org/10.3390/geosciences4030093 - 10 Jul 2014
Cited by 16 | Viewed by 11119
Abstract
The Miocene in Southern New Zealand was dominated by strike-slip tectonics. Stratigraphic evidence from this time attests to two zones of subsidence in the south: (a) a middle Cenozoic pull-apart basin and (b) a regionally extensive subsiding lake complex, which developed east and [...] Read more.
The Miocene in Southern New Zealand was dominated by strike-slip tectonics. Stratigraphic evidence from this time attests to two zones of subsidence in the south: (a) a middle Cenozoic pull-apart basin and (b) a regionally extensive subsiding lake complex, which developed east and distal to the developing plate boundary structure. The lake overlay a block of crust with a significantly weak mid-crustal section and we pose the question: can rheological transitions at an angle to a plate boundary produce distal subsidence and/or uplift? We use stratigraphic, structural and geophysical observations from Southern New Zealand to constrain three-dimensional numerical models for a variety of boundary conditions and rheological scenarios. We show that coincident subsidence and uplift can result from purely strike-slip boundary conditions interacting with a transition from strong to weak to strong mid-crustal rheology. The resulting pattern of vertical displacement is a function of the symmetry or asymmetry of the boundary conditions and the extent and orientation of the rheological transitions. For the Southern New Zealand case study, subsidence rates of ~0.1 mm/yr are predicted for a relative plate motion of 25 mm/yr, leading to ~500 m of subsidence over a 5 Ma time period, comparable to the thickness of preserved lacustrine sediments. Full article
(This article belongs to the Special Issue Geological Mapping and Modeling of Earth Architectures)
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