TY  - JOUR
A1  - Van der Meer, Q. H. A.
A1  - Scott, James M.
A1  - Waight, T. E.
A1  - Sudo, Masafumi
A1  - Schersten, A.
A1  - Cooper, Alan F.
A1  - Spell, Terry L.
T1  - Magmatism during Gondwana break-up: new geochronological data from Westland, New Zealand
JF  - New Zealand journal of geology and geophysics : an international journal of pacific rim geosciences
N2  - Newly determined Late Cretaceous Ar-40/Ar-39 ages on megacrystic kaersutite from four lamprophyre dikes, and a U-Pb zircon age on a trachyte, from central and north Westland (New Zealand) are presented. These ages suggest that the intrusion of mafic dikes (88-86 and 69 Ma) was not necessarily restricted to the previously established narrow age range of 80-92 Ma. The younger lamprophyre and trachyte dikes (c. 68-70 Ma) imply that tensional stresses in the Western Province were either renewed at this time, or that extension and related magmatism continued during opening of the Tasman Sea. Extension-related magmatism in the region not only preceded Tasman seafloor spreading initiation (starting at c. 83 Ma, lasting to c. 53 Ma), but may have sporadically continued for up to 15 Ma after continental break-up.
KW  - Gondwana break-up
KW  - geochronology
KW  - lamprophyre
KW  - central Westland
KW  - Fraser Complex
Y1  - 2013
U6  - https://doi.org/10.1080/00288306.2013.826699
SN  - 0028-8306
SN  - 1175-8791
VL  - 56
IS  - 4
SP  - 229
EP  - 242
PB  - Routledge, Taylor & Francis Group
CY  - Abingdon
ER  - 
TY  - JOUR
A1  - Scott, James M.
A1  - Konrad-Schmolke, Matthias
A1  - O'Brien, Patrick J.
A1  - Günter, Christina
T1  - High-T, low-P formation of rare olivine-bearing symplectites in variscan eclogite
JF  - Journal of petrology
N2  - Extremely rare veinlets and reaction textures composed of symplectites of olivine (similar to Fo(43-55)) + plagioclase +/- spinel +/- ilmenite, associated with more common pyroxene + plagioclase and amphibole + plagioclase varieties, are preserved within eclogites and garnet pyroxenites in the Moldanubian Zone of the Bohemian Massif. Thermodynamic modelling integrated with conventional geothermometry conducted on an eclogite reveals that the symplectite-forming stage occurred at high T (similar to 850 degrees C) and low P (< 6 and > 2 center dot 5 kbar). The development of the different symplectite types reflects reactions that took place in micro-scale domains. The breakdown of high-P garnet controlled the formation of olivine-bearing and amphibole + plagioclase symplectites, whereas breakdown of high-P omphacite led to formation of pyroxene + plagioclase symplectites. In addition, post-eclogite facies but pre-symplectite stage porphyroblastic amphibole and phlogopite were also replaced by olivine-bearing symplectites. Material transfer calculations and thermodynamic modelling indicate that the formation of different symplectite types was linked despite their different bulk compositions. For example, the olivine-bearing symplectites gained Fe +/- Mg, whereas adjacent amphibole + plagioclase and pyroxene + plagioclase symplectites show losses in Fe and Mg; Al, Si and Ca were also variably exchanged. The olivine-bearing symplectites were particularly sensitive to Na despite the small concentration of this element. In eclogites where Na was readily available, the plagioclase composition in the olivine-bearing symplectites shifted from pure anorthite to bytownite, with the less calcic feldspar partitioning Si and inhibiting the formation of orthopyroxene. This regional high-T, low-P granulite-facies symplectite overprint may have been caused by advective heat loss from rapidly exhumed high-T, high-P granulitic bodies (Gfohl Unit) that were emplaced into and over the middle crust (Monotonous and Varied Series) during Carboniferous continent-continent collision.
KW  - olivine
KW  - symplectite
KW  - eclogite
KW  - thermodynamics
KW  - Variscan
Y1  - 2013
U6  - https://doi.org/10.1093/petrology/egt015
SN  - 0022-3530
SN  - 1460-2415
VL  - 54
IS  - 7
SP  - 1375
EP  - 1398
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Scott, James M.
A1  - Cooper, Alan F.
A1  - Palin, J. Michael
A1  - Tulloch, Andy J.
A1  - Kula, Joseph L.
A1  - Jongens, Richard
A1  - Spell, Terry L.
A1  - Pearson, Norman J.
T1  - Tracking the influence of a continental margin on growth of a magmatic arc, Fiordland, New Zealand, using thermobarometry, thermochronology, and zircon U-Pb and Hf isotopes
N2  - Geothermobarometric, radiogenic isotopic and thermochronologic data are used to track the influence of an ancient continental margin (Western Province) on development of an adjacent Carboniferous-Cretaceous magmatic arc (Outboard Median Batholith) in Fiordland, New Zealand. The data show a record of complicated Mesozoic Gondwana margin growth. Paragneiss within the Outboard Median Batholith is of Carboniferous to Jurassic age and records burial to middle crustal depths in Late Jurassic-Early Cretaceous during subduction-related plutonism and arc thickening. In contrast, Western Province metasedimentary rocks in the area of study immediately west of the Outboard Median Batholith are Late Cambrian-Early Ordovician in age, recrystallized at the amphibolite facies in the Late Devonian-Early Carboniferous and exhibit no evidence for Mesozoic textural or isotopic reequilibration. A phase of deformation, between 128 and 116 Ma deformed, exhumed, and cooled the Outboard Median Batholith to greenschist facies temperatures, while large parts of the Western Province underwent >= 9 kbar metamorphic conditions. Zircon grains from Mesozoic inboard plutons are isotopically more evolved (epsilon Hf(t) = +2.3 to +4.0) than those in the Outboard Median Batholith (epsilon Hf(t) = +9.4 to +11.1). The contrasting zircon Hf isotope ratios, absence of S-type plutons or Proterozoic-Early Paleozoic inherited zircon, and the apparent absence of Early Paleozoic metasedimentary rocks indicates that the Outboard Median Batholith is unlikely to be underlain by the Western Province continental lithosphere. The new data are consistent with the Outboard Median Batholith representing an allochthonous (although not necessarily exotic) arc that was juxtaposed onto the Gondwana continental margin along the intervening Grebe Mylonite Zone.
Y1  - 2009
UR  - http://www.agu.org/journals/tc/
U6  - https://doi.org/10.1029/2009tc002489
SN  - 0278-7407
ER  -