1
10
9
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http://theses.otagogeology.org.nz/files/original/1efe864953515ad287f66d2fee249471.pdf
262b89a2a3ce88efe74dcdea77c3104c
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Title
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Geology theses
OU Geology thesis
Thesis or dissertation completed by University of Otago Geology students
Location WKT (WGS84)
The location stored in WKT (WGS84) format
POLYGON ((170.382536924890672 -45.589280107697633,170.174004957660856 -45.553942919358377,170.230662222582623 -45.487456153096801,170.406206246536101 -45.554096778894859,170.382536924890672 -45.589280107697633))
Author last name
Last name of the Author
Dalton
Project type
Is it an MSc, PhD, BSc(Hons) or PGDipSci?
BSc(Hons)
Advisers
Who supervised/advised this student
Scott, J.M.
Abstract
The Abstract for this thesis
Harzburgitic and lherzolitic mantle xenoliths entrained in the Miocene by the alkali basalts of the Dunedin Volcanic Group and emplaced in East Otago, New Zealand have ‘locked-in’ the intricate history of the sub-continental lithospheric mantle (SCLM). Geochemical analysis of 36 peridotite samples from three neighbouring localities in East Otago reveals a remarkable degree of heterogeneity within the SCLM. Different realms of the SCLM have experienced diverse degrees of depletion by partial melt extraction and this has been followed by, in some cases significant, light rare-earth element (LREE) enrichment. Interrogation of clinopyroxene trace element geochemistry suggests mantle metasomatic processes are responsible for this enrichment with asthenosphere-derived carbonatite melts the most likely metasomatic agent, while the influence of silicate melts cannot be ruled out.
Radiogenic isotope systematics (Sr, Pb) indicate the East Otago SCLM has an enriched HIMU-like composition similar to the alkali basalts erupted during Cenozoic intraplate volcanism. Samples which have experienced the greatest degree of metasomatism have a narrow isotopic range compatible with HIMU-like compositions. It is suggested here that the HIMU-like signature observed in the East Otago SCLM is of metasomatic origin. Based on orthopyroxene-clinopyroxene trace element equilibrium diffusion modelling, it is thought that this metasomatic event occurred at least 100 Ma while Zealandia was contiguous with Gondwana. The presence of HIMU-like isotopic signatures in the mantle beneath West Antarctica and Eastern Australia may indicate a pervasive metasomatic event with a common HIMU-like metasomatic agent.
A ubiquitous core to rim decrease in Al2O3 concentrations and associated diffusion modelling is interpreted as recording the cooling of the East Otago SCLM following heating and thinning associated with the Cretaceous rifting of Zealandia from Gondwana. Following this geochemical evolution the peridotite xenoliths were entrained in alkali basalts with a HIMU-like signature. The source of these basalts remains uncertain with a HIMU-like signature now recognised in the East Otago SCLM and the convecting asthenosphere below.
Department
The department where the student is studying primarily.
Geology
Named locality
Named locality describing the field area location.
East Otago
Thesis description
Number of pages, maps, CDs, etc.
xiii, 162 pages A4
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2014Dalton
Creator
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Dalton, Hayden Boyd (Hayden)
Date
A point or period of time associated with an event in the lifecycle of the resource
2014
Title
A name given to the resource
Geochemical Evolution of the East Otago Mantle
Subject
The topic of the resource
Mantle geochemistry
Hazburgite
HIMU
lherzolite
mantle
peridotite
radiogenic isotopes
xenoliths
-
http://theses.otagogeology.org.nz/files/original/05c7e23b700d398c2032f60ad398a6d8.pdf
d9a7c5f5e23e858a491c50594d5ff014
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Title
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Geology theses
OU Geology thesis
Thesis or dissertation completed by University of Otago Geology students
Author last name
Last name of the Author
McIntosh
Project type
Is it an MSc, PhD, BSc(Hons) or PGDipSci?
MSc
Advisers
Who supervised/advised this student
Reay, A.
Abstract
The Abstract for this thesis
The Murdering Beach flow (MBF) is an inclusion-rich lava flow located within a small bay 16km northeast of Dunedin and was erupted during the First Main Eruptive Phase (Benson, 1941) of the Dunedin volcano. It contains a large variety of lithic inclusions and megacrysts many of which are commonly associated with calcite thought to be of primary magmatic origin.
The MBF contains phenocrysts of clinopyroxene, rounded nepheline, and sodalite within a microphenocrystic aggregate of clinopyroxene, feldspathoids, alkali feldspar and titanomagnetite and an aphanitic matrix of feldspathoids and glass.
Nepheline is commonly rounded in shape, possibly due to resorption, and displays highly birefringent micaceous overgrowths considered to be polymorphic nepheline. Sodalite is invariably associated with carbonate.
A large and diverse suite of clinopyroxene phenocrysts are also present within the MBF and exhibit a variety of zoning, rimming and resorption textures. Three petrographically distinct groups of clinopyroxene are recognised; these groups are also distinguishable geochemically. Fe-depleted clinopyroxene rims, not previously described from rocks of the Dunedin volcano, are thought to have developed from low pressure re-equilibration of the clinopyroxene phenocrysts with the MBF. The presence of strongly resorbed and euhedral clinopyroxene phenocrysts within the MBF may have resulted from "delayed fractionation" and rapid cooling of the MBF.
The heterogeneous appearance of the MBF is not reflected in its major element chemistry. The composition of the MBF is enigmatic in that its high alkali content together with its relatively high Mg-number indicate that the MBF exhibits characteristics of both primitive and more evolved lavas. The alkali-rich nature of the MBF, together with the presence of mantle derived inclusions within this flow suggests an origin for the MBF of fractionation of mantle derived liquids. The similarity of the MBFs trace element pattern to that of crustally fractionated rocks from the Dunedin volcano suggests however, that on the basis of trace element patterns alone it is difficult to distinguish between rocks derived by low as opposed to high pressure fractionation processes.
The MBF contains a diverse suite of upper mantle- and lower crustal-derived inclusions. The spinel lherzolite and clinopyroxenite inclusions are typical of the Cr-diopside group (Wilshire and Shervais, 1975}, while the feldspathic clinopyroxenite and poikilitic-amphibole dominated inclusions are typical of the more Fe-rich Al-augite group (Wilshire and Shervais, 1975). The spinel lherzolite inclusions display metamorphic textures and are interpreted to be fragments of upper mantle wallrock. The clinopyroxenite and feldspathic clinopyroxenite inclusions commonly display modified igneous textures, and may have formed either from dikes of alkali basaltic magma injected into the host peridotite which were subsequently deformed, or as magma chamber cumulates which were also similarly deformed.
Equilibration temperatures ranging from 996- 1069°C were obtained for coexisting enstatite and diopside within the spinel lherzolite and clinopyroxenite inclusions, and are consistent with an upper mantle origin for these inclusions.
The poikilitic amphibole-dominated inclusions most likely represent high pressure precipitates of alkaline magmas, formed within the upper mantle or lower crust. The gabbroic inclusions are independent of the rest of the inclusion suite, and trace element data presented in this study shows that they are unrelated to the origin of the MBF, and are derived from the upper crustal plutonic roots of the Dunedin volcano.
Textural evidence suggests that glass present within many of the inclusions was formed by partial melting. However there is also evidence that host rock infiltration may be responsible for some of the glass present in the inclusions.
The MBF also contains a large megacryst suite, dominated by aluminous clinopyroxene, with subordinate amounts olivine, kaersutite and titanomagnetite. The euhedral shape and large size of the megacrysts is consistent with them forming as high pressure precipitates of the MBF or related magmas.
Major and trace element modelling carried out in this study suggests the composition of the MBF has resulted from fractionation of magma of basanitic composition, by the removal of aluminous clinopyroxene and kaersutite, and minor olivine and Ti-spinel of similar composition to the megacrysts present within the MBF.
Evidence presented in this study suggests that the range of compositions within the Dunedin volcano produced by low pressure fractionation, are equally capable of being produced by high pressure fractionation at upper mantle depths.
A model for the origin of the MBF is proposed, involving the generation of alkali basaltic magmas by partial melting of enriched, metasomatised spinel lherzolite within the upper mantle, followed by significant high pressure fractionation to the derivative liquid prior to xenolith entrainment. The presence of xenoliths within mantle-derived alkali basaltic lavas therefore does not place limitations upon the degree of fractionation of these lavas that may have occurred.
Department
The department where the student is studying primarily.
Geology
Named locality
Named locality describing the field area location.
Murdering Beach
Thesis description
Number of pages, maps, CDs, etc.
x. 206 p. ill. 30cm.
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Identifier
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1989McIntosh
Creator
An entity primarily responsible for making the resource
McIntosh, P
Date
A point or period of time associated with an event in the lifecycle of the resource
1989
Title
A name given to the resource
Geochemistry of the Murdering Beach Flow, East Otago, New Zealand
Subject
The topic of the resource
Geochemistry
Volcanology
lava flow
lherzolite
upper mantle
xenoliths
-
http://theses.otagogeology.org.nz/files/original/748412a34b31c94fc0438d5eca2350c0.pdf
f48bdb017bf5c136773d23c88b330046
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Title
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Geology theses
OU Geology thesis
Thesis or dissertation completed by University of Otago Geology students
Author last name
Last name of the Author
Paulsen
Project type
Is it an MSc, PhD, BSc(Hons) or PGDipSci?
MSc
Advisers
Who supervised/advised this student
Cooper, A.F.
Abstract
The Abstract for this thesis
Mt Morning is a 2723 m high, undissected, mainly basanitic volcano with trachytic and phonolitic assemblages. It is located 92 km southwest of Scott Base, at the foothills of the Royal Society Range. Rocks of the Erebus Volcanic Province, a part of the McMurdo Volcanic Group, are exposed on two ridges on the northern flank of the mountain, the western Riviera Ridge and the eastern Hurricane Ridge.
Several pyroclastic deposits were mapped on Mount Morning, most of them monomict. However, one outcrop of a poorly bedded lapilli tuff, on the upper slopes of Riviera Ridge, contained a great diversity of lithic clasts. These clasts include phonolites, basanites, basement rocks and crustal xenoliths. This deposit was chosen as study area because of the range of clasts that provides a lithological cross-section through Mount Morning, from basement to phonolites.
Volcanic rocks include basanite and phonolites clasts, phonolite flow stratigraphically underlying the lapilli tuff, and glass shards from the eruption depositing the lapilli tuff. These rocks are derived from the main eruptive sequence on Mount Morning. The phonolites show a variety of fractionating stages, which is interpreted to be due to crystal fractionation, and possibly re-incorporation of fractionated crystals in a zoned magma chamber during eruption. The glass-shards represent the most evolved phonolitic magma reported from the mountain. The phonolites are thought to have been derived from crystal fractionation from the basanite magmas.
Crustal xenoliths found have a variety of origins. Crustal xenoliths include; nepheline syenites that show the same chemical characteristics as the phonolites; a syenite derived from a silica saturated sub-volcanic complex; and a biotite gabbro that has its origin outside the McMurdo Volcanic Group. The biotite gabbro is derived from a hydrous magma, possibly of an arc origin.
A fenite xenolith was also found as a clast in the lapilli tuff. It is a result of alkali metasomatism of a granitic protolith, possibly beneath Mount Morning. Fenitisation has not been reported from southern Victoria Land before. The protolith, possibly a granite outcropping at the base of Riviera Ridge, similar to the Granite Harbour Intrusives from the Transantarctic Mointains, is made up of quartz, alkali feldspar, plagioclase feldspar and mica, all of which have been altered to varying degrees by fenitising fluids rich in Na (with some K). Along the edges of the grains, plagioclase and alkali feldspar have altered, quartz has dissolved, and mica has been both recrystallised and been replaced by Na-rich members of pyroxene, amphibole, and both Na and K rich phases of feldspar. The presence of anastomosing veins crosscutting a plagioclase feldspar grain indicates the presence of a strong acid, possibly hydrofluoric acid (HF). Fluorine has been found as fluorite in a xenolith from the lapilli tuff, and this is an indicator of a fluorine environment beneath Mount Morning.
Department
The department where the student is studying primarily.
Geology
Named locality
Named locality describing the field area location.
Antarctica
Mount Morning
Thesis description
Number of pages, maps, CDs, etc.
ix, 169 leaves : ill. (chiefly col.), col. maps ; 30 cm + 1 CD-ROM (4 3/4 in.)
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Identifier
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2007Paulsen
Creator
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Paulsen, Hanne-Kristin.
Date
A point or period of time associated with an event in the lifecycle of the resource
2007
Title
A name given to the resource
Lithological cross section through Mount Morning, Antarctica : a story told from xenolithic assemblies in a pyroclastic deposit
Subject
The topic of the resource
Lithostratigraphy
Petrology
Volcanology
pyroclastic deposits
xenoliths
-
http://theses.otagogeology.org.nz/files/original/793ad8dcefe19b866a7d35b1feff7f7e.pdf
3f7cabd7689302a24cd08d33662ffd73
Dublin Core
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Title
A name given to the resource
Geology theses
OU Geology thesis
Thesis or dissertation completed by University of Otago Geology students
Location WKT (WGS84)
The location stored in WKT (WGS84) format
POLYGON ((169.307400573877857 -44.038058871607767,169.323631254914858 -44.03590323977074,169.323343943930183 -44.047208473257378,169.308776609552808 -44.049120129062636,169.307400573877857 -44.038058871607767))
Author last name
Last name of the Author
Crase
Project type
Is it an MSc, PhD, BSc(Hons) or PGDipSci?
BSc(Hons)
Advisers
Who supervised/advised this student
Scott, J.M.
Abstract
The Abstract for this thesis
Peridotite xenoliths entrained in alkaline magmas can preserve a record of processes that affected them in the lithospheric mantle. In Hidden Rivulet in the Haast area, the Alpine Dike Swarm entrained a variety of spinel facies peridotites that are predominantly of harzburgite composition. A large proportion of the spinel phases in these rocks form distinctive orthopyroxeneclinopyroxene symplectites and represent the decompression of garnet peridotite followed by equilibration in the spinel facies at some point in the past. Spinel Cr# and olivine Mg# as well as HREE indicate that high degrees of partial melting removed essentially all of the primary clinopyroxene, and likely some of the orthopyroxene, in these peridotites. However, the mantle has been overprinted by metasomatism, with two types inferred from the geochemistry of secondary clinopyroxene. The first event, only affecting some peridotites, is silicate metasomatism as indicated by high Ti and LREE concentrations in clinopyroxene. The second type, affecting all of the peridotites, is carbonatite metasomatism as indicated by low Ti/Eu, high Th/U and high LREE of the clinopyroxene. As the peridotites were devoid (or very close to devoid) of clinopyroxene prior to metasomatism, the isotopic ratios of these grains should closely represent the composition of the metasomatic agents. Clinopyroxene radiogenic isotopes are comparable to that of the HIMU mantle reservoir. HIMU-like ratios have also been recorded in the host Alpine Dike Swarm, which suggests that the dike swarm could share a similar source to the metasomatic agent, or could be derived from melting of the HIMU-enriched mantle lithosphere. The last process prior to entrainment was the equilibration of major and trace elements at 900-1100degC.
Department
The department where the student is studying primarily.
Geology
Named locality
Named locality describing the field area location.
Hidden Rivulet
south Westland
Thesis description
Number of pages, maps, CDs, etc.
xii, 120 pages A4
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Identifier
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2014Crase
Creator
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Crase, Jordan
Date
A point or period of time associated with an event in the lifecycle of the resource
2014
Title
A name given to the resource
Mantle geochemistry beneath south Westland, New Zealand: A study on peridotite xenoliths from Hidden Rivulet
Subject
The topic of the resource
Mantle geochemistry
Alpine dike swarm
HIMU
HREE
LREE
spinel
xenoliths
-
http://theses.otagogeology.org.nz/files/original/48c1c7636fb4219e6db37effdea3886f.pdf
cc259c968f77c5dd720275ff6ca15eb8
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Title
A name given to the resource
Geology theses
OU Geology thesis
Thesis or dissertation completed by University of Otago Geology students
Location WKT (WGS84)
The location stored in WKT (WGS84) format
POLYGON ((169.062799728155198 -44.271413393530317,169.089291660416052 -43.929500731082406,169.440295555088682 -43.944920812282227,169.427151069625808 -44.088324124468734,169.219848049939827 -44.277917344763722,169.062799728155198 -44.271413393530317))
Author last name
Last name of the Author
Norrie
Project type
Is it an MSc, PhD, BSc(Hons) or PGDipSci?
MSc
Advisers
Who supervised/advised this student
Cooper, A.F.
Abstract
The Abstract for this thesis
Minerals, textures and bulk chemistries of mantle xenoliths from the Fish River, Haast Pass record a history of successive crystallisation, deformation, multiple metasomatism and lamprophyre melt generation. Outcropping in the upper Fish River are numerous dikes of alkaline lamprophyre, ultramafic lamprophyre, tinguaite and carbonatite which intrude the TZ2 to TZ4 Haast Schists. Fenitised schist and networks of very thin ankeritic veins are associated with the intrusions. Ultramafic lamprophyre dikes commonly contain rounded Cr-diopside group peridotites, Al-augite group cumulates, amphibole-apatite, gabbro and schist xenoliths and amphibole megacrysts. Many of the xenoliths and xenocrysts exceed 30 cm in diameter. The Cr-diopside group xenoliths are dominantly low-Al harzburgites. Whole rock chemistry suggests they represent compatible element-rich mantle residues formed from the extraction of a 20% partial melt at subsolidus temperatures. Undulose extinction in harzburgite olivine and bent exsolution lamellae in orthopyroxene indicate that the mantle experienced a period, or several periods, of subsolidus deformation. Thin orthopyroxenite layers and prevalent chromiteorthopyroxene- olivine-clinopyroxene symplectites also formed during mantle deformation events. Subsequent to deformation, the mantle experienced millimeter scale metasomatism by two distinct agents. The first was a low viscosity, grain boundary infiltrating melt which reacted with the host peridotite to produce high Mg#, high-Cr, mica, diopside and pargasitic amphibole along with LREE-enriched apatite and carbonate. Chromite in symplectite intergrowths was particularly reactive. Geochemical evidence including low Ti/ Eu and elevated Ca/ AI ratios suggests this melt was carbonatitic in character. Fe, K and Ti-rich, hydrous melts produced during alkaline magma genesis infiltrated the surrounding peridotite and crystallised as veins of Ti-rich phlogopite, amphibole, clinopyroxene and titanomagnetite. Metasomatism associated with this episode of melt intrusion is restricted to <1 0 mm wide zones along the margins of the veins as fluids expelled from the crystallising veins reacted with and recrystallised the host peridotite. Host orthopyroxene was much more reactive than host olivine. Among the mantle xenolith suite of the Fish River are rare chromite-dunite metacumulate xenoliths that consist almost entirely of coarse olivine porphyroclasts which poikilitically enclose spherical chromite grains. Many chromite grains are recrystallised and surrounded by a halo of fine-grained metasomatic minerals. The peculiar halo zone mineralogy of one of these xenoliths, including the growth ofrichteritic amphibole indicates the influence of a further, Narich metasomatic agent with a high Si/ AI ratio. The presence of chromite-dunite xenoliths and orthopyroxenite layers argues for a compositionally zoned mantle beneath the Fish River. Small degree, lithospheric melting of this volatile and LREE-enriched mantle produced a lamprophyre magma, which sampled and entrained fragments of the wall rock peridotite as it rose quickly to the surface. Segregation of the volatile-rich magma from the xenoliths near the surface produced dikes ofxenolith-rich magma residue.
Department
The department where the student is studying primarily.
Geology
Named locality
Named locality describing the field area location.
Fish River
Thesis description
Number of pages, maps, CDs, etc.
195 leaves : col. ill., maps ; 30 cm.
Dublin Core
The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/.
Identifier
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2000Norrie
Creator
An entity primarily responsible for making the resource
Norrie, Brendan Harwood, 1976-
Date
A point or period of time associated with an event in the lifecycle of the resource
2000
Title
A name given to the resource
Metasomatised mantle xenoliths from lamprophyre dikes of the Fish River, New Zealand
Subject
The topic of the resource
Igneous petrology
Mineralogy
lamprophyre dikes
metasomatism
xenoliths
-
http://theses.otagogeology.org.nz/files/original/c789fb80ddc0f3cdd1fb6401cc1d3ca7.pdf
efede91ed1da216fbaea17f354f3b86d
Dublin Core
The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/.
Title
A name given to the resource
Geology theses
OU Geology thesis
Thesis or dissertation completed by University of Otago Geology students
Location WKT (WGS84)
The location stored in WKT (WGS84) format
MULTIPOLYGON (((170.497481673411 -45.5623060915417,170.507239729514 -45.5624481285648,170.507911652799 -45.5702505300526,170.497856873926 -45.5698877077138,170.497481673411 -45.5623060915417)))
Author last name
Last name of the Author
Scanlan
Project type
Is it an MSc, PhD, BSc(Hons) or PGDipSci?
BSc(Hons)
Advisers
Who supervised/advised this student
Scott, J.M.
Abstract
The Abstract for this thesis
Xenoliths of Otago Schist have been pyrometamorphosed upon entrainment within the Miocene basanite at Ram Rock, North Otago. This has resulted in recrystallisation from a greenschist facies mineral assemblage (T < 400°C) to a sanidinite facies assemblage (T > 900°C).
Ram Rock xenoliths were analysed by scanning electron microscope electron dispersal spectrometry to characterise the mineralogy of xenoliths due to the very fine grain-size. The Otago Schist quartz-albite segregations have recrystallized to quartz with orthopyroxene coronas within rhyolitic glass. The micaceous segregations (muscovite, chlorite, garnet) have been completely replaced by olivine, spinel, plagioclase, cordierite, ilmenite, orthopyroxene and an alkali-rich mafic glass. The compositional segregations of the Otago Schist protolith are behaving as isolated blocks during pyrometamorphism, producing separate chemical domains of ultramafic and dacitic composition. Replacement textures indicate that the sanidinite facies minerals crystallised through two mechanisms: as the result of mineral reactions from the former greenschist facies minerals, or they nucleated within a melt and developed quench textures. The presence of quench textures and glass indicates that the xenoliths cooled rapidly to the glass transition temperature, likely through a combination of conductive cooling, minor convective cooling, and high viscosity inhibiting crystal growth.
Metasomatic interaction with the host basanite has enriched the xenolith in 2.3 wt% CaO, 0.6 wt% K2O, and 4.3 wt% SiO2 with minor enrichment of FeO, TiO2, and Na2O within minerals on the basalt-xenolith interface. Inferred mineral reactions give constraints on temperatures reached, with chlorite breakdown occurring at 870°C and muscovite partial melting and complete removal at 900-950°C. Quantitative geothermometry gives temperatures of ~960-1030°C for glass, while the more suitable orthopyroxeneliquid and plagioclase-liquid geothermometers give 940-980°C, allowing more precise constraints on temperatures reached.
Department
The department where the student is studying primarily.
Geology
Named locality
Named locality describing the field area location.
Ram Rock
North Otago
Thesis description
Number of pages, maps, CDs, etc.
135 pages A4
Dublin Core
The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/.
Identifier
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2016Scanlan
Creator
An entity primarily responsible for making the resource
Scanlan, Emma
Date
A point or period of time associated with an event in the lifecycle of the resource
2016
Title
A name given to the resource
Mineralogy, textures and reactions within pyrometamorphosed xenoliths of Otago Schist
Subject
The topic of the resource
Metamorphic Geology
Otago Schist
xenoliths
-
http://theses.otagogeology.org.nz/files/original/c57dd9fdc4aec96e78fd3d7b4bc849d6.pdf
d1112bee912e0236647698cb8c6030a0
Dublin Core
The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/.
Title
A name given to the resource
Geology theses
OU Geology thesis
Thesis or dissertation completed by University of Otago Geology students
Location WKT (WGS84)
The location stored in WKT (WGS84) format
POLYGON ((169.263864268419894 -43.81175268436828,169.263335905256469 -43.793870008714073,169.420986991937127 -43.797135904721642,169.419964627835355 -43.855464352785233,169.263802489138556 -43.852245398719276,169.263864268419894 -43.81175268436828))
Author last name
Last name of the Author
Wallace
Project type
Is it an MSc, PhD, BSc(Hons) or PGDipSci?
MSc
Advisers
Who supervised/advised this student
Cooper, A.F.
Coombs, D.S.
Reay, A.
Abstract
The Abstract for this thesis
In the Mataketake Range in South Westland the high grade axis of the Haast Schist abuts the Alpine Fault. A eugeosynclinal suite, now represented by quartzofeldspathic schist and minor amphibolites, metacherts and pegmatite, has been intensely deformed and metamorphosed under conditions of higher grade amphibolite facies, equivalent to sillimanite zone. The amphibolites contain green hornblende and plagioclase (An30-An50), accessory garnet, epidote (Ps 15-24), calcite, potassium feldspar, sphene, opaques and in one case salitic pyroxene (Wo49En34Fs17). In the quartzofeldspathic schist the anorthite content of the plagioclase increases from An 22-26 coexisting with albite in the garnet zone to An36 in the core of the Haast Antiform. Muscovite and biotite are ubiquitous. Staurolite is reported from lower grade amphibolite facies rocks. Metachert horizons have a simple mineralogy of quartz, garnet, tourmaline with accessory rutile and apatite. In the west of the area, pegmatites have been formed by partial melting and have been injected concordantly to foliation s1.
An initial phase of deformation of the schist produced isoclinal folds. The westerly vergence of the mesoscopic structures suggests that the Mataketake Range area lies on the upper limb of a recumbent fold, closing to the north west, with a fold axis plunging moderately steeply south south-west. A second phase of folding produced broad open structures about a subvertical axial plane (Haast Antiform, Thomas Synform, Moeraki Antiform and Mount Clark Synform) with fold axes trending 216° plunging 20°S. The third phase of deformation is restricted to the development of kink folds in a zone adjacent to the Alpine Fault.
A study of the ultracataclastic rock from along the Alpine Fault which forms the western boundary of the region studied was undertaken. Here the Alpine Fault is approximately 500 metres wide and has a foliation which dips 20° south east throughout much of the fault zone. The fault zone is composed of breccias, mylonites, augen mylonites, blastomylonites, ultramylonites and a half metre wide fault pug (which probably represents cataclasis due to recent movement). The ultramylonite is usually opaque but samples were identified which contained radiating microlites (good devitrification textures) and in one case a non vesicular glass (hyalomylonite) was located.
Electron microprobe analysis of the glass indicated that it has Sio2 : Or : Ab ratio similar to that of a granite minimum melting liquid at 500-1000 bars and a comparison between the chemistry of the hyalomylonite and possible rock from which it may be derived indicates that the hyalomylonite differs fro~ these possible source rocks. The conclusion has been reached that the hyalomylonite is the product of a process of fractional melting of the rock in, or adjacent to, the Alpine Fault Zone. Based on the evidence that vesiculation has not occurred, and that there is approximately 3-5% water in the sample, it has been suggested that melting occurred at 750 C for a pressure range of 1/2-2 kb (a depth of 2-7 km).
Using these considerations and estimating that the displacement that produced melting was in the range 0.3 to 6 metres it can be shown that stresses of the order of 200 to 250 bars were involved in faulting.
Members of a basic alkali dike swarm (lamprophyres) were located in the headwaters of the Moeraki River. The dike swarm is composed of kersantites, camptonites, monchiquites, odinites, ouchitites and mica peridotite all of which have been pneumatolytically altered by late stage carbonatitic fluids. Chemical analyses of coexisting mineral phases are presented and an attempt made to show that some of the trachytic members of the dike swarm may have developed from the camptonitic or odinitic members.
One member of the dike swarm is a carbonatitic hornblende-mica peridotite which contains copious amounts of xenolithic material. The xenolithic suite comprises schist, gabbro, harzburgite and lherzolites with megacrysts of clinopyroxene. Analyses of the coexisting phases in the nodules indicates that the lherzolites and harzburgites are stable in the spinel-lherzolite field and that they would be a stable assemblage at pressures equivalent to a depth of lOOkm. The clinopyroxene megacrysts may represent a cognate xenolith from a magma which has fractionated at depth, while the gabbroic nodules represent cumulous material differentiating at shallower levels still (at the base of the crust). The schist xenoliths represent material stoped from the conduit walls as intrusion has occurred. The suggestion has been made that intrusion may be in the form of a fluidised solid-gas system, and the body may be termed a diatreme.
Department
The department where the student is studying primarily.
Geology
Named locality
Named locality describing the field area location.
Moeraki River
Westland
Thesis description
Number of pages, maps, CDs, etc.
152 leaves : illus. ; 30 cm.
Dublin Core
The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/.
Identifier
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1973Wallace
Creator
An entity primarily responsible for making the resource
Wallace, Robert Cleland.
Date
A point or period of time associated with an event in the lifecycle of the resource
1973
Title
A name given to the resource
Some aspects of the geology about the Moeraki River, South Westland
Subject
The topic of the resource
Map
Metamorphic geology
Structural geology
Alpine Fault
lamprophyre
staurolite
xenoliths
-
http://theses.otagogeology.org.nz/files/original/ddba1a24d73b1296ff98d4623565e771.pdf
5a7fae61d55f369b87cd4bf94dfb2d7f
Dublin Core
The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/.
Title
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Geology theses
OU Geology thesis
Thesis or dissertation completed by University of Otago Geology students
Author last name
Last name of the Author
Maidens
Project type
Is it an MSc, PhD, BSc(Hons) or PGDipSci?
BSc(Hons)
Advisers
Who supervised/advised this student
Reay, A.
Abstract
The Abstract for this thesis
The garnet clinopyroxenite xenoliths found in the Kakanui Mineral Breccia (Kakanui, South Island, New Zealand) are thought to have originated from a mantle cumulate at a depth of some 60 to 70 km. It is most likely that the garnet-clinopyroxene assemblage seen in these rocks is the original mineralogy, unlike similar xenoliths found in Australia, Hawaii, and Israel (for example), which are presumed to have exsolved from a high pressure clinopyroxene cumulate.
The clinopyroxene in some of the garnet clinopyroxeni tes has been partially replaced by a kaersutitic amphibole. Some of this replacement is due to direct precipitation of oikocrysts from an amphibolite (=basaltic) liquid, and some to hydration of the pyroxene by metasomatism, probably associated with the amphibolite liquid.
The garnet clinopyroxenites are accidental inclusions within the breccia, bearing no relation to the host melanephelinite. They were entrained within the melanephelinite and erupted shortly thereafter, around 34 million years ago. The rapid ascent to the surface caused decompression melting in some of the garnet pyroxenites.
Rare orthopyroxene has been found for the first time in these nodules. As the pyroxen~jn the garnet pyroxenites is an Fe-Al- Na- augite, the name "eclogite" cannot be given to them as it has previously.
Department
The department where the student is studying primarily.
Geology
Named locality
Named locality describing the field area location.
Kakanui
Thesis description
Number of pages, maps, CDs, etc.
79 leaves : ill. (some col.), map ; 30 cm.
Dublin Core
The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/.
Identifier
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1992Maidens
Creator
An entity primarily responsible for making the resource
Maidens, Ellen, 1970-
Date
A point or period of time associated with an event in the lifecycle of the resource
1992
Title
A name given to the resource
Some remarks on the garnet clinopyroxenites at Kakanui : a comprehensive description and interpretation thereof
Subject
The topic of the resource
geochemistry
garnet clinopyroxene
geochemistry
Kakanui Mineral Breccia
xenoliths
-
http://theses.otagogeology.org.nz/files/original/14d071dddb26af7295b49c7c9f472cdb.pdf
1dd106a5aa5a5f07ab84b70c193b35fc
Dublin Core
The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/.
Title
A name given to the resource
Geology theses
OU Geology thesis
Thesis or dissertation completed by University of Otago Geology students
Author last name
Last name of the Author
Garden
Project type
Is it an MSc, PhD, BSc(Hons) or PGDipSci?
BSc(Hons)
Advisers
Who supervised/advised this student
Reay, A.
Abstract
The Abstract for this thesis
Two garnet bearing tuffs are known in North Otago, Kakanui and Alma. The Kakanui Mineral Breccia contain a diverse range of upper mantle derived megacrysts and xenoliths while the Alma contains a limited assemblage of megacrysts and xenoliths. Within the Kakanui Mineral Breccia, three magmas were identified through a detailed EMP and LAM study of the megacryst and garnet pyroxenite suite. Crystallisation pressures for the megacrysts f'ere determined by near liquidus experiments using the nephelinite host composition for the starting material, and geothermometry and geobarometry for the garnet pyroxenite suite (Zack et al (1997). Megacryst crystallisation occurred between 25-15kb and 1200-1150°C with the bulk occurring between 22-17kb. The garnet pyroxenites crystallised between 15-16kb and 930°C. The Kakanui Mineral Breccia underwent a complex petrogenesis involving three different magmas, the nephelinite host (parent to megacrysts suite}, an evolved nephelinite (parent to garnet pyroxenite suite) and an Alkali Olivine Basalt (triggering magma by magma injection). The magma ascent was initiated by the injection of Alkali Olivine Basalt into the megacryst bearing nephelinite. This AOB interacted j with the nephelinite host (mixing causing heterogeneity) and possibly added xenocrysts of higher magnesium garnet compared to the megacryst suite garnet ofthe nephelinite. The nephelinite host intersected a solid garnet pyroxenite pod trapped within lherzolite formed from an evolved nephelinite parent, which reacted with the ; volatile rich host to form metasomatic kaersutite. The origin of the plagioclase bearing garnet pyroxenite is potentially resolved as al'\ j \ extremely evolved garnet pyroxenite (late stage crystallisation). A new megacryst phase from the Kakanui Mineral Breccia is confirmed, zircon, the chemistry is unique to other zircons in the South Island, Hf!Zr ratio suggests crystallisation from a nephelimte or an undersaturated rock. A similar Mineral Breccia at Alrna, is derived from a more evolved magma sourced deeper in the Mantle with unknown relationship to Kakanui.
Department
The department where the student is studying primarily.
Geology
Named locality
Named locality describing the field area location.
Kakanui Mineral Breccia
Thesis description
Number of pages, maps, CDs, etc.
ix. 165 p, diagms, 30 cm, +CD-Rom (4 3/4 in.)
Dublin Core
The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/.
Identifier
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2001Garden
Creator
An entity primarily responsible for making the resource
Garden, Benjamin P
Date
A point or period of time associated with an event in the lifecycle of the resource
2001
Title
A name given to the resource
The Kakanui Mineral Breccia: Experimental and mineral geochemistry
Subject
The topic of the resource
Geochemistry
geochemistry
Kakanui Mineral Breccia
megacrysts
xenoliths