This thesis is missing page 16, no other copies of this thesis have the page. -Digitization Centre / Metasomatism was taken by Goldschmidt (1922) as being metamorphism involving introduction and removal of certain substances, with a corresponding change in the chemistry and mineralogy of the rock concerned. Using this definition, there is strong evidence of metasomatism having played an important role in the transformation of part of the Kamiskotia mafic intrusion from a norite to a greenschist facies rock. The importance of metasomatism has generally proved difficult to evaluate because of disagreement on a quantitative approach to the problem. Two of the approaches suggested in the literature have been employed to characterize the chemical changes accompanying metamorphism of the Kamiskotia complex; one assuming constant volume, the other assuming constant alumina. The latter approach, supported by most recent work in this area (Carmichael, 1970; Korzhinsky, 1964) is favoured. It defines a mobility series that agrees quite well with Korzhinsky's for all elements except iron. It is concluded that metamorphism, of the Kamiskotia norite has been accompanied by significant removal of potash, soda, iron and silica besides the addition of water and carbon dioxide. Reactions, constructed on the basis of mineral relationships observed in thin section combined with the calculated chemical changes are proposed. The source of the metasomatic fluids and the site of deposition of removed material is speculated upon. / Thesis / Bachelor of Science (BSc)

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L'objectif de cette thèse est l'étude de l'association magnétite-skarn-magmatisme. Dans ce but, deux gisements de magnétite (Yamansu et Cihai) ont été sélectionnés dans l'Est du Tianshan (NW Chine). Dans les deux gisements, l'assemblage grenat-pyroxène-magnétite a été reconnu, mais les mécanismes de formation de la minéralisation y sont différents. Cet assemblage a ensuite été alteré par un stade hydrothermal. Les études minéralogiques et géochimiques ainsi que les zonations observées suggèrent, que dans le gisement de Yamansu (YMD), le skarn et la minéralisation sont liés à la circulation d'un fluide riche en fer; alors que pour le gisement de Cihai (CMD), la mise en place du minerai est probablement associée à un magmatisme mafique/ultramafique. A YMD, selon l'anisotropie de la susceptibilité magnétique (AMS) et une étude paléomagnétique, le basalte et le skarn massif à grenat, tout deux encaissant les corps à magnétite massive, étaient en position horizontale lors de leur formation. L'attitude actuelle de ce gisement serait donc due à la phase tectonique majeure. La magnétite dans CMD présente les caractéristiques d'une magnetite magmatique, plutôt qu'hydrothermale. Dans ce gisement, la contamination du magma par des formations sédimentaires a pu contribuer à séparer efficacement un liquide riche en oxyde de fer d'un bain silicaté. / The aim of this thesis was to investigate the magnetite-skarn-magmatism association, of which two study objects (Yamansu and Cihai magnetite deposits) were selected from eastern Tianshan, China. Both of the Yamansu and Cihai magnetite deposit illustrate garnet-pyroxene-magnetite assemblage in prograde stage and hydrothermal assemblage in retrograde stage which essentially defined as skarn-related deposit, but with different forming mechanisms. Yamansu magnetite deposit (YMD) is a typical metasomatic skarn deposit confirmed by the mineral assemblage and chemical composition, zonation etc., whereas to Cihai magnetite deposit (CMD) probably associated to sedimentary assimilation into mafic/ultramafic magma and fractionation. According to anisotropy of magnetic susceptibility (AMS) and paleomagnetic study, the basalt and the massive garnet skarn which clamp massive magnetite ore bodies were coincidently horizontal in YMD. In addition, it was the Fe-rich fluid caused extensive skarnization in YMD. The magnetite in CMD is magmatic origin, rather than hydrothermal according to mineralogy and geochemical study. External material contamination of the mafic/ultramafic magma probably efficiently separated the magnetite and silicate at the peripheral part of the large mafic/ultramafic pluton in high temperature.

Basalts from Askja, Iceland have high MgO (5-18 wt %) and high Fe2O3 (5-18 wt %: Baratoux et al., 2011; Mangold et al., 2013, this study) similar to Martian basalts, which have Fe2O3 from 10-33 wt % McSween et al, 2006; Ming et al., 2008]) and MgO around 11 wt. % (McSween et al., 2009). Askja’s cold desert climate provides a good weathering analogueanalog (Mountney and Russell, 2004). Askja is located in the Northern Volcanic Zone of Iceland and basalts have been weathered to form mafic volcaniclastic deposits in a 40-km long sand sheet to the E-SE of the Askja caldera complex (Fig. 1; (Kuritani et al., 2011). The 2014-2015 Holuhraun eruption was emplaced onto the southeastern part of the sand sheet (Fig. 1) and altered the regional geomorphology and may have impacted the geochemistry of the sand sheet itself by addition of wind-blown ash and crystals, plus weathering of the lava flow (MgO content of ~7.1 wt % Geiger et al., 2016). Mangold et al. (2011) found that Icelandic sands show little chemical variations but that study was limited in the number of samples (12 sand samples and 12 rock seven rock, seven sand; Mangold et al., 2011). Here we expand on that study and we have created a morphological and geochemical database with the goal of identifying relevant trends to past and present Martian environments. The Askja sand sheet, between ~10 cm and ~10 m thick, covers 240 km2 (Mountney and Russell). Mountney and Russell described three distinct sections of the sand sheet. The southwest section is deflationary and defined by very fine to medium grained basaltic sand with cobbles and boulders of lithologies sourced from adjacent to and distal from the sand sheet. The central part is inflating and is dominated by very fine-grained sand, relict lava fields, and small to large sand ripples. The northeast portion is also inflating but that accumulation is limited to topographic depressions. The northeast, characterized by sand mostly composed of pumice from the 1875 Askja eruption and basalt clasts from local lava fields, was not studied in detail here due to the difference in chemistry. Martian basaltic eolian sediments may record a long history of local and global climate change and they may have been potential habitats where water, nutrients and organic carbon mixed below the surface (Blake et al., 2013; Fisk et al., 2013). Basaltic sand fields on Earth have not been characterized as well as felsic sands, but represent a unique analog to deposits such as the Stimson Fm. on Mars (Mangold et al., 2011; Banham et al., 2016; Gupta et al., 2016; Ming et al., 2016; Newsom et al., 2016; Yen et al., 2016) . Eolian dominated weathering prevalent at Askja volcano, Iceland, likely also occurred on Mars and Askja mafic volcaniclastic dunes could be the best morphological and compositional analogueanalog for Martian eolian dunes (Edgett and Lancaster, 1993).

Layered mafic intrusions represent an important aspect of magmatism on earth and have occurred from Archean to present times. Literature on the geochemistry and petrology of these intrusions abounds but their physical properties, which could provide significant constraints on their formation, have seldom been investigated. Classic petrological methods such as whole-rock geochemistry, textural analysis and mineral chemistry have been applied to several intrusions of various ages. Most of these methods are relatively expensive or time intensive which limits high resolution studies. On the contrary, magnetic methods are typically inexpensive and fast and have been successfully applied to various occurrences of mafic rocks. In this study, several magnetic methods have been applied to a 600 m-long continuous borehole core drilled through one of the world's largest layered mafic intrusion, the Great Dyke of Zimbabwe. The main goal of this study is to constrain the magmatic history of the intrusion. More specifically, it is important to determine if the intrusion functioned as an open system, characterized by multiple magma pulses, or as a closed system, undergoing differentiation after a single magmatic pulse. The magnetic methods have also been validated by other independent approaches including image analysis, and electron microprobe. This study demonstrates that magnetic methods can be used to rapidly obtain critical information on the internal structure of this type of intrusion before applying more costly chemical analyses. The main scientific result of this study is to document the closed system nature of the Great Dyke of Zimbabwe, at least throughout the sequence investigated.

Cinder Cone is the most recent cinder cone eruption in the continental United States at ~350 years old. This study examines the physical characteristics of the explosive deposit of the volcano in order to infer eruption timing, style, and mechanisms. Building on previous work and using spatial extent, field relationships, and grain size, componentry, and textural data of ten samples from one column, this study demonstrates that Cinder Cone erupted in at least two distinct phases with at least two distinct eruption styles. This speaks to the changing magma supply and transport processes occurring beneath the volcano. Curiosities about the eruption include the extensive degree of contamination that contributed abundant quartz xenocrysts to all the deposits. Future work includes determining the extent and mechanism/s of contamination and tephra component creation. These data are important for informing hazard assessments of areas with abundant cinder cone volcanoes.

名古屋大学年代測定総合研究センターシンポジウム報告

>Magister Scientiae - MSc / The 535 Ma post-orogenic Yzerfontein Pluton is a composite pluton that comprises rocks of mafic, intermediate and felsic compositions belonging to the shoshonitic series. The Yzerfontein Pluton forms part of the Cape Granite Suite of the Late-Proterozoic to Early-Cambrian Pan-African Saldania Belt. In this study, major- and trace-element data for the various rocks of the pluton, which act as hosts to extensive hydrothermal veining, are presented and integrated with the petrographic examination of the host rocks in order to constrain their petrogenesis.

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