The origin of tourmaline nodules, bizarre spherical to irregular textures documented worldwide, remains a geologic mystery. Although previously described by numerous researchers, the physical and chemical parameters that govern their formation have yet to be resolved. Commonly containing tourmaline, quartz, and occasionally feldspar, nodules are surrounded by a halo of leucocratic host rock, and are typically eight to ten centimeters in diameter. Tourmaline nodules of the present study are contained within the Paleoproterozoic Scrubber Granite of the southern Gascoyne Complex in Western Australia. </p> <p>This study integrated field observations, nodule petrography, tourmaline crystal chemistry, tourmaline fluid inclusion analyses, whole rock chemistry of nodule cores, leucocratic halo zones and host granite zones, stable and radiogenic isotope signatures of tourmaline separates as well as comparisons with other tourmaline nodule studies to propose the most scientifically sound theory for the formation of tourmaline nodules in the Scrubber Granite. </p> Numerous nodule morphologies, including spherical and C-shaped nodules, along with other features such as tube-like nodules and tourmaline veins occur in massive, porphyritic, foliated and sheared phases of the Scrubber Granite. Microscopically, tourmaline displays prismatic, sub-rounded and massive textures. Microthermometric studies completed on tourmaline fluid inclusions revealed that the nodule-forming fluid contained 14 to 15 weight percent NaCl + CaCl2. Based on stable isotope studies and homogenization temperatures, fluid temperatures were constrained between 450 and 700¢ªC. The ¥ä18O and ¥äD concentrations of the nodule-forming fluid at this temperature range plot above the typical magmatic water field. Epsilon Nd values indicate that the tourmaline nodules of the Scrubber Granite may have been disturbed by a later metamorphic event.</p>Tourmaline nodules of the Scrubber Granite are herein proposed to have formed from the exsolution and rise of buoyant pockets or bubbles of volatile fluid derived from the crystallizing Scrubber Granite magma.
| Identifer | oai:union.ndltd.org:USASK/oai:usask.ca:etd-01222006-175756 |
| Date | 23 January 2006 |
| Creators | Shewfelt, Debbie Amy |
| Contributors | Ansdell, Kevin M. |
| Publisher | University of Saskatchewan |
| Source Sets | University of Saskatchewan Library |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://library.usask.ca/theses/available/etd-01222006-175756/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Saskatchewan or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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