A re-examination of hydrothermal alteration and Fe-Ti oxide relationships in the Skaergaard Layered Mafic Intrusion, East Greenland
Fractionation between Fe isotopes in igneous systems and hydrothermally-altered rocks is small but significant, and detailed petrographic understanding of rocks is needed to discern the origin of such fractionations. One hypothesis proposed to explain the causes of Fe isotope fractionation in igneou...
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East Carolina University
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fteastcaroluni:oai:TheScholarship.intra.ecu.edu:10342/6768 2023-05-15T16:03:55+02:00 A re-examination of hydrothermal alteration and Fe-Ti oxide relationships in the Skaergaard Layered Mafic Intrusion, East Greenland Cummings, Tiffany Lynn Heimann, Adriana Geological Sciences 2018-05-23T21:11:23Z application/pdf http://hdl.handle.net/10342/6768 en eng East Carolina University http://hdl.handle.net/10342/6768 Geochemistry mineralogy geology Skaergaard Master's Thesis text 2018 fteastcaroluni 2022-08-06T22:21:51Z Fractionation between Fe isotopes in igneous systems and hydrothermally-altered rocks is small but significant, and detailed petrographic understanding of rocks is needed to discern the origin of such fractionations. One hypothesis proposed to explain the causes of Fe isotope fractionation in igneous rocks involves hydrothermal alteration. Movement of hydrothermal fluids through the system could result in removal of light Fe isotopes, leaving a heavier Fe isotope composition in the rocks. Previous oxygen isotope ([delta]18O) analyses of bulk-rocks, pyroxene, and plagioclase indicate that the Skaergaard intrusion hosted its own hydrothermal system. To provide petrographic context to interpret bulk-rock, bulk-mineral, and in-situ Fe isotope compositions (of Fe-Ti oxides), this study characterizes hydrothermal alteration via oxygen isotope geochemistry of rocks and minerals and the nature of fine-scale exsolution relationships among Fe-Ti oxides in the Skaergaard intrusion. Petrographic, SEM-EDS, TEM, and XRD analyses show exsolutions of ilmenite, hematite, and spinel of different sizes and shapes within Ti-rich magnetite and ilmenite. Characterization of the textural relationships show the following associations: 1) discrete magnetite and ilmenite crystals (0.2-1 mm) in mutual contact, in which ilmenite exsolved from original titanomagnetite or crystalized separately; 2) very thin (1 [micro]m) exsolutions of hematite within ilmenite; 3) coarse (~50 [micro]m) triangular exsolutions of ilmenite within magnetite; 4) very-fine scale (0.1[micro]m), box-like exsolutions of Fe-Ti oxide within titanomagnetite visible only via SEM at 24,000x magnification; 5) very fine-grained (0.5-5 [micro]m) exsolutions of a transparent mineral phase. TEM analysis indicates that the very fine, box-type exsolutions within magnetite are secondary ilmenite containing small amounts of Mg, Al, and Mn, whereas thicker, triangular lamellae are early ilmenite close to pure Ti-Fe oxide in composition. Very fine-grained transparent phases ... Master Thesis East Greenland Greenland East Carolina University: The ScholarShip at ECU Greenland |
institution |
Open Polar |
collection |
East Carolina University: The ScholarShip at ECU |
op_collection_id |
fteastcaroluni |
language |
English |
topic |
Geochemistry mineralogy geology Skaergaard |
spellingShingle |
Geochemistry mineralogy geology Skaergaard Cummings, Tiffany Lynn A re-examination of hydrothermal alteration and Fe-Ti oxide relationships in the Skaergaard Layered Mafic Intrusion, East Greenland |
topic_facet |
Geochemistry mineralogy geology Skaergaard |
description |
Fractionation between Fe isotopes in igneous systems and hydrothermally-altered rocks is small but significant, and detailed petrographic understanding of rocks is needed to discern the origin of such fractionations. One hypothesis proposed to explain the causes of Fe isotope fractionation in igneous rocks involves hydrothermal alteration. Movement of hydrothermal fluids through the system could result in removal of light Fe isotopes, leaving a heavier Fe isotope composition in the rocks. Previous oxygen isotope ([delta]18O) analyses of bulk-rocks, pyroxene, and plagioclase indicate that the Skaergaard intrusion hosted its own hydrothermal system. To provide petrographic context to interpret bulk-rock, bulk-mineral, and in-situ Fe isotope compositions (of Fe-Ti oxides), this study characterizes hydrothermal alteration via oxygen isotope geochemistry of rocks and minerals and the nature of fine-scale exsolution relationships among Fe-Ti oxides in the Skaergaard intrusion. Petrographic, SEM-EDS, TEM, and XRD analyses show exsolutions of ilmenite, hematite, and spinel of different sizes and shapes within Ti-rich magnetite and ilmenite. Characterization of the textural relationships show the following associations: 1) discrete magnetite and ilmenite crystals (0.2-1 mm) in mutual contact, in which ilmenite exsolved from original titanomagnetite or crystalized separately; 2) very thin (1 [micro]m) exsolutions of hematite within ilmenite; 3) coarse (~50 [micro]m) triangular exsolutions of ilmenite within magnetite; 4) very-fine scale (0.1[micro]m), box-like exsolutions of Fe-Ti oxide within titanomagnetite visible only via SEM at 24,000x magnification; 5) very fine-grained (0.5-5 [micro]m) exsolutions of a transparent mineral phase. TEM analysis indicates that the very fine, box-type exsolutions within magnetite are secondary ilmenite containing small amounts of Mg, Al, and Mn, whereas thicker, triangular lamellae are early ilmenite close to pure Ti-Fe oxide in composition. Very fine-grained transparent phases ... |
author2 |
Heimann, Adriana Geological Sciences |
format |
Master Thesis |
author |
Cummings, Tiffany Lynn |
author_facet |
Cummings, Tiffany Lynn |
author_sort |
Cummings, Tiffany Lynn |
title |
A re-examination of hydrothermal alteration and Fe-Ti oxide relationships in the Skaergaard Layered Mafic Intrusion, East Greenland |
title_short |
A re-examination of hydrothermal alteration and Fe-Ti oxide relationships in the Skaergaard Layered Mafic Intrusion, East Greenland |
title_full |
A re-examination of hydrothermal alteration and Fe-Ti oxide relationships in the Skaergaard Layered Mafic Intrusion, East Greenland |
title_fullStr |
A re-examination of hydrothermal alteration and Fe-Ti oxide relationships in the Skaergaard Layered Mafic Intrusion, East Greenland |
title_full_unstemmed |
A re-examination of hydrothermal alteration and Fe-Ti oxide relationships in the Skaergaard Layered Mafic Intrusion, East Greenland |
title_sort |
re-examination of hydrothermal alteration and fe-ti oxide relationships in the skaergaard layered mafic intrusion, east greenland |
publisher |
East Carolina University |
publishDate |
2018 |
url |
http://hdl.handle.net/10342/6768 |
geographic |
Greenland |
geographic_facet |
Greenland |
genre |
East Greenland Greenland |
genre_facet |
East Greenland Greenland |
op_relation |
http://hdl.handle.net/10342/6768 |
_version_ |
1766399617087307776 |