Lucy Newton
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B.Sc. (Honours) Thesis
Metamorphism and Provenance of the Holly Lake Metamorphic Complex, Hottah Terrane, NWT - A Petrographic and Shrimp U-Pb Detrital Zircon Study
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This thesis reports the results of 2010 fieldwork and U-Pb detrital zircon geochronology on semi-pelites and psammites of the Holly Lake Metamorphic Complex (HLMC). The oldest exposed unit of the Hottah terrane, the HLMC offers limited outcrops on the western margin of the Wopmay orogen along Leith Ridge, south of Great Bear Lake and northwest of Hottah Lake. The present study was undertaken in order to determine the metamorphic history, age and possible provenance sources for the HLMC; data that will aid in testing previously proposed tectonic interpretations of the Hottah terrane.
Outcrops within the Leith Ridge study area are composed of variably migmatitic, interlayered semi-pelitic and psammitic horizonsm). The rocks have undergone two distinct metamorphic events: a high temperature-low pressure event (> 700o C, < 6 Kbar); and retrograde metamorphism. Peak mineral assemblages include K-feldspar + sillimanite + relict cordierite + leucosomes, representing upper amphibolites to lower granulate facie conditions.
U-Pb Sensitive High Resolution Ion Microprobe (SHRIMP) analysis was completed on 75 detrital zircons from a HLMC psammite sample. The data shows a polymodal age distribution with dominant modes at 2558, 2460 and 1970 Ma, with less significant ones at 2420 and 2026 Ma. The youngest group of five zircon analyses places the maximum deposition age at 1959 + 9 Ma. This data reveals a mainly mid to early Paleoproterozoic and Neoarchean provenance for the HLMC.
Considering the age determinations, Neoarchean detrital zircons are interpreted as either derived from nonexposed Archean rocks in the Hottah terrane, adjacent terranes to the south or southwest, or the Slave craton to the east. Moreover, the age populations of the HLMC vary from crystallization ages of the Archean Slave craton. This is either further evidence that the Hottah terrane is allochtonous with respect to the Slave craton or that the Slave craton evolved through the Noeoarchean and Paleoproterozoic and of this evolution are preserved within the Hottah terrane. Regardless, the wide range of detrital zircon ages is interpreted to reflect a complex Paleoproterozoic evolution in Hottah terrane.
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Pages: 107
Supervisors: L. Ootes / Nick Culshaw