Porphyry copper deposits (PCDs) are associated with shallow-level, subvolcanic intrusions. While PCDs have been studied extensively, the petrology of the host intrusions have received relatively little attention because hydrolytic alteration often destroys the primary petrologic features. However, these features are key to understanding the trans-crustal arc magmatic processes that result in PCDs. The Don Manuel porphyry copper system of the Miocene-Pliocene PCD belt of central Chile, contains significant alteration, but it is localized, allowing investigation of the primary petrology in relatively fresh portions. Fieldwork and examination of drill cores enabled characterization of the Don Manuel igneous complex (DMIC). The DMIC consists of six intrusive units ranging from 53-74 wt.% Si02. Highresolution CA-ID-TIMS U-Pb and whole-rock 40Ar/39Ar dating indicate that the intermediate to felsic units were emplaced in pulses between 4.0-3 .6 Ma, making it the youngest documented PCD system in the Andes. The episodic emplacement of this igneous complex occurred on a timescale similar to eruption and degassing events in arc volcanic systems. Petrographic, geochemical and isotopic data establish the origin and assembly of the diverse magmas that comprise the DMIC. The magmas have undergone polybaric differentiation from parents with varying initial water contents. Mineral chemistry, coupled ~ith thermobarometry, constrain the petrogenesis of the DMIC, indicating that wet magmas began differentiating in the lower to middle crust and continued to evolve in shallow crustal reservoirs. Intermediate porphyry dikes associated with copper mineralization contain diverse crystal cargos that represent mush entrained from different depths, crystals originating in different magmas, and crystals grown in-situ from hybridized magmas. The petrologic complexity and episodic timescale observed in the porphyry copperrelated magmas is analogous to the open system, trans-crustal processes indicated arid observed in arc volcanic systems. Examination of other PCDs through this framework could provide additional information about key ore ingredients such as volatiles, metals, and sulfur.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:702924 |
| Date | January 2016 |
| Creators | Gilmer, Amy K. |
| Publisher | University of Bristol |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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