Implications of in situ zircon U-Pb, Lu-Hf, oxygen-isotope, and trace element geochemistry on the petrogenetic history of the northern Hogem batholith in the Quesnel terrane, north-central British Columbia, Canadian Cordillera
Creators: Jones, Gabrielle
Publisher: name: University of Alberta Library
Year: 2022

<p>The Cordilleran orogen of western Canada is a type example of accretionary tectonism and thus an ideal location to study continental growth by oceanic and continental arc magmatism and terrane accretion. Cordilleran Intermontane terranes are interpreted as accreted oceanic arcs that contributed significant crustal material to the western North American margin during the Mesozoic; however, uncertainties regarding the pre-accretionary history and basement of these terranes hinder understanding the relative roles of new juvenile crust and reworked crust in the building of this major orogeny. An improved understanding of these issues also has broader implications for models of Phanerozoic juvenile crustal growth and accretionary tectonics. The Hogem batholith in north-central Quesnel terrane, British Columbia comprises Triassic to Cretaceous-aged intrusions. It provides a natural laboratory to better understand the magma sources, nature and antiquity of the batholith, the basement to the Quesnel terrane, and the tectonic history in this area through time.<br>
This study presents new combined zircon U-Pb/Hf, δ18O and trace element data for 13 intrusive plutonic rocks from the Hogem batholith, supplemented by apatite and titanite U-Pb+Sm-Nd and whole rock major oxide and trace element geochemical data. New zircon U-Pb dates coincide with previous geochronology results and expand the crystallization age range of four intrusive suites, from 206.8±0.9 to 127.1±1.6 Ma, revealing the batholith’s composite and protracted 80-million-year magmatic history. Notably, the age range of the Mesilinka intrusive suite, 135.4±0.9 to 127.1±1.6 Ma, corresponds with a period otherwise marked by magmatic quiescence across the Cordillera. The crystallization ages of the Thane Creek (207 to 194 Ma) and Duckling Creek (182 to 174 Ma) intrusive suites overlap with prolific periods of porphyry Cu±Au-Mo mineralization in the Canadian Cordillera. Zircon trace element geochemistry results (Eu/EuN* ≥0.4, Ce/CeC* &gt;100, ΔFMQ &gt;0) suggest zircon crystallized in oxidized and hydrous magma conditions at near-solidus temperatures (750 to 650°C), which indicates potentially favourable magma conditions for porphyry mineralization in the Thane and Duckling Creek suites. Zircon Hf-O isotope results are consistent with a predominantly juvenile, mantle-derived source for the pre- to syn-accretionary Thane Creek and Duckling Creek suites. Xenocrystic zircons from the post-accretionary Osilinka suite (ca. 160 Ma) reveal an inherited juvenile Hf-O signature from the melt source, while zircon Hf-O results from the Mesilinka suite (135 to 127 Ma) suggest a mix of juvenile mantle- and recycled supracrustal-derived magma sources. There is no indication that the magmas that formed the Hogem batholith experienced significant interaction with ancient North American continental basement. <br>
Overall, the generally juvenile Hf-O signatures of zircon from plutonic rocks studied here contrast with previous isotope studies of plutonic rocks in southern and northern Quesnellia and suggest disparate basement compositions and accretionary styles across the Quesnel terrane during the Mesozoic. These findings form the basis of a model for the production and preservation of juvenile crust in the Quesnellia arc, which supports the overall trend to juvenile Hf isotope compositions in Phanerozoic circum-Pacific accretionary belts. This model may be applied to better understanding juvenile crustal growth and orogen-craton interactions in other accreted terranes in the North American Cordillera as well as within global Phanerozoic accretionary orogens.</p>