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TitlePetrology of explosive Middle-Upper Triassic ultramafic rocks in the Mess Creek area, northern Stikine terrane
AuthorMilidragovic, DORCID logo; Joyce, N LORCID logo; Zagorevski, AORCID logo; Chapman, J BORCID logo
SourceBritish Columbia Ministry of Energy and Mines, British Columbia Geological Survey Paper 2016-1, 2016 p. 95-111 Open Access logo Open Access
LinksOnline - En ligne
Alt SeriesEarth Sciences Sector, Contribution Series 20150348
PublisherBritish Columbia Ministry of Energy and Mines
Mediapaper; on-line; digital
File formatpdf
ProvinceBritish Columbia
NTS104G/02; 104G/03; 104G/06; 104G/07
AreaMess Creek; Shaft Creek
Lat/Long WENS-131.3333 -130.7500 57.5000 57.1667
Subjectsigneous and metamorphic petrology; geochronology; igneous petrology; ultramafic rocks; facies; facies analyses; pyroclastics; argon argon dates; Stikine terrane; Stuhini Group; Stikinia; Mesozoic; Triassic
Illustrationslocation maps; stratigraphic sections; photographs; photomicrographs; tables; plots
ProgramGEM2: Geo-mapping for Energy and Minerals Western Cordillera, Regional porphyry transitions
Released2016 01 01
AbstractThe Mess Lake facies of the Stuhini Group (Middle to Upper Triassic) in northwestern British Columbia includes a unit of pervasively serpentinized, olivine-rich, subaqueous lapilli breccia, lapilli tuff, and ash tuff. Relatively high whole-rock MgO concentrations (29-38 wt.%; loss on ignition-free) of pyroclastic samples from this unit refl ect signifi cant accumulation of olivine. These ultramafi c pyroclastic rocks also exhibit strong enrichment in Ba and depletion in Nb+Ta relative to La, consistent with derivation from slab-metasomatized mantle asthenosphere in a volcanic arc setting. The restored parental liquid is a primitive, mantle-derived, arc magma that contained up to 16-20 wt.% MgO. The unit contains fresh volcanic glass indicating low-grade regional metamorphism, and suggesting that it postdates emplacement of the nearby Hickman pluton, which yielded 40Ar/39Ar hornblende ages of 222.2 ±2.8 Ma, 221.6 ±2.5 Ma, and 220.1 ±2.7 Ma. The Alaskan-type ultramafi c plutons of the Polaris suite (Middle to Late Triassic) and a post-Hickman basaltic diatreme, containing picritic fragments, are spatially associated and broadly coeval with the ultramafi c pyroclastic rocks of the Mess Lake facies, but a petrogenetic link has yet to be established.
Summary(Plain Language Summary, not published)
This report presents preliminary results and models developed through GEM2 program on volcanic and plutonic rocks in British Columbia and Yukon. It details the distribution and characteristics of rare volcanic rocks on the basis of field and laboratory analyses. It presents a new model for the origin of these rocks that requires unusual temperatures. The results presented herein help progress GEM2 model to ultimately redefine the regional tectonic models of the Cordillera.

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