BRITISH COLUMBIA COAST MOUNTAINS METASEDIMENTARY ROCKS: AGE CONSTRAINTS AND PROVENANCE

This project focuses on the tectonic affinity of a narrow belt of metasedimentary rocks in the southern Coast Mountains Batholith (SCMB) of British Columbia. The pendants consist mainly of marble, pelitic schist, and minor layers of metaclastic quartzite, the latter of which were sampled for U-Pb ages and Hf isotopes of detrital zircons in Knight, Loughborough and Bute Inlets.

The U-Pb ages for nine out of 10 samples range from 366 to 180 Ma (dominant ages of 198, 211, 216, 302, 310, 320, 327, 332, and 349 Ma). Their Hf(t) values range from +18 to +6. Zircons analyzed from nearby strata of Wrangellia yield similar U-Pb ages and juvenile εHft values. These similarities suggest that the metasedimentary rocks may be equivalent to Wrangellia and perhaps overlying strata. 

One of the samples has U-Pb ages that range from 600 to 189 Ma with major and minor peaks at 560 and 245 Ma, respectively. The Hf(t) values range from +6 to -0.6. The U-Pb ages of this sample are consist with what has been observed in the southern portion of Alexander terrane, but the Hf(t) values resemble the northern portion of the terrane. It is accordingly possible that these strata have a correlation to Alexander terrane. 

Altogether, our geochronologic and isotopic data suggest that the pendants likely belong to the Wrangellia and possibly Alexander terranes. However, due to the lack of comparable data from Paleozoic or Triassic strata to the east, we cannot rule out connections these samples might have with the Stikine terrane.