TY - JOUR
T1 - U-Pb age and Hf-isotope geochemistry of zircon from felsic volcanic rocks of the Paleoproterozoic Aillik Group, Makkovik Province, Labrador
AU - LaFlamme, Crystal
AU - Sylvester, Paul J.
AU - Hinchey, Alana M.
AU - Davis, William J.
N1 - Funding Information:
This research was funded by the Geological Survey of Newfoundland and Labrador , and an NSERC Discovery grant to P.J.S. The SHRIMP geochronology was conducted through the Uranium Resources of Canada Project under the Secure Energy Supply Program. Rebecca Lam is thanked for assistance with the Hf-isotope analyses. Tom Pestaj is thanked for assistance in the SHRIMP laboratory at the Geological Survey of Canada. Comments on the manuscript by Charlie Jefferson, Anders Scherstén and an anonymous journal reviewer were very helpful.
PY - 2013/1
Y1 - 2013/1
N2 - U-Pb zircon SHRIMP geochronology and Lu-Hf zircon LA-MC-ICPMS isotope geochemistry are used to constrain the ages of Paleoproterozoic felsic magmatism and their crustal sources in the Aillik Group, Makkovik Province of Labrador. This information is important for understanding the extent of crustal reworking vs. juvenile crustal growth in subduction-related magmatism during the Paleoproterozoic and improves framework knowledge for uranium exploration in the Central Mineral Belt of Labrador. U-Pb SHRIMP zircon geochronology from four felsic tuff samples collected from two different areas of the Aillik Group yield magmatic 207Pb/206Pb ages of 1852±7Ma (2σ), 1854±7Ma (2σ), 1861±7Ma (2σ), and 1862±7Ma (2σ). The ages fall within the range of previous U-Pb zircon dates reported for felsic volcanic rocks of the Aillik Group. Altogether these dates indicate that felsic volcanism spanned at least 30m.y. and was perhaps most intense during the last 10m.y. of that interval. A foliated syn-deformational monzogranite in the Aillik Group (Cross Lake granite) yields a 207Pb/206Pb zircon date of 1805±6Ma (2σ), which indicates that development of a pervasive planar fabric associated with northwestward thrusting of the Aillik Group continued after this time.Initial εHfst values for magmatic zircons from the four felsic tuffs (-4.8 to -1.9, -1.7 to +2.2, -11.8 to +3.8, -9.0 to -4.6) and monzogranite (-4.8 to -1.5) exhibit significant variability, which indicates heterogeneous sources. Most of the zircon grains have negative initial εHfst values and calculated crust formation Hf-isotope TDM model ages point to substantial contributions from melts of ancient crust, ranging in age from ca. 2200 to 2900m.y. and clustering at ca. 2500m.y. Inherited zircon grains in the felsic tuffs and monzogranite, mainly have U-Pb ages of ca. 1880-1920Ma, though others are older, up to ca. 2743Ma. Hf-isotope TDM model ages for the inherited zircons are similar to those of the magmatic zircons. The Hf-isotope results indicate that subduction-related felsic magmatism in the Makkovik Orogen involved significant crustal reworking (∼80%) during formation of the Aillik Group.
AB - U-Pb zircon SHRIMP geochronology and Lu-Hf zircon LA-MC-ICPMS isotope geochemistry are used to constrain the ages of Paleoproterozoic felsic magmatism and their crustal sources in the Aillik Group, Makkovik Province of Labrador. This information is important for understanding the extent of crustal reworking vs. juvenile crustal growth in subduction-related magmatism during the Paleoproterozoic and improves framework knowledge for uranium exploration in the Central Mineral Belt of Labrador. U-Pb SHRIMP zircon geochronology from four felsic tuff samples collected from two different areas of the Aillik Group yield magmatic 207Pb/206Pb ages of 1852±7Ma (2σ), 1854±7Ma (2σ), 1861±7Ma (2σ), and 1862±7Ma (2σ). The ages fall within the range of previous U-Pb zircon dates reported for felsic volcanic rocks of the Aillik Group. Altogether these dates indicate that felsic volcanism spanned at least 30m.y. and was perhaps most intense during the last 10m.y. of that interval. A foliated syn-deformational monzogranite in the Aillik Group (Cross Lake granite) yields a 207Pb/206Pb zircon date of 1805±6Ma (2σ), which indicates that development of a pervasive planar fabric associated with northwestward thrusting of the Aillik Group continued after this time.Initial εHfst values for magmatic zircons from the four felsic tuffs (-4.8 to -1.9, -1.7 to +2.2, -11.8 to +3.8, -9.0 to -4.6) and monzogranite (-4.8 to -1.5) exhibit significant variability, which indicates heterogeneous sources. Most of the zircon grains have negative initial εHfst values and calculated crust formation Hf-isotope TDM model ages point to substantial contributions from melts of ancient crust, ranging in age from ca. 2200 to 2900m.y. and clustering at ca. 2500m.y. Inherited zircon grains in the felsic tuffs and monzogranite, mainly have U-Pb ages of ca. 1880-1920Ma, though others are older, up to ca. 2743Ma. Hf-isotope TDM model ages for the inherited zircons are similar to those of the magmatic zircons. The Hf-isotope results indicate that subduction-related felsic magmatism in the Makkovik Orogen involved significant crustal reworking (∼80%) during formation of the Aillik Group.
KW - Aillik Group
KW - Crustal growth
KW - LA-MC-ICPMS Hf isotopes
KW - Labrador
KW - Makkovik Province
KW - Paleoproterozoic magmatism
KW - SHRIMP U-Pb zircon geochronology
UR - http://www.scopus.com/inward/record.url?scp=84867593216&partnerID=8YFLogxK
U2 - 10.1016/j.precamres.2012.09.005
DO - 10.1016/j.precamres.2012.09.005
M3 - Article
AN - SCOPUS:84867593216
VL - 224
SP - 129
EP - 142
JO - Precambrian Research
JF - Precambrian Research
SN - 0301-9268
ER -