TY - JOUR
T1 - U-Pb and Hf isotopic evidence for an Arctic origin of terranes in northwestern Washington
AU - Schermer, Elizabeth R.
AU - Hoffnagle, Eric A.
AU - Brown, Edwin H.
AU - Gehrels, George E.
AU - McClelland, William C.
N1 - Funding Information:
We thank Peter Dykes, Matt Holland, Kenny Frank, Marley Kirkham, Brandon Brayfield, and Austin Hart for field and laboratory support. Funding was provided by the Geological Society of America and Western Washington University to Hoffnagle, National Science Foundation (NSF) grant EAR-133853 to the Arizona LaserChron Center, NSF grant EAR1249115 to Schermer and Brown, and NSF grant EAR1242939 to Gehrels. Reviews by Associate Editor G. Lang Farmer and two anonymous reviewers helped us improve the manuscript.
Funding Information:
We thank Peter Dykes, Matt Holland, Kenny Frank, Marley Kirkham, Brandon Brayfield, and Austin Hart for field and laboratory support. Funding was provided by the Geological Society of America and Western Washington University to Hoffnagle, National Science Foundation (NSF) grant EAR-133853 to the Arizona LaserChron Center, NSF grant EAR-1249115 to Schermer and Brown, and NSF grant EAR-1242939 to Gehrels. Reviews by Associate Editor G. Lang Farmer and two anonymous reviewers helped us improve the manuscript.
Publisher Copyright:
© 2018 The Authors.
PY - 2018/2/5
Y1 - 2018/2/5
N2 - New field, U-Pb, and Lu-Hf zircon data constrain the geologic history, age, and origin of the Yellow Aster Complex (YAC) in northwestern Washington, providing insight into the tectonic history of this and related Paleozoic arc terranes of the western North American Cordillera. Mapping shows that the oldest YAC rocks consist of quartzofeldspathic paragneiss (meta-arkose) and quartzose calc-silicate paragneiss (metacalcareous siltstone) in gradational contact. Paragneisses are cut by syn-tectonic and post-tectonic intrusions and faulted against granitic orthogneiss. U-Pb zircon results show that (1) maximum depositional ages of paragneisses are Silurian to Early Devonian (432-390 Ma); (2) detrital zircons from quartzose calc-silicate paragneisses show a broad age peak from 1900 to 1000 Ma, while quartzofeldspathic paragneisses contain several distinct Precambrian age peaks, including at 2.0-1.8 Ga and 2.5-2.4 Ga; (3) paragneisses contain early Paleozoic grains with peaks ca. 420-400 and ca. 460-440 Ma; (4) pre-tectonic orthogneiss and syn-tectonic and post-tectonic dikes range from ca. 410-406 Ma; and (5) intrusive rocks contain apparently xenocrystic ca. 480-440 Ma grains. Lu-Hf isotope data show that nearly all Paleozoic zircons have negative εHf(t) values, and zircons in the meta-arkose samples are more negative than those in the calc-silicate. Zircons in several meta-arkose samples yield εHf(t)) values of -40 to -57, rare in the North American Cordillera, and requires the involvement of Mesoarchean to Eoarchean crustal components. The most likely source region with crust as old as Eoarchean and early Paleozoic magmatism is the Greenland Caledonides, which implies derivation from the Arctic margin of northeastern Laurentia or Baltica. The chemistry and petrology of the igneous rocks suggest that the terrane was in a continental arc setting before, during, and after deposition of the sedimentary rocks. The data constrain deformation, metamorphism, and magmatism in the YAC to a brief period in the Early Devonian, from ca. 410 to 400 Ma. Age and Hf patterns of the YAC are similar to elements of the Yukon-Tanana and Alexander terranes. Our study shows that the complex history of metamorphosed terranes requires analysis of multiple isotopic and petrologic proxies, and U-Pb analysis of both igneous (n = 50) and detrital (n = 400) zircons to confirm or refute terrane and provenance correlations.
AB - New field, U-Pb, and Lu-Hf zircon data constrain the geologic history, age, and origin of the Yellow Aster Complex (YAC) in northwestern Washington, providing insight into the tectonic history of this and related Paleozoic arc terranes of the western North American Cordillera. Mapping shows that the oldest YAC rocks consist of quartzofeldspathic paragneiss (meta-arkose) and quartzose calc-silicate paragneiss (metacalcareous siltstone) in gradational contact. Paragneisses are cut by syn-tectonic and post-tectonic intrusions and faulted against granitic orthogneiss. U-Pb zircon results show that (1) maximum depositional ages of paragneisses are Silurian to Early Devonian (432-390 Ma); (2) detrital zircons from quartzose calc-silicate paragneisses show a broad age peak from 1900 to 1000 Ma, while quartzofeldspathic paragneisses contain several distinct Precambrian age peaks, including at 2.0-1.8 Ga and 2.5-2.4 Ga; (3) paragneisses contain early Paleozoic grains with peaks ca. 420-400 and ca. 460-440 Ma; (4) pre-tectonic orthogneiss and syn-tectonic and post-tectonic dikes range from ca. 410-406 Ma; and (5) intrusive rocks contain apparently xenocrystic ca. 480-440 Ma grains. Lu-Hf isotope data show that nearly all Paleozoic zircons have negative εHf(t) values, and zircons in the meta-arkose samples are more negative than those in the calc-silicate. Zircons in several meta-arkose samples yield εHf(t)) values of -40 to -57, rare in the North American Cordillera, and requires the involvement of Mesoarchean to Eoarchean crustal components. The most likely source region with crust as old as Eoarchean and early Paleozoic magmatism is the Greenland Caledonides, which implies derivation from the Arctic margin of northeastern Laurentia or Baltica. The chemistry and petrology of the igneous rocks suggest that the terrane was in a continental arc setting before, during, and after deposition of the sedimentary rocks. The data constrain deformation, metamorphism, and magmatism in the YAC to a brief period in the Early Devonian, from ca. 410 to 400 Ma. Age and Hf patterns of the YAC are similar to elements of the Yukon-Tanana and Alexander terranes. Our study shows that the complex history of metamorphosed terranes requires analysis of multiple isotopic and petrologic proxies, and U-Pb analysis of both igneous (n = 50) and detrital (n = 400) zircons to confirm or refute terrane and provenance correlations.
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U2 - 10.1130/GES01557.1
DO - 10.1130/GES01557.1
M3 - Article
AN - SCOPUS:85044598300
SN - 1553-040X
VL - 14
SP - 835
EP - 860
JO - Geosphere
JF - Geosphere
IS - 2
ER -