U-PB DETRITAL ZIRCON ANALYSIS OF SEDIMENTARY ROCKS OF THE SOUTHEASTERN NEW ENGLAND AVALON TERRANE IN THE US APPALACHIANS: EVIDENCE FOR A SEPARATE CRUSTAL BLOCK

We conducted U–Pb LA-ICPMS analysis on seven samples from multiple previously interpreted subterranes of the southeastern New England composite terrane to constrain their origins. We focused on the southern part of the composite terrane, because the northern part is known to correlate well with Avalonian terranes in Canada, based on rock types and ages, U–Pb detrital zircon signatures of metasedimentary rocks, and Sm–Nd isotope geochemistry data.

Two samples of Neoproterozoic Plainfield Formation quartzite from the previously interpreted Hope Valley subterrane in the southwestern part of the southeastern New England Avalon terrane and two from the Neoproterozoic Blackstone Group quartzite from the adjacent Esmond-Dedham subterrane to the east have Tonian youngest detrital zircon age populations. One sample of Cambrian North Attleboro Formation quartzite of the Esmond-Dedham subterrane yielded an Ediacaran youngest detrital zircon age population. All five samples include abundant Mesoproterozoic zircon and smaller Paleoproterozoic and Archean populations, and are similar to those of the northern part of the southeastern New England Avalon terrane and the Avalonian terranes in Canada. Based on U-Pb detrital zircon data, there is no significant difference between the Hope Valley and Esmond-Dedham subterranes.

Detrital zircon from two samples of the Price Neck and Newport Neck formations of the Neoproterozoic Newport Group in southern Rhode Island is characterized by large ~650–643 and ~745–733 Ma age populations and minor zircon up to ~3.1 Ga. This signature is most consistent with a northwest African affinity. The Newport Group may thus represent a subterrane, terrane or other crustal block with a different origin and history than the southeastern New England Avalon terrane to the northwest. The boundary of this Newport Block may be restricted to the boundaries of the Newport Group, or it may extend farther northwest. It may have become part of the Avalon terrane prior to mid-Paleozoic amalgamation with Laurentia, or have arrived as a separate terrane. Alternatively, it may have arrived during the formation of Pangea, in which case the Pangean suture zone lies on land.