EARLY PALEOZOIC ROCKS OF THE ROWE-HAWLEY AND DOME BELTS OF WESTERN CT: STRATIGRAPHIC INSIGHTS AND ISSUES ARISING FROM DETRITAL ZIRCON DATA

Previously reported detrital zircon (dz) data from west CT are integrated with dz data from New England to assess the age and provenance of western CT metasediments, and to provide time-stratigraphic insight in rocks historically correlated based on lithology alone.

Rocks mapped as Rowe Fm contain dz derived from Laurentia only. The Collinsville and Cobble Mtn Fms yield ~1.0 Ga Laurentian grains, and ~600 Ma and pre-1.3 Ga Proterozoic zircons interpreted as peri-Gondwanan (pG). Structural/ intrusive relations indicate these rocks are Middle Ordovician or older.

In contrast, the Straits Schist (SS) contains Laurentian, pG (~625Ma) and Ordovician dz and is tentatively interpreted as Early Devonian based on a 414±4 Ma detrital zircon. Correlative strata to the north contain dated volcanic ashes that further constrain the age. An Early Devonian age allows time for burial and metamorphism that produced widespread Late Devonian zircon and monazite ages. However, this interpretation is inconsistent with staurolite U-Pb ages of ~400 Ma (Lanzirotti and Hanson, 1997) that would require unreasonably rapid heating rates in the Devonian.

Rocks mapped as Russell Mtn Fm (RM) in MA and basal Straits in CT (Rodgers,1985) contain a unique package of lithologies that includes quartzite, amphibolite, and marble. These rocks always occur below the Straits Schist (and the Goshen Fm in MA) suggesting by our interpretation a Silurian/ Early Devonian age. In CT, these rocks contain zircon of mixed provenance, as does the RM (Karabinos et al., 2018). There’s a compelling argument for correlation based on lithology and stratigraphic position, but the lack of Ordovician dz in the CT rocks is puzzling because they are ubiquitous in Silurian/Devonian rocks.

The Taine Mtn Fm from the Bristol Dome, structurally below the RM and SS, contains dz of pG provenance only, and contains zircons with ~550 Ma cores and ~500 Ma metamorphic rims. The dZ spectra are similar to those from the Moretown and Collinsville Fms in MA (Stamp et al., 2016). To the south, Bristol Gneiss dz yield a metamorphic age of 383±9 Ma, but one core is dated at ~540 Ma, suggesting that all the rocks in the core of the dome could be of pG affinity. This unique provenance likely requires tectonic emplacement of these rocks to peri-Laurentia prior to SS and RM deposition.