The Structure and Stratigraphy of Small Point, Maine: D3 Inverted Transtensional Map-Scale Folds of Neoacadian Provenance

• Main Author: Sive, Haley Russell
• Format: Text
• Language: unknown
• Published: SCARAB 2012
• Subjects: geology; deformation; transtension; metamorphism; shear; orogeny; Hermit Island; Hussey; Spring Point; Seal Island
• Online Access: https://scarab.bates.edu/honorstheses/45; https://scarab.bates.edu/context/honorstheses/article/1051/type/native/viewcontent

The Cape Small Synform lies in an area of the Northern Appalachians that has undergone successive deformation from at least two major orogenic events, the Salinic Orogeny (440-423 Ma) and the Acadian Orogeny (421 – 400 Ma) (van Staal et al. 2009) and contains evidence for Norumbega shearing deformation (Early Devonian-Carboniferous) (Swanson 1999). With a grant from the USGS EDMAP program, a 1:5,000 scale map has been created which sheds light on the complex history of folding and shearing. The study identifies 5 new lithologic units within the Scarboro Formation (youngest to oldest- amphibolite, garnet rich member, muscovite rich member, quartz-rich member, and rusty-weathering member), 2 new units in the Spring Point Formation (a calc silicate and a marble), and articulates 6 seven other members which are similar to those mapped by Hussey and Berry (2006) in the Cape Elizabeth and Diamond Island Formations. A previously unseen graded bed, located in the Cape Elizabeth silver schist implies a downward facing stratigraphy, and designates the previously named Cape Small Synform as a synformal anticline. This folding generation, which dominates the area, is related to D3, which took place during the Neoacadian Orogeny creating a complex regional fold that changes from open in the south to tight in the north. The upright folds deform two previous events: D1, an isoclinal recumbent folding event during the Salinic orogeny observable in foliation of quartz-rich beds of Bald Head; and D2, an isoclinal recumbent refolding deformation event evidenced by folded quartz veins and foliation at Bald Head related to a local Early Acadian event. Strike and dip measurements taken for both meso- and macro-scale D3 folds suggest the existence of two synformal anticlines (Head Beach fold (190/21), and Hermit Island fold (191/39)), and two anticlinal synforms (Cape Small fold (193/22), the Seal Island fold (165/8)). The well-exposed trough of the Cape Small synformal anticline shows hinge parallel extension, which is linked to deformation outside of a purely compressive regime. Thus a wench dominated, transtensional environment (Venkat-Ramani and Tikoff 2002) is proposed to explain both hinge parallel extension and the connection of this Acadian orogenic folding to the subsequent Norumbega shearing.