| Abstract: |
To improve identification of crustal rock types within the continent‐ocean transition (COT) offshore Nova Scotia based on the standard approach of analyzing P‐wave velocities (Vp), we incorporate S‐wave velocity (Vs) modeling and determine Vp/Vs ratios. In this work, we construct detailed layered Vp and Vs models using four component wide‐angle ocean bottom seismometer data from profiles SMART‐2 and ‐3 across the central and southwestern Scotian margin, respectively. Along profile SMART‐3, the lower continental crust displays low Vp/Vs ratios (∼ ${\sim} $1.7), akin to felsic granulite. Vp/Vs ratios (1.7–1.9) within the COT suggest that syn‐rift volcanism and magmatism resulted in a basalt‐dominated upper crust overlying a thick layer (4–10 km) of laterally heterogeneous gabbroic underplate that jointly cover an estimated profile area of ∼ ${\sim} $1,230 km2 ${\text{km}}^{2}$. On Profile SMART‐2, we observe upper continental crust (Vp/Vs< ${< } $ 1.7) with highly felsic composition within the continental and the COT domains. Serpentinized mantle (Vp/Vs> ${ >} $ 1.9) is interpreted within the seaward‐most segment of the transitional lower crust, alongside gabbroic underplate, based on its Vp/Vs ratio of 1.7–1.8 and high Vp of 6.9–7.4 km/s, notably thickening beneath the East Coast Magnetic Anomaly near the landward COT limit. Syn‐rift volcanism and magmatism SMART‐2 profile area is estimated at ∼ ${\sim} $ 513 km2 ${\text{km}}^{2}$. Our results portray the southwestern Scotian margin as magma‐rich, the northeastern as magma‐poor, and the central margin as a hybrid zone amalgamating characteristics from both. Regardless of margin type, the thinnest transitional crust is consistently observed toward its seaward termination leading into the full‐scale seafloor spreading. Plain Language Summary: Developing knowledge about the Earth's crust found beneath the seafloor is challenging, yet important from the perspective of both basic science (e.g., understanding continental breakup) and societal impacts (e.g., petroleum exploration). Our findings on the Nova Scotia margin using controlled source seismic data reveal diverse rock types, such as granite, basalt, granulite, gabbro, and various mantle rocks providing insights into the region's geological past. Different parts of offshore Nova Scotia show distinct rock compositions, hinting at unique geological processes. Offshore southwestern Nova Scotia, there was abundant magma underplating which added massive crustal units and prevented seawater from reaching the mantle. Other regions, like offshore northeastern Nova Scotia, have minimal amounts of magma, allowing the mantle to be altered by seawater that penetrated through fractured crust above as the North Atlantic took shape. Central Nova Scotia offshore displays hybrid characteristics with traits from both the northeastern and southwestern offshore. Through our work, we seek to deepen our understanding of the plate tectonic processes that, over millions of years, split up continents into diverging plates to form ocean basins. Key Points: Vp/Vs models on Profile SMART‐2 reveal a hybrid central Nova Scotian Margin with elements of both magma‐rich and magma‐poor riftingExtent/location of interpreted basalts and gabbroic underplate at central/SW Scotian margin match that of the East Coast Magnetic AnomalyEvidence of serpentinized mantle beneath hyperextended crust across the central/NE margins suggest amagmatic extension before breakup [ABSTRACT FROM AUTHOR] |
