Evolution of the Antarctic Peninsula lithosphere: Evidence from Mesozoic mafic rocks

Abstract

New geochronology from a thick (>800m) basaltic succession along the eastern margin of the Antarctic Peninsula confirm a Middle Jurassic age (178±1Ma). This marginally postdates the adjacent Ferrar large igneous province of the Transantarctic Mountains and predates the extensive silicic volcanism of the Mapple Formation (~170Ma) of the Antarctic Peninsula. The geochemistry of other rare, but broadly contemporaneous, basaltic successions of the Antarctic Peninsula, along with Cretaceous-age mafic dykes, are used to interpret the influences of lithospheric and asthenospheric mantle sources during the Mesozoic. Two significant high magmatic addition rate events occurred along the Antarctic Peninsula continental margin at 170 and 110Ma and can be correlated to events along the South American Cordillera. These ‘flare-up’ events are characterised by extensive silicic (mostly ignimbrite) volcanism of the Chon Aike Province (V2 event: 170Ma) and significant granitoid batholith emplacement of the Lassiter Coast intrusive suite (110Ma). The 170Ma event is exposed across large parts of the northern Antarctic Peninsula, whilst the 110Ma event is more widespread across the southern Antarctic Peninsula. The basaltic volcanism described here precedes the ‘flare-up’ event at 170Ma and has geochemical characteristics that indicate a thickened lithosphere prevailed. A major dyke swarm that followed the 170Ma event indicates that extensive lithospheric thinning had occurred, which allowed the ascent of depleted mafic melts. The thinning was the direct result of widespread lower crustal/upper lithospheric melting associated with the silicic volcanism. In the southern Antarctic Peninsula, the lithosphere remained over thickened until the emplacement of the major batholiths of the Lassiter Coast intrusive suite at 110Ma and was then immediately followed by the emplacement of more asthenosphere-like melts indicating extensive lithospheric thinning.