Geochemistry and isotopic evolution of the Mesoproterozoic Cape Meredith Complex, West Falkland

Whole-rock major and trace element geochemical and Rb-Sr/Sm-Nd isotopic dat a are presented for the Mesoproterozoic (similar to1.0 Ga) metamorphic and igneous rocks of the Cape Meredith Complex, West Falkland. The data indicat e that the oldest rocks, the similar to1.1 Ga supracrustal gneisses of the Big Cape Formation, which form three petrographic and geochemical groups (m afic amphibolite, quartz-plagioclase-biotite-hornblende intermediate gneiss and acid gneiss), probably represent a juvenile calc-alkaline, basalt-ande site-rhyolite volcanic sequence, with epsilon (epsilon NdT) values and T-Nd (DM) ages of similar to +3 to +6 and similar to 1100 to 1400 Ma respectivel y. It is argued on geochemical grounds that these metavolcanics were extrud ed in an island-are at around 1120 Ma. The Big Cape Formation was intruded by granitoids during and after a collisional orogenic event at around 1090 Ma. The oldest, foliated, (G1) granodiorite was emplaced as thin sheets at approximately 1090 to 1070 Ma and is characterized by epsilon Nd Values of similar to +1.5 to 4 (T-DM = similar to 1200 to 1400 Ma), showing its juven ile nature. The similar to 1070 Ma (G2) syntectonic granitoid gneisses and similar to 1000 Ma G3 post-tectonic granites also exhibit juvenile characte ristics (epsilon (Nd) = similar toO to +5 and T-DM = 2200 to 1200 Ma, respe ctively). The granitoids show a time-composition evolution from Na-rich (G1 ) granodiorite to potassic, high-High Field Strength Element granites (G3). The geochemical and isotopic characteristics and geological evolution of t he Cape Meredith Complex is comparable with that of the adjacent Gondwana c rustal blocks in Natal (SE Africa) and Dronning Maud Land (East Antarctica) , supporting models that demonstrate these areas evolved in a contiguous, j uvenile are environment prior to, and during, a major orogenic event at sim ilar to1.1 Ga. These events were associated with the birth of the Rodinian supercontinent. The three areas remained juxtaposed during Rodinia break-up and were subsequently incorporated into Gondwana in the same relative posi tions.