Tectonic implications of fore-arc magmatism and generation of high-magnesian andesites: Alexander Island, Antarctica
Alexander Island, situated off the west coast of the Antarctic Peninsula, contains a suite of Late Cretaceous to Early Tertiary subduction-related magmatic rocks. The rocks occupy a fore-arc position 100–200 km trenchward of the main arc (Antarctic Peninsula) and they become younger northward along the length of the island. Major and trace element geochemistry for 222 samples shows the suite to be a medium to high-K calc-alkaline series, ranging in composition from picro-basalt to rhyolite. Andesite samples show a large range in MgO and Mg#, with nine samples representing high-magnesian andesites.Sr and Nd isotopic data indicate that the andesites range isotopically to more depleted mantle compositions than the associated basalts. The dacite/rhyolites can be related compositionally to the andesites by assimilation of typical Pacific rim accretionary material. To produce high-magnesian andesite lavas, it is necessary to introduce a suitable source of heat into the fore-arc, thus enabling partial melting of depleted sub fore-arc hydrous peridotite. A causative link with ridge subduction prior to magmatism is proposed, with successive ridge–trench collisions producing a temporal migration of the magmatism and high geothermal gradients in an anomalously hot fore-arc region.
Privacy & Cookies Policy
Necessary cookies are absolutely essential for the website to function properly. This category only includes cookies that ensures basic functionalities and security features of the website. These cookies do not store any personal information.
Any cookies that may not be particularly necessary for the website to function and is used specifically to collect user personal data via analytics, ads, other embedded contents are termed as non-necessary cookies. It is mandatory to procure user consent prior to running these cookies on your website.