Bimodal magmatism in northeast Palmer Land, Antarctic Peninsula: Geochemical evidence for a Jurassic ensialic back-arc basin
Major- and trace-element (XRF and INAA) and Nd-isotope analyses are presented on a Jurassic bimodal association of basic greenstones and silicic metavolcanic rocks from the Black Coast, northeast Palmer Land, Antarctic Peninsula. The greenstones are divided into three sub-groups, indistinct in the field, but which have geochemical characteristics of island arc tholeiites (group I), E-type MORB (group II), and continental arc basalts (group III). The tholeiites of group I and II have a similar range of ϵNd values (+3.7 to −1.2) and were produced from a heterogeneous, large ion lithophile element (LILE)-enriched, mantle source. The rocks of group III show a much stronger enrichment in LILE than groups I and II, and were derived from a mantle source with slightly lower ϵNd values (−2.3 to −5.0). The silicic volcanic rocks have low ϵNd values (−7.1 to −8.7) indicating a dominant crustal source, although trace element concentrations show a within-plate affinity. The origin and tectonic setting of this bimodal suite is discussed in relation to Mesozoic subduction along the proto-Pacific margin of the Antarctic Peninsula and southern South America and intra-continental extension associated with the break-up of Gondwana. It is concluded that the mafic greenstones and silicic metavolcanic rocks formed in an ensialic back-arc basin setting where, during a period of continental lithospheric attenuation, the rise of a mantle diapir may have caused widespread bimodal magmatism. The geographical extent of the Palmer Land basin is unknown at present, but it may be part of a much larger Weddell Sea or proto-Weddell Sea back-arc basin system.
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.