The role of crustal and mantle sources in the genesis of granitoids of the Antarctic Peninsula and adjacent crustal blocks

• Main Authors: Millar, I.L., Willan, R.C.R., Wareham, C.D., Boyce, A.J.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Geological Society 2001
• Subjects: QE Geology; Antarctic; The Antarctic; Antarctic Peninsula; West Antarctica; Whitmore Mountains; Antarc*; Antarctica
• Online Access: https://eprints.gla.ac.uk/603/; https://eprints.gla.ac.uk/603/1/Journ_Geol_Soc_158%285%29_855-867.pdf; http://www.ingentaconnect.com/content/geol/jgs;jsessionid=2c0c3b2lngepy.henrietta?

Magmatic rocks from the Antarctic Peninsula show marked variations in isotope composition, which reflect changes in the geodynamic evolution of the peninsula through time. Most Antarctic Peninsula granitoids formed as a result of subduction: they fall on well-defined trends on plots of Nd, Pb-207/Pb-204 and delta O-18 against Sr-87/Sr-86(i). between a component derived from subduction-modified mantle or juvenile basaltic underplate (epsilon Nd-i gt 6, Pb-207/Pb-204=15.61, delta O-18=5.5 parts per thousand, Sr-87/Sr-86 lt 0.704) and an end- member interpreted as a melt of Proterozoic lower crust (epsilon Nd=-7, Pb-207/Pb-204=15.67, delta O-18=10 parts per thousand, Sr-87/Sr-86=0.709). A small group of granitoids. emplaced before or during Gondwana break-up, plot on distinct trends towards high Sr-87/Sr-86(i) compositions. reflecting mixing between melts derived from Proterozoic lower crust and melts of middle-upper crustal rocks (epsilon Nd-i=-9, Pb- 207/Pb-204=15.64, delta O-18=10 parts per thousand, Sr-87/Sr- 86=0.726). with little or no input of new material derived from the mantle or from juvenile basaltic underplate. These granitoids are thought to have formed as a result of crustal attenuation during the initial rifting phase of Gondwana break- up. Similar trends are shown by data from granitoids of the adjacent crustal blocks of West Antarctica, The isotope data suggest that an enriched Ferrar/Karoo-type lithosphere was not involved in the genesis of granitoids of the Antarctic Peninsula or of the Ellsworth-Whitmore Mountains crustal block.