Coupling, decoupling and metasomatism:Evolution of crust-mantle relationships beneath NW Spitsbergen

• Published in: Lithos
• Main Authors: Griffin, W. L., Nikolic, N., O'Reilly, Suzanne Y., Pearson, N. J.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2012
• Subjects: Arctic; Bockfjorden; Breibogen; Greenland; Hoek; Hekla; Spitsbergen
• Online Access: https://researchers.mq.edu.au/en/publications/944a76b6-d70c-48a3-9b79-67559875a025; https://doi.org/10.1016/j.lithos.2012.03.003; http://www.scopus.com/inward/record.url?scp=84865191203&partnerID=8YFLogxK

The Bockfjord area of NW Spitsbergen (Norwegian Arctic) exposes a long history of crustal evolution, culminating in the Caledonian (400-500. Ma) orogeny; prior to the opening of the N. Atlantic Ocean, this area was part of the Laurentian (Greenland) side of the orogen. The N-striking Breibogen-Bockfjorden (BB) fault marks the western margin of a large graben filled with Devonian redbeds. West of the fault the basement consists of gneisses, schists and granites of the Hekla Hoek formation, inferred to represent a Caldeonian thrust sheet. U-Pb and Hf-isotope data for detrital zircons from this area show that the Hekla Hoek protoliths formed at ca 1.8. Ga, but were heavily reworked ca 800-1000. Ma ago, and again during the Caledonian orogeny.Quaternary alkali-basalt volcanism has provided abundant xenoliths of mantle and crustal rocks from both sides of the BB fault. Lower-crustal xenoliths are mainly mafic to intermediate granulites. Whole-rock Sr-, Nd- and Hf-isotope data for the granulites from both sides of the BB fault show significant disequilibrium, implying the removal of melts late in the evolution of the lower crust. Most zircons from eight xenoliths have Neoarchean/Paleoproterozoic and Paleozoic U-Pb ages; several also contain zircons with ages and/or Hf model ages >. 3.2. Ga.The peridotite xenoliths are dominantly spinel lherzolites, metasomatized to varying extents. Xenoliths from basalts east of the BB fault commonly contain metasomatic amphibole, phlogopite and apatite; peridotites from west of the fault rarely display these phases. West of the fault, there is no clear correlation between cpx REE patterns and whole-rock Al contents; east of the fault there is a clear negative correlation between LREE enrichment and whole-rock Al 2 O 3 . In-situ Re-Os isotope analysis of sulfides in the peridotites shows another dichotomy. Xenoliths from west of the fault contain sulfides with Re depletion (T RD ) model ages extending back to 3.3Ga, with major populations at 2.4-2.6Ga, 1.6-1.8Ga and 1.2-1.3Ga; the ...