Batholith tectonics: Formation and deformation of ghost stratigraphy during assembly of the mid-crustal Andalshatten batholith, central Norway

• Published in: Geosphere
• Main Authors: Anderson, Heather S. (TTU), Yoshinobu, Aaron S. (TTU), Nordgulen, Øystein, Chamberlain, Kevin
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2013
• Subjects: Absolute Age; Aureoles; Batholiths; Cross Sections; Europe; Diorites; Emplacement; Displacements; Faults; Granites; Granodiorites; Host Rocks; Igneous Rocks; Leucogranite; Magmas; Metamorphic Rocks; Nesosilicates; Norway; Ordovician; Orthosilicates; Paleozoic; Plutonic Rocks; Scandinavia; Silicates; Tectonics; Titanite; Tonalite; Upper Ordovician; Western Europe; Xenoliths; Zircon; Helgeland Nappe Complex; Andalshattan Batholith; Helgeland; Andalshatten
• Online Access: https://hdl.handle.net/2346/89955; https://doi.org/10.1130/GES00824.1

Geosphere is open access. Users have the right to read, download, copy, distribute, print, search, or link to the full texts of these articles. The Andalshatten batholith (322 km2, >700 km3) is a predominantly granodioritic high-K, calc-alkaline igneous body that was assembled in the mid-crust across four lithologically distinct nappes within the Helge land Nappe Complex, central Norway. Extensive vertical and horizontal exposures of metamorphic screens and xenoliths within the batholith provide an unparalleled view of the nature of magma emplacement, host rock displacement, and batholith assembly, i.e., batholith tectonics. The mapped intrusion consists of at least five distinct lithologic phases, including schlieren-banded to gneissic granodiorite (11% of batholith area), coarse-crystalline to K-feldspar megacrystic granodiorite (69%), amphibole-bearing diorite (11%), tonalite (2%), and minor leucogranite. Contacts between phases are both sharp and/or gradational and are interpreted to reflect comagmatic behavior over the duration of crystallization of the phases separated by a given contact. New chemical abrasion–thermal ionization mass spectrometry 206Pb/238U zircon weighted mean ages of 442.67 ± 0.14 Ma and 441.53 ± 0.40 Ma for 2 samples of the voluminous megacrystic granodiorite from disparate localities indicate distinct periods of zircon crystallization separated by ~1 Ma; titanite ages for these samples are 441.30 ± 0.21 Ma and 436.10 ± 2.80 Ma, respectively. No observable contacts were identified between these two lithologically similar localities. Of the mapped intrusion area, ~8% (>24 km2) comprises screens (kilometer scale) and xenoliths (subkilometer scale) of metamorphic rocks that reflect the skeletal framework of the host rock nappes into which the granodioritic magmas intruded. This ghost stratigraphy maintains broad continuity with host rock lithology and structural trends. The largest screens show no evidence of internal, emplacement-related ductile deformation, but appear to be ...