Systematic mineralogical diversity in A-type granitic intrusions: Control of magmatic source and geological processes

Research Article| March 01, 2016 Systematic mineralogical diversity in A-type granitic intrusions: Control of magmatic source and geological processes Angeliki Papoutsa; Angeliki Papoutsa † 1Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada †angeliki_papoutsa@hotmail.com Search for other works by this author on: GSW Google Scholar Georgia Pe-Piper; Georgia Pe-Piper 2Department of Geology, Saint Mary’s University, Halifax, Nova Scotia B3H 3C3, Canada Search for other works by this author on: GSW Google Scholar David J.W. Piper David J.W. Piper 3Natural Resources Canada, Geological Survey of Canada (Atlantic), Bedford Institute of Oceanography, P.O. Box 1006, Dartmouth, Nova Scotia B2Y 4A2, Canada Search for other works by this author on: GSW Google Scholar Author and Article Information Angeliki Papoutsa † 1Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada Georgia Pe-Piper 2Department of Geology, Saint Mary’s University, Halifax, Nova Scotia B3H 3C3, Canada David J.W. Piper 3Natural Resources Canada, Geological Survey of Canada (Atlantic), Bedford Institute of Oceanography, P.O. Box 1006, Dartmouth, Nova Scotia B2Y 4A2, Canada †angeliki_papoutsa@hotmail.com Publisher: Geological Society of America Received: 01 Dec 2014 Revision Received: 16 Jun 2015 Accepted: 17 Aug 2015 First Online: 08 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 © 2015 Geological Society of America GSA Bulletin (2016) 128 (3-4): 487–501. https://doi.org/10.1130/B31245.1 Article history Received: 01 Dec 2014 Revision Received: 16 Jun 2015 Accepted: 17 Aug 2015 First Online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Angeliki Papoutsa, Georgia Pe-Piper, David J.W. Piper; Systematic mineralogical diversity in A-type granitic intrusions: Control of magmatic source and geological processes. GSA Bulletin 2016;; 128 (3-4): 487–501. doi: https://doi.org/10.1130/B31245.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The origin and causes of mineralogical diversity of A-type granites are debated. The series of A-type granite plutons, with distinct mineralogical differences, emplaced along an Upper Paleozoic crustal-scale shear zone in the Cobequid Highlands, Nova Scotia, provide an opportunity to examine the origin of different A-type plutons in a similar tectonic setting. Based on the ferromagnesian minerals present, the plutons are classified into sodic granites with sodic amphibole, calcic granites with calcic amphibole, and biotite granites. Sodic and calcic granites occur exclusively in complex intrusions with subequal amounts of gabbro in the eastern shear zone, whereas plutons in the western shear zone, with lesser gabbro, are solely biotite granites. Trace elements and radiogenic isotopes show that the three granite types have different sources. Intensive parameters including temperature, pressure, and water-in-melt contents were estimated from mineralogical and geochemical data. Modeling of these geochemical data suggests that the biotite and calcic granites were derived by 20%–40% partial melting of intracrustal feldspathic rocks, whereas the sodic granites are extreme fractionates (90%) of coeval mafic magma. We propose that supply of Upper Paleozoic mafic magma, probably related to regional extension and decompression melting beneath the Magdalen Basin, created a deep crustal hot zone in the eastern Cobequid Highlands, and extreme fractionation of underplated mafic sills produced the sodic granites. Heat transfer from crystallizing mafic magma induced partial melting of the surrounding crust, creating batches of biotite and calcic granitic melts in different depths. Fractionated and crustally derived melts segregated along crustal-scale faults, constructing the complex plutons in the east. Melting of the crust was further facilitated by the release of water from the crustal rocks upon heating. In the eastern shear zone, water was released predominantly by magmatic rocks and in lesser amounts compared to the west, where Neoproterozoic sedimentary and volcaniclastic rocks are more abundant. The volatile-rich granitic melts in the western part of the shear zone were crystallized rapidly, stabilizing only biotite. This study demonstrates that the mineralogical variations in A-type granites arise from rather similar magma compositions, but they are important petrogenetic indicators of varying sources, specific magmatic processes, and emplacement conditions. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

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