Plagioclase compositions give evidence for in situ crystallization under horizontal flow conditions in mafic sills

Research Article| October 01, 2012 Plagioclase compositions give evidence for in situ crystallization under horizontal flow conditions in mafic sills Rais Latypov; Rais Latypov * 1Department of Geosciences, University of Oulu, Linnanmaa 90014, Finland *E-mail: rais.latypov@oulu.fi. Search for other works by this author on: GSW Google Scholar Vera Egorova Vera Egorova 1Department of Geosciences, University of Oulu, Linnanmaa 90014, Finland2Institute of Geology and Mineralogy SB RAS, Novosibirsk, Russia Search for other works by this author on: GSW Google Scholar Author and Article Information Rais Latypov * 1Department of Geosciences, University of Oulu, Linnanmaa 90014, Finland Vera Egorova 1Department of Geosciences, University of Oulu, Linnanmaa 90014, Finland2Institute of Geology and Mineralogy SB RAS, Novosibirsk, Russia *E-mail: rais.latypov@oulu.fi. Publisher: Geological Society of America Received: 03 Jan 2012 Revision Received: 03 May 2012 Accepted: 11 May 2012 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2012 Geological Society of America Geology (2012) 40 (10): 883–886. https://doi.org/10.1130/G33173.1 Article history Received: 03 Jan 2012 Revision Received: 03 May 2012 Accepted: 11 May 2012 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Rais Latypov, Vera Egorova; Plagioclase compositions give evidence for in situ crystallization under horizontal flow conditions in mafic sills. Geology 2012;; 40 (10): 883–886. doi: https://doi.org/10.1130/G33173.1 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 SocietyGeology Search Advanced Search Abstract The relative roles of crystal settling and in situ crystallization in the formation of igneous bodies are still a subject of debate in igneous petrology. Both processes predict that minerals must become more evolved in composition inward. Our study of three dolerite sills from Siberia indicates, however, that this is not always the case. In particular, the ∼100-m-thick Vavukansky dolerite sill shows a systematic inward increase in An content of plagioclase across lower (from ∼An63 to ∼An82) and upper (from ∼ An63 to ∼An80) marginal zones. This is followed by inward decreases in the An content of plagioclase in the interior part of the sill that ends in a sandwich horizon (An55–58). These trends in plagioclase composition are not consistent with either approach, but can be explained by in situ crystallization involving two distinct stages. During the initial stage the sill evolved as an open system that was continuously filled by magmas, becoming more primitive with time. This gave rise to marginal zones with minerals showing reverse compositional trends (e.g., an inward increase in the An content of plagioclase). During the subsequent stage the sill evolved as a closed system by fractional crystallization. This resulted in minerals showing normal compositional trends (e.g., an inward decrease in the An content of plagioclase). Several other mafic sills and layered intrusions show similar variations in plagioclase compositions, indicating that open-system, in situ crystallization may be a common process in the origin of igneous bodies. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.