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Origins of mafic microgranular enclaves and enclave swarms in granites: Field and geochemical relations

2018; Geological Society of America; Volume: 131; Issue: 3-4 Linguagem: Inglês

10.1130/b32028.1

1943-2674

Cármen Rodríguez, António Castro,

earthquake and tectonic studies

Research Article| November 08, 2018 Origins of mafic microgranular enclaves and enclave swarms in granites: Field and geochemical relations Carmen Rodríguez; Carmen Rodríguez † 1Departamento de Ciencias de la Tierra, Universidad de Huelva, 21007 Huelva, Spain2Instituto de Ciências da Terra, Universidade de Évora, 7002-554 Évora, Portugal †Corresponding author: c2r2dealmodovar@gmail.com Search for other works by this author on: GSW Google Scholar Antonio Castro Antonio Castro 1Departamento de Ciencias de la Tierra, Universidad de Huelva, 21007 Huelva, Spain3Instituto de Geociencias IGEO-CSIC, 28040 Madrid, Spain Search for other works by this author on: GSW Google Scholar GSA Bulletin (2019) 131 (3-4): 635–660. https://doi.org/10.1130/B32028.1 Article history received: 02 Feb 2018 rev-recd: 27 Jul 2018 accepted: 18 Sep 2018 first online: 08 Nov 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Carmen Rodríguez, Antonio Castro; Origins of mafic microgranular enclaves and enclave swarms in granites: Field and geochemical relations. GSA Bulletin 2018;; 131 (3-4): 635–660. doi: https://doi.org/10.1130/B32028.1 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 Mafic microgranular enclaves from polygenetic and monogenetic swarms in the Gredos sector of the Central System batholith (central Spain) were sampled and studied to elucidate field, geochronological, and geochemical relations. Among-enclave variations in terms of major elements demonstrate contamination with the pelitic country rocks, and not with the host granitic magma. Magmatic enclaves from monogenetic swarms in Gredos are interpreted as fragments from the chilled margins generated at the sidewall of ascent conduits. In situ U-Pb zircon age determinations by sensitive high-resolution ion microprobe yielded two sets of ages. One corresponds to the ages of crystallization at 290 ± 3.1 Ma and 300 ± 3.4 Ma of two enclaves from two different monogenetic swarms. These ages are slightly younger than the zircon ages of the host granodiorites (ca. 319–312 Ma). A secondary set of ages present in the two studied samples (at 322 ± 6.7 Ma and 320 ± 8.5 Ma) corresponds to the age of the main Variscan regional migmatization of host Neoproterozoic pelitic metasediments. These older ages are interpreted as xenocrystic cores that were derived from the pelitic host during magma ascent. Together with the geochemical relations, they prove quenching against the regional host in conduits and not against the host granodiorite as classically thought. Monogenetic swarms can be seen as high-energy pulses denoting the switching from steady-state to transient flow regimes within magma ascent conduits. By contrast, polygenetic swarms are generated by collapse of accumulated resisters of igneous and metamorphic origin that were previously present in migmatites at the top of subhorizontal, layer-type intrusions. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.