Hostname: page-component-78c5997874-94fs2 Total loading time: 0 Render date: 2024-11-10T17:38:50.404Z Has data issue: false hasContentIssue false
  • English
  • Français

An Early Ordovician tonalitic–granodioritic belt along the Schistose-Greywacke Domain of the Central Iberian Zone (Iberian Massif, Variscan Belt)

Published online by Cambridge University Press:  16 January 2012

A. RUBIO-ORDÓÑEZ ,
P. VALVERDE-VAQUERO ,
L. G. CORRETGÉ ,
A. CUESTA-FERNÁNDEZ ,
G. GALLASTEGUI ,
M. FERNÁNDEZ-GONZÁLEZ  and
A. GERDES
A. RUBIO-ORDÓÑEZ
Affiliation:
Área de Petrología y Geoquímica, Departamento de Geología, Universidad de Oviedo, c/ Arias de Velasco s/n, Oviedo (Asturias), 33005, Spain
P. VALVERDE-VAQUERO*
Affiliation:
Área de Laboratorios, Instituto Geológico y Minero de España (IGME), c/ La Calera 1, 28760, Tres Cantos (Madrid), Spain
L. G. CORRETGÉ
Affiliation:
Área de Petrología y Geoquímica, Departamento de Geología, Universidad de Oviedo, c/ Arias de Velasco s/n, Oviedo (Asturias), 33005, Spain
A. CUESTA-FERNÁNDEZ
Affiliation:
Área de Petrología y Geoquímica, Departamento de Geología, Universidad de Oviedo, c/ Arias de Velasco s/n, Oviedo (Asturias), 33005, Spain Unidad de Microsonda Electrónica, Centro Cientifico Técnico ‘Severo Ochoa’, Universidad de Oviedo, Campus ‘El Cristo’, 33006, Oviedo (Asturias), Spain
G. GALLASTEGUI
Affiliation:
Instituto Geológico y Minero de España (IGME), c/ Matemático Pedrayes 25, 33005, Oviedo (Asturias), Spain
M. FERNÁNDEZ-GONZÁLEZ
Affiliation:
Unidad de Microsonda Electrónica, Centro Cientifico Técnico ‘Severo Ochoa’, Universidad de Oviedo, Campus ‘El Cristo’, 33006, Oviedo (Asturias), Spain
A. GERDES
Affiliation:
Institut für Geowissenchaften, Goethe Universität, Altenhöferallee 1, 60438, Frankfurt, Germany
*
†Author for correspondence: p.valverde@igme.es
Get access Rights & Permissions [Opens in a new window]

Abstract

The Zarza la Mayor and Zarza de Montánchez tonalites and Arroyo de la Luz granodiorite are part of a tonalitic–granodioritic belt located along the Schistose-Greywacke Domain of the Central Iberian Zone. These intrusions are also part of the Central Extremadura Batholith, a set of plutons ranging from tonalite to leucogranite that have been considered a prime example of Variscan syn-kinematic plutonism. New LA-ICP-MS and CA-ID-TIMS U–Pb dating reveals that the Zarza la Mayor tonalite–granodiorite is an Early Ordovician intrusion. The LA-ICP-MS data show that there is an absence of inherited cores, despite some complex internal zoning with obvious resorption features in some of the zircon crystals. Dating of monazite and zircon by CA-ID-TIMS provides a concordant age of 478.1 ± 0.8 Ma. This age coincides with electron microprobe analysis (EMPA) monazite chemical ages for the Zarza de Montánchez (482 ± 10 Ma) and Arroyo de la Luz (470 ± 15 Ma) intrusions. These new data indicate the presence of an Early Ordovician belt of calc-alkaline tonalite–granodiorite in the Schistose-Greywacke Domain – the Beira Baixa–Central Extremadura tonalite–granodiorite belt – which resembles a continental magmatic arc. This belt is contemporaneous with the Ollo de Sapo magmatic event further north in the Central Iberian Zone.

Keywords

Early Ordoviciantonalite–granodioriteU–Pb geochronologyIberian MassifLA-ICP-MSID-TIMSEMPA
Type
Rapid Communication
Information
Geological Magazine , Volume 149 , Issue 5 , September 2012 , pp. 927 - 939
Copyright
Copyright © Cambridge University Press 2012

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Álvaro, J. J., Ezzouhairi, H., Ribeiro, M. L., Ramos, J. F. & Solá, R. 2008. Early Ordovician volcanism in the Iberian Chains (NE Spain) and its influence on the preservation of shell concentrations. Bulletin de la Societe Geologique de France 179, 569–81.CrossRefGoogle Scholar
Antunes, I. M. H. R., Neiva, A. M. R., Silva, M. M. V. G. & Corfu, F. 2008. Geochemistry of S-type granitic rocks from the reversely zoned Castelo Branco pluton (central Portugal). Lithos 103, 445–65.CrossRefGoogle Scholar
Antunes, I. M. H. R., Neiva, A. M. R., Silva, M. M. V. G. & Corfu, F. 2009. The genesis of I- and S-type granitoid rocks of the Early Ordovician Oledo pluton, Central Iberian Zone (central Portugal). Lithos 111, 168–85.CrossRefGoogle Scholar
Aramburu, C., Truyols, J., Arbizu, M., Méndez-Bedia, I., Zamarreño, I., García-Ramos, J. C., Suárez de Centi, C. & Valenzuela, M. 1992. El Paleozoico Inferior de la Zona Cantábrica. In Paleozoico Inferior de Ibero-América (eds Gutiérrez-Marco, J. G., Saavedra, J. & Rábano, I.), pp. 397–421. Badajoz: Universidad de Extremadura Publicaciones.Google Scholar
Arden, J. W. & Gale, N. H. 1974. Separation of trace amounts of uranium and thorium and their determination by mass spectrometric isotope dilution. Analytical Chemistry 46, 687–91.CrossRefGoogle Scholar
Bascones, L., Martín Herrero, D. & Corretgé, L. G. 1987. Hoja y Memoria explicativa del Mapa Geológico Nacional a escala 1:50,000 serie 2, n° 620, Zarza la Mayor. Madrid: IGME.Google Scholar
Bea, F., Montero, P. & Zinger, T. 2003. The nature, origin, and thermal influence of the granite source layer of Central Iberia. Journal of Geology 111, 579–95.CrossRefGoogle Scholar
Bea, F., Montero, P., Talavera, C. & Zinger, T. 2006. A revised Ordovician age for the Miranda do Douro orthogneiss, Portugal. Zircon U-Pb ion-microprobe and LA-ICPMS dating. Geologica Acta 4, 395–401.Google Scholar
Bea, F., Montero, P., Gonzalez-Lodeiro, F. & Talavera, C. 2007. Zircon inheritance reveals exceptionally fast crustal magma generation processes in Central Iberia during the Cambro-Ordovician. Journal of Petrology 48, 2327–39.CrossRefGoogle Scholar
Black, L. P., Kamo, S. L., Allen, C. M., Davis, D. W., Aleinikoff, J. N., Valley, J. W., Mundil, R., Campbell, I. H., Korsch, R. J., Williams, I. S. & Foudoulis, C. 2004. Improved 206Pb/238U microprobe geochronology by the monitoring of a trace-element-related matrix effect; SHRIMP, ID-TIMS, ELA-ICP-MS and oxygen isotope documentation for a series of zircon standards. Chemical Geology 205, 115–40.CrossRefGoogle Scholar
Carracedo, M., Gil Ibarguchi, J. I., García de Madinabeitia, S. & Berrocal, T. 2005. Geocronología de los granitoides hercínicos de la serie mixta. Revista de la Sociedad Geológica de España 18, 77–88.Google Scholar
Castro, A. 1986. Structural pattern and ascent model in the Central Extremadura batholith, Hercynian belt, Spain. Journal of Structural Geology 8, 633–45.CrossRefGoogle Scholar
Castro, A., Patiño Douce, A. E., Corretgé, L. G., De La Rosa, J. D., El-Biad, M. & El-Hmidi, H. 1999. Origin of peraluminous granites and granodiorites, Iberian massif, Spain: an experimental test of granite petrogenesis. Contributions to Mineralogy and Petrology 135, 255–76.CrossRefGoogle Scholar
Cocherie, A. & Albarede, F. 2001. An improved U-Th-Pb age calculation for electron microprobe dating of monazite. Geochimica et Cosmochimica Acta 65, 4509–22.CrossRefGoogle Scholar
Cordani, U. G., Nutman, A. P., Andrade, A. S., Santos, J. F., Azevedo, M. R., Mendes, M. H. & Pinto, M. S. 2006. New U-Pb SHRIMP zircon ages for pre-Variscan orthogneisses from Portugal and their bearing on the evolution of the Ossa-Morena Tectonic Zone. Anais da Academia Brasileira de Ciencias 78, 133–49.CrossRefGoogle ScholarPubMed
Corretgé-Castañón, L. G. 1969. Las diferenciaciones aplíticas cupuliformes en la tonalita de Zarza la Mayor-Ceclavín (Cáceres) y su interpretación petrogenética. Acta Geológica Hispánica 5 (IV), 119–23.Google Scholar
Corretgé, L. G. 1971. Estudio petrológico del batolito de Cabeza de Araya. PhD thesis, Departamento de Petrología y Geoquímica. Salamanca, Universidad de Salamanca, Spain. Published thesis.Google Scholar
Corretgé, L. G., Bea, F. & Suárez, O. 1985. Las características geoquímicas del batolito de Cabeza de Araya (Cáceres, España): Implicaciones petrogenéticas. Trabajos de Geología 15, 219–38.Google Scholar
Chappell, B. W. & White, A. J. R. 1992. I- and S-type granites in the Lachlan Fold Belt. Transactions of the Royal Society of Edinburgh: Earth Sciences 83, 1–26.CrossRefGoogle Scholar
Díez Balda, M. A., Vegas, R. & González Lodeiro, F. 1990. Structure (Central Iberian Zone). In Pre-Mesozoic Geology of Iberia (eds Dallmeyer, R. D. & Martínez García, E.), pp. 172–88. Berlin-Heidelberg: Springer-Verlag.Google Scholar
Díez Montes, A., Martínez Catalán, J. R. & Mulas, F. B. 2010. Role of the Ollo de Sapo massive felsic volcanism of NW Iberia in the Early Ordovician dynamics of northern Gondwana. Gondwana Research 17, 363–76.CrossRefGoogle Scholar
Fernández-Suárez, J., Gutiérrez-Alonso, G., Jenner, G. A. & Tubrett, M. N. 1999. Crustal sources in Lower Palaeozoic rocks from NW Iberia: insights from laser ablation U-Pb ages of detrital zircons. Journal of the Geological Society, London 156, 1065–8.CrossRefGoogle Scholar
Fernández-Suárez, J., Gutiérrez-Alonso, G., Jenner, G. & Turbett, M. N. 2000. New ideas on the Proterozoic-Early Palaeozoic evolution of NW Iberia: insights from U–Pb detrital zircon ages. Precambrian Research 102, 185–206.CrossRefGoogle Scholar
Fernández, C. & Castro, A. 1999. Pluton accommodation at high strain rates in the upper continental crust. The example of the Central Extremadura batholith, Spain. Journal of Structural Geology 21, 1143–49.CrossRefGoogle Scholar
Fernández, C., Becchio, R., Castro, A., Viramonte, J. M., Moreno-Ventas, I. & Corretgé, L. G. 2008. Massive generation of atypical ferrosilicic magmas along the Gondwana active margin: implications for cold plumes and back-arc magma generation. Gondwana Research 14, 451–73.CrossRefGoogle Scholar
Fernández González, M., Cuesta Fernández, A., Rubio-Ordóñez, A. & Valverde-Vaquero, P. 2009. Datación química U-Th-Pb de monacita por microsonda electrónica (CHIME-EPMA Dating): Puesta a punto y resultados. In VII Congreso Ibérico; X Congreso Nacional de Geoquímica, pp. 170–77. Soria: Diputación Provincial de Soria.Google Scholar
Förster, H. J. 1998. The chemical composition of REE–Y–Th–U-rich accessory minerals from peraluminous granites of the Erzgebirge–Fichtelgebirge region, Germany. I. The monazite-(Ce)–brabantite solid solution series. American Mineralogist 83, 259–72.CrossRefGoogle Scholar
Gallastegui, G., Aramburu, C., Barba, P., Fernández, L. P. & Cuesta, A. 1992. El volcanismo del Paleozoico inferior de la Zona Cantábrica. In Paleozoico Inferior de Ibero-América (eds Rábano, J., Gutiérrez-Marco, J. C. & Saavedra, J.), pp. 43–5. Badajoz: Universidad de Extremadura Publicaciones.Google Scholar
García de Figuerola, L. C., Corretgé, L. G. & Suárez, O. 1971. Estudio petrológico de la formación plutónica de Zarza la Mayor (Provincia de Cáceres). Boletín Geológico y Minero de España 32, 217–33.Google Scholar
García de Figuerola, L. C., Corretgé, L. G. & Bea, F. 1974. El dique de Alentejo-Plasencia y haces de diques básicos de Extremadura (Estudio comparativo). Boletín Geológico y Minero de España 85, 308–37.Google Scholar
Gebauer, D., Martínez García, E. & Hepburn, J. C. 1993. Geodynamic significance, age and origin of the Ollo de Sapo Augengneiss (NW Iberian Massif, Spain). In Annual Meeting of the Geological Society of America, abstracts, p. 342. Boston: Geological Society of America.Google Scholar
Gerdes, A. & Zeh, A. 2006. Combined U-Pb and Hf isotope LA(MC)ICP-MS analyses of detrital zircons: comparison with SHRIMP and new constraints for the provenance and age of an Armorican metasediment in Central Germany. Earth and Planetary Science Letters 249, 47–62.CrossRefGoogle Scholar
Gerstenberger, H. & Haase, G. 1997. A highly effective emitter substance for mass spectrometric Pb isotope ratio determinations. Chemical Geology 136, 309–12.CrossRefGoogle Scholar
Gil Serrano, G., Pérez Rojas, A. & Pineda Velasco, A. 1982. Hoja y Memoria explicativa del Mapa Geológico Nacional a escala 1.50,000 serie 2, n° 730, Montánchez. Madrid: IGME.Google Scholar
Gutiérrez-Alonso, G., Fernández-Suárez, J., Gutiérrez-Marco, J. C., Corfu, F., Murphy, J. B. & Suárez, M. 2007. U-Pb depositional age for the upper Barrios Formation (Armorican Quartzite facies) in the Cantabrian zone of Iberia: implications for stratigraphic correlation and paleogeography. In The Evolution of the Rheic Ocean: From Avalonian-Cadomian active margin to Alleghenian-Variscan collision (eds U. Linneman, D. Nance, P. Kraft & G. Zulauf), pp. 287–96. Geological Society of America, Special Papers no. 423.Google Scholar
Isachsen, C. E., Coleman, D. S. & Schmitz, M. 2007. PbMacDat program. Available at http://www.earth-time.org.Google Scholar
Jackson, S. E., Pearson, N. J., Griffin, W. L. & Belousova, E. A. 2004. The application of laser ablation-inductively coupled plasma-mass spectrometry to in situ U–Pb zircon geochronology. Chemical Geology 211, 47–69.CrossRefGoogle Scholar
Jaffey, A. H., Flynn, K. F., Glendenin, L. E., Bentley, W. C. & Essling, A. M. 1971. Precision measurement of half-lives and specific activities of U235 and U238. Physical Review C 4, 1889.CrossRefGoogle Scholar
Janousek, V., Gerdes, A., Vrana, S., Finger, F., Erban, V., Friedl, G. & Braithwaite, C. J. R. 2006. Low-pressure granulites of the Lisov Massif, Southern Bohemia: Visean metamorphism of Late Devonian plutonic arc rocks. Journal of Petrology 47, 705–44.CrossRefGoogle Scholar
Julivert, M. & Mártinez, F. J. 1987. The structure and evolution of the Hercynian Fold Belt in the Iberian Peninsula. In The Anatomy of Mountain Belts (eds Schaer, J. P. & Rodgers, J.), pp. 65–103. Princeton: Princeton University Press.CrossRefGoogle Scholar
Lancelot, J. & Allegret, A. 1982. Radiochronologie U/Pb de l'orthogneiss alcalin de Pedroso (Alto Alentejo, Portugal) et évolution anté-hercynienne de l'Europe occidentale. Neues Jahrbuch für Mineralogie – Monatshefte 9, 385–94.Google Scholar
Lancelot, J. R., Allegret, A. & de Leon, M. I. P. 1985. Outline of Upper Precambrian and Lower Paleozoic evolution of the Iberian Peninsula according to U-Pb dating of zircons. Earth and Planetary Science Letters 74, 325–37.CrossRefGoogle Scholar
Ludwig, K. R. 1991. PBDAT, v.1.23.Google Scholar
Ludwig, K. R. 1999. ISOPLOT/Ex. version 2.00.Google Scholar
Ludwig, K. R. 2001. Users’ manual for Isoplot/ex rev. 2.49: a geochronological toolkit for Microsoft Excel. Berkeley Geochronology Center Special Publication 1a, 56 pp.Google Scholar
Mattauer, M. 2004. Orthogneisses in the deepest levels of the Variscan belt are not a Precambrian basement but Ordovician granites: tectonic consequences. Comptes Rendus Geosciences 336, 487–89.CrossRefGoogle Scholar
Mattinson, J. M. 2005. Zircon U-Pb chemical abrasion (“CA-TIMS”) method: Combined annealing and multi-step partial dissolution analysis for improved precision and accuracy of zircon ages. Chemical Geology 220, 47–66.CrossRefGoogle Scholar
Montel, J.-M., Foret, S., Veschambre, M., Nicollet, C. & Provost, A. 1996. Electron microprobe dating of monazite. Chemical Geology 131, 37–53.CrossRefGoogle Scholar
Montero, P., Bea, F., González-Lodeiro, F., Talavera, C. & Whitehouse, M. J. 2007. Zircon ages of the metavolcanic rocks and metagranites of the Ollo de Sapo Domain in central Spain: implications for the Neoproterozoic to Early Palaeozoic evolution of Iberia. Geological Magazine 144, 963–76.CrossRefGoogle Scholar
Montero, P., Talavera, C., Bea, F., Lodeiro, F. G. & Whitehouse, M. J. 2009. Zircon geochronology of the Ollo de Sapo Formation and the age of the Cambro-Ordovician rifting in Iberia. Journal of Geology 117, 174–91.CrossRefGoogle Scholar
Neiva, A. M. R., Williams, I. S., Ramos, J. M. F., Gomes, M. E. P., Silva, M. M. V. G. & Antunes, I. M. H. R. 2009. Geochemical and isotopic constraints on the petrogenesis of Early Ordovician granodiorite and Variscan two-mica granites from the Gouveia area, central Portugal.Lithos 111, 186–202.CrossRefGoogle Scholar
Pankhurst, R. J., Rapela, C. W., Saavedra, J., Baldo, E., Dahlquist, J., Pascua, I. & Fanning, C. M. 1998. The Famatinian magmatic arc in the central Sierras Pampeanas: an Early to Mid-Ordovician continental arc on the Gondwanan margin. In The proto-Andean Margin of Gondwana (eds Pankhurst, R. J. & Rapela, C. W.), pp. 343–67. Geological Society of London, Special Publication no. 142.Google Scholar
Pankhurst, R. J., Rapela, C. W. & Fanning, C. M. 2000. Age and origin of coeval TTG, I- and S-type granites in the Famatinian belt of NW Argentina. Transactions of the Royal Society of Edinburgh: Earth Sciences 91, 151–68.CrossRefGoogle Scholar
Parrish, R. R. 1987. An improved micro-capsule for zircon dissolution in U-Pb geochronology. Chemical Geology (Isotope Geoscience Section) 66, 99–102.CrossRefGoogle Scholar
Portugal Ferreira, M. 1982. A magmatic arc in the Iberian segment of the Hercynian chain: the northwest-southeast lineament between Oporto (Portugal) and Zarza la Mayor (Spain). Memorias e Noticias. Publicaçoes do Museu e Laboratorio Mineralógico e Geológico da Universidade de Coimbra 94, 32–47.Google Scholar
Pupin, J. P. & Turco, G. 1972. Une typologie originale du zircon accessoire. Bulletin de la Société Française du Cristallografie 95, 348–59.CrossRefGoogle Scholar
Quesada, C. 1991. Geological constraints on the Paleozoic tectonic evolution of tectonostratigraphic terranes in the Iberian Massif. Tectonophysics 185, 225–45.CrossRefGoogle Scholar
Richter, S., Goldberg, S. A., Mason, P. B., Traina, A. J. & Schwieters, J. B. 2001. Linearity tests for secondary electron multipliers used in isotope ratio mass spectrometry. International Journal of Mass Spectrometry 206, 105–27.CrossRefGoogle Scholar
Romão, J., Dunning, G., Marcos, A., Dias, R. & Ribeiro, A. 2010. The Mação-Penhascoso laccolith granite: age and implications (SW-Central Iberian Zone). e-Terra 16, 1–4.Google Scholar
Rubio-Ordóñez, A., Corretgé, L. G. & Cuesta, A. 2007. Morfología de los circones como indicadores petrogenéticos de la asociación tonalita-leucogranito: el caso del plutón de Zarza la Mayor (Cáceres-España). Geogaceta 41, 187–90.Google Scholar
Rubio, J. I. 1982. Nota sobre las dioritas del NW. de Zarza la Mayor (Cáceres). Cuadernos del Laboratorio Xeolóxico de Laxe 3, 75–81.Google Scholar
Schäfer, G. 1969. Geologie und petrographie im östlichen Katilischen Hauptscheidegebirge (Sierra de Guadarrama, Spanien). Münsterche Forschungen zur Geologie und Palaeontologie 10, 1–207.Google Scholar
Scherrer, N. C., Engi, M., Gnos, E., Jakob, V. & Liechti, A. 2000. Monazite analysis; from sample preparation to microprobe age dating and REE quantification. Schweizerische Mineralogische und Petrographische Mitteilungen 80, 93–105.Google Scholar
Solá, A. R., Pereira, M. F., Williams, I. S., Ribeiro, M. L., Neiva, A. M. R., Montero, P., Bea, F. & Zinger, T. 2008. New insights from U-Pb zircon dating of Early Ordovician magmatism on the northern Gondwana margin: The Urra Formation (SW Iberian Massif, Portugal). Tectonophysics 461, 114–29.CrossRefGoogle Scholar
Stacey, J. S. & Kramers, J. D. 1975. Approximation of terrestrial lead isotope evolution by a two-stage model. Earth and Planetary Science Letters 26, 207–21.CrossRefGoogle Scholar
Suzuki, K. & Adachi, M. 1991. The chemical Th-U-total Pb isochron ages of zircon and monazite from the gray granite of the Hida Terrane, Japan. The Journal of Earth Sciences, Nagoya University 38, 11–38.Google Scholar
Valverde-Vaquero, P. 2009. Método de datación U-Pb ID-TIMS en el laboratorio geocronológico del IGME (Tres Cantos). Comunicaciones VII Congreso Ibérico de Geoquímica, pp. 758–65. Soria: Diputación Provincial de Soria.Google Scholar
Valverde-Vaquero, P., Carrión, C., Reyes Andrés, J., Martín Rubí, J. A. & Paradas Herrero, A. 2005. Un estándar de monacita para dataciones U-Th-Pb: IGME 6883-A. Comunicaciones V Congreso Ibérico de Geoquímica, pp.1–6. Soria: Diputación Provincial de Soria.Google Scholar
Valverde-Vaquero, P., Dörr, W., Belka, Z., Franke, W., Wiszniewska, J. & Schastok, J. 2000. U-Pb single-grain dating of detrital zircon in the Cambrian of central Poland: implications for Gondwana versus Baltica provenance studies. Earth and Planetary Science Letters 184, 225–40.CrossRefGoogle Scholar
Valverde-Vaquero, P. & Dunning, G. R. 2000. New U-Pb ages for Early Ordovician magmatism in Central Spain. Journal of the Geological Society, London 157, 15–26.CrossRefGoogle Scholar
von Raumer, J. F., Stampfli, G. M., Borel, G. D. & Bussy, F. 2002. The organization of pre-Variscan basement areas at the north-Gondwanan margin. International Journal of Earth Sciences (Geologische Rundschau) 91, 35–52.CrossRefGoogle Scholar
Wiedenbeck, M., Allé, P., Corfu, F., Griffin, W. L., Meier, M., Oberli, F., Quadt, A. V., Roddick, J. C. & Spiegel, W. 1995. Three natural zircon standards for U-Th-Pb, Lu-Hf, trace element and REE analyses. Geostandards newsletter 19, 1–23.CrossRefGoogle Scholar
Williams, M. L., Jercinovic, M. J. & Terry, M. P. 1999. Age mapping and dating of monazite on the electron microprobe: Deconvoluting multistage tectonic histories. Geology 27, 1023–26.2.3.CO;2>CrossRefGoogle Scholar