par FRÉDÉRic LAPIQUE, MiCliEL CHAMPENOIS et ALAfN CHEILLETZ Centre de Recherches Pétrographiques et Géochimiques, 15, rue N.D. des Pauvres,
B.P. 20, 54501 Vandoeuvre, Cedex, France
Résumé. - L'analyseur d'images présenté ici est un système vidéographique interactif qui permet à l'utilisateur de dessiner en surimposition sur une image vidéo couleur. Ce système est basé sur un micro-ordinateur IBM-PC, utilisé pour le stockage et le traitement des données extraites de l'image provenant d'un ensemble vidéo couleur haute définition (caméra + moniteur). Les programmes associés ont été développés pour des applications en minéralogie, pétrologie ou géologie structurale et permettent d'obtenir des paramètres tels que surface, périmè- tre, facteur de forme, orientation, ainsi que la détermination de l'ellipsoïde de déformation finie.
Mots-clés : analyse d'images, système vidéographique, déformation finie, analyse modale, analyse morphologi- que.
An interactive videographic analyser : deseription and applications
Abstract. - �Ihe image analyser presented here is an interactive videographic system which allovs the operator to draw by superimposition on the colour video image. This system is based on an IBM-PC microcomputer which is used for storage and treatment of the video data provided by a high resolution colour video camera. Associated programs have been developed for mineralogical. petrological or structural applications which perform the calculation of parameters such as surface, perimeter. shape factor, orientation or finite strain ellipsoïd détermina- tion.
Key-words : image analysis, videographic system. finite strain, modal analysis, morphological analysis.
Sommaire ALBAREDE F. and TAMAGNAN V.
Modelling the recent geochemical evolution of the Piton de la Fournaise volcano,
réunion Island, 1931-1986 ... 81 PICHAVANT M., KONTAK D.J., VALENCIA HERRERA J. and CLARK A.H.
The miocene-pliocene macusani volcanics, SE Peru
I. Mineralogy and magmatic evolution of a two-mica aluminosilicate-bearing
ignimbrite suite ... 82 PICHAVANT M., KONTAK D.J., BRIQUEU L., VALENCIA HERRERA J. and
CLARK A.H.
The miocene-pliocene macusani volcanics, SE Peru
II. Geochemistry and origin of a felsic peraluminous magma... 83 PICHAVANT M. and MON'I'EL J.M. '
Petrogenesis of a two-mica ignimbrite suite: the macusani volcanics, SE Peru ... 84 PICHAVANT M.
Sur l'équivalence entre termes plutoniques et volcaniques dans les séries
leucogranitiques... 84 FRANCE-LANORD C. and LE FORT P.
Crustal melting and granite genesis during the Himalayan collision orogenesis ... 85 PARSONS I. and BROWN W.L.
Sidewall crystallization in the Klokken intrusion: zoned ternary feldspars and
coexisting minerals ...,... 85 BROWN W.L. and PARSONS I.
Zoned ternary feldspars in the Klokken intrusion: exsolution microtextures and
mechanisms 86
MAURY R.C., LETERRIER J. et JACQUES D.
Critères de distinction des magmas tholéiitiques et calco-alcalins d'arc insulaire :
exemple de l'arc de Luzon, Philippines ... 87 DEBON F. and LE FORT P.
A cationic classification of common plutonic rocks and their magmatic associations :
principles, method, applications ... 87 DEBON F. and LE FORT P. e SABATE P.
Uma classificacao quimico-mineralogica das rochas plutonicas comuns e suas
associacoes, metodo e aplicacoes ... 88 GIULIANI G.
Geoquimica de alguns granitoïdes da faixa de dobramentos sergipana... 88 STUSSI J.M. and PLOQUIN A.
French palaeozoic granitoïd mapping: chronological, typological and metallogenetical
pattern ... 89 FRIEDRICH M., RAZAFIMAEFA N., CUNEY M. et STUSSI J.M.
Les granites peralumineux du NW Massif Central. Signatures et hétérogeneites des
sources ... 89
78
HOLTZ F. et LETERRIER J.
Typologie des granitoïdes hercyniens du nord-Portugal. Exemple des complexes de
granite à 2 micas du domaine de Montalègre ... 90 DEBON F. et ZIMMERMANN J.L.
Le pluton hercynien de Bassiès (Pyrénées, zone axiale) : typologie chimique, âge et
remaniements isotopiques... 91 ALIBERT C., DEBON F. et TERNET Y.
Le pluton à structure concentrique du Néouvielle (Hautes-Pyrénées) : typologie
chimique, âge et genèse ... 91 STUSSI J.M. et MORTAJI A.
Granites à épidote précambriens de Tagragra d'Akka, anti-Atlas occidental, Maroc ... 91 BANZET G., LE FORT P., DEBON F. et PECHER A.
Vaugnérites, durbachites et granitoïdes magnésio-potassiques : interactions croûte-
manteau dans le haut-Dauphiné occidental (Alpes externes) ... 92 MONTEL J.M., MARIGNAC C. et WEISBROD A.
Géochimie des vaugnérites des Cévennes médianes... 93
Coiuril) Mineral!'el",1 (1��100'10U, ,- - 104 - 8)
Contributions to Mineralogy and Petrology
� Springer-Verlag 1988
The Miocene-Pliocene Macusani Volcanics, SE Peru
I. Mineralogy and magmatic evolution
of a two-mica aluminosilicate-bearing ignimbrite suite
Miche) Pichavant', Daniel J. Kontak'., Jacinto Valcncia licrrcra3 and Alan H. Clark2 2 ' Centre de Recherches Pétrographiques et Géochimiques BP 20, F-54501 Vandoeuvre les Nancy, France ' Department of Geological Sciences, Queen's University KingslOn. Ontario K7L 3N6, Canada 3 Instituto Pcruano de Energia Nuclear Av. Canada. 1470. Lima 13, Peru
Abstract. The Miocene-Pliocene Macusani volcanics, SE Peru. outcrop in three separute tectonic intermontane ba- sins devcloped on a Paleozoic-Mesozoic volcano-sedimen- tary séquence. Several ignimbrite sheets arc recognized and K - Ar dates record at least semi-continuous volcanic activi- ty from 10 to 4 Ma in the Macusani field. The volcanics in the Macusani basin comprise crystal-rich (45% crystals) ash-tlow tuf and rare obsidians glasses, both with unusual mineralogy, similar to two-mica peraluminous leucogran- ites. The mineralogical assemblage (quartz, sanidine Or 69 - 75. plagioclase, biotite, muscovite and andalusite (both coexisting in the entire volcanic field), sillimanite. schbrl-rich tourmaline, cordierite-type phases, hercynitic spinel, fluor-apatite, ilmenite, monazite, zircon, niobian-ru- tile) is essentially constant throughout the entire Macusani field. Two distinct générations of plagioclase are recog- nized. i-i:. group 1 (An,o_2o) and group Il (An3o-,s). Silli- manite forms abundant inclusions in nearly ail phases and is earlier than andalusite which occurs as isolated pheno- crysts. Biotite (AI-, Ti-, Fe- and F-rich) shows pronounced deficiencies in octahedral cations. Muscovite is also F-rich and displays limited biotitic and celadonitic substitutions. There is no systematic variation in minerai chemistry with stratigraphie position. The mineralogical data provide a ba- sis for distinction between an early magmatic and a main magmatic stage. The early stage corresponds to the mag- matic evolution at or near the source region and includes both restites and early phenocrysts. Some biotites (with tex- tures of disequilibrium melting to Fe - Zn spinel), part of the sillimanite, apatite and monazite, possibly some tour- maline and cordierite-type phases are restites. However, the restite content of the magma was low (5 vol. % maximum). The group Il plagioclase are interpreted as early pheno- crysts. During this stage, températures were as high as 800° C. pressure was no more than 5-7.5 kbar, /o2 was in- termediate between \VM and QFM and ail was low. The biotite melting textures and thé coexistence of restites and early phenocrysts imply fast heating rates in the source re- gion. The transition between the early and thé main mag- matic stage was abrupt (andalusite crystallization in place of sillimanite, group I vs. group II plagioclase) and sug- gests rapid ascent of the magma from its source région. During the main crystallization stage, température was 650° C or lower at a pressure of 1.5-2 kbar. 0,�0 (calculatcd from equilibrium between muscovite, quartz, sanidine and andalusite) are around 1, suggesting conditions close to H20-saluration. f,'F is around 1 bar but the f"zo/f"F ratios are significantly different between samples. fil, ranges be- tween 138 and 225 bar. This study shows that felsic, strongly peraluminous, leucogranitic magmas having anda- lusite and muscovite phenocrysts may be generated under H20-undersaturated conditions.
Preseeil nrlolre.c.s: Nova Scotia Department of Mines and Etiergy PO Box 1087, Halifax, Nova Scotia AI 13 2XI, Canada
CRPG Contribution n°769 O((I',i/l1 rrq/lc�ls 10: M. Pichavant
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