The Zamora Batholith is an intrusive complex that is located in the south-east ex-treme of Ecuador. It has dimensions of 200x50 km approximately. It is mainly lo-cated in the Zamora Chinchipe province from which it takes its name.

This study consisted in the petrographic and geochemical characterization of the Zamora Batholith in the area covered by 1:50.000 geological maps of Centro Shaime, Guayzimi, Paquisha, Los Encuentros and El Pangui. Fieldwork was done by the “Project of Geologic Mapping 1:50.000 (mining prospective zones)" of the National Institute of Geologic, Mining, Metallurgic Research of Ecuador. This research was performed with 59 thin sections and 10 whole-rock chemical analysis done in the C.I.C of the Granada University.

The Zamora Batholith intrudes Triassic to Jurassic volcanic rocks. It is overlaid by sandstones of the Hollin Formation of the Upper Aptian age and shale and limestone from the Napo Formation. Post-cretaceous deposits of ash and lava flows of andesitic to rhyolitic compositions cover the batholith.

Petrography of the Zamora Batholith ranges from tonalite to monzo-granite with the same qualitative mineralogy. Rocks are composed by different proportions of pla-gioclase, amphibole, feldspar K, quartz, biotite, opaque, pyroxene and epidote, as accessory minerals has zircon, sphene and apatite. To the south of the Conguime and Guayzimi towns, the dominant petrography is medium to coarse grained am-phibole granodiorite with tonalitic and monzo-granitic subordinates. To the north monzo-granites are dominant rocks and subordinate granodiorites. To the East of Santa Elena, the syeno-granites are associated with El Hito porphyritic granite that intrudes to Zamora Batholith. Frequently the batholith has propylitic alteration; which produces a primary association of chlorite, epidote, calcite and pyrite.

Thin sectionsa, b. Tonalites, abundant plagioclase.c,d,e,f. Granodiorites, crystals of amphibole of 1-2 cm.g,h. Monzo-granites, abundant feldspar K and biotite.

Classification of plutonic igneous rocks. M<90. Mafic, intermediate and felsic (Le Maitre et al., 2002). South dominantly granodiorites, north dominantly monzo- granite, and Hito dominantly syeno granite.

Granitoids have dioritic to granitic compositions (60.09 to 73.6 wt.% SiO2) and are I – type, medium to high-K calc-alkaline. They have slightly peraluminous affinities (ASI=1,00 to 1,16). CaO is moderate to high (CaO=3.58), alkalis have averages of Na2O=3,09 and K2O=3,28. The concentrations of Na2O/K2O are moderate ranging between 0.7 and 1.7, with an average value of 1.04.

Correlations between major element and silica, and relationships between trace elements indicate that fractional crystallization is a dominant process in the magma evolution.

Negative correlations of MgO, FeO and slightly CaO with increasing SiO2 (wt.%) are consistent with plagioclase, amphibole, biotite and epidote fractionation. Negative correlation of FeO, TiO2 and P2O5 suggesting a iron oxides, apatite, and sphene fractionation. Fractionation of apatite and sphene is also supported by the good correlation between P2O5 and TiO2 with CaO respectively.

Most granitoids are also slightly peraluminous, but we believe this characteristic is due to rock alteration. The Zamora Batolith is a plutonic complex generated within a magmatic arc in normal conditions of maturity.

Contents of Ba and Sr are moderate. Content of Zr is low (61 to 161 ppm). Multi-element diagrams normalized to chondritic values and to primitive mantle show Nb and Ta negative anomaly. Considering multi-element diagrams, rocks are slightly enriched in LILE (Large ion-Lithophile-elements) mainly in Rb, Cs and Ba and slightly positive anomalies in K and Sr, other incompatible elements have negative anomalies such as HFSE (High Field Strength Elements) Ti, Nb, Ta. Values of (Eu/Eu*)N are in the range of 0.54 to 1.03. (Eu*=(SmN*GdN)1/2). The slight Eu anomalie is justified by epidote-feldspar coexistence (Bea et al., 1996).

PETROGRAPHY AND GEOCHEMISTRYOF THE ZAMORA BATHOLITHIN THE SOUTH OF THE SUB-ANDEAN ZONE(ECUADOR)ID: 1652459

REPUBLIC OF ECUADORSOUTH AMERICA

TONALITE

GRANODIORITESOUTH

MONZO-GRANITENORTH

RL: Coast Region; CW: Western Cordillera;CI: Interandean Valley; CR: Real Cordillera;

RA: Amazon Region

Location of the study area, located in southeast Ecuador within the sub-Andean region.

1. Introduction

Author:F. M. Villares (Fabian_Villares@inigemm.gob.ec)Author Institution:Instituto Nacional de Investigación Geológico Minero Metalúrgico, Dirección de Geología, Quito, Pichincha, Ecuador.

2. Petrography of the Zamora Batolith

3. Geochemistry of the Zamora Batolith

REFERENCES·Bea, F. (1996). Residence of REE, Y, Th and U in granites and crustal protoliths; Implications for the chemistry of crustal melts. Journal of Petrology, 37, pp.521-552.··Bea, F., Corretgé, L. y Fershtater, G. (2000). A systematic typology of granitoid rocks from major element composition I: the upper silica range. Boletín de la Sociedad· Española de Mineralogía, 23, pp.121-133.·Borodin, L.S. (1988). Petrochemical trends and classification of the gabbro-granitoid series. International Geology Review, 30, pp.1189-1198.·Chappell, B. & White R. (1974). Two constrasting granite types. Pacific Geology 8, pp.173-174.·Frost, B. R., Barnes, C. G., Collins, W. J., Arculus, R. J., Ellis D. J. & Frost C. D. (2001). A Geochemical Classification for Granitic Rocks. Journal of Petrology, v. 42, 11, pp.2033-2048.·Le Maitre, R., (editor), Streckeisen, A., Zanettin, B., Le Bas, J., Bonin, B., Bateman, P., Bellieni, G., Dudek, A., Efremova, S., Keller, J., Lamere, J., Sabine, P., Schmid, R., Sorensen, H. and Woolley, A. (2002). Igneous Rocks. A Classifications and Glossary of Terms. Recommen-dations of the International Union of Geological Sciences Subcommission on the Systematics of Igneous Rocks. Cambridge, New York, Melbourne: Cambridge University Press. 2nd ed. pp. xvi + 236. ISBN o 52166215 X.·Le Maitre, R., Bateman, P., Dudek, A., Keller, J., Lameyre, J.. Le Bas, J., Sabine, A., Schmid, R., Sorensen, H., Streckeisen, A., Woolley, R. & Zanettin, B. (1989). A Classification of Igneous Rocks and Glossary of terms: Recommendations of the International Union of Geological Sciences Subcommission on the Systematics of Igneous Rocks. Blackwell Scientific Publications, Oxford, U.K.·Litherland M., Aspden, J. and Jemielita R. (1994). The Metamorphic belts of Ecuador., Brithish Geological Survey, Overseas Memoir, 11, pp.147.·Maniar, P. and Piccoli, P. (1989). Tectonic discrimination of granitoids. Geological Society of America Bulletin, 101, pp.635-643.·Peccerillo, A., Taylor, S. (1976). Geochemistry of Eocene cal-alkaline volcanic Rocks from the kastamonu area, Northern Turkey. Contrib. Mineral. Petrol., 58, pp.63-81.·Sun, S. (1980). Lead isotopic study of young volcanic rocks from mid ocean ridges, ocean islands and islands arcs. Royal Society of London Philosophical Transactions, ser, A: Mathematical and Physical Sciences. V. 297, pp.409-445.··Sun, S. and Mcdonough, W. (1989). Chemical and isotopic systematic of oceanic basalts: implications for mantle composition and processes., In: Saunders, Norry (Eds.), Magmatism in the Ocean Basins., Geol. Soc. London Spec. Pub.,42, pp.313-345.·Whalen, B., Currie, L., Chappell, E. (1987). A-type granites: geochemical characteristics, discrimination and petrogenesis. Contributions to Mineralogy and Petrology, 95, pp.407-419.

1a1b23a3b456*67*78*89*910*10

quarzolitequartz-rich granitoidsalkali feldspar granitesyeno-granitemonzo-granitegranodioritetonalitequartz alkali feldspar syenitealkali feldspar syenitequartz syenitesyenitequartz monzonitemonzonitequartz-monzodiorite, quartz-monzogabbromonzodiorite, monzogabbroquartz diorite, quartz gabbrogabbro (%An plagioclase > 50%)diorite (%An plagioclase < 50%) A P

Q

10

56 7 8 9 10

6*

2 3a 3b

1b

1a

4 5

7*

HITOSOUTHNORTH

SOUTH NORTH

8* 9* 10*20

60

90

35 65 90

SOUTH NORTH LITHERLAND et al. (1994)

7

6

5

4

3

2

1

0

16141210

86420

45

Shoshonitic Series

High-K Calc-Alkaline Series

Alk

Ca+Th

Calc-Alkaline Series

Arc Tholeite Series

K 2O

SiO2 SiO2

K 2O+

Na2O

4050 55 60 65 70 75 45 50 55 60 65 70 75

a) Peccerillo and Taylor (1976)

a) Diagram of Rare earth elements normalized to condrites (Sun y McDonough, 1989)b) spidergram normalized to condrites (Sun, 1980)c) spidergram normalized to primitive mantle (Sun y McDonough, 1989)d) spidergram normalized to N-MORB (Sun y McDonough, 1989).

a) (FeOt / FeOt+MgO) vs SiO2, (Frost et al., 2001) b) Borodin (1988) c) Diagram of Maniar y Piccoli (1989)

d) Granitoids classification, Type I & S according to Whalen et al., (1987)

e) Diagram of Bea et al. (2000) f, g) Type S and Type I after Chappell and White (1974).

b) TAS, Le Maitre et al (1989)

(La/Sm)N=5,4-2,27(Gd/Yb)N=1,04-1,54(Eu/Eu*)N: 0,54-1,03(La/Yb)N: 4,3-9,25(La/Lu)N: 4,17-8,09K/Rb: 280-390; average=334,5U<3,42Y<24,33Nb<7,46Ta<0,36Th<11,1Cs<4,73Th/U: average 3,6

0 1 2 3 4 5 6

1.41.31.21.11.00.90.80.70.6

ASI

Si02

S

I

50 55 60 65 70 75 80

1.0

0.9

0.8

0.7

0.6

0.5

0.4

FeOt

/(Fe

Ot+

MgO

)

SiO2

ferroan

magnesian

0.5 1.0 1.5 2.0

3

2

1

0

Al/(

Na+

K)

Al/(Ca+Na+K)

Metaluminous

Peralcaline

Peraluminous

0.4 0.8 1.2 1.6 2.0

2.0

1.5

1.0

0.5

0

-0.5

log

(Na+

K/Ca

)

Ac

Extr

Alk Alk

Sub Alk

Ca

Th

Ms,BtHb,An

Kf,Ab

1 1.0

1000.0

100.0

10.0

1.0

Nb

10000Ga/Al

I & S

0.5 1.0 1.5 2.0 2.5

0.5

0.3

0.1

-0.1

-0.3

-0.5

DF-2

DF-1

A2-type

DF for SiO2 64-70%

A1-type

M-ty

pe I-typ

e

SG-type

SC-type

0 1 2 3 4 5 6

6

5

4

3

2

1

0

K 2O

Na2O

S I

SOUTH

NORTH

a) b)

c) d)