The Santa Eulália Plutonic Complex (SEPC) is a late-Variscan granitic body located in the northern part of the Ossa Morena Zone, a inner zone of the Variscan Iberian Massif. The SEPC host rocks are composed of meta-igneous and metasedimentary units, from Upper Proterozoic to Paleozoic ages, with a NW-SE structure, cross-cut by the SEPC. The SEPC host rocks, with low grade metamorphism show well preserved primary sedimentary or igneous mineralogical, textural and structural features. The thermal effect induced by the SEPC is restricted to the roof pendants. At N and NE of the SEPC, textures and paragenesis resulting from thermal metamorphism, are not related to the SEPC intrusion but to a previous magmatism, controlled by the NW-SE regional anisotropies.
The restriction of the thermal effects to the pluton roof may be caused by a combination of several interrelated factors: higher volume of granitic mass, thermal effect by advection of fluids and longer period of prevalence of high thermal conditions.
The geochemical study of SEPC host rocks shows the heterogeneous character and diversity of metasedimentary, igneous and meta-igneous rocks. The whole rock geochemical data indicate that all the metasedimentary lithologies derived from an upper continental crustal source and the igneous and meta-igneous rocks show no evidence of metasomatic effects by the SEPC emplacement.
El Complejo Plutónico de Santa Eulalia (CPSE) es un cuerpo granítico tardi-Varisco situado en la parte norte de la Zona de Ossa Morena, en la zona interior del Macizo Ibérico Varisco. Las rocas encajantes del CPSE están compuestas por unidades meta-ígneas y metasedimentarias, de edades que van desde el Proterozoico Superior hasta el Paleozoico, con una estructura de dirección NW-SE, cortada por el CPSE. Las rocas encanjantes del CPSE, con metamorfismo de bajo grado conservan estructuras, mineralogía y textura primarias. El efecto térmico inducido por el CPSE se limita a los
La restricción de los efectos térmicos al techo del pluton puede ser causada por una combinación de varios factores interrelacionados: mayor volumen de masa granítica, un efecto térmico por la advección de fluidos y el período de prevalencia de altas condiciones térmicas.
Los datos geoquímicos de las rocas encanjantes del CPSE muestran el carácter heterogéneo y la diversidad de rocas sedimentarias, metasedimentarias, ígneas y meta-ígneas. El análisis de los datos geoquímicos indica que todas las litologías sedimentarias y metasedimentarias han derivado de la corteza continental superior, mientras las rocas ígneas y meta-ígneas tienen una composición que no muestra evidencias de efectos metasomáticos por el emplazamiento del CPSE.
The Ossa Morena Zone (OMZ) is one of the inner zones of the Variscan Iberian Massif, which is considered to be accreted to the Iberian Autochthonous terrane during the Cadomian cycle (Ribeiro
The OMZ is characterized by a poliphase ductile deformation and metamorphism. Two or three Variscan phases are recognizable at OMZ. D1 structures display WNW-ESE strike and have around 370 Ma in age; D2 phase is characterized by the development of N-S or NNW-SSE folding and shear; finally, D3 structures display a NW-SE trend and are dated at 306 Ma (Moita
In the portuguese part of the OMZ several sectors with distinct stratigraphy and structure are identified by Oliveira
Geological map of the SEPC and host rocks with sampling sites location (adapted from Oliveira
The Santa Eulália Plutonic Complex (SEPC) is a late-Variscan granitic pluton in the SW sector of the Iberian Orogen. This granite with 400 km2 cross-cuts the regional NW-SE Variscan structures, namely a major high-grade and high-strain shear zone in the contact between two axial geotectonic zones of the Iberian Variscan Belt: Central Iberian Zone (CIZ) and Ossa Morena Zone (OMZ).
In the published geological map (Gonçalves,
In this study the evaluation of the thermal effects promoted by the SEPC intrusion are presented as a part of a multidisciplinary study. This evaluation is supported mainly by petrographic study, complemented by lithogeochemical data.
The SEPC is a ring igneous complex composed, from the rim to the core, of a medium- to coarse-grained pink granite (G0-group), involving large (kilometric) elongated masses of mafic (gabbroic) to intermediate (granodioritic) rocks, and a central gray medium-grained granite (G1-group) typically biotitic, sometimes showing a slight porphyritic tendency, namely in a few outcrops located near the contact with the peripheral G0-type ring (Lopes
The SEPC host rocks show lithological diversity and are composed of igneous and meta-igneous and metasedimentary units, from Upper Proterozoic to Lower Paleozoic ages (
Sampling for petrographic and geochemical study.
Sample | Unit | Lithology | |
---|---|---|---|
|
SE 4 | Carbonate Formation | Carbonate rock |
SE 6a | Série Negra | Siliciclastic rock | |
SE 6b | Carbonate Formation | Dolomitic limestone | |
SE 6c | Carbonate Formation | Marble | |
SE 7 | Terrugem Volcanic-sedimentary Complex | Pelitic rock | |
SE 8a | Vila Boim Formation | Pelitic rock | |
SE 8b | Vila Boim Formation | Pelitic rock | |
SE 8c | Vila Boim Formation | Pelitic rock | |
SE 9b | Carbonate Formation | Carbonate rock | |
ASM 026 | Vila Boim Formation | Pelitic rock | |
ASM 027 | Terrugem Volcanic-sedimentary Complex | Quartz-pelitic rock | |
ASM 110 | Série Negra | Pelitic rock | |
ASM 111 | Série Negra | Amphibolite | |
ASM 116 | Vila Boim Formation | Pelitic rock | |
ASM 123 | Vila Boim Formation | Quartz-pelitic rock | |
ASM 124 | Carbonate Formation | Carbonate rock | |
ASM 125 | Série Negra | Pelitic rock | |
ASM J58 | Vila Boim Formation | Pelitic rock | |
Af 3 | Terrugem Volcanic-sedimentary Complex | Quartz-pelitic rock | |
Af 6 | Barrancos Formation | Quartz-pelitic rock | |
JD1 | Carbonate Formation | Marble | |
|
SE 2 | Vila Boim Formation | Basic volcanic rock |
SE 11 | Pre-Variscan peralkaline rock | Alkaline rock | |
SE 9a | Carbonate Formation | Basic rock | |
SE 9c | Carbonate Formation | Acid rock | |
SE 9d | Carbonate Formation | Basic rock | |
SE 12a | Série Negra | Amphibolite | |
SE 12b | Pre-Variscan peralkaline rock | Alkaline rock | |
SE 13 | Pre-Variscan peralkaline rock | Metasomatized alkaline rock |
The lithostratigraphic units, as well as the major thrust are represented in
It should be noted that the roof pendants consist of lithological fragments of host rocks, located at the roof of the granitic body. These fragments preserve the regional structure of the surrounding rocks. The roof pendants of the SEPC have cartographic expression, namely in the western sector of the granitic massif, in G0 facies, at SW of the Alter do Chão shear zone (
The SEPC host rocks are composed of low to high-grade metamorphic rocks. In the NE-sector of Alter do Chão shear zone two lithostratigraphic units are present: a low grade metasedimentary Ediacaran unit (
In the SW sector of the Alter do Chão shear zone, a low-grade metasedimentary and metavolcanic Cambrian sequence is composed of quartz-pelitic (samples ASM 027, ASM 123, Af 3 and Af 6), basic (sample SE 9a), carbonate (sample SE 9b) and acid (sample SE 9c) rocks. The roof pendants lithologies are composed of pelitic (samples ASM 026, ASM 116, ASM 125 and ASM J58), carbonate (samples ASM 124 and SE 4) and volcanic rocks (sample SE 2).
The lithostratigraphic units are bounded by major high-strain transcurrent faults placing side by side different rock types and different metamorphic grades. All these units show a regional vertical structure (
The petrographic study was based on 18 sampling sites (
On the ESE margin of the SEPC, the pelitic rocks of the
Photomicrographs of selected thin sections: a) Phyllite of
On the northern margin of the SEPC, quartz-pelitic rocks of the
Metasomatized alkaline rocks, adjacent to the NE contact of the SEPC (sample SE 13) present homogeneous texture with a banded structure preserved. The mineralogy of these rocks is composed of clinopyroxene, scapolite, riebeckite, epidote, perthite potassium feldspar, plagioclase and opaque minerals (
Whole rock major and minor (%) and trace (ppm) elements composition of the SEPC host rocks.
SE 2 | SE 4 | SE 7 | SE 8a | SE 8b | SE 8c | SE 9a | SE 9b | SE 9c | SE 9d | SE 11 | SE 12a | SE 12b | SE 13 | |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Type of rock | Basic | Carbonate | Pelitic | Pelitic | Pelitic | Pelitic | Basic | Carbonate | Acid | Basic | Alkaline | Amphi-bolite | Alkaline | Metaso-matized alkaline |
|
57.6 | 10.2 | 60.1 | 60.4 | 72.9 | 81.34 | 46.8 | 17.0 | 74.7 | 48.5 | 61.3 | 49.8 | 60.5 | 33.9 |
|
15.9 | 1.9 | 17.9 | 18.3 | 14.2 | 9.36 | 15.9 | 3.4 | 13.2 | 16.5 | 18.2 | 15.4 | 16.7 | 10.0 |
|
5.41 | 0.85 | 6.59 | 6.46 | 3.07 | 2.8 | 8.85 | 1.89 | 1.02 | 9.98 | 4.93 | 11.7 | 6.16 | 3.6 |
|
0.05 | 0.03 | 0.09 | 0.01 | 0.01 | 0.006 | 0.04 | 0.07 | 0.03 | 0.03 | 0.13 | 0.18 | 0.23 | 0.09 |
|
3.49 | 1.54 | 2.12 | 1.77 | 0.08 | 0.04 | 4.94 | 15.8 | 0.30 | 5.10 | 0.28 | 6.09 | 0.39 | 2.37 |
|
5.02 | 48.1 | 0.81 | 0.39 | 0.3 | 0.13 | 5.19 | 23.2 | 0.55 | 4.05 | 1.27 | 11.9 | 3.49 | 28.7 |
|
7.24 | 0.17 | 0.75 | 1.89 | 7.97 | 5.27 | 4.99 | 1.39 | 3.32 | 5.20 | 6.09 | 2.87 | 5.38 | 1.92 |
|
0.45 | 0.75 | 3.97 | 4.58 | 0.24 | 0.11 | 0.72 | 0.31 | 4.71 | 0.16 | 6.08 | 0.44 | 5.41 | 1.95 |
|
2.19 | 0.08 | 0.86 | 0.82 | 0.65 | 0.42 | 2.85 | 0.15 | 0.02 | 2.95 | 0.35 | 1.59 | 0.46 | 0.54 |
|
0.81 | 0.03 | 0.11 | 0.20 | 0.15 | 0.07 | 0.79 | 0.05 | <0.01 | 0.83 | 0.10 | 0.17 | 0.11 | 0.16 |
|
0.56 | 35.47 | 5.24 | 4.03 | 0.39 | 0.53 | 7.89 | 33.19 | 1.59 | 7.17 | 0.67 | 0.69 | 0.62 | 15.64 |
|
98.67 | 99.1 | 98.52 | 98.86 | 99.98 | 100.1 | 99.01 | 96.46 | 99.35 | 100.4 | 99.39 | 100.9 | 99.46 | 98.91 |
|
66 | 273 | 855 | 295 | 51 | 21 | 83 | 14 | 77 | 48 | 132 | 153 | 1807 | 314 |
|
267 | 3042 | 60 | 58 | 111 | 60 | 908 | 61 | 47 | 998 | 101 | 233 | 145 | 2511 |
|
64 | 3 | 29 | 27 | 20 | 18 | 33 | 6 | 18 | 32 | 13 | 32 | 16 | 17 |
|
509 | 22 | 190 | 157 | 160 | 192 | 328 | 30 | 56 | 338 | 472 | 111 | 201 | 145 |
|
30 | 30 | 110 | 30 | 30 | 30 | 480 | 30 | 30 | 30 | 70 | 100 | 120 | 50 |
|
23 | 2 | 28 | 25 | 15 | 2 | 30 | 5 | 23 | 31 | 22 | 18 | 23 | 13 |
|
48.7 | 3.10 | 42.5 | 37.2 | 22.6 | 7 | 44.9 | 8.60 | 9.20 | 46.2 | 45.2 | 12.6 | 27.3 | 20.0 |
|
0.5 | 1.3 | 7.2 | 3.3 | 0.5 | 0.5 | 0.8 | 0.5 | 4.8 | 0.5 | 2.0 | 0.5 | 1.0 | 2.8 |
|
33.3 | 3.5 | 50.3 | 42.3 | 26.3 | 14.5 | 45.6 | 11.8 | 9.5 | 45 | 90.6 | 6.4 | 31.1 | 22.5 |
|
78.8 | 7.1 | 100 | 87.9 | 55.7 | 31.9 | 93 | 22.5 | 19.4 | 93.9 | 155 | 15.9 | 58.2 | 44.8 |
|
10.9 | 0.8 | 11.3 | 9.69 | 6.05 | 3.61 | 11.1 | 2.48 | 2.37 | 11.5 | 14.3 | 2.49 | 7.16 | 5.21 |
|
48.7 | 3.1 | 42.5 | 37.2 | 22.6 | 14.5 | 44.9 | 8.6 | 9.2 | 46.2 | 45.2 | 12.6 | 27.3 | 20 |
|
12.6 | 0.7 | 8 | 7.2 | 4.4 | 3 | 9.6 | 1.6 | 2.9 | 9.6 | 5.4 | 3.8 | 4.9 | 3.9 |
|
3.54 | 0.12 | 1.49 | 1.59 | 0.92 | 0.65 | 2.94 | 0.36 | 0.24 | 2.98 | 1.25 | 1.49 | 2.85 | 0.85 |
|
12.6 | 0.6 | 7 | 6.4 | 4 | 2.9 | 8.9 | 1.3 | 3.2 | 8.9 | 4.2 | 5.4 | 4.4 | 3.1 |
|
2.2 | 0.1 | 1 | 1 | 0.6 | 0.5 | 1.2 | 0.2 | 0.5 | 1.2 | 0.5 | 0.9 | 0.5 | 0.5 |
|
13 | 0.5 | 5.5 | 5.4 | 3.3 | 3.1 | 6.3 | 1.2 | 2.9 | 6.1 | 2.6 | 5.3 | 3.1 | 2.9 |
|
2.7 | 0.1 | 1.1 | 1 | 0.7 | 0.6 | 1.1 | 0.2 | 0.5 | 1.1 | 0.5 | 1.1 | 0.6 | 0.6 |
|
7.4 | 0.3 | 3.1 | 3 | 2 | 0.26 | 3.1 | 0.6 | 1.6 | 3.1 | 1.5 | 3.1 | 1.5 | 1.7 |
|
1.16 | 0.05 | 0.46 | 0.43 | 0.29 | 1.6 | 0.45 | 0.1 | 0.23 | 0.45 | 0.22 | 0.46 | 0.25 | 0.25 |
|
7.4 | 0.3 | 3.1 | 2.9 | 2 | 0.26 | 2.8 | 0.6 | 1.5 | 2.8 | 1.7 | 2.9 | 1.7 | 1.6 |
|
1.21 | 0.04 | 0.51 | 0.49 | 0.33 | 4.3 | 0.37 | 0.08 | 0.2 | 0.37 | 0.31 | 0.4 | 0.27 | 0.23 |
|
12.5 | 0.5 | 5.2 | 4.2 | 4.1 | 0.5 | 6.9 | 0.7 | 2.8 | 7.1 | 8.4 | 2.7 | 4.7 | 3 |
|
2 | 0.1 | 1.5 | 1 | 0.7 | 0.26 | 3.8 | 0.1 | 1.9 | 4 | 6.1 | 0.3 | 2.7 | 1.2 |
|
<5 | 5 | 24 | <5 | 5 | 5 | 5 | 5 | 53 | 5 | 10 | 5 | 26 | 5 |
|
<0.4 | 0.4 | 0.9 | 0.4 | 0.4 | 0.4 | 0.4 | 0.4 | 0.4 | 0.4 | 0.4 | 0.4 | 0.4 | 0.4 |
|
5.7 | 1.4 | 19.2 | 11.8 | 7.2 | 5.3 | 4.1 | 2.3 | 22.2 | 4.3 | 13.9 | 0.4 | 3.3 | 7.3 |
|
2.4 | 1 | 2.7 | 2.5 | 1.4 | 1.2 | 1.6 | 0.9 | 10.3 | 1.5 | 3.1 | 0.3 | 0.9 | 2.5 |
Analitical methods: Whole-rock major and trace element analyses were carried out at ACTLABS (Ancaster, Ontario, Canada). The samples were analysed by inductively coupled plasma emission spectrometry, ICP-AES for major elements and trace elements were determined by inductively coupled plasma mass spectrometry (ICP-MS). The precision of the analyses are about 1% for major elements and for most trace elements, namely the rare-earth elements, are commonly within 10% (Hofmann,
Carbonate Formation samples, even when located a few meters from the SEPC, do not show recrystallization due to thermal contact. These samples are impure carbonate rocks and heterogranular calc-silicate rocks, with primary mineralogical and textural features still preserved, namely detrital micas and granular variations which mark the stratification (S0). These features are not observed in the samples of the same unit when located in roof pendants (sample SE 4) where the texture is strongly poligonized and the mineralogical composition is calcite, vesuvianite, tremolite, epidote and opaques (
The siliciclastic and the volcanic rocks, both of the Vila Boim Formation and of the Terrugem Volcanic-sedimentary Complex, outcropping at SW of the Alter do Chão shear zone, present metamorphic thermal effects only in the roof pendants. At roof of the SEPC the basic volcanic rock are amphibolitized and the siliciclastic rocks show paragenesis with fibrolite, polygonal quartz, calcite, plagioclase, cordierite, andalusite and quartz “pool” involving the plagioclase with metamorphic texture. This kind of texture indicate partial melting process (
The geochemical composition of the host rocks shows very well the diversity of metasedimentary and meta-igneous lithologies (
The Rare Earth Elements (REE) patterns were plotted in separeted graphs according to the sedimentary or igneous character of the samples (
REE patterns of: (a) Metasedimentary rocks; (b) Meta-igneous rocks (C1 from Evenson
The pelitic and carbonate metasedimentary rocks show a typical continental crust REE pattern with high LREE fractionation (La/Sm=1.06–10.56), marked negative Eu anomaly and low HREE fractionation (Gd/Yb=1.38–2.57), but with different ΣREE values. The carbonate rocks show the lower values of ΣREE, and the more pelitic rocks (samples SE 7 and SE 8a) show the highest values (
The lithological and metamorphic diversity of the host rocks imply different degrees of evidence for thermal effects of the SEPC. Undoubtedly the pelitic rocks and impure carbonate lithologies (limestones and dolomitic limestones) of low grade are the most favorable to constraint contact effects. It is much more difficult the discrimination of these effects on igneous rocks or high grade metamorphic rocks.
In the pelitic and impure carbonate lithologies surrounding the SEPC, the mineralogical, textural and structural features of the very-low to low grade metamorphic conditions previous to the SEPC intrusion are preserved, namely the sedimentary bedding. The thermal effects of this intrusion are expressed only by very small post-kinematic crystals of biotite, transverse or mimetic, over the foliation in the pelitic rocks (
In the alkaline host rocks, intrusive in the metasedimentary rocks of the
On the other hand all the lithologies present in the roof pendants, namely pelitic, carbonate and basic volcanic rocks, exhibit a strong thermal effect, without metasomatic evidence. The occurrence of thermal effects restricted to the pluton roof may be caused by a combination of several interrelated factors: the volume ratio granite/host rocks is much higher in the roof pendants than in the surrounding host rocks, higher volume of granitic mass, thermal effect by advection of fluids, longer period of prevalence at elevated thermal conditions.
The previous very-low to low metamorphic grade of the host rocks of the SEPC, indicates an intrusion in a shallow and cold crustal level, and thus implying a thermal shock. However the absence of lateral thermal effects could be explained by quick cooling and the low volume ratio granite/rock wall.
The SEPC is a late-Variscan granitic body located in the northern part of the Ossa Morena Zone. The SEPC host rocks are composed of igneous, meta-igneous, and metasedimentary units, from Upper Proterozoic to Paleozoic ages, with a NW-SE structure. The SEPC host rocks, show very-low to high grade metamorphism. Those with very-low to low grade metamorphism present primary sedimentary or igneous mineralogical, textural and structural features well preserved. Both at east or at west, the host rocks comprise phyllite and quartz-phyllite, in chlorite zone conditions, without any thermal effects even at short metric distance from the contact.
The thermal effects of the SEPC intrusion on the igneous and meta-igneous rocks (granites, migmatites, gabbros, alkaline rocks, basic and acid volcanic rocks) are not evident, because the mineralogy and texture of these rocks are stable at high temperature. At N and NE of the SEPC, textures and paragenesis of high-T are not related to the SEPC intrusion but to a previous magmatism (Barquete granite and peralkaline rocks), controlled by the NW-SE regional anisotropies. These rocks show evidences of dynamo thermal metamorphism previous to SEPC.
The restriction of the thermal effects to the pluton roof may be caused by a combination of several interrelated factors: higher volume of granitic mass, thermal effect by advection of fluids, longer period of prevalence of high thermal conditions.
The geochemical study of the SEPC host rocks shows the heterogeneous character and diversity of metasedimentary, igneous and meta-igneous rocks. The whole rock geochemical data indicate that all the metasedimentary lithologies derived from an upper continental crustal source. The geochemical composition of the igneous and meta-igneous rocks do not show evidence of metasomatic effects by the SEPC emplacement.
These data suggest that the thermal effects of the SEPC in the host rocks are mostly restricted to the roof pendants.
This work has been financially supported by PTDC/CTE-GIX/099447/2008 (FCT-Portugal, COMPETE/FEDER). The authors are grateful to Carlos Villaseca and Patrícia Moita whose comments greatly helped to improve the manuscript.