| Título: | 300 Million years of episodic hydrothermal activity:stable isotope evidence from hydrothermal rocksof the Eastern Iberian Central System |
| Autores: | Tornos Arroyo, Fernando ; Delgado Huertas, Antonio ; Casquet, César ; Galindo Francisco, Mª del Carmen |
| Tipo de documento: | texto impreso |
| Editorial: | Springer Science Business Media, 2000 |
| Dimensiones: | application/pdf |
| Nota general: | info:eu-repo/semantics/openAccess |
| Idiomas: | |
| Palabras clave: | Estado = Publicado , Materia = Ciencias: Geología: Geoquímica , Tipo = Artículo |
| Resumen: |
The Eastern Iberian Central System has abundant ore showings hosted by a wide variety of hydrothermal rocks; they include Sn-W, Fe and Zn-(W) calcic and magnesian skarns, shear zone- and episyenitehosted Cu-Zn-Sn-W orebodies, Cu-W-Sn greisens and W-(Sn), base metal and fluorite-barite veins. Systematic dating and fluid inclusion studies show that they can be grouped into several hydrothermal episodes related with the waning Variscan orogeny. The first event was at about 295 Ma followed by younger pulses associated with Early Alpine rifting and extension and dated near 277, 150 and 100 to 20 Ma, respectively (events n IV). The ?18O-?D and ?34S studies of hydrothermal rocks have elucidated the hydrological evolution of these systems. The event 1 fluids are of mixed origin. They are metamorphic fluids (H20-COrCH4-NaCl; ?18SO = 4.7 to 9.3‰; ?D ab.-34‰) related to W-(Sn) veins and modified meteoric waters in the deep magnesian Sn-W skarns (H20-NaCl, 4.5 6.4 wt% NaCl eq.; ?I8O = 7.3 7.8‰; ?D = -77 to -74‰) and epizonal shallow calcic Zn-(W) and Fe skarns (H20-NaCl, ?18O = -0.4 to 3.4‰; ?D = -75 to -58‰). They were probably formed by local hydrothermal cells that were spatially and temporally related to the youngest. Variscan granites, the metals precipitating by fluid unmixing and fluid-rock reactions. The minor influence of magmatic fluids confirms that the intrusion of these granites was essentially water-undersaturated, as most of the hydrothermal fluids were external to the igneous rocks. The fluids involved in the younger hydrothermal systems (events n nI) are very similar. The waters involved in the formation of episyenites, chlorite-rich greisens, retrograde skarns and phyllic and chlorite-rich alterations in the shear zones show no major chemical or isotopic differences. Interaction of the hydrothermal fluids with the host rocks was the main mechanism of ore formation. The composition (H20-NaCl fluids with original salinities below 6.2 wt% NaCl eq.) and the ?18O (-4.6 to 6.3‰) and ?D (-51 to -40‰) values are consistent with a meteoric origin, with a ?18O-shift caused by the interaction with the, mostly igneous, host rocks. These fluids circulated within regional-scale convective cells and were then channelled along major crustal discontinuities. In these shear zones the more easily altered minerals such as feldspars, actinolite and chlorite had their ?18O signatures overprinted by low temperature younger events while the quartz inherited the original signature. In the shallower portions of the hydrothermal systems, basement-cover fluorite-barite-base metal veins formed by mixing of these deep fluids with downwards percolating brines. These brines are also interpreted as of meteoric origin (?18O that leached the solutes (salinity >14 wt% NaCl eq.) from evaporites hosted in the post -Variscan sequence. The ?D values are very similar to most of those recorded by Kelly and Rye in Panasqueira and confirm that the Upper Paleozoic meteoric waters in central Iberia had very negative ?D values (?-52‰) whereas those of Early Mesozoic age ranged between -65 and -36‰. |
| En línea: | https://eprints.ucm.es/id/eprint/11645/1/Tornos__2000.pdf |
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