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| Titel |
Fluid-rock interaction in the Miocene Tejeda intrusive complex, Gran Canaria, Canary Islands |
| VerfasserIn |
E. Donoghue, V. R. Troll, C. Harris |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250019519
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| Zusammenfassung |
| The intra-caldera volcaniclastic deposits of the Miocene Tejeda caldera on Gran Canaria host
a ~12 km diameter intrusive complex, comprising ~500 peralkaline trachytic to
phonolitic cone sheets, surrounding a central core of hypabyssal syenite stocks. Both
intrusive rock types display textural and mineralogical features indicative of secondary
fluid-rock interaction, including (i) deuteric mineral phases (e.g. aegirine, riebeckite,
analcime), (ii) exsolved alkali feldspar and Fe-Ti oxide phenocrysts, (iii) pervasive
phyllosilicate and zeolite replacement, and (iv) dendritic Mn-oxide coatings, suggesting the
intrusive complex sustained an active hydrothermal system during emplacement,
cooling, and after solidification. Altered cone sheets have δ18O values ranging from
0.1 to 10.0 per mil (n = 22), and δD values between –62 to –149 per mil (n = 28).
Altered syenites have δ18O values of 0.9, 1.5, and 2.5 per mil, and corresponding δD
values of –91, –99, and –121 per mil. The majority of samples are depleted in 18O
relative to the typical δ18O-range for unaltered trachytes and syenites (δ18O = 6-8 per
mil), indicative of interaction with low-δ18O fluids at high temperature. A positive
correlation between δD and δ18O, which parallels the global meteoric water line,
suggests local meteoric water was the dominant hydrothermal fluid source. No
systematic variation in δ18O or δD was detected across the cone sheet swarm, reflecting
overprinting of isotopic compositions during successive intrusive events. However, the
highest δ18O values (8.2-10.0 per mil) occur in clay- and zeolite-rich cone sheets
from the central part of the intrusive complex, suggesting overall inward-cooling or
‘shrinking’ of the hydrothermal system. By combining mineralogical and isotopic data,
two phases of alteration can be distinguished in the Tejeda Intrusive Complex: (i)
high-temperature (~300-500C) deuteric alteration by late-magmatic, alkali-rich fluids,
and (ii) lower temperature ( |
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