ISSN:
1432-0967
Source:
Springer Online Journal Archives 1860-2000
Topics:
Geosciences
Notes:
Abstract Diorite plutons at Al Hadah Saudi Arabia, which constitute part of the pan-African magmatic sequence (ca. 600 Ma), exhibit extensive development of epidote. The epidote alteration is concentrated along veins and dyke margins, and is characterised by transformation of plagioclase (Ab 67)+hornblende+biotite+quartz to epidote+hornblende+tremolite−actinolite+plagioclase (Ab 99)±quartz. The reactions involve addition of CaO and total Fe2O3, depletion of MgO, Na2O and K2O, with variable gains or losses of SiO2. Epidotised alteration products are hydrated and oxidised relative to the diorite precursor. The whole rock δ18O of fresh diorite is + 8.2‰ to + 8.8‰, whereas epidote domains have δ18O whole rock of +9.8‰ to +10.48‰ and negative Δ18Oquartz-plagioclase, implying oxygen isotope exchange with fluids at low temperatures. Epidotisation is considered to have accompanied influx of fluids into plutons during cooling and contraction. The fluids were probably deep formation waters with relatively high Ca2+/Na+ ratios, moving up thermal gradient.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00371549
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