Imprint of meteoric water on the stable isotope compositions of igneous and secondary minerals, Kap Edvard Holm Complex, East Greenland

• Published in: Contributions to Mineralogy and Petrology
• Main Authors: Brandriss, Mark E., O’neil, J. R., Nevle, Richard J., Bird, D. K.
• Other Authors: Department of Geological Sciences, 1006 C.C. Little Building, University of Michigan, Ann Arbor, MI, 48109, USA, US, Department of Geological and Environmental Sciences, Stanford University, Stanford, CA, 94305–2115, USA, US, Ann Arbor
• Format: Article in Journal/Newspaper
• Language: English
• Published: Springer-Verlag; Springer-Verlag Berlin Heidelberg 1995
• Subjects: Legacy; Geology and Earth Sciences; Chemistry; Science; Greenland; Kap; East Greenland; Kap Edvard Holm; North Atlantic
• Online Access: https://hdl.handle.net/2027.42/42218; https://doi.org/10.1007/s004100050090

Hydrogen and oxygen isotope analyses have been made of hydrous minerals in gabbros and basaltic xenoliths from the Eocene Kap Edvard Holm intrusive complex of East Greenland. The analyzed samples are of three types: (1) primary igneous hornblendes and phlogopites that crystallized from partial melts of hydrothermally altered basaltic xenoliths, (2) primary igneous hornblendes that formed during late–magmatic recrystallization of layered gabbroic cumulates, and (3) secondary actinolite, epidote and chlorite that formed during subsolidus alteration of both xenoliths and gabbros. Secondary actinolite has a δ 18 O value of −5.8‰ and a δD value of −158‰. These low values reflect subsolidus alteration by low–δ 18 O, low–δD hydrothermal fluids of meteoric origin. The δD value is lower than the −146 to −112‰ values previously reported for amphiboles from other early Tertiary meteoric–hydrothermal systems in East Greenland and Scotland, indicating that the meteoric waters at Kap Edvard Holm were isotopically lighter than typical early Tertiary meteoric waters in the North Atlantic region. This probably reflects local climatic variations caused by formation of a major topographic dome at about the time of plutonism and hydrothermal activity. The calculated isotopic composition of the meteoric water is δD=−110 ± 10‰, δ 18 O ≈−15‰. Igneous hornblendes and phlogopites from pegmatitic pods in hornfelsed basaltic xenoliths have δ 18 O values between −6.0 and −3.8‰ and δD values between −155 and −140‰. These are both much lower than typical values of fresh basalts. The oxygen isotope fractionations between pegmatitic hornblendes and surrounding hornfelsic minerals are close to equilibrium fractionations for magmatic temperatures, indicating that the pegmatites crystallized from low–δ 18 O partial melts of xenoliths that had been hydrothermally altered and depleted in 18 O prior to stoping. The pegmatitic minerals may have crystallized with low primary δD values inherited from the altered country rocks, but these values were ...