Low‐K tholeiites and high‐K igneous rocks from Woodlark Island, Papua New Guinea
作者:
P. M. Ashley,
R. H. Flood,
期刊:
Journal of the Geological Society of Australia
(Taylor Available online 1981)
卷期:
Volume 28,
issue 1-2
页码: 227-240
ISSN:0016-7614
年代: 1981
DOI:10.1080/00167618108729158
出版商: Taylor & Francis Group
数据来源: Taylor
摘要:
Woodlark Island, the largest above‐sea portion of the Woodlark Rise, has an exposed basement of pre‐Miocene (?Cretaceous‐Eocene) low‐K tholeiitic basalt and dolerite, and minor sediments. The basement is unconformably overlain by Early Miocene limestone and volcaniclastic sediments and later Miocene high‐K volcanics and comagmatic intrusives. Pleistocene to Recent sediments partly blanket the Tertiary sequence. Basement low‐K tholeiites vary only slightly in composition and are interpreted as ocean floor or possible marginal basin material. The high‐K suite appears to be chemically similar to late Tertiary to Recent high‐K igneous rocks of mainland Papua New Guinea. It includes porphyritic hornblende‐, clinopyroxene‐, biotite‐ and magnetite‐bearing shoshonite, latite and toscanite, and intrusive equivalents that range from olivine normative to strongly quartz normative compositions (S1Q2 46% to 75%). Computer mixing models indicate that separation of the pheno‐crysts in the shoshonites, particularly pargasitic hornblende, is a feasible mechanism for producing the more silica‐rich monzonites and latites.
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