ポナペ島で発見された斜長岩質はんれい岩とその起源について

概要

論文の詳細を見る
Ponape Island, the largest island of the East Caroline Islands, is located at Lat. N. 6°55′ and Long. E. 158°15′. The author obtained a xenolith of anorthositic gabbro at the Fall Tokiwa of the River Panparipi on December 13th, 1971. The host rock is dark gray and compact olivine basalt. Olivine phenocrysts are less than 1% in mode. Olivine nodules, ellipsidal and drop shape, are striking. The xenolith, hypidiomorphic-granular to allo-triomorphic-granular, shows cataclastic texture and granulation, and is composed of plagioclase, augite, olivine, ilmenite and secondary minerals. The xenolith has some characters of metamorphic rock and is not simple igneous rock. Concerning to the origin of this rock, the author considered this rock has the same origin as many massive anorthosites. Many massive anorthosites were formed in pre-Cambrian continental crust. Although there is not corresponding layer which has seismic wave velocity of 6.0 to 6.7 km/sec, the thickness of the crust is known as 15 to 20 km under the East Caroline Ridge. This value of the thickness is three to four times as thick as normal oceanic crust. The author suggest a possibility of the existence of pre-Cambrian continental crust under Ponape Island or the East Caroline Islands.
地学団体研究会の論文
1978-01-25