Comparison of New England Orogen and Japanese terranes

主要研究结果如下：（1）澳大利亚东部古生代新英格兰造山带和日本西南部中生代造山带虽然形成时间不同，但具有许多共同的地质特征。例如，澳大利亚的下古生代Djungati岩和日本的Tamba-Mino-Ashio岩具有相似的岩性序列，从放射虫层状硅质岩到硅质页岩再到浊积岩，这似乎表明洋盆地层增生到大陆边缘。(2)新英格兰造山带和日本造山带均以增生杂岩为主。然而，详细的实地观察发现，有一些差异，在日本的增生杂岩包括大量的混杂岩，而澳大利亚的同行很少。它可能与俯冲和增生过程和/或暴露状态有关（澳大利亚东部的强风化可能容易风化相对较弱的混杂岩）。(3)麦夸里港地区的岩脉分为高镁超基性（SiO2：35 - 45%）岩脉和低镁基性（SiO2：45 - 55%）岩脉。高镁脉岩以局部成岩的棕色角闪石为特征。低SiO2含量的岩脉包括橄榄石斑晶和铬尖晶石斑晶。虽然高镁脉岩一直被认为是玻安岩（如Aitchison，1994），但化学成分、矿物学特征和野外证据表明，脉岩是由高镁科马提岩岩浆侵入形成的。(4)对泥盆纪Gamilaroi岩的初步放射虫生物地层学研究表明，以前被认为在泥盆纪罕见的具有三刃刺的放射虫在这个时候是丰富和多样的。通过与日本泥盆纪放射虫的对比研究，有可能明确泥盆纪“太平洋”的放射虫地理区。

Main results obtained by this project are as follows :(1) Although Paleozoic New England orogen in eastern Australia and Mesozoic terranes in Southwest Japan formed at different time, they have many geological characteristics in common. For example, the lower Paleozoic Djungati terrane in Australia and Tamba-Mino-Ashio terrane in Japan have a similar lithological sequence changing from radiolarian bedded chert through siliceous shale to turbidite, which seems to show oceanic basin stratigraphy accreting to continental margins.(2) Both the New England orogen and Japan are mainly composed of accretion complexes. Detailed field observation, however, revealed that there are some differences ; accretion complexes in Japan include large amount of melanges, while Australian counterpart has little of them. It may be related to the processes of subduction and accretion and/or state of exposure (heavy weathering in eastern Australia might easily weathered relatively weak melanges).(3) Dikes in the Port Macquarie area are divided into high-Mg ultrabasic (SiO2 : 35 - 45%) and low-Mg basic (SiO2 : 45 -55%) dikes. The high-Mg dikes are characterized by the occurrence of pargasitic brown hornblende. The dikes with low SiO2 contents include olivine and chromspinel phenocrysts. Although the high-Mg dikes have been regarded as boninite (e.g.Aitchison, 1994), chemical compositions, mineralogical characteristics and field evidence indicate that the dikes formed by intrusion of high-Mg komatiite magma.(4) Preliminary radiolarian biostratigraphic study on Devonian Gamilaroi terrane rocks shows that the Radiolaria with three-bladed spines previously thought to be rare in the Devonian were abundant and diverse by this time. Comparative study with the Devonian radiolarians in Japan has possibility to make clear the radiolarian biogeographic provinces of the "Pacific" in Devonian time.