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地体虽然形成时间不同，但具有许多共同的地质特征。例如，澳大利亚下古生代Djungati地体和日本Tamba-Mino-Ashio地体具有相似的岩性序列，从放射虫层状硅质页岩到浊积岩，似乎显示了洋盆地层向大陆边缘的增加。(2)新英格兰造山带和日本造山带均以增生杂岩为主。然而，详细的实地观察显示存在一些差异；日本的吸积复合体含有大量的混杂物，而澳大利亚的吸积复合体则很少含有混杂物。这可能与俯冲和增生过程和/或暴露状态有关（澳大利亚东部的严重风化可能容易风化相对较弱的混杂岩）。(3)麦夸里港地区岩脉分为高镁超基性岩脉（SiO2: 35 ~ 45%）和低镁基性岩脉（SiO2: 45 ~ 55%）。高镁岩脉以寄生褐角闪石为特征。低SiO2含量的岩脉包括橄榄石和铬晶石斑晶。虽然高镁岩脉被认为是博镁岩（eg . aitchison, 1994），但化学成分、矿物学特征和野外证据表明，这些岩脉是由高镁科马提岩岩浆侵入形成的。(4)对泥盆系Gamilaroi地层岩石放射虫生物地层的初步研究表明，以往认为泥盆系罕见的三叶棘放射虫数量丰富，种类多样。通过与日本泥盆纪放射虫的对比研究，有可能厘清“太平洋”泥盆纪放射虫的生物地理分布。

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.