Editorial     

ASAHIKO TAIRA  MASAYUKI KOMATSU  KISABURO KODAMA 《Island Arc》1992,1(1):1-1

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Editorial     

ASAHIKO TAIRA  MASAYUKI KOMATSU  KISABURO KODAMA 《Island Arc》1995,4(3):155-155

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Editorial     

ASAHIKO TAIRA  MASAYUKI KOMATSU  KISABURO KODAMA 《Island Arc》1996,5(2):89-89

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Nature and growth rate of the Northern Izu–Bonin (Ogasawara) arc crust and their implications for continental crust formation     

ASAHIKO  TAIRA  SANEATSU  SAITO  KAN  AOIKE  SUMITO  MORITA  HIDEKAZU  TOKUYAMA  KIYOSHI  SUYEHIRO  NARUMI  TAKAHASHI  MASANAO  SHINOHARA  SCHOICHI  KIYOKAWA  JIRO  NAKA & ADAM  KLAUS 《Island Arc》1998,7(3):395-407

The bulk composition of the continental crust throughout geological history is thought by most previous workers to be andesitic. This assumption of an andesitic bulk composition led to an early hypothesis by 72 ) that the continental crust was created by arc magmatism. This hypothesis for the origin of continental crust was challenged by several authors because: (i) the mean rate of arc crust addition obtained by 50 ) is too small to account for some certain phases of rapid crustal growth; and (ii) the bulk composition of ocean island arcs, the main contributor to the Archean and early Proterozoic crust, is basaltic rather than andesitic ( 4 ; 49 ). New data from the Northern Izu–Bonin arc are presented here which support the 72 ) hypothesis for the origin of the continental crust by andesitic arc magma. A geological interpretation of P wave crustal structure obtained from the Northern Izu–Bonin arc by 66 ) indicates that the arc crust has four distinctive lithologic layers: from top to bottom: (i) a 0.5–2-km-thick layer of basic to intermediate volcaniclastic, lava and hemipelagite (layer A); (ii) a 2–5-km-thick basic to intermediate volcaniclastics, lavas and intrusive layer (layer B); (iii) a 2–7-km-thick layer of felsic (tonalitic) rocks (layer C); and (iv) a 4–7-km-thick layer of mafic igneous rocks (layer D). The chemical composition of the upper and middle part of the northern Izu–Bonin arc is estimated to be similar to the average continental crust by 73 ). The rate of igneous addition of the Northern Izu–Bonin arc since its initial 45-Ma magmatism was calculated as 80 km³/km per million years. This rate of addition is considered to be a reasonable estimate for all arcs in the western Pacific. Using this rate, the global rate of crustal growth is estimated to be 2.96 km³/year which exceeds the average rate of crustal growth since the formation of the Earth (1.76 km³/year). Based on this estimate of continental growth and the previously documented sediment subduction and tectonic erosion rate (1.8 km³/year, 24 ), several examples of growth curves of the continental crust are presented here. These growth curves suggest that at least 50% of the present volume of the continental crust can be explained by arc magmatism. This conclusion indicates that arc magmatism is the most important contributor to the formation of continental crust, especially at the upper crustal level.  相似文献   

Grain fabric of a laboratory antidune   总被引：1，自引：0，他引：1  

KOJI YAGISHITA  ASAHIKO TAIRA 《Sedimentology》1989,36(6):1001-1005

The grain fabric of a laboratory antidune composed of coarse- to medium-grained sand shows a high-angle upcurrent imbrication both on the upstream and downstream sides. Such a grain fabric differs from a normal dune or a megaripple, where grain alignment displays an upcurrent imbrication relative to the depositional slope in the foreset lamina and/or near parallelism with the slope surface in the toe-set lamina. Recognition of antidunes in ancient rocks is difficult, but detailed examination of grain fabric of cross-stratification makes it possible to distinguish antidunes or ‘backset’ bedding from normal dunes or megaripples.  相似文献