| Research Abstract |
Sandstone-mudstone suites from major terranes in Honshu, Hokkaido and Korea show significant contrasts in whole rock geochemical compositions. In Honshu, the Shimanto-Tanabe, Sambagawa, and Kurosegawa suites show major, trace, and rare earth element signatures typical of relatively evolved CIA or ACM sediments. Chondrite-normalized REE patterns are fractionated, with average La_N/Yb_N of 10.4-10.9,8.2, and 9.2, and Gd_N/Yb_N ratios of 1.72-1.33,1.45, and 1.71, respectively. The lower Gd_N/Yb_N ratios suggest concentration of zircon and garnet. Negative Eu anomalies occur in all three suites (average Eu/Eu^* 0.77-0.73,0.63, and 0.79, respectively). High La_N/Yb_N ratios (average 11.00) and larger negative Eu/Eu anomalies (0.64) in the silicic Oshima terrane (Hokkaido) indicate a relatively mature source. Lower La_N/Yb_N and Eu/Eu^* (average 9.74 and 0.69) in lower Yezo Group-Idonnappu Zone rocks decrease further in the upper part (6.76 and 0.78), reflecting a greater mafic component. Av
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erage La_N/Yb_N ratio (13.5) in the Gyeongsang Supergroup (Korea) is greater than in the correlative Kanmon Group (8.8), but average Eu/Eu* values are comparable (0.78-0.79). Nd model (ages from the Shimanto, Sambagawa. Oshima and Yezo-Idonnappu terranes contrast significantly. Shimanto model ages range from 0.74 to 1.6 Ga, although most lie between 1.0-1.4 Ga, intermediate between potential Ryoke and Higo Ryoke terrane sources. Two Sambagawa schists yield comparable model ages of 1.04 and 1.2 Ga, lending support to a Shimanto protolith. Oshima terrane model ages are significantly older (1.44-1.85 Ga), comparable with values for the Yangtze craton, their probable source. Model ages in the lower Yezo-Idonnappu suite are consistently younger (1.05-1.31 Ga), and are younger still (0.71-0.93 Ga) in upper Yezo-Idonnappu rocks, possibly reflecting contributions from oceanic crust recycled within the accretionary complex. Normalization of elemental abundances against average Japan Orogenic are upper crust(JOAUC) shows negative anomalies for some elements (e.g.Fe,Mn,Mg,Ca,P,Sc,V,Cr and Ni) in some suites, although the REE and HFSE generally compare well. Depletion is most marked in the Oshima, Yezo-Idonnappu, and Shimanto terranes, and in sandstones compared to mudstones. The anomalies suggest the JOAUC average could be amended for some elements. Less
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