Early Cretaceous plutonic rocks in the Kitakami Mountains, northeast Japan, related to the westward subduction along the eastern margin of the East Asian continent, intruded the Jurassic accretionary complex and a microcontinental block. These plutonic rocks are classified into types A and B. The former is further subdivided into high‐Sr, low‐Sr, and intermediate series. High‐Sr series rocks occur as the central parts of three zoned plutons in the North Kitakami belt; named the Hashigami, Tanohata, and Miyako plutons. The high‐Sr series rocks show distinct chemical characteristics compared with those of the low‐Sr series. In particular, the high‐Sr series is characterized by SiO2 greater than 61 wt %, higher Na2O and lower K2O concentrations, and slightly higher Al2O3 and lower total FeO and MgO concentrations. In trace element chemistry, the high‐Sr series rocks are richer in Sr and Ga, and poorer in Rb, Pb, and Y. These characteristics resemble those of the high‐Al2O3 trondhjemite, tonalite, and dacite (high‐Al TTD). Mass balance calculation indicates that the high‐Sr series magma can be derived by partial melting of hypothetical oceanic crust (mid‐oceanic ridge basalt (MORB), plus 5% altered MORB, plus 5% sediments) leaving garnet, clinopyroxene, quartz, rutile, and apatite as restite. On the basis of the phase relations for tholeiitic basalt and the estimated geothermal gradient of the subducted slab, slab melting is considered to have occurred at a depth of 2.0 to 2.2 GPa (about 70 to 80 km), and the age of subducted oceanic crust may be younger than 10 to 25 Ma. The coexistence of the magma derived from the subducted slab with that derived from the mantle wedge is a particularly important characteristic of the Early Cretaceous magmatism in the Kitakami Mountains. This suggests that the mantle beneath the Cretaceous forearc was warmer than for normal forearcs. Subduction of the Farallon‐Izanagi ridge may have caused the warm mantle.

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2004). Two subgroups of A-type granites in the coastal area of Zhejiang and Fujian Provinces, SE China: age and geochemical constraints on their petrogenesis.ABSTRACT: Late Cretaceous (90-100 Ma) A-type granites are widespread in the coastal area of the Zhejiang and Fujian Provinces, SE China. According to mineralogical and geochemical characteristics, the A-type granites in this belt can be further divided into aluminous and peralkaline subgroups. The aluminous subgroup often contains aluminous-rich minerals (e.g. spessartine and Mn-rich muscovite), while the peralkaline subgroup usually contains riebeckite, arfvedsonite and aegirine. Geochemically, the aluminous A-type granites show lower Nb, Zr, Ga, Y and REE abundances, and lower FeO*/MgO and Ga/Al than the peralkaline subgroup. When they occur in the same area, the two subgroups of A-type granites display quite similar initial Nd isotopic compositions, which are indicative of mixing of ancient basement crustal rocks with variable amounts of mantle materials. Integrated geological and geochemical investigations indicate that both the aluminous and the peralkaline magmas are highly evolved and reflect the residual liquids left after high degrees of fractional crystallisation in a deep magma chamber. The present authors suggest that the mineralogical and geochemical differences between the aluminous and peralkaline subgroups are likely to have been generated via different differentiation paths controlled by varying fluorine contents of the parent magmas.

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