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摘要
The steeply tilted Tottabetsu plutonic complex (TPC) provides an exceptional cross-sectional view of a frozen felsic magma chamber. The entire pluton is apparently cylindrical in shape, but the active magma chamber at any one time was much thinner, tabular in shape. The pluton is stratified, with a topmost granitic unit ( zone III), an underlying dioritic unit ( zone II), and a lowermost gabbroic unit ( zone I). Field, petrographic, and geochemical data suggest that zones I and II developed at the aggrading floor of a felsic magma chamber. Only part of zone III appears to have crystallized from the roof. Successive stoping events, recorded as included country-rock blocks in zones I and II, apparently prohibited growth of the roof solidification zone. The complex record of hotter replenishments and fractional crystallization is preserved in the stratigraphy of zones I and II as either alternating comagmatic sheets and cumulate layers or an upward fractionation trend with a major compositional reversal exhibited by the cumulates. The magmas injected during the development of zone I were basalts to basaltic andesites, while those injected during the development of zone II were andesites to dacites. The overall compositional difference between zones I and II is essentially attributed to the compositional difference of the injected magmas. By contrast, zone III comprises monotonous granites whose geochemical variation suggests that they represent mixtures of fractionates complementary to the cumulates formed from both the resident felsic magma and the recharged intermediate magma. Buoyant fractionates released from the crystallizing recharge magma presumably rose as plumes and mixed with the resident magma. Thus, the TPC reveals the protracted history of pluton construction from a long-lasting, melt-rich magma chamber.
- 出版日期2007-5
- 单位中国地震局地震研究所
