【摘要】 荣成地区的M类榴辉岩特别富集18O,这样富18O的榴辉岩在大别山-苏鲁超高压变质带还尚未见报导。异常高的δ18O值表明M类榴辉岩与围岩-大理岩在变质过程中发生过强烈的氧同位素交换。稳定同位素、流体包裹体等证据揭示氧同位素交换可能发生在超高压岩石的折返过程中,由于叠加的麻粒岩相退变质作用使同俯冲的新元古代海相碳酸盐岩发生了去碳酸盐化作用,产生了富CO2的变质流体。这种退变质流体特别富18O,成为M类榴辉岩与围岩碳酸盐岩交换的媒介。所观测到的M类榴辉岩内矿物之间,以及榴辉岩与围岩大理岩之间都基本达到了高温下的氧同位素平衡。由于荣成地区各类榴辉岩记录的变质温度普遍高于大别山和苏鲁南段的榴辉岩,因此这一地区的榴辉岩在折返过程中一般都叠加有麻粒岩相和／或角闪岩相的退变质作用。退变质流体,特别是麻粒岩相退变质期间产生的富CO2流体,是造成这一地区M类榴辉岩有别于其它地区M类榴辉岩-特别富18O的根源。更多还原

【Abstract】 The M-eclogites, hosted in marble, from Rongcheng region, Shandong Province, China were reported to be enriched extremely in 18O. So extremely 18O-enriched eclogites, however, have not been reported from other regions of the Dabie-Sulu UHP metamorphic zone so far. In the Rongcheng region, the extremely high δ18O values of M-eclogite suggest that a strong oxygen isotopic exchange happened between the M-eclogite and its country-rock, marble, during metamorphisms. The evidences from stable isotopes and fluid-inclusions reveal that the oxygen isotopic exchange probably took place during exhumation of the UHP slab, since an overlying granulite-facies metamorphism resulted in decarbonation of the country-rock, the Neoproterozoic marine carbonates, that produced metamorphic fluids enriched in CO2. The metamorphic fluids were enriched extremely in 18O and became a media for oxygen isotopic exchange between the M-eclogite and country-rock carbonate. The oxygen isotope equilibria were mostly attained among the marjor minerals in the M-eclogites, such as garnet, omphacite, quartz, and others, and between the M-eclogite and carbonate at higher temperature. Because the eclogites from the Rongcheng region commonly have the oxygen isotopic temperatures higher than that from the Dabie terrain and the southern Sulu terrain, they generally overlain granulite-facies and/or amphibolite-facies metamorphisms during the exhumation. The retrogressive fluids, especially the fluids enriched in CO2 produced during the granulite-facies metamorphism, were locally active that resulted in the M-eclogites enriched extremely in 18O in the Rongcheng region as distinct from common M-eclogites from the Dabie-Sulu UHP zone besides this region.更多还原