ИСТИНА

During exhumation from the lower crust, high-grade complexes actively interact with ancient cratons. The interaction produces fluxes of fluids and magmas from the buried cratonic sequences to the overthrusting granulites. Composition of these fluids and magmas is predetermined by composition of granite-greenstone material of the adjacent cratons. The Archean greenstone sequences commonly include carbonate lithologies varying from marine dolomites to hydrothermal calcite veins. Such carbonate-bearing layered sequences could serve as sources both for CO2 and granitoid melts invading the granulites. In the present study, we report evidences for carbonate-bearing source for granitoid magmas effecting the Southern Marginal Zone (SMZ) of the Neoarchean Limpopo complex, South Africa [1]. These magmas intruded the SMZ in the period of time 2.67-2.68 Ga after metamorphic peak (2.71-2.72 Ga) during the exhumation of the SMZ onto the Northern Kaapvaal craton [2]. Following to fluid inclusion data and mineral equilibria modeling, the magmas carried CO2-rich fluids. Recently we reported the 13CPDB values for graphite (-6.5 to -8.6 ‰) and fluid inclusions (-4.10±1.2 ‰) from the granitoids [3]. These values differ from 13CPDB = -15.0 to -12.5 ‰, which have been known for graphite from metapelites of the SMZ [4]. We assumed that the magmas and their fluids have originated from the source outside the granulite complex. The «heavy» isotope signatures correspond to the source within the cratonic greenstone sequences, which involved Archean hydrothermal carbonate veins (13CPDB >-9 ‰). In addition, we present new data of the carbonate-bearing polyphase inclusions in garnets from the granitoids. Following to morphology, these inclusions were interpreted as inclusions of crystallized carbonate-silicate melts. The inclusions contain predominantly (Mg, Fe)CO3 with XMg = 0.24 - 0.78. A common silicate component of the inclusions is Fe-Mg-bearing pyrophyllite. Raman spectra revealed CO2, CH4 and liquid H2O in the inclusions. Carbonate-silicate inclusions coexist with polyphase inclusions composed of biotite, quartz, K-feldspar, plagioclase, sillimanite, which represent relics of granitic melts. Carbonate-silicate and silicate inclusion show compositional trends, that implies genetic relations between carbonate-silicate and granitic melts. Relics of the fluidized carbonate-silicate melts in garnets of the granites support the conclusion on the carbonate-bearing source for the granite magmas deduced from the carbon isotope study. Depletion of the inclusions in Ca and enrichment in Mg, Fe and Al implies that this source included metapelites intercalated with carbonate rocks. During anataxis, this source produced some carbonatitic melts, which were subsequently dispersed in the voluminous granite melts, while issued CO2 propelled granite intrusion.