【摘 要】
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Whole rock elemental and Sr-Nd isotope geochemistry and in situ zircon Hf isotope geo-chemistry were used to identify the sources of the Neoproterozoic granites from the Socorro batholith, Socorro-Guaxupé Nappe (SGN), South Brasilia Orogen, Brazil. Zircon
【机 构】
：
Instituto de Geociências,USP,CEP 05508-900 S?o Paulo-SP,Brazil
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Whole rock elemental and Sr-Nd isotope geochemistry and in situ zircon Hf isotope geo-chemistry were used to identify the sources of the Neoproterozoic granites from the Socorro batholith, Socorro-Guaxupé Nappe (SGN), South Brasilia Orogen, Brazil. Zircon trace elements and Hf isotope geo-chemistry provided information about sources and crystallization (T, fO2) conditions. Three main types of granites built the bulk of the batholiths, beginning with probably pre-collisional ～640–630 Ma char-nockites, and ending with ～610 Ma voluminous post-collisional high-K calc-alkaline (HKCA) I-type gran-ites (Bragan?a Paulista-type). Several types of leucogranites were generated from 625 to 610 Ma, spanning the interval from collisional to post-collisional tectonics. Two charnockite bodies occur in the study area: the ～640 Ma Socorro charnockite has remarkable chemical similarities with Bragan?a Paulista-type gran-ites, but higher εNd(t)= -6.1 and average zircon εHf(t)= -9.1 and lower 86Sr/87Srt (0.7093) values, indicative of more juvenile and water-poor source. The ～633 Ma Atibaia charnockite has distinct geochemical signature (lower Mg# and Sr content; higher Zr), more negative εNd(t)= -14.1, similar average zircon εHf(t)= -8.9, and much higher 86Sr/87Srt=0.7197, probably reflecting a larger component from old crust. The predominant ～610 Ma Bragan?a Paulista-type granites were emplaced in a post-collisional setting, and correspond to porphyritic biotite-hornblende monzogranites of high-K calc-alkaline character with 61 wt.％–67 wt.％ SiO2, high Mg# (39–42), Sr/Y (19–40), La/Yb (12–69), highly negative εNd(t) (-12.3 to - 12.9) and zircon εHf(t) (-12 to -17) and 87Sr/86Srt=0.7119–0.7131. These features are interpreted as indicative of magma genera-tion in a thickened crust, where melts from enriched mantle sources emplaced in the lowermost crust, heated host old continental crust rocks (gneisses and granulites) and partially mixed with their melting products. Leucogranite plutons (SiO2>72 wt.％) occurring in the southern portion of the batholith have a range of geochemical and isotope signatures, reflecting melting of crustal sources in space and time be-tween ～625 Ma (Bocaina Pluton) and ～610 Ma (Bairro da Pedreira Pluton). Highly negative εNd(t) (-16.2) and average zircon εHf(t)= -16, and high 87Sr/86Srt (0.7156–0.7171) are consistent with relatively old ortho- and paragneiss sources similar to those which generated regionally abundant migmatites and anatectic granites in the collisional to post-collisional setting.
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