TIME CONSTRAINT BASED ON ZIRCON DATING FOR THE JACAREACANGA GROUP (TAPAJÓS PROVINCE, AMAZON CRATON, BRAZIL) Almeida, M.E. 1 , Ferreira, A.L. 1 , Macambira, M.J.B. 2 , and Sachett, C.R. 2 1 - Geological Survey of Brazil - CPRM (Manaus - Amazonas) – marcelo_almeida@cprm-ma.gov .br 2 – Federal University of Pará / Laboratory of Isotope Geology (Belém - Pará) – moamac@ufpa.br Keywords: zircon dating, metassedimentary rocks, Tapajós Province INTRODUCTION - During long time the Jacare- acanga meta-volcano sedimentary sequence have been interpreted as Archean greenstone belt terrain. However, recent data are indicating younger U-Pb ages about 2.1 Ga. In the Tapajós Province (Amazon Craton), the Cuiú- Cuiú Complex (2.00-2.03 Ga), Creporizão granitoids (1.99-1.96 Ga) and Jacareacanga Group are the oldest rocks. The Jacareancaga Group is composed by quartz- mica schists, quartzites, ferruginous quartzite, metachert, and minor talc-tremolite-chlorite schist, actinolite-epidote schist, hornfels, metargilites and metawackes metamorphosed in low to medium-grade conditions. The aim of the present paper is to estabilish the maximum age of Jacareacanga sedimentation and identify probable sources in Espírito Santo region (Espírito Santo muscovite-biotite schist). In this research, similar and new results are obtained by zircon evaporation methodology. This research shows geochronological data about the Espírito Santo muscovite-biotite schist related to Jacareacanga Group (Ferreira et al., 2000) in Tapajós Province (Amazon Craton). The area is located near Amazonas and Pará States boundary (Northern Brazil; figure 1) and the sample was obtained at Espírito Santo ( garimpo ) small-scale gold mine (06 o 00’48”S, 58 o 08’17”W). GEOLOGICAL SETTING - Jacareacanga Group and Cuiu-Cuiu Complex (figure 1) represent the basement rocks in Tapajós Province (TP). The Cuiu-Cuiu Complex is composed by dioritic-tonalitic-granodioritic orthogneiss and metagranitoids, with some undeformed granitoids and minor amphibolites and migmatites (Cuiú-Cuiú Complex: 2.00-2.03 Ga). The Jacareancanga Group is represented by quartz-mica schists, quartzites (including ferruginous quartzite and metachert), and minor talc-tremolite-chlorite schist, actinolite-epidote schist, hornfels, metargilites and metawackes in low to medium-grade metamorphic conditions. These rocks show NNE-SSW and N-S old foliation crosscut by the NW-SE transposed foliation. Regional sinistral shear zones characterize these last structures. This orogenic domain also included the Creporizão calc-alkaline granites and mylonites (1.96- 1.99 Ga). These rocks are intruded by different granitoid and volcanic rocks (figure 1): a) calc-alkaline granodiorites and mainly monzogranites with minor diorites and quartz- monzodiorites (Parauari Intrusive Suite 1.88-1.89 Ga); b) subalkaline A-type granites - Maloquinha Intrusive Suite (1.87-1.88 Ga); c) high-K calc-alkaline granite - Caroçal Granite (1.87 Ga); d) riebeckite-arfvedsonite orthoclase granite - Pepita Granite (1.87 Ga) and e) A- type anorogenic rapakivi granite - Igarapé Escondido and Porquinho Granite (1.78 Ga; Teles Pires event). These granitoids have acid to intermediate co-genetic volcanism, represented by rhyolites, dacites, tuffs, breccias and ignimbrites (Iriri Group: 1.87-1.89 Ga), andesites, trachyandesites, latites and andesite-basalts (Bom Jardim Formation). Undeformed mafic rocks are represented by: a) gabbros, diorites and related rocks - Rio Novo Gabbro, Quartz Monzogabbro Jenipapo and Ingarana intrusive Suite (1.89 Ga); b) Crepori diabase (1.78 Ga); c) Cachoeira Seca troctolite (1.00 Ga), and younger diabase dyke swarm (Piranhas and Periquito diabases respectively with 0.51 and 0.20 Ga ages). Finally, the TP shows Proterozoic (Buiuçu Formation: <1,78 Ga) and Phanerozoic sedimentary rocks (Alto Tapajós and Amazon Paleozoic basins and Cretaceous sediments). A wide variety of gold mineralization styles ocurs in TP includint shear zones-quartz vein, quartz-lode, porphyry- hosted stockwork and epithermal adularia-sericite types. GEOCHRONOLOGICAL RESULTS - The site sample shows deep weathering profile, where a saprolite rock was collected and heavy minerals were concentrated by panning. The fresh rock (muscovite- biotite schist) shows planar foliation (S1), crenulation cleavage (S2) and mineral assemblage composed by biotite, muscovite and quartz with rare feldspar, chlorite,