Petrographic analysis was carried out in a submerged rock-body on the north shelf of Rio Grande do Norte state. It is 18 km far from the actual coastline and it is named Urca do Minhoto. Quartz, bioclasts, feldspar and rock-fragments are the most important framework grains. Calcium carbonate cement occurs in three distinct types: micritic porefiling and equant spar, both of them filling the pore space, and isopachous prismatic rims, precipitated on the grain border. Grain-size varies from very-fine sand to granules. The grain packing suggests a shallow cementation environment (eodiagenesis).

We present new petrographic and chemical data together with calculated P-T equilibrium conditions of peridotite xenoliths enclosed in kimberlites from Rondônia, Northern Brazil (Cosmos-1 and Carolina-1) and Minas Gerais, Southeastern Brazil (Canastra-1) located in the Azimuth 125º Lineament. The composition of the mantle minerals is distinct in both areas, which can be related to the diversity of the lithospheric mantle beneath the southwestern portion of the Amazonian Craton and the Brasília Belt. New and compiled chemical data indicate that subcalcic G10 garnet occurs in samples from the Canastra-1 kimberlite and other occurrences of the Alto Paranaíba Igneous Province and can be related to the remnants of the Archean lithospheric mantle of the São Francisco Craton beneath the area. The garnets from Rondônia are mostly G5 (pyroxenitic) and G9 (lherzolitic) with a higher abundance of G3 (eclogitic) and G4 (pyroxenitic/eclogitic) relative to the Alto Paranaíba Igneous Province. Higher pressures and temperatures were calculated for the samples from Rondônia (40-60 kbar and 1030-1380 ºC) compared to samples from Minas Gerais (25-40 kbar and 730-1000 ºC). The peridotite xenoliths from Rondônia show P-T equilibrium conditions in the diamond stability field and can be the source of at least part of the diamond from the area. The P-T stability fields of the xenoliths from both locations are aligned close to the 40 mW/m2 geotherm. The data indicate that the cratonic 40 mW/m2 geothermal gradient in Rondônia may be related to a process of thermal relaxation of the lithospheric mantle after the Paleoproterozoic to Mesoproterozoic tectonothermal events of the southwestern Amazonian Craton until the sampling of the xenoliths by the magma in the Permian-Triassic.Composition and P-T conditions of the lithospheric mantle beneath the Azimuth 125º Lineament, Northern and Southern Brazil: constraints from peridotite xenoliths enclosed in diamond-bearing kimberlites Accepted manuscript -Uncorrected pre-proof This is a PDF file containing an unedited and non-definitive version of a manuscript that has been accepted for publication by the Journal of the Geological Survey of Brazil -JGSB, which serves to provide early visibility of the article. Being an uncorrected preproof version, errors may appear during the production process (language review, formatting and proof review), and these can affect the final content of the article and all legal disclaimers (https://jgsb.cprm.gov.br/index.php/journal/6).

We present new petrographic and chemical data together with calculated P-T equilibrium conditions of peridotite xenoliths enclosed in kimberlites from Rondônia, Northern Brazil (Cosmos-1 and Carolina-1) and Minas Gerais, Southeastern Brazil (Canastra-1) located in the Azimuth 125º Lineament. The composition of the mantle minerals is distinct in both areas, which can be related to the diversity of the lithospheric mantle beneath the southwestern portion of the Amazonian Craton and the Brasília Belt. New and compiled chemical data indicate that subcalcic G10 garnet occurs in samples from the Canastra-1 kimberlite and other occurrences of the Alto Paranaíba Igneous Province and can be related to the remnants of the Archean lithospheric mantle of the São Francisco Craton beneath the area. The garnets from Rondônia are mostly G5 (pyroxenitic) and G9 (lherzolitic) with a higher abundance of G3 (eclogitic) and G4 (pyroxenitic/eclogitic) relative to the Alto Paranaíba Igneous Province. Higher pressures and temperatures were calculated for the samples from Rondônia (40-60 kbar and 1030-1380 ºC) compared to samples from Minas Gerais (25-40 kbar and 730-1000 ºC). The peridotite xenoliths from Rondônia show P-T equilibrium conditions in the diamond stability field and can be the source of at least part of the diamond from the area. The P-T stability fields of the xenoliths from both locations are aligned close to the 40 mW/m2 geotherm. The data indicate that the cratonic 40 mW/m2 geothermal gradient in Rondônia may be related to a process of thermal relaxation of the lithospheric mantle after the Paleoproterozoic to Mesoproterozoic tectonothermal events of the southwestern Amazonian Craton until the sampling of the xenoliths by the magma in the Permian-Triassic.Composition and P-T conditions of the lithospheric mantle beneath the Azimuth 125º Lineament, Northern and Southern Brazil: constraints from peridotite xenoliths enclosed in diamond-bearing kimberlites Accepted manuscript -Uncorrected pre-proof This is a PDF file containing an unedited and non-definitive version of a manuscript that has been accepted for publication by the Journal of the Geological Survey of Brazil -JGSB, which serves to provide early visibility of the article. Being an uncorrected preproof version, errors may appear during the production process (language review, formatting and proof review), and these can affect the final content of the article and all legal disclaimers (https://jgsb.cprm.gov.br/index.php/journal/6).

No abstract

Peraluminous granitoids were recently mapped in the Rio Piranhas-Seridó Domain, the northeast portion of the Borborema Province. These bodies occur as stock and intrusive dikes in the metapelites of the Seridó Formation, constituting the Jardim do Seridó Suite. This suite has two facies. The first and most expressive facies consists of a medium-grained and whitish leucocratic monzogranite with muscovite, garnet, and biotite, while the second is represented by fine-grained and greyish leucocratic granodiorites with biotite, cropping out mainly on the edges of the main body. The thermobarometric conditions for the crystallization of the monzogranites were estimated between 2-5 kbar and 690-950 ºC, whereas the lithochemical data indicate a syn-collisional peraluminous signature. Neoproterozoic garnet-biotite schist xenoliths of the Seridó Formation are sometimes observed partially assimilated in the main body (stock). A U-Pb zircon age of 592 ± 2 Ma obtained in the main body is considered as the crystallization age of the Jardim do Seridó Suite, corroborating the proposed existence of peraluminous magmas associated with the Brasiliano Orogenesis in the Rio Piranhas-Seridó Domain. The chemical and petrographic data identified this suite as fertile to that it can generate dikes of rare elements-bearing pegmatites.

Santa Fé-3: discovery of a new kimberlite-like intrusion in the Borborema Province, northeast Brazil.We report the discovery of a kimberlite-like intrusion, named here Santa Fé-3, in the Borborema Province, NE Brazil. The discovery resulted from investigation of a mineral anomaly characterized by the presence of kimberlite indicator minerals (KIM) especially mantle garnet, ilmenite, clinopyroxene and spinel. Santa Fé-3 is a volcaniclastic kimberlite breccia, weathered, yellow-greenish in color, exhibiting inequigranular texture and containing xenoliths, deep facies autoliths, magmaclasts (pseudomorphs after olivine) and macrocrysts assemblage dispersed in a serpentine-rich groundmass. Santa Fé-3 occurs in pipe shape, with approximately 50 m length and 30 m width at surface, which intruded into Paleoproterozoic banded gneisses, and is associated to Cenozoic olivine basalt sheet. Although several other data need to be acquired, all the observed characteristics are very similar to those of the Santa Fe-1 and 2 kimberlitic intrusions that occur some kilometers to the north.

Discovery and confirmation of the first kimberlitic intrusions in the Borborema Province, NE Brazil. Two kimberlitic bodies were recognized and studied on northern Rio Grande do Norte state during fieldworks of the Diamond Brazil Project. These intrusions have been named Santa Fé-1 and Santa Fé-2 and are located in the Rio Piranhas-Seridó domain, Borborema Province. The Santa Fé-1 and Santa Fé-2 pipes have areas of 27 ha and 9 ha, respectively, and exhibit a volcaniclastic kimberlite breccia texture containing ilmenite, garnet, spinel and clinopyroxene in abundance. Eclogite garnet contains Na 2 O > 0.07 wt.% and has been classified as G3"D" and G4"D". According to ground magnetic and gravity survey data, these kimberlitic intrusions are cylindrical bodies, magnetically stratified and discordantly hosted into highly magnetic and dense rocks, which correspond to granodioritic and tonalitic orthogneisses and migmatites of the Arabia Complex (2546 ± 4.2 Ma, SHRIMP U-Pb zircon). The recognition of kimberlitic pipes with expressive dimensions in a previously not prospective setting opens new horizons to exploration of primary sources for diamonds in the Borborema Province and especially in the Rio Grande do Norte state.