No abstract

No abstract

Coastal floods are currently a strong threat to socioeconomic activities established on the margins of lagoons and estuaries, as well as to their ecological equilibrium, a situation that is expected to become even more worrying in the future in a climate change context. The Ria de Aveiro lagoon, located on the northwest coast of Portugal, is not an exception to these threats, especially considering the low topography of its margins which has led to several flood events in the past. The growing concerns with these regions stem from the mean sea level (MSL) rise induced by climate changes as well as the amplification of the impacts of storm surge events, which are predicted to increase in the future due to higher mean sea levels. Therefore, this study aims to evaluate the influence of MSL rise on the inundation of Ria de Aveiro habitats and to assess the changes in inundation patterns resulting from frequent storm surges (2-year return period) from the present to the future, assessing their ecological and socioeconomic impacts. For this, a numerical model (Delft3D), previously calibrated and validated, was used to simulate the lagoon hydrodynamics under different scenarios combining MSL rise and frequent storm surge events. The numerical results demonstrated that MSL rise can change the vertical zonation and threaten the local habitats. Many areas of the lagoon may change from supratidal/intertidal to intertidal/subtidal, with relevant consequences for local species. The increase in MSL expected for the end of the century could make the lagoon more vulnerable to the effect of frequent storm surges, harming mostly agricultural areas, causing great losses for this sector and for many communities who depend on it. These extreme events can also affect artificialized areas and, in some cases, endanger lives.

Located on the western continental tip of the Fernando de Noronha transform fracture (FNTF), northeastern Brazil, the Eocene-Oligocene Mecejana Phonolitic Province (MPP) was subjected to a multi-methodological study, comprising field and microscopic characterization, mineral and whole rock chemistry, and Sr-Nd isotopes. These rocks intrude the Precambrian crystalline basement, forming mainly plugs oriented in the NE-SW direction. They are composed of alkali basalt, phono-tephrite, tephri-phonolite, and phonolite with phenocrysts of nepheline and sanidine, and minor diopside, aegirine-augite, aegirine, kaersutite, biotite and titanite. Chemically, they are sodic (Na2O/K2O > 1) and display LREE enrichment, concave upward or flat HREE patterns, weak to strong Eu anomaly, and high contents of Nb, Ta and Zr. They delineate two chemical groups, the less evolved one comprising basalt to tephri-phonolites and the more evolved constituted by phonolites. Oxide and trace element modeling points out to an evolution by fractional crystallization, leaving olivine-rich gabbro and foidolite / nepheline syenite cumulates, respectively. The analyzed samples have Sr-Nd isotopic ratios akin to OIB rocks (positive εNd of +3.0 to +0.9 at 30 Ma) and low to high 87Sr/86Sri (at 30 Ma) of 0.70264-0.70955. The data suggest a three stages evolution model for the MPP: (1) <5% partial melting of a metasomatized phlogopite-amphibole-garnet peridotite generates an alkali basalt melt; (2) polybaric differentiation of this melt at crustal level (~570-220 MPa, 1040-645 oC) leads firstly to phono-tephrites and tephri-phonolites and then to (3) foidolite and nepheline syenite. Petrographic, chemical, and isotopic characteristics of the MPP and similar rocks of the Fernando de Noronha islands suggest the control by the FNTF and reactivation of NE-SW trending deep-rooted Precambrian faults allowing channeling and emplacement of the alkaline magmas.

RESUMOO mapeamento geoquímico do Quadrilátero Ferrífero foi realizado pela CPRM -Serviço Geológico do Brasil com dados geoquímicos de uma área de 45.000 km 2 entre os meridianos 42 o 30´W e 45 o W e paralelos 19 o 30´S e21 o S. Sedimento ativo de corrente na fração < 80# (ou 0.175 mm), foi pulverizado a < 150# (~0,100 mm), digerido com água régia quente e analisado para 53 elementos (ICPMS). Foram elaborados mapas uni-e multi-elementares. Sedimento de corrente é um meio efetivo no mapeamento geoquímico regional. Estruturas geoquímicas, unidades litológicas e processos de mineralização foram reconhecidos com a densidade de amostragem de 1 amostra por 12 km 2 . A densidade de amostragem é um fator chave na qualidade dos mapas geoquímicos produzidos. Deve-se tomar cuidado na interpretação dos resultados devido à sua natureza; estes dados não identificam anomalias geoquímicas específicas ou depósitos minerais individuais. A interpretação dos sedimentos de correntes não é direta e os processos secundários envolvidos na evolução deste material devem ser considerados. Estes dados podem ser usados na exploração mineral para se delinear alvos favoráveis para estudos mais detalhados. Depósitos minerais muitas vezes ocorrem em provinciais geoquímicas caracterizadas por elevadas concentrações de elementos de interesse econômico e farejadores. Depósitos minerais tendem a se localizar ao longo de unidades estratigráficas específicas e/ou trends estruturais por grandes áreas. Estes dados geoquímicos podem ser utilizados em estudos ambientais, apoiar tomadores de decisão na definição de políticas públicas e no manuseio sustentável do solo. Palavras-Chave: mapeamento geoquímico, sedimento de corrente, Quadrilátero Ferrífero, exploração mineral, mapeamento geológico ABSTRACTThe geochemical survey of Iron Quadrangle was performed by the Geological Survey of Brazil -CPRM involving geochemical data from the area between 42 o 30´W and 45 o W and 19 o 30´S and 21 o S, totalling 45.000 km 2 . Active stream sediment was analyzed. Fine fractions (< 80# or 0.175 mm) were pulverized to -150# fraction (~ 0.100 mm), digested by hot acqua regia and analyzed for 53 elements by ICPMS. Maps of raw and manipulated data (element concentrations and multi-elemental scores) were made. Stream sediment (< 80# fraction) is an effective sampling medium for regional geochemical surveys. Geochemical structures, lithological units and mineralization processes were recognized with the sample density of 1 sample per 12 km 2 . Sample density has a key role in the quality of the geochemical maps produced. Caution must be taken when interpreting the results because of its nature; these data do not necessarily pinpoint specific geochemical anomalies or single ore deposits. The interpretation of stream sediment samples is not straightforward and must take into account secondary processes involved in the evolution of sampling media. These data may be used in mineral exploration to delineate favorable targets for more detailed studies. Mineral deposits often occur in...

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.

No abstract

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.