Condutividade térmica de rochas: uma aplicação para granitos ornamentais

This dissertation focuses on rock thermal conductivity and its correlations with petrographic, textural, and geochemical aspects, especially in granite rocks. It aims at demonstrating the relations of these variables in an attempt to enlighten the behavior of thermal effect on rocks. Results can be useful for several applications, such as understanding and conferring regional thermal flow results, predicting the behavior of thermal effect on rocks based upon macroscopic evaluation (texture and mineralogy), in the building construction field in order to provide more precise information on data refinement on thermal properties emphasizing a rocky material thermal conductivity, and especially in the dimension stone industry in order to open a discussion on the use of these variables as a new technological parameter directly related to thermal comfort. Thermal conductivity data were obtained by using Anter Corporation s QuicklineTM -30 a thermal property measuring equipment. Measurements were conducted at temperatures ranging between 25 to 38 OC in samples with 2cm in length and an area of at least 6cm of diameter. As to petrography data, results demonstrated good correlations with quartz and mafics. Linear correlation between mineralogy and thermal conductivity revealed a positive relation of a quartz percentage increase in relation to a thermal conductivity increase and its decrease with mafic minerals increase. As to feldspates (K-feldspate and plagioclase) they show dispersion. Quartz relation gets more evident when compared to sample sets with >20% and <20%. Sets with more than 20% quartz (sienogranites, monzogranites, granodiorites, etc.), exhibit to a great extent conductivity values which vary from 2,5 W/mK and the set with less than 20% (sienites, monzonites, gabbros, diorites, etc.) have an average thermal conductivity below 2,5 W/mK. As to textures it has been verified that rocks considered thick/porphyry demonstrated in general better correlations when compared to rocks considered thin/medium. In the case of quartz, thick rocks/porphyry showed greater correlation factors when compared to the thin/medium ones. As to feldspates (K-feldspate and plagioclase) again there was dispersion. As to mafics, both thick/porphyry and thin/medium showed negative correlations with correlation factor smaller than those obtained in relation to the quartz. As to rocks related to the Streckeisen s QAP diagram (1976), they tend to fall from alcali-feldspates granites to tonalites, and from sienites to gabbros, diorites, etc. Thermal conductivity data correlation with geochemistry confirmed to a great extent mineralogy results. It has been seen that correlation is linear if there is any. Such behavior could be seen especially with the SiO2. In this case similar correlation can be observed with the quartz, that is, thermal conductivity increases as SiO2 is incremented. Another aspect observed is that basic to intermediate rocks presented values always below 2,5 W/mK, a similar behavior to that observed in rocks with quartz <20%. Acid rocks presented values above 2,5 W/mK, a similar behavior to that observed in rocks with quartz >20% (granites). For all the other cases, correlation factors are always low and present opposite behavior to Fe2O3, CaO, MgO, and TiO2. As to Al2O3, K2O, and Na2O results are not conclusive and are statistically disperse. Thermal property knowledge especially thermal conductivity and its application in the building construction field appeared to be very satisfactory for it involves both technological and thermal comfort aspects, which favored in all cases fast, cheap, and precise results. The relation between thermal conductivity and linear thermal dilatation have also shown satisfactory results especially when it comes to the quartz role as a common, determining phase between the two variables. Thermal conductivity studies together with rocky material density can function as an additional tool for choosing materials when considering structural calculation aspects and thermal comfort, for in the dimension stone case there is a small density variation in relation to a thermal conductivity considerable variation

Petrologia do plúton Serra da Macambira, neoproterozóico da faixa seridó, província Borborema (NE do Brasil)

The final stage of Brasiliano/Pan-African orogeny in the Borborema Province is marked by widespread plutonic magmatism. The Serra da Macambira Pluton is an example of such plutonism in Seridó Belt, northeastern Borborema Province, and it is here subject of geological, petrographic, textural, geochemical and petrogenetic studies. The pluton is located in the State of Rio Grande do Norte, intrusive into Paleoproterozoic orthogneisses of the Caicó Complex and Neoproterozoic metassupracrustal rocks of the Seridó Group. Based upon intrusion/inclusion field relationships, mineralogy and texture, the rocks are classified as follows: intermediate enclaves (quartz-bearing monzonite and biotite-bearing tonalite), porphyritic monzogranite, equigranular syenogranite to monzogranite, and late granite and pegmatite dykes. Porphyritic granites and quartz-bearing monzonites represent mingling formed by the injection of an intermediate magma into a granitic one, which had already started crystallization. Both rocks are slightly older than the equigranular granites. Quartz-bearing monzonite has K-feldspar, plagioclase, biotite, hornblende and few quartz, meanwhile biotite-bearing tonalite are rich in quartz, poor in K-feldspar and hornblende is absent. Porphyritic and equigranular granites display mainly biotite and rare hornblende, myrmekite and pertitic textures, and zoned plagioclase pointing out to the relevance of fractional crystallization during magma evolution. Such granites have Rare Earth Elements (REE) pattern with negative Eu anomaly and light REE enrichment when compared to heavy REE. They are slight metaluminous to slight peraluminous, following a high-K calc-alkaline path. Petrogenesis started with 27,5% partial melting of Paleoproterozoic continental crust, generating an acid hydrous liquid, leaving a granulitic residue with orthopyroxene, plagioclase (An40-50), K-feldspar, quartz, epidote, magnetite, ilmenite, apatite and zircon. The liquid evolved mainly by fractional crystallization (10-25%) of plagioclase (An20), biotite and hornblende during the first stages of magmatic evolution. Granitic dykes are hololeucocratic with granophyric texture, indicating hypabissal crystallization and REE patterns similar to A-Type granites. Preserved igneous textures, absence or weak imprint of ductile tectonics, association with mafic to intermediate enclaves and alignment of samples according to monzonitic (high-K calcalkaline) series all indicate post-collisional to post-orogenic complexes as described in the literature. Such interpretation is supported by trace element discrimination diagrams that place the Serra da Macambira pluton as late-orogenic, probably reflecting the vanishing stages of the exhumation and collapse of the Brasiliano/Pan-African orogen.