Figure 1.
Schematic geologic map of Alto Moxotó Terrane, highlighting its main lithostructural elements at small scale.
Figure 2.
Scheme of 1/100,000 sheets from the Brazilian Geological Survey (CPRM) used in this research, as well as the main shear zones belonging to Alto Moxotó Terrane (TAM) and its limits.
Figure 3.
Schematic geological section transversal to the Eastern sector of Alto Moxotó Terrane - TAM (Eastern Paraíba).
Figure 4.
Schematic geologic section transversal to the Central sector of Alto Moxotó Terrane - TAM (Southern Paraíba).
Figure 5.
Schematic geologic section of the Westernmost part of the central sector of Alto Moxotó Terrane - AMT (Northern Pernambuco).
Figure 6.
Schematic geologic section of the South-western sector of Alto Moxotó Terrane - AMT (Central-southern of Pernambuco).
Figure 7.
Hypotetic scheme of the global evolution of the central part of Borborema Province (Transversal Zone and surroundings) from the Paleoproterozoic (pre-Orosirian plate - A) to the Upper Ediacaran.
Figure 8.
Nd evolutionary diagram for the main pre-Rhyacian nuclei identified for Alto Moxotó Terrane (TAM). A set of parallel traight lines, mostly intercepting the depleted mantle curve between 2.5 and 3.5 Ga has been observed. The ENd values obtained in this study varied from -21 to -3.5. The highest values, on the right of the diagram, correspond to the so-called “Riacho das Lages Complex” (Santos et al. 2017Santos L.C.M.L. 2017. Processos acrescionários da porção central de Gondwana Ocidental: exemplos dos terrenos Alto Moxotó e Alto Pajeú da Província Borborema, NE Brasil. PhD Thesis, Instituto de Geociências, Universidade de Brasília, Brasília, 255 p.), Airi region (PE). See concordia diagrams (next figures).
Figure 9.
PAPE 36 - Concordia diagram for Fazenda Oiti migmatitic complex, North Itatuba-PB. Upper intercept indicates an age of 2911 ± 69 Ma (error ca. 2.3%) and MSWD = 4.0. The value of the lower intercept (1147 ± 28 Ma) has no tectonic significance (in our opinion). This Mesoarchean age of the easternmost sector of Alto Moxotó Terrane (TAM) is special, no similar ages have been found in this or in any other sector. It must be further checked.
Figure 10.
PAPE 41 - Concordia diagram for the zircons of extremely banded and sheared gneisses (“stromatic structure”) from Parari, East of São João do Cariri (Paraíba). Upper intercept indicates an age of 2456 ± 64 Ma, chosen according to the best set of points (error ca. 2.6%). The error of the lower intercept is large and must be related to radiogenic Pb losses (Brasiliano overprinting).
Figure 11.
PAPE 3R - Concordia diagram for the zircons of an extremely banded and sheared gneiss (such as PAPE 41, above), 17 km South of Boa Vista (Paraíba). Two cords are identified: the first of 2723 ± 160 Ma (error ca. 6%) is attributed to the formation of melanosomatic protoliths, with MSWD = 4.0. Another cord is well marked with an age of 1989 ± 21 Ma (error ca. 1%). We attribute this cord to a possible superposition of an Orosirian regional metamorphism, as already commented in the text.
Figure 12.
PAPE 5R - Concordia diagram for the migmatitic complex (in part paleosomatic samples, probably of metasedimentary origin) of Sítio Aconchego (Boqueirão municipality, Paraíba). Two cords could be drawn, the former with an age of 2532 ± 31 Ma (error ca. 1.2%) with MSWD = 2.3, which we attribute to the protolith portion. The latter indicates an age of the order of 1530 Ma (with a large error) that could be related to a probable late metamorphic event (Orosirian? Brasiliano?).
Figure 13.
PAPE 84 - Concordia diagram drawn with varied samples from Pedreira Carlos (Boqueirão municipality-Paraíba), which is a very complex migmatitic context both in phases and structures, with different types of protoliths (hornblende biotite gneisses, meta-quartzdiorites, metadiorites, etc.). The obtained alignment is of good quality, in which the upper intercept indicates an age of ca. 2674 ± 30 Ma (error ca. 1.1%), MSWD = 4.7. There is indication (not complete) of a lower intercept for an age of ca. 1532 Ma (with a large error). Like in
Figure 11 this could be indicating superposition of late Paleoproterozoic or Neoproterozoic metamorpism.
Figure 14.
PAPE 39 - Concordia diagram for the finely banded (stromatic structure) migmatitic complex (hornblende-and biotite-bearing paleosome), cropping out at a roadcut 17 km East of Monteiro-Paraíba. The main cord indicates (upper intercept) an age of 2658 ± 30 Ma (error ca. 1.2%, MSWD = 1.7), of excellent quality. The lower intercept does not seem to have geological significance (related to Brasiliano events?). Some Brasiliano data are observed in the lower part of the diagram. It is worth noting that even using the Rb-Sr method, this age was preserved in the outcrop.
Figure 15.
PAPE 25 - Concordia diagram for the quartz-dioritic orthogneiss that constitutes the paleosome of a complex migmatite from a cut of the Transposition Channel close to Custódia (Pernambuco). The upper intercept indicates an age of 2600 ± 13 Ma (error ca. 0.5%). A lower intercept (ca. 1950 Ma) could be drawn (it does not seem adequate to indicate an age), probably suggesting superposition of Orosirian events.
Figure 16.
FL-50 - Concordia diagram for the coarse-grained metatonalite of the proximities of Airi (South-Western portion of TAM), informally attributed to “Riacho das Lages Complex” (Santos 2017Santos L.C.M.L. 2017. Processos acrescionários da porção central de Gondwana Ocidental: exemplos dos terrenos Alto Moxotó e Alto Pajeú da Província Borborema, NE Brasil. PhD Thesis, Instituto de Geociências, Universidade de Brasília, Brasília, 255 p.). The upper intercept indicates an age of 2625 ± 14 Ma (error ca. 0.5%, MSWD = 3.9), and the lower intercept shows an age of 560 ± 36 Ma, which probably corresponds to the overprinting of the Brasiliano Cycle.
Figure 17.
FL-105 - Concordia diagram for the banded meta-granodiorite of the proximities of Airi (SW Pernambuco), attributed to “Riacho das Lages Complex” (Santos 2017Santos L.C.M.L. 2017. Processos acrescionários da porção central de Gondwana Ocidental: exemplos dos terrenos Alto Moxotó e Alto Pajeú da Província Borborema, NE Brasil. PhD Thesis, Instituto de Geociências, Universidade de Brasília, Brasília, 255 p.). The upper intercept indicates an age of 2643 ± 18 Ma (error ca. 0.7%), and the lower intercept an age of 645 ± 85 Ma, attributed to Brasiliano events. The obtained MSWD was 1.9, reiterating the good quality of the diagram.
Figure 18.
Nd evolutionary diagram for the Floresta Suite rocks (Eastern and Central sectors of Alto Moxotó Terrane (TAM). The resulting scenario is a harmonic group of almost parallel straight lines intercepting the depleted mantle curve between 2.45 and 3.1 Ga (100% of the lines), which very much resemble the results obtained with the pre-Rhyacian nuclei (
Fig. 7). The differences are the better harmonic arrangement of the evolutionary line. E
Nd values are between -25 and -35, showing a relatively long crustal residence time. Just one line intercepts the mantle curve at ca. 3.4 Ga.
Figure 19.
PAPE BOQ - Concordia diagram drawn for the (intensely) sheared anorthositic orthogneiss from the spillway of Boqueirão Dam (Epitácio Pessoa, SE of Paraíba). The upper intercept indicates an age of 2136 ± 15 Ma (attributed to intrusion or to the first metamorphism), and the lower intercept an age of 528 ± 21 Ma (attributed to the Brasiliano tectonism). The MSWD of 1.6 attests the quality of results.
Figure 20.
PAPE ANÉ1 - Concordia diagram for the laminated thin diatexite that occurs in Albuquerque Né (Pernambuco) at South of the geologic section in
Figure 5. In the distribution of sub-concordant points (continuous loss of Pb isotopes since 2200 Ma), it is possible to estimate a cord with upper intercept around 2180 Ma and a lower intercept around 550 Ma (Brasiliano events), according to the best exposed points as it possible to see in the next
Figure 20.
Figure 21.
PAPE ANÉ 2 - Concordia diagram drawn for Albuquerque Né diatexite (see
Fig. 19), with emphasis on many points clustered around the lower intercept. This group points to an age of 560 ± 1.8 Ma (error ca. 0.35%) and MSWD = 6.1. This shows a substantial rejuvenation affecting this Paleoproterozoic diatexite (see
Fig. 19) during the Brasiliano Cycle (Ediacaran) events.
Figure 22.
PAPE 194a - Concordia diagram for the sheared fine diatexite of Fazenda Melancias (East of Village of Grossos,
Fig. 5, South of São José do Egito). The distribution of points is sub-concordant from 2100 Ma, with ample concentration around 600 Ma. For this diagram, it was possible to draw a cord from the upper interceptat of ca. 2100 Ma (considering the lower interceptat ca. 620 Ma). The data concentrated close to the lower intercept will be seen and discussed in
Figure 23.
Figure 23.
PAPE 194b - Concordia diagram drawn for the diatexite of Fazenda Melancias, considering the great concentration of points marking the lower intercept (see
Fig. 22). With these data it is possible to draw a cord indicating an age of 620 ± 7 Ma (error ca. 1.2%) and MSWD = 0.71. This age (lower Ediacaran) points to pervasive reworking along the Brasiliano Cycle, which has affected this diatexite, originally Paleoproterozoic in age.
Figure 24.
Nd evolutionary diagram for the Sertânia Supergroup. The group of straight lines is very irregular (varied sources - metasedimentary and metaigneous rocks), in which three more or less distinct groups could be discriminated. These straight lines are intercepting the depleted mantle curve between 1.8 and 3.1 Ga and signaling ENd values from -17 to - 45, attesting a long crustal residence.
Figure 25.
PAPE 270 - Concordia diagram for the banded meta-gabbro intercalated in Sertânia sequence, with clearly preserved magmatic banding (S0 // Sp). The outcrop is located South of Salgado do São Felix-Paraíba. The well-marked age in the upper intercept is 2106 ± 10 Ga (error ca. 0.4%), MSWD = 1.6. The lower intercept does not seem to have geologic significance (ca. 322 ± 240 Ma), besides the very high error.
Figure 26.
PAPE 161 - Concordia diagram for bimodal felsic metavolcanic rocks intercalated with Sertânia metasediments, Rio da Barra/Pernambuco. The upper intercept indicates an age of 2041 ± 11 Ma, with lower intercept without apparent geologic meaning (see very high error).
Figure 27.
PAPE 164 - Concordia diagram drawn for the orthogneissic sill intercalated with mesozonal biotite gneisses, collected in the flanks of Henrique Dias railway (North of Arcoverde-Pernambuco). The age given by the upper intercept is 2031 ± 13 Ma (error ca. 0.64%, MSWD = 2.3). The lower intercept with no apparent geologic meaning radiogenic losses, very high error.
Figure 28.
PAPE SF - Concordia diagram drawn for the coarse-grained (meta-clastic) schist of Serra do Fogo, 18 km South of Monteiro-Paraíba, on the flank of an ample synform of Sertânia Supergroup, probably part of the basal fractions of this unit. The upper intercept indicates a Rhyacian age of 2150 ± 6 Ma, and the lower intercept an age of ca. 532 ± 10 Ma (attributed to Brasiliano events).
Figure 29.
PAPE 191 - Concordia diagram for the biotite schists located 12 km South of Tuparetama-Pernambuco (see
Fig. 5). The upper intercept once again points out an age to the Upper Rhyacian-Orosirian limit, 2048 ± 6 Ma (error ca. 0.3%, MSWD = 0.99). The lower intercept points out an age of 645 ± 26 Ma, attributed to the Brasiliano Cycle events (the North-trending nappism of this the area is striking).
Figure 30.
PAPE NT - Concordia diagram for the biotite schist located North of Tuparetama (see
Fig. 5). Two cords were drawn, the older with an age/upper intercept at 2138 ± 9 Ma (presumably Rhyacian original age) and the lower intercept at 592 ± 9 Ma (Brasiliano Cycle). The other cord points to an age of 2032 ± 5 Ma that is probably related to an Orosirian regional evet, with lower intercept pointing at 959 Ma, which (in our opinion) is devoid of geologic significance (it could somehow be a mark of Cariris Velhos Cycle).
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