Provenance and Tectonic Studies in the Amazon Fan. Farid Chemale Jr.. Instituto de Geociências Universidade de Brasília

Transcrição

1 Provenance and Tectonic Studies in the Amazon Fan Farid Chemale Jr.. Instituto de Geociências Universidade de Brasília

2 Contribution of Amazon Cone project Supported by FINEP/PETROBRAS/BP/ELF/EXXON MOBILE/AGIP Developed between 2000 to 2002

3 Summary 1. Introduction and Goals 2. Drainage system of Amazon region and adjacent areas 3. Main geological units 4. Stratigraphy and Provenance of Pre-Cone Section 5. Amazonas Cone Pb-Pb and Sm-Nd isotopes and Low-temperature Thermochronology 6. Main tectono-sedimentary events of the Amazon Cone 7. Conclusions and Future Research Strategies

4 (i) The Amazon Fan contains a large contribution of Andean material (ii) However one of key points is to establish which proportion came from the Andean mountains and from the cratonic Amazonian area

5 Goals.Integration of geological information of Amazon Craton, Phanerozoic overs and Setentrional Andes. Establish the main source areas and tectonic events of the Pre-Amazon an Section and Amazon Fan based on isotope studies

6 Amazonian region with the main drainage systems de drenagem

7 MAIN GEOLOGICAL UNITS OF THE AMAZONIAN REGION AMAZONIAN CRATON PHANEROZOIC COVER SETENTRIONAL ANDES

8 SIMPLIFIED GEOLOGICAL MAP OF NORTHERN SOUTH AMERICA (compiled by Chemale et al., 2002 after Tassinari et al., 2009 and maps of the Geolgical Surveys of Peru, Equador, Colômbia and Venezuela)

9 Stratigraphy and Provenance of Pre-Cone Section of the Amazonas Mouth Basin (Lower Cretaceus to Middle Miocene) Based on U-Pb in situ dating of detrital zircons (core and cutting samples)

10 Provenance and Sedimentary Deposits Detrital material preserve the history of source areas; Analises reflect with good resolution the isotope information of the source

11 Age ±1s fraction Age ±1s fraction RESULTS

12 Inverse Stratigraphy Neoproterozoic and Paleoproterozoic sources

13 Neoproterozoic and Paleoproterozoic contribution ( local Mesoproterozoic and Archean)

14 Neoproterozoic/Eopal. and Paleoproterozoic Increase of Neoproterozoic to Eopaleozoic contribution

15 Contribuição Neoproterozoic/Eop e Paleoproterozoic Sensível aumento da contribuição Neoproterozóica a Upper section there is also a Mesoproterozoic contribution

16 MAPA GEOLÓGICO SIMPLIFICADO DO NORTE DA AMÉRICA DO SUL Main source of the Brasiliano Zircons (Neoproterozoic to Eopaleozoic) (compiled by Chemale et al., 2002 after Tassinari et al., 2009 and maps of the Geolgical Surveys of Peru, Equador, Colômbia and Venezuela)

17 INTEGRAÇÃO DOS DADOS ESTRATIGRÁFICOS E GEOCRONOLÓGICOS MIOCENO MÉDIO Proto-Amazonas river

18 Amazonas FAN Pb-Pb e Sm-Nd Isotopes Amazonas Fan

19 Age of crustal formation vs. mean time of crustal residence The sediments and sedimentary rocks present very often mixed age signature (two or more source area)

20 Depth (m) T DM (in Ma) Pliocene Middle Miocene Early Miocene POÇO D Early Pliocene Late Miocene Late Miocene Pb 206 /Pb 207 Middle Miocene Early Miocene Number of sample Model age histogram for samples of APS-33E Change of source areas at boundary (i) Lower/Middle Miocene, (ii) Middle/Upper Miocene, (iii) Upper Miocene/Pliocene Fine-grained sedimentary rocks (shale, mudstone) were analyzed.

21 Sm-Nd information for the source area ACP study of the Amazon Fan Archean f Sm/Nd e Nd (o)* TDM (Ga) from -0,31 to -0,66 from to to 3.07 MIP Paleoproterozoic f Sm/Nd e Nd (o)* TDM from to from -6.6 to to 3.10 VTP Paleoproterozoic f Sm/Nd e Nd (o)* TDM from to from -2.2 to to 2.85 RJP Paleo to Mesoproterozoic f Sm/Nd e Nd (o)* TDM from to from to to 2.40 R-SI/SP Mesoproterozoic f Sm/Nd e Nd (o)* TDM from to from 0.2 to to 2.47 Sands of Rio Madre Dios (Bolivia and Peru) TDM 1,33 a 1,62 Ga

22 Geochronological Provinces of the Amazonian Craton (Tassinari et al., 2000)

23

24 Pb/ 204 Pb 207 Pb/ 204 Pb Amazonian Craton rocks older cratonic rocks 6 This work 15.6 Amazon fan Pb/ 204 Pb 5 Andean igneous rocks 17.0 This study Pb/ 204 Pb Andean igneous rocks Amazon delta Amazon River suspended sediments Nazca Plate sediments Amazon fan

25 Results of Pb-Pb and Sm-Nd isotopes studies in the fine-grained rocks We recognize at least two major change in the sediment supply of Amazon Fan: (1)At boundary Early Miocene and Middle Miocene (2)At boundary Middle Miocene and Late Miocene (3) In the Lower Pliocene There are some local supply of older material in the section dominated by the clay-rich material from the Andean mountains in the Amazon Fan, which came directly from the Archean and Paleoproterozoic Provinces

26 tectono-sedimentary

27

28 Apatite FT Apparent ages obtained from drill core sample (off-shore)

29 Ages (Ma) Apparent age of a drill core sample = 9+/- 2Ma WMA Grains Arkosean Sandstone FT data on apatite from Arkosean Sandstone (depth = 3838m). Number of grains = 14, (W M Age ) = 9 ± 2 Ma (Error = 1SD), P ( 2 v) ~0.02 (including 10 of 14 = 0.20). Stratigraphic age: Pleistocene (~1.8 Ma)

30 Thermal hystory of onshore samples

31 Stratigraphic age: Granodiorit2 Age 2100 Ma (Paleoproterozoic) TRÊS DENUDATION EVENTS 2.8 Ma 10 Ma 24 Ma - Histograms of thermal history of sample from the Amapa Guyana Shield

32 Stratigraphic ages: 1800 Ma e 2800 Ma Denudation events: 69 Ma, 43 Ma, 23 Ma, 12 Ma e Ma - Histograms of thermal history of sample from the Carajas Region (MG-01 e CRN-08) Guaporé Shield

33 AFTA RESULTS The analysed samples show complex history for a long time in the temperature interval of 60 to 110 o C (PAZ partial annealing zone) Through the moddeling we can recognize three younger intervals related to regional uplift event: (1) Transition Early Micocene/Middle Miocene (ca Ma) (2) Uplift of Andean Mountain (9.3 to 12 Ma), beginn of the Amazon Fan deposition and Amazon River system (3) Uplift of continental area as result of isostatic compensation ( Ma)

34 Seção esquemática transversal ao longo do Cone do Amazonas Modificado de CTPETRO/FINEP/FAURGS Projeto Cone do Amazonas

35 1. Lower and Middle Miocene is marked by strong contribution of Pre-cambrian to Eo paleozoic rocks with main sources areas cut by the Tocatins River and Protoamazonas river (Pre-Amazon Fan) 2. Based on Apatite FT studies we recognize three main denudation events ( Ma and Ma) 3. Pb-Pb and Sm-Nd isotope : (i) strongly sedimentation of Precambrian rocks to the continental platform at Early Miocene. (ii) At the boundary Early Miocene/Middle Miocene the Andean rocks began progressively to become a major source for the fine-grained sediments (iii) the Late Miocene and Pliocene sediments record also contribution of the Archean and Paleoproterozoic source rocks

36 Systematic sampling of drill holes (cores and cuttings) of the Amazon Fan. Further isotopic studies (Low Temperatture Termocronology, Sm-Nd, Pb-Pb, Lu-Hf, Sr-Sr and U-Pb and Lu- Hf zircon) Better understanding the processes involved in the sedimentation of the 10 km thick sedimentary package of the Amazon Fan (sedimentation rate, transport, paleoclima, quantifying of source areas, dynamic modelling, on so on)

37 Kick off meeting Brasília 2-3 May 2012

38 The results of drill core and cutting samples allow some preliminary conclusions but it should be necessary more information. We analyzed four drill core samples with very few grains in the apatite separate. From the four drill core samples (Tab. 1) we could get some reasonable information in the apatites of core sample APS-10b (depth 3480 m). We identify two apparent ages in drill core sample APS-10b (depth 3480 m) between 200 and 270 Ma, interpreted as ages of source area rocks. Twelve grains yield means apparent age of 9 2 Ma, interpreted here as a geological process that affected the earlier ages. However the confined track length has not been measured (absence of them after track revelation) because we worked with few number of grains (only 14) and very low track density (Fig. 4).

39 Por meio dos dados isotópicos podem ser reconhecidos três intervalos de denudação na margem continental (associado a eventos de soerguimento regionais): (i) Mioceno Inferior (ca Ma), que é marcado pela forte contribuição de rochas pré-cambrianas do antigo Rio Tocatins e proto Amazonas (Seção Pré-Cone) (ii)entre 12 e 9.3 Ma que é relacionado ao evento Quechua II nos Andes, quando ocorreu soerguimento significativo nos Andes Setentrionais e, consequente ajuste isostático na margem norte e leste da América do Sul. Este estágio corresponde a implantação do Rio Amazonas como a presente situação e início da deposição do Cone do Amazonas (iii)entre 2.95e from 3.2 to 2.5 Ma que corresponde a um processo substancial de soerguimento da margem continental. O soerguimento da área continental é interpretado como resultado da compensação isostática devido a sobrecarga da pilha sedimentar do Cone do Amazonas no decorrer de 7 Ma (taxa média de sedimentação em torno de 600 m/ma. A taxa média de sedimentação deste período

40 A distribuição dos comprimentos de traços de uma amostra (evidenciadas nos histogramas a, b ou c) é diretamente função do tipo de história térmica (a, b ou c) a que a amostra estava submetida desde seu resfriamento abaixo de 110ºC. A área entre 60 e 110º C é dita Zona de Apagamento Parcial (ZAP) onde ocorre o encurtamento da maioria dos traços (modificado de Wagner, et al.,1972).