Provenance and Tectonic Studies in the

Amazon Fan

Farid Chemale Jr.. (fchemale@unb.br)

Instituto de Geociências

Universidade de Brasília

Contribution of Amazon Cone project

Supported by

FINEP/PETROBRAS/BP/ELF/EXXON

MOBILE/AGIP

Developed between 2000 to 2002

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

Summary

(ii) However one of key points

is to establish which proportion

came from the Andean

mountains and from the

cratonic Amazonian area

(i) The Amazon Fan contains

a large contribution of

Andean material

1.Integration of geological information of Amazon Craton, Phanerozoic

covers and Setentrional Andes

2. Establish the main source areas and tectonic events of the Pre-Amazon

Fan Section and Amazon Fan based on isotope studies

Goals

Amazonian region with the main drainage systems de drenagem

MAIN GEOLOGICAL UNITS

OF THE AMAZONIAN REGION

AMAZONIAN CRATON

PHANEROZOIC COVER

SETENTRIONAL ANDES

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)

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)

Provenance and Sedimentary Deposits

•Detrital material preserve the history of source areas;

• Analises reflect with good resolution the isotope information of the source

0

1

2

3

4

5

6

7

8

9

200 600 1000 1400 1800 2200 2600 3000

Age ±1s fraction

526.8 3.4 0.45

974 13 0.05

1314 71 0.05

1803 41 0.09

2108 10 0.32

2681 15 0.05

0

2

4

6

8

10

12

14

1800 1900 2000 2100 2200 2300 2400 2500

Age ±1s fraction

2127 9.5 0.92

2211 21 0.08

RESULTS

• Inverse Stratigraphy

• Neoproterozoic and Paleoproterozoic sources

Neoproterozoic and Paleoproterozoic contribution

( local Mesoproterozoic and Archean)

Neoproterozoic/Eopal. and Paleoproterozoic

Increase of Neoproterozoic to Eopaleozoic

contribution

Contribuição Neoproterozoic/Eop e Paleoproterozoic

Sensível aumento da contribuição Neoproterozóica a

Upper section there is also a Mesoproterozoic

contribution

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)

Proto-Amazonas river

MIOCENO MÉDIO

INTEGRAÇÃO DOS DADOS ESTRATIGRÁFICOS E GEOCRONOLÓGICOS

Amazonas FAN –Pb-Pb e Sm-Nd Isotopes

Amazonas

Fan

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)

Dep

th (

m)

POÇO D

Early

Pliocene

Late

Miocene

Early

Miocene

Middle

Miocene

2 4 6 8 10 12 14 16 18

1000

1200

1400

1600

1800

2000

2200

Late Miocene

Mid

dle

Mio

cen

e

Ea

rly

Mio

cen

e

TD

M (in

Ma

)

Number of sample

Plio

cen

e

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.

Pb206/Pb207

Sm-Nd information for the source area

study of the Amazon Fan

•

ACP Archean

f Sm/Nd e Nd (o)* TDM (Ga)

from -0,31 to -0,66 from -16.10 to -48.6 2.40 to 3.07

MIP Paleoproterozoic

f Sm/Nd e Nd (o)* TDM

from -0.09 to -0.67 from -6.6 to -42.8 2.06 to 3.10

VTP Paleoproterozoic

f Sm/Nd e Nd (o)* TDM

from -0.18 to -0.54 from -2.2 to -37.0 1.47 to 2.85

RJP Paleo to Mesoproterozoic

f Sm/Nd e Nd (o)* TDM

from -0.32 to -0.62 from -13.2 to -29.6 1.70 to 2.40

R-SI/SP Mesoproterozoic

f Sm/Nd e Nd (o)* TDM

from -0.09 to -0.56 from 0.2 to -21.3 0.93 to 2.47

Sands of Rio Madre Dios (Bolivia and Peru) TDM

1,33 a 1,62 Ga

Geochronological Provinces of the

Amazonian Craton (Tassinari et al., 2000)

Amazonian Craton

rocks

Andean igneous

rocks

Amazon fan

This work

10 15 20 25 30

15

16

17

18

206 Pb/ 204 Pb

207 Pb/ 204 Pb

207 Pb/ 204 Pb

206 Pb/ 204 Pb

15.7

15.6

15.5

15.8

18.0 19.0 17.0

Amazon River

suspended sediments

Amazon fan Amazon delta

Andean igneous rocks Nazca Plate sediments

This study

older cratonic

rocks

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

tectono-sedimentary

Apatite FT Apparent ages obtained

from drill core sample (off-shore)

-1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16-50

0

50

100

150

200

250

300

350

400

WMA

Ag

es (

Ma)

Grains

FT data on apatite from Arkosean Sandstone (depth = 3838m). Number

of grains = 14, (W M Age ) = 9 ± 2 Ma (Error = 1SD), P (2v) ~0.02

(including 10 of 14 = 0.20).

Stratigraphic age: Pleistocene (~1.8 Ma)

Arkosean Sandstone

Apparent age of a drill core

sample = 9+/- 2Ma

Thermal hystory of onshore samples

2.8 Ma

10 Ma

24 Ma

Stratigraphic age:

Granodiorit2

Age 2100 Ma

(Paleoproterozoic)

TRÊS DENUDATION

EVENTS

- Histograms of thermal history of sample from the

Amapa – Guyana Shield

- Histograms of thermal history of sample from the

Carajas Region (MG-01 e CRN-08) –Guaporé Shield

Stratigraphic ages: 1800 Ma e 2800 Ma

Denudation events: 69 Ma, 43 Ma, 23 Ma, 12 Ma e 2.6-2.1 Ma

AFTA RESULTS

The analysed samples show complex history for a long time in the

temperature interval of 60 to 110oC (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. 22-16 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

(3.2-2.1 Ma)

Seção esquemática transversal

ao longo do Cone do Amazonas

Modificado de CTPETRO/FINEP/FAURGS – Projeto Cone do Amazonas

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 (9.3-12 Ma and 2.1-3.2 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

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)

Kick off meeting Brasília 2-3 May 2012

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).

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. 22-24 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 An-

des, quando ocorreu soerguimento significativo nos Andes Setentrio-

nais 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

(Plio-pleistoceno) é estimada em torno de 1200 m/Ma

A distribuição dos

comprimentos de traços

de uma amostra (evi-

denciadas nos histo-

gramas a, b ou c) é

diretamente função do

tipo de história térmica

(a, b ou c) a que a

amostra estava subme-

tida desde seu resfria-

mento abaixo de 110ºC.

A área entre 60 e 110º C

é dita Zona de Apaga-

mento Parcial (ZAP)

onde ocorre o encurta-

mento da maioria dos

traços (modificado de

Wagner, et al.,1972).