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Precambrian basement within the septentrional Andes: Age and geological
evolution
Article · January 1980
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Umberto Giuseppe Cordani
University of São Paulo
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PRECAmRIAN -BASEmNT WITllIN THE SEPTENTRIONAI. ANDES : -AGE AND GEOLOGICAI. EVOLU- .-,=.:` on t`he .natufe. o-f.`.`thB.`úóic`aniám ih'-.
TI0N. L. ANDRE, S.. -DEUTSCH.-.&-J.` MICHOT,``.
J. ALVAREZ and U.G.CORDANI.
-Several outcrops of igneous and metamorphic roc.ks, belonging to the Andean Along the `southBrn :bordBi cicf thB `t
lgnimbrlt.es an`d vol`canlc~ tufs f`c]ri
basement, are descrí1]ed in Colombia. .Some of them have yielded clearly pre- rock§, taken from boreholes and q`
cambrian radiometríc ages , :such as t:he Dibü11a gneisses of the` Sierra Nevada de geDchemica-l
"Ni, zn).h ` approaóh
:Í> ,`(maJc)r`
-Á anc]` t]
Santa Ma`r,ta. massif (?rpund 1300 n.y:) , a few gneísses and¡ ambri-bolites of the
- Santander.massif, and some isolat.éd. outcr.ops within t:he Central. `and . East.érn They show evidenc`é á+ io.w grBensc-t
Cordilleras-, (940-.1600 ü;y..` age range) . Addi¬í-onal .radiometric dates were obtai-- .^ data of 390 ri.Y. are.1ntei`pr`eted `{
"ned.on sohe gneissic ,.rpcks 'o-f. the Garzon nassiÍ , confirming i'ts suppos`ed lat.e` _ rcick.s caused by t:he loúer` devciniai
` -\. precatnbrian.age.. Ihe imore `§igni'ficant results are the Rb-Sr whole rock deTermi`=. The§e metavo.Icanics. can be divldet
is -mainly composed -of i`hyc]lite§ ai
::t=:::h:::r::da:::t::±58u:.;=E
'/sr86 `ratí-o of 0.704 .
L;s= ¥t:2exa:g±¥Eí;::r:o±¥;: í:=En:n:t::Íe;:g;,`.. tholelitic.trend} .is `i`epr.e§ented` l
xenol±.ths in dacitic rcic}ks. These
.. part .of the lineament, appear` tci- ]
These geneíall-y .1ate Precaiibrian ages obtained so far on the basement rock§ of ' tlc magma by xenoliths. >'The gengs:
the Septentrioná1 Andes a're riot compatible with the-observed age provinces -`of a§ nQ dlaba§1`c c]ykes are found. `
the Guyana Shield. ín Colonbia, Venezuela, the Guianas and northern Brazil,. -This volcanlsm, by lts. gec]giaphic¬
whích are substantially.older. .However, a time correlation can be found with the quB§tion c)f its po§ition r.elal
the Rondonian mobile belt (1050-1400 m.y.) , whích occupies the sout:hwestémmost
par.t of Eui.opB, accctrding t;o the i
part of Amazoní:an crátoníc region. This beit exhibits NW-SE structurai trends
and may extend below the Llanos towards the Garzon massif . Within the Andean
mountain chaín, the,st:ruttures could bend to a N-S general direction, and a
further correiation éan be suggested with the Grenviiie age provínce of North
America, of simílar age.
Origím of large mas3seB of 1
ANI)REEV Gennadíi , Geologics
The Synnyr massif in the iNo
the largegt alkaline massiv
pseudoleucitic syenites ín
the body vary from 10 to 20
Nature, origine et évolution des basaltes aicaiins de ia région de Lisbonne, to 3,5 km. Such large accum
Portugal has no analogties. The alkal
ALVES, C.A. Matos; RODRIGUES, B.N.; SERRALHEIRO, A.; SANTOS, A.R. et FARIA, ly differ from the Bame one
A.P.,Centro de-Geologi`a (iN.ic), Facu,]dede de Ciéncias, Lisboa, Portugal cloee to granitío rocks by
The admixture conten`tEi in t
on étudie le "c.ompléxe basaltique" d]áge tertiaire et nature alcaline á oli- are identioal to the .conten
Phe increaEie of the potasgi
;:::hf:i-;:er::::nt::i:,:::::n:t::ig:;::edia:::y::o|:fi::eáu,::::::::::fu:e:t neously with the decreaBe o
dc)nnées et considérations gé`nétiques. dans le cadre géodynamique de 1 'ouvertu- Bíble to eiolude the` uBe of
re de I'Atlantique et de la rotation de la peninsule lberique, en comparat- the oi.igin of leuoitic rook
son avec certaines series des Tles atlantiques et en particulier avec 1 'Ar- nesiB of the Synnyr alkalin
"chTpe] de Madére. `<-: the alkaline rocks and sali
On essaye ]a détérmination du magma basaltique original á partir de la con- ::u*gH:fa:::a!::e::a::#:
sidération des diagrammes basés sur un indice d'évolution.magmatique (PCA), the alkaline ones undei. the
et étant données les teneurs de certains éléments des TR`on choisi un modé- preceded the meltÍJig stage.
Ie de manteau supérieur et on adopte iin schéma de dérivation basaltique. and aluminium as. basi`c oomp
rooks were Beparated aB`a r
ation when the mBgma was li
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