Petrološki i geohemijski efekti procesa parcijalnog stapanja metasomatizma u subkontinentalnom omotaču ispod južne Libije
Petrological and geochemical effects of partial melting and metasomatic processes in the subcontinental mantle underneath south Libya : doctoral dissertation
Докторанд
Radivojević, MašaМентор
Cvetković, VladicaЧланови комисије
Toljić, MarinkoPrelević, Dejan
Banješević, Miodrag
Метаподаци
Приказ свих података о дисертацијиСажетак
U disertaciji su prikazani rezultati proučavanja kenozojskih bazalta i u njima pronaĎenih ksenolita
iz oblasti Jabal Eghei (juţna Libija). UtvrĎeno je da su bazalti obrazovani u dvema vulkanskim
epizodama; za vreme prve epizode (16-4 Ma) nastali su tranzicioni bazalti (TB), a za vreme druge
(4–≤1 Ma) formirani su alkalni bazalti/bazaniti (AB/B). Primarne magme i TB i AB/B nastale su
stapanjem sličnog metasomatizovanog granatskog peridotita uz najvaţniju razliku u stepenu
stapanja (TB: 3–5 %, AB/B: ≤1%). TB pokazuju korelaciju izmeĎu K/Ar starosti i nekih
geohemijskih parametara (npr. La/Ce i K/Nb), što ukazuje da se za vreme prve epizode odvijala
postepena promena petrogenetsko-geodinamičkih uslova.
Ksenoliti omotača su pronaĎeni u mlaĎim AB/B lavama, dominantno su predstavljeni fertilnim
lerzolitom i dele se u dve strukturne grupe: 1) nedeformisani (protogranularni) i 2) deformisani
(porfiroklastični ±ekvigranularni) ksenoliti. Nedeformisani ksenoliti su postigli ravnoteţu na višim
te...mperaturama (>1000 oC) i osiromašeniji su bazaltnom komponentom (do 10-13 %) od
deformisanih (<1000 oC, odnosno 2-7 %), pri čemu obe strukturne grupe sadrţe tragove tzv.
‘skrivenog‘ metasomatizma, dok neki deformisani ksenoliti pokazuju tragove i tzv. ‘nevidiljvog‘
metasomatizma.
Na osnovu sinteze podataka o bazaltima i ksenolitima predloţen je geohemijsko-geodinamički
model evolucije gornjeg omotača ispod područja Jabal Eghei u juţnoj Libiji, koji obuhvata četiri
perioda: 1) predvulkanski period (>20 Ma), 2) vreme metasomatizma (20-16 Ma), 3) period
obrazovanja TB (~16 – ~4 Ma), i 4) period zahvatanja ksenolita i erupcije AB/B (~4 – ~1 Ma).
The Thesis reports and discusses the results of investigations of late Cenozoic basalts and basaltborne mantle xenoliths of the Jabal Eghei area (south Libya). The basalts formed during two
volcanic episodes, first at 16-4 Ma and second at 4–≤1 Ma, during which transitional basalts (TB)
and alkali basalt/basanite (AB/B) originated, respectively. Both TB and AB/B primary melts formed
via partial melting of a similar metasomatized garnet-bearing peridotite mantle, with the only
difference in the amount of melting, ranging 3–5 %, and ≤1% for TB and AB/B, respectively. TB
shows a correlation between the K/Ar ages and some geochemical parameters (e.g., La/Ce and
K/Nb), which indicates that the first volcanic episode was associated with gradual changes in
petrogenetic-geodynamic conditions.
Mantle xenoliths (found in younger AB/B lavas, only) are represented by fertile lherzolite and are
distinguished into: 1) non-deformed (protogranular) and 2) deformed (porphyroclastic
±equigranular) xenol...iths. The non-deformed xenoliths equilibrated at higher temperature (>1000
oC) and are more depleted (10-13 %) than the deformed ones (<1000 oC and 2-7 %, respectively).
Both groups of xenoliths display evidence of cryptic metasomatism, whereas some non-deformed
samples have preserved traces of so-called ‘stealth‘ metasomatism.
The synthesis of all the available data on the basalts and the xenoliths allowed us to propose a
simplified model of geochemical-geodynamic evolution of the lithospheric mantle underneath
southern Libya; the model involves four different steps: 1) the pre-volcanic period (>20 Ma), 2) the
time of metasomatism (20–16 Ma), 3) the formation of TB (16–4 Ma), and 4) the capture of
xenoliths and the euption of AB/B (4–1 Ma).