ISSN:
0016-7835
Keywords:
Key words Pan-African
;
tectonics
;
geochemistry
;
crustal extension
;
island arc tholeiite
;
calc-alkali gabbro
Source:
Springer Online Journal Archives 1860-2000
Topics:
Geosciences
Notes:
Abstract The Neoproterozoic Ougda magmatic complex occurs within platformal carbonate rocks in the western part of the Pan-African fold belt of the Tuareg shield (NW Africa). It is composed of ∼800 Ma old, relatively high P–T (i.e., Grt+Cpx-bearing: P〉5 kbar; T∼900 °C), tholeiitic mafic/ultramafic cumulates and related rocks intruded by intermediate to mafic calc-alkali plutons (e.g., Cpx+Hbl-bearing gabbro) and dikes. Apparent contrasts in structural level of crystallization indicate that the calc-alkali rocks are significantly younger than the tholeiites, which temporally correlate with a period of regional extension in this part of Africa. Intrusion of the calc-alkali rocks may have occurred during the formation of an arc after the tholeiitic rocks had been (diapirically?) emplaced within the shelf carbonates, and prior to (〉630 Ma) the Pan-African orogeny. Data reported herein indicate that the Ougda complex records the inception and demise of a Neoproterozoic ocean basin. Similar crustal sections have been described from collisional (e.g., Aleutian islands) and extensional (e.g., Ivrea-Verbano zone) settings, indicating that processes operating in both environments can generate nearly indistinguishable igneous suites; the prevalence of shallow-level calc-alkali rocks in both settings may mask the presence of more mafic, tholeiitic rocks at depth.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s005310050101
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