OVERVIEW OF THE SOMALI MINERAL POTENTIAL ZONES

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SUMMARY OF SOMALIA GEOLOGY

 


Somalia is underlain principally by Mesozoic and Tertiary marine and Continental-margin sedimentary rocks deposited uncomfortably on              Precambrian Metamorphic and igneous rocks. Quaternary and Holocene alluvial and alluvial Deposits cover much of the southeastern coastal area. The Precambrian rocks Are exposed in the northern block-fault mountains and in a broad uplift in the Bur region, along the Indian Ocean in southern Somalia. The structure of the region is dominated by the apparently faultcontrolled, southwest-trending margin of the Indian Ocean; the rifted and block-faulted, east-northeast trending margin of the Gulf of Aden; and the complexly faulted East African Rift on the west. These structures were formed by major crustal plate movements related to formation of the Indian Ocean, Gulf of Aden, and Red Sea during the Miocene. These tectonic features are characterized by normal faulting and isostatic uplift related to regional extension.

Precambrian

The Precambrian rocks of Somalia are divided into an older unit, consisting of amphibolite-facies biotite and amphibole gneiss, migmatite, amphibolite, quartzite calc-silicate rock, and marble; and a younger unit, consisting of greenschist facies variegated slate, quartzite, dolomitic marble, and metaconglomerate. the older unit as forming all Precambrian outcrops in Somalia except for a zone where the younger unit is discontinuously exposed northeast of Erigavo to near Bender Cassion. indicate that this relative chronology is based on comparison with similarly metamorphosed rocks in Ethiopia. Their younger unit generally corresponds to the Inda Ad Series as used in Somalia  This two-fold stratigraphy in northern Somalia has been questioned by Greenwood (1960) and Osman and others (1976), who suggest that an unconformity has not been established between the two units.

Bur Area

Precambrian rocks of the Bur Region are divided into four units: (1) biotite gneiss; (2) calc-silicate rocks, marble, and quartzite; (3) mafic intrusive rocks; and (4) biotite monzogranite.

The calc-silicate, marble, and quartzite unit is inferred to unconformably overlie the biotite gneiss unit Unit 1 contains subordinate intercalated amphibolite and

quartzite. Unit 2 contains subordinate biotite gneiss and varies from predominantly calc-silicate and marble on the east to predominantly quartzite and banded iron formation on the west These layered rocks are metamorphosed to amphibolite facies and are tightly to isoclinally folded. The foliation generally strikes northwest except in minor domes and

near a forcefully emplaced monzogranite complex east of Dinsor. The foliation generally dips to the northeast but shows many local reversals suggestive of isoclinal folding and widely varying dips in and near the monzogranite complex. Mafic intrusive rocks form five plutons of moderate size probably largely composed of gabbro but may also include diorite. The monzogranite is pink to yellow, medium to coarse grained, commonly contains large phenocrysts of microcline and biotite, and locally is devoid of mafic minerals. This unit also contains subordinate aplite, syenogranite, and syenite. The syenogranite and syenite contain appreciable coarse magnetite. 

Part one to be continue 

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