Drakensberg and Lebombo Groups

Ama-lava akhukhula umhlabakazi

Map Lebombo Drakensberg

Ukuchitheka kwama-lava ngaphezu kwe-Gondwana eminyakeni eyizigidi ezinga 180 eyedlule, kukhomba ukuqala kokuhlukana kwe-Gondwana. Izinsalela zama-lava ayenohlonze akha izintaba zaseLesotho neLebombo. Ukuqoqeka kwe-basalt enohlonze oluyikhilomitha nohafu yesikhathi se-Jurassic ibonakala igudla izintaba zoKhahlamba.

Uplift

1

I-Gondwana yaphakamiseka yaklayeka emngceleni ophakathi kwe-Africa ne-Antarctica. Lokhu kwenza umsele nokuhlukana kwemihlabakazi yombili.

Rift widens

2

Umsele wanwebeka noqweqwe lolwandle lwaqala ukwakheka phakathi kwemihlabakazi. Izinhlayiya zomhlabathi zabekeka olwandle lwaseNdiya olusanda kwakheka.

Mid oceanic ridge

3

Ukuklayeka kwanqamuka emngceleni wemihlabakazi ngenxa yokwembathiswa izinhlayiya ezaziqhamuka emifuleni. Ulwandle olusha lusaqhubeka nokwakheka emagqumeni aphakathi nolwandle.

Sills are horizontal and dykes are vertical intrusions of igneous rocks. Dolerite sills are common throughout inland KZN in sedimentary rocks of the Karoo supergroup.

Drakensberg Amphitheatre
The 'High Berg' is made up of basalt lavas from the Drakensberg group. Amphitheatre, Drakensberg (Photo: T. Reinhardt)

I-magma (itshe eliluketshezi elishisayo) yazivulela indlela eyangaphezu komhlabathi kwiminkenke eluchungechunge. Ukuqina kwe-magma phakathi kwale minkenke kwakheka ama-dolerite angama-sill kanye nama-dyke.

Dolerite dyke in basalt lava (move your mouse here)

The sills often form flat areas and weather to form a very dark red soil. A sill may also form resistant cliffs, such as at the Howick falls.

Howick Falls
Howick Falls

Photo source: https://en.wikipedia.org/wiki/Howick_Falls#/media/File:Howick-Falls-November-2009.jpg

Intabamlilo yokugcina yaholela ekwakheni izintaba zaseLebombo. Lokhu kwalandelwa ukuphakamiseka nokuklayeka okwahlukanisa i-Africa ne-Antarctica.

Lebombo Mountains
Lebombo mountain, south of Jozini
Lebombo Mountain Mkuze Falls
Lebombo mountain and Mkuzi falls, south of Jozini
General mineral composition of igneous rocks and their silica content

Basalt (igneous – volcanic)

Volcanic eruption

Basalt

The basalt was extruded at the surface as a volcanic eruption of lava. It is equivalent to dolerite (see chart above), except that it cooled quickly making the crystals very small (i.e. fine grained). The typical white to greenish blebs in the basalt were formed later when the minerals infilled preserved gas bubbles. Basalt is the most common rock on the Earth surface. It is dark coloured, fine-grained basic (low silica (45-52% and relatively high calcium, iron and magnesium) volcanic rock, composed mainly of the minerals calcium plagioclase and pyroxene, usually augite, with or without olivine. 

Dolerite (igneous – volcanic)

Volcanic eruption

Dolerite

Dolerite is a medium- to fine grained, dark crystalline rock which formed underground when lava feeding the volcanoes cooled in its feeder pipes – sills (horizontal) and dykes (vertical). Dolerite dykes and sills are very common, often seen intruding other rock layers. Because of its high iron content, dolerite weathers to a bright red soil. Dolerite is the medium grained equivalent of basalt and gabbro.

Rhyolite (igneous – volcanic)

Volcanic eruptions

GEM_KZNGeolrhyolite

Rhyolite lavas are fine grained, but differ from basalt in their lighter colour (normally light pinkish) due to a higher silica and lower magnesium and iron content than basalt lavas (which are dark). Some rhyolite lavas will have larger crystals of quartz and feldspar in a finer-grained groundmass.

When rhyolite lava erupts on the surface , smaller crystals often respond to the flow by aligning themselves into bands. This effect is called flow-banding.