The Geochemistry And Geochronology Of The Barby Formation In The Sinclair Area, Southern Namibia

SSA Research THERESIA R. MALOBELA 102 PAGES (21002 WORDS) Thesis
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ABSTRACT

Volcanic and sedimentary rocks of the Sinclair Supergroup occur in the Konkiep

Terrane of Southern Namibia. Three volcanic and sedimentary cycles are recognised.

The Barby Formation belongs to the second cycle which consists of the Kunjas

Formation, Barby Formation and the Guperas Formation. In this work, the volcanic

rocks of the Barby Formation, a key unit in the Sinclair area are described and dated.

The coeval Spes Bona Syenite and the Tiras Granite are also described and dated. The

rock types in the Barby Formation are rhyolites, basaltic trachyandesites, trachybasalts

and trachydacites as well as volcanoclastic rocks. The rocks are largely undeformed

and partly altered by deuteric processes and also mildly metamorphosed. Based on

geochemistry of the rock samples and previous work, the bulk of rock types are calcalkaline

although some alkaline rocks are present. U-Pb dating and Lu-Hf isotopic

microbeam analyses were made on zircon and baddeleyite grains from four samples

using cathodoluminescent images. A Barby rhomb porphyry sample gives an U-Pb

baddeleyite age of 1217 ±2 Ma and a Barby felsic tuff has an 207Pb/206Pb zircon age of

1214 ±5 Ma. The Spes Bona Syenite which intrudes the Barby formation has a U-Pb

baddeleyite age of 1217 ±3 Ma and an indistinguishable Rb-Sr biotite isochron age of

1238 ±20 Ma, showing that there was no regional metamorphic event. Subduction zone

assemblages are generally made of high potassium basalts or calc-alkaline association.

The Barby Formation records such assemblages. The Barby Formation reflects a

subduction event which took place during the assembly of the Rodinia supercontinent.

It is slightly younger at 1204 ±9 Ma and reflects the end of subduction-related

volcanism due to the collision of Namaqua terranes with the Konkiep Terrane. The

Spes Bona syenite and the Barby units have Lu-Hf crustal residence ages between

iii

1682 and 1873 Ma suggesting the two units probably formed from a mixture of

juvenile and older crustal material.

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APA

SSA, R (2021). The Geochemistry And Geochronology Of The Barby Formation In The Sinclair Area, Southern Namibia. Afribary.com: Retrieved May 10, 2021, from https://afribary.com/works/the-geochemistry-and-geochronology-of-the-barby-formation-in-the-sinclair-area-southern-namibia

MLA 8th

Research, SSA. "The Geochemistry And Geochronology Of The Barby Formation In The Sinclair Area, Southern Namibia" Afribary.com. Afribary.com, 27 Apr. 2021, https://afribary.com/works/the-geochemistry-and-geochronology-of-the-barby-formation-in-the-sinclair-area-southern-namibia . Accessed 10 May. 2021.

MLA7

Research, SSA. "The Geochemistry And Geochronology Of The Barby Formation In The Sinclair Area, Southern Namibia". Afribary.com, Afribary.com, 27 Apr. 2021. Web. 10 May. 2021. < https://afribary.com/works/the-geochemistry-and-geochronology-of-the-barby-formation-in-the-sinclair-area-southern-namibia >.

Chicago

Research, SSA. "The Geochemistry And Geochronology Of The Barby Formation In The Sinclair Area, Southern Namibia" Afribary.com (2021). Accessed May 10, 2021. https://afribary.com/works/the-geochemistry-and-geochronology-of-the-barby-formation-in-the-sinclair-area-southern-namibia