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28-490: The Barberton Greenstone Belt consists of a sequence of mafic to ultramafic lavas and metasedimentary rocks emplaced and deposited between 3.5 and 3.2 Ga. The granitoid rocks were emplaced over a 500-million-year time span and can be divided into two suites: The tonalite-trondhjemite-granodiorite (TTG) suite (emplaced approximately 3.5–3.2 Ga), and the granite– monzogranite – syenite granite (GMS) suite (emplaced approximately 3.2–3.1 Ga). The GMS suite are found over large parts of

56-635: A state or national park , it is patrolled by rangers armed with machine guns who accompany expeditions for protection against rhinos and elephants . Mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron . Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine , pyroxene , amphibole , and biotite . Common mafic rocks include basalt , diabase and gabbro . Mafic rocks often also contain calcium -rich varieties of plagioclase feldspar. Mafic materials can also be described as ferromagnesian . The term mafic

84-625: A listing published in October 2022. The organisation defines an 'IUGS Geological Heritage Site' as 'a key place with geological elements and/or processes of international scientific relevance, used as a reference, and/or with a substantial contribution to the development of geological sciences through history.' The outcrops of the Barberton Greenstone Belt had previously been inscribed on UNESCO 's list of World Heritage Sites in 2008 as 'Barbeton Makhonjwa Mountains. Although not

112-473: A major structural lineament and mountain pass, Tonale Pass , in the Italian and Austrian Alps . The name was first applied by Gerhard vom Rath in 1864. The term adamellite was originally applied by A. Cathrein in 1890 to orthoclase -bearing tonalite (likely a granodiorite ) at Monte Adamello, Italy, in 1890, but later came to refer to quartz monzonite , and is now a deprecated term. Trondhjemite

140-480: A possible genetic relation between the two formations and support the theory that a combined continent Vaalbara existed ~3.45 Ga. In respect of the research carried out on this 'unique remnant of ancient Earth's crust', the 'Archaean Barberton Greenstone Belt' was included by the International Union of Geological Sciences (IUGS) in its assemblage of 100 'geological heritage sites' around the world in

168-469: A sequence of mafic to ultramafic lavas and metasedimentary rocks emplaced and deposited between 3.5 and 3.2 Ga. The granitoid rocks were emplaced over a 500 million year time span and can be divided into two suites. The TTG suite (emplaced approximately 3.5–3.2 Ga) contains tonalites , trondhjemites and granodiorites ; and the GMS suite (emplaced approximately 3.2–3.1 Ga) includes granites , monzogranites and

196-498: A silica content between 45 and 55 wt% , corresponding to the silica content of basalt in the TAS classification . Such rocks are enriched in iron, magnesium and calcium and typically dark in color. In contrast, the felsic rocks are typically light in color and enriched in aluminium and silicon along with potassium and sodium . The mafic rocks also typically have a higher density than felsic rocks. The term roughly corresponds to

224-567: A small syenite –granite complex. According to a study by Yearron et al. (2003): Some controversy exists pertaining to the origin and emplacement of Archaean felsic suites. According to a dissertation by Louzada (2003): "The upper part of the Hooggenoeg Formation is characterized by ultramafic massive and pillow lavas , a trondhjemitic suite of silicified felsic intrusive and flow banded rocks, and sedimentary chert beds. Veins of felsic, chert and ultramafic material intrude

252-575: Is a portmanteau of "magnesium" and "ferric" and was coined by Charles Whitman Cross , Joseph P. Iddings , Louis V. Pirsson , and Henry Stephens Washington in 1912. Cross' group had previously divided the major rock-forming minerals found in igneous rocks into salic minerals, such as quartz , feldspars , or feldspathoids , and femic minerals, such as olivine and pyroxene . However, micas and aluminium-rich amphiboles were excluded, while some calcium minerals containing little iron or magnesium, such as wollastonite or apatite , were included in

280-403: Is an igneous , plutonic ( intrusive ) rock , of felsic composition, with phaneritic (coarse-grained) texture. Feldspar is present as plagioclase (typically oligoclase or andesine ) with alkali feldspar making up less than 10% of the total feldspar content. Quartz (SiO 2 ) is present as more than 20% of the total quartz-alkali feldspar-plagioclase-feldspathoid ( QAPF ) content of

308-622: Is an orthoclase -deficient variety of sodium -rich tonalite with minor biotite as the only mafic mineral, named after Norway 's third largest city, Trondheim . Tonalites, together with granodiorites , are characteristic of calc-alkaline batholiths formed above subduction zones . Volcanic rocks : Subvolcanic rocks : Plutonic rocks : Picrite basalt Peridotite Basalt Diabase (Dolerite) Gabbro Andesite Microdiorite Diorite Dacite Microgranodiorite Granodiorite Rhyolite Microgranite Granite This igneous rock -related article

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336-466: Is not used as a rock classification in the IUGS classification scheme. Mafic rocks are sometimes more precisely defined as igneous rocks with a high proportion of pyroxene and olivine, so that their color index (the volume fraction of dark mafic minerals) is between 50 and 90. Most mafic volcanic rocks are more precisely classified as basalts . Chemically, mafic rocks are sometimes defined as rocks with

364-463: The International Union of Geological Sciences (IUGS) classification of igneous rocks, include some light-colored ferromagnesian minerals, such as melilite , in the mafic mineral fraction. Accessory minerals , such as zircon or apatite, may also be included in the mafic mineral fraction for purposes of precise classification. When applied to rocks, the term mafic is used primarily as a field term to describe dark-colored igneous rocks. The term

392-634: The Barberton granite–gneiss terrane is made up of granite sheets. The structurally higher parts are underlain by an anastomosing network of steeply dipping, variably deformed dikes and sheets. According to a study done by Westraat et al. (2005): "Multiple intrusive relationships and geochronological evidence suggests that granite sheeting and the assembly of the pluton occurred over a period of 3–13 million years. The spatial and temporal relationship between deformation and magma emplacement reflects episodes of incremental dilation related to deformation along

420-691: The Hooggenoeg Formation were most likely not parental for the felsic rocks. Subduction processes may have played a role in the generation of the felsic rocks, but a tectonic setting for the ultramafic rocks remains uncertain. The felsic units of the Hooggenoeg Formation are very similar to those of the Panorama Formation of the Early Archaean Coppin Gap greenstone belt of Western Australia (See Yilgarn Craton ). Similarities in geological setting, petrography , and geochemical ( trace elements in particular) characteristics suggest

448-584: The Kaapvaal Craton and their emplacement coincides with the first stabilisation of the central parts of the craton. "The GMS suite in the Barberton granite-greenstone terrane shows very different internal and external characteristics from the earlier TTG suite. Individual plutons may cover several thousand square kilometres and these composite granitoid bodies have traditionally been referred to as batholiths, alluding to their compositionally and texturally heterogeneous nature and enormous areal extent. For

476-492: The S2 impact, which dates to 3.26 billion years ago, probably caused extremely strong earthquakes worldwide, megatsunamis thousands of meters high, as well as boiling the surface of the oceans, resulting in tens of meters of global ocean evaporation. Earth would have also been plunged into darkness lasting years to decades. The Barberton Mountain is a well preserved pre-3.0 Ga granite-greenstone terrane. The greenstone belt consists of

504-403: The area. Apparently each block represents a cycle of arc-related magmatism and sedimentation. The Hooggenoeg Formation of the Barberton Greenstone Belt is dated at 3.45 Ga. and evolved through magmatism. This crustal development phase was followed by a period of Mesoarchaean cratonic magmatism (3.1–3.0 Ga) and is marked by the formation of a large crescent-shaped, juvenile arc that was accreted onto

532-413: The belt. The depositional environment is thought to be a shoaling shallow sea in which the Hooggenoeg Formation has been deposited in a west-block down, listric faulted, synsedimentary setting." The Hooggenoeg Formation felsic rocks can be divided into two groups: an intrusive group of interlocking and shallow intrusive rocks, and a porphyritic group of rocks from the veins. Lavas from the upper part of

560-422: The bounding shear zones and granite sheeting. The transition to the mainly subhorizontal granite sheets at higher structural levels of the tabular Mpuluzi batholith indicates the intrusion of the granites during subhorizontal regional shortening, where the reorientation of the minimum normal stress to vertical attitudes at the shallow levels of emplacement allowed for vertical dilation and subhorizontal emplacement of

588-408: The felsic unit are too altered to be assigned to one of these groups. The intrusive group is related to the tonalite - trondhjemite - granodiorite TTG-suite Stolzburg Pluton , which intruded along the southern margin of the Barberton Greenstone Belt. Melting of an amphibolite quartz eclogite has been suggested as a probable origin for these high-Al 2 O 3 felsic magmas. Ultramafic rocks of

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616-455: The femic minerals. Cross and his coinvestigators later clarified that micas and aluminium amphiboles belonged to a separate category of alferric minerals. They then introduced the term mafic for ferromagnesian minerals of all types, in preference to the term femag coined by A. Johannsen in 1911, whose sound they disliked. The term mafic is still widely used for dark-colored ferromagnesian minerals. Modern classification schemes, such as

644-434: The granite sheets." The Barberton Greenstone Belt records impact events in 8 layers containing spherules (tiny spheres which form from condensed vapour created by the impact) dubbed S1 through S8, spanning from about 3.5 to 3.2 billion years ago, which likely represent at least 4 but perhaps as many as 8 or more impact events. The impactors that generated these events are thought to have been much larger than those that created

672-418: The largest known still existing craters/impact structures on Earth ( Vredefort and Chicxulub ), with the impactors having an estimated diameter of ~20–50 kilometres (12–31 mi), with the craters generated by these impacts having an estimated diameter of 400–1,000 kilometres (250–620 mi). The Barberton deposits are thought to have been distant from the impacts. The most powerful of the impacts such as

700-495: The most part, the plutons appear undeformed." The Barberton area underwent two tectonic episodes of terrane accretion at about 3.5 and 3.2 Ga. Early stages of shield development are exposed in the Barberton Mountains where the continent formation first took place by magmatic accretion and tectonic amalgamation of small protocontinental blocks. Several small diachronous blocks (3.6–3.2 Ga) have been found in

728-411: The northern and western margins of the evolving Kaapvaal shield. Archaean greenstone belts are hypothesized to have been formed from passive margin oceanic crust that became part of an extensive subduction-undercut margin. The TTG intrusions are thought to have been formed by post-subduction magmatism when subduction was halted, perhaps by arrival of a micro- craton . The 3.1 Ga Mpuluzi batholith in

756-677: The older basic rock class. Mafic lava , before cooling, has a low viscosity , in comparison with felsic lava, due to the lower silica content in mafic magma . Water and other volatiles can more easily and gradually escape from mafic lava. As a result, eruptions of volcanoes made of mafic lavas are less explosively violent than felsic-lava eruptions. Volcanic rocks : Subvolcanic rocks : Plutonic rocks : Picrite basalt Peridotite Basalt Diabase (Dolerite) Gabbro Andesite Microdiorite Diorite Dacite Microgranodiorite Granodiorite Rhyolite Microgranite Granite Tonalite Tonalite

784-465: The rock. Amphiboles and biotite are common accessory minerals . In older references tonalite is sometimes used as a synonym for quartz diorite . However the current IUGS classification defines tonalite as having greater than 20% quartz, while quartz diorite varies its quartz content from 5 to 20%. The name is derived from the type locality of tonalites, adjacent to the Tonale Line,

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