Vredefort Dome Shattercones na Shock Metamorphics

© David Fleminger

Ku gandliwa ko Engetelela ka Misava

E handle ka xirhengele xa Vredefort, kutlumbiwa ka misava loku kusiye swotala endzhaku, swin’wani switsariwe emaribyeni. Swilo leswi swikumeke eka tindzhawu tohlaya letinga khumbeka eka planet hinkwayo, naswona sweswi switekiwa tani hi swigandlu leswitiyisisaka mahlori ya muxaka lowu. Xosungula kuna leyara yo bumbula ya swilo leswnga hangalaka loko kuhumelela mahlori lawa yanga ta na mpfula ya matimba loko yina eka ndzhawu yoringana tikilomitara ta madzana dzana. Leyara leyikulu ya ribye leringa sala endzhaku ko khukhuriwa himpfula na swikamba swakona hiswona swobumbula exikarhi ka ndzhawu leyi ya dome, leswi lalaka loko uya u suka exikarhi ka ndzhawu yoleyo.

Xikombiso xotiya lexi landzelaka lexi kombaka matimba lawakulu i ku cinca ka maribye hi woxe. Loko ku buluka kuva kona exibakabakeni, swivanga leswaku kuva na mahiselo lawa ya hundzaka 10 000 degrees centigrade naswona leswi switisa ntshikelelo lowufikaka eka madzanadzana yati gigapascals. Nhlayo ya matimba lawa yakulu na kutisa ku hisa loku endlaka leswaku maribye ya cinca yava eka xivumbeko xin’wana. Maendlelo lawa yavuriwa ‘shock metamorphics’. Xin’wani xa swikombiso swale rivaleni swa laha kungava nati metamorphic leti i ‘shattercones’.

A Shattercone

Shattercone ahi leswi u swikumaka loko u wisa ice-cream. Kambe, loku iku pandzeka kokarhi loku humelelaka emaribyeni loko kuhundza gandlati rokarhi. Mbuyelo wakona wutikomba hikuva ku huma xivumbeko xa triangle lexi sukelaka eka tindzhawu leti fanaka. Ti shattercones tivonakarisiwa eka matlhelo yohambana hambana eka ndzhawu ya Vredefort Dome, naswona kuvikiwa leswaku loko wo longoloxa kahle ti shattercones, unga kota kutiva leswaku kubuluka lokungava kona akuri ka muxaka wihi.

Xobiha xakona hileswaku, vampfhumba va manguva lawa vasungula ku tshovelela ti shattercones tani hi xikombiso xaleswaku va ke vanga fika eka ndzhawu liya. Lawa i maendlelo lawa ya talaka kuhumelela lawa ya faneleke ku yimisiwa naswona nhlayiso wati shattercones kutava xin’wana xa leswi endliwaka hi vurhangeri na vulawuri bya Dome leyintshwa.

Metamorphosis ya Maribye

Xin’wana xa swikombiso swa maribye ya Vredefort i milayeni leyifanaka na misiha yo dzwihala leyi vonakaka eka maribye yovonikela ya granite. Milayeni leyi ya hambana kuya hiku leha naku bumbula, kambe yin’wana ya ringana. Muxaka lowu wa nghilazi, ribye ro dzwihala wuvuriwa ‘pseudotachylite’ naswona rivumbeka loko kuri na mahiselo ya xiyimo xale henhla swinene lawa ya endlaka leswaku ribye ri cinca tikhemikali leti tinga eka rona. Kufana na maribye ya tachylite lawa ya kumekaka laha kungava nati volcano na laha ku khuhlanaka exikarhi ka ti tectonic plates swiendla leswaku kuhuma kuhisa. Rito ‘pseudo’ ra tirhisiwa loko kungari na vumbhoni bya volcano.

Mahiselo lawa yohlamarisa na ntshikelelo swihumesiwa loko ya banana leswi tlhelaka swiendla metamorphosis leyikulu swinene ya maribye, leyivuriwaka ‘granophyre’. Lexi i xiyimo xa swiphemu swa maribye yo dzwihala lawa yanga hlengeletana loko yarikarhi ya phemeleleka, kutani ya endla ribye lerikulu, ra melt-rock, leri andlalekaka kuringana tikilomitara to hlaya nyana. Nhlangano lowu wa maribye lawa na swiphemu swa zircon endzhaku ka kufayana ka maribye lawa swiendle leswaku vativi va sayense vakota ku nyika singita leringa humelela e Vredefort masiku yohlawuleka ya 2.023 wa mabiliyoni wa malembe.

Shock-Deformation Features

Exikarhi ka swin’wana swankoka eka swihlawulekisi swa maribye lawa ya fayaneke leswikumekaka eka lawa yotala eka tindzhawu leti yanga fayana kona i coesite na stishovite. Lawa i mavito ya matimba swinene lawa yanga nyikiwa timinerali letikumekaka emaribyeni tani hi quartz. Lawa yavakona loko kutshikeleriwa quartz yitlhela yihisiwa laha yikondzaka yi cinca kufikela yiva eka xivumbeko xa crystal lattice. Masalela ya timinerali leti hivumbirhi katona yatala ku kumeka eka swirhengele leswikumekaka endzhaku kaloko kuve na mahlori yotano, xikan’we nalaha ku ringeteriwaka matlharhi ya nuclear.

Vito ra ntolovelo raku endliwa ka leswi rivuriwa ‘shocked quartz’. Vumbhoni byohetelela bya shock metamorphism abyi vonaki hi matihlo ya nyama. Vulavisisi bya xiyimi xale henhla, laha maribye ya tsemeleriwaka kutani yaya kamberiwa ehansi ka electron microscope, yakombete leswaku leswi swihumelele eka xiyimo xa atomic. Leswi swihumelela tani hi nkavanyeto wa lowu fanaka na xihahampfuka eka swipetlupetlu swa quartz, loko swihumesiwa, swiva xikombiso lexinga tiya xa ku fayana loku.

Ku gandliwa ka Dayimani

Yin’wani yotsakisa ya maendliwelo yosusa xivumbeko xa maribye leyinga kumengakiki e Vredefort i ‘impact diamonds’. Tindzalama letintsongo swinene, leti pimiwaka hikwalomu ka milimita loko tihelerile, tivumbeka loko kuve na kutlumbana eka maribye lawa yanga tala carbonk. Kuhisa lokuvaka kona aka kubanana ka maribye ku hlangana na carbon ku endla mamiliyoni yati dayimani letintsongo. Ku fayana ka Popigai e Siberia kuhumese mamiliyoni yati tons ta tidayimani, kambe akuna munhu loyi anga yi cela kumbe kuti tirhisa.

Ku katsana ka ti shattercones, pseudotachylite, shocked quartz na yan’wana hinkwawo ya shock metamorphics swikumekile e Vredefort xikan’we nale ka kufayana kun’wana. Loko ya hlanganile ya tekiwa tani hi nsayino waku fayana ka maribye naswona yatirhisiwile ku kombisa kufayana kun’wana loku nga tshama kuva kona kotala loku nga tivekeki eka planet.

Translated by Ike Ngobeni