Inguqukosimo nama shattercones-eVredefort Dome

© David Fleminger

Impembelelo engaphezulu komhlaba

Ngaphandle komgodi waseVredefort, umthelela ushiye ngamuva imikhakha eminingi, eqoshiwe emadwaleni. Lezi zici zitholakale kwezinye izindawo eziningi ezinomthelela emhlabeni wonke, futhi manje zibhekwa njengezimpawu zomcimbi womthelela ongaphezulu komhlaba.

Okokuqala, kunezingqimba ezithintekayo ezawela emvuleni enamandla ngaphesheya kwendawo engamakhilomitha angamakhulu ambalwa. Lolu ungqimba lwamadwala lukhulu kakhulu esifundeni se-dome, lube luncane lapho usuka phakathi nendawo.

Isiboniso esilandelayo samandla amakhulu ushintsho emadwaleni ngokwawo. Uma inkanyezi eqhumayo ihlasela, ingaba namazinga okushisa angaphezu kuka-10 000 futhi nokucindezela okukhulu. Inani elikhulu lamandla nokushisa kubangela amatshe azungezile ukuba ashintshe abe amafomu amasha. Le nqubo ibizwa ngokuthi 'inguqukosimo esishaqisayo'. Esinye sezinto ezicacile kulezi zici zenguqukosimo 'ama-shattercones'.

I-Shattercone

I-shattercone ayiyona into oyithola uma uphonsa uswidi wakho. Esikhundleni salokho, iphethini elithile lokuvuvukala elisakaze phezu kwamadwala njengoba kuqhutshwa ingxubevalo. Umphumela ukubunjwa okuphindaphindiwe okuyisithupha, okuvela endaweni ejwayelekile.

Lawa ma-shattercones avuliwe ezindaweni eziningi kulo lonke i-Vredefort Dome, futhi kuthiwa uma uhlela wonke ama-shattercones ngendlela efanele, ungakwazi ukuphuma ohlwini lwenkanyezi eyaqhumayo. Ngeshwa, izivakashi zanamuhla ziqala ukuqeda ama-shattercones njengezikhumbuzo. Lo mkhuba odabukisayo okufanele umiswe ukuze kuvikelwa amashattercones kuyoba omunye wemithwalo yeqembu eniphethe iDome.

Inguqukosimo yamadwala

Esinye isici esivelele sezintambo zaseVredefort yizimvini zempahla emnyama ehamba ngegranayithi elula. Lezi zigaba zihluka ngobude nobukhulu, kodwa ezinye zikhulu kakhulu. Lolu hlobo lwamadwala aluhlaza, olumnyama lubizwa ngokuthi 'pseudotachylite' futhi lwakhiwa uma izinga lokushisa eliphakeme kakhulu lenza ukuba idwala ligcwale futhi liguqule ukwakhiwa kwamakhemikhali. Amatshe afanayo we-tachylite atholakala ezungeze izintaba-mlilo kanye nemigqa (lapho ukunyakaza komhlaba kubangela ukuthi kukhishwe ukushisa). Igama elithi 'pseudo' lengezwe uma kungekho bufakazi bokusebenza kwentabamlilo.

Ukushisa okumangalisayo nokucindezelwa okukhishwe umthelela nakho kwakha esinye isisindo esikhulu samatshe, okuthiwa 'granophyre'. Lokhu kuwuphawu olumnyama lwamadwala amahle aqoqwe amaqabunga futhi ahlanganiswa nezingxenye ezincane, amancane, aqhekeza ngamakhilomitha amaningana. Ukuhlolwa kwe-zircon yezinhlayiyana kulezi zindawo ezithintekayo zasiza ososayensi ukunikeza umcimbi we-Vredefort usuku oluthile lwamamabhiliyoni angu 2.023.

Izici Zeziyiko ezabangelwa umthelela

Phakathi kwezinye izici ezibalulekile ezivame kakhulu kumasayithi amaningi anomthelela yi-coesite ne-stishovite. Lawa amagama anikwe amafomu amabili we-quartz (i-mineral ejwayelekile emadwaleni). Zidalwa lapho i-quartz icindezelekile futhi ishaywa ngezinga elithinta isakhiwo sayo se-crystal lattice. Imidwebo yamabili amaminerali atholakala njalo emathinini wemigodi, nasezindaweni eziseduze zokuhlola amabhomu. Igama elijwayelekile lalo hlobo lokudonshulwa 'iquartz eshaqekile'.

Ubufakazi bokugcina ikuthi inguqukosimo ayibonakali ngeso nje. Ukuphenywa okucophelela, lapho amadwala ahlanjululwa kahle futhi ahlolwe ngaphansi kwesibonakhulu, sibonise ukukhubazeka okuncane ezingeni le-athomu. Lokhu kubonakala njengokuphazanyiswa kwezindiza emakristini we-quartz futhi, lapho sikhona, kuyisibonakaliso esinamandla somcimbi womthelela.

Amadayimane ashukumisayo

Esinye isiyiko esithakazelisayo asitholakali ku-Vredefort 'yithonya ledayimane'. Lezi zinngxenye ezincane e, ezilinganisa ingxenyana ye-millimeter yonkana, zakhiwa lapho inkanyezi ihlasela edwaleni elicebile. Ukushisa okuvela kumthelela kuthinta nekhabhoni ukudala izigidi zamadayimane ahamba phambili. Umgumbini wasePigigai eSiberia uqukethe izigidi zamathani amadayimane omthelela, kodwa akekho oye wabasebenzisa.

Ukuhlanganiswa kwama-shattercones, i-pseudotachylite, i-quartz kanye nayo yonke enye inguqukosimo yomthelela itholakale e-Vredefort nakweminye imigodi yezintabamlilo. Ngokubambisana, kuthathwe njengesignesha yomthelela futhi isetshenziselwe ukukhomba inqwaba yamasayithi omthelela ngaphambilini angaziwa emhlabeni jikelele.