iiShattercones kunye ne Shock Metamorphics zase Vredefort Dome

© David Fleminger

Untlitheko Olusuka Ngaphandle KoMhlaba

Ngaphandle kwe Vredefort crater, oluntlitheko lukhulu lwashiya ngasemva iintsalela ezininzi, zishicilelwe ematyeni. Ezi mpawu sele zisuka kufunyanwa nakwinqwaba yezinye iindawo ezakhe zafumana untlitheko, apha kwiplanethi yonke iphela. Kwaye ngoku sele zibonwa njengezikhumbuzo zontlitheko olusuka ngaphandle koMhlaba.

Okokuqala, kukho umandlalo ongqindilili owenziwe zizinto ezawayo ngethuba kunetha imvula enkulu, neyanetha ungama ongamawaka ekhilomitha ukusuka kulendawo yexhwayelo. Lomandlalo ngumxube wamatye kunye nenye imvuthuluka njee, kwaye ungqindilili kanye embindini walendawo inde dome, kodwa uya uswabuluka njengokuba uhambela embindini.

Enye into eyenza kucace ukuba kwakukhe kwabakho isehlo kulendawo, lutshintsho olusematyeni ubuqu. Xa ibolide ibetheka, ingakhupha amaqondo obushushu angaphaya kwama 10 000 degrees centigrade kwaye ifaka uxinzelelo lwamakhulu-khulu eegigapascal. Esi sinyhikanyhika samandla kunye nobushushu sibangela amatye angqongileyo ukuba atshintshe isimo nendlela ayiyo. Olu tshintsho lwaziwa njenge ‘shock metamorphics’. Enye yezona mpawu ze metamorphic zicace gca zii ‘shattercones’.

iShattercone

Ishattercone ayiyonto uyifumana xa uwise i-ice-cream. Yiphatheni ethile yokuqhekeka enwenwa phezu kwamatye xa kugqitha amandla wombane. Iziphumo ibangunxantathu abaphinda-phindeneyo abaqala endaweni enye.

Ezi shattercones zivelile kwindawo eziliqela kuyo yonke indawo yase Vredefort Dome, kwaye kuthiwa ukuba ulandela kakuhle umgca wezi shattercone, ungakwazi ukubona ukuba lomgca we bolide uqala phi. Ngelishwa, abatyeleli balemihla sele beqala ukuqhekeza bakhuphe ezi shattercones, ukuze bazigcine njengezikhumbuzo zotyelelo lwabo kulendawo. Lo ngumkhwa ombi kwaye kufanele upheliswe kwaye ukhuselo lwe shattercones izakuba yolunye lwamaxanduva ye Dome Management Authority entsha/ Abezolawulo lweDome Abasemagunyeni.

Ukutshintsha Kwamatye

Olunye uphawu olucacileyo lwamatye ase Vredefort yimigca emnyama ezobeke kumatye akhanyayo. Lemigca iyashiyana ngobude nobungqindilili, kodwa eminya iyabonakala gca. Lendidi yelitye elimnyama nelingathi liyigilasi ibizwa nge ‘pseudotachylite’. Eli litye lenzeka xa amaqondo obushushu aphezulu kakhulu enyibilikisa ilitye aze atshintshe indlela iikhemikhali zalo ezime ngayo. Amatye afana ne tachylite ayafunyanwa ngakwiindawo ebezine ntaba-mlilo (volcano) okanye apho ukukhuhlana phakathi kwe tectonic plate kukhupha ubushushu. Eli gama lithi ‘pseudo’ lifakelelwa xa kungekho bungqina bentaba-mlilo

Lamaqondo obushushu aphezulu kunye noxinzelela olukhutshwa luntlitheko, lwaye lwabanga utshintsho olukhulu kumatye abizwa nge ‘granophyre’. Eli litye lingumxube wamasuntwana amatye amancinci aqokeleleneyo aze abumba ilitye elikhulu elizii khilomitha eziliqela. Ubuchule bokujonga iminyaka ngohlobo lwe Radiometric dating ye zircon particles kulamatye atshintshwe luntlitheko anceda ukuba iigeologists zakwazi ukunika isiganeko sase Vredefort umhla ochanekileyo okwiminyaka engama 2.023 eebhiliyoni.

Iimpawu zeShock-Deformation

Phakathi kwezinye iimpawu ezibalulekileyo ze shock-deformation, ezixhaphakileyo kwiindawo esele zisuka kuhlaselwa luntlitheko olusuka ngaphandle eMhlabeni zii coesite kunye ne stishovite. La ngamagama amabi anikwa iintloob ezimbini ezingqindilili ze quartz (iminerali exhaphakileyo ematyeni). Zenzeka xa iquartz ishicilelekile kwaye igqatsheke kangangokuba itshintsha ukumila kwayo kwe crystal lattice.

Iintsalela zezi minerali zombini zifunyanwa rhoqo kwi impact craters, nakwindawo ezingqonge apho kuvavanyelwa khona ibhombo/iziqhushumbisi ze nuclear. Igama eliqhelekileyo lwalendidi yokukutshintsha yi ‘shocked quartz’.

Ubungqina bokugqiba be shock metamorphism abunakubonwa ngeliso lenyama. Uphando olucoselelweyo, nalapho amatye asikwa ngobuchule aze ahlolwe phantsi kwe electron microscope, lubonakalise micro-deformations ezikwisigaba se atomic. Oku kutshintsha kuvela njengophazamiseko lwe planar kwi quartz crystals kwaye, kungoku nje angumzekelo wesiganeko sontlitheko.

Iidayimani ze Impact

Enye ishock deformation enikisa umdla, nengafumanekiyo eVredefort zii ‘dayimani ze impact’, Obu bucwebe bedayimani bumeta isuntswana le milimitha ububanzi, budaleka xa imeteorite ibetheka elityeni elizele yi khabon. Ubushushu obuphuma koluntlitheko busebenzisana ne khaboni ukwenza izigidi zee dayimani ezincinci. I-Popigai crater ekwilizwe lase Siberia idume ngokuqulatha izigidi zee toni ze dayimani yokuntlitheka.

Kodwa akukabikho namnye oseze necebo lokuzisebenzisa. Umxube wee shattercones,iipseudotachylite, iishocked quartz kunye nazo zonke ezinye iishock metamorphics, sele zifunyenwe e Vredefort kunye nee impact craters ezininzi. Xa zizonke ezizinto zithathwa njengee mpawu zesiganeko sontlitheko, kwaye zisetyenziswa ukubona inqwaba yezinye iindawo ekwantlitheka kuzo iibolide kwihlabathi jikelele.