Zusammenfassung
Neue Isotopen- und Altersdaten aus dem metamorphen Grundgebirge von Sri Lanka zeigen, daß dieses Gebiet nicht, wie vielfach vermutet, Teil des archaischen Granulitkomplexes von Südindien war, sondern seine strukturelle und metamorphe Entwicklung während der panafrikanischen Orogenèse zwischen ca. 950 Ma und ca. 550 Ma hatte. Diese Orogenèse ist das Resultat der Kollision zwischen West-Gondwana (Afrika und Südamerika) und Ost-Gondwana (Südindien, Australien und Antarktis) und führte zur Bildung eines der längsten Kollisionsgürtel des Superkontinentes, dem Mosambik-Gürtel, der sich von Mosambik bis nach Äthiopien und in den Sudan erstreckt. Der West- und Zentralteil Sri Lankas mit den Wanni und Highland/Southwestern Komplexen wird vom Vijayan Komplex im Osten und Südosten durch eine Überschiebungszone getrennt, die möglicherweise eine Sutur darstellt. Die Gesteine im Westen und in den Highlands werden als der Rest eines ehemals weiträumigen passiven Kontinentalrandes interpretiert, zu dem wohl auch die lithologisch ähnlichen Abfolgen der hochmetamorphen Gebiete in Mosambik, Tansania und Madagaskar gehörten. Der Vijayan Komplex war wohl Teil der separaten plutonischen Suite eines aktiven Kontinentalrandes, und seine Kollision mit dem Highland/ Southwestern Komplex markiert das endgültige Verschweißen von West- und Ost-Gondwana zu einem Superkontinent vor ca. 550 Ma. Die Granulite Sri Lankas können nicht mit den deutlich älteren Granuliten des Gürtels der Eastern Ghats in Südost Indien korreliert werden sondern ähneln eher den hochgradigen Gesteinen in Südost Madagaskar. Damit ist die Lage Sri Lankas nahe Madagaskar in einer Gondwana Rekonstruktion wahrscheinlicher als nahe der Südostküste Indiens.
Abstract
New age and isotopic data show that the high-grade basement rocks of Sri Lanka were not linked to the Archaean granulite domain of southern India but experienced their main structural and metamorphic development during the Pan-African event some 950 to 550 Ma ago. This occurred when West Gondwana and East Gondwana collided to form one of the longest collisional structures in the Supercontinent — the Mozambique belt that extends from Mozambique to Ethiopia and Sudan. A major tectonic boundary, interpreted as a thrust zone, divides the Highland/Southwestern Complex in the central part of Sri Lanka from the Vijayan Complex in the E and SE. The former is interpreted to represent the remnant of a once extensive passive margin extending west, in a Gondwana reconstruction, via Madagasgar to Tanzania and Mozambique. The Vijayan Complex may have been part of a separate continental margin plutonic assemblage, and its collision with the Highland/ Southwestern Complex marks the final amalgamation of East and West Gondwana into a supercontinent some 550 Ma ago. The Sri Lankan granulites cannot be correlated with the distinctly older granulites of the Eastern Ghats belt of India, and this suggests that Sri Lanka was situated close to the SE coast of Madagascar in a Gondwana reconstruction.
Résumé
De nouvelles données isotopiques et géochronologiques montrent que les roches métamorphiques du socle du Sri Lanka ne constituent pas, comme on l'a souvent cru, une partie du complexe granulitique archéen de l'Inde méridionale, mais qu'elles ont vécu leur propre histoire tectono-métamorphique au cours de l'orogenèse panafricaine, entre 950 et 550 Ma. Cette orogenèse est le résultat de la collision entre le Gondwana occidental (Afrique et Amérique du Sud) et le Gondwana oriental (Inde du sud, Australie et Antarctique) et constitue une des plus grandes chaînes de collision du Supercontinent: la chaîne du Mozambique, qui s'étend du Mozambique jusqu'au Soudan et en Ethiopie. Un contact tectonique majeur, interprété comme un charriage, sépare le »Highland/South-western Complex« (partie centrale du Sri Lanka) du »Vijayan Complex« (partie est et sud-est). Le premier de ces complexes est interprété comme un reste d'une ancienne marge passive de grande étendue, à laquelle appartenaient aussi les séries lithologiquement analogues du domaine très métamorphique du Mozambique, de Tanzanie et de Madagascar. Le «Vijagan Complex« a pu être une partie d'un ensemble plutonique séparé de marge active; sa collision avec le »Highland/Southwestern Complex« marque la réunion finale en un super-continent il y a quelque 550 Ma, des Gondwanas oriental et occidental. Les granulites du Sri Lanka ne peuvent pas être corrélées avec celles de la chaîne des Eastern Ghats (Inde du sud-est) qui sont nettement plus anciennes; elles se rapprochent plutôt des roches très métamorphiques du sud-est de Madagascar. On en déduit que la position du Sri Lanka, dans une reconstruction du Gondwana, devait être plus proche de Madagascar que de la côte sud de l'Inde.
Краткое содержание
Новейшие данные по оп ределению возраста метаморфных основны х горных пород в СриЛа нке, полученные с помощью геохронологических методов, установили, ч то эта область не является архейски м гранитным комплекс ом Южной Индии, как счита ли до сих пор, но структурное и метамо рфное развитие этого комплекса оказывает ся современником панафриканского орогенеза, т.е. протека ло между 950 и 550 Ма тому назад. Этот о рогенез явился следствием ко ллизии западной Гонд ваны — Африка и Южная Амери ка — и восточной Гондваны — Южная Инди я и Антарктика. и привел к образованию некого самого длинно го коллизионного пояса сверхматерика, пояса Мозамбик, простиравш егося от Мозамбика до Эфиопии и Судана. Запа дная и центральная часть Сри-Ланки с комп лексом Ванни и высоко горьем на юго-западе отделяе тся от комплекса Виджаян на востоке и ю го-востоке зоной надвигов, котор ая, возможно, представ ляет собой просто шов. Поро ды на западе и таковые высокогорья рассматривают, как остаток бывшего обши рного пассивного мат ерикового края, к которому относ ят свиты пород Мозамбика, проя вляющие высшую степе нь метаморфизма, а также Танзании и Мадагаска ра, которые сходны по сво ему литологическому составу. Комплекс Вид жтян был, возможно, частью некой плутони ческой серии активного материков ого края, и его коллизи я с высокогорным юго-зап адным комплексом при вела к окончательному спе канию западной и восточной Гондваны в сверхматерик до 550 Ма тому назад. Граниты Ср и-Ланки нельзя коррел ировать со значительно более древними гранулитам и пояса восточного Гат са на юго-восточной части Индии, но они про являют сходство с высоко метаморфным и породами, залегающи ми на юго-восточной част и Мадагаскара. Таким образом, местоп оложение Сри-Ланки в Гондване оказалось б лиже к Мадагаскару, че м к юго-востоку Индии.
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Kröner, A. African linkage of Precambrian Sri Lanka. Geol Rundsch 80, 429–440 (1991). https://doi.org/10.1007/BF01829375
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DOI: https://doi.org/10.1007/BF01829375