Low‐temperature evolution of the Morondava rift basin shoulder in western Madagascar: An apatite fission track study

Abstract

[1] The evolution of the rift shoulder and the sedimentary sequence of the Morondava basin in western Madagascar was mainly influenced by a Permo-Triassic continental failed rift (Karroo rift), and the early Jurassic separation of Madagascar from Africa. Karroo deposits are restricted to a narrow corridor along the basement-basin contact and parts of this contact feature a steep escarpment. Here, apatite fission track (AFT) analysis of a series of both basement and sediment samples across the escarpment reveals the low-temperature evolution of the exhuming Precambrian basement in the rift basin shoulder and the associated thermal evolution of the sedimentary succession. Seven basement and four Karroo sediment samples yield apparent AFT ages between $330 and $215 Ma and $260 and $95 Ma, respectively. Partially annealed fission tracks and thermal modeling indicate post-depositional thermal overprinting of both basement and Karroo sediment. Rocks presently exposed in the rift shoulder indicate temperatures of >60 C associated with this reheating whereby the westernmost sample in the sedimentary plain experienced almost complete resetting of the detrital apatite grains at temperatures of about $90-100C. The younging of AFT ages westward indicates activity of faults, re-activating inherited Precambrian structures during Karroo sedimentation. Furthermore, our data suggest onset of final cooling/exhumation linked to (1) the end of Madagascar's drift southward relative to Africa during the Early Cretaceous, (2) activity of the Marion hot spot and associated Late Cretaceous break-up between Madagascar and India, and (3) the collision of India with Eurasia and subsequent re-organization of spreading systems in the Indian Ocean.

Cenozoic Dynamic Topography of Madagascar

“…(2004) and Giese et al. (2012), who show that a Mesozoic phase of burial and reheating followed by more recent exhumation occurs around northwestern and western coastlines. Note that many of our thermal histories are poorly constrained during Mesozoic times and that they could be consistent with reheating until Cenozoic times, followed by cooling to surface temperatures during the Neogene period (Figures 6c, 6d, 7c, 7d, , and ).…”

Crustal structure of southern Madagascar from receiver functions and ambient noise correlation: Implications for crustal evolution

“…The formation of the Morondava basin was mainly controlled by a predominantly Permo‐Triassic continental failed rift (known as Karoo rift) and the breakup of Madagascar, India, and Seychelles from Africa during the Jurassic. The separation of Madagascar from India‐Seychelles in the Late Cretaceous caused further extension in the Cenozoic [ Geiger et al , ; Giese et al , ; Piqué et al , ; Schandelmeier et al , ].…”

A prograding margin during global sea‐level maxima: an example from Mahajanga Basin, northwest Madagascar

“…Besairie, ). Such a time gap, however, is present in the Morondava Basin to the south and is interpreted to have resulted from significant tectonic uplift and basin axis tilting due to the fragmentation of eastern Gondwana (Luger et al ., ; Giese et al ., ). Interestingly, a time gap was recognized by Besairie () on outcrop in Upper Jurassic–Early Cretaceous strata, but this unconformity is not evident on the 2D profiles (Fig.…”

“…Increased sediment delivery to the basin margin could be attributed to significant tectonic uplift in the Madagascan hinterlands to the east, climate change or an interplay between these two factors. Mountains in eastern Madagascar possibly formed during Early Cretaceous as a result of sedimentary loading within the Mahajanga and Morondava basins (Seward et al, 2004;Emmel et al, 2012) and due to regional stress changes along the evolving plate boundaries between India, Australia, Antarctica and Madagascar, and resulting transpression between India and Madagascar (Luger et al, 1994;Giese et al, 2012;Gaina et al, 2013Gaina et al, , 2015. In addition to a changing plate circuit, an expansion of the southern arid belt (Chumakov et al, 1995) coupled with the northward migration of Madagascar into the subtropical zone (Fig.…”

“…The sedimentary fill appears to have been deposited in small grabens and half grabens surrounded by rotated basement blocks and horsts (e.g. Luger et al, 1994;Geiger et al, 2004;Tari et al, 2004;Giese et al, 2012;Figs 4 and 8). The sedimentary fill is interpreted to be age equivalent to the Late Triassic to Early Jurassic fluvial and lacustrine deposits that accumulated in grabens and half grabens as rifting between Africa and Madagascar began (Besairie, 1972).…”