John Foden

Hutton's Principle of Uniformitarianism suggests that the present is the key to the past, and in the present, Earth's topography is dominated by the Himalaya. The geological record clearly preserves past mountain ranges, but few have purported to have the effect on Earth's surface systems (such as the atmosphere, hydrosphere, biosphere and ocean chemistry) that the Himalaya does today. The Neoproterozoic East African Orogen is an exception. Not only is it the scale of the modern Himalaya, but it affected ocean chemistry in a similar manner to the Himalaya. Here we posit that the East African Orogen is the only other Himalayan-scale mountain range, and the only orogen that contends with the Himalaya as the largest mountain range of the last billion years. In this manuscript we review and reconstruct the orogen. We then use existing metamorphic data triaged to exclude subduction-zone metamorphism, to estimate the elevation-time evolution of the orogen. We demonstrate that the available metamorphic record supports our assertion that the East African Orogen is amongst the largest orogens in the geological record. We also integrate spatially-located metamorphic data with a full-plate tectonic reconstruction of the evolving orogen to show how different plate interactions created the evolving topography.

Hutton’s Principle of Uniformitarianism suggests that the present is the key to the past, and in the present, Earth’s topography is dominated by the Himalaya. The geological record clearly preserves past mountain ranges, but few have purported to have the effect on Earth’s surface systems (such as the atmosphere, hydrosphere, biosphere and ocean chemistry) that the Himalaya does today. The Neoproterozoic East African Orogen is an exception. Not only is it the scale of the modern Himalaya, but it affected ocean chemistry in a similar manner to the Himalaya. Here we posit that the East African Orogen is the only other Himalayan-scale mountain range, and the only orogen that contends with the Himalaya as the largest mountain range of the last billion years. In this manuscript we review and reconstruct the orogen. We then use existing metamorphic data triaged to exclude subduction-zone metamorphism, to estimate the elevation-time evolution of the orogen. We demonstrate that the available metamorphic record supports our assertion that the East African Orogen is amongst the largest orogens in the geological record. We also integrate spatially-located metamorphic data with a full-plate tectonic reconstruction of the evolving orogen to show how different plate interactions created the evolving topography.

Plate reorganization events involve fundamental changes in lithospheric plate-motions and can influence the lithosphere-mantle system as well as both ocean and atmospheric circulation through bathymetric and topographic changes. Here, we compile published data to interpret the geological record of the Neoproterozoic Arabian-Nubian Shield and integrate this with a full-plate tectonic reconstruction. Our model reveals a plate reorganization event in the late Tonian period about 720 million years ago that changed plate-movement directions in the Mozambique Ocean. After the reorganization, Neoproterozoic India moved towards both the African cratons and Australia-Mawson and instigated the future amalgamation of central Gondwana about 200 million years later. This plate kinematic change is coeval with the breakup of the core of Rodinia between Australia-Mawson and Laurentia and Kalahari and Congo. We suggest the plate reorganization event caused the long-term shift of continents to the southern hemisphere and created a pan-northern hemisphere ocean in the Ediacaran.

Plate reorganization events involve fundamental changes in lithospheric plate-motions and can influence the lithosphere-mantle system as well as both ocean and atmospheric circulation through bathymetric and topographic changes. Here, we compile published data to interpret the geological record of the Neoproterozoic Arabian-Nubian Shield and integrate this with a full-plate tectonic reconstruction. Our model reveals a plate reorganization event in the late Tonian period about 720 million years ago that changed plate-movement directions in the Mozambique Ocean. After the reorganization, Neoproterozoic India moved towards both the African cratons and Australia-Mawson and instigated the future amalgamation of central Gondwana about 200 million years later. This plate kinematic change is coeval with the break-up of the core of Rodinia between Australia-Mawson and Laurentia and Kalahari and Congo. We suggest the plate reorganization event caused the long-term shift of continents to the southern hemisphere and created a pan-northern hemisphere ocean in the Ediacaran.

Plate reorganization events are a characteristic of plate tectonics that punctuate the Phanerozoic. They fundamentally change the lithospheric plate-motion circuit, influencing the planet’s tectonic-mantle system and both ocean and atmospheric circulation through changes in bathymetry and topography. The development of full-plate reconstructions for deep time allows the geological record to be interrogated in a framework where plate kinematic reorganizations can be explored. Here, the geological record of the one of the most extensive tracts of Neoproterozoic crust on the planet (the Arabian-Nubian Shield) is interpreted to reflect a late Tonian plate reorganization at ca. 800-715 Ma that switched plate-convergence directions in the Mozambique Ocean, bringing Neoproterozoic India towards both the African cratons and Australia-Mawson, instigating the closure of the intervening ocean and the future amalgamation of central Gondwana ca. 200 million years later. This plate kinematic change is coeval with constraints on break-up of the core of Rodinia between Australia-Mawson and Laurentia and Kalahari and Congo.

There is a view that a supercontinent, called Pannotia, existed for a short time at the end of the Neoproterozoic. This hypothetical continent requires collision between Neoproterozoic India, Australia-Mawson and the African and South American continents to occur before formation of Iapetus as Laurentia rifted off Amazonia.Data from the last decade demonstrate the complexity of consumption of the Mozambique Ocean that separated Neoproterozoic India from the African Neoproterozoic continents (Congo-Tanzania-Bangweulu, the Sahara Metacraton and Kalahari). In particular, the presence of pre-Neoproterozoic terranes that lie within the East African Orogen of Arabia, east Africa, Madagascar and South India demonstrate the multi-phase collision of the this ocean closure?. Here we examine the Cryogenian to Cambrian tectonic geography of the closure of the Mozambique Ocean from a full-plate perspective. We focus on the northern East African Orogen, where Gondwana-formation shortening and crustal thickening has been considerably less than seen in East Africa/Madagascar/South India. We focus on the Neoproterozoic India–Azania–Sahara Metacraton collision represented by the northernmost part of Madagascar (the Bemarivo Domain), and throughout Arabia. We conclude that final ocean closure and formation of central Gondwana occurred in the latest Ediacaran and into the Cambrian, along a suture that passes under the Rub' al Khali region of Arabia and through the northeast of Madagascar. It separates the extended Neoproterozoic India margin (now in Oman, The Seychelles and the northern Bemarivo Domain), from the growing kernel of Gondwana (the east-most parts preserved in Saudi Arabia, Yemen and Central Madagascar).Considering the early Ediacaran formation of Iapetus, there is growing evidence that Pannotia never existed as connected continental crust, yet the ‘Pannotian geodynamic cell’ with lithosphere divided into continental and oceanic hemispheres had formed. The closure of the Mozambique Ocean represented the termination of >500 million years of subduction at this locale. The termination of this subduction with the formation of Gondwana, and the initiation of the Terra Australis Orogen led to the present geodynamic configuration.

Madagascar occupied an important place in the amalgamation of Gondwana and preserves a record of several Neoproterozoic events that are linked to orogenesis of the East African Orogen. In this study, we integrate remote sensing, field data and thermochronology to unravel complex deformation in the Ikalamavony and Itremo domains of central Madagascar. The deformation sequence comprises a gneissic foliation (S ₁ ), followed by south- to SW-directed, tight to isoclinal, recumbent folding (D ₂ ). These are overprinted by north-trending upright folds that formed during an approximately east–west shortening event (D ₃ ). Together these produced type 1 and type 2 fold interference patterns throughout the Itremo and Ikalamavony domains. We show that the Itremo and Ikalamavony domains were deformed together in the same orogenic system, which we interpret as the c . 630 Ma collision of Azania with Africa along the Vohibory Suture in southwestern Madagascar. In eastern Madagascar, deformation is syn- to post-550 Ma, and probably formed in response to final closure of the Mozambique Ocean along the Betsimisaraka Suture that amalgamated Madagascar with the Dharwar Craton of India. Apatite U–Pb and novel laser ablation triple quadrupole inductively coupled plasma mass spectrometry (LA-QQQ-ICP-MS) muscovite and biotite Rb–Sr thermochronology indicates that much of central Madagascar cooled through c . 500°C at c . 500 Ma. Supplementary material: A detailed geological map of central Madagascar (Supplementary A), detailed methods and geo- and thermochronology results (Supplementary B), isotopic data for geo- and thermochronology (Supplementary C) and Landsat images and structural interpretation examples (Supplementary D) are available at https://doi.org/10.6084/m9.figshare.c.4840575

The Omani basement is a critical window into the Neoproterozoic tectonic geography of the Mozambique Ocean and the amalgamation of Gondwana. It is located east of the juvenile arc terranes of the Arabian–Nubian Shield, yet the relationship between the two is not well understood. Magmatic and detrital zircon samples were analysed from four main basement terranes: Mirbat, the Huqf, Jebel Ja'alan and Al Jobah. The U–Pb (zircon) ages from igneous samples give ages between 838 and 765 Ma. The Lu–Hf and oxygen isotopes show that the zircons are juvenile (ɛ _Hf ( t ) values 10.5–8.7), with low δ ¹⁸ O values ( c. 2–6‰). Detritus from sediments in Mirbat, the southernmost basement outcrop, preserves a main age peak at c. 786 Ma, with Lu–Hf between +6.05 and +12.64. Lu–Hf isotopic data for Proterozoic detrital zircons from Jebel Ja'alan suggest that this region was depositionally connected to a source yielding both evolved Tonian and Neoarchean to Paleoproterozoic detritus. These sources could correlate to the terranes in India and South China, which record similarly low δ ¹⁸ O values. These data support a model in which Oman formed in its own tectonic domain, accreting onto the Neoproterozoic active margin of a continent. Supplementary material : All U–Pb, hafnium and oxygen data, and figures including all weighted average plots and initial ¹⁷⁶ Hf/ ¹⁷⁷ Hf v. ²⁰⁶ Pb/ ²³⁸ U age to aid in identifying Pb-loss in the data are available at https://doi.org/10.6084/m9.figshare.c.4682363