Evolving Marginal Terranes During Neoproterozoic Supercontinent Reorganization: Constraints From the Bemarivo Domain in Northern Madagascar

Abstract

Madagascar is a key area for unraveling the geodynamic evolution of the transition between the Rodinia and Gondwana supercontinents as it contains several suites of c. 850–700 Ma magmatic rocks that have been postulated to correlate with other Rodinian terranes. The Bemarivo Domain of northern Madagascar contains the youngest of these units that date to c. 750–700 Ma. We present zircon Hf and O isotope data to understand northern Madagascar's place in the Neoproterozoic plate tectonic reconfiguration. We demonstrate that the northern component of the Bemarivo Domain is distinct from the southern part of the Bemarivo Domain and have therefore assigned new names—the Bobakindro Terrane and Marojejy Terrane, respectively. Magmatic rocks of the Marojejy Terrane and Anaboriana Belt are characterized by evolved εHf(t) signatures and a range of δ18O values, similar to the Imorona‐Itsindro Suite of central Madagascar. These magmatic suites likely formed together in the same long‐lived volcanic arc. In contrast, the Bobakindro Terrane contains juvenile εHf(t) and mantle‐like δ18O values, with no probable link to the rest of Madagascar. We propose that the Bobakindro Terrane formed in a juvenile arc system that included the Seychelles, the Malani Igneous Suite of northwest India, Oman, and the Yangtze Belt of south China, which at the time were all outboard from continental India and south China. The final assembly of northern Madagascar and amalgamation of the Bobakindro Terrane and Marojejy Terrane occurred along the Antsaba subduction zone, with collision occurring at c. 540 Ma.

Extending full-plate tectonic models into deep time: Linking the Neoproterozoic and the Phanerozoic

“…Although arc-related magmatism has been recognised in the northern East African Orogen for a number of decades (e.g. Stern, 1994), the recognition of similar-aged arc magmatism in the higher-grade southern East African Orogen of Madagascar, Southern India and East Antarctica has been more controversial and under-appreciated until recently (Archibald et al, 2018(Archibald et al, , 2017Armistead et al, 2019;Plavsa et al, 2015;Ruppel et al, 2018). In one particular example, work over the last decade on Western Dronning Maud Land in East Antarctica has identified an extensive Stenian-Tonian juvenile arc system (named TOAST; (Elburg et al, 2015;Ruppel et al, 2018)).…”

“…Further outboard still, and later accreting onto the Indian margin, the Bobakindro Terrane of northern Madagascar (Armistead et al, 2019) consists of juvenile magmatism that dates from ca. 750-705 Ma (Armistead et al, 2019;Collins, 2006;Thomas et al, 2009).…”

“…Amalgamation of the Arabian-Nubian Shield (ANS) after Blades et al (2019bBlades et al ( , 2015, Armistead et al (2019) and Collins et al (submitted) and the incorporation of the ANS, Azania and TOAST into Gondwana along the East African Orogen at: (a) 800 Ma and (b) 520 Ma. Tan polygons are areas of continental lithosphere in the Neoproterozoic that we model, blue polygons are areas of present-day continental lithosphere that are inferred to exist during the Neoproterozoic, but without having firm geological evidence or that have been affected by subsequent deformation (e.g.…”

“…Alessio et al (2018) andArmistead et al (2019), the northwest margin of India is here interpretedas an extensive Stenian-Tonian accretionary margin that extends as far as the Omani basement and northernmost Madagascar. The pre-Ediacaran basement rocks in Rajasthan and Pakistan share similarities with those of Oman.…”

Proterozoic Basin Evolution and Tectonic Geography of Madagascar: Implications for an East Africa Connection During the Paleoproterozoic

“…The c. 850-750 Ma Imorona-Itsindro Group, which has relatively evolved ε Hf (t) values ranging from approximately 0 to −30 (Archibald et al, 2015), is a likely candidate for some of the younger detritus within these sequences. The c. 750 Ma southern Bemarivo Belt, which has evolved ε Hf (t) values ranging from approximately 0 to −15 (Armistead et al, 2019), is also a likely candidate for some of this younger detritus, particularly those samples located in northern Madagascar. Constraints on the minimum depositional age are given by zircon rim analyses of c. 615-560 Ma for the Molo Group (Cox et al, 2004) and c. 520 Ma for the Anaboriana-Manampotsy Belt (Collins, Kröner, et al, 2003).…”