Gondwana

Freshwater mussels cannot spread through oceanic barriers and represent a suitable model to test the continental drift patterns. Here, we reconstruct the diversification of Oriental freshwater mussels (Unionidae) and revise their taxonomy. We show that the Indian Subcontinent harbors a rather taxonomically poor fauna, containing 25 freshwater mussel species from one subfamily (Parreysiinae). This subfamily most likely originated in East Gondwana in the Jurassic and its representatives arrived to Asia on two Gondwanan fragments (Indian Plate and Burma Terrane). We propose that the Burma Terrane was connected with the Indian Plate through the Greater India up to the terminal Cretaceous. Later on, during the entire Paleogene epoch, these blocks have served as isolated evolutionary hotspots for freshwater mussels. The Burma Terrane collided with mainland Asia in the Late Eocene, leading to the origin of the Mekong’s Indochinellini radiation. Our findings indicate that the Burma Terrane had played a major role as a Gondwanan “biotic ferry” alongside with the Indian Plate.

From being “the cradle” of raw diamonds in the world in the eighteenth century, India has turned into an insignificant producer of rough diamonds today. Yet, even now, the indigenous Gonds mine diamonds artisanally in a remote location in central India, largely hidden away from public vision. This article presents an exposition of artisanal diamond mining in central India from the humanistic tradition in geography to illuminate the “realm” of the Gonds, where magic and social relations rule imaginaries of the diamonds in the particular place. It argues that the imaginations of diamonds and their mining by indigenous miners in Panna are shaped through the prism of their particular regional history, myth, geography, and culture. Without faith in the restrictive authority of science, capital, and state, and refusing domestication, the miners dig, smuggle, and spend for the savoir vivre. They remain dynamic and rely on traditional ideas of luck, masculinity, and success. They bind themselves to work and to each other in ways that preclude the possibility of amassing wealth and direct wealth in ways that reaffirm their dependence on the miner's life. The argument is illustrated through the story of protagonist Ramu, who proudly spends the earnings from his big diamond find. Based on ethnographic fieldwork in Panna, Madhya Pradesh State in central India, this article explores the magic of artisanal diamond mining, shows how place shapes such mining, and shows how informal mining shapes the context.

The Aktyuz metamorphic terrane in the Kyrgyz northern Tianshan consists of granitoid gneisses and migmatites with subordinate paragneisses, greenschists, presumed meta-ophiolites, and garnet amphibolite dykes that contain HP eclogite relicts. The gneisses and migmatites were previously considered to be Archaean and Palaeoproterozoic in age on the basis of α-Pb and U–Pb multigrain zircon dating. Zircons from a post-tectonic granite were previously dated at 692 ± 15 Ma, constraining the time of main deformation and metamorphism in the Aktyuz terrane to the Precambrian.The chemical characteristics of most granitoid samples are consistent with melting of chemically evolved crustal material, which is supported by Nd and Hf isotopic data. Zircon U–Pb SHRIMP ages were obtained for the main varieties of metamorphic rocks, for a gabbro of a low-grade ophiolite complex and for several post-kinematic igneous rocks. In addition, metamorphic muscovite was dated by the 40Ar–39Ar method, and whole-rock Sm–Nd isotopic systematics were obtained on several granitoid rocks. Our magmatic zircon crystallization ages for granitoid gneisses in the Aktyuz and Kemin Complexes range from 778 ± 6 to 844 ± 9 Ma which we interpret to reflect the time of magmatic emplacement of the gneiss protoliths. These rocks reflect an episode of Neoproterozoic granitoid magmatism, which is also documented in southern Kazakhstan, the Kyrgyz Middle Tianshan, the Chinese Central Tianshan and the Tarim Craton. Nd and Hf isotopic systematics show these rocks to be derived from Mesoproterozoic to Archaean sources. The calc-alkaline composition of these rocks seems compatible with a subduction setting, but is most likely inherited from the source, therefore the tectonic scenario for emplacement of the gneiss protolith remains unknown. Two ages of 562 ± 7 and 541 ± 3 Ma and negative εNd(t)-values for granitoid gneisses document a later crustal melting episode. Muscovite 40Ar/39Ar ages of ca. 470 Ma for Aktyuz gneisses constrain the main fabric-forming metamorphism to the Early Palaeozoic. A migmatitic paragneiss, which was previously interpreted as Palaeoproterozoic, contains detrital zircons with an age spectrum from 503 to 1263 Ma; the youngest grain suggests a maximum Cambrian age of protolith deposition. An ophiolitic metagabbro of the Kemin Complex yielded an Early Cambrian age of 531 ± 4 Ma, which is close to the age of ophiolites in the adjacent Djalair–Naiman belt of Kazakhstan, suggesting a possible genetic link. Two samples of quartz diorite from the post-kinematic Dolpran pluton yielded Early Ordovician zircon ages of 471.9 ± 3.5 and 472.0 ± 3.1 Ma. The presence of a 783 ± 7 Ma xenocrystic zircon points at Precambrian crust at depth, which may explain an earlier, discordant apparent age obtained by multigrain zircon dating of this pluton. Undeformed rhyolite and basalt in the East Kyrgyz Range, previously classified as Neoproterozoic and Cambrian, yielded Late Ordovician ages of 451.9 ± 4.6 and 448.9 ± 5.6 Ma respectively.Our data imply that the Aktyuz terrane is not a single segment of continuous Precambrian continental crust but represents a complex amalgamation of Neoproterozoic continental and Early Palaeozoic ophiolitic slivers, which were stacked together in a subduction and collisional setting. Large fragments of continental crust were subducted to HP eclogite-facies conditions, which led to eclogite metamorphism in the mafic dykes. The main deformational event occurred during the latest Cambrian to earliest Ordovician between 503 and 472 Ma.► Granitoid gneisses in the Aktyuz terrane of the Kyrgyz Tianshan were dated at 844-778 Ma and 562-541 Ma. ► These gneisses were derived from intracrustal melting of early Precambrian crust. ► An ophiolite, previously interpreted as Palaeoproterozoic, yielded a Cambrian age of 531 Ma. ► Eclogite relicts occur in mafic dykes in Neoproterozoic gneisses, which underwent HP metamorphism in the early Palaeozoic. ► HP metamorphism reflects subduction of the North Tianshan microcontinental margin prior to collision with the Anrakhai arc.