The Kaladgi Basin is one of the several Proterozoic sedimentary basins of India. This basin has a binary evolutionary history with an angular unconformity separating the older deformed and younger undeformed rock sequences of the Kaladgi Supergroup, named the Bagalkot and Badami Groups, respectively. The Bagalkot Group is known to be of late Paleoproterozoic-Mesoproterozoic age. However, the timings of deposition of the Badami Group sediments and the closure of the basin have been speculative. We carried out C-O-Sr isotope studies of the marine carbonate successions of this basin namely Chitrabhanukot, Chikshellikeri, Lakshanhatti (Bagalkot Group), and Konkankoppa (Badami Group). Our results indicate that δ13C of all the carbonate formations have preserved the primary marine signature. Restricted variation of δ13C in the carbonates of the Bagalkot Group (0 ± 2 ‰) suggests a steady state organic carbon burial; whereas, much wider range of variation of δ13C in the Konkankoppa Limestone of Badami Group (-2.2 to + 3.5 ‰) hints at a dynamic organic carbon burial scenario. These signatures are consistent with the C-isotope stratigraphy of the Meso-Neoproterozoic times. The 206Pb-207Pb dating of the youngest unit of the Kaladgi Supergroup, the Konkankoppa Limestone yielded a depositional age of 604 ± 25 Ma. This age, considered together with the primary 87Sr/86Sr ratio of 0.70781, extends the active sedimentation of the Badami Group well into the Ediacaran Period. These data confirm the existence of a long duration depositional hiatus, of >500 million years, between the Bagalkot and the Badami Groups. Results of this study also refutes the claim that the sedimentation in most of the Proterozoic basins of peninsular India ended by 1000 Ma.

Meteorite impact craters are morphologic features that can develop characteristic radial, centripetal, and concentric drainage patterns. With age, fluvial activity denudes this morphologic feature, thereby erasing the evidence of a prominent geologic event. Apart from morphology and age, the target lithology and climate also influence crater denudation. In this study, we derive an index, called the Denudation Index (DI), which is a measure of rim degradation caused by fluvial activity. DI was derived by summing the average of first order drainages that retains radial and centripetal patterns to the total number of streams. DI was obtained through the extraction of drainages from digital elevation models (DEM) for 71 craters formed since the Phanerozoic eon. The DI was correlated with the morphology, age, lithology and paleoclimate. Paleoclimatic data corresponding to each crater was generated by reconstructing the crater paleo-positions through GPlates and superimposing the same to the Scotese's Global Climate Model with an interval of 1 Ma. The study revealed that denudation is more prominent in a complex crater's formation on a crystalline target rock than in simple crater on a sedimentary target. Craters in the equatorial rainy climate are more denudating than other climates. Thus, this study provides a new, rather novel, method of expressing the denudation of a crater. Furthermore, this study shows that the drainage network is a unique signature that can be used for depicting the denudation of morphologic features, especially a prominent one like the meteorite impact crater. (c) 2021 Elsevier B.V. All rights reserved.

The impact origin of Ramgarh crater in India has been a topic of debate for several decades due to its conspicuous morphology, with recent studies confirming the structure as a complex impact crater. In this work, we present the results from an integrated petrographic and geochemical study to evaluate the impact origin of the crater, in conjunction with introduction of a new geochronological data for the crater through zircon U-Pb systematics. Petrographic studies of the target Vindhyan sedimentary rocks show the presence of shock fabrics such as planar fractures, decorated planar deformation features, brecciation, melted grain boundaries, diaplectic glass, and vitrified matrix. Geochemically, the lithounits have high concentrations of Cr, Ni, Cu, and the corresponding chondrite normalized values show notably elevated levels than crustal average. The elevated levels of Cr, Ni and Cu in the target rocks indicate its interaction with an extra-terrestrial object. The positive correlation between Ni and Co, higher concentration of Cr (9-623.35 ppm), and more importantly the average Ni/Cr (-0.006- - 1.3), Ni/Co (-1.8 to -22) and Cr/Co (-57--368) ratios in the target lithounits of Ramgarh, point to a differentiated achondrite being the possible impactor. The zircon U-Pb geochronological data from two samples in this study do not show significant Pb-loss and U enrichment. However, the relatively younger age of 528-395 Ma, depicted by quartzite sample (AN-4), along with the discordance and distinguishable Pb-loss, might hint that the impact event at Ramgarh have occurred between this timeframe. This age is considerably closer to the PrecambrianCambrian Boundary (543 Ma) and, it also encompasses the age corresponding to the mid-Ordovician Meteor Event (OME) (467.5 +/- 0.28 Ma). As this study infers that the potential impactor at Ramgarh is a differentiated achondrite and not a L-chondrite, the OME age can be ignored, further narrowing the age of Ramgarh impact structure. Our study also confirms the Ramgarh structure as an impact crater, and constrains the possible timing of the impact.

The paleo-positions of terrestrial meteorite impact craters along with distance and displacement registered since formation due to plate tectonics were deciphered using GPlates, an interactive GIS-based plate tectonic recon-struction and modeling software. The results of the study are intriguing as several craters have traversed across the globe, both from the Eastern to Western hemisphere and from the Southern to Northern hemisphere, and vice versa. The oldest crater studied was Foelsche, which traversed from the Southern to Northern hemisphere and from the Western to Eastern hemisphere while covering a distance of 39080 km in the past 981 million years and recording a relatively shorter displacement of 10470 km. On the other hand, Ja euro nisja euro rvi and Suvasvesi South have traveled longer distances (27781 and 29050 km, respectively) and are among the most displaced craters (17400 and 16988 km, respectively). Similarly, the paleo-position, distance, and displacement for all craters, with ages <1100 Ma, were computed in the study. Based on the derived paleo-position, we have accessed the possibility of any selective distribution of craters across different latitudinal segments. As Earth is a planet that recorded dynamic variations in the terrestrial surface area across different geological ages, calculating the same was an arduous task. The land area within each of the three latitudinal segments, viz. 0-30 degrees, 30-60 degrees, and 60-90 degrees, in which a crater formed was calculated for the geological time corresponding to an impact cratering event. This calculated land area within the respective lat-itudinal zone at each instance of a crater's formation was then compared with the total land area on Earth. The results showed that 0-30 degrees and 30-60 degrees segments have equal crater frequencies whereas the 60-90 degrees segment has a lesser frequency. The latitudinal crater distribution on Earth was then compared with Moon and Mars. The results revealed that there is a non-selective distribution of terrestrial impact craters across different latitudinal segments, indicating a non-perceivable latitudinal dependency for impact events.

The paradigm of plate tectonics has aided in the identification of the journey of continents on the globe, their assembly into supercontinents, disruption, and re‐assembly. Here, we use meteorite impact craters as proxies for tracking the voyage of lithospheric plates. Employing the provisions in GPlates, an interactive geographic information system‐based plate tectonic reconstruction model, we were able to identify the palaeo‐position, and velocity of the 174 terrestrial impact craters, formed after 1,100 Ma, across the globe. These parameters of craters were evaluated for independent tectonic plates and were correlated with global tectonic events. For example, the similarity in the velocity of Beaverhead (900 Ma) and Holleford (550 Ma) craters since 550 Ma is traced to the connection between the Eastern Basin and North America Craton commencing 1,100 Ma, and through the South Basin and Range. Likewise, the drastic reduction in the velocity of Spider Crater (700 Ma) in Australia after 600 Ma can be attributed to the subduction between east and west Gondwana. The accelerated motion of the Indian Plate at 63 Ma, when the lithosphere was hovering over the Réunion hotspot, is also explained. With the advent of more improved plate tectonic models and the discovery of more impact craters, improvised interpretations will be possible.

Earth's impact craters were analyzed to know the paleo-positions, distance and displacement they have undergone due to plate tectonics. Further, we have verified whether there is any selective dist...

The Sanjiang Orogen in the Southeastern Qinghai–Tibet Plateau is an ideal region to investigate the geodynamic processes related to the evolution of the Paleo-Tethys Ocean. New zircon SHRIMP U–Pb age data, whole-rock major and trace elements, and zircon Hf–O isotopic data of granodiorites and the associated dioritic enclaves from Baimaxueshan pluton in the eastern margin of the Qamdo–Simao Terrane provide key evidence for the subduction products of the Paleo-Tethyan oceanic lithosphere. Zircon U–Pb ages indicate that the dioritic enclaves and their host granodiorites were synchronously emplaced at ~255 Ma. The host granodiorites are normal calc-alkaline I-type granitoids, and characterized by uniform zircon εHf(t) values (−6.7 to +1.5), a wide-ranging δ18O values (6.1 to 9.3‰), and negative whole-rock εNd(t) values (−7.3 to −5.8). We suggest that these rocks were derived from the partial melting of ancient mafic lower crust with varying contributions from mantle-derived components. The dioritic enclave samples yield εHf(t) values (−4.7 to +2.1) and δ18O (5.8 to 8.3‰), which are similar to those of the host granitoids. They most likely originated from magma mixing between mantle-derived and crust-derived melts at or close to the Moho. The similar emplacement age but distinct whole-rock εNd(t) values between the Lancangjiang arc-related andesites and granodiorites and Baimaxueshan pluton preclude the possibility that they were generated by the same magmatic source. However, the consistent emplacement ages and whole-rock εNd(t) values of the Jinshajiang subduction-related granites and Baimaxueshan granitoids suggested that they were both generated by the westward subduction of the Jinshajiang PaleoTethyan oceanic lithosphere.

The Dhala structure in Central India has been a topic of global interest ever since the report of an ancient meteorite impact event there. Here we present an integrated study of the petrology, geochemistry, and zircon U-Pb zircon geochronology and rare earth element geochemistry from the structure along with and an analysis of the grain morphology and textural features. Our results provide new insight into the nature and timing of the impact event. The zircon grains from the impactites show textures typical of shock deformation which we correlate with the impact event. We also identified the presence of reidite based on Raman spectroscopy and characteristics such as a persistent planar fracture, bright backscattered electron images, and a lack of zoning, which are all diagnostic features of this mineral formed during an impact event. Our zircon U-Pb data from the various rock types in the basement show magma emplacement at ca. 2.5–2.47Ga, and the Pb loss features suggest that the impact might have occurred between ca. 2.44Ga and ca. 2.24Ga. Another minor group of late Paleoproterozoic zircons with concordant ages of 1826 and 1767Ma in the brecciated quartz reefs along the margins of the impact crater from unfractured grains represent an younger thermal event after the impact. The rare-earth element patterns of the Neoarchean to early Paleoproterozoic zircon population reflect the effects of hydrothermal alteration on a peralkaline host rock. The abnormally high concentration of K2O in the impactite (up to 15.91wt%), is also consistent with metasomatic alteration associated with the impact event.