scholarly journals New insights into the formation and emplacement of impact melt rocks within the Chicxulub impact structure, following the 2016 IODP-ICDP Expedition 364

2021 ◽  
Author(s):  
Sietze J. de Graaff ◽  
Pim Kaskes ◽  
Thomas Déhais ◽  
Steven Goderis ◽  
Vinciane Debaille ◽  
...  
Keyword(s):  
Crystalline Basement ◽  
Impact Structure ◽  
Rock Unit ◽  
Geochemical Composition ◽  
Geochemical Characterization ◽  
Impact Melt ◽  
Bearing Unit ◽  
Chicxulub Impact ◽  
The Impact

This study presents petrographic and geochemical characterization of 46 pre-impact rocks and 32 impactites containing and/or representing impact melt rock from the peak ring of the Chicxulub impact structure (Yucatán, Mexico). The aims were both to investigate the components that potentially contributed to the impact melt (i.e., the pre-impact lithologies) and to better elucidate impact melt rock emplacement at Chicxulub. The impactites presented here are subdivided into two sample groups: the lower impact melt rock−bearing unit, which intrudes the peak ring at different intervals, and the upper impact melt rock unit, which overlies the peak ring. The geochemical characterization of five identified pre-impact lithologies (i.e., granitoid, dolerite, dacite, felsite, and limestone) was able to constrain the bulk geochemical composition of both impactite units. These pre-impact lithologies thus likely represent the main constituent lithologies that were involved in the formation of impact melt rock. In general, the composition of both impactite units can be explained by mixing of the primarily felsic and mafic lithologies, but with varying degrees of carbonate dilution. It is assumed that the two units were initially part of the same impact-produced melt, but discrete processes separated them during crater formation. The lower impact melt rock−bearing unit is interpreted to represent impact melt rock injected into the crystalline basement during the compression/excavation stage of cratering. These impact melt rock layers acted as delamination surfaces within the crystalline basement, accommodating its displacement during peak ring formation. This movement strongly comminuted the impact melt rock layers present in the peak ring structure. The composition of the upper impact melt rock unit was contingent on the entrainment of carbonate components and is interpreted to have stayed at the surface during crater development. Its formation was not finalized until the modification stage, when carbonate material would have reentered the crater.

scholarly journals Ocean resurge-induced impact melt dynamics on the peak-ring of the Chicxulub impact structure, Mexico

2021 ◽  
Author(s):  
Felix M. Schulte ◽  
◽  
Axel Wittmann ◽  
Stefan Jung ◽  
Joanna V. Morgan ◽  
...  
Keyword(s):  
Impact Structure ◽  
Physical Processes ◽  
Hydrothermal Conditions ◽  
Chemical Examination ◽  
Impact Melt ◽  
Target Rock ◽  
Single Process ◽  
Chicxulub Impact ◽  
The Impact

AbstractCore from Hole M0077 from IODP/ICDP Expedition 364 provides unprecedented evidence for the physical processes in effect during the interaction of impact melt with rock-debris-laden seawater, following a large meteorite impact into waters of the Yucatán shelf. Evidence for this interaction is based on petrographic, microstructural and chemical examination of the 46.37-m-thick impact melt rock sequence, which overlies shocked granitoid target rock of the peak ring of the Chicxulub impact structure. The melt rock sequence consists of two visually distinct phases, one is black and the other is green in colour. The black phase is aphanitic and trachyandesitic in composition and similar to melt rock from other sites within the impact structure. The green phase consists chiefly of clay minerals and sparitic calcite, which likely formed from a solidified water–rock debris mixture under hydrothermal conditions. We suggest that the layering and internal structure of the melt rock sequence resulted from a single process, i.e., violent contact of initially superheated silicate impact melt with the ocean resurge-induced water–rock mixture overriding the impact melt. Differences in density, temperature, viscosity, and velocity of this mixture and impact melt triggered Kelvin–Helmholtz and Rayleigh–Taylor instabilities at their phase boundary. As a consequence, shearing at the boundary perturbed and, thus, mingled both immiscible phases, and was accompanied by phreatomagmatic processes. These processes led to the brecciation at the top of the impact melt rock sequence. Quenching of this breccia by the seawater prevented reworking of the solidified breccia layers upon subsequent deposition of suevite. Solid-state deformation, notably in the uppermost brecciated impact melt rock layers, attests to long-term gravitational settling of the peak ring.

Impact-induced hydrothermal dissolution in pyroxene: Petrographic and geochemical characterization of basalt-dominated polymict impact breccias from the Vargeão Dome, Brazil

2021 ◽  
Author(s):  
Jennifer Epstein ◽  
Lidia Pittarello ◽  
Álvaro P. Crósta ◽  
Christian Koeberl
Keyword(s):  
Hydrothermal Alteration ◽  
Hydrothermal Fluids ◽  
Terrestrial Planets ◽  
Impact Structure ◽  
Impact Event ◽  
Southern Brazil ◽  
Geochemical Characterization ◽  
Heterogeneous Nature ◽  
The Impact

ABSTRACT Constraints on impact-related hydrothermal alteration are important to enable the reconstruction of the possible processes affecting the surface of other terrestrial planets, such as Mars. Terrestrial impact structures excavated in basaltic targets provide the opportunity for analog studies. In Brazil, seven impact structures have been confirmed so far. Three of them, Vargeão Dome, Vista Alegre, and Cerro do Jarau, were formed in the same basaltic province belonging to the Paraná Basin, and they have several common characteristics. Oxidized basaltic breccias locally containing sandstone clasts occur in all these structures. In this work, selected samples of such breccias from the Vargeão Dome impact structure in southern Brazil were petrographically and geochemically investigated to further constrain the effects of the postimpact hydrothermal alteration. The breccia matrix shows typical oxidation effects induced by postimpact hydrothermal fluids, which highlight its heterogeneous nature, related to the impact event, and mixing components from different pre-impact stratigraphic formations. The detection of partially dissolved exsolution lamellae in pyroxene and of related alteration products constrains the effects of hydrothermal alteration in the basalts of the Vargeão Dome, which could serve as a terrestrial analog for planetary studies.

Anisotropy of magnetic susceptibility (AMS) of impact melt breccia and target rocks from the Dhala impact structure, India

2021 ◽  
Author(s):  
Anuj Kumar Singh ◽  
Jayanta Kumar Pati ◽  
Shiva Kumar Patil ◽  
Wolf Uwe Reimold ◽  
Arun Kumar Rao ◽  
...  
Keyword(s):  
Magnetic Susceptibility ◽  
Anisotropy Of Magnetic Susceptibility ◽  
Impact Structure ◽  
Magnetic Phases ◽  
Impact Melt ◽  
Rock Samples ◽  
Average Value ◽  
Magnetic Fabrics ◽  
Target Rock ◽  
The Impact

ABSTRACT The ~11-km-wide, Paleoproterozoic Dhala impact structure in north-central India comprises voluminous exposures of impact melt breccia. These outcrops are discontinuously spread over a length of ~6 km in a semicircular pattern along the northern, inner limit of the monomict breccia ring around the central elevated area. This study of the magnetic fabrics of impact breccias and target rocks from the Dhala impact structure identified a weak preferred magnetic orientation for pre-impact crystalline target rocks. The pre- and synimpact rocks from Dhala have magnetite and ilmenite as common magnetic phases. The distributions of magnetic vectors are random for most impact melt breccia samples, but some do indicate a preferred orientation. Our anisotropy of magnetic susceptibility (AMS) data demonstrate that the shape of susceptibility ellipsoids for the target rocks varies from prolate to oblate, and most impact melt breccia samples display both shapes, with a slight bias toward the oblate geometry. The average value for the corrected degree of anisotropy of impact melt rock (P′ = 1.009) is lower than that for the target rocks (P′ = 1.091). The present study also shows that both impact melt breccia and target rock samples of the Dhala structure have undergone minor postimpact alteration, and have similar compositions in terms of magnetic phases and high viscosity. Fine-grained iron oxide or hydroxide is the main alteration phase in impact melt rocks. Impact melt rocks gave a narrow range of mean magnetic susceptibility (Km) and P′ values, in contrast to the target rock samples, which gave Km = 0.05–12.9 × 10−3 standard international units (SI) and P′ = 1.036–1.283. This suggests similar viscosity of the source magma, and limited difference in the degrees of recorded deformation. Between Pagra and Maniar villages, the Km value of impact melt breccias gradually decreases in a clockwise direction, with a maximum value observed near Pagra (Km = 1.67 × 10−3 SI). The poor grouping of magnetic fabrics for most impact melt rock samples implies local turbulence in rapidly cooled impact melt at the front of the melt flow immediately after the impact. The mean K1 for most impact melt samples suggests subhorizontal (<5°) flow in various directions. The average value of Km for the target rocks (4.41 × 10−3 SI) is much higher compared to the value for melt breccias (1.09 × 10−3 SI). The results of this study suggest that the melt breccias were likely part of a sheet-like body of sizeable extent. Our magnetic fabric data are also supported by earlier core drilling information from ~70 locations, with coring depths reaching to −500 m. Our extensive field observations combined with available widespread subsurface data imply that the impact melt sheet could have covered as much as 12 km2 in the Dhala structure, with an estimated minimum melt volume of ~2.4 km3.

Paleomagnetism and rock magnetism of East and West Clearwater Lake impact structures

2019 ◽  
Vol 56 (9) ◽  
pp. 983-993
Author(s):  
Jérôme Gattacceca ◽  
William Zylberman ◽  
Adam B. Coulter ◽  
François Demory ◽  
Yoann Quesnel ◽  
...  
Keyword(s):  
Rock Magnetism ◽  
Drill Hole ◽  
Hydrothermal Activity ◽  
Radiometric Dating ◽  
Impact Structure ◽  
The West ◽  
Impact Melt ◽  
Basement Rocks ◽  
East And West ◽  
The Impact

The East and West Cleawater Lake impact structures (Wiyâshâkimî Lake, Québec), ∼26 and 32 km in diameter, respectively, have been proposed to represent an impact doublet. We investigated their paleomagnetism to contribute to this debate. The paleomagnetic directions of the impact melt rocks and impact melt-bearing breccias from the West Clearwater structure are compatible with the radiometric age of 280–290 Ma previously determined for this structure and indicate that the impact occurred during a reverse polarity interval of the geomagnetic field. A similar remagnetization direction is found in the basement within 10 km of the structure center, whereas basement farther away from the center has escaped remagnetization by the impact. Samples for the East Clearwater structure come from two holes drilled in 1963 and 1964. Unfortunately, the drill hole through the melt rocks is tilted by 30° from the vertical with an unknown azimuth. The paleomagnetic inclination of these melt rocks cannot be constrained to better than between −28° and +32°. This is, however, distinct from the inclination of the melt rocks of the West Clearwater Lake impact structure (−27.8° ± 3.7°), suggesting that the two structures do not represent an impact doublet, in agreement with recent radiometric dating. The basement rocks and the melt rocks within 10 km of the center of the West Clearwater Lake impact structure show a magnetic signature of titanohematite that crystallized during postimpact hydrothermal activity under oxidizing conditions. This is not observed in the basement or the melt rocks from the East Clearwater Lake impact structure.

scholarly journals Supplemental Material: New insights into the formation and emplacement of impact melt rocks within the Chicxulub impact structure, following the 2016 IODP-ICDP Expedition 364

2021 ◽  
Author(s):  
Sietze J. de Graaff ◽  
et al.
Keyword(s):  
Reference Materials ◽  
Geochemical Data ◽  
Impact Structure ◽  
Impact Melt ◽  
Chicxulub Impact

Appendix S1, containing all geochemical data and specific core depths of all samples and geochemical results for geologic reference materials presented in the article. Figures S1–S3, containing thinsection photographs of representative pre-impact lithologies.

scholarly journals GROUNDWATER GEOCHEMISTRY OF RROGOZHINA AQUIFER (WESTERN ALBANIA)

2017 ◽  
Vol 50 (2) ◽  
pp. 818
Author(s):  
S. Luzati ◽  
A. Beqiraj ◽  
O. Jaupaj
Keyword(s):  
Iron Content ◽  
Mineralogical Composition ◽  
Geochemical Processes ◽  
Geochemical Composition ◽  
Geochemical Characterization ◽  
Silt Fraction ◽  
Clay Layers ◽  
Dissolution Of Minerals ◽  
Groundwater Composition

This paper aims to make a geochemical characterization of the groundwater of Rrogozhina aquifer which extends over the Albanian pre-Adriatic depression covering a surface of 2100 km2. It is a multilayered aquifer consisting of intercalations between water-bearing Pliocene sandstone and conglomerate with impermeable clay layers. This aquifer occurs under typically artesian conditions because of its impermeable clay basement and semi-impermeable Quaternary cover. The groundwater shows variable geochemical composition due to different mineralogical composition of its medium and vast extension of the aquifer. However, the mainly magmatic - carbonatic mineralogical composition of the water - bearing sandstones and conglomerates has determined a geochemical composition of groundwater consisting mostly of HCO3-Mg-Ca hydrochemical groundwater type. Dissolution of minerals seems to be the major geochemical processes in the formation of the groundwater composition. The above mainly magmatic composition of sandstones and conglomerates is also responsable for the high content of iron in the grounwater of this aquifer. Iron content is higher in sandstone related groundwater where the silt fraction is mainly composed by ironbearing minerals such as magnetite, epidote, granate, sphene, amphibole and pyroxene. The general mineralization and general hardness of groundwater range from 500 to 800 mg/l and from 11 to 25ºdH, respectively.

Shock-deformed zircon from the Chicxulub impact crater and implications for cratering process

Geology ◽  
2021 ◽  
Author(s):  
Jiawei Zhao ◽  
Long Xiao ◽  
Zhiyong Xiao ◽  
Joanna V. Morgan ◽  
Gordon R. Osinski ◽  
...  
Keyword(s):  
High Pressure ◽  
Thermal Evolution ◽  
Ground Truth ◽  
Large Impact ◽  
Impact Melt ◽  
Collapse Model ◽  
Chicxulub Impact Crater ◽  
International Ocean Discovery Program ◽  
Chicxulub Impact ◽  
The Impact

Large impact structures with peak rings are common landforms across the solar system, and their formation has implications for both the interior structure and thermal evolution of planetary bodies. Numerical modeling and structural studies have been used to simulate and ground truth peak-ring formative mechanisms, but the shock metamorphic record of minerals within these structures remains to be ascertained. We investigated impact-related microstructures and high-pressure phases in zircon from melt-bearing breccias, impact melt rock, and granitoid basement from the Chicxulub peak ring (Yucatán Peninsula, Mexico), sampled by the International Ocean Discovery Program (IODP)/International Continental Drilling Project (IODP-ICDP) Expedition 364 Hole M0077A. Zircon grains exhibit shock features such as reidite, zircon twins, and granular zircon including “former reidite in granular neoblastic” (FRIGN) zircon. These features record an initial high-pressure shock wave (>30 GPa), subsequent relaxation during the passage of the rarefaction wave, and a final heating and annealing stage. Our observed grain-scale deformation history agrees well with the stress fields predicted by the dynamic collapse model, as the central uplift collapsed downward-then-outward to form the peak ring. The occurrence of reidite in a large impact basin on Earth represents the first such discovery, preserved due to its separation from impact melt and rapid cooling by the resurging ocean. The coexistence of reidite and FRIGN zircon within the impact melt–bearing breccias indicates that cooling by seawater was heterogeneous. Our results provide valuable information on when different shock microstructures form and how they are modified according to their position in the impact structure, and this study further improves on the use of shock barometry as a diagnostic tool in understanding the cratering process.

Resurge morphology of the marine Lockne impact crater, Jämtland, central Sweden

1998 ◽  
Vol 135 (1) ◽  
pp. 121-127 ◽  
Author(s):  
ERIK F. F. STURKELL
Keyword(s):  
High Speed ◽  
Impact Crater ◽  
Crystalline Basement ◽  
Impact Structure ◽  
Middle Ordovician ◽  
The North ◽  
Sequence Of Events ◽  
Sedimentary Succession ◽  
The Impact ◽  
Erosion Surface

In the Brunflo area of Jämtland, central Sweden, a Cambrian to Ordovician sedimentary sequence rests on a Proterozoic crystalline basement. The area lies just outside the site of the middle Ordovician Lockne impact, and it later experienced Caledonian overthrusting. The degree of Caledonian tectonization of the Palaeozoic varies, but an autochthonous Cambrian and Ordovician sequence apparently occurs in the greater part of the area, particularly in the north. The pre-impact sedimentary succession is 81 m thick in the autochthon, with the Middle Ordovician Furudal Limestone as uppermost member. Brunflo village is located just outside the crater, 8–9 km north of its centre, but the area was affected by the impact. The impact-generated ejecta and resurge deposits rest on a surface which cuts the sedimentary strata at a low angle. This surface cuts at progressively higher stratigraphic levels at increasing distance from the crater. According to observations in the autochthon the impact generated an erosion surface dipping 1–2° towards the crater centre. The sequence of events that shaped this surface began with bombardment with high-speed ejecta closely followed by resurging water. The resurge mixed ejecta clasts with the products of resurge erosion to form the resurge deposits. No rim wall can be traced at the Lockne impact structure, probably because a rim wall, if it formed, collapsed in the modification stage owing to local lithological conditions and because the remains of it were completely eroded in the resurge phase. It is suggested the rim wall formed in sedimentary strata with unlithified clays at their base, and that this clay was unable to support it.

Explosive interaction of impact melt and seawater following the Chicxulub impact event

Geology ◽  
2019 ◽  
Vol 48 (2) ◽  
pp. 108-112 ◽  
Author(s):  
Gordon R. Osinski ◽  
Richard A.F. Grieve ◽  
Patrick J.A. Hill ◽  
Sarah L. Simpson ◽  
Charles Cockell ◽  
...  
Keyword(s):  
Volcanic Eruptions ◽  
Impact Event ◽  
Impact Melt ◽  
The Past ◽  
Geological Processes ◽  
Current Classification ◽  
Cenozoic Era ◽  
Geological Event ◽  
Chicxulub Impact ◽  
The Impact

Abstract The impact of asteroids and comets with planetary surfaces is one of the most catastrophic, yet ubiquitous, geological processes in the solar system. The Chicxulub impact event, which has been linked to the Cretaceous-Paleogene (K-Pg) mass extinction marking the beginning of the Cenozoic Era, is arguably the most significant singular geological event in the past 100 million years of Earth’s history. The Chicxulub impact occurred in a marine setting. How quickly the seawater re-entered the newly formed basin after the impact, and its effects of it on the cratering process, remain debated. Here, we show that the explosive interaction of seawater with impact melt led to molten fuel–coolant interaction (MFCI), analogous to what occurs during phreatomagmatic volcanic eruptions. This process fractured and dispersed the melt, which was subsequently deposited subaqueously to form a series of well-sorted deposits. These deposits bear little resemblance to the products of impacts in a continental setting and are not accounted for in current classification schemes for impactites. The similarities between these Chicxulub deposits and the Onaping Formation at the Sudbury impact structure, Canada, are striking, and suggest that MFCI and the production of volcaniclastic-like deposits is to be expected for large impacts in shallow marine settings.

scholarly journals Post-Impact Faulting of the Holfontein Granophyre Dike of the Vredefort Impact Structure, South Africa, Inferred from Remote Sensing, Geophysics, and Geochemistry

Geosciences ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 96
Author(s):  
Martin D. Clark ◽  
Elizaveta Kovaleva ◽  
Matthew S. Huber ◽  
Francois Fourie ◽  
Chris Harris
Keyword(s):  
South Africa ◽  
Remote Sensing ◽  
Crater Floor ◽  
Impact Structure ◽  
Impact Melt ◽  
Geophysical Modeling ◽  
Tectonic Events ◽  
Post Impact ◽  
The Impact

Better characterization features borne from long-term crustal modification processes is essential for understanding the dynamics of large basin-forming impact structures on Earth. Within the deeply eroded 2.02 Ga Vredefort Impact Structure in South Africa, impact melt dikes are exposed at the surface. In this study, we utilized a combination of field, remote sensing, electrical resistivity, magnetic, petrographical, and geochemical techniques to characterize one such impact melt dike, namely, the Holfontein Granophyre Dike (HGD), along with the host granites. The HGD is split into two seemingly disconnected segments. Geophysical modeling of both segments suggests that the melt rock does not penetrate below the modern surface deeper than 5 m, which was confirmed by a later transecting construction trench. Even though the textures and clast content are different in two segments, the major element, trace element, and O isotope compositions of each segment are indistinguishable. Structural measurements of the tectonic foliations in the granites, as well as the spatial expression of the dike, suggest that the dike was segmented by an ENE–WSW trending sinistral strike-slip fault zone. Such an offset must have occurred after the dike solidified. However, the Vredefort structure has not been affected by any major tectonic events after the impact occurred. Therefore, the inferred segmentation of the HGD is consistent with long-term crustal processes occurring in the post-impact environment. These crustal processes may have involved progressive uplift of the crater floor, which is consistent with post-impact long-term crustal adjustment that has been inferred for craters on the Moon.

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