Structural analysis of shatter cones from the Slate Islands, northern Lake Superior

1983 ◽  
Vol 20 (1) ◽  
pp. 1-18 ◽  
Author(s):  
R. M. Stesky ◽  
H. C. Halls
Keyword(s):  
Cross Section ◽  
Land Surface ◽  
Impact Crater ◽  
Elastic Anisotropy ◽  
Lake Superior ◽  
Meteorite Impact ◽  
Central Focus ◽  
Rock Types ◽  
Shatter Cones ◽  
Unusual Type

Shatter cones, an unusual type of fracturing produced by intense shock, are found widespread on the Slate Islands in northern Lake Superior. The islands have been interpreted as the central uplift of an eroded meteorite impact crater about 30 km in diameter. The cones are best developed in certain rock types: Keweenawan basalt flows and chilled margins of associated feeder dikes, and Archean diorite and foliated feldspar porphyry. At certain sites cones show an elongate cross section and anomalous orientation caused by foliation-induced elastic anisotropy in the host rock.In general the cones point upward and inward toward the centre of the Slate Islands group. After structural correction of some sites according to paleomagnetic data, there is increased convergence of cone axes to a central focus (the inferred impact point) that occurs at a height of about 1 km above the present land surface.

The Slate Islands: a probable complex meteorite impact structure in Lake Superior

1976 ◽  
Vol 13 (9) ◽  
pp. 1301-1309 ◽  
Author(s):  
H. C. Halls ◽  
R. A. F. Grieve
Keyword(s):  
Country Rock ◽  
Lake Superior ◽  
Impact Structure ◽  
Early Paleozoic ◽  
Meteorite Impact ◽  
Erosion Level ◽  
Igneous Activity ◽  
Shatter Cones ◽  
Host Rocks ◽  
Sedimentary Unit

Shock metamorphic effects in samples from the Slate Islands, Lake Superior (48°40' N, 87°00' W) suggest that the islands are part of a meteorite impact structure. The islands form the central uplift of a complex crater and are ringed by a submerged trough and annular ridge with a diameter of 30 km. Precambrian bedrock units are locally brecciated and cut by allochthonous breccia dikes. These dikes contain clasts of identifiable country rock and also fragments of a sedimentary unit, possibly Upper Keweenawan in age, which is no longer present in outcrop. The orienta tions of shatter-cones present in the breccia host-rocks indicate the interior of the islands as the approximate shock centre. Microscopic planar features, equivalent to those described from other impact sites, occur in quartz and plagioclase and the level of shock deformation increases towards the interior of the islands. The shock event postdates Keweenawan igneous activity (about 1.1 b.y. old) and, on the basis of the erosion level, may be early Paleozoic in age.

Chapter 4 The Loch Maree Group

2002 ◽  
Vol 26 (1) ◽  
pp. 29-44
Keyword(s):  
Cross Section ◽  
Detrital Zircon ◽  
Main Part ◽  
Close Association ◽  
Volcanic Origin ◽  
Metasedimentary Rocks ◽  
Rock Types ◽  
Depositional Age ◽  
Nd Model Age ◽  
Narrow Bands

The supracrustal rocks of the Loch Maree Group (LMG) consist of a variety of metasedimentary rocks interbanded with amphibolites considered to be of volcanic origin. The metasedimentary rocks fall into two distinct categories: a) schistose semipelites, which form the main part of the outcrop; and b) narrow bands of different rock types, including siliceous, carbonate-bearing and graphitic rocks, occurring in close association with the metavolcanic amphibolites. Both the compositional banding and the dominant foliation throughout the LMG outcrop are steeply dipping and trend uniformly NW-SE.The sequence of lithotectonic rock units from SW to NE (structurally upwards) is shown in the cross-section (Fig. 4.1) and briefly described in Table 4.1. The original names of the lithotectonic units (Park 1964) are retained for convenience. The depositional age of the LMG is presumed to be around 2.0 Ga, based on a Sm-Nd model age (O'Nions et al. 1983) and detrital zircon dates (Whitehouse et al. 1991 a, 2001) (see below).Semipelites form several distinct NW-trending belts separated by amphibolite sheets. The most prominent belt comprises the Flowerdale schist unit (see map) which occupies a broad belt about 700 m in width, extending in a northwesterly direction across the Gairloch district, but ending north of the mapped area, where the two amphibolites from either side converge, 3.5 km north of the Gairloch-Poolewe road. This belt is offset in the centre of the area by the Flowerdale fault, and has a total exposed length of about 15 km. Southwest of this belt is the

The preservation of the Agoudal impact crater, Morocco, under a landslide: Indication of a genetic link between shatter cones and meteorite fragments

Geomorphology ◽  
2017 ◽  
Vol 295 ◽  
pp. 76-83 ◽  
Author(s):  
Hassane Nachit ◽  
El Hassan Abia ◽  
Costanza Bonadiman ◽  
Mario Di Martino ◽  
Carmela Vaccaro
Keyword(s):  
Impact Crater ◽  
Genetic Link ◽  
Shatter Cones

scholarly journals The Carancas meteorite impact crater, Peru: Geologic surveying and modeling of crater formation and atmospheric passage

2009 ◽  
Vol 44 (7) ◽  
pp. 985-1000 ◽  
Author(s):  
T. KENKMANN ◽  
N. A. ARTEMIEVA ◽  
K. WÜNNEMANN ◽  
M. H. POELCHAU ◽  
D. ELBESHAUSEN ◽  
...  
Keyword(s):  
Impact Crater ◽  
Crater Formation ◽  
Meteorite Impact

scholarly journals The Whitecourt meteorite impact crater, Alberta, Canada

2010 ◽  
Vol 45 (9) ◽  
pp. 1429-1445 ◽  
Author(s):  
Randolf S. KOFMAN ◽  
Christopher D. K. HERD ◽  
Duane G. FROESE
Keyword(s):  
Impact Crater ◽  
Meteorite Impact

Simulasi Perancangan Drainase Muka Tanah pada Bandar Udara Achmad Yani Semarang Sebagai Salah Satu Usaha Pencegahan Banjir

WARTA ARDHIA ◽  
2013 ◽  
Vol 39 (4) ◽  
pp. 305-316
Author(s):  
Ataline Muliasari ◽  
Lupi Wahyuningsih
Keyword(s):  
Surface Water ◽  
Cross Section ◽  
Land Surface ◽  
Drainage Channel ◽  
Water Drainage ◽  
Hydraulic Radius ◽  
Channel Depth ◽  
Cross Sectional ◽  
Surface Drainage ◽  
Sectional Shape

Drainage is defined as surface water drainage, either by gravity or by pump which aims to prevent inundation, maintain and lower the water level im order to avoid the amount of water. Ahmad Yani Airport has a poor drainage systems. Furthermore, land subsidence in Semarang area potential for experiencing flooding when the rainy season with a fairly high rainfall. Based on the results of processing the data showed that it is needed the land surface drainage channel with a cross-sectional shape of a trapezium. When the width of the base of the cross section is 3 meters , then the required channel depth is 3.9 meters with a hydraulic radius is 0.82-meter, and hydraulic depth is 3.05 meters. Drainase didefinisikan sebagai pembuangan air permukaan, baik secara gravitasi maupun dengan pompa yang bertujuan untuk mencegah terjadinya genangan, menjaga dan menurunkan permukaan air sehingga genangan air dapat dihindarkan. Bandar Udara Ahmad Yani dengan kondisi sistem drainase yang kurang baik dan penurunan permukaan tanah di wilayah Semarang, maka bila musim penghujan tiba dengan curah hujan yang cukup tinggi selalu berpotensi untuk mengalami banjir. Berdasarkan hasil pengolahan data juga didapatkan hasil bahwa untuk menyesuaikan antara curah hujan di wilayah Semarang dengan luas area Bandar udara Achmad Yani diperlukan saluran drainase muka tanah berupa saluran dengan bentuk penampang trapezium. Bila lebar dasar dari penampang trapezim tersebut adalah 3 meter, maka diperlukan saluran sedalam 3,9 meter dengan Jari-jari hydraulic 0,82 meter, dan kedalaman hydraulic 3,05 meter.

Survival of Extremotolerant Bacteria from the Mukundpura Meteorite Impact Crater

Astrobiology ◽  
2019 ◽  
Vol 19 (6) ◽  
pp. 785-796 ◽  
Author(s):  
Rebecca S. Thombre ◽  
E. Shivakarthik ◽  
Bhalamurugan Sivaraman ◽  
Parag A. Vaishampayan ◽  
Arman Seuylemezian ◽  
...  
Keyword(s):  
Impact Crater ◽  
Meteorite Impact

scholarly journals Groundwater Chemistry of Some Selected Areas in Southeastern Norway

1980 ◽  
Vol 11 (1) ◽  
pp. 33-54 ◽  
Author(s):  
Jens-Olaf Englund ◽  
Jan Aug Myhrstad
Keyword(s):  
Land Surface ◽  
Mineral Water ◽  
Sea Water ◽  
Electrical Conductance ◽  
Reservoir Rock ◽  
Rock Fractures ◽  
Sea Salts ◽  
Reservoir Rocks ◽  
Rock Types ◽  
Groundwater Samples

Within three areas in Southeastern Norway, Lake Mjøsa district, Ås and Moss - Jeløy, groundwater samples for chemical analysis were collected during the years 1971–77 from 98 drilled wells in bedrocks. The water was taken at depths ranging from 15 m to 110 m below the land surface. The groundwater surface is usually present well below the overlying unconsolidated deposits of glacial, glacifluvial or marine origin. The movement of groundwater within the aquifers investigated is so slow that regional changes in water quality is not only dependent on weathering in the unsaturated zone, but also dependent on the solution of reservoir rocks below the groundwater surface. Variations in specific electrical conductance (20°C) largely reflects the different reservoir rock types. The highest values, around 550 μS/cm, are typically found in dark calcareous shales, while sandstones and gneisses give values around 300 μS/cm. The areas Ås and Moss-Jeløy are situated below the Late-Postglacial marine limit. The groundwater is here more or less influenced by ancient sea salts, perhaps also by fossil sea water, left over in sediments or in rock fractures. Brackish groundwater was also found. The composition of groundwater is largely governed by mineral-water equilibria. Most investigated water samples have not reached equilibrium with their surrounding minerals.

scholarly journals Shatter cones: (Mis)understood?

2016 ◽  
Vol 2 (8) ◽  
pp. e1600616 ◽  
Author(s):  
Gordon R. Osinski ◽  
Ludovic Ferrière
Keyword(s):  
Accurate Method ◽  
Small Region ◽  
Impact Craters ◽  
Meteorite Impact ◽  
Geological Features ◽  
Cone Formation ◽  
Apparent Diameter ◽  
Shatter Cones ◽  
Evidence Of Impact

Meteorite impact craters are one of the most common geological features in the solar system. An impact event is a near-instantaneous process that releases a huge amount of energy over a very small region on a planetary surface. This results in characteristic changes in the target rocks, from vaporization and melting to solid-state effects, such as fracturing and shock metamorphism. Shatter cones are distinctive striated conical fractures that are considered unequivocal evidence of impact events. They are one of the most used and trusted shock-metamorphic effects for the recognition of meteorite impact structures. Despite this, there is still considerable debate regarding their formation. We show that shatter cones are present in several stratigraphic settings within and around impact structures. Together with the occurrence of complete and “double” cones, our observations are most consistent with shatter cone formation due to tensional stresses generated by scattering of the shock wave due to heterogeneities in the rock. On the basis of field mapping, we derive the relationshipDsc= 0.4Da, whereDscis the maximum spatial extent of in situ shatter cones, andDais the apparent crater diameter. This provides an important, new, more accurate method to estimate the apparent diameter of eroded complex craters on Earth. We have reestimated the diameter of eight well-known impact craters as part of this study. Finally, we suggest that shatter cones may reduce the strength of the target, thus aiding crater collapse, and that their distribution in central uplifts also records the obliquity of impact.

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