IT iconb TECTONICS BLOG Rev. 2020-02-14

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Figure 1
Figure 1. Far-field crustal strain fields mapped around two large impact craters on the North American tectonic plate (NAP).  Circumferential blast patterns drawn around each crater include strain sectors dominated by compression (C -downrange) and reverse faulting, tension (T -uprange) and normal faulting, or mixed-mode (M) stresses and faulting within lateral sectors. The foreland is compressed and thickened in a lithospheric wedge downrange of the crater where compressive shear is focused and refracted back to the surface at great distances (fig. 2). The lithosphere is stretched and sheared with transform faults in the wake of each impact where igneous activity is common, and mixed-modes of crustal faulting occurs.  Crustal seismogenic zones inside 90oN to 90oS latitudes and 30oE to 150oW longitudes mapped from the US Geological Survey National Earthquake Information Center event query (Herman, 2006). Basins and uplifts mapped from Ewing and Lopez (1991) and Li (2006). LU – Llano uplift. CP – Colorado Plateau. ETOPO1 surface base theme from Amante and Eakins (2008).  





Figure 2
Figure 2.
Various parallel views of a 3D SketchUp Pro model of Earth IT far-field strain effects stemming from the Chicxulub impact event (A & B Top views, C - Left view, D -Isometric view). The model is oriented with the crater at the model center (coordinates 0,0,0) and the y-axis aligned downrange of the impact. Earth’s respective layers are rendered semi-transparent to show geospatial geometry of the strain effects and reflection geometry. The 3D pink ellipses (top views) represent first attempts at fitting 3D fault planes symmetrically about the impact to begin accounting for fault-related ITFF strains.







Chicxulub hub

Figure 3A. An orthographic map projection of Earth centered on -90o longitude and 20o latitude near the Chicxulub crater on the South shore of the Gulf of Mexico showing how tectonic plates currently spin about the crater. The red arrows are a selected few, stylized motion vectors pointing in the direction of horizontal drift based on historical GPS-monitoring of tectonic-plate motions. Actual motions are depicted to scale in figure 1. Tectonic plate boundaries show that the crust is fractured into small plates to the South, and rings drawn around the crater at 600, 1700, 2900, and 3800 km radii represent crest lines of circumferential welts.
3B.
A plot of the horizontal component of plate velocity versus distance from the crater for GPS stations located on the North American Plate (NAP) show a velocity boundary at about 2900 km radial distance, the same distance as the depth to the core-mantle boundary (table 1). AP – Atlantic plate, PP – Pacific Plate, COP – Cocos plate, CAP – Caribbean plate, SAP – South American plate.




Table 1



Figure 4

Figure 4.
Earth profile illustrating the interior phase boundaries and parameters used to calculate impact-related ground energy (Table 2), and to construct CAD models of the ITFF strain effects. The mean radius of Earth varies slightly, and the sperical radius of 6370 km is used here. Note the light-gray spherical traces stacked below an impact crater representing the traces of spherical reflections having the same radii as the phase boundaries. Constructive interference of primary reflectors from the core-mantle boundary and a mid-mantle phase change correspond to the radii of circumferential surface arches (positive-relief welts traced by rings in fig. 3A).






Figure 5Figure 5. A regional map of hypothetical ITFF strain fields associated with the Chesapeake crater. Note the traces of the crustal welts stemming from the Chicxulub (CX) and the constructive overlapping and spatial alignment of the 760-km and CX2900 arches with the Adirondack uplift and bulging of the continental shelf. ETOPO1 surface base theme from Amante and Eakins (2008).






Figure 6Figure 6A. Profile diagram of Earth’ near-surface geometry of p-wave refraction paths resulting from various take-off angles, and a model surface line used to construct crustal welts that likely have deep-seated origins stemming from refracted and reflected ground energy suddenly imparted by large bolide impacts. 6B. A 3D mesh was generated using AutoCAD R14 by duplicating and rotating the model surface line to construct equuidimensional sectors comprised of simple line segments connecting equally-spaced vertices. The mesh potrays the mapped circumferential crustal welts relative to the impact craters.


 Figure 7Figure 7. Four GE views of the hypothetical ITFF strain fields stemming from the Chicxulub and Chesapeake impact event with respect to A.) Hypothetical fault and wedge models displayed in Google Earth on the ETOPO1 base theme (Amante and Eakins, 2008), B.) Whole-Earth gravity (Sandwell and SMith, 2009). C.) Whole-Earth aeromagentics (Maus and others, in review), and D.) Continental geology by Era.


Gregory Charles Herman, PhD
Flemington, New Jersey, USA


Introduction * Chicxulub and Cheasapeake impacts * Ground energy * Strain effects * Computer models * Summary * References

Chapter 1. Impact tectonics; beyond the craters

Abstract

This work details a set of new hypotheses with illustrations showing how large-bolide (asteroid or comet) impacts on Earth have far-reaching strain effects extending well beyond the craters that contribute to plate tectonics. Prior impact-tectonics research in planetary geology has focused on cratering processes and near-crater strains whereas consideration is given here to the prospect of catastrophic, sudden upheavals occurring thousands of kilometers away from the ground energy introduced by hyperveolcity bolide impacts that dissipate rapidly at first then decay through time. A plate-tectonic paradigm that excludes impact-related tectonic effects cannot adequently explain the driving forces behind such catastropic events that terrestrial planets certainly endure, and that contribute to our differentiation of geological time on Earth. The hypotheses reflect over a decade’s research into the characterization of impact-tectonic far-field (ITFF) crustal and lithospheric strains surrounding the Chicxulub (~66 Ma) and Chesapeake (~35 Ma) impact craters on the North American plate (fig. 1). The main problem with identifying and cataloguing suddenly versus uniformly imparted ITFF strains is that there is currently no basis to do so. That is, current tectonic theory does not account for far-field, impact-generated secondary structures and plate reorganizations stemming from planetary accretion, and therefore doesn't consider catastrophic, causative agents behind such enigmatic geological features and processes like diatremes, hot-spots, kimberlites, and epeirogenic uplifts. Modern, remotely sensed Earth data are fundamental to the formulation of these hypotheses that incorporate far-field strain effects stemming from periodic large-bolide impacts that not only profoundly alter Earth's biological systems but correpsond to major tectonic shifts and uphevals with demostrable ties to ill-explained epeirogenic events like that of Laramide age in the North American plate. Moreover, simlar ITFF strains are mapped around the Chesapeake impact in the Mid-Atlantic region of the Eastern USA that are scaled-down with respect to the Chicxulub event. The computer-generated three-dimensonal (3D) geometric models of the ITFF strains detailed herein are currently being shared on the Internet so that others can scrutinize or refine the models going forward (fig. 2).

Introduction

Plate tectonics is a considered unifying geological theory that should evolve together with our ability to sense and characterize natural phenomena. Ribiero (2000) pointed out that Earth is an open, geodynamic system subject to external stimulation that current plate-tectonic theory simply doesn’t account for. Moderm empirical observation shows us that the perpetual, gradual tectonic shifts that we map and catalogue do not include causal mechanisms for enigmatic tectonic phenomenon like diatremes, hot-spots, kimberlites, and epeirogenic uplifts. With the advent and use of modern digital computing and remote sensing, clearer pictures are emerging on how geodynamic systems and plate tectonics work, and it's not all uniformly staged. Of note here is how far-reaching, lithospheric strain fields are imparted to Earth from large-bolide (asteroid or comet) impacts that are an integral part of our tectonic history (fig. 1). But it remains sketchy how these strain fields formed, how they overprint earlier orogenic belts and influence subsequent geodynamic movements. The main problem with differentiating and partioning terrestrial strain features between those suddenly versus gradually formed is that there currently is no basis to do so. That is plate-tectonic theory currently doesn’t factor in the energy absorbed from catastrophic, large-bolide impacts with the resulting momentum transfer and net strains. This hampers our understanding and characterization of many geological features that probably formed suddenly as a result of large-bolide collisions occurring at hypervelocity speeds (>3 km/sec).

This work focuses principally on crustal and lithospheric strains observed by integrating physiographic, geologic, and geophysical spatial data. More consideration and geophysical modelling of deep mantle strains will be required to understand the geodynamics behind the proposed ITFF lithospheric welts and faults shown herein as systematic impact-tectonic strain responses distributed circumferentially around craters (figs. 1-3). But is is important to note in this introduciton that geologic time on Earth reflects punctuated equilibreum (Gould and Eldredge, 1977) with many biological revolutions corresponding to the major eras and Epochs of geolocial time rather than having a unformly staged, plodding escalation of life's complexity. For example, large-reptile extinctions at the Mesozoic and Cenozoic Era boundary (K/T) coincide with the asteroid impact in the Gulf of Mexico with the resulting worldwide proliferation of placental-bearing mammals. The hypothesis set forth below provide some tools and methods to begin discriminating between the varius ITFF strain responses, and is only a beginning in an attempt to address aspects of long-lasting geodynamic perturbations imparted by punctuated large-impact events versus, rather than considering that our current tectonic setting merely stems from constant and gradual processes reflected by more traditional, uniformitarianistic thought. In contrast, the Moon is thought to have been spalled off Earth by collision with an extremely large extraterrestrial body early in the bombardment phase of our accretion history (~3.8 bya), but today, there is absolutely no accounting of any plate reorganizations or geodynamic changes resulting from any one of a large number of punctuated impact events reflected in geological time. Recast as a question, can the sudden excavation, compaction, and shearing of the lithosphere caused by oblique, hypervelocity bolide impacts raise mountains and form expansive basins at great distances beyond the crater in a geological instant?

The Chicxulub and Chesapeake Impact events

Impact-tectonics far-field (ITFF) strains are mapped and illustrated here with respect to the Chicxulub (~66.0 Ma) and Chesapeake (~ 35.5 Ma) impact craters (fig. 1). The Earth impact database (2011) lists the diameter of the former as 150 km and the latter at 40 km. Both craters have been intensively studied, and are portrayed here as having formed as a result of oblique, hypervelocity strikes from the southeast (SE) towards the northwest (NW) at 45o incident angles (figs. 1 and 2). The impact angle for the Chicxulub event may have been as low as 25o to 30o based on crater asymmetry, fern spikes and palynofloral extinctions across North America (Schultz and D’Honndt, 1996). However, determining the speed, obliquity, and direction of a bolide impact is fraught with uncertainty and is constrained only in the case of low-incident impacts (<30o) that develop visual variation in form including oblong crater shapes and symmetric, distal ejecta blankets (Schultz and Gault, 1990). A 45o incident angle is statistically the most probable one (Gault and Wedekind, 1978; Schultz and Gault, 1990; Ormo and others, 2013) and is used here for developing a virtual geometric models of the various ITFF strain fields (fig. 2). Hypothetical, expansive, brittle strain fields on Earth surrounding large impact craters that likely stem from the reflection and refraction of large seismic waves dispelling absorbed impact ground energy, and in the case of the Chicxulub event, also likely generated geodyamic perturbations inlcuding polarity reversal of the roation of the North American (tectonic) plate (NAP, fig. 3; Herman, 2006; 2009).

The Chicxulub impact crater is world renowned owing to its catastrophic disruption of biological systems on Earth and division of geological time at the Cretaceous-Paleogene time boundary (K-Pg). Gulick and others (2013) provides a thorough review of the geological and geophysical characterization of this site. The crater was discovered and confirmed between 1970 to 1990 and the impact 'event' is now recognized as one of Earth’s youngest, multi-ring impact structures produced by multiple bolide impacts, including a very large one that produced the main Chicxulub crater (170 km diameter) and several smaller ones clustered nearby that produce aeromagnetic potential-field anomalies and point to a multiple impact sites from a fragmented bolide that imparted a series of clusteredd percussions. This event is portrayed here to result from four, tightly clustered craters likely formed by the estimated 10 + 4- km diameter Nemesis bolide (Alvarez and others, 1980), and three smaller ones having 1-km model diameters (fig. 2).

The Chesapeake impact crater was discovered by the U.S. Geological Survey beginning in 1986 through deep coring efforts to establish an aquifer framework for the Chesapeake Bay area (fig. 5). The crater was confirmed and officially reported by 1992 and is currently tied for fifteenth place in the world with respect to the crater diameter (Poag and others, 1992; Powars and others, 1993; Earth Impact database, 2011). It has been reported as being the largest impact crater in the United States (Collins and Wunnerman, 2005) and the Earth’s largest submarine peak-ring impact crater (Poag, 1997). At least one other smaller bolide impact of approximately the same age occurs about 340 km to the northeast of the Chesapeake crater (Poag, 1993). Its crater symmetry suggests that it may have resulted from a projectile fragment that was ejected downrange of the Chesapaeke (Mathur and others, 2015). It is also liekly that the Chesapeake impact was also an event involving more than one strike of a fragmented bolide. The trajectory of the strike is uncertain, but portrayed here to be from the SE to the NW aligned up the axis of Chesapeake Bay, with the bay tributaries forking outward into the foreland from the primary compression path (fig. 5).

Another ITFF strain feature stemming from hypervelocity, oblique bolide impacts is a thickened wedge of lithsophere and crust situated downrange from the crater that is bilaterally disposed about a center line corresponding to the horizontal azimuth of the bolide’s trajectory (figs. 2 and 6). The nature and physical extent of this feature is poorly understood owing to the lack of definition and recognition of this phenomenon. Many laboratory experiments have been conducted using oblique bullet-sized projectiles into Earth materials to investigate cratering phenomenon but the conditions surrounding hypervelocity events cannot be duplicated by humans in the laboratory (Schultz, 2015). From a structural viewpoint, when rock is subject to compression it fractures and shears with characteristic geometry following established criteria (Anderson, 2017; Labuz and Zang, 2012). Accordingly, an indenter compressing material at an oblique angle focuses compressive stress and strain downrange of the crater (figs. 2 and 6A).  This phenomenon was found by Stickle and Schultz (2012;2014) in laboratory tests using aluminum projectiles fired obliquely into plexiglass targets that resulted in mesoscopic, downward-descending structural damage zones that they termed ‘tongues’ in the compressed foreland sector with take-off angles parallel to projectile oblique trajectories. Immediately in front of the crater the crust and lithosphere are depressed and excavated from an impact-generated plunger effect, and in the case of the Chicxulub impact, the likey creation of the Gulf of Mexico. Owing to the geometry of compressive seismic waves, the depressed and excavated material near the crater leads to foreland contraction and tectonic uplift because p-wave compression paths follow concave-upward refraction paths that descend, flatten out, and then refract upward to intersect Earth’s surface thousands of kilometers distance beyond the crater (fig. 6A). Textbook p-wave paths generated at Earth’s surface are depicted in figure 6A as flattening near the base of the asthenosphere at about 660 km depth, and follow a return path upward to the surface nearly 3000 kilometers radial distance from the crater.

Absorbed ground energy

But at what threshold value of energy flux do geodynamic changes on Earth result from such events? The total energy involved in plate tectonics at any given moment should immediately increase by the ground energy absorbed by Earth upon collision with a large, hypervelocity bolide. That is, if the total energy spent moving all of the tectonics plates at any given second in time suddenly increases by the ground energy imparted by an impact, then this relationship can be quantified as: 

Equation 1.  PTETotal (Post-impact) = PTE1 (Pre-impact) + impact ground energy (IGE).

Based on the present circumferential tectonic movements of the North and Central American tectonic plates (fig. 4), the absorbed ground energy from impacts must dissipate rapidly at first, then slowly through time in a yet defined (logarithmic?) manner. This is apparent for the Chicxulub event because the lithosphere is still rotating and grinding around a strain-hardened, cratered hub to dissipate an energy flux introduced eons ago. A recent estimate of the annual energy output (or total work done) by plate tectonics on Earth is on the order of 1019 joules, with 60% thought to be expended though earthquake seismicity (Swedan, 2013). That’s about ~1012 joules of work per second that Earth expends in moving its surface plates around. By comparison, the ground energy absorbed by a terrestrial planet from large bolides of the size responsible for the Chesapeake and Chicxulub craters is on the order of 1022 to 1018 joules using seismic efficiencies on the order of 10-2 to 10-6 (table 1; Shultz and Gault, 1975; Meschede and others, 2011). That’s apraoching or exceeding a million (109) times more energy suddenly being introduced into the plate-tectonic equation from a large impact. Elliot (1976) estimated the gravitational energy expended to emplace the largest thrust sheet in the Northern Rocky Mountains of Alberta Canada at about 1019 joules. In other words, there is more than enough ground energy introduced suddenly to terra firma from large-bolide impacts than it takes to raise mountains like the North American Rockies. That is not to say that catastrophic impact events are solely responsible for mountain builsing, just that impact tectonics may be one causative agent in a set including ordinary tectonic orogenesis.

Impact-tectonic far-field (ITFF) strain hypotheses

Based on these findings, five (5) new hypotheses are elaborated below with respect to the ITFF theme:

1) Large bolides with diameters over 1 kilometer that impact terrestrial planets produce widespread brittle strain fields in the lithosphere from the dissipation of imparted ground energy that extends outward beyond the crater for thousands of kilometers, and are therefore classified here as far-field strains versus those occurring near the crater. The threshold distance between distant versus close strains has not yet been fixed, but on Earth may lie at a radial distance approximating the 660-km depth to the subsurface seismic discontinuity at the base of asthenosphere between the upper and lower mantle (figs. 2, 5, and 6A) which plays an important role in the dynamic state of the Earth's interior.

2) Large, hypervelocity bolides that obliquely impact terrestrial planets leave telltale blast patterns circumferential to craters showing:

a) Compacted, sheared, and thickened lithosphere situated in the foreland sector lying downrange of the crater that is bilaterally disposed about the bolide trajectory. These foreland strains include lithospheric wedging portrayed here with basal geometry following refraction paths of compressional seismic waves (p-waves) that fan out into the foreland (fig. 6A).
b) Extended, stretched, and thinned lithosphere  up range in the hinterland sector opposing the foreland. Magma is commonly generated here through decompression melting and the eventual development of hot spots and aseismic ridges. This sector is referred to as the “forbidden zone” in impact cratering studies (Gault and Wedekind, 1978) owing to its characteristic lack of ejecta from low-incident impacts (<45o).
c) Bi-lateral, medial sectors in the lithosphere that fill gaps in the blast pattern between the foreland and hinterland sectors. These medial sectors likely involve lesser volumes of magmatism and a variety of mixed-mode faults. Variations in the geometry of a specific blast pattern are likely predicated by variations in both the physical nature of the projectile and target, impact obliquity and speed. Experimentation is needed in order to characterize these variations. These sectors have been shown experimentally to contain distal, symmetric ejecta blankets resembling butterfly-wings especially from impacts at very-low incidence angles (<10o; Gault and Wedekind 1978).

3) ITFF lithospheric strains include circumferential welting at radial distances of thousands of kilometers beyond the crater where primary seismic reflections from the impact are returned to Earth’s surface off deep, interior phase boundaries (figs. 2, 4 and 6). Associated mantle creep or brittle flexural lithospheric responses contributing to the development and timing of these welts are poorly understodd.

4) ITFF strains overprint and can perturb inherited tectonic processes on regional and sometimes global scales. On terrestrial planets like Earth having continuous and gradual plate tectonic shifts, very large-impacts can directly influence subsequent plate motions, but the threshold energy values between those having pronounced versus subtle or no geodynamic effects has yet to be determined.

5) The strain rates and geodynamic perturbations in plate movement occur rapidly upon impact and dissipate at decaying rates moderated by the propagation velocities of seismic waves and mantle creep. Whether periodic sudden increases in magma generation and plate motions ensue immediately upon impact and slowly dissipate through time in a systematic manner has not been generally considered or characterized with mathematics or geophyscial models.

When considering how impact ground energy (IGE) systematically dissipates into finte-strains within Earth's crust, lithosphere, and asthenosphere, it becomes cessary to account for the various brittle, ductile, and melt bulk-stain responses. The dissipation of imact ground energy from conductive heat loss to the atmosphere is not considered here as consideraton is given below only to impact-tectonic strains. Accrordingly,

Equation 2:  IGETotal = IGEB (brittle strains) + IGED (ductile strains) + I + IGEM (melting)

It is unclear if brittle strain responses to suddenly imposed shear stresses occur in the upper asthenosphere because of high strain rates, or if they do occur, what their depth limit is, and how their development and spatial distribution is influenced by varying the impact criteria listed in table 2. This topic certainly merits more consideration and testing, but analog tests using physical models is hampered by the difficulty of mimicking the projectile velocity, or the physical conditions producing planetary layering, or the time needed to dissipate the energy flux. The brittle strains are portioned into those commonly seen at Earth’s surface. They include brittle fracturing (no interstitial fault slip) and the three principal fault types exhibiting dominantly normal, reverse, and transform fault slips:

Equation 3: IGEB = IGEBF (fracturing) IGEBR (reverse faulting) + IGEBN (normal faulting) + IGEBT (transform faulting).

The ductile strains include any permanent bulk compaction and folding. Bulk compaction accounts for any penetrative, permanent solid recrystallization, reduction in porosity or increase in material density as a result of crystal plasticity and shock metamorphism. Folding strains include the buckling and flexures directly stemming from impact stresses. I am unaware of any scientific experimentation or reports of the amount of work done or energy spent from folding geological material. The set of ductile strain mechanisms for dissipating IGE is therefore:

Equation 4: IGED = IGEM (melting) + IGEC (bulk compaction) + IGEF (folding)

Melt production includes all terrestrial material directly melted by conductive heating or friction, the latter of which includes pseudotachylyte formed along brittle or ductile shear planes that may sole out along p-wave refraction paths (figl 4) or distributed within impact-generated lithospheric wedges. The total accounting of impact-induced ground energy therefore includes a set of seven possible strain responses:

Equation 5: IGETotal = IGEM (melting) + IGEC (bulk compaction) + IGEDF (folding) + IGEBF (fracturing) +  IGEBR (reverse faulting) + IGEBN (normal faulting) + IGEBT (transform faulting)

Computer models

Soon after mapping ITFF strains surrounding the Chicxulub impact (Herman, 2006) I began using computer-aided drafting systems to build virtual, three-dimensional (3D) globes of Earth including its seismological layering to visualize and examine the structural and geophysical controls on the observed strain fields (figures 2, 4, 6 and table 1). I currently use Trimble's SketchUp Pro computer-aided-drafting (CAD) software to develop ITFF strain models, whereas earlier modelling efforts used AutoCAD. SkethUP output models are compatible with Google Earth (GE), one of today’s most robust and universally employed virtual globes that provides seamless integration of complimentary geological and geophysical data sets to visualize and test the modelling results. 

This approach has facilitated the search for other large impacts on Earth but progress is hampered by the lack of recognition or confirmation of other large craters, many of which are undiscovered or unconfirmed as they too lay buried deep beneath younger sedimentary blankets like the two aforementioned that evaded discovery for a very long time. Large craters also probably lie concealed beneath thick ice sheets or at the bottom of the seas making confirmation difficult in either case. The current Earth Impact Database (2011) has only one confirmed impact mapped in the oceanic realm which emphasizes how nascent of view we have on these processes. Nevertheless, at the time I concluded a focused study on ‘orogenic’ structures in the Pennsylvania Salient (Herman, 1984) I found ‘out of sequence’ structures and shock-like penetrative fabric in the Silurian quartzites, but was unaware of the concurrent discovery of the Chesapeake Invader (Powers and others, 1993; Poag, 1999). Since then, from working in in adjacent regions of Pennsylvania, New Jersey and New York, there is ample evidence of brittle structural overprinting including sulfide-mineralized faults and veins in the central Mid-Atlantic continental region within lower Tertiary and older bedrock with probable tectonic ties to the Chesapeake crater (Mathur and others, 2015; Herman and others, 2015).Table 2 Any geodynamic consequences arising from the Chesapeake impact are not apparent like those stemming from Chicxulub, but both impacts show similar lithospheric foreland contraction, uplift, and welting (figs. 1 and 5). After constructing spheres of radii equaling the main compositional phase boundaries in Earth’s interior (fig. 2), a foreland wedge was next constructed to envelope a volume of the lithosphere and asthenosphere where contraction and thickening occurs downrange of the oblique strike within the compressed blast sector (fig.2). This wedge is modelled to have a concave upward; spoon-shaped base that likely corresponds to pseudotachylyte shear planes following p-wave refraction geometry (fig. 6A). The sole geometry is modeled to flatten out in the case of Chicxulub near the base of the asthenosphere at about 660-km depth. The fan was built by copying the primary path, duplicating, and scaling them laterally using the cosine of successive, 10o radial sectors symmetrically disposed about the principal axis of compression through a 160o range across the foreland (fig. 2):

Equation 6: Length of the p-wave refraction path (Lp) = COS ( α ) where α = acute angle between the wedge  symmetry axis and the generated p-wave arc (fig. 6A)

The model wedge was built to show crustal depression and excavation immediately downrange of the crater but contraction and thickening beyond a crossover point where the sole fault flattens, then continues upward downrange to return shock energy to the planetary surface. This geometric transition corresponds to crustal arching and epeirogenic uplift as seen in Llano Texas and Westchester Pennsylvania with respect to the Chicxulub and Chesapeake impacts (figs. 1, 5, and 7). The sudden, brittle, contractional strain responses in the foreland sector would dissipate at some distance from the crater, modelled here for a 45o take-off angle to resurface at about 3000-km radial distance in a direction downrange and with diminishing length and depth fanning outward toward the hinterland (fig. 6A). As built, the Chicxulub wedge reaches a width of about 2500 km, roughly spanning the distance from the Gulf of California in the West to the New Madrid seismic zone in the NAP interior to the East (fig. 1).

The crustal welts were constructed using a model polyline that deviates from a spherical surface because flexural arches and troughs are placed at the observed radial distances from impact (fig. 6A). The model polyline was repeatedly duplicated and rotated about the crater in 10o sectors to assemble the spines of a 3D mesh surface (fig. 6B). These welts are modeled in a preliminary sense here with amplitudes on the order of 15 km such that elevation ranges between adjacent crests and troughs reach up to 30 kilometers (fig. 6A). The 2900 kilometer circumferential uplift around the crater is the most prominent of the ITFF welts where calculated earthquakes stemming from impact exceed Richter magnitude 9 or 10 just minutes after impact (table 2) and unlike anything experienced by humans in recorded history.

A final modelling component depicted in figure 7A reflects a preliminary attempt at manually fitting elliptical fault planes to surface or near-surface fault traces that are symmetrically disposed about the impact site at the continental scale. These fault traces include oceanic submarine spreading ridges and other concealed faults that bound subsurface basins and domes as revealed through geological and geophysical studies (fig. 1). Seismic elastodynamic theory equates the energy released on a fault surface to its physical area (Aki, 1972) and it therefore is possible to mathematically account for the absorbed and dissipated ITFF brittle ground strains stemming from large-impact events using a similar, but better constrained and more thorough approach. This task remains, but this preliminary model raises some very interesting geometric aspects that merit further study. For example, the fault pattern depicted in fig. 7A mimics material-failure patterns induced with uniaxial stress tests, and with differential scaling may prove to be applicable to other ITFF strain fields stemming from oblique impacts on terrestrial planets. With the SketchUp-Google Earth software compatibility one can instantaneously duplicate, scale, rotate, stretch and place such models virtually anywhere else on Earth, Mars, or the Moon (at this time) to assess their relevance in other cases. The models developed and represented here are currently available for download at www.impacttectonics.org/models/Chicxulub.html.

Summary

Because of the advent and rise of digital geospatial computing and from having access to openly shared geospatial data needed to decipher complex global geophsycial data, including GPS-based plate motions and historical crustal seismicity, we are now see overwhelming evidence of impact-tectonic signatures that overprint and perturb plate tectonic processes. But accepting an altered tectonic paradigm to allow for punctuated strains to be recognized and mapped amidst those stemming from otherwise uniform tectonic processes requires categorizing and quatifying the various strain mechanisms. Deciphering ITFF strains normally thought to stem from tectonic orogenies now becomes part of the detective process when deciphering compound structures imparted by both catstrophic and unform tectonic processes. A more thorough accounting of ITFF effects should prove to be an integral part of a mor einclusive plate-tectonic theory.

Recorded human history only reflects time when plate tectonics has operated at the gradual rates that we characterize using uniformitarian principles. Relatively constant horizontal motions on the order of millimeters to centimeters per year are the standard course stemming from recent, empirical observations. But catastrophic, instantaneous propagation of seismic waves radiating outward away from a large-impact sites are difficult to fathom because they can hypothetically raise mountains suddenly when terra firma gets rung like a bell and its carpet gets rumpled and welted. We have not experienced this as modern humans and our established viewpoints reflect our geologically brief existence. If we theoretically recognize the potential of impact tectonics to suddenly impart widespread tectonic revolutions as part of plate-tectonic theory we then become aligned with Gould and Eldredge's (1977) punctuated equilibrium as a more inclusive guiding principle of plate-tectonic theory, one that directly reflects our discretization of time. As Gould (1987) wisely stated “if we equate uniformity with the truth and relegate the empirical claims of catastrophism to the hush-hush unthinkable of theology, then we enshrine one narrow version of geological process as true a priori, and we lose the possibility of weighing reasonable alternatives.”

8.0 Acknowledgements

This work reflects my interaction with and influences from many people throughout my career. I was first introduced to geology 40 years ago by an older boss whose name I sadly can’t remember when we were working away from our central-Ohio base near Glacial National Park as contract industrial laborers at an aluminum refinery. Off-hour day trips into the park changed the direction of my life as I have since strived to understand how mountains rise. In that respect I was fortunate for my early training at Ohio University under the tutelage of Damian Nance who stoked my interest in structural geology and global tectonics.  A senior studies seminar taught by Damian and Tom Worsley opened my eyes to the ‘big picture’ and the exciting realization that geology is a relatively new and imperfect science with many unexplored frontiers. Peter Geiser at the University of Connecticut soon after provided the next level of formalized training in structural geology, and together with his brother Jim, introduced me to advanced structural concepts and modern computing applications in geological sciences. Equipped with these tools while at the New Jersey Geological Survey (NJGS) under the direction of State Geologists Haig Kasabach and Karl Muessig in successive administrations, I was able to conduct the field and laboratory work leading to this discovery of events occurring on the North American tectonic plate. However, the resulting excitement was then tempered by the realization (and directives) in the midst of my career that I could not commit to an academic pursuit on civil service time. Nevertheless, my continued pursuit of this topic during off hours gained support from a couple of friends and colleagues who I hereby acknowledge and wholeheartedly thank for helping me through that time. Manny Charles has always supported this effort. We met at the NJGS, shared a mutual interest in structural geology, and I remember fondly when he handed me a hardcopy of The Chesapeake Invader by Wiley Poag in the early 1980’s at the office. My MSc thesis dealt with unravelling foreland structures of Pennsylvania but I concluded that work without understanding many aspects of the driving factors. But soon after the discovery of a deeply buried impact crater under the mouth of Chesapeake Bay, many major pieces of the regional puzzle began falling systematically into place, and Manny has been my primary sounding board through all of it. On the other hand, my friend and career-long mapping partner Don Monteverde (NJGS) provided key insights in the field but critical viewpoints on the emerging hypothesis that I also benefited from, because this work will undoubtedly be likewise challenged by the rigors of peer-review and scientific debate. Other former colleagues at the NJGS that I also acknowledge for having a hand in this work include Butch Grossman, Mike Serfes, Steve Spayd, and Mark French. I also thank J. Mark Zdepski, a long-time local friend and fellow geologists for listening to me rant and rave for many years about the lack of understanding and appreciation of impact-tectonic effects in the general geological community. Only a few years ago while attending the annual field conference of Pennsylvania geologists, Gail Blackmer suggested that I contact Ryan Mathur at Juniata College about his work on impact-generated sulfide-mineralized veins that he was obtaining Miocene radiometric ages from within the Pennsylvania fold-and-thrust belts. That was greatly appreciated as Ryan filled a critical gap in the hypotheses by obtaining absolute age dates on post-impact, far-field tectonic structures that independently confirmed early hypotheses. Lastly I thank Heidi Sue for making our home my comfort zone and sharing in my dreams.

References

Amante, C. and Eakins, B. W., 2008, ETOPO1 1 Arc-Minute Global Relief Model: Procedures, Data Sources and Analysis, National Geophysical Data Center, NESDIS, NOAA, U.S. Department of Commerce, Boulder, CO, http://www.ngdc.noaa.gov/mgg/global/relief/ETOPO1/docs/ETOPO1.pdf

Anderson, T. L., 2017, Fracture Mechanics; Fundamentals and Applications, Fourth Edition: CRC Press, Boca Raton, Fla., 688 p.

Aki, K., 1972, Scaling law of earthquake source-time function, Geophysical Journal of the Royal Astronomical Society, v. 31, p. 3-25

Alvarez, L.W., Alvarez, W., Asaro, F., Michel, H.V., 1980, Extraterrestrial Cause for the Cretaceous-Tertiary Extinction: Science, vol. 208, Issue 4448, p. 1095-1108, DOI: 10.1126/science.208.4448.1095

Collins, G. S., Melosh, H. J., and Marcus, R. A., 2005, Earth Impact Effects Program: A Web-based computer program for calculating the regional environmental consequences of a meteoroid impact on Earth: Meteoritics & Planetary Science 40, No. 6, 817–840 (2005)

Collins, G. S. and Wünnemann, K., 2005, How big was the Chesapeake Bay impact? Insight from numerical modeling: Geology. V. 33, No.12, p. 925–928.

Elliot, D., 1976, The energy balance and deformation mechanisms of thrust sheets: Royal Society of London Philosophical Transactions, Series A., v. 283, p. 289-312.

Earth Impact Database, 2011, http://www.unb.ca/passc/ImpactDatabase/> (accessed April/20/2019)
Gault D. E. and Wedekind J. A., 1978. Experimental studies of oblique impact. Proceedings of the 9th Lunar and Planetary Science Conference. p. 3843–3875.

Gould, S. J., 1987, Time’s arrow, Time’s cycle: Myth and Metaphor in the Discovery of Geological Time: Harvard University Press, 222 p.

Gould, S. J. and Eldredge, N., 1977, Punctuated equilibria: the tempo and mode of evolution reconsidered: Paleobiology, v. 3. No. 2, p. 115-151.

Gulick, S. P. S., G. L. Christenson, P. J. Barton, R. A. F. Grieve, J. V. Morgan, and J.
Urrutia-Fucugauchi, 2013, Geophysical characterization of the Chicxulub impact crater, Review of Geophysics, v. 51, p. 31–52, doi:10.1002/rog.20007

Herman, G. C., 2015, Neotectonics of the New York Recess, in Herman, G. C., and Macaoay Ferguson, S., Neotectonics of the New York Recess: 32nd Annual proceedings and field guide of the Geological Association of New Jersey, Lafayette College, Easton, Pa., p. 80-151

Herman, G. C., 2006, Neotectonic setting of the North American Plate in relation to the Chicxulub impact: Geological Society America Abstracts with Programs, Vol. 38, No. 7, p. 415.

Herman, G.C., 1984, A structural analysis of part of the Valley and Ridge Province of Pennsylvania, University of Connecticut, Storrs, CT, 107 p.
Labuz, J. F. and Zang, A., 2012, Mohr–Coulomb Failure Criterion: Rock Mechanics and Engineering, v. 45, p. 975–979. DOI 10.1007/s00603-012-0281

Mathur, R., Gold, D. P., Ellsworth, C. J., Doden, A. G., Wilson, M., Ruiz, J., Scheetz, B. E., and Herman, G. C., 2015, Chapter 3, Re-Os isotope evidence an Early Tertiary episode of crustal faulting and sulfide-mineralization in Pennsylvania with probable ties to the Chesapeake Bay bolide impact in Maryland, USA, in Herman, G. C., and Macaoay Ferguson, S., Neotectonics of the New York Recess: 32nd Annual proceedings and field guide of the Geological Association of New Jersey, Lafayette College, Easton, Pa., p. 68-79.

Meschede, M.A., Myhrvold , C. L. and Tromp J., 2011, Antipodal focusing of seismic waves due to large meteorite impacts on Earth: Journal Geophysical International, v. 187, p. 529–537

Swedan, N. H. 2013: Energy of plate tectonics calculation and projection, Solid Earth Discussions, v. 5, p. 135-161, https://doi.org/10.5194/sed-5-135-2013

Trehu, A. M., Klitgord, K. D., Saywer, D. S., and Buffler, R. T., 1989, Atlantic and Gulf of Mexico continental margins, in Pakiser, L. C., and Mooney, W. D., Geophysical framework of the continental United States: Boulder , Colorado, Geological Society of America Memoir 172, p. 349-382.

Maus, S., U. Barckhausen, H. Berkenbosch, N. Bournas, J. Brozena, V. Childers, F. Dostaler, J. D. Fairhead, C. Finn, R. R. B. von Frese, C. Gaina, S. Golynsky, R. Kucks, H. Lühr, P. Milligan, S. Mogren, D. Müller, O. Olesen, M. Pilkington, R. Saltus, B. Schreckenberger, E.Thébault, and F. Caratori Tontini, EMAG2: A 2-arc-minute resolution Earth Magnetic Anomaly Grid compiled from satellite, airborne and marine magnetic measurements, Geochemistry, Geophysics, Geosystems, in review, http://geomag.org/info/Smaus/Doc/emag2.pdf .

Ormo, J., Rossi, A. P., and Housen, K. R., 2013, A new method to determine the direction of impact: Asymmetry of concentric impact craters as observed in the field (Lockne), on Mars, in experiments, and simulations: Meteoritics and Planetary Science v. 48, No. 3, p. 403–419
doi: 10.1111/maps.12065

Poag, C.W., 1997, Chesapeake Bay bolide impact: A convulsive event in Atlantic Coastal Plain evolution, in Segall, M.P., Colquhoun, D.J., and Siron, D., eds., Evolution of the Atlantic Coastal Plain - Sedimentology, stratigraphy, and hydrogeology: Sedimentary Geology, v. 108, p. 45-90

Poag, C.W., 1999, The Chesapeake Invader: Princeton University Press, 198 p.

Poag, C. W., Powars, D.S., Poppe, L.J., Mixon, R.B., Edwards, L.E., Folger, D.W. and Bruce,S., 1992, Deep sea drilling project Site 612 bolide event: New evidence of a late Eocene impact-wave deposit and a possible impact site, U.S. east coast. Geology, v. 20, pp. 771-774. 1992.

Poag, C.W., Poppe, L.J., Commeau, J.A. and Powars, D.S., 1993, The Toms Canyon 'crater', New Jersey OCS—the seismic evidence: Geological Society of America Abstracts with Programs, v. 25, p. A-378.

Powars, D.S., Poag, C.W, and Mixon, R.B., 1993, The Chesapeake Bay "impact crater"—Stratigraphic and seismic evidence [abs.]: Geological Society of America Abstracts with Programs, v. 25,A-378.

Ribiero, Antonio, 2002, Soft plate and impact tectonics: Springer-Verlag, Berlin, Heidelberg, New York, 344 p.

Sandwell, D. T., and W. H. F. Smith, 2009, Global marine gravity from retracked Geosat and ERS-1 altimetry: Ridge segmentation versus spreading rate, Journal of. Geophysical Research, v. 114, B01411, doi: 10.1029/2008JB006008

Schultz, P. H., and D. E. Gault, 1975, Seismic effects from major basin formation on the Moon and Mercury: The Moon, V. 12, p. 157-177.

Schultz, P. H., and S. D'Hondt, 1996, Cretaceous-Tertiary (Chicxulub) impact angle and its consequences, Geology, v. 24, p. 963-967

Schultz, P. H., and D. E. Gault, 1990, Prolonged global catastrophes from oblique impacts, in Proceedings of the Global Catastrophes in Sharpton, V. L. and Ward, P. D., eds., Earth History: An Interdisciplinary Conference on Impacts, Volcanism, and Mass Mortality, Geological Society of America Special Paper 247, p. 239-261.

Shultz, P. H., 2015, Scaling laboratory experiments to natural planetary experiments: Bridging the Gap III: Impact Cratering In Nature, Experiments, and Modeling, held 21-26 September, 2015 at University of Freiburg, Germany. LPI Contribution No. 1861, 1099.pdf, 2 p.

Stickle, A. M., and Schultz, P. H., 2012, Subsurface damage from oblique impacts into low‐impedance layers, Journal of Geophysical Research, v. 117, E07006, doi: 10.1029/2011JE004043

Stickle, A. M., and P. H. Schultz, 2014, Discrete shear failure planes resulting from oblique hypervelocity impacts, Journal of Geophysical Research Planets, v. 119, p. 1839–1859, doi:10.1002/2013JE004597.

IT iconb Abstract * Introduction * Chicxulub and Cheasapeake impacts * Ground energy * Strain effects * Computer models * Summary * References