Disintegration Of Rocks Research Articles

Neotectonics and geodynamics of the Kuznetsk Basin

This work describes the peculiarities of neotectonics and geodynamic development of the Kuznetsk Basin since the Oligocene. The complex of studies included structural-geomorphological analysis with interpretation, satellite image data processing, and field observations. The studies we carried out allowed us to reveal that the modern dislocations in the Kuznetsk Basin are characterized by an arched-block style of tectonic movement. The modern structural pattern of the Kuznetsk Basin is a combination of wide uplifts separated by narrow depressions and weak zones (fault zones, fracture zones, and zones of rock disintegration) of northwestern, northeastern, submeridional, and sublatitudinal strike. As a result of these studies, the relationships between modern and ancient tectonic structures and the geodynamic features of the development of modern dislocations that depend on the degree of activization of tectonic structures have been revealed. Statistical analysis of the results of the interpretation allowed us to reveal areas of high permeability and higher dislocation density in the geological setting with a higher concentration of methane.

Numerical solution of hard rock disintegration process – part 2

Abstract This paper focuses on a numerical analysis of a hard rock (ore) disintegration process. A bit moves into the ore and subsequently disintegrates it. The disintegration (i.e. fracture of ore) is solved via a deterministic approach (FEM) and a probabilistic approach (FEM in combination with the SBRA - Simulation-Based Reliability Assessment method, i.e. Monte Carlo simulations, stochastic inputs). The ore is disintegrated by deactivating the finite elements satisfying fracture conditions. The results are compared with experiments. The application of the SBRA method is a new and innovative trend in this area. Finally, the probabilistic reliability assessment is mentioned.

Particle breakage of argillaceous siltstone subjected to stresses and weathering

Particle breakage is an important phenomenon that is observed in high rockfill dams as the dam material is subjected to both weathering and stresses. This paper presents a study of the particle breakage of an argillaceous siltstone used in a rockfill dam in southwest China that is 261.5m in height. The region is characterized by abundant rainfall and a wide variation in temperature (10–60°C). A series of oedometer tests were performed with specimens subjected to different types of weathering. The study aims to examine the development of particle breakage of an argillaceous siltstone and the manner in which the particle size distribution of the weathered material changes over time. The results highlight that the combined effect of water and thermal weathering is a major factor controlling the disintegration of soft rocks. Particle breakage is characterized by three mechanisms: angular fracture, particle cracking and particle breakup. The weathering rate, defined as the rate of particle breakage over a weathering cycle, declines as the number of cycles increases. The ultimate particle breakage induced by weathering approaches a constant despite different axial stresses.

Laboratory investigation of disintegration characteristics of purple mudstone under different hydrothermal conditions

Disintegration of rock is one of the primary processes of soil formation and geomorphology and is affected considerably by water and heat. This study focused on the disintegration characteristics under laboratory conditions of typical purple mudstone from the Tuodian group of Jurassic red beds (J3t) in Tuodian Town, Shuangbai county, Yunnan Province of southern China. The fresh mudstone was subjected to alternating applications of water, heat and hydrothermal interaction during five treatments: wetting-drying (WD), saturation (ST), refrigeration-heating (RH), a combination of wettingdrying and refrigeration-heating (WDRH), and a combination of saturation and refrigeration-heating (STRH). Each treatment was run in twenty-four cycles. The results showed that there are three types of disintegration: collapsing disintegration, exfoliation disintegration and imperceptible disintegration. The cumulative disintegration rate (percentage of cumulative disintegrated mass to the initiative sample mass passed through a 2 mm sieve) produced a ‘S’-shape function when related to treatment cycle time and closely fit a logistic model (R2 > 0.99). The rank order of the cumulative disintegration rate resulting from the five treatments was as the following: WDRH > STRH > ST > WD > RH. Because of alternating periods of moisture and dryness, WD caused the most disintegration, while RH alone resulted in imperceptible disintegration. Additionally, there was a negative correlation between the disintegration rate of each treatment cycle (percentage of disintegrated mass to the treated sample mass) and treatment cycle number. There was a positive correlation between this rate and temperature change under moist conditions, indicating that a change in temperature greatly accelerates the disintegration of parent rock when water was supplied.

A new method of rock disintegration and foraminiferal extraction with the use of liquid nitrogen [LN2]. Do conventional methods lead to biased paleoecological and paleoenviromental interpretations?

An extremely fast, easy, and clean method of rock disintegration and foraminifera extraction from variously lithified porous rocks with the use of liquid nitrogen [LN 2 ] is proposed. This method markedly limits the time of rock disintegration from days to only minutes, is safe for foraminifera, and does not require special chemical labs. In the experiment, the LN 2 method was used to decompose rock samples and simultaneously to extract the foraminifera hidden within. The proposed method disintegrates the rocks to a finer fraction than conventional methods such as the Glauber's Salt method, allowing to collect more smaller planktonic and benthic foraminifera, resulting in marked changes in foraminiferal assemblages e.g., the planktonic/benthic ratio [P/B defined as P/P+B], leading to new conclusions. The comparison between the LN 2 and Glauber's Salt [GS] methods and obtained results are provided. ► Fast and easy microfossil extraction with use of liquid nitrogen is proposed. ► The time needed for rock disintegration is limited from days to only minutes. ► The new method gives more reliable results e.g. P/B ratio. ► New perspectives and possibilities in paleoenvironmental interpretations. ► The method seems to be applicable for variously lithified porous rocks.

Economics of a hydraulic hammer for forest road construction in a mountainous area

 This research deals with productivity and cost of rock disintegration and side casting of materials with the use of a hydraulic hammer mounted on a PC 220 Komatsu crawler excavator, which is used on rocky slopes of Hyrcanian forests of Iran. A continuing time study was applied during the road construction. To estimate the volume of rock disintegration, the average end area equation was used. The increasing cut-slope height decreased productivity. The productivity of hydraulic hammer averaged at 5.5 m<sup>3</sup>·h<sup>–1</sup> for the mean work volume of 5.07 m<sup>3</sup>·m<sup>–1</sup>. The unit cost of the system was 7.7 €·m<sup>–3</sup>. From the economic point of view a new machine with multipurpose system could be recommended for forest road construction operations in rocky areas.  

Heat generation in solid fossil fuels as a factor of epigenetic inhomogeneity of geological environment

Consequences of heat generation caused by exothermic changes in organic matter in the subsurface have been considered. It has been shown that once existed deposits containing solid organic matter and then self-heated, spontaneously ignited, and burnt under subsurface conditions can be traced by not only thermally altered rocks (including ore mineralization, etc.), but also landforms (positive and negative) and increased levels of both dislocations and geofiltration heterogeneity. Elevated temperatures (sometimes up to 1000–1200°C), causing transformation of both organic and mineral matter, create preconditions for deformation of host rocks: void emptying due to loss of a large mass (more precisely, volume) of matter (mainly organic), explosive activity of generated fluids, and the corrosive nature of some of them. As a result, the bed integrity is disturbed, stockwork fracturing (and permeability) develops, and rocks are subjected to impact of corrosive solutions. The role of solid organic matter in the disintegration of rocks has been analyzed. It has been pointed out that not only high temperatures can cause deformation alteration of rocks, but also dislocating nature of the environment can cause heat generation. In any case, there will be spatial alignment of both thermally altered and dislocated rocks.

A3 Slope materials, landslide causes and landslide mechanisms

Soils in hilly or mountainous areas are normally divided into two types: in situ weathered soils and transported soils. Table A3.1 provides a simplified classification and description of the common soils encountered in the humid tropics and subtropics and their engineering behaviour, based mainly on Fookes (1997). View this table: Table A3.1. Common soil types found in the humid tropics and subtropics ### A3.1.1 In situ weathered soils Deep in situ weathered soils are often developed under humid tropical and subtropical climates (e.g. Ruxton & Berry 1957) and are the result of intense chemical decomposition and, to a lesser extent, mechanical disintegration of the parent rock. The classification of these soils is based on the degree of weathering that has occurred to the parent rock (Moye 1955; Ruxton & Berry 1957; Little 1969; Anon 1977, 1995; IAEG 1981; BSI 1999). Further discussion on weathering classifications is provided in Hencher (2008) and Norbury (2010). Figure A3.1 shows the classification used to describe weathered rock and soil sequences in the humid tropics and subtropics by Fookes (1997). Text box A3.1 outlines some of the engineering properties associated with each of these weathering grades. Weathering grades IV, V and VI are usually classified as soil because, from an engineering perspective, they tend to behave more as soil than as rock. They are termed highly weathered rock, completely weathered rock and residual soil, respectively (BSI 1999), but because all three effectively behave as soil, they are also frequently referred to collectively as tropical residual soil (Fookes 1997). Due to processes of erosion and mass movement, it is usual in hilly and mountainous areas for deep residual soils to be limited in extent and confined to areas of gentle slope such as on geologically-controlled benches and broad ridge crests. Frequently, the weathering profiles found on most mountain …

Numerical modeling of overburden rehandling with draglines

The numerical modeling techniques are exposed and some mathematical problems are formulated to determine final spatial positions of the technology components included in open cutting with direct dumping, such as a disintegration of broken rocks, a rock pile and a dragline. The discussed formulations were integrated in algorithms and programs designed for automated composition of operating procedures for blasted overburden rehandling by draglines.

Modeling vapor diffusion within cold and dry supraglacial tills of Antarctica: Implications for the preservation of ancient ice

We modeled water–vapor diffusion within Mullins till, a relatively dry supraglacial till in southern Victoria Land, Antarctica, that rests directly on Mullins Glacier, purportedly one of the oldest alpine glaciers in the world. Like most supraglacial tills in cold-desert environments, Mullins till contains three characteristic facies: a weathered facies representing the oxidation of iron-bearing minerals and the physical disintegration of surface rocks; a sand-wedge facies representing the episodic infill of thermal cracks associated with contraction-crack polygons; and an underlying fresh facies representing the addition of englacial debris (sourced from rockfall) as overlying ice sublimes. Using a one-dimensional model for Fickian vapor diffusion through porous media, we show that the rate of subsurface ice sublimation varies by ~ 5.5% beneath till facies and that over timescales of 10 5 years diffusion through “porous” sand wedges contributes to the development of deep troughs surrounding high-centered polygons. Applying site-specific meteorological data collected over a four-year period, we show that ice loss at the stagnant terminus of Mullins Glacier is ~ 6.6 × 10 −5 m a −1, a value that (although low and assuming an ice thickness of ~ 150 m) is consistent with complete ice loss under current environmental forcing in ~ 2.5 Ma. Our sensitivity tests indicate that the vast majority of sublimation occurs during the summer months. Calculated summertime losses drop to zero with either a reduction in soil and ice surface temperatures of ~ 6.4 °C or an increase in atmospheric relative humidity from 44% to 75%, both of which could arise from an increase in cloud cover over Mullins Glacier. Sublimation responses to meteorological forcing are not uniform across Mullins Glacier. A summer increase in soil temperature of 2 °C results in negligible change in ice sublimation at Mullins terminus, but a 27% increase in ice loss in upper Mullins Valley. The key factor is the thickness of Mullins till, which is greater near the glacier terminus. For till thicknesses exceeding ~ 25 cm, non-linear variations in soil temperature result in downward vapor fluxes, capable of producing thin, cm-scale lenses of secondary pore that cap the surface of buried glacier ice. This downward vapor flow, sourced from modern snowfall and/or elevated atmospheric relative humidity, is one of the key factors that enable long-term preservation of buried glacier ice. Overall, our results highlight the subtle relations among changes in till texture, till thickness, and meteorological forcing on the rate of subsurface ice loss and provide insight into the plausible range of conditions under which multi-million-year-old ice can exist beneath thin supraglacial tills, <~50-cm thick, in southern Victoria Land, Antarctica.

Mechanism of rock-bed scour due to impinging jet

Scour of rock bed downstream of high dams is mainly caused by the transient forces as a result of the propagation of fluctuating pressures, which is significantly controlled by the rock fracture-structure. The physical mechanism of rock disintegration and scour pool forming are analysed herein by considering the fracture-structure of rock bed. A two-dimensional discrete fracture network is imitated applying the Monte-Carlo method. The model of transient flow is established along with each discrete fracture to simulate numerically the propagation of fluctuating pressure waves. Applying the method of automatic tracing of rock blocks layer by layer, the mechanism of disorganization of fractured rock, both the transient physical and dynamic characteristics of isolated rocks, and the damage process of the rock bed are discussed. Finally, a stability criterion of rock blocks and the evaluation method of equilibrium scour depth are established.

Distribution of radon activity in the atmosphere above Wzgórza Niemczansko-Strzelinskie (South-WestPoland) and its dependence on uranium and thorium content in the underlying rock and indirect ground basement

Radon activity in the atmosphere and its behavior in the environment have been investigated using LR-115 nuclear track detector. The complex geological structure of Wzgorza Niemczansko-Strzelinskie (south-west Poland) enabled this problem to be studied in various geological conditions. The eU and eTh content in rocks and soil was measured by gamma-spectrometer GR-320. Uranium content of bedrock reached its maximum value of 15 ppm in the case of quartz-graphite schist. Thorium reached its maximum value of 35 ppm in the case of granodiorite. Radon activity was measured by means of long-term exposure of LR-115. The mean value of atmospheric radon activity was 21 Bqm-3 in the air 2 m above the ground surface. The highest radon activities were measured in the area of granite and quartz-graphite schist outcrops and in the area of mylonitic rocks of the Niemcza Zone. Radon activity in close to ground cup detectors varies from 25 to 300 Bqm-3, these values depend on uranium and thorium content in indirect ground basement (soil and weathered rocks). Not only uranium and thorium content but also rock disintegration due to tectonic events (shear zones) influenced atmospheric radon activity. Seasonal variation is not strong, although higher values were measured in the autumn- winter period.

Relative contribution of various climatic processes in disintegration of clay-bearing rocks

The climatic processes of heating and cooling, wetting and drying, and freezing and thawing affect the disintegration characteristics of clay-bearing rocks (shales, claystones, mudstones, and siltstones) to varying degrees. Although heating and cooling, wetting and drying, and freezing and thawing are known to be the main processes responsible for physical disintegration of rocks under natural conditions, most of the previous investigators have used methods based only on water content variations (e.g., jar slake, slake index, and slake durability index tests) to assess the disintegration of clay-bearing rocks. Such assessments may not be adequate to explain the field behaviour of clay-bearing rocks subjected to a full range of climatic processes. In order to evaluate the combined effects as well as relative contributions of various climatic processes on the disintegration behaviour, samples of selected clay-bearing rocks, consisting of 5–6 particles, each weighing 85–150 g, were subjected to multiple cycles of heating and cooling, wetting and drying, and freezing and thawing. These treatments resulted in fragmentation of samples with fragments ranging from 50 to 2 mm and finer in dimensions. A new approach, referred to as the disintegration ratio, and defined as the area under the grain size distribution curve of the disintegrated material to the total area encompassing all grain size distribution curves of the samples, was used to account for fragmentation into varying sizes. Statistical analyses were performed to investigate the relationship between fragmentation, mineralogical composition, and physical properties.

Structural defects in natural plastically deformed diamonds: Evidence from EPR spectroscopy

Structural defects formed as a result of plastic deformation in natural diamond crystals have been studied by EPR spectroscopy. The spectra of brown, pink-brown, black-brown, pink-purple, and gray plastically deformed diamonds of type Ia from deposits in Yakutia and the Urals were recorded. The results of EPR spectroscopy allowed us to identify various deformation centers in the structure of natural diamonds and to show that nitrogen centers were transformed under epigenetic mechanical loading. Abundant A centers, consisting of two isomorphic nitrogen atoms located in neighboring structural sites, were destroyed as a result of this process to form a series of N1, N4, W7, M2, and M3 nitrogen centers. Such centers are characterized by an anisotropic spatial distribution and a positive charge, related to the mechanism of their formation. In addition, N2 centers (probably, deformation-produced dislocations decorated by nitrogen) were formed in all plastically deformed diamonds and W10 and W35 centers (the models have not been finally ascertained) were formed in some of them. It has been established that diamonds with various types of deformation-induced color contain characteristic associations of these deformation centers. The diversity of associations of deformation centers indicates appreciable variations in conditions of disintegration of deep-seated rocks, transfer of diamonds to the Earth’s surface, and formation of kimberlitic deposits. Depending on the conditions of mechanical loading, the diamond crystals were plastically deformed by either dislocation gliding or mechanical twinning. Characteristic features of plastic deformation by dislocation gliding are the substantial prevalence of the N2 centers over other deformation centers and the occurrence of the high-spin W10 and W35 centers. The attributes of less frequent plastic deformation by mechanical twinning are unusual localization of the M2 centers and, in some cases, the N1 centers in microtwinned lamellae. Numerous data on models of deformation centers in natural diamonds, including the M2 and M3 centers, which were observed in the studied collection for the first time, are discussed.

Provenance of Miocene sandstones in northern Iraq: constraints from framework petrography, bulk-rock geochemistry and mineral chemistry

Modal analysis, bulk-rock geochemistry and phase chemistry of sandstones of the Miocene Fat'ha and Injana formations, northern Iraq, show that the clastics were derived from heterogeneous sources that include basic igneous and metamorphic rocks as well as older sedimentary rocks. The sandstones are generally carbonate-rich lithic arenites. Their geochemistry supports the petrographic results and indicates that they are all Fe-rich, lithic or quartz arkosic sandstones. According to geochemical data, garnets are derived from metamorphic sources, hornblende is of igneous origin, and clinopyroxenes, are produced by basic igneous rocks. Epidote is most probably to be a product of disintegration of metamorphic rocks, essentially, metamorphosed igneous rocks. Rutile geochemistry implies low-grade metamorphic and basic to ultrabasic igneous sources. Chemical composition of chromian spinels indicates that they are derived from Alpine-type peridotite. The ophiolitic-radiolarite belts of Taurus-Zagros as well as the uplifted Cretaceous and Paleocene strata of north and northeastern Iraq are likely to be the major source of clastics to the Fat'ha–Injana basin, a foreland basin formed as a result of the continental Arabian and Turkish/Iranian plates collision.

Assessment of physical disintegration characteristics of clay-bearing rocks: Disintegration index test and a new durability classification chart

Clay-bearing rocks cover large areas on the earth surface and are highly sensitive to changes in their water content. It is well known that strength and deformability properties of these rocks also deteriorate due to wetting and drying processes, causing numerous engineering problems. Due to the importance of disintegration of the clay-bearing rocks in geo-engineering practice, several simple test methods and classification systems have been proposed to assess durability The slake durability index test is one of the most widely used of these tests. However, due to mechanical breaks occurring during the test, immersion of samples in water for only 10 min and the assumption that fragments larger than 2 mm are durable, the slake durability test has some limitations. In addition, the field behaviour of clay-bearing rocks and the associated disintegration have not been fully considered in previous studies. In this study, a comprehensive research program was conducted on different clay-bearing rocks selected from Turkey to assess their disintegration characteristics under both field and laboratory conditions. Based on field and laboratory investigations, new approaches and a durability classification system are recommended to assess disintegration characteristics of clay-bearing rocks. The disintegration index test suggested in this study can minimize some of the limitations of the slake durability test. The comparison between the disintegration index values of the laboratory specimens and those of the samples from the same outcrops exposed to atmospheric conditions for 1 year showed close agreement. Based on these observations, a durability classification system consisting of six classes is suggested. The proposed classification system uses a new parameter called slake durability rating to determine the degree of disintegration of any clay-bearing rock. In addition, general information related to physical and mechanical properties of any class can be obtained from the explanation part of each class. This system may be useful to practitioners for identifying the type and degree of disintegration that may occur on a freshly exposed rock face.

Geomorphology of the Pohorje mountains

The Pohorje mountain range, young mountains with prevailing metamorphic rocks and dacite, continues to uplift above the igneous laccolith in the area of the rapid rising asthenosphere in the transition to the Pannonian basin also due to changes in temperature and, resultantly, of the density of uplifting dacite- and other intrusions which have not metamorphosed the surrounding sediments. On the Pohorje by the river Drava (hereinafter the Drava Pohorje), the drainage network does not match the orography, because, between the Vuzenica-Radlje basin and Fala, the Drava epigenetically deepened its gorge into the marginal range of Kobansko. Modest plateaus on the ridge of the Pohorje originate from the time when the base level maintained a cover of the so-called Eibiswald strata between the Karavanke and the Kobansko in the upper Miocene. The originally larger ridge plateau in the centre of the Pohorje was lowered by erosion and periglacial processes; it has been preserved as an inclined plateau on the Eastern Pohorje. Explained through the recent tectonic shifting, established by means of GPS in the years 1996–2002 at the peak Velika Kopa, is the southeastwards curving of the five valleys above the Legen terrace where, supposedly, original headwaters of the Spodnja Mislinja came from. Due to its geological, geomorphological and hydrological peculiarities the Legen Quaternary terrace deserves that it should be declaired the ‘geopark’, the first one in Slovenia. Even more explicit and extensive is the westwards curving of the valleys on the northern slope of the Pohorje, and their northeastward orientation in the Ribnica-Lovrenc-Selnica valley system. In the east section of the Lovrenc valley system above Fala the brook Rečnikov potok has not adjusted its course to the recent tectonic subsiding, so that its valleys run obliquely to the slope inclination. The up to 700 metres deep Mislinja rift lowered the central ridge of the Pohorje to 1299 metres. Blowing intensely across it, the northeastern Pleistocene cold winds made possible the origination of two smaller glaciers in the upper drainage basin of the Radoljna. The gently sloping Pohorje landforms are not the result of the old age but of the disintegration of granular rocks to permeable sand, above which the thick cover of continuous roots of grasses and prevailing spruce reduces the erosion.

Probabilistic Analysis of the Hard Rock Disintegration Process

This paper focuses on a numerical analysis of the hard rock (ore) disintegration process. The bit moves and sinks into the hard rock (mechanical contact with friction between the ore and the cutting bit) and subsequently disintegrates it. The disintegration (i.e. the stress-strain relationship, contact forces, reaction forces and fracture of the ore) is solved via the FEM (MSC.Marc/Mentat software) and SBRA (Simulation-Based Reliability Assessment) method (Monte Carlo simulations, Anthill and Mathcad software). The ore is disintegrated by deactivating the finite elements which satisfy the fracture condition. The material of the ore (i.e. yield stress, fracture limit, Young’s modulus and Poisson’s ratio), is given by bounded histograms (i.e. stochastic inputs which better describe reality). The results (reaction forces in the cutting bit) are also of stochastic quantity and they are compared with experimental measurements. Application of the SBRA method in this area is a modern and innovative trend in mechanics. However, it takes a long time to solve this problem (due to material and structural nonlinearities, the large number of elements, many iteration steps and many Monte Carlo simulations). Parallel computers were therefore used to handle the large computational needs of this problem.

Effects of Cyclic Wetting and Drying on Physical and Mechanical Properties of Neogene Sandstones and Siltstones from Boso Peninsula, Japan

This paper reports field observations and new experimental data designed to clarify the response of sandstones and siltstones to cyclic wetting and drying. A methodology is proposed to understand the mechanism of disintegration of rocks due to cyclic wetting and drying. These methods were chosen after critical analysis of field observations of coast typified by cliffs where frequent moisture changes to the rocks were observed to be operative. The importance of mineralogical composition and physical properties of rocks on the overall breakdown mechanism is emphasized. The experimental results showed that the water absorption capacity appears to exert highly significant control over the rate of disintegration of rocks investigated. The results also revealed that fracture induced deterioration only occur in siltstones. The proportion of the initial flaws in the rock fabric is important for determining the rate of disintegration. We suggested that the data are consistent with a model that assumes that the coupled relationship between the amount of swelling minerals and the small scale heterogeneity (flaws) of the material are major controlling factors for fracture initiation within the rock mass and the consequent repetitive breakdown. The findings obtained from this study may offer practical considerations in understanding the mechanism of rock mass breakdown, and enable design for the control of minor rockfall and cliff degradation to be made on a rational basis.

Tectonics, fracturing of rock, and erosion

We argue that by fracturing rock, not by raising it relative to base level, tectonics plays its most important role in causing rapid incision of valleys and rapid erosion of hillslopes. Tectonic deformation riddles the upper crust with fractures, which not only provide avenues for water flow and thus promote weathering and further disintegration of rock but also fragment bedrock into debris that is readily extracted and transported by surface processes. Bends in active faults require straining of adjacent rock masses. Aftershocks that occur subsequent to slip on primary faults reflect penetrative brittle deformation of the upper crust. At least some aftershocks must nucleate or lengthen cracks, which contribute to the comminution of these rock masses. Scaling rules suggest that dimensions of ruptures for very small (M &lt; −2) earthquakes can be meters or less. The Gutenberg‐Richter recurrence relationship implies that such earthquakes are common, as high‐magnification seismographs in low‐noise environments confirm. Moreover, large differences among fault plane solutions for aftershocks show that the small faults on which they occur are not parallel to one another; some faults must intersect. Thus the upper crust in tectonically active regions should be fragmented into blocks down to the scale of boulders or smaller. Dismembered rock arrives at the Earth's surface already prepared to be transported away. As a corollary, both deeply exhumed lower crust and posttectonic igneous rock, never deformed under brittle conditions and not deformed recently, should be less susceptible to detachment and subsequent transport than fractured rock.