共查询到20条相似文献，搜索用时 936 毫秒
1.
Edgardo Can-Tapia George P. L. Walker Emilio Herrero-Bervera 《Journal of Volcanology and Geothermal Research》1997,76(1-2)
We studied the anisotropy of magnetic susceptibility (AMS) of 22 basaltic flow units, including S-type pahoehoe, P-type pahoehoe, toothpaste lava and 'a'
emplaced over different slopes in two Hawaiian islands. Systematic differences occur in several aspects of AMS (mean susceptibility, degree of anisotropy, magnetic fabric and orientation of the principal susceptibilities) among the morphological types that can be related to different modes of lava emplacement. AMS also detects systematic changes in the rate of shear with position in a unit, allowing us to infer local flow direction and some other aspects of the velocity field of each unit. 'A'
flows are subject to stronger deformation than pahoehoe, and also their internal parts behave more like a unit. According to AMS, the central part of pahoehoe commonly reveals a different deformation history than the upper and lower extremes, probably resulting from endogenous growth. 相似文献
2.
The present study is probably the first of its kind in the Deccan Volcanic Province (DVP) that deals in detail with the morphology and emplacement of the Deccan Trap flows, and employs modern terminology and concepts of flow emplacement. We describe in detail the two major types of flows that occur in this province. Compound pahoehoe flows, similar to those in Hawaii and the Columbia River Basalts (CRB) constitute the older stratigraphic Formations. These are thick flows, displaying the entire range of pahoehoe morphology including inflated sheets, hummocky flows, and tumuli. In general, they show the same three-part structure associated with pahoehoe flows from other provinces. However, in contrast to the CRB, pahoehoe lobes in the DVP are smaller, and hummocky flows are quite common. 'Simple' flows occur in the younger Formations and form extensive sheets capped by highly vesicular, weathered crusts, or flow-top breccias. These flows have few analogues in other provinces. Although considered to be a'a flows by previous workers, the present study clearly reveals that the simple flows differ considerably from typical a'a flows, especially those of the proximal variety. This is very significant in the context of models of flood basalt emplacement. At the same time, they do not display direct evidence of endogenous growth. Understanding the emplacement of these flows will go a long way in determining whether all extensive flows are indeed inflated flows, as has recently been postulated.Most of the studies relating to the emplacement of Continental Flood Basalt (CFB) lavas have relied on observations of flows from the CRB. Much of the current controversy surrounding the emplacement of CFB flows centers around the comparison of Hawaiian lava flows to those from the CRB. We demonstrate that the DVP displays a variety of lava features that are similar to those from the CRB as well as those from Hawaii. This suggests that there may have been more than one mechanism or style for the emplacement of CFB flows. These need to be taken into account before arriving at any general model for flood basalt emplacement.Editorial responsibility: T. Druitt 相似文献
3.
Flood basalts, such as the Deccan Traps of India, represent huge, typically fissure-fed volcanic provinces. We discuss the
structural attributes and emplacement mechanics of a large, linear, tholeiitic dyke swarm exposed in the Nandurbar–Dhule area
of the Deccan province. The swarm contains 210 dykes of dolerite and basalt >1 km in length, exposed over an area of 14,500 km2. The dykes intrude an exclusively basaltic lava pile, largely composed of highly weathered and zeolitized compound pahoehoe
flows. The dykes range in length from <1 km to 79 km, and in thickness from 3 to 62 m. Almost all dykes are vertical, with
the others nearly so. They show a strong preferred orientation, with a mean strike of N88°. Because they are not emplaced
along faults or fractures, they indicate the regional minimum horizontal compressive stress (σ
3) to have been aligned ~N–S during swarm emplacement. The dykes have a negative power law length distribution but an irregular
thickness distribution; the latter is uncommon among the other dyke swarms described worldwide. Dyke length is not correlated
with dyke width. Using the aspect ratios (length/thickness) of several dykes, we calculate magmatic overpressures required
for dyke emplacement, and depths to source magma chambers that are consistent with results of previous petrological and gravity
modelling. The anomalously high source depths calculated for a few dykes may be an artifact of underestimated aspect ratios
due to incomplete along-strike exposure. However, thermal erosion is a mechanism that can also explain this. Whereas several
of the Nandurbar–Dhule dykes may be vertically injected dykes from shallow magma chambers, others, particularly the long ones,
must have been formed by lateral injection from such chambers. The larger dykes could well have fed substantial (≥1,000 km3) and quickly emplaced (a few years) flood basalt lava flows. This work highlights some interesting and significant similarities,
and contrasts, between the Nandurbar–Dhule dyke swarm and regional tholeiitic dyke swarms in Iceland, Sudan, and elsewhere.
Editorial responsibility: J. White 相似文献
4.
Sébastien Loock Hervé Diot Benjamin Van Wyk de Vries Patrick Launeau Olivier Merle Fabienne Vadeboin Michael S. Petronis 《Journal of Volcanology and Geothermal Research》2008
Anisotropy of magnetic susceptibility (AMS) data analysis is a convenient method used to investigate strain and flow during lava flow emplacement. In order to make a sound interpretation, the origin of the AMS signal must be verified. Two questions must be answered: 1) what phase, or phases carry the AMS signal and 2) when was the AMS fabric acquired? The verification steps themselves can provide extra data for interpreting lava flow conditions. Here, we present a methodology to answer the two questions in a 6 km-long Chaîne des Puys trachybasaltic lava flow that descended into the future site of Clermont Ferrand (France) 45,000 years ago. Knowledge of lava flow emplacement will be useful specifically to this site, if a reactivation of the volcanic chain occurs. The results are also of more general interest to understand lava flow emplacement dynamics. 相似文献
5.
Measurements of the anisotropy of magnetic susceptibility (AMS) of natural lavas have shown that AMS varies with depth within a lava flow. We have investigated the reasons for such variation by studying the effects of temperature and strain rate on the AMS of recent lava in the laboratory. Samples of lava from Kilauea were melted and subjected to a range of strain rate and cooling histories. The results show that the degree of anisotropy is a function of both the thermal and shearing history of a sample. High degrees of anisotropy were found only in samples that were deformed at temperatures close to those encountered during eruption and then rapidly quenched. Lavas subjected to similar shear stresses at high temperatures had low degrees of anisotropy if allowed to cool down slowly without further deformation. Additionally, lava subjected to complex shearing yield a lower degree of anisotropy even when high strain rates were imposed on it. These results lead to the conclusion that only the last phase of deformation is detectable using AMS and that high strain rates will not result in high degrees of anisotropy if either deformation ends while lava is still fluid or if the orientation of the maximum shear stress varies with time. The relation between the orientation of the principal susceptibilities and that of shear is less sensitive to variation on shear with time. Consequently, flow directions can be inferred confidently with this type of measurements. 相似文献
6.
天池火山东北侧造盾玄武岩可划分出8个流动单元,熔岩流的流动距离主要集中在30~50km,熔岩流宽度以5km左右为主。通过由野外调查获得的天池火山东北侧不同熔岩流单元的地表坡度、熔岩流厚度等,结合温度、密度与黏度等物理参数,按照熔岩流速度公式恢复的头道组和早白山组0.5m厚晶体含量5%的玄武岩熔岩流流速集中在0~1m/s之间。晶体含量为30%、厚度为0.5m的晚白山组和老房子小山组玄武岩熔岩流的流动速度集中在0~0.12m/s之间。厚度增大至2m左右,晶体含量不变的头道组和早白山组的玄武岩熔岩流流动速度可加快至11m/s。天池火山2m厚的碱性熔岩流在12h内达到或接近了它的最远距离,而各组内2m厚拉斑玄武岩熔岩流在20h内接近了最远距离。0.5m厚的熔岩流在10d内接近最大距离。50km是预计的熔岩流长度,在未来制定减灾措施时,可将此长度作为重要依据之一。天池火山熔岩流灾害主要表现为熔岩流动时对房屋建筑、农田、道路、林地、电站的毁坏,火灾及大量的人口伤亡 相似文献
7.
Geochemical data and mapping from a Karoo flood basalt crater complex reveals new information about the ascent and eruption
of magma batches during the earliest phases of flood basalt volcanism. Flood basalt eruptions at Sterkspruit, South Africa
began with emplacement of thin lava flows before abruptly switching to explosive phreatomagmatic and magmatic activity that
formed a nest of craters, spatter and tuff rings and cones that collectively comprise a crater complex >40 km2 filled by 9–18 km3 of volcaniclastic debris. Rising magma flux rates combined with reduced access of magma to external water led to effusion
of thick Karoo flood basalts, burying the crater-complex beneath the >1.5 km-thick Lesotho lava pile. Geochemical data is
consistent with flood basalt effusion from local dikes, and some lava flows likely shared or re-occupied vent sites active
during explosive eruptions at Sterkspruit. Flood basalt magmas involved in Sterkspruit eruptions were chemically heterogenous.
This study documents the rapid (perhaps simultaneous) eruption of three chemically distinct basaltic magmas which cannot be
simply related to one another from one vent site within the Sterkspruit crater complex. Stratigraphic and map relationships
indicate that eruption of the same three magma types took place from closely spaced vents over a short time during formation
of the bulk of the crater-complex. Two magma types recognized there have not been recognized in the Karoo province before.
The variable composition of flood basalts at Sterkspruit argues that magma batches in flood basalt fields may be small (0.5–1 km3) and not simply related to one another. This implies in turn that heterogeneities in the magma source region may be close
to each other in time and space, and that eruptions of chemically distinct magmas may take place over short intervals of space
and time without significant hybridisation in flood basalt fields. 相似文献
8.
This study focuses on Middle Miocene tholeiitic flood basalt lava flows from the Oregon Plateau, northwestern USA (Steens
Basalt), and is the first to comprehensively document and evaluate their morphology. Field observations of flows from several
sections within and proximal to the main exposures at Steens Mountain have been supplemented with textural and geochemical
data, and are used to offer preliminary insights into their emplacement. Compound pahoehoe flows of variable thickness appear
to be common throughout the study area, laterally and vertically. These tend to be plagioclase phyric and the morphology and
disposition of constituent flow lobes are quite similar to those from other provinces such as Hawaii and the Snake River Plain.
Classic a’a flows with brecciated upper and basal crusts are not abundant, but by no means uncommon. Flows with characters
different from typical pahoehoe and a’a are also common. Such flows display a range in morphology; flows with preserved upper
crusts but brecciated basal crusts, as well as those displaying well-developed flow-top breccias and preserved basal crusts
(rubbly pahoehoe) are observed. The Steens Basalt appears to display greater morphological and textural diversity at the outcrop
scale than that described for some other flood basalt provinces. The abundant compound pahoehoe flows (often rich in plagioclase
phenocrysts) were likely emplaced during slow but sustained eruptive episodes; their constituent lobes show clear evidence
for endogenous growth. The relatively aphyric flows with brecciated surfaces (including a’a) hint at higher strain rates and/or
higher viscosity, probably caused by higher effusion rates. A couple of sections are characterized by compositionally similar,
but morphologically different flows that were possibly part of the same eruption. While differences in pre-eruptive topography
could explain this, it is also possible that certain physical parameters changed substantially and abruptly during eruption
and that such changes were accompanied by differentiation processes within the plumbing system. It is possible that such observations
indicate temporal fluctuations within complex magmatic and eruptive systems, and deserve closer scrutiny. 相似文献
9.
Emplacement conditions of the c. 1,600-year bp Collier Cone lava flow, Oregon: a LiDAR investigation
A long-standing question in lava flow studies has been how to infer emplacement conditions from information preserved in solidified flows. From a hazards perspective, volumetric flux (effusion rate) is the parameter of most interest for open-channel lava flows, as the effusion rate is important for estimating the final flow length, the rate of flow advance, and the eruption duration. The relationship between effusion rate, flow length, and flow advance rate is fairly well constrained for basaltic lava flows, where there are abundant recent examples for calibration. Less is known about flows of intermediate compositions (basaltic andesite to andesite), which are less frequent and where field measurements are limited by the large block sizes and the topographic relief of the flows. Here, we demonstrate ways in which high-resolution digital topography obtained using Light Detection and Ranging (LiDAR) systems can provide access to terrains where field measurements are difficult or impossible to collect. We map blocky lava flow units using LiDAR-generated bare earth digital terrain models (DTMs) of the Collier Cone lava flow in the central Oregon Cascades. We also develop methods using geographic information systems to extract and quantify morphologic features such as channel width, flow width, flow thickness, and slope. Morphometric data are then analyzed to estimate both effusion rates and emplacement times for the lava flow field. Our data indicate that most of the flow outline (which comprises the earliest, and most voluminous, flow unit) can be well explained by an average volumetric flux ～14–18?m3/s; channel data suggest an average flux ～3?m3/s for a later, channel-filling, flow unit. When combined with estimates of flow volume, these data suggest that the Collier Cone lava flow was most likely emplaced over a time scale of several months. This example illustrates ways in which high-resolution DTMs can be used to extract and analyze morphologic measurements and how these measurements can be analyzed to estimate emplacement conditions for inaccessible, heavily vegetated, or extraterrestrial lava flows. 相似文献
10.
Statistical analysis of the magnetic fabric of samples from several successive lava flows emplaced under similar conditions can allow determination of the mean flow direction when magnetic fabric data from individual flows do not lead to reliable results. A difference between the obtained flow direction and the present dip direction indicates that the flows were tilted after emplacement. For 2 successive series of flows on the Jeanne d’Arc Peninsula presently NNW dipping, this method shows lava emplacement along a SSW–NNE direction. This indicates a gentle tilting acquired during a period of weak deformation in the whole archipelago. Additionally, the magnetic fabric data allow the reconstruction of the different conditions of emplacement of these two series of lava flows and of formation of the local thick conglomerate interbedded between these series. 相似文献
11.
Simon A. Kattenhorn Conrad J. Schaefer 《Journal of Volcanology and Geothermal Research》2008,170(3-4):181-197
Thermal–mechanical analyses of isotherms in low-volume basalt flows having a range of aspect ratios agree with inferred isotherm patterns deduced from cooling fracture patterns in field examples on the eastern Snake River Plain, Idaho, and highlight the caveats of analytical models of sheet flow cooling when considering low-volume flows. Our field observations show that low-volume lava flows have low aspect ratios (width divided by thickness), typically < 5. Four fracture types typically develop: column-bounding, column-normal, entablature (all of which are cooling fractures), and inflation fractures. Cooling fractures provide a proxy for isotherms during cooling and produce patterns that are strongly influenced by flow aspect ratio. Inflation fractures are induced by lava pressure-driven inflationary events and introduce a thermal perturbation to the flow interior that is clearly evidenced by fracture patterns around them. Inflation fracture growth occurs incrementally due to blunting of the lower tip within viscoelastic basalt, allowing the inflation fracture to pivot open. The final stage of growth involves propagation beyond the blunted tip towards the stress concentration at the tapered tip of a lava core, resulting in penetration of the core that causes quenching of the lava and the formation of a densely fractured entablature. We present numerical models that include the effects of inflation fractures on lava cooling and which support field-based inferences that inflation fractures depress the isotherms in the vicinity of the fracture, cause a subdivision of the lava core, control the location of the final portion of the lava flow to solidify, and cause significant changes in the local cooling fracture orientations. In addition to perturbing isotherms, inflation fractures cause a lava flow to completely solidify in a shorter amount of time than an identically shaped flow that does not contain an inflation fracture. 相似文献
12.
Summary Evidence for flow structure within hexagonal columns of basalt has been sought, using measurements of the anisotropy of magnetic susceptibility. The observed magnetic grain alignment indicates that the flow was essentially uniform and horizontal across the hexagons which were sampled. The flow probably occurred during emplacement of the lava; there is no evidence of convection within the hexagons, either from the degree of grain alignment or its orientation. 相似文献
13.
L.J. Applegarth H. Pinkerton M.R. James S. Calvari 《Journal of Volcanology and Geothermal Research》2010
Basaltic 'a'ā lava flows often demonstrate compound morphology, consisting of many juxtaposed and superposed flow units. Following observations made during the 2001 eruption of Mt. Etna, Sicily, we examine the processes that can result from the superposition of flow units when the underlying units are sufficiently young to have immature crusts and deformable cores. During this eruption, we observed that the emplacement of new surface flow units may reactivate older, underlying units by squeezing the still-hot flow core away from the site of loading. Here, we illustrate three different styles of reactivation that depend on the time elapsed between the emplacement of the two flow units, hence the rheological contrast between them. For relatively long time intervals (2 to 15 days), and consequently significant rheological contrasts, superposition can pressurise the underlying flow unit, leading to crustal rupture and the subsequent extrusion of a small volume of high yield strength lava. Following shorter intervals (1 to 2 days), the increased pressure caused by superposition can result in renewed, slow advance of the underlying immature flow unit front. On timescales of < 1 day, where there is little rheological contrast between the two units, the thin intervening crust can be disrupted during superposition, allowing mixing of the flow cores, large-scale reactivation of both units, and widespread channel drainage. This mechanism may explain the presence of drained channels in flows that are known to have been cooling-limited, contrary to the usual interpretation of drainage as an indicator of volume-limited behaviour. Because the remobilisation of previously stagnant lava can occur swiftly and unexpectedly, it may pose a significant hazard during the emplacement of compound flows. Constant monitoring of flow development to identify areas where superposition is occurring is therefore recommended, as this may allow potentially hazardous rapid drainage events to be forecast. Reactivation processes should also be borne in mind when reconstructing the emplacement of old lava flow fields, as failure to recognise their effects may result in the misinterpretation of features such as drained channels. 相似文献
14.
The Palaeogene Faroe Islands Basalt Group (FIBG) comprises three eruptive sequences or formations, all emplaced into a subaerial environment during the development of the extensive continental flood basalt province that stretches from East Greenland through the Faroe Islands and into the Faroe-Shetland Basin. The Beinisvørð Formation, having a tabular-classic facies architecture, is composed of a sequence of simple flows each comprising a single sheet lobe. The Beinisvørð Formation is overlain by the distinctly contrasting Malinstindur Formation that has a compound-braided facies architecture. The Enni Formation occurs at the top of the sequence and consists of a mixture of simple and compound flows with tabular-classic and compound-braided facies architectures, respectively. Surface and internal characteristics of the sheet lobes of the Beinisvørð and Enni formations indicate emplacement through inflation, which is more obvious for the tube-fed compound flows of the Malinstindur and Enni formations. The difference between the simple and compound flow sequences of the FIBG is, most likely, linked to the manner in which the lava was supplied during the eruption and the eruptive style of the volcanic system. The sheet lobes were erupted over laterally extensive areas from fissure systems which had a continuous supply of lava, which contrasts with the tube-fed compound flows which were erupted in a gradual, piecemeal manner from point-sourced, low shield volcanoes with limited areal extents. 相似文献
15.
William W. Chadwick Jr. Tracy K. P. Gregg Robert W. Embley 《Bulletin of Volcanology》1999,61(3):194-206
Lineated sheet flows are flat-lying, glassy lava flows characterized by a regular surface pattern of parallel grooves or
furrows aligned with the flow direction. They are unique to the submarine environment. We propose that the lineations are
developed within the collapsed interiors of partially ponded lobate sheet flows that initially inflate and then drain out
during emplacement. During lava drainout, the original lobate crust founders and a new crust begins to grow on the subsiding
lava surface. Lineated flow texture is created where molten lava emerges laterally from beneath a growing crust. The lineations
are formed by raking of the emerging lava surface by irregularities on the bottom edge of the crust and are preserved owing
to rapid chilling by seawater. Therefore, lineated sheet flows are the product of a specific sequence of events over a short
period of time during the course of a deep submarine eruption.
Received: 23 November 1998 / Accepted: 22 February 1999 相似文献
16.
The 1614–1624 lava flow of Mt. Etna was formed during a long-duration flank eruption involving predominantly pahoehoe flows which produced unusual surface features including mega-tumuli (here defined) and terraces. Detailed mapping of the flow units, surface features, and associated tubes reveals a complex sequence of emplacement for the field. The stair-stepped terraces appear to have been formed as a consequence of self-damming of tube-fed flows which developed «perched» ponds of lava. Surges of lava through tubes elevated sections of crusted lava at the distal ends of the flow to generate tumuli, some as high as 130 m, as a consequence of pressure via «hydrostatic head» conditions within the tube. Although pahoehoe lavas and the related features described here are atypical of Mt. Etna, they may reflect styles of eruption and lava emplacement found on volcanoes elsewhere. 相似文献
17.
Ascertaining the emplacement mechanism of oceanic basaltic lavas is important in understanding how ocean floor topography is produced and oceanic plates evolve, particularly during the early stages of crustal development of a supra-subduction zone. A detailed study of the volcanic stratigraphy at International Ocean Discovery Program (IODP) Site U1438 in the Amami Sankaku Basin, west of the Kyushu–Palau Ridge, has revealed the development of lava accretion and ridge topography on the Philippine Sea plate at about 49 Ma. Igneous basement rocks penetrated at Site U1438 are the uppermost 150 m of ~6 km-thick oceanic crust, and comprise, in a downhole direction, sheet flows (12.6 m), lobate sheet flows (61.3 m), pillow lavas (50.7 m), and thin sheet flows (25.3 m). The lowermost sheet flows are intercalated with layers of limestone and epiclastic tuff. Lithofacies analysis reveals that the lowermost sheet flows, limestone, and tuff formed on an axial rise, the pillow lavas were emplaced on a ridge slope, and the lobate sheet flows formed off ridge on an abyssal plain. The lithofacies of the basement basalt corresponds to the upper portions of fast-spreading oceanic crust, suggesting that subduction initiation was associated with intermediate to fast rates of seafloor spreading. The surface sheet flows are olivine–clinopyroxene-phyric basalt and differ from the lower basalt flows that contain phenocrysts of olivine and plagioclase, with or without clinopyroxene. The depleted chrome-spinel composition and olivine–clinopyroxene phenocryst assemblage in the surface sheet flows suggests a slight contribution of water for magma generation not present for the lower basalt flows. Considering the lithological difference between the backarc and forearc oceanic crust in the Izu–Bonin–Mariana arc, with sheet flow dominant in the former, seafloor spreading occurred faster in the later stage of subduction initiation. 相似文献
18.
Richard J. Brown S. Blake N. R. Bondre V. M. Phadnis S. Self 《Bulletin of Volcanology》2011,73(6):737-752
Newly identified ??a?? lava flows outcrop intermittently over an area of ~110?km2 in the western Deccan Volcanic Province (DVP), India. They occur in the upper Thakurvadi Formation in the region south of Sangamner. The flows, one of which is compound, are 15?C25?m thick, and exhibit well-developed basal and flow-top breccias. The lavas have microcrystalline groundmasses and are porphyritic or glomerocrystic and contain phenocrysts of olivine, clinopyroxene or plagioclase feldspar. They are chemically similar to compound p??hoehoe flows at a similar stratigraphic horizon along the Western Ghats. Petrographic and geochemical differences between ??a?? flows at widely spaced outcrops at the same stratigraphic horizon suggest that they are the product of several eruptions, potentially from different sources. Their presence in the DVP could suggest relative proximity to vents. This discovery is significant because ??a?? lavas are generally scarce in large continental flood basalt provinces, which typically consist of numerous inflated compound p??hoehoe lobes and sheet lobes. Their scarcity is intriguing, and may relate to either their occurrence only in poorly preserved or exposed proximal areas or to the flat plateau-like topography of flood basalt provinces that may inhibit channelization and ??a?? formation, or both. In this context, the ??a?? flow fields described here are inferred to be the products of eruptions that produced unusually high-effusion-rate lavas compared to typical flood basalt eruptions. Whether these phases were transitional to lower intensity, sustained eruptions that fed extensive low effusion rate p??hoehoe flow fields remains unclear. 相似文献
19.
《Journal of Volcanology and Geothermal Research》2006,149(3-4):240-262
Miocene successions in western Turkey are dominated by lacustrine, fluvial and evaporitic sedimentary deposits. These deposits include considerable amounts of volcaniclastic detritus derived from numerous NE-trending volcanic centres in western Turkey as well as in the Bigadiç region. Early Miocene syn-depositional NE-trending olivine basalt and trachyandesite bodies that formed as intrusions and lava flows occur within the Bigadiç borate basin. Olivine basalts occur as partly emergent intrusions, and trachyandesite dykes fed extensive lava flows emplaced in a semi-arid lacustrine environment.Peperites associated with the olivine basalt and trachyandesites appear to display contrasting textural features, although all the localities include a large variety of clast morphologies from blocky to fluidal. Fluidal clasts, mainly globular, ameboidal and pillow-like varieties, are widespread in the peperite domains associated with olivine basalts, apparently due to large-volume sediment fluidisation. In contrast, fluidal clasts related to trachyandesites are restricted to narrow zones near the margins of the intrusions and have commonly elongate and polyhedral shapes with digitate margins, rather than globular and equant varieties. Blocky and fluidal clasts in the olivine basalt peperite display progressive disintegration, suggesting decreasing temperature and increasing viscosity during fragmentation. Abundance of blocky clasts with respect to fluidal clasts in the trachyandesite peperite indicates that the fluidal emplacement and low-volume sediment fluidisation in the early stages were immediately followed by quench fragmentation due to the high viscosity of the magma.Size, texture and abundance of the blocky and fluidal clasts in the olivine basalt and trachyandesite peperites were mainly controlled by sediment fluidisation, pulsatory magma injection and magma properties such as composition, viscosity, vesicularity, and size, abundance and orientation of phenocrysts. Variously combining these contrasting features to varying degrees may form diverse juvenile clast shapes in peperitic domains. 相似文献