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271.
Letizia Spampinato Sonia Calvari Clive Oppenheimer Luigi Lodato 《Journal of Volcanology and Geothermal Research》2008
The 26 October 2002–28 January 2003 eruption of Mt. Etna volcano was characterised by lava effusion and by an uncommon explosivity along a 1 km-long-eruptive fissure on the southern, upper flank of the volcano. The intense activity promoted rapid growth of cinder cones and several effusive vents. Analysis of thermal images, recorded throughout the eruption, allowed investigation of the distribution of vents along the eruptive fissure, and of the nature of explosive activity. The spatial and temporal distribution of active vents revealed phases of dike intrusion, expansion, geometric stabilization and drainage. These phases were characterised by different styles of explosive activity, with a gradual transition from fire fountaining through transitional phases to mild strombolian activity, and ending with non-explosive lava effusion. Here we interpret the mechanisms of the dike emplacement and the eruptive dynamics, according to changes in the eruptive style, vent morphology and apparent temperature variations at vents, detected through thermal imaging. This is the first time that dike emplacement and eruptive activity have been tracked using a handheld thermal camera and we believe that its use was crucial to gain a detailed understanding of the eruptive event. 相似文献
272.
273.
武功山片麻岩特征及侵位机制 总被引:2,自引:0,他引:2
张芳荣 《华东地质学院学报》2000,23(2):146-149
江西武功山片麻岩,前人存在两种观点,混合成因和岩浆成因,近年来,作者等人通过1:5万区调,对武功山片麻岩取得了一些新的认识,认为武功山片麻岩是岩浆成因,属岩浆多次脉动形成的气球膨胀式强力侵位机制。 相似文献
274.
R. A. JAMIESON 《Journal of Metamorphic Geology》1986,4(1):3-22
Abstract Mctamorphic rocks of the St Anthony Complex of north-western Newfoundland are best interpreted in terms of a high-temperature shear zone formed between down-going continental margin rocks and overriding oceanic lithosphere in a subduction zone. High-grade rocks, immediately beneath the oceanic lithosphere peridotite, display retrograde meta-morphism in high-strain zones, whereas lower grade rocks, near the base of the metamorphic complex, display prograde metamorphism in high-strain zones. Mylonite zones in meta-basitcs at all levels in the complex contain the assemblage epidote-hornblende-albite-sodic oligoclase. These observations suggest that the 'inverted metamorphic gradient'within the St Anthony Complex results from the fortuitous preservation of residual metamorphic assemblages from different crustal levels within an epidote amphibolite facies shear zone. The degree of re-equilibration is strongly dependent on the degree of strain, and is best achieved in synmetamorphic mylonite zones. This interpretation of the St Anthony Complex can be extended to other sub-ophiolite metamorphic sheets, which show very similar relationships. It is proposed that most metamorphic sheets beneath ophiolites are high temperature shear zones, the P-T paths of which preserve records of burial and exhumation in subduction zones. 相似文献
275.
湖南大坳钨锡矿区构造控矿规律及其在找矿中的应用效果 总被引:10,自引:1,他引:9
从矿床特征入手,对控矿构造进行具体分析,从区内岩浆活动和区域构造应力场演化规律的角度,论证了区内构造的形成机制,探讨了构造对钨锡成矿作用和矿体空间分布规律的控制。认为区内构造的形成与岩浆多阶段脉动侵位密切相关,热液致裂和NNE向断裂的左行剪切所产生的力偶作用使控矿构造产生多次脉动活动和矿化作用,控矿构造的空间分布特征及其性质决定了钨锡矿化类型和矿脉(体)的产出特征,构造控矿具有定位性、等距性、定向性及分带性等规律,应用该规律,取得了较好找矿效果。 相似文献
276.
Elizabeth?McClelland Colin?J.?N.?WilsonEmail author Leon?Bardot 《Bulletin of Volcanology》2004,66(6):492-513
Palaeomagnetic data from lithic clasts collected at 46 sites within layers 1 and 2 of the 1.8-ka Taupo ignimbrite, New Zealand, have been used to determine the palaeotemperatures and thermal structure of the deposit on its emplacement. Equilibrium temperatures from sites less than 30–40 km from vent are 150–300 °C, whereas at greater distances site equilibrium temperatures increase up to 400–500 °C. This variation is seen in both layer 1 and 2 deposits, with values for layer 1 being somewhat cooler, and with its increase in temperature occurring at a greater distance from vent. A temperature maximum at ~50 km from vent coincides with a zone of pink thermal-oxidation colouration of pumices previously inferred to reflect higher emplacement temperatures. Additional palaeomagnetic data collected by us and others from pumice clasts show comparable temperature variations, but these temperature estimates are shown here to be due to a chemical remanence and unreliable for accurate temperature estimates. Cooler temperatures in proximal parts of the ignimbrite are consistent with admixture of >20% cold lithic clasts at source and interaction with the pre-eruption Lake Taupo. The similar, but offset, increases in equilibrium temperatures for medial and distal layers 1 and 2 are consistent with both layers being deposited from the same flow. However, any proximal deposits left by the later, hotter material must have been subsequently eroded, or be so thin that our collection failed to sample them. Radial asymmetries in equilibrium temperatures as well as other physical parameters suggest that the deposit emplacement temperature is primarily determined at source, rather than by interaction with air during transport. These data support previous interpretations that a concentrated basal flow played a dominant role in emplacement and deposition of the Taupo ignimbrite.Editorial responsibility: T. Druitt 相似文献
277.
Jean-Louis Vigneresse 《Resource Geology》2006,56(3):293-314
Abstract. Continental collisions are the place where granitic plutons result from the melting of crustal components. Granitic plutons are built up by successive input of magma with a variable composition and hence temperature and chemistry. The intrusion of a new magma batch has consequences on the element mobility in the melt. Diffusion in already formed crystals is limited, due to the short time interval between magma input, and because of the low values of element diffusivity in solids. Because the new magma is generally hotter than the magma chamber, the temperature in the contact zone is modified. It activates diffusion by and modifies its characteristic length for element mobility in the melt. A new intrusion also modifies the partition coefficients, decreasing compatibility and increasing the incompatibility. The change in temperature has also effects on fluid exsolution controlled by crystallization, or second boiling. The present paper examines the intrusion of magma (fel‐sic or mafic) into a felsic magma chamber with a time interval of 30 ky. The intrusion of magma with similar composition, hence low (±100d?C) temperature difference has few effects. The diffusion lengths for elements rarely exceed one order of magnitude. The fluids released by the cooling magma are balanced by their reincorporation into the warming magma. In contrast, the intrusion of mafic magma into felsic magma chamber results in temperature difference that can reach ±300d?C. It may change the diffusion length up to two orders of magnitude for elements having large activation energy. Partition coefficients also vary by more than one order of magnitude. The effect is enhanced in the warming felsic magma, and damped in the mafic magma. In consequence elements like As, Sn, Sr, W, Zr are driven from the mafic magma toward the felsic magma. The release of H2O and CO2 are balanced between the two magma types. However the mafic magma releases an important amount of S that cannot re‐dissolves into the felsic magma and remains in the fluid phase. This simple model also addresses processes acting during ore formation. In particular, it examines the behavior of ions with a four valences state, as Sn and W, which has implications on the incorporation of other elements sharing a similar structure. It points out the necessity of external factors (S, halogens content and redox conditions) for controlling ore formation. 相似文献
278.
浙江梧村岩体是一个主要由石英二长岩、二长岩组成的中生代复式岩体。通过详细的野外填图和地质地球化学研究,发现该岩体具有结构和成分演化序列。依据侵入体之间及其与围岩的接触关系、岩石的矿物成分及岩石地球化学、结构构造等特征,可将其划分为大山、沐尘、下坞等3个岩石单元,归并为梧村超单元。从早期到晚期,岩浆的侵入具有明显的反序特征,这种"反序"现象是因为存在带状岩浆房。三个单元在格局上呈刺破式同心带状型式,这种就位很可能属于刺穿式底辟作用。 相似文献
279.
Nestor Vegas Seta Naba Jean Luc Bouchez Mark Jessell 《International Journal of Earth Sciences》2008,97(6):1165-1180
The Fada N′Gourma area in Burkina Faso is underlain by Paleoproterozoic rocks that make the northeastern West-African Craton.
This region is composed of NE-trending volcano-sedimentary belts and foliated tonalites, affected by several shear zones.
A generation of younger, ∼2100 Ma-old, non-foliated biotite-bearing granites intrudes the former rock units. We have investigated
the younger granite pluton of Kouare that was previously considered as forming a single body with the pluton of Satenga to
the west, a pluton which likely belongs to the ∼20 Ma more recent Tenkodogo-Yamba batholith. Magnetic fabric measurements
have been combined with microstructural observations and the analysis of field and aeromagnetic data. The granite encloses
angular enclaves of the host tonalites. Magmatic microstructures are preserved inside the pluton and solid-state, high-temperature
deformation features are ubiquitous at its periphery. The presence of steeply plunging lineations in the pluton of Kouare
and its adjacent host-rocks suggests that large volumes of granitic magmas became crystallized while they were ascending through
the crust that was softened and steepened close to the contact. Around Kouare, the foliation in the host tonalites conforms
with a map-scale, Z-shaped fold in between NNE-trending shear zones, implying a bulk clockwise rotation of the material contained
in-between the shear zones, including the emplacing pluton. Regionally, the Fada N′Gourma area is concluded to result from
NW-shortening associated with transcurrent shearing and vertical transfer of granitic magmas. This study concludes that the
∼2200 Myears old juvenile crust of Burkina Faso was brittle before the intrusion of the biotite-granites, became softened
close to them and that gravity-driven and regional scale wrench tectonics were active together. 相似文献
280.
AbstractThe shape and structural development of the box-like Parrabel Dome (PD) within the Hastings Block is poorly understood because it has only been weakly cleaved, complexly folded and extensively faulted in comparison to the adjoining blocks. Better characterising this block will provide important controls on the tectonics of the southern New England Orogen. The structural development of the PD and southern Hastings Block (SHB) provides evidence of the degree of rotation, translation and deformation of the Hastings Block, a key terrane within the southern New England Orogen. A major decollement under the Hastings Block–Nambucca Block was suggested to facilitate south-directed deformation caused by the developing Coffs Harbour Orocline. The orientation of bedding and the stratigraphic facing of some fault blocks within the northern Hastings Block (NHB) are consistent with development of the PD, while other fault blocks indicate significant disruption of the NHB prior to, during and after dome development. A deep-seated fault is suggested by the gravity worm analysis consistent with the boundary zone between the PD, NHB-Yarrowitch Block and the east-dipping and younging sequences in the SHB. The eastern limb of the PD underwent clockwise rotation after formation. Fault blocks have been rotated and translated within a restraining bend as the NHB moved post-PD formation northwest along the interface between the NHB and SHB.
- KEY POINTS
The Hastings Block was translated and rotated into its current position from the southeastern end of the Tamworth Belt.
Gravity worm data indicate a boundary between northern and southern Hastings Block.
The Hastings and Nambucca blocks have been detached from the basement Gondwana rocks.
Fault block analysis within the Parrabel Dome, northern Hastings Block indicates relocation of some blocks by faulting.