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21.
Mineral chemistry of a Cenozoic igneous complex,the Urumieh–Dokhtar magmatic belt,Iran: Petrological implications for the plutonic rocks 
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下载免费PDF全文 Maryam Honarmand Nematollah Rashidnejad Omran Franz Neubauer Ghasem Nabatian Mohammad Hashem Emami Manfred Bernroider Jamshid Ahmadian Mohammad Ebrahimi Xiaoming Liu 《Island Arc》2016,25(2):137-153
The Niyasar plutonic complex, one of the Cenozoic magmatic assemblages in the Urumieh‐Dokhtar magmatic belt, was the subject of detailed petrographic and mineralogical investigations. The Niyasar magmatic complex is composed of Eocene to Oligocene mafic rocks and Miocene granitoids. Eleven samples, representing the major rock units in the Niyasar magmatic complex and contact aureole were chosen for mineral chemical studies and for estimation of the pressure, temperature, and oxygen fugacity conditions of mineral crystallization during emplacement of various magmatic bodies. The analyzed samples are composed of varying proportions of quartz, plagioclase, K‐feldspar, hornblende, biotite, titanite, magnetite, apatite, zircon, garnet, and clinopyroxene. Application of the Al‐in‐hornblende barometer indicates pressures of around 0.2 to 0.4 kbar for the Eocene–Oligocene mafic bodies and around 0.5 to 1.7 kbar for the Miocene granitoids. Hornblende‐plagioclase thermometry yields relatively low temperatures (661–780 °C), which probably reflect late stage re‐equilibration of these minerals. The assemblage titanite–magnetite–quartz as well as hornblende composition were used to constrain the oxygen fugacity and H2O content during the crystallization of the parent magmas in the Miocene plutons. The results show that the Miocene granitoids crystallized from magmas with relatively high oxygen fugacity and high H2O content (~5 wt% H2O). The Miocene granitoids show similar range of oxygen fugacity, H2O contents and mineral chemical compositions, which indicate a common source for their magmas. Although the crystallization pressures of the Miocene plutons discriminate various categories of plutonic bodies emplaced at depths of about 5.7–6.5 km (Marfioun pluton), about 4.2 km (Ghalhar pluton) and 1.9–2.3 km (Poudalg pluton), they were later uplifted to the same level by vertical displacement of faults. The emplacement depths of the Niyasar plutons suggest that the central part of the Urumieh‐Dokhtar magmatic belt has experienced an uplift rate of ca. 0.25–0.4 mm/yr from the Miocene onwards. 相似文献
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23.
An internally consistent thermodynamic dataset with uncertainties and correlations: 2. Data and results 总被引：4，自引：0，他引：4
Abstract This, the second of two papers, represents the application of a least squares approach, discussed in the previous paper, to the generation of an internally consistent thermodynamic dataset involving 60 reactions among 43 phases, in the system K2 O–Na2 O–CaO–MgO–Al2 O3 –SiO2 –H2 O–CO2 . We make the assumption that all the thermodynamic data, with the exception of enthalpies of formation of the phases, are well known, and solve for an internally consistent set of enthalpies which reproduces the 60, experimentally determined, phase equilibrium reactions. An important difference between our dataset and that of previous alternatives in the literature is that we are able to determine the uncertainties on, and correlations between, the enthalpies of formation for all phases in the set, and hence are able to apply simple error propagation techniques to determine the uncertainties in any phase equilibrium calculations performed using this dataset. Selection of reactions, for geothermometry and geobarometry, may be more readily made by choosing equilibria with small uncertainties in their thermodynamics. Our data are in reasonably close agreement with the high temperature molten oxide calorimetry results on silicate minerals where available, a fact which lends a degree of confidence to the results. 相似文献
24.
Z. J. Zhang 《Island Arc》1999,8(2):259-280
Garnet–clinopyroxene–amphibole rocks from the Songshugou mafic–ultramafic complex ( ca 1029 Ma) in the Qinling Mountains, central China, occur in a metabasite unit that is situated structurally beneath the peridotite body. These rocks have many records testifying to a multistage metamorphic history for the metabasites. Through petrographic and mineralogic investigations, at least three metamorphic stages were recognized: (i) a pre-eclogite stage of the amphibolite-facies condition as inferred from inclusions in garnet; (ii) an eclogite-facies stage as inferred from Pl-Cpx symplectites and from their reconstructed omphacite compositions (Jd17–35 ); and (iii) a post-eclogite stage characterized by various reaction textures such as coronas and reaction zones around garnets, clinopyroxenes and fine-grained mineral aggregates after garnets and clinopyroxenes. A textural relationship observed in the field and thin-section scales indicates that a breakdown of the Grt–Cpx–Amp assemblage led to the Grt-free and the Cpx-free assemblages, that is, Amp + Pl assemblage at the end. The eclogite-facies metamorphism of the metabasites, discussed in the present report, was related to subduction at the age intervening between ca 983 and ca 1029 Ma. Regional geologic data indicate that the eclogite-related subduction took place during the opening of the Kuanping marginal basin in the southern margin of the North China craton, and slightly before the formation of the Danfeng magmatic arc ( ca 984 Ma). The exhumation and emplacement of the eclogite-facies domain probably resulted from a collision between the Danfeng magmatic arc terrain and a fragment of the North China craton (i.e. the Qinling Complex) during 790–890 Ma. 相似文献
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Erdin Bozkurt 《Geodinamica Acta》2013,26(1-3):3-30
AbstractTurkey forms one of the most actively deforming regions in the world and has a long history of devastating earthquakes. The belter understanding of its neotectonic features and active tectonics would provide insight, not only for the country but also for the entire Eastern Mediterranean region. Active tectonics of Turkey is the manifestation of collisional intracontinental convergence- and tectonic escape-related deformation since the Early Pliocene (~5 Ma). Three major structures govern the neotectonics of Turkey; they are dextral North Anatolian Fault Zone (NAFZ), sinistral East Anatolian Fault Zone (EAFZ) and the Aegean–Cyprean Arc. Also, sinistral Dead Sea Fault Zone has an important role. The Anatolian wedge between the NAFZ and EAFZ moves westward away from the eastern Anatolia, the collision zone between the Arabian and the Eurasian plates. Ongoing deformation along, and mutual interaction among them has resulted in four distinct neotectonic provinces, namely the East Anatolian contractional, the North Anatolian, the Central Anatolian ‘Ova’ and the West Anatolian extensional provinces. Each province is characterized by its unique structural elements, and forms an excellent laboratory to study active strike-slip, normal and reverse faulting and the associated basin formation. © 2001 Éditions scientifiques et médicales Elsevier SAS 相似文献
26.
H. H. STOWELL 《Journal of Metamorphic Geology》1989,7(3):343-358
ABSTRACT The western metamorphic belt of the Coast Plutonic Complex, south-east Alaska and adjacent British Columbia, contains strongly deformed rocks and a prominent topographic low: the Coast Range megalineament. Near Holkham Bay, south-east Alaska, the lineament separates the western metamorphic belt into: a western low-grade (greenschist facies) terrane, and an eastern medium-grade (amphibolite facies) terrane. Sphalerite compositions of grains in direct contact with pyrite and pyrrhotite in chlorite-muscovite zone rocks in the low-grade terrane give pressures of about 8 kbar; compatible with pressures of 8-10 kbar at 500°C calculated from plagioclase-biotite-garnet-muscovite assemblages adjacent to the Windham Bay pluton about 15 km away. A pressure of 4.8 ± 0.7 kbar was calculated from sphalerite compositions in staurolite zone rocks east of the Coast Range megalineament. This is indistinguishable from pressures of 4.8 ± 1 kbar at 585°C and 5.1 ± 1 kbar at 680°C (plagioclase-garnet-aluminum silicate-quartz equilibria), and 4.1 ± 1 kbar at 585°C (plagioclase-biotite-garnet-muscovite equilibrium) determined for the medium-grade terrane. An identical pressure of 4.8 ± 0.7 kbar was calculated from sphalerite compositions in biotite zone rocks adjacent to the lineament; this is considerably higher than a pressure of 3.1 ± 1 kbar at 525°C obtained using plagioclase-biotite-garnet-muscovite geobarometry from shear zones within the lineament. The discrepancy may be explained by later equilibration of mineral phases within the shear zones. The geothermobarometry suggests relatively low temperatures and high pressures for the low-grade terrane (6-10 kbar), and intermediate temperatures and pressures for the medium-grade terrane to the east (4-6 kbar). Comparison of the barometers indicate that sphalerite can be used to estimate metamorphic pressures, similar to those estimated from silicate mineral chemistry when pyrrhotite-sphalerite-pyrite assemblages are used. 相似文献
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Archaean granulite facies metamorphism of the Lewisian of Tiree, Inner Hebrides, north-west Scotland
I. CARTWRIGHT 《Journal of Metamorphic Geology》1992,10(6):727-744
The Lewisian of Tiree, north-west Scotland, underwent granulite facies metamorphism prior to 2.4 Ga. The temperatures and pressures estimated from garnet–clinopyroxene, garnet–orthopyroxene, hornblende–plagioclase and garnet–biotite geothermometers and clinopyroxene–plagioclase–garnet–quartz and orthopyroxene–plagioclase–garnet–quartz geobarometers are 810 ± 50° C and 10.5 ± 1.5 kbar. The imprecision of pressure estimates stems largely from uncertainties in garnet activity models. Calculations of blocking temperatures for Fe–Mg interdiffusion in clinopyroxene and garnet suggest that these temperatures and pressures represent only slightly reset peak-metamorphic conditions.
Down-temperature re-equilibration resulted in chemical zoning over the outer 50–100 μm of the mafic minerals. P–T paths calculated from this mineralogical zoning suggest nearly isobaric cooling. However, the growth of late sillimanite in metapelites requires that the retrograde P–T path had a significant decompression component, suggesting that the mineralogical zonation does not define the retrograde P–T path. The discrepancy between the P–T path calculated from mineralogical zonation and that implied by mineral reactions probably results from the net-transfer geobarometry reactions closing at higher temperatures than the exchange geothermometers.
The Tiree rocks have a similar history to the mainland Scourian complex. Granulite facies metamorphism accompanied by partial melting occurred prior to the intrusion of the Scourie dykes at c. 2.4 Ga, and the rocks underwent retrogression both prior to and after dyke emplacement. However, peak metamorphic temperatures and pressures on Tiree were lower than those recorded in the Scourian complex, and the Tiree rocks may have been at a different crustal level at that time. 相似文献
Down-temperature re-equilibration resulted in chemical zoning over the outer 50–100 μm of the mafic minerals. P–T paths calculated from this mineralogical zoning suggest nearly isobaric cooling. However, the growth of late sillimanite in metapelites requires that the retrograde P–T path had a significant decompression component, suggesting that the mineralogical zonation does not define the retrograde P–T path. The discrepancy between the P–T path calculated from mineralogical zonation and that implied by mineral reactions probably results from the net-transfer geobarometry reactions closing at higher temperatures than the exchange geothermometers.
The Tiree rocks have a similar history to the mainland Scourian complex. Granulite facies metamorphism accompanied by partial melting occurred prior to the intrusion of the Scourie dykes at c. 2.4 Ga, and the rocks underwent retrogression both prior to and after dyke emplacement. However, peak metamorphic temperatures and pressures on Tiree were lower than those recorded in the Scourian complex, and the Tiree rocks may have been at a different crustal level at that time. 相似文献
28.
Abstract Activity-composition relations in oligoclase near the peristerite gap are investigated in pelites from the Central Menderes Massif. The pressure of metamorphism is estimated independently, from garnet-rutile-ilmenite-kyanite-quartz, as being in the range 4–7 kbar. In the temperature range, 450–600°C approximately, both the Newton-Haselton calibration of the garnet-plagioclase-kyanite-quartz geobarometer and a related simple treatment of garnet-plagioclase-muscovite-biotite give a wide range of apparent pressures, correlated with plagioclase composition and ranging up to 11–12 kbar where the plagioclase is most sodic. This effect is attributed to failure of the activity model for plagioclase used in the Newton-Haselton treatment. It is inferred that, in the present area, γplag An decreases with increasing X plag An in the range An15 -An25 . The data can be interpreted in terms of high γ plag An in the high-albite structure at these temperatures, modified to lower values by 'e'ordering in the more calcic oligoclases. The ordering appears to be independent of the peristerite gap, and the data do not support the interpretation of the gap as a solvus. Garnet-plagioclase assemblages are unreliable as geobarometers where the plagioclase is more sodic than approximately An20 and T < 700°C, and should instead be used to investigate the γ -X behaviour of the plagioclase where independent geobarometry can be used as a constraint. 相似文献
29.
华北地块北缘晚古生代-中生代花岗岩体侵位深度及其构造意义 总被引：13，自引：5，他引：13
运用斜长石-角闪石温压计对华北地块北缘内蒙古隆起及燕山褶断带内不同时期花岗质侵入岩的结晶压力及侵位深度进行了估算。结果表明,晚古生代—早中生代期间,在内蒙古隆起及燕山褶断带之间,存在有强烈的差异性隆升及剥露过程,但这种差异性隆升及剥露在早侏罗世以来的表现则不明显。晚古生代—早中生代差异性隆升及剥露可能是导致内蒙古隆起上大量基底岩石出露、中—新元古代及古生代沉积盖层缺失及燕山褶断带中—新元古代及古生代沉积盖层大量保留的主要原因。内蒙古隆起强烈的隆升及剥露过程发生在晚石炭世—早侏罗世期间,其东部的剥露幅度比中东部明显偏小。晚古生代-早中生代期间内蒙古隆起的强烈剥露及其与燕山褶断带之间的差异性隆升可能与古亚洲洋板块向华北地块的俯冲、消减、碰撞及华北北缘区域性断裂(如平泉-古北口-赤城-尚义断裂、赤峰-围场-多伦断裂)的活动有关。燕山褶断带的强烈隆升与剥露发生则在晚侏罗世—早白垩世之后。晚体罗世—早白垩世以来,华北地块北缘南北两侧均有一次明显的剥露过程,这一剥露可能与本区及中国东部地壳强烈伸展有关。 相似文献
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Abstract The enthalpy of reaction of plagioclase and pyroxene to produce garnet and quartz has been a major source of error in granulite geobarometry because of relatively uncertain enthalpy values available from high-temperature solution calorimetry and compiled indirectly from experimental phase equilibria. Recent, improved calorimetric measurements of ΔHR are shown to yield palaeopressures which are internally consistent between orthopyroxene and clinopyroxene calibrations for many South Indian granulites from the Archaean high-grade terranes of southern Karnataka and northern Tamil Nadu. This represents a considerable improvement over previous calibrations, which gave disparate results for the two independent barometers involving orthopyroxene and clinopyroxene, requiring a 2-kbar ‘empirical adjustment’to force agreement. Palaeopressures thus calculated for 30 well-documented two-pyroxene garnet granulites from South India give internally consistent pressures with a mean of 8.1°1.1 kbar at 750°C, consistent with the presence of both kyanite and sillimanite in many areas. Those samples for which garnet–pyroxene exchange thermometers give plausible granulite-range temperatures and whose minerals are minimally zoned give the best agreement of the two barometers. Samples which yield low palaeotemperatures and different rim and core compositions of minerals yield pressures for the orthopyroxene assemblage as much as 2 kbar lower than for the assemblage with clinopyroxene. This disparity probably represents post-metamorphic-peak re-equilibration. We conclude that considerable confidence may be placed in geobarometry of two-pyroxene granulites where apparent palaeotemperatures are in the granulite facies range (>700°C) and where mineral zonation is minimal. Of the several possible sets of activity–composition relations in use, those constructed from analysis of phase equilibria give slightly higher palaeopressures and appear more consistent with analytical data from the Nilgiri Hills uplift, where kyanite is the only aluminium silicate reported to be stable in peak-metamorphic assemblages. The present results support a palaeopressure gradient, increasing generally from south to north, across the Nilgiri Hills as inferred by previous geobarometry. 相似文献