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1.
《地学前缘(英文版)》2019,10(3):1073-1099
Compositionally zoned plutons, both layered and concentrically arranged, provide granitic exposures where the mechanisms and timing of the magmatic emplacement processes can be studied. The importance of in-situ geochemical differentiation and the magma replenishment rates are revealed by geochemistry and field relations, together with the increasingly accurate U–Pb geochronology, which has promoted the knowledge about the pluton incremental assembly theories.The Flamenco pluton, located in the Coastal Range of northern Chile, is part of the Upper Triassic to Early Cretaceous Andean intrusives formed in the western active margin of South America, and present a normal zoned structure with mafic magmatic facies (mostly gabbros and Qtz-diorites) close to the contacts with the host metasediments, and tonalites, granodiorites and granites in the inner areas. A combined study of the field relations, geochemistry and zircon geochronology of the magmatic facies was applied to determine the emplacement sequence of the Flamenco pluton, revealing three distinguishable domains separated by metasedimentary septa. The SW area is constituted by mostly homogeneous leucocratic granodiorites that yielded an age of 213 Ma as the best estimation for their emplacement age. Distinctive geochemical characteristics, such as the absence of an Eu anomaly, the depletion in HREE, or the highest Sr, Sr/Y and Ce/Yb values among the granodioritic facies of the pluton, involve lower T and/or higher P conditions at the magmatic source according to experimental studies. These conditions were established during an early stage of the Andean magmatic arc building that is firstly defined here as Upper Triassic. The NW and E domains of the pluton were sequentially emplaced between 194 Ma and 186 Ma and both the field relations and the detailed geochronological results suggest that the mafic facies intruded latter in the emplacement sequence. To the NW, Qtz-dioritic and gabbroic externally emplaced pulses gave a younger crystallization age of 186.3 ± 1.8 Ma, and promoted the granoblastic textures and metamorphic zircon overgrowths that characterize the granodiorites located in the contact with the intermediate and felsic inner magmas, which yielded a best estimation of their emplacement age of 192 ± 1.5 Ma. On the other hand, in the eastern domain, magma-magma relations are observed between gabbros and previously intruded tonalites and granodiorites. Both the mafic and intermediate facies show two main subgroups of ages that yielded 194.7 ± 1.5 Ma to 188.3 ± 2.1 Ma and 193.1 ± 2.2 Ma to 185.5 ± 1.4 Ma respectively. These differences are related to the variations in the magmatic addition rates, which may extend the super-solidus conditions in the eastern domain of the magmatic reservoir as is confirmed by the wider age ranges yielded by these magmatic facies. Zircon overgrowths in the host rocks yield similar ages (around 220 Ma and 205 Ma) than the oldest results obtained in the intrusive facies, indicating that metamorphism correlates with the initial stages of plutonic emplacement.Geochronological results differ between 9 Myr and 41 Myr in the eight studied samples for non-inherited ages and gave very close mean ages (within analytical uncertainty) for all the intrusive units. However, we examine other characteristics such as zircon morphology, internal structure, geochemistry and statistical data to assess if the scattering of the geochronological data may be related to the different processes involved in the construction of the Flamenco pluton. We concluded that this detailed study of U–Pb zircon ages, including individual and significative groups of analyses, is useful to determine accurately the emplacement sequence and the genetic relation between the intrusive units, together with the evidences depicted by the geochemistry and field relations. 相似文献
2.
Structural mapping of the Pasupugallu pluton, an elliptical intrusive gabbro-anorthosite body, emplaced into the western contact zone between the Eastern Ghats Mobile Belt and the Archaean East Dharwar Craton, along the east coast of India, reveals concentric, helicoidal and inward dipping magmatic and/or tectonic foliations. We identify a <1 km-wide structural aureole characterized by pronounced deflection of regional structures into margin parallel direction, mylonitic foliations with S-C fabrics, sigmoidal clasts, moderately plunging stretching lineations, non-cylindrical intrafolial folds, and stretched elliptical mafic enclaves in the aureole rocks. Our results suggest that the pluton emplacement is syn-tectonic with respect to the regional ductile deformation associated with the terrane boundary shear zone at the western margin of the Eastern Ghats. We present a tectonic model for the emplacement of the pluton invoking shear-related ductile deformation, rotation and a minor component of lateral expansion of magma. The intrusive activity (1450-800 Ma) along the western margin of the Eastern Ghats can be correlated with the significant event of recurring mafic, alkaline and granitic magmatism throughout the global Grenvillian orogens associated with the continent-continent collision tectonics possibly related to the amalgamation and the breakup of the supercontinent Rodinia. 相似文献
3.
《Gondwana Research》2014,25(2):685-706
Large granite batholiths were emplaced at the Gondwana active margin during Lower Ordovician in South America. These have contributed to crustal growth by net addition of silicic rocks to the continental crust. New U–Pb SHRIMP zircon age determinations, together with thermobarometric and geochemical data, yield that batholith magma intrusion is the responsible of heating and self-granulitization of early gabbro pulses. Partially molten granulitic gabbros, which appear as either early intruded into the metasedimentary host or as large inclusions within the batholith-forming Qtz-diorites, contain Opx-bearing, trondhjemitic leucosomes surrounding Hbl + Opx + Pl mafic mesosomes forming typical agmatitic structures. Hornblende–Plagioclase equilibria, applied to mineral pairs of granoblastic aggregates in textural equilibrium of metagabbro mesosomes, yield temperatures in the range 850–910 °C for core-to-core pairs and in the range 1000–1075 °C for rim-to rim pairs, at pressures of about 0.7 GPa. SHRIMP zircon age revealed that the whole batholith was emplaced over a narrow time interval of 20 Ma from 465 to 485 Ma, with most ages clustered at about 470 Ma. The age of metagabbros is 473 ± 7 Ma for older zircons and 454 ± 4 for younger zircons. These ages are almost coincident within error with the age of host migmatites (477 ± 5 Ma) and those of batholith intrusion of 476 ± 9 Ma and 475 ± 3 Ma for Qtz-diorites and 475 ± 5 Ma for granites. Zircon overgrowths of these intrusive rocks yield sages clustered around 450 Ma, revealing a protracted thermal history, more complex than previously believed. The geochemical study reveals that Qtz-diorites, tonalites and granodiorites form a continuous trend produced by magmatic fractionation from a parental dioritic magma. A weak adakitic tendency, with Sr/Y > 15 in several samples, implies the presence of Grt in the source or magma chamber at a minimum pressure of 1.0 GPa, higher than the depth of emplacement at 0.7 GPa. The high temperature of magma emplacement, which induced the incipient self-granulitization of early magmatic pulses, together with the cotectic-like fractionation linking coeval Qtz-diorites, tonalites and granodiorites, is compatible with fractionation at the lower crust of a deep-generated, infracrustal, (sublithospheric?) intermediate magma. 相似文献
4.
5.
Abstract Petrological study of highly strained carbonate and pelitic rocks within the contact aureole surrounding the western part of the Papoose Flat pluton yields thermal profiles (plots of metamorphic temperature versus distance) across the aureole that show temperature gradients which are relatively flat and narrow (<100m). The gradients occur close to the contact and indicate a slight decrease in temperature from 500–550°C at the pluton/wall rock contact to 450–500°C at the outer margin of the aureole. One thermal profile across low-strain metasedimentary rocks located in the southern part of the aureole shows that thermal effects from emplacement extend no further than 600 m from the contact. Coexistence of andalusite and cordierite in pelitic rocks of the aureole constrain pressures to <4 kbar. Thermal modelling using an analytical solution of the conductive heat flow equation for a rectangular-shaped pluton reproduces the observed thermal maxima and profile shape. Conductive rather than convective cooling also is supported by isotopic and field evidence for limited fluid flow along the strongly deformed margin of the pluton. Simple thermal models coupled with observed high-temperature deformation features and a measured 90% attenuation of stratigraphic units in the plastically deformed western part of the pluton's aureole indicate that strain rates may have been of the order of 10-12 s-1. Evidence for episodic heating, such as two distinct generations of andalusite growth in pelites from the aureole, alternatively may indicate a longer heating event and, therefore, slower strain rates. Thermal models also indicate that parts of the pluton still may have been above the solidus during deformation of the pluton margin and aureole. 相似文献
6.
Kryštof Verner Jiří Žák Jaroslava Pertoldová Josef Šrámek Jiří Sedlák Jakub Trubač Patricie Týcová 《International Journal of Earth Sciences》2009,98(3):517-532
The Plechy pluton, southwestern Bohemian Massif, represents a late-Variscan, complexly zoned intrusive center emplaced near
the crustal-scale Pfahl shear zone; the pluton thus provides an opportunity to examine the interplay among successive emplacement
of large magma batches, magmatic fabric acquisition, and the late-Variscan stress field associated with strike-slip shearing.
The magmatic history of the pluton started with the emplacement of the porphyritic Plechy and Haidmühler granites. Based on
gravity and structural data, we interpret that the Plechy and Haidmühler granites were emplaced as a deeply rooted, ∼NE–SW
elongated body; its gross shape and internal fabric (steep ∼NE–SW magmatic foliation) may have been controlled by the late-Variscan
stress field. The steep magmatic foliation changes into flat-lying foliation (particularly recorded by AMS) presumably as
a result of divergent flow. Magnetic lineations correspond to a sub-horizontal ∼NE–SW finite stretch associated with the divergent
flow. Subsequently, the Třístoličník granite, characterized by steep margin-parallel magmatic foliation, was emplaced as a
crescent-shaped body in the central part of the pluton. The otherwise inward-younging intrusive sequence was completed by
the emplacement of the outermost and the most evolved garnet-bearing granite (the Marginal granite) along the southeastern
margin of the pluton.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
7.
Anisotropy of magnetic susceptibility (AMS) analysis has been carried out in the thermometamorphic aureole surrounding the
Late Miocene Monte Capanne pluton (Elba Island, Central Italy). The identification and separation of the main carriers of
the magnetic susceptibility by low-temperature and high-field AMS measurements demonstrate that a correct knowledge of the
magnetic fabric is needed in order to use AMS for tectonic interpretations. Magnetic fabric data, combined with structural
data from the aureole, and their comparison with data from the pluton itself, were used to constraint the mode of pluton emplacement.
Results document an intimate linkage between the magmatic flow pattern and the syn-metamorphic fabrics acquired during pluton
emplacement in the host rocks. The magnetic/structural fabric in the aureole rocks is dominated by flattening deformation
and no systematic relationship with any regional tectonic feature is observed. These results suggest that local processes
induced by magma ascent in the upper crust might have played a primary role in space generation for pluton emplacement in
the Tuscan Magmatic Province, suggesting a revaluation of the modes of pluton emplacement during the post-orogenic evolution
of the northern Apennine system as a whole. 相似文献
8.
The Nisa-Alburquerque granitic batholith (southern Variscan Belt, Iberian Peninsula) has been studied by petrological, structural
and geophysical approaches, obtaining contrasting models for its deep structure and emplacement sequence. In order to test
these models and gain knowledge on the thermal increase induced by the intrusion, we have studied its contact aureole, which
was developed in similar country rock lithologies (mica schists alternating with metasandstones and feldespatic schists) all
along the northern external contact of the batholith. Our results indicate no change in metamorphic grade and some variations
in aureole width, which narrows toward the western sectors of the batholith. Cordierite is the only contact metamorphic mineral
developed together with a high temperature biotite probably related to the granite thermal input. By considering these new
data, together with zircon saturation temperatures within the granite and previous petrological and geophysical studies, we
propose a model in which the feeder zones of the granitic magmas were an eastern main one and a western secondary one. We
have also made comparisons of the metamorphic grade in the country rocks and the xenoliths within the granite. Most of the
xenoliths have the same metamorphic facies as the country rocks (Crd-zone), though some of them contain slightly different
assemblages (And + Crd), which could be explained in different ways: (1) differences in the primary schist compositions, (2)
increased time-span of xenoliths in contact with the melt and (3) xenolith incorporation at slightly higher depths during
final granite ascent. 相似文献
9.
The Old Woman Mountains in south-eastern California are a Late Cretaceous low-pressure metamorphic terrane where multiple magmatic intrusions generated broad regions of elevated metamorphic temperatures. In the Scanlon Gulch area, two sheet-like, Late Cretaceous granitoid plutons are in contact with the Scanlon shear zone, a 1-km-thick sheet of isoclinally folded and transposed metamorphic rocks. The metaluminous Old Woman granodiorite underlies the shear zone and the peraluminous Sweetwater Wash granite overlies it. Both plutons record emplacement ages of ∼74 Ma. Thermobarometry and phase relations in the shear zone suggest that peak metamorphism was at 650 ± 50† C and 4.3 ± 0.5 kbar. Late Cretaceous metamorphic temperatures were less elsewhere in the Old Woman Mountains, away from the intrusions.
One-dimensional thermal models are used to investigate how differences in the time between the emplacement of plutons would affect the thermal evolution of the central Old Woman Mountains. The prediction of a thermal history inferred from petrological and thermochronological data requires the rapid emplacement of the two plutons around the shear zone; simulations with delays of more than 1 Myr in the emplacement of the second pluton failed to predict peak metamorphic temperatures. Calculations which consider only the emplacement of a single pluton yield metamorphic temperatures that are too low. The time separating the intrusions is by far the most sensitive parameter in the calculations; assumptions concerning the treatment of the initial geothermal gradient and the latent heat of crystallization have relatively small effects on the predicted thermal histories. Our results suggest that for certain geometries, relatively short-lived magmatic events involving rapid emplacement of multiple intrusions can produce low-pressure metamorphism. 相似文献
One-dimensional thermal models are used to investigate how differences in the time between the emplacement of plutons would affect the thermal evolution of the central Old Woman Mountains. The prediction of a thermal history inferred from petrological and thermochronological data requires the rapid emplacement of the two plutons around the shear zone; simulations with delays of more than 1 Myr in the emplacement of the second pluton failed to predict peak metamorphic temperatures. Calculations which consider only the emplacement of a single pluton yield metamorphic temperatures that are too low. The time separating the intrusions is by far the most sensitive parameter in the calculations; assumptions concerning the treatment of the initial geothermal gradient and the latent heat of crystallization have relatively small effects on the predicted thermal histories. Our results suggest that for certain geometries, relatively short-lived magmatic events involving rapid emplacement of multiple intrusions can produce low-pressure metamorphism. 相似文献
10.
Tectonized slices of foliated quartz-diorite/ quartz-gabbro rocks are exposed along the north Giudicarie line between Dimaro and Rumo (Western Trentino region, north-east Italy). They show geochemical and mineralogical similarities with the north-east corner of the Adamello batholith (Presanella pluton) and may be regarded as a northern apophysis lamella of Adamello. The intrusive bodies were emplaced within the Adria crust at a relatively shallow depth (approximately
equal to 3 kbar) along a proto-Giudicarie line under transtensive conditions during late Oligocene. Only near Rumo has contact metamorphism on the Austroalpine basement been observed, whereas in other outcrops it has been tectonically removed by later movements along the Giudicarie line. In the Samoclevolamella a magmatic flow texture, which developed during the emplacement of a crystal mush at shallow depth, is recorded by the preferred alignment of plagioclase and hornblende. A solid state foliation, outlined by quartz crystal aggregates, green hornblende and biotite, has been observed mostly in the Rumolamella. This indicates that a later ductile deformation, which developed under decreasing temperatures, overprinted the intrusive rocks. This deformation probably reflects late Oligocene strike-slip movements along the Tonale and Giudicarie lines. Finally semi-brittle to brittle deformation overprints the foliated igneouslamellae producing cataclasites and pseudotachylites. Sometimes these structures are subsequently cut by prehnite and epidote bearing veins. During this event, the intrusivelamellae were decoupled from their contact aureole and carried over the Insubric Flysch of the southern Alps. This last tectonic phase may be correlated to the Upper Miocene neo-Alpine transpressive event along the Giudicarie Line.
Correspondence to: S. Martin 相似文献
11.
Federico Rossetti Francesca Tecce Andrea Billi Mauro Brilli 《Contributions to Mineralogy and Petrology》2007,153(6):743-760
Fluid–rock interaction was investigated in the inner aureole of the Late Miocene Monte Capanne pluton on Elba Island (Tuscany,
central Italy) by integrating structural, petrological, fluid inclusion, and stable isotope analyses. In the north-western
sector of the aureole (Procchio–Spartaia area), calc–silicates alternate with nearly pure carbonate layers at the metre scale.
Close to the pluton, the prograde metamorphic sequence includes calc–silicates that transition within a few metres to overlying
nearly pure calcite marbles. The calc–silicates are extensively metasomatised to form massive wollastonite-grossular-bearing
exoskarn. The mineralogical assemblage found in the marbles and the unshifted carbon and oxygen isotopic ratios in calcite
attest that the fluid phase was internally buffered. On the other hand, the calc–silicates constituted channels for infiltration
of disequilibrium fluids of magmatic origin. Fluid infiltration was enhanced by hydrofracturing and structurally-controlled
by existing planar anisotropies in calc–silicates (layering and lithological boundaries). At the metamorphic peak (∼600°C
and 1.5–2 kbar), the marble–calc–silicate interface acted as a barrier to fluids exsolved from the crystallising intrusions,
separating two different flow patterns in the inner aureole: a high fluid–flux region on its higher grade side (Wol-zone)
and a low fluid–flux region on the lower-grade side (Cpx zone). Results of this study: (1) documented that fluid pathways
in the aureole rocks at the top of the pluton were largely horizontal, controlled by the lithological layering and the pluton–host
rock contact; and (2) elucidated the primary control exerted by the structural and rheological properties of the host rocks
on the geometry of fluid flow during pluton emplacement. 相似文献
12.
Thermal Constraints on the Emplacement Rate of a Large Intrusive Complex: The Manaslu Leucogranite, Nepal Himalaya 总被引：4，自引：0，他引：4
The emplacement of the Manaslu leucogranite body (Nepal, Himalaya)has been modelled as the accretion of successive sills. Theleucogranite is characterized by isotopic heterogeneities suggestinglimited magma convection, and by a thin (<100 m) upper thermalaureole. These characteristics were used to constrain the maximummagma emplacement rate. Models were tested with sills injectedregularly over the whole duration of emplacement and with twoemplacement sequences separated by a repose period. Additionally,the hypothesis of a tectonic top contact, with unroofing limitingheat transfer during magma emplacement, was evaluated. In thislatter case, the upper limit for the emplacement rate was estimatedat 3·4 mm/year (or 1·5 Myr for 5 km of granite).Geological and thermobarometric data, however, argue againsta major role of fault activity in magma cooling during the leucograniteemplacement. The best model in agreement with available geochronologicaldata suggests an emplacement rate of 1 mm/year for a relativelyshallow level of emplacement (granite top at 10 km), uninterruptedby a long repose period. The thermal aureole temperature andthickness, and the isotopic heterogeneities within the leucogranite,can be explained by the accretion of 20–60 m thick sillsintruded every 20 000–60 000 years over a period of 5Myr. Under such conditions, the thermal effects of granite intrusionon the underlying rocks appear limited and cannot be invokedas a cause for the formation of migmatites. KEY WORDS: granite emplacement; heat transfer modelling; High Himalayan Leucogranite; Manaslu; thermal aureole 相似文献
13.
Bryan E. Chenhall Brian G. Jones Paul F. Carr 《Australian Journal of Earth Sciences》2013,60(3):389-401
Contact metamorphism has been recognized along a 4 km wide belt adjacent to the shallow‐dipping eastern margin of the Arthursleigh Tonalite, an Early Devonian pluton of the Marulan Batholith, eastern New South Wales. In Ordovician psammitic and pelitic rocks three zones of progressive contact metamorphism range from muscovite + biotite + chlorite assemblages in the outer zone to K‐feldspar + cordierite assemblages adjacent to the pluton and in metasedimentary xenoliths. Retrograde phenomena include extensive replacement of metamorphic minerals by ‘sericite’ and chlorite. Calcareous metasediments adjacent to the tonalite typically contain assemblages of quartz + calcic plagioclase + ferrosalite + sphene, or wollastonite + calcite + diopside with minor grossularite and vesuvianite. Thermal effects in volcanic rocks along the western margin of the pluton are confined to recrystallization of the groundmass. The regional geology indicates confining pressures of approximately 1 kbar at the time of emplacement of the tonalite. Contact metamorphic temperatures were estimated from two‐feldspar geothermometry to attain a maximum of approximately 590°C for rocks in the innermost zone of the aureole and 700°C for the xenoliths. Fluid compositions attending progressive contact metamorphism were water‐rich (Xco2<0.2) and, during cooling, these fluids probably account for the extensive retrograde hydration observed in the aureole. 相似文献
14.
Pelitic schists from contact aureoles surrounding mafic–ultramafic plutons in Westchester County, NY record a high‐P (~0.8 GPa) high‐T (~790 °C) contact overprint on a Taconic regional metamorphic assemblage (~0.5 GPa). The contact metamorphic assemblage of a pelitic sample in the innermost aureole of the Croton Falls pluton, a small (<10 km2) gabbroic body, consists of quartz–plagioclase–biotite–garnet–sillimanite–ilmenite–graphite–Zn‐rich Al‐spinel. Both K‐feldspar and muscovite are absent, and abundant biotite, plagioclase, sillimanite, quartz and ilmenite inclusions are found within subhedral garnet crystals. Unusually low bulk‐rock Na and K contents imply depletion of alkalic components and silica through anatexis and melt extraction during contact heating relative to typical metapelites outside the aureole. Thermobarometry on nearby samples lacking a contact overprint yields 620–640 °C and 0.5–0.6 GPa. In the aureole sample, WDS X‐ray chemical maps show distinct Ca‐enriched rims on both garnet and matrix plagioclase. Furthermore, biotite inclusions within garnet have significantly higher Mg concentration than matrix biotite. Thermobarometry using GASP and garnet–biotite Mg–Fe exchange equilibria on inclusions and adjacent garnet host interior to the high‐Ca rim zone yield ~0.5 ± 0.1 GPa and ~620 ± 50 °C. Pairs in the modified garnet rim zone yield ~0.9 ± 0.1 GPa and ~790 ± 50 °C. Thermocalc average P–T calculations yield similar results for core (~0.5 ± ~0.1 GPa, ~640 ± ~80 °C) and rim (~0.9 ± ~0.1 GPa, ~800 ± ~90 °C) equilibria. The core assemblages are interpreted to record the P–T conditions of peak metamorphism during the Taconic regional event whereas the rim compositions and matrix assemblages are interpreted to record the P–T conditions during the contact event. The high pressures deduced for this later event are interpreted to reflect loading due to the emplacement of Taconic allochthons in the northern Appalachians during the waning stages of regional metamorphism (after c. 465 Ma) and before contact metamorphism (c. 435 Ma). In the absence of contact metamorphism‐induced recrystallization, it is likely that this regional‐scale loading would remain cryptic or unrecorded. 相似文献
15.
广西海洋山花岗岩体侵位构造特征 总被引：1，自引：0，他引：1
花岗岩是大陆地壳的重要组成部分,是地球动力学演化的示踪剂。花岗岩体侵位构造的研究对于揭示花岗岩体的变形历史和侵位机制具有重要的科学价值。本文研究了海洋山花岗岩体的内部构造、与岩浆侵位应力有的围岩构造及热接触变质带特征,探讨了岩体和围岩的应变状态。研究发现,从岩浆侵位到冷凝固结,海洋山花岗岩体经历了液态流动、塑性变形和“半固态”冷凝阶段的演化。岩体各单元的应变类型分别是单轴压扁、平面应变、单轴压缩, 相似文献
16.
In the central Minto Block of northern Québec, the Lake Minto and Goudalie domains are dominated, respectively, by orthopyroxene-bearing plutonic suites (granite-granodiorite and diatexite) and a tonalitic gneiss complex, both of which contain scattered remnant paragneisses. Two main granulite-grade mineral assemblages are observed in the paragneiss: garnet (Grt)-orthopyroxene (Opx)-plagioclase-quartz (GOPQ) and garnet (Grt)-cordierite (Crd)-sillimanite-plagioclase-quartz (GCSPQ). These show distinct lithological associations, with the GCSPQ assemblages occurring exclusively within the diatexite in the Lake Minto domain. Petrogenetic grid considerations demonstrate that the GOPQ rocks are higher grade than the GCSPQ rocks. Maximum temperatures for GOPQ rocks, obtained from equilibria based on Al solubility in orthopyroxene in equilibrium with garnet, range from 950 to 1000d? C, significantly higher than garnet-orthopyroxene Fe-Mg exchange temperatures of 700 ± 50d? C, the latter probably representing a closure temperature below peak conditions. The Al temperatures were corrected for late cation exchange by adjusting the Fe/(Fe + Mg) ratios in garnet and orthopyroxene, to achieve internal consistency between the GOPQ thermometers and barometers. Grt-Crd thermometry records temperatures of 750±50d? C. Peak P-T conditions range from 5-6 kbar and 750-800d? C in the Goudalie and eastern Lake Minto domains, to 7-10 kbar and 950-1000d? C in the western and central Lake Minto domain. This variability contrasts with the uniform crustal pressures of 5 ± 1 kbar recorded by the GCSPQ assemblages in the diatexites and the hornblende granodiorites (c. 4-5 kbar) across the same area. The GOPQ rocks are inferred to record earlier P-T conditions that prevailed before the formation of GCSPQ assemblages and the intrusion of the granodiorites. Partial P-T paths in GOPQ rocks from both domains, based on net transfer equilibria corrected for Fe-Mg resetting, document cooling of 100-250d? C from thermal-peak conditions, concomitant with a modest pressure decrease of 2-3 kbar. Although textures diagnostic of isobaric cooling are not developed, the paths are consistent with a tectonic model in which granulite metamorphism and crustal thickening in the Minto Block were consequences of magmatic underplating. The progression from higher P-T conditions recorded by GOPQ assemblages to lower P-T conditions recorded by GCSPQ assemblages is attributed to variable amounts of synmagmatic uplift and cooling in a single, continuous thermal event in the Minto crust, associated with protracted crustal magmatism. In the Goudalie and eastern Lake Minto domains, where GOPQ and GCSPQ rocks and Hbl granodiorites have similar P-T conditions of equilibration, the crust may not have been thickened as much as further west, where GOPQ P-T conditions are significantly higher than those of the hornblende granodiorites and the GCSPQ rocks. 相似文献
17.
Roger Bateman 《Australian Journal of Earth Sciences》2013,60(3-4):253-265
The Bruinbun pluton is a small, massive, I‐type granitoid intruded into the meta‐sedimentary Hill End Trough, in eastern N.S.W. It is a multiple pluton representing two discrete magma pulses, the granodiorite core intruding the adamellite margin. A weak alignment of orthoclase megacrysts in the granitoids is best developed adjacent to both the internal and external intrusive contacts, and is considered by the writer to be a product of magmatic flow. Part of the northern contact and the southern and western contacts dip inward at moderate angles, whereas the eastern contact is vertical to outward‐dipping. The pluton is inferred to be mushroom‐shaped, and slightly tilted. The intensity of aureole deformation is low. The aureole has been flexed into concordancy with the pluton roof, and a rudimentary rim fold‐zone is present around lower levels of the pluton. Intrusion of the granitoid is inferred to be primarily by uplift of its roof and depression of its floor. The highest‐grade contact metamorphic parageneses developed are: cordierite‐K feldspar‐biotite‐quartzite ± andesine ± epidote in metapelites, and ferrohornblende‐biotite‐muscovite‐andesine‐epidote‐quartz in metavolcarenites. No intrusion‐related foliation or lineation was formed. 相似文献
18.
U-Pb sphene dating of metamorphism: the importance of sphene growth in the contact aureole of the Red Mountain pluton,Laramie Mountains,Wyoming 总被引：1，自引：0，他引：1
L. A. Verts Kevin R. Chamberlain C. D. Frost 《Contributions to Mineralogy and Petrology》1996,125(2-3):186-199
The relative importance of thermal diffusion versus new growth or recrystallization on U-Pb isotopic data from sphene is
assessed through a study of amphibolites and granite gneisses within the contact aureole of the Red Mountain pluton, Laramie
anorthosite complex, Wyoming. Samples were collected along a traverse approximately perpendicular to the margin of the intrusion
over a distance of 0.13 to 2.65 km from the contact. The 207Pb/206Pb ages of sphene from amphibolite samples range between 1.43 Ga, the intrusive age of the Red Mountain pluton, to 1.78 Ga,
the age of regional metamorphism. The 207Pb/206Pb ages of sphene in rocks metamorphosed above 700° C are within error of the intrusive age of the pluton, and appear to have
resulted from diffusional resetting of preexisting sphene and the metamorphic growth of additional sphene at 1.43 Ga. At greater
distance from the contact the 207Pb/206Pb ages range from 1.45 to 1.72 Ga. This 300 million year spread in ages is interpreted to result from two periods of sphene
growth, one produced during regional metamorphism at 1.78 Ga and another generation of newly grown or recrystallized sphene
that formed during contact metamorphism at 1.43 Ga. These two age populations may be identified on the basis of petrographic
textures, the morphologies and color differences of grain separates as well as by the U-Pb systematics. In rocks metamorphosed
to temperatures less than 700° C, sphene growth was the dominant process controlling the response of the U-Pb isotope system
to contact metamorphism. Sphene grew well outside the zone of obvious contact metamorphism. The U-Pb sphene ages were reset
by diffusion only at high temperatures, supporting the experimentally determined closure temperature estimates for the U-Pb
system in sphene of around 650° C (Cherniak 1993). This study demonstrates that U-Pb ages of sphene can be used to date metamorphism
not only in areas with a simple geologic history, such as igneous intrusion or single metamorphic or deformational events,
but also to date multiple events so long as different generations of sphene can be identified and separated.
Received: 22 August 1995 / Accepted: 17 April 1996 相似文献
19.
南秦岭迷魂阵岩体LA-ICP-MS锆石U-Pb年代学和Lu-Hf同位素特征 总被引：1，自引：1，他引：0
位于陕西省的姜家沟-磨沟峡-小岭镇地区的迷魂阵岩体,为南秦岭构造带中一个古老地块内的深成侵入体。该岩体主要由闪长岩、石英闪长岩和花岗闪长岩组成。根据野外地质关系和LA-ICPMS锆石U-Pb定年结果,可将迷魂阵岩体的岩浆作用分为两个阶段:早期岩浆作用阶段主要形成闪长岩,其侵位时代为885±4Ma;晚期岩浆阶段主要形成石英闪长岩-花岗闪长岩,其侵位时代为~737±4Ma。定年锆石原位Lu-Hf同位素分析揭示早期闪长质岩浆主要形成于亏损地幔的部分熔融,晚期石英闪长岩-花岗闪长岩岩浆主要来源于早期闪长质岩浆的结晶分异,并经历了地壳物质的混染或者壳幔岩浆混合作用。 相似文献
20.
During the Cretaceous, the South China Block (SCB) experienced a widely distributed extensional event including numerous plutons emplacement and basin opening. Investigations on the tectonic regime coeval with pluton emplacement, and emplacement mechanism of the pluton remain relatively rare in the SCB. In order to address these questions, a multidisciplinary approach, including field structural and petrographic observations, anisotropy magnetic susceptibility (AMS) and paleomagnetic analyses, was carried out on the Qingyang–Jiuhua granitic massif which intrudes into the Lower Yangtze fold belt in the northeastern part of the SCB. The Qingyang–Jiuhua massif is composed of the granodioritic Qingyang and monzogranitic Jiuhua plutons dated by zircon U–Pb method at ca. 142 Ma, and ca. 131 Ma, respectively. Our structural observations show that the intrusion of the Qingyang–Jiuhua massif does not modify the fold strike. A weak ductile deformation of the country rocks and granitoid can be only observed in the boundary zone with limited contact metamorphism. In the contact aureole of the massif, the foliation follows the pluton contour, and the mineral lineation is rare. When present, it exhibits a down-dip attitude. Field and microstructural observations indicate isotropic magmatic textures in most parts of the massif. The AMS analysis of 93 sites reveals weak values for the anisotropy degree (PJ < 1.2) and oblate magnetic fabric dominance (T > 0) for most of the measured samples. Two principal foliation patterns are identified: horizontal foliations in the center of the plutons, and vertical foliations on the boundaries. Magnetic lineation strike is largely scattered, and weakly inclined at the scale of the entire massif. The paleomagnetic investigations indicate that (a) the younger Jiuhua pluton did not produce a remagnetization in the older Qingyang pluton, (b) no relative movement can be observed between these two plutons, (c) the entire massif did not experience any important relative movement with respect to South China, considering the paleomagnetic uncertainties. Integrating the newly obtained results with previous observations, our study favors a permissive emplacement mechanism for the two plutons, i.e. vertical magma intrusion into an opening space controlled by the NW–SE brittle stretching of the upper crust, which is in agreement with a weak extensional regional tectonic framework of the SCB. 相似文献