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1.
Syenites are important or predominant components of several plutonic complexes, emplaced between 456 and 415 Ma along the NW margin of the Caledonian orogenic belt, adjacent to the Lewisian foreland, in W and NW Scotland. Although there are, in detail, chemical differences between the syenites from each centre, they form a well-defined compositional group overall. Ratios amongst their trace elements (especially very high values of La/Nb) are quite different from those trachytes and syenites formed by fractional crystallisation of ocean-island basalts and their continental equivalents, emplaced in regions of anorogenic crustal tension. Instead, the Scottish Caledonian syenites closely resemble chemically the fractional-crystallisation residua of potassic subduction-related magmas, such as the shoshonitic series. A comendite minor intrusion from a swarm associated with the Loch Borralan and Loch Ailsh syenitic complexes is remarkably similar in composition to Recent obsidian from the shoshonitic volcano of Lipari, in the Aeolian Arc. Published Sr- and Pb-isotopic ratios preclude a significant component of either upper (Proterozoic Moine schists) or lower crust (granulite-facies Archaean Lewisian or Proterozoic Grenvillian gneisses) in all these syenites, except in local syenitic facies of the Glenelg-Ratagain complex. Fractional crystallisation appears to be the mechanism by which the liquids which formed these syenites evolved from basic parental magmas. The phases involved in this process may have included plagioclase, alkali feldspar, pyroxene, amphibole, biotite, garnet, Fe-Ti oxide, sphene, allanite, apatite, zircon and zirconolite, and therefore all the ratios amongst even the so-called incompatible elements may have changed during the evolution of the leucocratic magmas. Nevertheless, a detailed study of the Glen Dessarry complex shows that the changes are insufficient to disguise the geochemical nature of the parental magmas. These appear to be picritic shoshonite (MgO> 15%, Ni>400ppm, La/Yb20, La/Nb>5) for the Glen Dessarry, Loch Borralan and Loch Ailsh syenites, and picritic ultrapotassic magmas (MgO>15%, Ni>400 ppm, La/ Yb60, La/Nb>7) — such as would crystallise to minettes — for the Loch Loyal and Glenelg-Ratagain syenites. Mafic shoshonites were erupted amongst the 410 Ma Lome lavas of this region and also occur as widespread approximately-contemporaneous volcanic feeder plugs. Minettes of similar age are also common as dykes in NW Scotland. Numerous large tonalite-granite complexes, with minor diorites and gabbros, were emplaced in W and NW Scotland between 435 and 400 Ma. These are generally acknowledged to be mixtures of magmas from crustal and mantle sources. Their more mafic members show compositional features, such as very high Ba and Sr, which group them with the rare syenites and the Lorne lavas of the same region into a distinctive geochemical province, within which shoshonitic and allied magmas were the mantle-derived component. Two models are presented to account for the generation of strongly-potassic, subduction-related magmas several hundred km behind a NW-directed subduction zone, or during the period immediately following continental collision.  相似文献   

2.
Ian Parsons  Peter Smith 《Lithos》1974,7(4):217-225
Solvus curves under both ‘dry’ and ‘hydrothermal’ (PH2O = 1 kbar) conditions have been determined for two microperthitic alkali feldspar starting materials from the Loch Ailsh syenite complex, Assynt, Scotland. One sample (Ab74 Or24 An2) possessed a K-phase showing dominant monoclinic symmetry to both powder and single-crystal X-ray methods, the other (Ab88Or30An2) had maximum microcline as K-phase. These materials gave essentially identical solvi for both types of experiment, interpreted as indicating similar degrees of local order in the K-phase, but with differing domain size, leading to the different X-ray properties. The ‘dry’ solvus curves confirm the determination of the microcline-low albite solvus of Bachinski & Müller. The hydrothermal curves are used to estimate PH1O <3.5 kbars, T > 755 °C for emplacement of the Loch Ailsh syenites.  相似文献   

3.
The Siluro-Ordovician Loch Borralan (c. 430 Ma) and Loch Ailsh Complexes (c. 439 Ma) comprise a suite of intrusive rocks ranging in composition from clinopyroxenites, through potassic melasyenites to quartz syenites. The rock suite at Loch Borralan also includes nepheline syenite. Geochemical data in the literature indicate that the intrusions are alkaline, with pronounced enrichments in LILE and LREE relative to contemporaneous calc-alkaline magmatic centres further to the south-east, although they share similar high LILE/Nb, subduction-related characteristics. The Loch Borralan Complex is associated with marginal gravity and magnetic anomalies which can be interpreted in terms of a shallow body less than 400 m thick. Analysis of rocks and drill core revealed widespread elevated Pt and Pd values in pyroxenites and syenites in both complexes. The highest concentrations, up to about 900 ppb Pt+Pd, occur in pyroxenites in the Loch Borralan Complex. Extensive archived drill core provides an excellent section through the marginal pyroxenites, which host the PGE at Loch Borralan. The pyroxenites show unusual petrological features; early clinopyroxene is followed by biotite, apatite, magnetite, sphene and plagioclase with later garnet, which might be metasomatic in origin. Sulphides occur in minor amounts. High-temperature shearing produced local granulation and mylonitisation. Later brittle deformation caused extensive micro-fracturing and the introduction of minor carbonate veining. Platinum-group minerals (PGM) were located in a number of samples with high PGE assay values. These occur as clusters of grains around 1–2 m in diameter, and are difficult to identify uniquely. A few grains appear to be magmatic; these are Pt and PtPd sulphides that occur enclosed in clinopyroxene or garnet. All other grains occur in late fractures or along grain boundaries. These include sperrylite (PtAs2), Pd antimonides and PdBi tellurides, along with hessite (Ag2Te). They occur in microfractures accompanied by carbonate and barite and fine-grained sulphides and are probably of secondary origin. The PGE in the pyroxenites may have been introduced during the magmatic phase of the intrusion but the observed distribution of PGM results from low-temperature, hydrothermal remobilisation following brittle deformation and introduction of fluids.
Michael T. StylesEmail: Phone: +44-115-9363414Fax: +44-115-9363352
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4.
The equilibrium temperatures for coexisting plagioclase and potassium feldspar pairs have been calculated for various textural varieties of feldspar from 3 post-metamorphic granites from the Georgia Piedmont; the Danburg, Siloam, and Stone Mountain plutons. Assuming an intermediate structural state for the feldspars at time of equilibration, crystallization temperatures match those expected from experimental data for quartz monzonite magmas (650 to 780° C). The variations in solidus temperature, recorded in the feldspars, may be used to estimate relative differences in depth of intrusion. Sharp reversals in plagioclase compositional trends may be caused by isothermal decreases in confining pressure associated with upward migration through the crust. In fine grained and slowly cooled intrusions, albite tends to be lost from the alkali feldspar grains, and recrystallizes as separate unzoned grains of oligoclase, thus erasing the previous thermal history. Perthite exsolution and re-equilibration within the alkali feldspar grains appears to continue down to temperatures of 400° C or so, although the zoned plagioclase does not homogenize. The recrystallization associated with changes in structural state may facilitate exsolution within alkali feldspar grains.  相似文献   

5.
Robert J. Stull 《Lithos》1978,11(3):243-249
Mantled feldspars that formed by resorption, development of skeletal plagioclase crystals, and filling with alkali feldspar are common in the Golden Horn batholith, Washington. Subhedral plagioclase mantles have weak normal zoning from An17 to An10. Plagioclase zoning and twinning are crosscut by resorption channels. Resorption cavities and channels are coated with albite (An10). Anhedral, perthitic orthoclase within the plagioclase is optically continuous with orthoclase in channels and on the mantle exterior.This texture resulted from resorption of calcic cores of plagioclase as pressure decreased when water-undersaturated granite magma intruded to a shallow crustal level. At shallow level, only alkali feldspar and quartz crystallized and were available to fill the skeletal plagioclase.  相似文献   

6.
Abstract Microprobe analyses of feldspars in granite mylonites containing flame perthite give compositions that invariably plot as three distinct clusters on a ternary feldspar diagram: orthoclase (Or92–97), albite and oligoclase-andesine. The albite occurs as grains in the matrix, as flame-shaped lamellae in orthoclase, and in patches within plagioclase grains. We present a metamorphic model for albite flame growth in the K-feldspar in these rocks that is related to reactions in plagioclase, rather than alkali feldspar exsolution. Flame growth is attributed to replacement and results from a combination of two retrograde reactions and one exchange reaction under greenschist facies conditions. Reaction 1 is a continuous or discontinuous (across the peristerite solvus) reaction in plagioclase, in which the An component forms epidote or zoisite. Most of the albite component liberated by Reaction 1 stays to form albite in the host plagioclase, but some Na migrates to form the flames within the K-feldspar. Reaction 2 is the exchange of K for Na in K-feldspar. Reaction 3 is the retrograde formation of muscovite (as ‘sericite’) and has all of the chemical components of a hydration reaction of K-feldspar. The Si and Al made available in the plagioclase from Reaction 1 are combined with the K liberated from the K-feldspar, to produce muscovite in Reaction 3. The muscovite forms in the plagioclase, rather than the K-feldspar, as a result of the greater mobility of K relative to Al. The composition of the albite flames is controlled by both the peristerite and the alkali feldspar miscibility gaps and depends on the position of these solvi at the pressure and temperature that existed during the reaction. Using an initial plagioclase composition of An20, the total reaction can be summarized as: 20 oligoclase + 1 K-feldspar + 2 H2O = 2 zoisite + muscovite + 2 quartz + 15 albiteplagioclase+ 1 albiteflame. This model does not require that any additional feldspar framework be accreted at replacement sites: Na and K are the only components that must migrate a significant distance (e.g. from one grain to the next), allowing Al to remain within the altering plagioclase grain. The resulting saussuritization is isovolumetric. The temperature and extent of replacement depends on when, and how much, water infiltrates the rock. The fugacity of the water, and therefore the pressure of the fluid, may have been significantly lower than lithostatic during flame growth.  相似文献   

7.
The equilibrium precipitate formed by exsolution in alkali feldspar containing calcium in solid solution is a two-phase intergrowth of plagioclase and quartz. It is the kinetics of the precipitation, however, which decides whether or not this reaction will take place. It is shown that lamellar growth of plagioclase and quartz is only accomplished by the advancement of an incoherent boundary originating at an alkali feldspar — alkali feldspar boundary or at an interface between alkali feldspar and plagioclase.  相似文献   

8.
The island of Lundy forms the southernmost igneous complex of the British Tertiary Volcanic Province (BTVP) and consists of granite (≈ 90%) emplaced into deformed Devonian sedimentary rocks (Pilton Shale) and associated with a swarm of dykes of dolerite/basalt, minor trachyte and rhyolite composition. The dolerites are of varied olivine basalt composition and are associated with peralkaline trachyte and subalkaline/peralkaline rhyolite with alkali feldspar and quartz ± alkali amphibole ± pyroxene mineralogy. The dyke swarm is therefore an anorogenic bimodal dolerite/basalt–trachyte/rhyolite BTVP association. Although the dyke association is bimodal in major element terms between dolerite/basalt and minor trachyte/rhyolite, the mineralogy and trace element geochemistry indicate that the dykes may be regarded as a cogenetic dolerite—peralkaline trachyte/rhyolite association with minor subalkaline rhyolites. Sr and Nd isotope data indicate derivation of these magmas from a similar BTVP mantle source (with or without minor contamination by Pilton Shale, or possibly Lundy granite). The petrogenesis of the Lundy dyke association is therefore interpreted in terms of extensive fractional crystallization of basaltic magma in a magma chamber of complex geometry below the (exposed) Lundy granite. Fractional crystallization of a representative dolerite magma (olivine ± clinopyroxene ± plagioclase) yields trachyte magma from which the crystallization of alkali feldspar (anorthoclase) ± plagioclase (oligoclase) + Fe–Ti oxide + apatite results in peralkaline rhyolite. Rarer subalkaline rhyolites result from fractionation from a similar dolerite source which did not achieve a peralkaline composition so allowing the crystallization and fractionation of zircon. The basalt–(minor trachyte)/rhyolite bimodality reflects rapid crystallization of basalt magma to trachyte (and rhyolite) over a relatively small temperature interval (mass fraction of melt, F = ≈ 0.15). The rapid high level emplacement of basalt, trachyte and rhyolite dyke magmas is likely to have been associated with the development of a substantial composite bimodal basalt–(minor trachytel)/rhyolite volcano above the BTVP Lundy granite in the Bristol Channel.  相似文献   

9.
Co-existing plagioclase and alkali feldspars of the Sierra Nevada granites and plagioclases of the mafic inclusions have been analysed using an ARL EMX electron microprobe analyser. Each Sierran rock type contains co-existing feldspar pairs within specific compositional ranges. Core plagioclase compositions of the mafic inclusions are only slightly higher or lower in anorthite than the host rock plagioclases and cluster between An30 and An40. The chemical inhomogeneity of the Sierran potash feldspars and this effect on the Barth k value prohibits the use of the feldspars as geothermometers for these particular rocks. Results of the electron microprobe, x-ray, and petrographic study and the experimental hydrothermal investigation of the granites suggest but do not prove that both the plagioclase composition and the mafic inclusion mineralogy can be explained in terms of a model which considers the inclusions to be the refractory residue left over from the partial melting of crustal material.Submitted to the Faculty of the Department of the Geophysical Sciences, The University of Chicago, in partial fulfillment for the degree of Doctor of Philosophy.  相似文献   

10.
Evan R. Phillips 《Lithos》1974,7(3):181-194
Myrmekite, first detected by Michel-Lévy in 1875 and named by Sederholm in 1899, is an intergrowth between vermicular quartz and (sodic) plagioclase situated next to potash feldspar. In felsic plutonic rocks it occurs as: rims bordering granular plagioclase, intergranular blebs set between adjacent microperthite crystals, lobes associated with muscovite in deformed alkali feldspar megacrysts or as bulbous growths at their margins, and rims on plagioclase inclusions held within orthocalse megacrysts. A literature review based largely on papers published in the past quarter century shows that hypotheses for myrmekite genesis fall mainly into five categories: simultaneous or direct crystallization, replacement of potash feldspar by plagioclase, replacement of plagioclase by potash feldspar, solid-state exsolution, and recrystallizing quartz involved with blastic plagioclase.  相似文献   

11.
Variation in the primary textures of “Cordilleran” granitic rocks is described relative to three identifiable stages of the crystallisation interval; namely: (1) crystallisation in suspension; (2) growth of a touching crystal framework; (3) interstitial crystallisation. Crystals that initially grow in isolation will start to impinge and form small clusters as crystallisation proceeds and the volume of solid material increases, eventually forming a continuous interconnected crystal framework. Subsequent crystallisation involves solidification of the melt occupying the interstices of the framework, and therefore shows similarities to the way in which the porosity occludes in sedimentary systems. A case study of textural development in Cordilleran granitic rocks from the zoned Linga superunit of the Peruvian Coastal Batholith, reveals that compositional zonation from granodiorite through to syenogranite is accompanied by a systematic variation in the textures, specifically those of the three felsic phases (plagioclase, quartz and alkali feldspar). Plagioclase was the first phase to appear on the liquidus, and was joined by the other two phases as crystallisation proceeded and the melt evolved. The melt fraction at which quartz and alkali feldspar started to crystallise influenced the early growth of plagioclase, and the way in which the texture developed through each stage of the crystallisation interval. The geometry of plagioclase progressively changes from a touching framework of crystals in the granodiorite, to small aggregates or isolated crystals suspended in an equant mosaic of the other felsic phases in the syenogranite. This variation can be explained by an earlier evolution of the melt to the cotectic (i.e. at higher melt fractions) as the rocks become more acidic, and hence a greater contribution of alkali feldspar and quartz to the growth of the framework at the expense of plagioclase and the mafic phases. Textural observations are comparable to the crystallisation pathways of the felsic phases modelled in the quaternary An-Ab-Or-Qz system from the bulk compositions. All compositions lie in the plagioclase volume, and evolved to three-phase saturation on the cotectic via either the quartz/plagioclase divariant surface (granodiorites) or the alkali feldspar/plagioclase divariant surface (monzogranite and syenogranite).  相似文献   

12.
Seck's (1971a) compositional data on coexisting feldspars in the Or-Ab-An ternary at 650° C and 1 kb were used to calculate the activity-composition relations in binary alkali feldspar and binary plagioclase. The energy constants in Guggenheim's expression for excess free energy of mixing are A 0=3920 and A 1=657 cal/mole for alkali feldspar, in excellent agreement with values obtained by Thompson and Waldbaum (1969), and 1320 and 373 cal/ mole for plagioclase. Using Orville's (1972) data from ion-exchange experiments between plagioclase and Na—Ca chloride solutions at 700° C and 2 kb, we obtained 967 cal/mole for A 0 and 715 cal/mole for A 1 in the plagioclase crystalline solution.Activity-composition relations for plagioclase are interpreted in terms of a continuous, random substitution of CaAl for NaSi across the high structural state plagioclase series. This interpretation is consistent with that obtained from a consideration of lattice parameters.  相似文献   

13.
Liquidus phase equilibria have been determined in the system CaAl2Si2O8-NaAlSi3O8-KAlSi3O8-NaAlSiO4-KAlSiO4 (An-Ab-Or-Ne-Ks) at a pressure of water of 5 kb, for low anorthite contents. The main effects of increasing anorthite content on phase relationships in the system Ab-Or-Ne-Ks include the expansion of the plagioclase stability field towards the potassium-rich part of the system, and an accompanying contraction of the alkali feldspar, leucite, nepheline and kalsilite stability fields; and an increase in liquidus temperatures throughout most of the compositional range. Two quaternary invariant points have been identified in the system, one a reaction point between the fields of alkali feldspar, plagioclase, nepheline and kalsilite at approximately An4, and the other probably a quaternary eutectic between the fields of alkali feldspar, plagioclase, leucite and kalsilite at approximately An6. A shallow minimum trough in liquidus temperatures occurs on the two-feldspar surface, and this would be expected to control the paths of liquids cooling under equilibrium conditions. Phase relationships in this quaternary system have been applied to the interpretation of the histories of the potassium-rich rocks of the Roman Volcanic Region, Italy. Differentiation of the phonolitic series in this region may have occurred by two-feldspar fractionation.  相似文献   

14.
The development of rapakivi texture in feldspars from the Ketilidian granitoids of south Greenland has been investigated using Sr, O and H isotopes. A low temperature signature is found in the Sr and O data which seemingly contradicts some textural features that point to a magmatic origin of the plagioclase mantles around the K-feldspar ovoids. An origin for these mantles involving exsolution from an original alkali feldspar solid solution is proposed, which involves growth of mantles over a range of conditions determined by the mobility of the exsolving sodic feldspar. This mobility may be enhanced at high temperatures in the presence of melts or increased fluid pressures and at lower temperatures by the processes responsible for the transformation of K-feldspar to microcline. Rapakivi granites with both white and dark green feldspar occur in south Greenland but show no major isotopic differences, although the dark alkali feldspars contain significantly more fluid. Equivalent fluids in the white alkali feldspars may have escaped during plagioclase exsolution.  相似文献   

15.
The textural features and mineralogy of chrome-spinel bearing rocks from the layered ultrabasic intrusion of Rhum indicate that in situ reaction of chromite with olivine, plagioclase and interstitial liquid has taken place. The compositions of the chrome-spinels vary throughout parts of the intrusion and also in a systematic way across a thin picotite rich seam at a feldspar cumulate — olivine cumulate junction. The origin of the chrome-spinel is discussed in relation to other occurrences of chromite in layered ultrabasic rocks.  相似文献   

16.
Graphic intergrowths of alkali feldspar+quartz, and plagioclase+quartz, occur together in pegmatites in the eastern part of the Czechoslovak Moldanubicum. They form zones between the finer-grained wall zone and the central blocky feldspar+quartz core. The normative Or-Pig-Q compositions of the graphic intergrowths and the Or-Ab-An contents of their feldspars show broad variations generally, but have a restricted range within individual pegmatites. At two localities studied in more detail, coexisting feldspars show gradual changes in composition, from the margins up to the innermost graphic pegmatite, compatible with fractional crystallization along the feldspar solidus-solvus intersection in the Or-Ab-An-Q-H2O system, at different vapour pressures in different pegmatites. Two models are demonstrated for low and high pressure cases. The feldspar compositions from central blocky zones deviate from the magmatic fractional crystallizations paths; this corresponds with the general assumption that they crystallized from supercritical gaseous fluids.In these and in similar pegmatites, coexisting alkali feldspar+quartz and plagioclase + quartz intergrowths are interpreted as the last products of cotectic crystallization from an ultimately fractionated granitic magma. Positive correlation of Ab solid solution and quartz content in the potassic intergrowths suggests that these characteristics may be indicative of the relative pressure and temperature effective during their crystallization, when compared in pegmatites of the same bulk composition.  相似文献   

17.
内蒙古乌拉山金矿田内主要出露晚太古代乌拉山群区域变质岩和规模不一的花岗岩体以及不同时代、不同种类的脉状地质体。含金矿脉中主要矿物共生组合为碱性长石、石英、斜长石、碳酸盐矿物(方解石、白云石)和少量金属硫化物。矿床的显著特征为碱性长石交代作用强烈，碱性长石也广泛产于该地区其他各种类型的岩石中。本文采用电子显微探针分析了共生碱性长石和斜长石的化学成分，并采用三元二长石温度模型估计了碱性长石的平衡温度。结果表明，第一成矿阶段的碱性长石一石英含金矿脉中碱性长石的形成温度为353℃，第二成矿阶段石英含金矿脉中碱性长石的形成温度为281℃，矿脉碱性长石形成压力约为5kbar。这些结果与同类矿石中平衡共生的碳酸盐矿物和云母类矿物的地质温度计估计的形成温度以及共生石英中流体包裹体的均一温度非常一致。因此，乌拉山金矿床形成和富集的温度可估测为260～380℃，压力约为5kbar。此外，应用二长石温度计计算了本地区区域变质片麻岩和花岗岩中碱性长石的平衡温度，所得温度比采用共生铁铝榴石和黑云母温度计估计的温度要低约250℃。这表明共生的铁铝榴石和黑云母的平衡温度可能代表其寄主变质岩变质期温度及寄主花岗岩原生温度，而区域变质岩和花岗岩中的碱性长石在经历了随后多次热液作用后，可能重新平衡再生，这也与前人对乌拉山金矿的矿床地质和同位素研究的结果一致。  相似文献   

18.
Petrographic examinations and electron microprobe analyses of Proterozoic granitic rocks, SE Sweden aimed to characterize and unravel the mechanisms and conditions of plagioclase alterations. These alterations include saussuritization, albitization and replacement of plagioclase by K‐feldspar. The hydrothermal alterations, which are inferred to have occurred at ca. 250–400°C, resulted in concomitant formation of Al‐rich titanite, epidote, calcite, pumpellyite, prehnite and iron oxides. Replacement of plagioclase by K‐feldspar occurs in red‐stained zones, which have developed close to thin fractures owing to the precipitation of tiny Fe‐oxide pigment particles within the altered plagioclase, whereas saussuritized plagioclase has less systematic spatial relationships to these fractures. Albitization of plagioclase occurred in rocks that are poor in biotite compared to rocks that suffered extensive saussuritization. The chemical and textural characterization of various types of plagioclase alterations allows elucidation of the granitic hydrothermal systems. Features of feldspar alteration in the granitic rocks are similar to those encountered in feldspathic sandstones and should hence be considered in studies on diagenetic changes of siliciclastic successions during basin evolution. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

19.
锡山钨锡多金属矿是粤西阳春盆地内一个中型石英脉型矿床,成矿岩体岩性为钾长花岗岩,主要矿物组成为钾长石、斜长石、石英、黑云母,副矿物包括锆石、磷灰石、金红石、钛铁矿和铌铁矿等。文章利用电子探针技术对主要矿物的矿物学特征进行了研究,结果表明花岗岩中斜长石为钠长石,钾长石为透长石,黑云母属于铁叶云母。黑云母化学成分显示其w(Ti)介于0.19~0.39,具有低的氧逸度(log f(O2)Ni-Ni O),指示其有利于钨锡矿床的形成且仍具有较好的找矿潜力。结合已有的区域地质资料,文章认为锡山钨锡多金属矿床是岩石圈伸展背景下的产物。  相似文献   

20.
The end of an orogenic Wilson cycle corresponds to amalgamation of terranes into a Pangaea and is marked by widespread magmatism dominated by granitoids. The post-collision event starts with magmatic processes still influenced by subducted crustal materials. The dominantly calc-alkaline suites show a shift from normal to high-K to very high-K associations. Source regions are composed of depleted and later enriched orogenic subcontinental lithospheric mantle, affected by dehydration melting and generating more and more K- and LILE-rich magmas. In the vicinity of intra-crustal magma chambers, anatexis by incongruent melting of hydrous minerals may generate peraluminous granitoids bearing mafic enclaves. The post-collision event ends with emplacement of bimodal post-orogenic (PO) suites along transcurrent fault zones. Two suites are defined, (i) the alkali-calcic monzonite–monzogranite–syenogranite–alkali feldspar granite association characterised by [biotite+plagioclase] fractionation and moderate [LILE+HFSE] enrichments and (ii) the alkaline monzonite–syenite–alkali feldspar granite association characterised by [amphibole+alkali feldspar] fractionation and displaying two evolutionary trends, one peralkaline with sodic mafic mineralogy and higher enrichments in HFSE than in LILE, and the other aluminous biotite-bearing marked by HFSE depletion relative to LILE due to accessory mineral precipitation. Alkali-calcic and alkaline suites differ essentially in the amounts of water present within intra-crustal magma chambers, promoting crystallisation of various mineral assemblages. The ultimate enriched and not depleted mantle source is identical for the two PO suites. The more primitive LILE and HFSE-rich source rapidly replaces the older orogenic mantle source during lithosphere delamination and becomes progressively the thermal boundary layer of the new lithosphere. Present rock compositions are a mixture of major mantle contribution and various crustal components carried by F-rich aqueous fluids circulating within convective cells created around magma chambers. In favourable areas, PO suites pre-date a new orogenic Wilson cycle.  相似文献   

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