Showing papers on "Granulite published in 1990"

Granulites and crustal evolution

Abstract: The NATO ARW granulite conference: a report.- Crustal Evolution.- Genesis of continental crust: evidence from island arcs, granulites, and exospheric processes.- The granulite - granite connexion.- Heat, fluids, and melting in the granulite facies.- Granites, granulites, and crustal differentiation.- Regional Syntheses.- Europe.- Evolution of the lower crust in the Ivrea zone: a model based on isotopic and geochemical data.- The granulite belt of Lapland.- North and South America.- A model for the granulite-migmatite association in the Archean basement of southwestern Montana.- Multi stage late Archaean granulite facies metamorphism in Northern Labrador, Canada.- Archean tectonic setting of granulite terranes of the Superior Province, Canada, a view from the bottom.- The granulites of the Jequie complex and Atlantic Coast mobile belt, Southern Bahia, Brazil - An expression of Archean/Early Proterozoic plate convergence.- From Africa to India.- Pressure-Temperature-Time paths of granulite metamorphism and uplift, Zambesi belt, N.E. Zimbabwe.- Thermal history and tectonic setting of the Namaqualand granulites, Southern Africa: clues to Proterozoic crustal development.- The granulite-facies rocks of the Limpopo belt, Southern Africa.- Crustal evolution of the granulites of Madagascar.- Nature and scale of fluid-rock exchange in granulite grade rocks of Sri Lanka: a stable isotope study.- The granulite terrane of the Nilgiri Hills (Southern India): characterization of high-grade metamorphism.- Fluids and Petrological Equilibria.- Granulites of Satnuru and Madras: A study in different behaviour of fluids.- Scapolite phase equilibria: additional constraints on the role of CO2 in granulite genesis.- Synmetamorphic fluid inclusions in granulites.- Fluid inclusions in granulites: peak vs. retrograde formation.- Thermometry and barometry of mafic granulites based on garnet - clinopyroxene - plagioclase - quartz assemblages.- Geochemistry and Geophysics.- Geochronology in Granulites.- Origin of granulites: geochemical constraints from Archean granulite facies rocks of the Sino-Korean craton, China.- The oxygen isotope composition of lower crustal granulite xenoliths.- Ionprobe investigation of rare earth element distributions and partial melting of metasedimentary granulites.- Geochemistry of intermediate/- to high-pressure granulites.- Thermal data and crustal structure. Role of granites and the depleted lower crust.- Some thermal aspects of granulite history.- Key word/subject index.

Episodic rapid uplift in the Himalaya revealed by 40Ar/39Ar analysis of detrital K-feldspar and muscovite, Bengal fan

Abstract: Detrital K-feldspar and muscovite samples from Ocean Drilling Program Leg 116 cores have been dated by the {sup 40}Ar/{sup 39}Ar technique and have depositional ages from 0 to 18 Ma. From 4 to 13 individual K-feldspars and 1 to 12 individual muscovites have been dated from 7 stratigraphic levels. In every level at least one K-feldspar and one muscovite yielded a minimum age identical, within uncertainty, to the age of deposition. These results indicate that a significant portion of the material in the Bengal fan is first-cycle detritus derived from the Himalaya. Therefore, the substantial amount of sediment deposited in the distal fan in early to middle Miocene time can be ascribed to a significant pulse of uplift and erosion in the collision zone at this time. Moreover, these data indicate that throughout the Neogene, some part of the Himalayan orogen was undergoing rapid erosion (1 to 10 mm/yr); this erosion must have been less than or equal to uplift relative to sea level. The lack of granulite facies rocks in the eastern Himalaya and Tibetan plateau suggests to us that very rapid uplift must have been distributed in brief pulses over different parts of the mountain belt. These datamore » are incompatible with tectonic models in which the Himalaya and Tibetan plateau are uplifted either uniformly over the past 40 m.y. or mostly within the past 2 to 5 m.y.« less

Granites, Granulites, and Crustal Differentiation

Abstract: Partial melting and the ascent of granitoid magma are among the main processes leading to differentiation of the continental crust. Recent experimental studies and modelling indicate that fertile crustal rocks will typically produce 30 to 40 vol% melt at temperatures of 850°–900°C, even under fluid-absent conditions. Quartz-saturated pelitic rocks will yield 25 to 50 vol% melt at ~ 850°C, while metabasic and intermediate rocks will form 15 to 50 vol% melt at T ≤ 900°C. Production of a large quantity of melt in this temperature range will have the effect of buffering metamorphic temperature in the melting zone. The temperature will not exceed 850°–900°C until the partial fusion process is complete. Fusion of ~ 40% of the lower crust would consume a large amount of energy: the buffering capacity (?H) of a fluid-absent partial melting reaction (at 850°C) being about 50 cal per gram of melting rock. This means that metamorphic T will rarely exceed 850°–900°C during a first, major, thermal event. At this stage, crustal magma production will depend on the fertility of the source rock and the intensity of the thermal anomaly responsible for the metamorphism. With a fertile lower crust, such a thermal event will generate S- and I-type granitoid liquids and leave behind granulitic residues composed of Qtz + Kfs (or Pl) + Grt + Sil + Ru, Qtz + Pl + Opx + Grt, or Opx + Cpx + Pl (± Grt), depending on the composition of the protolith. During a second thermal event (affecting recycled, melt-depleted crust), high-temperature A-type magmas could be produced. During any subsequent thermal event (without introduction of aqueous fluids) there would be no buffering effects linked to either subsolidus or melting reactions. The buffer capacity of the crust would be exhausted, and temperatures of around 1000°C could readily be reached, given a sufficient heat supply. Depending on rock composition, unusual high-T assemblages such as spinel + quartz, sapphirine + quartz, orthopyroxene + sillimanite, and osumilite may develop.

Fluid controlled eclogitization of granulites in deep crustal shear zones, Bergen arcs, Western Norway

Abstract: During the Caledonian orogeny large parts of the western margin of the Baltic shield were disrupted, sliced and stacked. Caledonian deformation resulted in a massif thickening of the continental crust. Mafic granulites and granulite facies meta-anorthosites build up a large portion of the Bergen Arcs terrane in southwestern Norway. The rocks represent typical Precambrian continental lower crust. These rocks experienced extensive eclogitization in response to stacking and crustal thickening during the Caledonian orogenic cycle. Eclogite formation resulted from shear deformation and associated infiltration of H2O-rich fluids (XH2O≥0.75). During an early stage, eclogite facies mineralogy formed in extension fractures (veins). The veins are probably related to hydraulic fracture systems which transported the inferred fluid phase. During the main stage, eclogitization occurred along shear zones ranging from centimeters to tens of meters in thickness. Eclogite forming reactions are shown to consume H2O, alkalies and to release SiO2. Much of the SiO2 released by the eclogitization process can be found in late quartz vein systems. The eclogitization took place at a temperature of about 700°C and a pressure between 18 and 21 kbar. Fluid infiltration was supported by a decrease in rock volume during reaction (ΔVsolids<0). The negative volume change of reaction occurs despite that the process of eclogitization involves hydration reactions. The formation of eclogite from granulite produces approximately 15 KJ heat per 100 cm3 original granulite. Numerical modeling of the regional temperature effects associated with partial hydration of the lower crust suggests that these processes may not cause large perturbations on the geotherm. Both, transport of heat and matter by advection of the fluid phase is negligible on a regional scale.

Geochemistry of Intermediate/- to High-Pressure Granulites

Abstract: Geochemical data from the literature for high-pressure granulites have been compiled with the aim of evaluating the compositional differences between granulite terrains of various ages and xenoliths and the processes responsible for granulite formation. Although complete compositional overlap exists between the different granulite groups, median compositions of Archean granulite facies terrains are more evolved (having higher SiO2 and lower MgO) than post-Archean terrains, which are in turn more evolved than granulite xenoliths. The degree of LREE enrichment changes systematically as well, with Archean terrains having the highest (La/Sm)N and (La/Yb)N and xenoliths the lowest. In contrast to the secular changes observed in upper crustal composition, the median K2O content for Archean granulites is slightly higher than that of post-Archean terrains. K, Rb, Cs, Th and U distribution patterns of granulites are the same for terrains and xenoliths, suggesting similar depletion processes operate in both. It is possible to classify granulites on the basis of their LILE contents and thereby to predict their LILE characteristics if their K contents are known. K/U and K/Th ratios are significantly higher in granulites than in the upper continental crust and do not correlate with K content. Using the median values of K, K/Th and K/U for Archean granulite terrains, a heat production of 0.48 µW/m3 is calculated — a value similar to estimates based on individual terrains. Suggestions that mantle heat flow is overestimated in Archean shields due to the effects of lateral heterogeneities in heat-producing elements in the crust mean that Archean granulite terrains cannot be excluded as being representative of the lower crust in these regions on the basis of heat flow arguments. The heat production calculated for post-Archean terrains is somewhat higher (0.53 µW/m3) than the Archean value and that of xenoliths is very low (0.08 µW/m3). Model trace element contents of partial melting residues of metapelitic rocks, using recent experimental results to constrain restite phase proportions, are different from those observed in aluminous granulites. However, if melt segregation was inefficient, the trace element characteristics of the model restite are closer to those observed in aluminous granulites, but the residues are no longer LILE depleted. This suggests that (1) granite residues may be sampled as undepleted granulites, and (2) partial melting is not the process by which granulites become depleted in LILEs. Finally, positive Eu anomalies postulated to exist in the lower crust are observed mainly in cumulates, suggesting that crystal accumulation rather than partial melt removal may be the process responsible for imparting the negative Eu anomaly on the upper crust.

The Granulite — Granite Connexion

Abstract: Granulites may be produced in either fluid-present or fluid-absent metamorphism. Fluid-present granulites can be formed by relatively low-T dehydration reactions, in the presence of a fluid dominated by a species other than H2O (e.g., CO2). Small quantities of H2O-rich fluid may be present at the onset of granulite facies conditions (≥ 650°C). This will promote limited degrees of partial fusion and the formation of granulitic migmatites, but will not produce mobile granitoid magma. Much of the lowermost crust is composed of non-restitic metagabbros and cumulates. However, the middle and lower crust also contain a substantial component of granulitic restite. This is derived through fluid-absent partial melting of common crustal rock-types that had been through earlier hydration cycles. Only fluid-absent granulites, produced at T ≥ 850°C, can have intimate, cogenetic connexions with voluminous granitoids. Non-restitic, mafic granulites represent basaltic magma that provided the heat source for metamorphism and melting of the overlying rocks. Restitic granulites are the refractory, residual complements of the granitoid magmas emplaced at higher levels. Silicic magmatism is most commonly a manifestation of crustal growth through under- and intra-plating of mantle-derived magma.

Chronologic and isotopic framework for Early Proterozoic crustal evolution in the eastern Mojave Desert region, SE California

Abstract: The Early Proterozoic geologic evolution of the eastern Mojave Desert region, as defined by characteristics of its supracrustal rocks, granitoids, metamorphism, structural history, and Pb and Nd isotopic signature, contrasts sharply with other Proterozoic provinces of the southwestern United States. The oldest supracrustal rocks of the Mojave Desert region contain zircons over 2.0 Ga, corroborating Nd isotopic evidence for a much older crust here than elsewhere in the southwestern United States. Granitoids widely emplaced within these supracrustal rocks range from 1.76 to 1.64 Ga. The earlier plutons and surrounding supracrustal rocks were metamorphosed to granulite and high amphibolite facies throughout the province at about 1705 Ma in a migmatite-producing event that we term (informally) the Ivanpah orogeny. Subsequent granitoids, emplaced from 1.69 to 1.67 Ga, were voluminous along a north trending belt in the middle of the Mojave province. Younger plutons were emplaced at about 1.66 Ga in several places and at about 1.64 Ga along the extreme southern part of the province. Commonalities between the Proterozoic evolutions of the Mojave and Arizona crustal provinces do not conclusively establish the time that the provinces were juxtaposed; the data only suggest that the juxtaposition occurred between about 1.76 and 1.64 Ga.

Archaean and Proterozoic high-grade terranes of East Antarctica (40–80°E): a case study of diversity in granulite facies metamorphism

Abstract: In recent years there has been a tendency for workers in high-grade terranes to seek and identify unified and somewhat generalized models for the origin of granulites, usually based on observations in classic terranes such as the Adirondacks (Bohlen 1987) and southern India (e.g. Newton et al. 1980, Hansen et al. 1984). In particular, some studies have emphasized a perceived uniformity in granulite P-T conditions and P-T-t (pressure-temperature-time) paths (Newton & Perkins 1982, Bohlen 1987), and hence have modelled granulite terranes in terms of one particular tectonic setting such as a mag-matic arc. In contrast, Harley (1989a) has emphasized diversity in the important features of granulite terranes, most notably in their P-T conditions of formation and P-T-t paths but also in their lithological constitution and age structures, and has considered a spectrum of possible tectonic settings and mechanisms for granulite formation.

Archean-Proterozoic Evolution of Indian Charnockites: Isotopic and Geochemical Evidence from Granulites of the Eastern Ghats Belt

Abstract: Pyroxene granulites and charnockites are associated with metasedimentary khondalite (garnet-sillimanite gneiss) and migmatites in the Eastern Ghats mobile belt. Various stages of in situ granulitization similar to those observed in southern India and Sri Lanka are present. Geochemically the granulite suite around Visakhapatnam is bimodal, with acid and mafic variants. There is an increase in the concentration and fractionation of the rare earth elements (REE) from pyroxene granulites to charnockites, and six Sm-Nd models ages ($$T_{DM}$$) range from 2.86 to 2.35 Ga, with 2.1 Ga for a younger granite. The charnockites, a pyroxene granulite, and granite define a Pb/Pb isochron age of $$1176 \pm 201 Ma$$. U-Pb ages of zircons and monazites from a charnockite near Phulbani, Orissa, yield near concordant data with ages of $$985 \pm 5 Ma$$ and $$965 \pm 7 Ma$$, respectively. The new isotopic data and the available ages from the northeastern part of the Eastern Ghats in Orissa suggest a major charnockite formati...

Garnet porphyroblast-bearing leucosomes in metapelites: mechanisms, phase diagrams, and an example from Broken Hill, Australia

Abstract: Mafic porphyroblasts are commonplace in leucosomes in metamorphic rocks at uppermost amphibolite facies and in the granulite facies. Large, 5 cm or more in diameter, garnet porphyroblasts are common in leucosomes in low-to medium-pressure granulite facies metapelites such as those in the Broken Hill area, Australia. Although there is significant consensus regarding the origin of those porphyroblasts — that they form as a consequence of incon-gruent melting reactions in which hydrous minerals are consumed — there are various interesting questions which need to be answered. For example: if the porphyroblasts are melting products, why then are they preserved during cooling when the melt crystallizes and the hydrous mineral becomes stable again? Intuitively, one would expect complete, or at least major retrogression of the porphyroblasts. This is not usually observed, and is generally absent in the garnet porphyroblasts at Broken Hill.

High temperature-low pressure Cretaceous metamorphism related to crustal thinning (Eastern North Pyrenean Zone, France)

Abstract: The Mesozoic sediments in the Eastern North Pyrenean Zone have suffered a high temperature-low pressure metamorphism which reached its climax before the major deformation event. The mineral associations in pelitic rocks are consistent with temperatures of 500°–600°C and a maximum pressure of 3–4 kb. Post-metamorphic brittle deformation has disturbed the initial thermal pattern. The Albo-Cenomanian (98–87 Ma) metamorphism is related to thermal anomalies contemporaneous with the crustal thinning in the North Pyrenean Zone. The distribution of paleotemperatures suggests that the intensity of metamorphism may have been related to the magnitude of crustal attenuation. High-grade rocks are associated with lherzolites and granulites, whereas low-grade rocks are associated with higher-level crustal material (gneisses and micaschists). Crustal thinning and metamorphism developed during sinistral transcurrent displacement of Iberia with respect to Europe.

Two‐stage decompression in orthopyroxene–sillimanite granulites from Forefinger Point, Enderby Land, Antarctica: implications for the evolution of the Archaean Napier Complex

Abstract: Magnesian metapelites of probable Archaean age from Forefinger Point, SW Enderby Land, East Antarctica, contain very-high-temperature granulite facies mineral assemblages, which include orthopyroxene (8–9.5 wt% Al2O3)–sillimanite ± garnet ± quartz ± K-feldspar, that formed at 10 ± 1.5 kbar and 950 ± 50°C. These assemblages are overprinted by symplectite and corona reaction textures involving sapphirine, orthopyroxene (6–7 wt% Al2O3), cordierite and sometimes spinel at the expense of porphyroblastic garnet or earlier orthopyroxene–sillimanite. These textures mainly pre-date the development of coarse biotite at the expense of initial mesoperthite, and the subsequent formation of orthopyroxene (4–6 wt% Al2O3)–cordierite–plagioclase rinds on late biotite. The early reaction textures indicate a period of near-isothermal decompression at temperatures above 900°C. Decompression from 10 ± 1.5 kbar to 7–8 kbar was succeeded by biotite formation at significantly lower temperatures (800–850°C) and further decompression to 4.5 ± 1 kbar at 700–800°C. The later parts of this P–T evolution can be ascribed to the overprinting and reworking of the Forefinger Point granulites by the Late-Proterozoic (c. 1000 Ma) Rayner Complex metamorphism, but the age and timing of the early high-temperature decompression is not known. It is speculated that this initial decompression is of Archaean age and therefore records thinning of the crust of the Napier Complex following crustal thickening by tectonic or magmatic mechanisms and preceding the generally wellpreserved post-deformational near-isobaric cooling history of this terrain.

Petro-tectonic Imprints in the Sapphirine Granulites from Anantagiri, Eastern Ghats Mobile Belt, India

Abstract: Sapphirine granulite occurring as lenses in charnockite at Anantagiri, Eastern Ghat, India, displays an array of minerals which developed under different P-T-X conditions. Reaction textures in conjunction with mineral chemical data attest to several Fe-Mg continuous reactions, such as spinel+rutile+quartz+MgFe −1 =sapphirine+ilmenite cordierite=sapphirine+quartz+MgFe −1 sapphirine+quartz=orthopyroxene+sillimanite+MgFe −1 orthopyroxene+sapphirine+quartz=garnet+MgFe −1 orthopyroxene+sillimanite=garnet+quartz+MgFe −1 orthopyroxene+sillimanite+quartz+MgFe −1 =cordierite. Calculated positions of the reaction curves in P-T space, together with discrete P-T points obtained through geothermobarometry in sapphirine granulite and the closely associated charnockite and mafic granulite, define an anticlockwise P-T trajectory. This comprises a high-T/P prograde metamorphic path which culminated in a pressure regime of 8.3 kb above 950°C, a nearly isobaric cooling (IBC) path (from 950°C, 8.3 kb, to 675°C, 7.5kb) and a terminal decompressive path (from 7.5 to 4.5 kb). Spinel, quartz, high-Mg cordierite, and sapphirine were stabilized during the prograde high-T/P metamorphism, followed by the development of orthopyroxene, sillimanite, and garnet during the IBC. Retrograde low-Mg cordierite appeared as a consequence of decompression in the sapphirine granulite. Deformational structures, reported from the Eastern Ghat granulites, and the available geochronological data indicate that prograde metamorphism could have occurred at 3000±100 and 2500±100 Ma during a compressive orogeny that was associated with high heat influx through mafic magmatism. IBC ensued from P max and was thus a direct consequence of prograde metamorphism. However, in the absence of sufficient study on the spatial variation in P-T paths and the strain histories in relation to time, the linkage between IBC and isothermal decompression (ITD) has remained obscure. A prolonged IBC followed by ITD could be the consequence of one extensional mechanism which had an insufficient acceleration at the early stage, or ITD separately could be caused by an unrelated extensional tectonism. The complex cooled nearly isobarically from 2500 Ma. It suffered rapid decompression accompanied by anorthosite and alkaline magmatism at ~1400-1000 Ma.

Crustal Evolution of the Granulites of Madagascar

Abstract: In its pre-drift position, before the end of the Paleozoic, Madagascar was adjacent to Kenya and Tanzania and was located on the eastern front of the Mozambican belt, juxtaposed against the Indian Craton. The crust of Archean age was reactivated during the Proterozoic (2.6 Ga, 1.1 Ga?, 850–550 Ma). The metamorphic events were generally high grade and formed extensive granulite terrains. In the north of the island, granulites associated with belts of basic and ultrabasic magmatic rocks indicate high grade conditions: T≈1000°C and P≈6 kb. Aluminous rocks contained Q, Al-rich Opx, Ga, Sill, Rut and/or Ilm, Sp, Feld and probably osumilite and sapphirine. Primary Opx contain garnet lamellae and are aluminousrich (7–10 wt % Al2O3). Near isobaric retrogression and hydration produced orthoamphibole-cordierite gneisses. In the south of Madagascar, the metamorphic grade increases from greenschist to granulite grade going from west to east. Supracrustal metabasites (sapphirine-corundum amphibolites, serendibite and clintonite clinopyroxenites, etc.) have undergone a prograde event. The synmetamorphic, anorogenic gabbro-anorthosite intrusive complex is related to an increased geothermal gradient going from W (high-P granulite facies) to E (intermediate-P granulite facies). Isobaric cooling was followed by decompression (P-T path concave towards the T-axis). Gneisses with Al-rich Opx, Ga, Cord, Sp+Q, are common in the SE and suggest high T. A widespread anatectic event produced Q-Kf-Pl-Ga-Cord-Sill-Bio gneisses and biotite rich residues which contain Sapph, Korn and grandidierite. It is proposed that the magmatic intraplating, the very high T metamorphism, the P-T path concave towards the T-axis and the variation in the geothermal gradient are the consequences of continental lithospheric thinning by extension followed by a compressive event.

Progress in Tectonic and Petrogenetic Studies in an Exposed Cross-Section of Young (~100 Ma) Continental Crust, Southern Sierra Nevada, California

Abstract: The southern Sierra Nevada offers an oblique section through young Cordilleran-type batholith generated crust spanning surface (volcanic) to deep (granulitic) levels. Regional mapping and Pb/U zircon geochronology reveal structural continuity through this crustal section for volcanic, plutonic and metamorphic assemblages developed at ~100 Ma, making it one of the youngest sections in the world. Construction of a synthetic cross-section is well-constrained by the oblique section map pattern, abundant age data, and a published crustal structure section that was based on geophysical and lower crustal xenolith data from across the shallow levels of the batholith. The synthetic cross-section depicts the state of the sialic crustal section during its ~100 Ma petrogenesis. Critical features of the section are as follows: (1) Much of the pre-Cretaceous crust was completely reconstituted by batholith generation; (2) Major influxes of mantle-derived tonalitic to gabbroic magmas drove crustal-level melting and magma mixing; (3) Pre-existing sialic components within the batholithic magmas were contributed primarily from partial to complete melts of craton derived metasedimentary material; (4) Silicic magmas emplaced at shallow crustal levels represent moderately to well-mixed and fractionated systems, while those frozen at deeper levels appear to be more heterogeneous both lithologically and geochemically; (5) Granulite facies metamorphic assemblages in the deep crustal rocks developed primarily in a retrograde regime descending from gabbro and tonalite solidus conditions; (6) Upward rise of silicic magmas was accompanied by downward return flow of metamorphic host rocks, and locally ignimbrite sections of only slightly older age than enclosing plutons were transported to considerable depth as well; (7) Much of the upper crust responded to the intrusion of silicic magmas by large-scale extension which also promoted major ignimbrite eruptions; and (8) Within the deeper levels of the composite batholith and off its flanks, at moderate to shallow crustal levels, low-angle detachments may have developed as a primary structural feature. Each of these points as well as a number of other interesting problems form the basis for a broad spectrum of current and future research efforts.

Geology of crystalline rocks of northern Fiordland: Details of the granulite facies Western Fiordland Orthogneiss and associated rock units

Abstract: A c. 700 km2 area of northern Fiordland (South Island, New Zealand) is described in which Early Cretaceous high-pressure metamorphic rocks and virtually unmetamorphosed plutonic rocks occur. The dominant rocks are orthogneisses developed from synmetamorphic basic-intermediate intrusive complexes, the youngest and most widespread of which is the Early Cretaceous Western Fiordland Orthogneiss (WFO). The latter has undergone granulite facies metamorphism and occurs throughout much of western Fiordland. In the study area, the WFO protolith intruded a country rock of amphibolite facies metasediments and orthogneisses. Fragments of the country rock are rafted within WFO and are represented by George Sound Paragneiss and Rafted Granitoid Gneisses. External country rock is represented by Arthur River Complex and Jagged Gneiss (possibly related to the Anita Ultramafites); it may also include Indecision Creek Complex and Mount Anau Complex. The George Sound Paragneiss is correlated with the Central Fiordla...

Heat, Fluids, and Melting in the Granulite Facies

Abstract: Various geothermobarometric studies have yielded temperatures of 650°C to > 1000°C, and pressures of 3 to > 18kbar, for equilibration of granulite facies assemblages. This range of values, and their uncertainties, probably reflect diffusion closure rather than simply formation conditions. Geohygrometry and phase equilibria, together with fluid inclusion studies, have revealed a wide range of fluid involvement in granulite facies metamorphism from fluid-absent to H2O- or CO2-rich. A major penological problem is to distinguish those granulites which escaped partial melting, even at the above P-T conditions which mostly lie above the H2O-saturated solidus for a wide range of likely lower continental rock types.

Granulite facies metamorphism of metabasic and intermediate rocks in the Highland Series of Sri Lanka

Abstract: The island of Sri Lanka is located to the south-east of India and is formed predominantly of Precambrian rocks that occur in several major terrains: the granulite facies Highland Series in the central part of the island, from which several authors separated a South West Group (eg Cooray 1965; Katz 1971, 1972); and the West and East Vijayan, both of which are predominantly composed of migmatitic granitic gneisses of middle to upper amphibolite facies conditions (Cooray 1962, Katz 1971, Oliver 1985) and border the Highland Series (Fig 101) Due to its variety of rock types, which include granitic to basic meta-igneous rocks and metasediments (quartzites, metapelites, calc-silicate rocks, marbles), and due to the juxtaposition of amphibolite and granulite facies terranes in a relatively small area, Sri Lanka has been and still is the subject of petrological, geochronological, and structural interest