Cordierite-bearing Rocks Research Articles

Eclogites and other high-pressure rocks in the Himalaya: a review

Abstract Himalayan high-pressure metamorphic rocks are restricted to three environments: the suture zone; close to the suture zone; and (mostly) far (>100 km) from the suture zone. In the NW Himalaya and South Tibet, Cretaceous-age blueschists (glaucophane-, lawsonite- or carpholite-bearing schists) formed in the accretionary wedge of the subducting Neo-Tethys. Microdiamond and associated phases from suture-zone ophiolites (Luobusa and Nidar) are, however, unrelated to Himalayan subduction–collision processes. Deeply subducted and rapidly exhumed Indian Plate basement and cover rocks directly adjacent to the suture zone enclose eclogites of Eocene age, some coesite-bearing (Kaghan/Neelum and Tso Morari), formed from Permian Panjal Trap, continental-type, basaltic magmatic rocks. Eclogites with a granulite-facies overprint, yielding Oligocene–Miocene ages, occur in the anatectic cordierite ± sillimanite-grade Indian Plate mostly significantly south of the suture zone (Kharta/Ama Drime/Arun, north Sikkim and NW Bhutan) but also directly at the suture zone at Namche Barwa. The sequence carpholite-, coesite-, kyanite- and cordierite-bearing rocks of these different units demonstrates the transition from oceanic subduction to continental collision via continental subduction. The granulitized eclogites in anatectic gneisses preserve evidence of former thick crust as in other wide hot orogens, such as the European Variscides.

Origin and Formation of Tourmaline-rich Cordierite-bearing Metapelitic Rocks from Alpe Sponda, Central Alps (Switzerland)

Origin and Formation of Tourmaline-rich Cordierite-bearing Metapelitic Rocks from Alpe Sponda, Central Alps (Switzerland)

Last stage of Variscan granitoid magmatism in the Strzelin Massif (SW Poland): petrology and age of the biotite-muscovite granites

New petrographic and geochemical data show some differences between Variscan Bt-Ms granites occurring either as small plutons or dykes in the Strzelin Massif (SW Poland). The granites of the Gromnik and Gorka Sobocka plutons are rich in micas and crystallized from wet magmas; the granites in the dykes and in the Gebczyce pluton are mica-poorer and cordierite-bearing rocks, derived from “dryer” magmas. The lower initial eNd values in the Bt-Ms granites of the dykes, compared with those in the plutons, reflect a more signature of the former, possibly due to local crustal assimilation, via AFC, shortly before emplacement. Much more radiogenic initial 87 Sr/ 86 Sr ratios in the dykes, up to 0.726, further suggest the involvement of extraneous, hydrous crustal fluids enriched in 87 Sr during the evolution of late-stage magma derivatives. The new U-Pb SHRIMP zircon age of 296 ± 6 Ma for the Gebczyce Bt-Ms granite shows that this body belongs to the third stage of magmatism in the Strzelin Massif. The U-Pb SHRIMP zircon data for the Bt-Ms granite dykes provide ages similar to those of their host rocks: c. 295 Ma for the Gesiniec tonalite and the enclosed Bt-Ms granite, and c. 285 Ma for the Strzelin biotite granite and its Bt-Ms granite dykes. These new data from peraluminous rock-types complement our previous studies focused on the tonalites, granodiorites and biotite granites, and shed light on the late-stage igneous evolution of the Strzelin Massif.

High-T–low-P thermal anomalies superposed on biotite-grade rocks, Wongwibinda Metamorphic Complex, southern New England Orogen, Australia: heat advection by aqueous fluid?

The Wongwibinda Metamorphic Complex is characterised by ∼400 km2 of biotite-grade rocks with irregular, km-scale zones of cordierite-bearing high-T rock (T > 550°C). Cordierite-bearing rocks include different textures: (i) cordierite–K-feldspar–spotted hornfels; (ii) sheared cordierite–K-feldspar–augen schists; and (iii) migmatites with or without comparatively coarse garnet poikiloblasts. Integrated petrography, mineral chemistry and mineral equilibria modelling indicate metamorphic peak conditions in samples of hornfels of approximately P ≤ 250 MPa and T = 570–620°C. Two samples of sheared rock preserve peak conditions of approximately T = 670–690°C or T < 600°C and P ≤ 200 MPa, consistent with rapid cooling or variable thermal structure in the Glen Mohr Shear Zone. Electron microprobe U–Th–Pb monazite data indicate a date of 291.5 ± 1.8 Ma for the shear zone, indistinguishable from the age of Hillgrove Plutonic Suite granitoids in the complex. Monazite ages are complex in the hornfels samples that were likely, on the basis of structural relationships, metamorphosed early in the history of the Wongwibinda Metamorphic Complex (ca 300 Ma). Previous monazite dating of migmatite samples (ca 297 Ma) suggests that the metamorphic cycle was short-lived, lasting less than ca 10 m.y. Metamorphic field gradients are <15–23°C km−1 across much of the complex but locally steep (>50–100°C km−1) around the high-T rocks. Rejection of most heat sources leaves regional conductive heating as the most plausible explanation for the smooth, broad and shallow metamorphic field gradient in the biotite-grade rocks. Another mechanism of heat transfer is required to explain the local, steep metamorphic field gradients and development of high-T cordierite-bearing rocks. The spatial association of quartzite units centred within two cordierite-bearing high-T domains and an increased abundance of quartz veins above the cordierite isograd suggests heat advection by aqueous fluid locally perturbed the broad conductive heating. Fluid was channelled within shear zones and locally infiltrated nearby rocks. Variable fluid flux and strain have produced the range of different textures in cordierite-bearing rocks of the Wongwibinda Metamorphic Complex.

Constraints on the timing of granite emplacement, deformation and metamorphism in the Shamva area, Zimbabwe

In order to constrain the temporal relationship between granite (sensu lato) emplacement and metamorphism, isotope work was carried out on the minerals zircon and apatite (U–Pb), garnet (Pb–Pb) and hornblende (Ar–Ar) from wall rock samples in the Shamva area in Zimbabwe. The area, encompassing parts of the Chinamora and Murehwa batholiths and a wedge-shaped greenstone belt segment in between, is commonly quoted in the literature as an example illustrating pluton emplacement processes and deformational models for the Archean. New U–Pb dating of apatite from a boudinaged pegmatite within mafic schists in the batholith–greenstone contact zone has yielded an age of 2619 +28/–24 Ma. This age is interpreted as the best estimation of the intrusion age of this unit, depending on the assumed closure temperature, and provides an upper age limit for the syntectonic emplacement of the now gneissic granites. Pb–Pb dating of late kinematic garnets in cordierite-bearing rocks within the greenstone belt wall rocks gives an age of 2623±8 Ma. Together, this timing of relatively late, syntectonic plutonism and metamorphic mineral growth at ca. 2.62 Ga compares well with existing zircon crystallization ages for felsic volcanics (2645±4 Ma, 2643±8 Ma) and post-tectonic porphyritic monzogranites (2601±14 Ma). Ar–Ar hornblende ages for mafic schists from different areas within the greenstone belt wall rocks range between 2621 and 2498 Ma and have been interpreted to indicate mixing between metamorphic ages and cooling ages. The data support a geological model whereby volcanism and sedimentation are associated with an early phase of regional deformation at ca. 2.64 Ga, which may have started earlier and lasted longer, and evolves into the voluminous emplacement of granites (now gneissic granites) in the batholiths at approximately 2.62 Ga. Emplacement of post-tectonic tabular monzogranites takes place at ca. 2.60 Ga.

日高変成帯主帯南端部に分布する花こう岩類の地質および化学組成 特に含きん青石花こう岩類について

日高変成帯主帯南端部に分布する花こう岩類の地質および化学組成 特に含きん青石花こう岩類について

Petrology of thermally metamorphosed pelitic rocks in the Champawat Area, Kumaun Himalaya

In the Champawat area, Kumaun Himalaya, greenschist facies regionally metamorphosed rocksviz chlorite-phyllite and schist have been subjected to thermal metamorphism due to emplacement of batholithic granite/granodiorite body. As a consequence, biotite, garnet, andalusite, fibrolite, sillimanite and perthite minerals have formed in the contact rocks. The conspicuous absence of cordierite and staurolite reported from such aureole rocks is due to higher FeO/MgO ratio of the bulk rock composition in the former while the absence of staurolite is due to low Al2O3/FeO+MgO ratio in the schists. AFM diagram demonstrates that in muscovite-bearing schist, the bulk composition of chlorite- and cordierite-bearing rocks are restricted to low FeO/MgO side and thus the restricted occurrence of former and the absence of latter in the contact rocks of the area. This is further evident from the common occurrence of almandine-rich garnet in the rocks.

PETROCHEMISTRY OF AN UPPER PRECAMBRIAN METASEDIMENTARY BELT IN SOUTHERN BAHIA - THE SIGNIFICANCE OF CORDIERITE

Petrology and chemistry of an Upper Precambrian metasedimentary belt in Southern Bahia (Brazil) have been studied. The Belt consists essentially of muscovite-biotite gneisses and of sillimanite-grade rocks (kinzigites) containing lenses of acid-and sub-acid granulites, and pluton-like bodies of migmatitic-granitic rocks. Cordierite-bearing rocks are widely spread within the sillimanite-grade rocks. Cordierite appears always as the last paragenetic mineral and probably is formed through the reaction sillimanite+garnet+quartz = cordierite. Chemical data indicate that the original material for mica gneisses and sillimanite-grade rocks consisted of a misture of graywaekes and pelitic rocks. Comparison with modern pelagic sediments reveals low contents of metals (Fe, Mn, Ni, etc.), relatively mobile in marine environments, thus suggesting possible submarine leaching. Bulk chemistry (showing low alkali and silica contets) was found to control closely cordierite formation which is considered related to the removal of fractions of anatectic silicate liquids. The more general significance of cordierite in metasediments is discussed stressing the role of the partial H 2 0 pressure in the metamorphic fluids. The presence of even small amounts of H 2 0-undersaturated melts strongly reduces the molar H 2 0 fraction and favours the stabilization of cordierite. Preservation of cordierite under more hydrous conditions depends on the further development of the P-T metamorphic regime.

Growth of cordierite in the Archean metasediments near Yellowknife, district of Mackenzie, Canada

The widespread occurrence of cordierite in the Archean metasediments near Yellowknife was attributed by earlier workers to the contact metamorphism associated with the granite. However, detailed field and textural studies on the cordierite-bearing rocks near Sparrow Lake indicate that the growth of cordierite is not restricted to the „aureole“ around the Sparrow Lake granite. Fabric relations demonstrate that cordierite grew under regional metamorphic conditions existing before and after the intrusion of the granite. Emplacement of the Sparrow Lake pluton is considered to represent the culmination stage of regional tectonism that manifested itself as deformation, metamorphism and granite intrusion in the Sparrow Lake area.

An 40Ar/ 39Ar age spectrum for a cordierite-bearing rock: Isolating the effects of excess radiogenic 40Ar

Cordierite-bearing rocks commonly contain excess radiogenic 40Ar and therefore yield anomalously old conventional K-Ar dates. Mechanical separation of cordierite cannot always be used to circumvent this problem. The 40Ar/ 39Ar incremental release technique was successfully used to isolate the effects of excess radiogenic 40Ar in a cordierite-bearing rock. An 40Ar/ 39Ar age spectrum was obtained for a cordierite-bearing rock whose true cooling age could be presumed by dating equivalent cordierite-free rocks. The initial gas fraction in the age spectrum exhibits an extremely high apparent age. Each successive step shows a decrease in apparent age. The apparent age of the last increment yielding a significant quantity of gas is in reasonable agreement with the presumed cooling age. The release pattern obtained suggests that radiogenic 40Ar associated with cordierite is released primarily at low temperatures. At higher temperatures the 40Ar released is primarily that derived from in-situ decay of 40K in the other minerals present. The 40Ar/ 39Ar incremental release technique may therefore be useful in isolating the effects of excess radiogenic 40Ar in cordierite-bearing rocks. This would enable the determination of true cooling ages for this rocks.

Chemical mineralogy of some cordierite-bearing rocks near Yellowknife, Northwest Territories, Canada

Meta-graywacke and meta-argillite of Archean age near Yellowknife contain biotite, cordierite, gedrite and sillimanite isograds towards the Sparrow Lake granite pluton. The chemistry of biotite, cordierite, gedrite and garnet in rocks that up-grade from the cordierite isograd indicate a small range of chemical composition, particularly with reference to Mg, Fe and Mn. The analyses show further that among the coexisting ferromagnesian minerals Fe/Fe+ Mg ratio decreases in the sequence: garnet, gedrite, biotite, cordierite while Mn/Fe+Mg+Mn ratio decreases in the sequence garnet, gedrite, cordierite, biotite. The same order is also observed in the “distribution diagrams”. The regular distribution of Mg, Fe and Mn among the coexisting phases demonstrate that chemical equilibrium was attained and preserved in these Archean rocks. Mg-Fe distribution between cordierite and biotite appears to be dependent on the temperature of crystallization or metamorphic grade.

Sulfurization of Basalt Under Thermal Metamorphic Conditions to Produce Cordierite-Bearing Rocks

Hydrothermal experiments with fresh basalt in a high pS2 environment yielded cordierite–sulfide-bearing assemblages. These results suggest that during thermal metamorphism of a volcanic exhalative sulfide deposit, progressive sulfurization of the enclosing basalts takes place. Cordierite–anthophyllite and cordierite–andalusite assemblages will result if Fe combines with S to form sulfides and Ca is removed, possibly as CaSO4.

The role of partial fusion in the genesis of certain cordierite-bearing rocks

Synopsis Cordierite-bearing xenolithic rocks, including quartz-cordierite-norites, which occur in association with basic igneous rocks in many parts of north-east Scotland, represent Dalradian country rocks which have undergone partial melting at the time of intrusion of the basic magma.

Paragenetic relations of aluminosilicates and gedrite from Fishtail Lake, Ontario, Canada

The aluminosilicates occur in close association with gedrite in cordierite-bearing and cordierite-free schists and gneisses. In cordierite-bearing rocks, sillimanite is incompatible with gedrite; it is either completely enclosed in cordierite, or in lithologically distinct layers from those in which the gedrite occurs. In cordierite-free rocks, sillimanite and gedrite appear in close proximity, apparently because the lime content of the rock is sufficiently high so that it lies outside the cordierite composition field. Kyanite (andalusite) and gedrite are found in close association as a result of the breakdown of cordierite to kyanite (andalusite) and chlorite in a potash-deficient environment.

The cordierite-bearing rocks of the Haddo House and Arnage districts, Aberdeenshire

Petrological investigations of certain xenolithic rocks in northeast Scotland support the hypothesis that these rocks represent Dalradian country rock material which has undergone partial melting; a conclusion which rejects existing hypotheses for the formation of these rocks by a process of magmatic assimilation.

On some cordierite-bearing rocks of the Meguro district in Hidaka Province, Hokkaido, with special reference to a large cordierite

The Meguro district is situated in the the southern part of the Hidaka metamorphic belt in Hokkaido . The major rock types in the area are composed of the so-called migmatites and various metamorphic rocks. This paper presents a short description for the petrographic nature of the cordierite-bearing rocks found in the metamorphic rocks. The rocks are composed essentially of plagioclase, alkali-feldspar, quartz, biotite, muscovite, cordierite, sillimanite and many accessory or secondary minerals. A large cordierite listed in the sub-title of this paper have been examined optically, and by X-rays. The results of the examination are presented, and some problems are briefly discussed.

Charnockitic and Related Cordierite-Bearing Rocks from Dangin, Western Australia

VI. SummaryA series of charnockitic rocks and associated cordierite-bearing rocks from Western Australia has been described and compared with charnockitic rocks from other localities. This charnockitic suite is considered to be a series of basic intrusions into an older series of paraschists. It has, in places, been considerably contaminated by assimilation of the aluminous metasediments and in such cases is now represented by cordierite-bearing rocks. The basic charnockitic rocks and their contaminated equivalents have been subsequently invaded, under deep-seated conditions by granitic magma or emanations, and now appear as recrystallized remnants of the original masses. They have suffered extensive granitization which has yielded the acid charnockites (hypersthene-alkali felspar gneisses) in which the hypersthene is considered to have been derived from the older hypersthene-bearing basic charnockites. In view of the similarity to the Indian and Antarctic charnockites it appears possible that the charnockitic rocks of these areas are of similar origin, and that charnockite (hypersthene granite) rather than being the result of crystallization from a magma, is due to the granitization of older hypersthene-bearing rocks. If charnockite is of magmatic origin then it is most probable that this magma was of palingenetic origin and that the hypersthene is a relict from the earlier rocks and not the product of crystallization of the charnockite magma. Dunn (1942, p. 23) considers that the evidence afforded by Indian rocks is not opposed to the view that the hypersthene gneisses (charnockites) are the product of partial or complete palingenesis of very deep-seated rocks which had lost their water content.

The Evolution of the Granodioritic Rocks of the South-Eastern End of the Kopaonik Batholith, Yugoslavia

Summary and ConclusionsThe composite granodiorite batholith of the Kopaonik Mountains forms one of the more southerly members of the peri-Adriatic tonalitic intrusions. In the area discussed in this paper it intrudes a series of sedimentary rocks which range from dominantly calcareous to pelitic types. Metamorphism of these rocks has produced crystalline limestones, skarns, and calc-silicate hornfelses, which grade downwards into mica-, amphibole-, epidote-, and locally cordierite-bearing rocks. The pelitic and amphibole-bearing hornfelses are in immediate proximity to the batholith on the surface. The amphibole-bearing types are mainly confined to a relatively small area, well within the zone of high-grade metamorphism and overlying the southerly pitching nose of the intrusion. With them are associated hornfelses which carry porphyroblasts of albitic feldspar. It appears that the persistence of the amphibole and the development of these feldspar porphyroblasts may have been caused by hydrous and probably sodic emanations which permeated the sediments above and ahead of the advancing igneous mass.

Anthophyllite-Cordierite-Granulites of the Lizard

The region of Trelease Mill and Polkernogo, west of St. Keverne, forms one of the type outcrops of the Old Lizard Head Series north of the main Lizard gabbro. This small rather poorly exposed tract is distinguished not only because it has yielded the only recorded cordierite-bearing rocks among the Lizard schists but more particularly on account of the occurrence of the rarer rock types carrying anthophyllite together with abundant cordierite.