Assimilation and metamorphism at a basalt-limestone contact, Tokatoka, New Zealand

1980 ◽  
Vol 43 (330) ◽  
pp. 797-807 ◽  
Author(s):  
C. K. Baker ◽  
Philippa M. Black
Keyword(s):  
Rock Type ◽  
Olivine Basalt ◽  
Dilution Effect ◽  
Parent Magma ◽  
Contact Metamorphism ◽  
Small Scale ◽  
Metamorphic Assemblage ◽  
Assimilation Process ◽  
Partial Resorption ◽  
Limestone Assimilation

SummarySmall-scale assimilation of limestone during the intrusion of an olivine basalt feeder dyke into an Eocene argillaceous, siliceous biomicrite in the Tokatoka area has resulted in the incorporation of large amounts of calcium into the parent magma. Initial effects of assimilation have caused partial resorption of the early-formed igneous mineralogy and the precipitation of calcic, iron-rich clinopyroxenes (ferrosahlite to hedenbergite), wollastonite, schorlomite, and pyrrhotine. Pyroxene compositions show a trend of strong enrichment in Catschermak and ferrosilite components. Derivative hydrothermal solutions, rich in Ca, Si, Al and alkalis have precipitated and altered anhydrous phases to tobermorite, thomsonite, prehnite, pectolite, cebollite, hydrogrossular, gismondine, analcime, Sr- and Ba-bearing zeolites, and calcite.Modelling of the basalt-limestone assimilation process by least-squares mixing methods has shown that the observed chemical variation can largely be accounted for by the dilution of the basalt with up to 30 wt. % decarbonated limestone. Desilication of the liquid, a result of this dilution effect, has been accommodated in the chemistry of the early-formed mineralogy rather than by the crystallization of minerals characteristic of an undersaturated rock type.Contemporaneous with the intrusion of the basalt was the high-temperature contact metamorphism of the limestone. This produced assemblages of rankinite, kilchoanite, larnite, spurrite, grossular, and tobermorite. Subsequent injection of the basalt and hybrid phases into fractures has resulted in the alteration of the primary metamorphic assemblage to wollastonite, scawtite, foshagite, hydrogrossular, calcite, and vaterite.

scholarly journals Ozone Chemistry during the 2002 Antarctic Vortex Split

2005 ◽  
Vol 62 (3) ◽  
pp. 860-870 ◽  
Author(s):  
Jens-Uwe Grooß ◽  
Paul Konopka ◽  
Rolf Müller
Keyword(s):  
Ozone Depletion ◽  
Polar Region ◽  
Polar Vortex ◽  
Dilution Effect ◽  
Lagrangian Model ◽  
Chemical Effect ◽  
Small Scale ◽  
Air Masses ◽  
Antarctic Polar Vortex ◽  
The Antarctic

Abstract In September 2002, the Antarctic polar vortex was disturbed, and it split into two parts caused by an unusually early stratospheric major warming. This study discusses the chemical consequences of this event using the Chemical Lagrangian Model of the Stratosphere (CLaMS). The chemical initialization of the simulation is based on Halogen Occultation Experiment (HALOE) measurements. Because of its Lagrangian nature, CLaMS is well suited for simulating the small-scale filaments that evolve during this period. Filaments of vortex origin in the midlatitudes were observed by HALOE several times in October 2002. The results of the simulation agree well with these HALOE observations. The simulation further indicates a very rapid chlorine deactivation that is triggered by the warming associated with the split of the vortex. Correspondingly, the ozone depletion rates in the polar vortex parts rapidly decrease to zero. Outside the polar vortex, where air masses of midlatitude origin were transported to the polar region, the simulation shows high ozone depletion rates at the 700-K level caused mainly by NOx chemistry. Owing to the major warming in September 2002, ozone-poor air masses were transported into the midlatitudes and caused a decrease of midlatitude ozone by 5%–15%, depending on altitude. Besides this dilution effect, there was no significant additional chemical effect. The net chemical ozone depletion in air masses of vortex origin was low and did not differ significantly from that of midlatitude air, in spite of the different chemical composition of the two types of air masses.

scholarly journals Igneous stratigraphy and internal structure of the Little Minch Sill Complex, Trotternish Peninsula, northern Skye, Scotland

1991 ◽  
Vol 128 (1) ◽  
pp. 51-66 ◽  
Author(s):  
Sally A. Gibson ◽  
Adrian P. Jones
Keyword(s):  
Internal Structure ◽  
Magma Chamber ◽  
Thermal Gradient ◽  
Olivine Basalt ◽  
Small Scale ◽  
Basalt Magma ◽  
Alkali Olivine Basalt ◽  
Modal Layering ◽  
Crustal Magma

AbstractDetailed sampling of the Little Minch Sill Complex reveals that it is composed of both single and multiple sills. These are formed of three main, genetically related units: picrite, picrodolerite and crinanite, which are the result of differentiation of an alkali-olivine basalt magma (approximately 10% MgO) in an upper-crustal magma chamber. Variations in igneous stratigraphy and the presence of internal chills in the Trotternish sills suggest that they were emplaced by multiple intrusion and subsequently differentiated in situ. Changes in petrography adjacent to pegmatite veins and textures within picrite units indicate compaction and filter-pressing were important processes after emplacement. Rhythmic layering (1 cm to 1 m thick) is conspicuous in the sills near contacts but does not involve cryptic mineral variation. Such modal layering may be more common than realised in relatively small-scale intrusions and maybe modelled in terms of in situ differentiation under conditions of significant undercooling in a changing thermal gradient at the synthetic for-sterite-diopside-anorthite eutectic.

scholarly journals Reef growth and limestone erosion

2015 ◽  
Author(s):  
David Blakeway
Keyword(s):  
Coral Reef ◽  
Coral Reefs ◽  
Rock Type ◽  
Small Scale ◽  
Growth Forms ◽  
Reef Growth ◽  
Extraterrestrial Life ◽  
Fluid Medium ◽  
Biogenic Structures ◽  
Steep Slopes

Because the shapes and forms of many coral reefs resemble karst (erosion landforms created by dissolution of limestone), it is widely believed that those reefs have grown on karst foundations, and that Holocene growth perpetuates the underlying topography. However, this concept has become difficult to reconcile with the growing amount of seismic and coring evidence demonstrating that several karst-like reef features are entirely constructional. Here I use cellular automata simulations to show that coral reefs resemble karst limestones not because they are built on karst foundations, but because reef growth and limestone erosion are fundamentally the same process, running in opposite directions. Coral reef landscapes are in fact inverse karst—the basic spectrum of reef growth forms mirrors the basic spectrum of limestone erosion forms. In both growth and erosion, the development of form is a self-organised phenomenon emerging from the cumulative action of small-scale processes. The essential morphological control in both cases is slope stability, which depends on the composition of each system: coral type in reefs and lithology (rock type) in limestones. Solid, well cemented reefs and limestones, which can maintain steep slopes without collapsing, produce nodular reefs and pinnacle karst respectively, whereas unconsolidated, friable reefs and limestones, which frequently collapse, produce cellular reefs and cone karst.The growth forms produced in the model should theoretically apply to all modular skeleton-building organisms growing in a fluid medium, and may therefore provide useful templates in the search for extraterrestrial life. While none of the model forms can be considered unequivocally diagnostic of life, because all could conceivably arise through inanimate crystallisation, the model’s seemingly accurate rendition of biogenic carbonate morphology on earth suggests that it may provide a useful foundation for evaluating and exploring the range of macroscale self-organised biogenic structures that could arise on other planets.

scholarly journals Mineralogy of a High-Temperature Skarn, in High CO2 Activity Conditions: The Occurrence from Măgureaua Vaţei (Metaliferi Massif, Apuseni Mountains, Romania)

Minerals ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 677
Author(s):  
Ştefan Marincea ◽  
Delia-Georgeta Dumitraş ◽  
Cristina Sava ◽  
Frédéric Hatert ◽  
Fabrice Dal Bo
Keyword(s):  
Solid Solution ◽  
High Temperature ◽  
Upper Cretaceous ◽  
Contact Metamorphism ◽  
High Co2 ◽  
Shallow Level ◽  
Apuseni Mountains ◽  
Hydrothermal Stage ◽  
Metamorphic Assemblage ◽  
Hydrothermal Event

A shallow-level monzodioritic to quartz-monzodioritic pluton of the Upper Cretaceous age caused contact metamorphism of Tithonic–Kimmeridgian reef limestones at Măgureaua Vaţei (Metaliferi Massif, Apuseni Mountains, Romania). The preserved peak metamorphic assemblage includes gehlenite (Ak 33.64–38.13), monticellite, wollastonite-2M, Ti-poor calcic garnet, and Ca-Tschermak diopside (with up to 11.15 mol.% Ca-Tschermak molecule). From the monzodioritic body to the calcitic marble, the periplutonic zoning can be described as: monzodiorite/agpaitic syenite-like inner endoskarn/wollastonite + perovskite + Ti-poor grossular + Al-rich diopside/wollastonite + Ti-poor grossular + diopside + vesuvianite/gehlenite + wollastonite + Ti poor grossular + Ti-rich grossular (outer endoskarn)/wollastonite + vesuvianite + garnet (inner exoskarn)/wollastonite + Ti-rich garnet + vesuvianite + diopside (outer exoskarn)/calcitic marble. Three generations of Ca garnets could be identified, as follows: (1) Ti-poor grossular (Grs 53.51–81.03 mol.%) in equilibrium with gehlenite; (2) Ti-rich grossular (Grs 51.13–53.47 mol.%, with up to 19.97 mol.% morimotoite in solid solution); and (3) titanian andradite (Grs 32.70–45.85 mol.%), with up to 29.15 mol.% morimotoite in solid solution. An early hydrothermal stage produced retrogression of the peak paragenesis toward vesuvianite, hydroxylellestadite (or Si-substituted apatite), clinochlore, “hibschite” (H4O4-substituted grossular). A late hydrothermal event induced the formation of lizardite, chrysotile, dickite, thaumasite, okenite and tobermorite. A weathering paragenesis includes allophane, C-S-H gels and probably portlandite, unpreserved because of its transformation in aragonite then calcite. Overprints of these late events on the primary zoning are quite limited.

Clinopyroxenes from the Upper Layered Series Kap Edvard Holm, East Greenland

1971 ◽  
Vol 38 (293) ◽  
pp. 49-57 ◽  
Author(s):  
R. Elsdon
Keyword(s):  
Optical Properties ◽  
Single Crystals ◽  
Olivine Basalt ◽  
Parent Magma ◽  
Chemical Compositions ◽  
Measurable Effect ◽  
Layered Series ◽  
East Greenland ◽  
X Ray ◽  
Alkali Olivine Basalt

SummaryChemical compositions, unit-cell contents, and optical properties of six clinopyroxenes from the Upper Layered Series are presented. There is a gradual enrichment in iron upwards in the intrusion although there is no measurable effect on the optical properties, possibly because of Cr variation and exsolution of Fe and Ti as oxides. The chemistry of the clinopyroxenes is consistent with crystallization from a water-rich magma of transitional nature between tholeiite and alkali-olivine basalt. X-ray oscillation photographs of single crystals reveal the presence of sub-microscopic exsolution lamellae of pigeonite, a feature consistent with the transitional nature of the parent magma. Exsolution lamellae of titanomagnetite are ubiquitous and were formed at subsolidus temperatures in response to high buffered oxygen fugacity. Comparisons are made between the properties of clinopyroxenes from the Lower, Middle, and Upper Layered Series, and the conditions of crystallization of each series.

The Geology of the Snøfjella and Dovrefjella in Vestspitsbergen

1959 ◽  
Vol 96 (1) ◽  
pp. 45-57 ◽  
Author(s):  
John Preston
Keyword(s):  
Rock Type ◽  
Olivine Basalt ◽  
Alkaline Rock ◽  
Metamorphic Condition ◽  
General Picture

AbstractThe area yields marbles, schists, and quartzites, probably of Hecla Hoek age, a series similar in lithology to those in the Kongsfjorden region. Their structure and metamorphic condition fit in with the general picture of Caledonian trend and of increasing orogenic activity westwards. Later faulting along the western edge of a graben has broken this ground up into independent blocks as witnessed by the disposition of the Devonian conglomerates. The youngest rocks are a southerly outlier of the plateau basalts best seen around Woodfjorden, remnants of at least two flows are preserved, both of olivine basalt rich in olivine phenocrysts and carrying inclusions of a more alkaline rock type.

An enriched mantle source for Italy's melilitite-carbonatite association as inferred by its Nd-Sr isotope signature

2000 ◽  
Vol 64 (4) ◽  
pp. 625-639 ◽  
Author(s):  
F. Castorina ◽  
F. Stoppa ◽  
A. Cundari ◽  
M. Barbieri
Keyword(s):  
South African ◽  
Mantle Source ◽  
Volcanic Rocks ◽  
Poor Correlation ◽  
Nd Isotope ◽  
Origin And Evolution ◽  
Enriched Mantle ◽  
Assimilation Process ◽  
Western Australian ◽  
Limestone Assimilation

AbstractNew Sr-Nd isotope data were obtained from Late Pleistocene carbonatite-kamafugite associations from the Umbria-Latium Ultra-Alkaline District of Italy (ULUD) with the aim of constraining their origin and possible mantle source(s). This is relevant to the origin and evolution of ultrapotassic (K/Na ≫2) and associated rocks generally, notably the occurrences from Ugandan kamafugites,Western Australian lamproites and South African orangeites. The selected ULUD samples yielded 87Sr/86Sr and 143Nd/144Nd ranging from 0.7100 to 0.7112 and from 0.5119 to 0.5121 respectively, similar to cratonic potassic volcanic rocks with higher Rb/Sr and lower Sm/Nd ratios than Bulk Earth. Silicate and carbonate fractions separated from melilitite are in isotopic equilibrium, supporting the view that they are cogenetic. The ULUD carbonatites yielded the highest radiogenic Sr so far reported for carbonatites. In contrast, sedimentary limestones from ULUD basement formations are lower in radiogenic Sr, i.e. 87Sr/86Sr = 0.70745–0.70735. The variation trend of ULUD isotopic compositions is similar to that reported for Ugandan kamafugites and Western Australian lamproites and overlaps the values for South African orangeites in the εSr-εNd diagram. A poor correlation between Sr/Nd and 87Sr/86Sr ratios in ULUD rocks is inconsistent with a mantle source generated by subduction-driven processes, while the negligible Sr and LREE in sedimentary limestones from the ULUD region fail to account for a hypothetical limestone assimilation process. The Nd model ages of 1.5–1.9 Ga have been inferred for a possible metasomatic event, allowing further radiogenic evolution of the source, a process which may have occurred in isolation until eruption time. While the origin of this component remains speculative, the Sr-Nd isotope trend is consistent with a simple mixing process involving an OIB-type mantle and a component with low εNd and high εSr.

scholarly journals Mineral chemistry and thermobarometry of the staurolite-chloritoid schists from Poshtuk, NW Iran

2012 ◽  
Vol 149 (6) ◽  
pp. 1077-1088 ◽  
Author(s):  
ADEL SAKI ◽  
MOHSSEN MOAZZEN ◽  
ROLAND OBERHÄNSLI
Keyword(s):  
Mineral Chemistry ◽  
High Heat ◽  
Contact Metamorphism ◽  
Textural Features ◽  
High Heat Flow ◽  
Alpine Orogeny ◽  
Nw Iran ◽  
Metamorphic Assemblage ◽  
Northwestern Iran ◽  
Magmatic Intrusions

AbstractThe Poshtuk metapelitic rocks in northwestern Iran underwent two main phases of regional and contact metamorphism. Microstructures, textural features and field relations indicate that these rocks underwent a polymetamorphic history. The dominant metamorphic assemblage of the metapelites is garnet, staurolite, chloritoid, chlorite, muscovite and quartz, which grew mainly syntectonically during the later contact metamorphic event. Peak metamorphic conditions of this event took place at 580 °C and ~3–4 kbar, indicating that this event occurred under high-temperature and low-pressure conditions (HT/LP metamorphism), which reflects the high heat flow in this part of the crust. This event is mainly controlled by advective heat input through magmatic intrusions into all levels of the crust. These extensive Eocene metamorphic and magmatic activities can be associated with the early Alpine Orogeny, which resulted in this area from the convergence between the Arabian and Eurasian plates, and the Cenozoic closure of the Tethys oceanic tract(s).

Metamorphic processes at high temperature and low pressure: the petrogenesis of the metasomatized and assimilated rocks of Carneal, Co. Antrim

1975 ◽  
Vol 280 (1294) ◽  
pp. 225-269 ◽  
Keyword(s):  
High Temperature ◽  
Low Pressure ◽  
Small Scale ◽  
New Mineral ◽  
Chemical Analyses ◽  
Rock Types ◽  
Silica Ratio ◽  
Rock Suite ◽  
Metasomatic Replacement ◽  
Limestone Assimilation

The Tertiary dolerite plug at Carneal cuts basalt lavas and incorporates blocks of chalk and flint from underlying Cretaceous rocks. Assimilation by the dolerite of the pure limestone and flint took place under the very rare highest-temperature, low-pressure conditions. Only about twenty-five examples of the resulting metamorphosed and metasomatized rocks are known in the world, few fully described. The rock suite enables the conditions and mechanisms of assimilation to be deduced. The pressure, about 200 x 10 5 Pa (200 bar), and the temperature, estimated as 1050-1100 °C, produced an exomorphic suite of larnite, spinel, merwinite, spurrite, scawtite and related assemblages, with wollastonite, quartz, plagioclase, hydrogrossular, xonotlite and related minerals representing flint. Complementary desilication of the igneous rocks gives the endomorphic suite of pyroxene-rich dolerite, pyroxenite, titanaugitemelilite-rock and aegirine- and nepheline-bearing types. Chemical analyses o titanaugite, sahlite, melilite, wollastonite and the main rock types are provided and optical and other properties of the minerals. Two related mechanisms of limestone assimilation occurred. Most of the rocks resulted from the incorporation of the chalk in the olivine-dolerite magma, paradoxically, the addition of 18-26 % CaO to the dolerite magma so lowers the silica ratio that 17-18% additional S i0 2 is required to produce the endomorphic hybrids, with the complementary exomorphic suite. The second mechanism, a metasomatic replacement, preserves existing mineral (and fossil) textures. Mineral textures and the preservation of a cyclostome bryozoan now composed of wollastonite (by silicification of calcite) show the metasomatism to have been a tranquil process despite the high temperature. To produce the vein assemblage of merwinite, hydrogrossular and melilite, this mechanism required 63 % CaO and 23 % H 2 0 , an addition which is only slightly more hydrous than calcium hydroxide. These mechanisms are evidence for the production of peralkaline rocks by limestone assimilation but only on a very small scale. The retrograde phase of metamorphism produced minerals in order of approximately increasing water content, including xonotlite, bicchulite (a new mineral), thomsonite, tobermorite, tacharanite and plombierite.

scholarly journals The geology of two small layered hornblende peridotite (picrite) plutons in South Greenland

1970 ◽  
Vol 92 ◽  
pp. 1-43
Author(s):  
J.P Berrange
Keyword(s):  
Parent Magma ◽  
Contact Metamorphism ◽  
Magmatic Differentiation ◽  
Chemical Classification ◽  
Hornblende Gabbro ◽  
Gravity Settling ◽  
A Minor ◽  
Chemical Evidence

Two ultramafic dykes, which pinch and swell both vertically and horizontally and have a form similar to some kimberlite bodies, were intruded 1700 to 1335 m.y. ago during the 2nd episode of Ketilidian plutonism. Contact metamorphism of the adjacent granite was slight -albite-epidote hornfels facies. Petrological, mineralogical and chemical evidence indicates that the parent magma was picritic in composition, that it underwent flowage differentiation as a result of rapid intrusion, and then magmatic differentiation with gravity settling. The internal picritic (chemical classification) layered group crystallised first and includes hornblende peridotites, hornblende-hypersthene peridotites and rare harzburgite. The border group which crystallised later is formed of hypersthene-olivine hornblendites that chemically are picrites, and mica hornblendites that chemically are monzonites with affinities to kentallenite. Hornblende gabbro is a minor late differentiate. Steeply dipping banding cuts the earlier rhythmic layering and is thought to have formed by diffusion of material into cooling cracks developed prior to complete solidification. There are local concentrations of sulphides and platinoids. Three complete silicate analyses and a number of analyses for the platinoids, Au, Cr, Co, Cu, Ni, Ag, Pb and Zn are presented.

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