Crustal evolution by arc magmatism

1981 ◽  
Vol 301 (1461) ◽  
pp. 279-291 ◽  
Keyword(s):  
Plate Tectonics ◽  
Granulite Facies ◽  
High Water ◽  
Magmatic Rock ◽  
Arc Magmatism ◽  
Middle Crust ◽  
Arc Magmas ◽  
Rock Types ◽  
Magmatic Rocks ◽  
Water Contents

Arc magmas generated at depths near 100 km by dehydration of subducting slabs are olivine-rich melabasalts, but the magmas that reach the surface in mature continental magmatic arcs have an average composition near that of rhyodacite. Depth-varying fractionations and equilibrations profoundly modify the initial magmas. Plate tectonics has operated throughout Proterozoic and Phanerozoic time much as it does now, and so many deeply eroded terrains must expose products of arc magmatism. Most exposed middle and deep continental crust consists of igneous rocks plus older rocks equilibrated at magmatic temperatures, variably deformed and metamorphosed subsequently; each crustal level displays a typical assemblage of magmatic rock types, which are here deduced to be products mostly of arc magmatism. Pre-arc mantle consists of depleted dunite and harzburgite. Rising arc magmas precipitate much additional olivine, and add the equivalent of 10 or 15% of basalt in clinopyroxene, orthopyroxene, garnet and spinel. The seismic M. discontinuity may be controlled primarily by the shallow limit of the depth zone in which crystallization is mostly of ultramafic components, and the fractionated magmas that reach the crust are mostly of gabbroic to granodioritic compositions. The lower crust is characterized by differentiated layered complexes, which often contain mafic or ultramafic basal cumulates, medial floated-plagioclase anorthosite, and upper quartz-poor pyroxene—mesoperthite granites, and by other magmatic rocks. Magmatic rocks are more voluminous than pre-existing rocks. Supracrustal rocks are in middle granulite facies, and much granitic material has been melted from them by magmatic heat. The magmatically modified middle crust consists primarily of migmatites in lower granulite facies in the deeper part, and upper amphibolite facies in the shallower part. Much dissociation of hydrous mineral assemblages is caused by the magmatic heat, producing water-rich, aluminous magmas, assimilation and anatexis. The high water contents restrict rise of the equilibrated magmas; voluminous pegmatites are expelled into the wall rocks, and crystallization is forced. Sheets of two-mica granites characterize the upper part of the middle crust. The comparatively dry magmas that rise into the upper crust are mostly tonalite to adamellite. These magmas spread out in steep-sided batholiths above the migmatites, erupt as ash flow sheets from calderas, and produce voluminous far-travelling volcanic ash. Inverted metamorphic gradients and outward-verging structures are produced beneath the spreading batholiths. Magmatic arcs are extensional at all crustal levels.

scholarly journals Petrogenesis of Secondary Diatexites and the Melt Budget for Crustal Reworking

2020 ◽  
Vol 61 (3) ◽  
Author(s):  
E W Sawyer
Keyword(s):  
Mass Balance ◽  
Partial Melting ◽  
Rock Type ◽  
Granulite Facies ◽  
Initial Amount ◽  
Middle Crust ◽  
Rock Types ◽  
Mass Balance Models ◽  
Crustal Reworking

Abstract This study investigates the petrogenesis of diatexite migmatites and leucogranites in a granulite facies terrain and quantifies the melt budget for it. The anatectic rock types in the Ashuanipi Subprovince are: (1) melt-depleted orthopyroxene metatexite migmatite, (2) secondary diatexite migmatite formed where anatectic melt intruded, entrained and accumulated in the metatexite, and (3) leucogranite. The FeO, MgO, TiO2, Cr, Co and Sc contents of the diatexites are controlled by the fraction of entrained metatextite. However, most diatexites and many leucogranites are richer in (Na2O+CaO) but depleted in K2O relative to an anatectic melt + metatexite mixture. This, and the predominance of plagioclase + orthopyroxene frameworks in the diatexites, indicates loss of fractionated melt. Mass-balance models using the metatexite and compositions of fractionated melts and crystallised solids obtained from simulated crystallisation of the anatectic melt indicate that ‘typical’ diatexite formed by mixing ∼40% metatexite with ∼60% anatectic melt, and then when 8 to 30% crystallised, most (>73%) of the remaining melt was expelled, likely by shear-enhanced compaction. The processes making the diatexites and leucogranites expelled ∼50% of the initial amount of melt; some formed the K2O-rich leucodiatexites and leucogranites in the terrain, but most escaped. A melt budget for the present Ashuanipi surface made by combining mass-balance calculations and the area of each rock type reveals that it once held 3.05 times more melt than was generated there. The adjacent Opinaca Subprovince contains 10 times more leucogranite than partial melting there produced; moreover, its leucogranites are compositionally similar to fractionated melts expelled from the Ashuanipi. Combining these crustal levels and assuming a gradient of 30oC km-1, then ∼400 000 km3 of melt representing >68% of the total generated during crustal reworking in the Ashuanipi remained in the middle crust where temperatures were above the solidus.

High water contents in Tonga arc magmas

2006 ◽  
Vol 70 (18) ◽  
pp. A111
Author(s):  
L.B. Cooper ◽  
T. Plank ◽  
R.J. Arculus
Keyword(s):  
High Water ◽  
Arc Magmas ◽  
Water Contents

A review of the composition and evolution of hydrocarbon gases during solidification of the Ilímaussaq alkaline complex, South Greenland

2001 ◽  
pp. 159-166 ◽  
Author(s):  
Jens Konnerup-Madsen
Keyword(s):  
Nepheline Syenite ◽  
Subsequent Development ◽  
High Water ◽  
Vapour Phase ◽  
Low Carbon ◽  
Low Oxygen ◽  
Alkaline Complex ◽  
Hydrocarbon Gases ◽  
Wide Range ◽  
Water Contents

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Konnerup-Madsen, J. (2001). A review of the composition and evolution of hydrocarbon gases during solidification of the Ilímaussaq alkaline complex, South Greenland. Geology of Greenland Survey Bulletin, 190, 159-166. https://doi.org/10.34194/ggub.v190.5187 _______________ Fluid inclusions in minerals from agpaitic nepheline syenites and hydrothermal veins in the Ilímaussaq complex and in similar agpaitic complexes on the Kola Peninsula, Russia, are dominated by hydrocarbon gases (predominantly methane) and hydrogen. Such volatile compositions differ considerably from those of most other igneous rocks and their formation and entrapment in minerals reflects low oxygen fugacities and a wide range of crystallisation temperatures extending to a low-temperature solidus. Their composition reflects initial low carbon contents and high water contents of the magma resulting in the exsolution of a waterrich CO2–H2O dominated vapour phase. Fractionation of chlorides into the vapour phase results in high salinities and the subsequent development of a heterogeneous vapour phase with a highly saline aqueous-rich fraction and a methane-dominated fraction, with preferential entrapment of the latter, possibly due to different wetting characteristics. The light stable isotope compositions support an abiogenic origin for the hydrocarbons in agpaitic nepheline syenite complexes.

Constraints on the formation of the giant Daheishan porphyry Mo deposit (NE China) from whole-rock and accessory mineral geochemistry

2021 ◽  
Author(s):  
Kai Xing ◽  
Qihai Shu ◽  
David R Lentz
Keyword(s):  
High Water ◽  
Accessory Mineral ◽  
Ne China ◽  
Accessory Minerals ◽  
Slab Rollback ◽  
Continental Arc ◽  
Arc Setting ◽  
Porphyry Mo Deposit ◽  
T Values ◽  
Water Contents

Abstract There are more than 90 porphyry (or skarn) Mo deposits in northeastern China with Jurassic or Cretaceous ages. These are thought to have formed mainly in a continental arc setting related to the subduction of the Paleo-Pacific oceanic plate in the Jurassic and subsequent slab rollback in the early Cretaceous. The Jurassic Daheishan porphyry Mo deposit is one of the largest Mo deposits in NE China, which contains 1.09 Mt Mo with an average Mo grade of 0.07%. To better understand the factors that could have controlled Mo mineralization at Daheishan, and potentially in other similar porphyry Mo deposits in NE China, the geochemical and isotopic compositions of the ore-related granite porphyry and biotite granodiorite, and the magmatic accessory minerals apatite, titanite and zircon from the Daheishan intrusions, were investigated so as to evaluate the potential roles that magma oxidation states, water contents, sulfur and metal concentrations could have played in the formation of the deposit. Magmatic apatite and titanite from the causative intrusions show similar εNd(t) values from -1.1 to 1.4, corresponding to TDM2 ages ranging from 1040 to 840 Ma, which could be accounted for by a mixing model through the interaction of mantle-derived basaltic melts with the Precambrian lower crust. The Ce and Eu anomalies of the magmatic accessory minerals have been used as proxies for magma redox state, and the results suggest that the ore-forming magmas are highly oxidized, with an estimated ΔFMQ range of + 1.8 to + 4.1 (+2.7 in average). This is also consistent with the high whole-rock Fe2O3/FeO ratios (1.3–26.4). The Daheishan intrusions display negligible Eu anomalies (Eu/Eu* = 0.7–1.1) and have relatively high Sr/Y ratios (40–94) with adakitic signatures; they also have relatively high Sr/Y ratios in apatite and titanite. These suggest that the fractionation of amphibole rather than plagioclase is dominant during the crystallization of the ore-related magmas, which further indicates a high magmatic water content (e.g., >5 wt%). The magmatic sulfur concentrations were calculated using available partitioning models for apatite from granitoids, and the results (9–125 ppm) are indistinguishable from other mineralized, subeconomic and barren intrusions. Furthermore, Monte Carlo modelling has been conducted to simulate the magmatic processes associated with the formation of the Daheishan Mo deposit, and the result reveals that a magma volume of ∼280 km3 with ∼10 ppm Mo was required to form the Mo ores containing 1.09 Mt Mo in Daheishan. The present study suggests that a relatively large volume of parental magmas with high oxygen fugacities and high water contents is essential for the generation of a giant porphyry Mo deposit like Daheishan, whereas a specific magma composition (e.g., with unusually high Mo and/or S concentrations), might be less critical.

A comprehensive review on the medicinal importance; biological and therapeutic efficacy of Lagenaria siceraria (Mol.) (bottle gourd) Standley fruit

2021 ◽  
Vol 21 ◽  
Author(s):  
Muhammad Zahoor ◽  
Muhammad Ikram ◽  
Nausheen Nazir ◽  
Sumaira Naz ◽  
Gaber El-Saber Batiha ◽  
...  
Keyword(s):  
Herbal Medicines ◽  
High Water ◽  
Bottle Gourd ◽  
Herbal Remedies ◽  
Lagenaria Siceraria ◽  
Synthetic Drugs ◽  
Domestic Plant ◽  
Phytochemical Constituents ◽  
Cucurbitaceae Family ◽  
Water Contents

: Herbal remedies have been employed for the treatment and management of different diseases for ages. Herbal medicines are a promising choice over modern synthetic drugs because of their low side effects and are thus considered safe and effective in treating human diseases. Lagenaria siceraria (Mol.) Standley fruit (Bottle gourd) belongs to the Cucurbitaceae family that has been used in a different system of traditional medication to treat various diseases. This is a domestic plant that provides food as well as medication. This vegetable has low caloric values and high water contents. The edible portion of it contains phytochemicals like vitamins, proteins, choline, minerals, terpenoids, flavonoids etc. Several bioactive compounds have been isolated from L. siceraria, including triterpenoids, sterols, cucurbitacins, flavones, C-glycosides and β-glycosides. Researchers have evaluated various parts of this plant viz., fruit, root, flowers, and leaves for pharmacological activities like antianxiety, antidepressant, diuretic, antimicrobial, cytotoxic, antihyperlipidemic, cardioprotective, analgesic, anti-inflammatory, anthelmintic, anti-hyperglycemic, antihepatotoxic, anti-urolithiatic, antistress, antiulcer, anticancer, hepatoprotective, anthelmintic, immunomodulatory, and antioxidant. In this review, an attempt has been made to explore its phytochemical constituents, traditional, medicinal, and pharmacological uses to highlight the therapeutic importance of this well-known plant. This would be helpful in reviving its importance and highlight its several promising aspects to encourage researchers for further research on L. siceraria.

Monomeric and aggregation emissions of tetraphenylethene in a photo-switchable polymer controlled by cyclization of diarylethene and solvent conditions

2017 ◽  
Vol 5 (38) ◽  
pp. 9952-9962 ◽  
Author(s):  
Ravinder Singh ◽  
Hsin-Yen Wu ◽  
Atul Kumar Dwivedi ◽  
Ashutosh Singh ◽  
Chien-Min Lin ◽  
...  
Keyword(s):  
High Water ◽  
Water Contents

AIE behaviour of TPE with open and closed forms of DAE in a photo-switchable polymer is studied in high water contents.

scholarly journals Soil Disturbance and the Potential for Erosion After Mechanical Site Preparation

2002 ◽  
Vol 19 (1) ◽  
pp. 5-13 ◽  
Author(s):  
Jorge Alcázar ◽  
Paul M. Woodard ◽  
Richard L. Rothwell
Keyword(s):  
Soil Erosion ◽  
Mineral Soil ◽  
High Water ◽  
Soil Disturbance ◽  
Site Preparation ◽  
Treatment Area ◽  
Soil Movement ◽  
Mechanical Site Preparation ◽  
Physical Conditions ◽  
Water Contents

Abstract Physical soil properties created by three mechanical site preparation treatments (ripper ploughing, disc trenching, and blading) and a control were evaluated to determine the success of these different mechanical site preparation treatments in creating plantable microsites and to estimate the potential for soil erosion created by each treatment. Three sites with fine textured soils and high water contents near Whitecourt, Alberta, Canada), were selected for study. The topography at all sites was similar and characterized by slopes 3.7 to 20% in steepness and approximately 190 to 270 m in length extending from the height of land to stream bottoms. The number of planting sites and the soil characteristics suggest ripper ploughing as the best site preparation treatment in this study, with the hinge microsite as the preferred planting spot. All three treatments significantly improved the physical conditions of the soil compared to the control, although the differences among treatments were small. Soil erosion was observed on areas where blading and ripper ploughing exposed mineral soil. Gullies, which exposed the roots of seedlings, were created by water erosion in the blading treatment area. Sediment deposition in trenches was observed on ripper ploughed areas, and at times, seedlings within this treatment area were partially buried as a result of this soil movement.

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