scholarly journals Melilite-bearing rocks within alkaline-ultrabasic complexes: derivatives from SiO2-poor, Ca-rich mantle magma?

2019 ◽  
Keyword(s):  
Mantle Magma

Seismic tomography model reveals mantle magma sources of recent volcanic activity at El Hierro Island (Canary Islands, Spain)

2014 ◽  
Vol 199 (3) ◽  
pp. 1739-1750 ◽  
Author(s):  
Araceli García-Yeguas ◽  
Jesús M. Ibáñez ◽  
Ivan Koulakov ◽  
Andrey Jakovlev ◽  
M. Carmen Romero-Ruiz ◽  
...  
Keyword(s):  
Canary Islands ◽  
Volcanic Activity ◽  
Seismic Tomography ◽  
Recent Volcanic Activity ◽  
El Hierro ◽  
Magma Sources ◽  
Mantle Magma

Isotopic data bearing on the origin of Mesozoic and Tertiary granitic rocks in the western United States

1984 ◽  
Vol 310 (1514) ◽  
pp. 743-753 ◽  
Keyword(s):  
Granitic Rocks ◽  
Precambrian Basement ◽  
Regional Survey ◽  
Regional Patterns ◽  
Peraluminous Granite ◽  
Isotopic Compositions ◽  
Geographic Coverage ◽  
Magma Flux ◽  
Archean Basement ◽  
Mantle Magma

A regional survey of initial Nd and Sr isotopic compositions has been done on Mesozoic and Tertiary granitic rocks from a 500 000 km 2 area in California, Nevada, Utah, Arizona, and Colorado. The plutons, which range in composition from quartz diorite to monzogranite, are intruded into accreted oceanic geosynclmal terrains in the west and north and into Precambrian basement in the east. Broad geographic coverage allows the data to be interpreted in the context of the regional pre-Mesozoic crustal structure. Initial Nd isotopic compositions exhibit a huge range, encompassing values typical of oceanic magmatic arcs and Archean basement. The sources of the magmas can be inferred from the systematic geographic variability of Nd isotopic compositions. The plutons in the accreted terrains represent mantle-derived magma that assimilated crust while differentiating at deep levels. Those emplaced into Precambrian basement are mainly derived from the crust. The regional patterns can be understood in terms of: (1) the flux of mantle magma entering the crust; (2) crustal thickness; and (3) crustal age. The mantle magma flux apparently decreased inland; in the main batholith belts purely crustal granitic rocks are not observed because the flux was too large. Inland, crustal granite is common because mantle magma was scarce and the crust was thick, and hot enough to melt. The values of peraluminous granite formed by melting of the Precambrian basement depend on the age of the local basement source.

Tonalites in crustal evolution

1981 ◽  
Vol 301 (1461) ◽  
pp. 293-303 ◽  
Keyword(s):  
Partial Melting ◽  
Plate Tectonics ◽  
Mafic Magma ◽  
Wall Rock ◽  
Continental Margins ◽  
Geological Time ◽  
Roof Rocks ◽  
Basaltic Crust ◽  
Dominant Part ◽  
Mantle Magma

Tonalites, including trondhjemite as a variety, played three roles through geological time in the generation of Earth’s crust. Before about 2.9 Ga ago they were produced largely by simple partial melting of metabasalt to give the dominant part of Archaean grey gneiss terranes. These terranes are notably bimodal; andesitic rocks are rare. Tonalites played a crucial role in the generation of this protocontinental and oldest crust 3.7- 2.9 Ga ago in that they were the only low-density, high-SiO 2 rocks produced directly from basaltic crust. In the enormous event giving the greenstone-granite terranes, mostly 2.8-2.6 Ga ago, tonalites formed in lesser but still important proportions by partial melting of metabasalt in the lower regions of down-buckled greenstone belts and by remobilization of older grey gneisses. Tectonism in the Archaean (3.9- 2.5 Ga ago) perhaps was controlled by small-cell convection (McKenzie & Weiss 1975). Little or no ophiolite or eclogite formed, and only minor andesite. Plate tectonics of modern type (involving large, rigid plates) commenced in the early Proterozoic. Uniformitarianism thus goes back one-half of the age of the earth. Tonalites compose about 5-10 % of crust generated in Proterozoic and Phanerozoic time at convergent oceanic-continental margins. They occur here as minor to prominent members of the compositionally continuous continental-margin batholiths. A simple model of generation of these batholiths is offered: mantle-derived mafic magma pools in the lower crust above a subduction zone reacts with and incorporates wall-rock components (Bowen 1922), and breaches its roof rocks as an initial diapir. This mantle magma also develops a gradient of partial melting in its wall rocks. This wall-rock melt accretes in the collapsed chamber and moves up the conduit broached by the initial diapir, the higher, less siliceous fractions of melting first, the lower, more siliceous (and further removed) fractions of melting last. The process gives in the optimum case a mafic-to-siliceous sequence of diorite or quartz diorite through tonalite or quartz monzodiorite to granodiorite and granite. The model implies that great masses of cumulate phases and refractory wall rock form the roots of continentalmargin batholiths, and that migmatites overlie that residuum and underlie the batholiths.

Evolution of the late Pleistocene Mojanda–Fuya Fuya volcanic complex (Ecuador), by progressive adakitic involvement in mantle magma sources

2008 ◽  
Vol 71 (3) ◽  
pp. 233-258 ◽  
Author(s):  
Claude Robin ◽  
Jean-Philippe Eissen ◽  
Pablo Samaniego ◽  
Hervé Martin ◽  
Minard Hall ◽  
...  
Keyword(s):  
Late Pleistocene ◽  
Volcanic Complex ◽  
Magma Sources ◽  
Mantle Magma

Continuity of the North Qilian and North Altun orogenic belts of NW China: evidence from newly discovered Palaeozoic low-Mg and high-Mg adakitic rocks

2017 ◽  
Vol 155 (8) ◽  
pp. 1684-1704 ◽  
Author(s):  
SHENG-YAO YU ◽  
JIAN-XIN ZHANG ◽  
SAN-ZHONG LI ◽  
DE-YOU SUN ◽  
YIN-BIAO PENG ◽  
...  
Keyword(s):  
Nd Isotopes ◽  
Significant Information ◽  
The North ◽  
Tectonic Processes ◽  
Adakitic Rocks ◽  
Early Palaeozoic ◽  
T Values ◽  
Orogenic Belts ◽  
North Qilian ◽  
Mantle Magma

AbstractIn this study, the petrology, zircon U–Pb ages, Lu–Hf isotopic compositions, whole-rock geochemistry and Sr–Nd isotopes for newly recognized low-Mg and high-Mg adakitic rocks from the North Altun orogenic belt were determined. The results will provide important insights for understanding the continuities of the North Qilian and North Altun orogenic belts during early Palaeozoic time. The low-Mg adakitic granitoids (445 to 439 Ma) are characterized by high SiO2 (69–70 wt %), low Mg no. (43–48) and low Cr and Ni contents. In contrast, the high-Mg adakitic granitoids (425 to 422 Ma) have relatively lower SiO2 (65–67 wt %), higher Mg no. (60–62) and higher Cr and Ni contents. The low-Mg adakitic rocks have high initial 87Sr/86Sr ratios (0.7073–0.7084), negative εNd(t) (−1.9 to −4.0) and εHf(t) values (−6.8 to −2.0), and old zircon Hf model ages (1.4–1.7 Ga). In contrast, the high-Mg adakitic rocks show lower initial 87Sr/86Sr ratios (0.7044–0.7057), higher εNd(t) (−0.7 to 3.1) and positive εHf(t) values (2.0 to 6.9), with younger zircon Hf model ages (0.9–1.2 Ga). These results suggest that the low-Mg adakitic rocks were probably generated by the partial melting of thickened crust, whereas the high-Mg adakitic rocks were derived from the anatexis of delaminated lower crust, which subsequently interacted with mantle magma upon ascent. The data obtained in this study provide significant information about the geological and tectonic processes after the closure of the Altun Ocean. The continent–continent collision and thickening probably occurred during 450–440 Ma with the formation of low-Mg adakitic rocks, and the transition of the tectonic regime from compression to extension probably occurred at 425–422 Ma with the formation of high-Mg adakitic rocks. The geochemical, geochronological and petrogenetic similarities between the North Altun and North Qilian adakitic rocks suggest that these two orogenic belts were subjected to similar tectonomagmatic processes during early Palaeozoic times.

Sign in / Sign up

Export Citation Format

Share Document