scholarly journals Supplemental Material: Secular variations of magma source compositions in the North Patagonian batholith from the Jurassic to Tertiary: Was mélange melting involved?

2021 ◽  
Author(s):  
A. Castro ◽  
et al.
Keyword(s):  
Magma Source ◽  
The North ◽  
Secular Variations

<div>Geochemical and geochronologic data.<br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div>

scholarly journals Supplemental Material: Secular variations of magma source compositions in the North Patagonian batholith from the Jurassic to Tertiary: Was mélange melting involved?

2021 ◽  
Author(s):  
A. Castro ◽  
et al.
Keyword(s):  
Magma Source ◽  
The North ◽  
Secular Variations

<div>Geochemical and geochronologic data.<br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div>

scholarly journals Secular variations of magma source compositions in the North Patagonian batholith from the Jurassic to Tertiary: Was mélange melting involved?

Geosphere ◽  
2021 ◽  
Author(s):  
Antonio Castro ◽  
Carmen Rodriguez ◽  
Carlos Fernández ◽  
Eugenio Aragón ◽  
Manuel Francisco Pereira ◽  
...  
Keyword(s):  
Magma Source ◽  
Isotopic Ratios ◽  
Secular Evolution ◽  
The North ◽  
Secular Variations ◽  
Magma Sources ◽  
Geochemical Variations ◽  
Subduction Erosion ◽  
Ultramafic Cumulates ◽  
Trench Sediments

This study of Sr-Nd initial isotopic ratios of plutons from the North Patagonian batholith (Argentina and Chile) revealed that a secular evolution spanning 180 m.y., from the Jurassic to Neogene, can be established in terms of magma sources, which in turn are correlated with changes in the tectonic regime. The provenance and composition of end-member components in the source of magmas are represented by the Sr-Nd initial isotopic ratios (87Sr/86Sr and 143Nd/144Nd) of the plutonic rocks. Our results support the interpretation that source composition was determined by incorporation of varied crustal materials and trench sediments via subduction erosion and sediment subduction into a subduction channel mélange. Subsequent melting of subducted mélanges at mantle depths and eventual reaction with the ultramafic mantle are proposed as the main causes of batholith magma generation, which was favored during periods of fast convergence and high obliquity between the involved plates. We propose that a parental diorite (= andesite) precursor arrived at the lower arc crust, where it underwent fractionation to yield the silicic melts (granodiorites and granites) that formed the batholiths. The diorite precursor could have been in turn fractionated from a more mafic melt of basaltic andesite composition, which was formed within the mantle by complete reaction of the bulk mélanges and the peridotite. Our proposal follows model predictions on the formation of mélange diapirs that carry fertile subducted materials into hot regions of the suprasubduction mantle wedge, where mafic parental magmas of batholiths originate. This model not only accounts for the secular geochemical variations of Andean batholiths, but it also avoids a fundamental paradox of the classical basalt model: the absence of ultramafic cumulates in the lower arc crust and in the continental crust in general.

Subglacial drilling at Black Rapids Glacier, Alaska, U.S.A.: drilling method and sample descriptions

1999 ◽  
Vol 45 (151) ◽  
pp. 495-505 ◽  
Author(s):  
M. Truffer ◽  
R.J. Motyka ◽  
W.D. Harrison ◽  
K. A. Echelmeyer ◽  
B. Fisk ◽  
...  
Keyword(s):  
Pore Water ◽  
Alaska Range ◽  
Denali Fault ◽  
The North ◽  
Basal Ice ◽  
Secular Variations ◽  
Drilling Method ◽  
The Matrix ◽  
Black Rapids Glacier ◽  
Tectonic Boundary

AbstractWe employed a commercial wireline drill rig to investigate the subglacial conditions of Black Rapids Glacier, a well-studied surge-type glacier in the central Alaska Range. The four main goals were: to assess the capabilities of the commercial drilling industry for sampling subglacial material, to investigate the basal morphology, to determine the subglacial geology and to emplace borehole instruments. The drilling was done in an area where seasonal and secular variations in speed are large, and where seismic studies suggested the presence of a till layer. Four holes were drilled at three locations to a maximum depth of 620 m. Three holes yielded samples of basal ice and till, although recovery of the latter was generally poor. Bedrock was sampled in one or possibly two of the holes. In the area sampled, t he glacier is underlain by a till layer some 4–7 m thick, confirming the seismic interpretation. It consists of a sandy matrix at least 20–30% of which comprises larger clasts. Limited samples of the matrix indicate that near the top of the till the porosity is 40%, and t hat some of the pore water is frozen. Geologic studies suggest that the drilling area lies to the north of the Denali Fault, a major tectonic boundary followed by the glacier, and that most of the till is locally derived with transport distances of <2 km.

New paleomagnetic data for Ochotsk-Chukotka volcanic belt

2020 ◽  
Author(s):  
Ivan Lebedev ◽  
Olesya Usanova ◽  
Tanya Fadeeva ◽  
Florian Lhuillier ◽  
Baha Eid ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Volcanic Belt ◽  
Field Work ◽  
Magnetic Fabric ◽  
Time Interval ◽  
The North ◽  
Secular Variations ◽  
North Eastern ◽  
Chukotka Volcanic Belt ◽  
Normal Polarity

&lt;p class=&quot;db9fe9049761426654245bb2dd862eecMsoNormal&quot;&gt;&lt;span lang=&quot;EN-US&quot;&gt;The Okhotsk-Chukotka volcanic belt (OChVB), &amp;#160;located in the north-eastern part of Russia, is a unique volcanic structure, which has been formed over a wide time interval from Aptian (K1) to Cenomanian (K2) [Tihomirov, 2018]. Age of its formation nearly coincides with the occurrence of the Cretaceous geomagnetic superchron of normal polarity. Thus, the volcanic formations of the OChVB represent a promising object to study the characteristics of the geomagnetic field during the Cretaceous superchron (direction, paleointensity, secular variations) needed to test various models explaining superchrons&amp;#8217;s existence .&lt;/span&gt;&lt;/p&gt; &lt;p class=&quot;db9fe9049761426654245bb2dd862eecMsoNormal&quot;&gt;&lt;span lang=&quot;EN-US&quot;&gt;During the reconnaissance field work of the summer 2019 we have sampled volcanic rocks in 9 sections each includes from 8 to 30 sites corresponding either to lava flow or to tuff layers.&lt;/span&gt;&lt;/p&gt; &lt;p class=&quot;db9fe9049761426654245bb2dd862eecMsoNormal&quot;&gt;&lt;span lang=&quot;EN-US&quot;&gt;Up to date we have carried out AF demagnetization, petromagnetic and AMS studies. Demagnetisations studies demonstrate that the rocks contain paleomagnetic record of the ancient (primary?) magnetization of good to excellent quality. Petromagnetic experiments indicate that the main magnetic mineral in majority of studied volcanics is titanomagnetite with pseudo-single domain grain size. We use the magnetic fabric derived from AMS studies to test either the modern attitude (slight dipping up to 10-15&amp;#730;) of studied rocks is due to primary paleorelief or the rocks have experienced some tectonic deformations.&lt;/span&gt;&lt;/p&gt;

scholarly journals Geology of the Frontino-Morrogacho Gold Mining District and Metallogeny of the El Cerro Igneous Complex

2021 ◽  
Vol 48 (1) ◽  
pp. 7-47
Author(s):  
Felipe Arrubla Arango ◽  
Sergio Esteban Silva Sánchez
Keyword(s):  
Lateral Displacement ◽  
Shear Zones ◽  
Magma Source ◽  
Mining District ◽  
Gold Content ◽  
Igneous Complex ◽  
The North ◽  
Western Cordillera ◽  
Metallogenic Belt ◽  
Ore Mineralogy

The Frontino-Morrogacho gold district is located on the western flank of the Western Cordillera, NW of Antioquia Province. Gold mineralizations in the area are spatially and genetically associated with the cooling  of three mid- to late-Miocene age intrusive centers in the form of stocks and dikes (12-9 Ma): Cerro Frontino,  La Horqueta and Morrogacho (El Cerro Igneous Complex). These composite magmatic pulses, with  ultramafic to intermediate compositions, vary into diorite-, gabbro- and monzonitic-bearing phases.  Mineralization in the complex is present as several structurally controlled fault veins, shear-related veins,  sheeted quartz extension veins and quartz-carbonate tabular extension veins, with the development of  swarms and nests of veins-veinlets, breccias and stockworks. Structures range from centimeter-wide  individual veinlets to several meter-wide swarms of veins developed within broad mineralized structural  corridors, with a metallic signature that consists of Au + Ag + Cu + Zn + Pb + As (± Te ± Bi ± Sb ± Hg ± W)  assemblages. Veins are composed of multiple stages of mineralization, and the formation of these  structures is enhanced by the presence of a local regime of extension and E-trending structures, including  evidence of faults and shear zones with right-lateral displacement, which are likely involved in pluton  emplacement and cooling. The ore mineralogy is composed of pyrrhotite, pyrite, chalcopyrite, sphalerite,  galena and arsenopyrite assemblages formed in two or more mineralization stages, with complex Bi, Te, Sb  and Hg mineral specimens associated with Au and Ag. Mineralized structures of the district present a preferential E-strike with dominant vertical to subvertical and occasional subhorizontal S-dips and secondary N- and NW-strikes that are steep to vertically E-dipping. The Frontino-Morrogacho Gold district presents characteristics related to the architecture, mineralogy and  alteration of reduced (ilmenite-series) intrusion-related gold systems but is genetically associated with a  parental oxidized magma source. The gold content is associated with three different families involving electrum, tellurides and alloys: gold rich (66 to 78% Au, 22 to 34% Ag), average (50 to 60% Au, 40 to 50% Ag)  and silver rich (32 to 40% Au, 60 to 68% Ag). The formation of these bodies is associated with an N-S  magmatic-metallogenic trend of Au-Ag-Cu deposits, which extend for more than 300 km along the Western  Cordillera of Colombia. Similar plutonic suites span from the south of Chocó Province to the north of Antioquia Province, which indicates that the Frontino-Farallones-Botón arc can be proposed as an individual  metallogenic belt.

Early Permian to Late Triassic tectonics of the southern Central Asian Orogenic Belt: geochronological and geochemical constraints from gabbros and granites in the northern Alxa area, NW China

2020 ◽  
Vol 157 (12) ◽  
pp. 2089-2105
Author(s):  
Run-Wu Li ◽  
Xin Zhang ◽  
Qiang Shi ◽  
Wan-Feng Chen ◽  
Yi An ◽  
...  
Keyword(s):  
Tectonic Setting ◽  
Orogenic Belt ◽  
Central Asian Orogenic Belt ◽  
Late Triassic ◽  
Magma Source ◽  
Nw China ◽  
The North ◽  
Central Asian ◽  
Depleted Mantle ◽  
Southern Central

AbstractSituated between the North China Craton to the east and the Tarim Craton to the west, the northern Alxa area in westernmost Inner Mongolia in China occupies a key location for interpreting the late-stage tectonic evolution of the southern Central Asian Orogenic Belt. New LA-ICP-MS zircon U–Pb dating results reveal 282.2 ± 3.9 Ma gabbros and 216.3 ± 3.2 Ma granites from the Yagan metamorphic core complex in northern Alxa, NW China. The gabbros are characterized by low contents of Si, Na, K, Ti and P and high contents of Mg, Ca, Al and Fe. These gabbros have arc geochemical signatures with relative enrichments in large ion lithophile elements and depletions in high field strength elements, as well as negative εNd(t) (−0.91 to −0.54) and positive εHf(t) (2.59 to 6.37) values. These features indicate that a depleted mantle magma source metasomatized by subduction fluids/melts and contaminated by crustal materials was involved in the processes of magma migration and emplacement. The granites show high-K calc-alkaline and metaluminous to weakly peraluminous affinities, similar to A-type granites. They have positive εNd(t) (1.55 to 1.99) and εHf(t) (5.03 to 7.64) values. These features suggest that the granites were derived from the mixing of mantle and crustal sources and formed in a postcollisional tectonic setting. Considering previous studies, we infer that the final closure of the Palaeo-Asian Ocean in the central part of the southern Central Asian Orogenic Belt occurred in late Permian to Early–Middle Triassic times.

Les causes du magnétisme terrestre prouvées

1851 ◽  
Vol 5 ◽  
pp. 978-979
Keyword(s):  
Diurnal Variations ◽  
The Sun ◽  
The South ◽  
Terrestrial Magnetism ◽  
Aurora Borealis ◽  
The North ◽  
The Earth ◽  
Secular Variations ◽  
Magnetic Needle

The author considers the elements of terrestrial magnetism to be, that the force with which the magnetic needle maintains its position is not everywhere the same, and that its declination and inclination vary from one region to another. These elements, he states, undergo very different modifications, which may be reduced to the following:― 1. Variations with reference to the position of the sun to the south or to the north of the equator; 2. diurnal variations in different regions of the earth; 3. disturbances which proceed from changes of weather, and from volcanic irruptions, and those which are observed during the appearance of the aurora borealis; 4. secular variations.

scholarly journals Subglacial drilling at Black Rapids Glacier, Alaska, U.S.A.: drilling method and sample descriptions

1999 ◽  
Vol 45 (151) ◽  
pp. 495-505 ◽  
Author(s):  
M. Truffer ◽  
R.J. Motyka ◽  
W.D. Harrison ◽  
K. A. Echelmeyer ◽  
B. Fisk ◽  
...  
Keyword(s):  
Pore Water ◽  
Alaska Range ◽  
Denali Fault ◽  
The North ◽  
Basal Ice ◽  
Secular Variations ◽  
Drilling Method ◽  
The Matrix ◽  
Black Rapids Glacier ◽  
Tectonic Boundary

Abstract We employed a commercial wireline drill rig to investigate the subglacial conditions of Black Rapids Glacier, a well-studied surge-type glacier in the central Alaska Range. The four main goals were: to assess the capabilities of the commercial drilling industry for sampling subglacial material, to investigate the basal morphology, to determine the subglacial geology and to emplace borehole instruments. The drilling was done in an area where seasonal and secular variations in speed are large, and where seismic studies suggested the presence of a till layer. Four holes were drilled at three locations to a maximum depth of 620 m. Three holes yielded samples of basal ice and till, although recovery of the latter was generally poor. Bedrock was sampled in one or possibly two of the holes. In the area sampled, t he glacier is underlain by a till layer some 4–7 m thick, confirming the seismic interpretation. It consists of a sandy matrix at least 20–30% of which comprises larger clasts. Limited samples of the matrix indicate that near the top of the till the porosity is 40%, and t hat some of the pore water is frozen. Geologic studies suggest that the drilling area lies to the north of the Denali Fault, a major tectonic boundary followed by the glacier, and that most of the till is locally derived with transport distances of &lt;2 km.

Sign in / Sign up

Export Citation Format

Share Document