Isotopic evidence for the sources of Cretaceous and Tertiary granitic rocks, east-central Alaska: implications for the tectonic evolution of the Yukon-Tanana Terrane

2000 ◽  
Vol 37 (6) ◽  
pp. 945-956 ◽  
Author(s):  
John N Aleinikoff ◽  
G Lang Farmer ◽  
Robert O Rye ◽  
Warren J Nokleberg
Keyword(s):  
Tectonic Evolution ◽  
Crystalline Rocks ◽  
Pb Isotopes ◽  
Granitic Rocks ◽  
Conductive Layer ◽  
Pb Isotope ◽  
East Central ◽  
Mafic Rocks ◽  
O Isotopes ◽  
Mantle Magma

Magnetotelluric traverses across the southern Yukon-Tanana terrane (YTT) reveal the presence of a thick conductive layer (or layers) beneath Paleozoic crystalline rocks. These rocks have been interpreted to be flysch of probable Mesozoic age, on the basis of the occurrence of Jurassic-Cretaceous flysch in the Kahiltna assemblage and Gravina-Nutzotin belt flanking the YTT to the southwest and southeast, respectively. The Pb, Nd, Sr, and O isotopes in Cretaceous and Tertiary granitic rocks that crop out throughout the YTT were measured to determine if these rocks do in fact contain a component of flysch. Previous limited analyses indicated that the Pb isotopes of the granitic rocks could be a mixture of radiogenic Pb derived from Paleozoic crystalline rocks of the YTT with an increasing component of relatively nonradiogenic Pb with decreasing age. Our Nd, Sr, and O data, along with additional Pb isotope data, eliminate flysch as a likely source and strongly suggest that the nonradiogenic end-member was derived from mafic rocks, either directly from mantle magma or by melting of mafic crust. The lack of a sedimentary component in the granitic plutons suggests either that the plutons did not incorporate significant amounts of flysch during intrusion or that the conductive layer beneath the YTT crystalline rocks is not flysch.

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.

The oxygen isotope composition of the surface crystalline rocks of the Canadian Shield

1978 ◽  
Vol 15 (11) ◽  
pp. 1773-1782 ◽  
Author(s):  
Yuch-Ning Shieh ◽  
Henry P. Schwarcz
Keyword(s):  
Isotope Composition ◽  
Crystalline Rocks ◽  
Canadian Shield ◽  
Granitic Rocks ◽  
Baffin Island ◽  
Grenville Province ◽  
Metasedimentary Rocks ◽  
Rock Types ◽  
Northern District ◽  
Basic Rocks

The average 18O/16O ratios of the major rock types of the surface crystalline rocks in different parts of the Canadian Precambrian Shield have been determined, using 47 composite samples prepared from 2221 individual rock specimens. The sampling areas include Baffin Island, northern and southwestern Quebec, Battle Harbour – Cartwright, northern District of Keewatin, Fort Enterprise, Snowbird Lake, Kasmere Lake, and Saskatchewan, covering approximately 1 400 000 km2. The granitic rocks from the Superior, Slave, and Churchill Provinces vary only slightly from region to region (δ18O = 6.9–8.4‰) and are significantly lower in 18O than similar rock types from the younger Grenville Province (δ = 9.2–10.0‰). The sedimentary and metasedimentary rocks have δ18O = 9.0–11.7‰ and hence are considerably lower than their Phanerozoic equivalents, possibly reflecting the presence of a high percentage of little-altered igneous rock detritus in the original sediments. The basic rocks in most regions fall within a δ18O range of 6.8–7.6‰, except in northern and southwestern Quebec where the δ-values are abnormally high (8.5–8.9‰). The overall average 18O/16O ratio of the surface crystalline rocks of the Canadian Shield is estimated to be 8.0‰, which represents an enrichment with respect to probable mantle derived starting materials by about 2‰.

Granitic rocks from Rwanda: Vital clues to the tectonic evolution of the Karagwe–Ankole Belt

Lithos ◽  
2021 ◽  
Vol 404-405 ◽  
pp. 106490
Author(s):  
Claude Nambaje ◽  
M. Satish-Kumar ◽  
Ian S. Williams ◽  
Toshiro Takahashi ◽  
K. Sajeev
Keyword(s):  
Tectonic Evolution ◽  
Granitic Rocks

Determination of the characteristics of crystalline rocks by field experiments: a review

1986 ◽  
Vol 319 (1545) ◽  
pp. 139-156 ◽  
Keyword(s):  
Radioactive Waste ◽  
Field Experiments ◽  
The United States ◽  
Crystalline Rocks ◽  
Granitic Rocks ◽  
Rock Types ◽  
Basement Rocks ◽  
Deep Boreholes ◽  
High Level ◽  
Underground Research Laboratory

Crystalline rocks, particularly granitic rocks and basalts, are one of the principal rock types under consideration as a potential host rock for a high-level radioactive waste repository. Permeability in such rocks is related to discontinuities of various scales, and the quantification and prediction of groundwater flow within both the fractures and the intact rock between the fractures is the major goal of field experiments. The Canadian Underground Research Laboratory is unique in that the hydrogeological conditions within a large volume of rock surrounding the experimental shaft are being monitored before, during and after excavation and the results compared with model predictions. In Switzerland twelve deep boreholes are being drilled to over 1000 m to investigate crystalline basement rocks beneath a cover of sediments. The Stripa Mine in Sweden has hosted a major experimental programme including heater tests to stimulate the thermal effect of radioactive waste and hydrogeological tests at various scales down to individual fractures. The United States of America, the United Kingdom, France and Finland have also embarked on major experimental programmes. Continuing research is needed, with an emphasis on field experiments and research in underground rooms, to provide the data on which detailed risk assessments can be based.

Development of sulfide reference materials for in situ platinum group elements and S–Pb isotope analyses by LA-(MC)-ICP-MS

2018 ◽  
Vol 33 (12) ◽  
pp. 2172-2183 ◽  
Author(s):  
Yantong Feng ◽  
Wen Zhang ◽  
Zhaochu Hu ◽  
Yongsheng Liu ◽  
Kang Chen ◽  
...  
Keyword(s):  
Hydrothermal Synthesis ◽  
Reference Materials ◽  
Platinum Group Elements ◽  
Pb Isotopes ◽  
Synthetic Method ◽  
Pb Isotope ◽  
Icp Ms ◽  
Platinum Group ◽  
Isotope Analyses

A new synthetic method has been used to prepare sulfide reference materials for the in situ analysis of PGEs and S–Pb isotopes. The results indicate that the hydrothermal synthesis of the nanoparticles can serve as a potentially effective approach for the preparation of microanalysis reference materials.

The distribution of gold and silver in the crystalline rocks of the Malvern Hills

1936 ◽  
Vol 24 (152) ◽  
pp. 260-264 ◽  
Author(s):  
A. Brammall ◽  
D. L. Dowie
Keyword(s):  
Spectroscopic Data ◽  
Senior Author ◽  
Crystalline Rocks ◽  
Igneous Rocks ◽  
Granitic Rocks ◽  
Image Position

In re-examining the crystalline rocks of the Malvern Hills, the senior author has had occasion to apply quantitative spectroscopic data for the rarer constituents of hornblendes and micas. The recognition of silver in the spectrograms of biotite led to tentative fire-assays of granitic rocks in bulk-a procedure which revealed the presence also of gold.The assay results for this preliminary suite of granitic types are given below; values less than 5 grains per ton are returned as 'traces':The higher values appear to be related to the reddening of the felspars, which is a widespread 'late' pneumatolytic effect; it is conspicuous in the major granite masses and related pegmatites, but somewhat local and 'arterial' in its distribution over rocks of pre granite age. Among the igneous rocks of post-granite age, the intrusive granophyric quartz-diabase ('Ivy Scar' type) shows only feeble reddening; the newer dolerites are unaffected.

U-Pb Isotope Geochronology and Granitic Gneisses Nanoparticles from the Xiaomei Shear Zone: Implication for Caledonian Tectonic in the Hainan Island, China

2020 ◽  
Vol 12 (1) ◽  
pp. 39-47
Author(s):  
Zhou Yang ◽  
Shen Baoyun ◽  
Liu Hailing ◽  
Yan Yi ◽  
Yan Yan
Keyword(s):  
Shear Zone ◽  
Tectonic Evolution ◽  
Frictional Heating ◽  
Hainan Island ◽  
Ductile Shear Zone ◽  
Spherical Nanoparticles ◽  
Pb Isotope ◽  
Tectonic Event ◽  
Isotope Geochronology ◽  
Early Devonian

U-Pb ages of zircons from the granitic gneisses in the Xiaomei shear zone, Hainan Island, provide constraints on the age of granitic gneisses and tectonic evolution of Caledonian orogeny in Hainan Island. Zircons extracted from granitic gneisses are rounded and subrounded and characterized by oscillatory overgrowths enclosing inherited cores. The Early Devonian (414–411 Ma) ages of inherited zircons from the Xiaomei granitic gneisses are consistent with tectonic event that uplifted the Hainan island, resulting in the absence of Devonian strata. Meanwhile, nanoparticles are found in the granitic gneisses, including agglomerated nanoparticles and spherical nanoparticles in the ductile shear zone. The spherical nanoparticles in the shear zone are believed to have experienced a two-stage formation, from the linear spherical nanoparticles to planar spherical nanoparticles. With rise in temperature due to frictional heating during the shearing, spherical nanoparticles are deformed to agglomerated nanoparticles and the inherited zircons probably are recrystallized at 411 Ma.

Sign in / Sign up

Export Citation Format

Share Document