Topic
Yellow aster
About: Yellow aster is a research topic. Over the lifetime, 10 publications have been published within this topic receiving 142 citations.
Papers
TL;DR: In this paper, age determinations of zircons indicate that some of these rocks may have been derived at least in part from a >l,650m.y.-old source terrane.
Abstract: Pre-Late Cretaceous crystalline rocks in the core of the Northern Cascade Mountains of Washington are predominantly heterogeneous supracrustal gneiss and schist, and dioritic, quartz dioritic, and trondhjemitic plutons and bodies of orthogneiss. Migmatite derived from plutonic and supracrustal rocks is also widespread. Isotopic age determinations of zircons indicate that, of the supracrustal gneiss and schist, the Swakane Gneiss and possibly the Skagit Gneiss may have been deposited > 1,650 m.y. ago. Alternatively, some of these rocks may be younger but were derived at least in part from a >l,650-m.y.-old source terrane. A second group of supracrustal rocks, the Younger gneissic rocks of the Holden area, includes a metavolcanic unit about 265 m.y. old. Plutonic rocks and orthogneisses comprise four main age groups: 1,452 to 2,000 m.y., pyroxene gneiss of the Yellow Aster Complex; about 460 m.y., the Turtleback Complex of the San Juan Islands and younger orthogneiss of the Yellow Aster Complex; 220 m.y., plutonic and gneissic rocks of the Marblemount belt (Marblemount Meta-Quartz Diorite, Dumbell Mountain plutons); and 92 m.y., the Eldorado Orthogneiss. Strongly metamorphosed rocks of the Chelan Complex, chiefly quartz dioritic, have zircon Pb 206 /U 238 ages ranging from 100 to 183 m.y. These ages appear to be discordant, and the Chelan Complex may represent remobilized rocks from the 220-m.y.-old Marblemount belt. Ages of metamorphic minerals, zircons from pegmatitic material associated with migmatite, and zircons from synkinematic intrusive rocks indicate two major episodes of metamorphism in the Northern Cascade terrane, one about 415 m.y. ago and the other, 60 to 90 m.y. ago. Both episodes culminated in metamorphism to amphibolite facies grade—and in the case of the older episode, metamorphism to granulite facies grade—and both resulted in extensive migmatization of pre-existing rocks.
89 citations
TL;DR: The Vedder Complex as discussed by the authors is a high-pressure metamorphic unit of late Paleozoic age, which through the process of Mesozoic orogeny has become highly disrupted and imbricated with older and younger rocks over an extensive region.
Abstract: Tectonic fragments of schist and amphibolite that occur in the North Cascades of Washington near Groat Mountain, and in southern British Columbia on Vedder Mountain, yield Rb-Sr dates of 229 to 285 Ma. K-Ar dates are somewhat younger, ranging from 219 to 279 Ma. Mineral compositions and assemblages indicate high-pressure metamorphism, variable from blueschist to amphibolite facies. Rocks of the same age and metamorphic grade occur as tectonic slivers in the San Juan Islands (Garrison Schist) and as tectonic fragments at several localities in fault zones in the Chilliwack Group. The rocks are neither Yellow Aster Complex sensu striclo nor Shuksan Metamorphic Suite, with which parts were previously correlated. They are a separate high-pressure metamorphic unit of late Paleozoic age, herein called the Vedder Complex, which through the process of Mesozoic orogeny has become highly disrupted and imbricated with older and younger rocks over an extensive region.
18 citations
TL;DR: This article analyzed metavolcanic rocks of the western North Cascades of Washington, including the Chilliwack Group (CG), the Elbow Lake Formation (ELFm), and the Yellow Aster Complex (YAC), for clinopyroxene composition and whole-rock major, trace and rare-earth elements (REE9s) to determine their original chemistry and tectonic setting.
Abstract: Metavolcanic rocks of the western North Cascades of Washington, including the Chilliwack Group (CG), the Elbow Lake Formation (ELFm), and the Yellow Aster Complex (YAC), have been analyzed for clinopyroxene composition and whole-rock major, trace, and rare-earth elements (REE9s) to determine their original chemistry and tectonic setting. Covariant trends, elemental abundances, and ratios of high field-strength elements (HFSE9s) and REE9s indicate that the previously correlated CG and ELFm, and possibly equivalent basalts of the YAC, are separate rock units which evolved in distinct tectonic settings. Volcanic flows within the upper part of the upper Paleozoic CG are composed of tholeiitic basalt with lesser basaltic andesite and minor dacite. The CG originated as an intraoceanic island arc. Volcanic rocks of the ELFm are largely alkalic basalt, distinguished from the CG by HFSE enrichment and low Y/Nb and Zr/Nb. The ELFm is interpreted to represent structurally dismembered oceanic islands of Pennsylvanian to Jurassic age. An affinity with the Cache Creek terrane is suggested by correlation with the Orcas Chert of the San Juan Islands, which bears a Tethyan fauna. Basalt dikes of the YAC are of continental affinity, perhaps produced during an episode of continental rifting. High Cr and Ni contents, large-ion lithophile element enrichment, and transitional REE patterns distinguish YAC dikes from the CG and ELFm.
15 citations
1 Jan 1992
TL;DR: In this paper, single-grain zircon U-Pb data and Sm-Nd model ages were used to demonstrate that the swakane gneiss is a metaclastic rock derived from rocks of Middle Proterozoic age.
Abstract: Uncertainties regarding the protolith, age, and tectonic affinity of the Swakane gneiss (Swg), Skagit gneiss (Skg), and Yellow Aster complex (YAc) have long been obstacles to deciphering the tectonic history of the North Cascades. Single-grain zircon U-Pb data and Sm-Nd model ages now demonstrate these units are genetically unrelated metasediments derived from Early Proterozoic and younger sources. Zircon populations from Swg samples include rounded, subrounded, and euhedral grains. Three of four analyzed grains define a well-correlated discordia array that intercepts concordia at 1.4 Ga whereas the fourth grain has a 1.6 Ga 207Pb/206Pb age. the Sm-Nd depleted mantle model ages of two samples of Swg are 1.18 Ga and 1.27 Ga. The authors suggest that the Swg gneiss is a metaclastic rock derived chiefly from rocks of Middle Proterozoic age. A single analyzed zircon crystal extracted from garnet-biotite yields a nearly concordant age of 0.14 Ga. The YAc consists of fragments of metaplutonic rocks and quartz-pyroxene gneisses of uncertain protolith that are imbricated with Paleozoic and Mesozoic rocks of the Cretaceous Northwest Cascades thrust system. U-Pb data from 6 single zircons extracted from mylonitic quartz-pyroxene gneiss are interpreted to indicate the presence of Grenville orogen-derived grains of ca 0.9--1.3 Gamore » age whereas one analyzed zircon has an ca 0.6 Ga age. Analyses of abraded zircons from a post-mylonitic pegmatite dike indicate pegmatite crystallization at ca0.22 Ga and imply the presence of ca1.85 Ga xenocrystic zircons.« less
10 citations
TL;DR: In this article, a group of men gathered around a fire with a good supply of punch and cigars are described as having a high premium on witty remarks and in their desultory conversations there is a great deal of laughter over subjects that range from the theater to fashion and food, from gentlemanly sports to the foibles of women.
Abstract: Picture the scene, a group of men gathered around the fire with a good supply of punch and cigars. They have nothing in particular to do but talk and enjoy themselves. They put a high premium on witty remarks and in their desultory conversations there is a great deal of laughter over subjects that range from the theater to fashion and food, from gentlemanly sports to the foibles of women (Fig. 13.1).
7 citations
Related Topics (5)
Performance Metrics
| Year | Papers |
|---|---|
| 2014 | 2 |
| 2013 | 1 |
| 2005 | 1 |
| 2000 | 1 |
| 1997 | 1 |
| 1992 | 1 |