SHRIMP U-Pb dating of high-grade migmatites and related magmatites from northwestern Oates Land (East Antarctica): evidence for a single high-grade event of Ross-Orogenic age
13
Citation
0
Reference
20
Related Paper
Citation Trend
Abstract:
High- to very-high-grade migmatitic basement rocks of the Wilson Hills area in northwestern Oates Land (Antarctica) form part of a low-pressure high-temperature belt located at the western inboard side of the Ross-orogenic Wilson Terrane. Zircon, and in part monazite, from four very-high grade migmatites (migmatitic gneisses to diatexites) and zircon from two undeformed granitic dykes from a central granulite-facies zone of the basement complex were dated by the SHRIMP U-Pb method in order to constrain the timing of metamorphic and related igneous processes and to identify possible age inheritance. Monazite from two migmatites yielded within error identical ages of 499 ± 10 Ma and 493 ± 9 Ma. Coexisting zircon gave ages of 500 ± 4 Ma and 484 ± 5 Ma for a metatexite (two age populations) and 475 ± 4 Ma for a diatexite. Zircon populations from a migmatitic gneiss and a posttectonic granitic dyke yielded well-defined ages of 488 ± 6 Ma and 482 ± 4 Ma, respectively. There is only minor evidence of age inheritance in zircons of these four samples. Zircon from two other samples (metatexite, posttectonic granitic dyke) gave scattered 206Pb-238U ages.Keywords:
Migmatite
Basement
Cite
Middle Proterozoic sequences are economically important, yet tectonically enigmatic elements of Precambrian crust in Australia. Uncertainty exists concerning their crustal evolution, assembly and stabilization, lateral and vertical extent, and geological correlation (cf., Etheridge et al. 1987, Myers et al. 1996). Debate regarding the nature of crustal evolutionary processes responsible for the assembly of Proterozoic Australia relates to the issue of whether it has long been a single intact continent characterized by intracratonic, tectonic and magmatic activity or a collage of micro continents that were assembled by plate tectonic processes (e.g., Myers et al. 1996). The Georgetown Block, also known as Georgetown Inlier (White, 1965 and Withnall et al. 1980a), occupies about 50,000 km2 of the north Queensland Cairns-Townsville hinterland. The oldest rocks in the Georgetown region described by the previous studies (until, 1998) are the Palaeoproterozoic rocks belonging to the Etheridge Province. The Etheridge Province is divided into the Forsayth and Yambo Sub provinces. Etheridge Group forms a part of Forsayth Sub province (Withnall et.al 1980a). The Einasleigh Metamorphics (part of the Etheridge Group) are interpreted by Withnall et al. (1988) as an autochthonous sequence of metasediments and metavolcanics >17 km thick which were deposited in an intracratonic rift between 1700-1650 Ma and are correlated with lower grade metasediments of the Bernecker Creek Formation. To establish a framework to better constrain the crustal evolution of Precambrian blocks in North Queensland, a regional field, petrological, geochemical, Nd-isotopic and zircon geochronological study was undertaken on the Einasleigh Metamorphics, Georgetown Block (GTB). Field mapping has shown that the Einasleigh Metamorphics are an Archaean to Palaeoproterozoic basement complex, which comprise an older orthogneissic basement and two supracrustal sequences. The orthogneissic basement gneisses (termed the Black Soil Creek Gneiss BSCG) are medium to coarse grained, compositely layered migmatitic tonalitic, trondhjemitic and granodioritic gneiss (TTG) that are cut by homogeneous sheets of grey, fine to medium, tonalitic gneiss. A suite of mafic dykes and intrudes the gneiss complex by subordinate bodies of leucogabbro and komatiitic basalt. BSCG are tectonically intercalated with a varied suite of paragneisses dominated by garnet-biotite-sillimanite gneiss and quartzite termed the Stockman Creek Gneiss (SCG). A second supracrustal package (termed Junction Creek Gneiss - JCG) comprising sillimanite-cordierite-bearing paragneisses and felsic to mafic metavolcanics (previously interpreted as calc silicate units), which lacks mafic dykes is interpreted to have been deposited on or tectonically intercalated with the BSCG and SCG. Regionally extensive syntectonic sheets and bodies of granite interpreted as crustal melts cut all of the above units. During the final phase of thermotectonism under amphibolite to granulite facies metamorphic conditions, the gneiss complex was intruded by series of large gabbroic and amphibolite dykes, which cut all of the above units. The 207Pb/206Pb ages (multiple-grain, zircon evaporation analyses-thermal evaporation of radiogenic lead directly from untreated whole zircon grains) were obtained by using TIMS (Thermal Ionization Mass Spectrometer) for number of rock units within the Einasleigh Metamorphics in Georgetown Block. The zircon ages have confirmed the field-based relative chronology. Zircon from a meta-komatiite yielded the highest ages of 2821±4 Ma and 2826±3 Ma; these are within the error of Nd model ages. There is a possibility that these zircons are inherited from TTG gneisses. However, it was not possible to date zircons from any of the TTG gneiss samples studied. Possible metamorphic zircons from two pelitic gneiss samples belonging to Stockman Creek gneiss (SCG-Supracrustal 1) yielded 2230±22 Ma and 2279±23 Ma respectively. Zircons from three pelitic gneiss samples and two quartzites belonging to Junction Creek gneiss (JCG-Supracrustal 2) provided 1802±3 Ma, 1805±13 Ma, 1876±2.5 Ma, 1871±27 Ma and 1839±8 Ma ages respectively. The zircons from paragneisses could be detrital however the morphology of the zircons indicates that these could have grown during a metamorphic event. Granitic sheets from several localities within Junction Creek area gave zircon evaporation ages: 1652±3 Ma, 1613±3 Ma, 1635±13 Ma, 1640±13 Ma 1626±9 Ma, 1600±3 Ma, 1607±9 Ma, 1669±13 Ma and 1676±9 Ma. Zircon from Upper Stockman Creek granitic gneiss yielded 1664±27 Ma and 1675±29 Ma. The younger ages could be a result from discordant zircons. Pyrite-Chalcopyrite bearing pegmatite (Black Soil Creek-Prospect) has been dated at 1678±13 Ma. Syn-tectonic granites yield the following ages: The Lighthouse granite (1553±3 Ma), Forsayth granite (1563±3 Ma), Mistletoe granite (1550±8 and 1555±10 Ma), Goldsmith granite (1554±3 Ma), Welfern granite (1553±12 Ma) and Mt. Hogan granite (1550±13 and 1551±7 Ma). These ages are consistent with published SHRIMP U-Pb zircon ages. Two granitic sheets cutting metavolcanics (Lyndhurst) yielded ages of 1514±49 Ma and 1533±3 Ma. Digger creek granite displays significant major and trace element differences to the syn-tectonic granites. Zircon from two different samples of post-tectonic Digger Creek granite yielded 1336±3 Ma and 1333±17 Ma. Depleted mantle model ages, which range from Late Archaean to Early Proterozoic, are also consistent with the field-based relative chronology. At the time of crystallization the TTG gneisses had Nd isotopic compositions [8Nd(t)] that suggest derivation from a depleted mantle source. This suggests that the protoliths to the Black Soil Creek Gneiss Complex TTG Gneisses were derived from a depleted mantle source at 2598 Ma. Major element geochemistry of the TTG Gneisses from BSCG shows considerable similarities with previously known Archaean TTG lithologies. The whole rock Sm-Nd isochron plot for tonalitic gneiss from BSCGC yielded an age of 2598±420 Ma. The whole rock Sm-Nd isochron plot for garnet amphibolite from the JCG Supracrustal package yielded an age of 1312±340 Ma. The Proterozoic Granites yield a Sm-Nd isochron with a slope equivalent to an age of 2415±680 Ma. Einasleigh Metamorphics displays complex metamorphic and deformational history. Several metamorphic events have been dated by Sm-Nd isochron techniques. Internal (mineral and whole rock) Sm-Nd isochron for a meta-komatiite from BSCG yielded an age of 2165±36 Ma. Two garnet amphibolites from the JCG provided metamorphic ages of 1512±11 Ma and 1504±20 Ma. Nd mineral isochrons for younger gabbroic sills provide evidence for late Grenvilie age (1220±4 Ma), thermotectonism in the Georgetown Block. The reaction textures indicate that Einasleigh Metamorphics have followed an anticlockwise P-T path. TTG gneisses and the granitic gneisses have strongly fractionated rare earth element patterns that are similar to Archaean tonalite-trondhjemite-granodiorite suites that are interpreted to have formed by continental arc magmatism. TTG gneisses also display significant negative Nb, Ti, Sr and P anomalies in their primordial mantle-normalized multi-element spider diagrams, a feature typical of arc-related rocks. By contrast the younger granitoids (~1550 Ma), display geochemical features similar to within-plate granites and could have derived by melting of pre-existing crust consisting of TTG Gneiss. Igneous rocks related to the Barramundi Orogeny are not recorded in the Georgetown Block, at least in the areas studied. The second supracrustal package (1810-1870 Ma-JCG gneiss) probably formed during the Barramundi Orogeny (Etheridge et al. 1987). Field, geochemical and geochronological data indicate that the crustal evolution of the Georgetown Block is clearly more complex than envisaged by previous studies. The Einasleigh Metamorphics clearly comprises an older basement as well as two supracrustal sequences and the previous interpretation of the Einasleigh Metamorphics as dominated by paragneisses is incorrect. They do not represent an autochthonous package of metasedimentary rocks as suggested by Withnall et al. (1985, 1988 and 1998). The presence of this older basement complex indicates that crustal evolution of the Georgetown Block is significantly more complex than previously suggested, resembling the evolution of the Black Angel Gneiss Complex in the Mount Isa Block, (McDonald et al. 2000). The relative and absolute chronologies for components of the Einasleigh Metamorphics show that they evolved by several episodes of magmatic activity and thermotectonism during the Archaean and Proterozoic eras. The presence of arc-related TTG and granitic gneisses within the Georgetown Block further supports the view that Late Archaean to Early Proterozoic crustal growth in the North Australian craton was dominated by subduction and lateral accretion processes. New geochronological data provide further insights into the Australia/Laurentia correlation within Rodinia. The absolute chronology identified for the NAC (North Australian Craton), by McDonald et al. (2000) and in this study shows that it is a possible source for sediments preserved in the Belt Super group in the western USA (cf. Ross et al. 1985).
Geochronology
Cite
Citations (0)
Cite
Citations (42)
A detailed in situ isotopic (U–Pb, Lu–Hf) and geochemical study of zircon populations in a composite sequence of foliated to massive Cambro-Ordovician intrusions in the Deep Freeze Range (North Victoria Land, Antarctica), has highlighted great complexity in zircon systematics. Zircons in deformed granitoids and tonalites display complex internal textures, a wide spread of concordant U–Pb ages (between 522 and 435 Ma) and unusual trace-element compositions (anomalous enrichment of light rare earth elements, U, Th and Y) within single zircon grains. In contrast, zircons from undeformed samples display a limited range of U–Pb ages and trace-element compositions. Zircons from all age and textural populations in most of the deformed and undeformed samples show a relatively narrow range of εHf values, suggesting that the Lu–Hf system remained undisturbed. Inferred emplacement ages cover a time interval of about 30 Myr: from 508 to 493 Ma for the oldest strongly foliated synkinematic Howard Peaks megacrystic monzogranites and high-K calc-alkaline mafic to intermediate rocks of the 'Corner Tonalite' unit; from about 489 to 481 Ma for the younger massive shoshonitic mafic dyke suite and the high-K calc-alkaline Keinath granite. The observed isotopic and chemical variations in zircon are attributed to a sub-solidus recrystallization under hydrous conditions and varying temperature, in a setting characterized by a transpressional to extensional stress regime.
Trace element
Geochronology
Cite
Citations (78)
Granitic orthogneiss forms an important component of the Barkerville terrane of southeastern British Columbia. Rb–Sr whole-rock ages for the orthogneisses are ambiguous and range from Late Proterozoic to mid-Paleozoic, with large associated errors. U–Pb dating of zircon, monazite, and sphene has been employed in an attempt to establish precise crystallization ages for two of the orthogneiss bodies. U–Pb systematics for zircons from both bodies show the combined effects of inheritance of zircon cores and postcrystallization Pb loss. This complexity precludes a precise estimate of the age of emplacement of the granitic protoliths of the gneiss. The data do, however, constrain possible emplacement ages for the bodies to between 335 and 375 Ma (Late Devonian – mid-Mississippian).A U–Pb age of 174 ± 4 Ma for metamorphic sphene from one of the orthogneiss bodies is interpreted as dating the end of the second phase of deformation in the area. Two nearly concordant U–Pb ages of 114 and 117 Ma for monazite from the second body remain problematical. These data suggest either that the monazite grew during a relatively young shearing and (or) metamorphic event that locally affected the Barkerville terrane or that the closure temperatue for the U–Pb system in monazite is lower than had previously been inferred, or both.
Protolith
Devonian
Geochronology
Leucogranite
Cite
Citations (17)
The Chayu area is located at the southeastern margin of the Qinghai-Tibet Plateau. This region was considered to be in the southeastward extension of the Lhasa Block, bounded by Nujiang suture zone in the north and Yarlung Zangbo suture zone in the south. The Demala Group complex, a set of high-grade metamorphic gneisses widely distributed in the Chayu area, is known as the Precambrian metamorphic basement of the Lhasa Block in the area. According to field-based investigations and microstructure analysis, the Demala Group complex is considered to mainly consist of banded biotite plagiogneisses, biotite quartzofeldspathic gneiss, granitic gneiss, amphibolite, mica schist, and quartz schist, with many leucogranite veins. The zircon U-Pb ages of two granitic gneiss samples are 205 ± 1 Ma and 218 ± 1 Ma, respectively, representing the ages of their protoliths. The zircons from two biotite plagiogneisses samples show core-rim structures. The U-Pb ages of the cores are mainly 644–446 Ma, 1213–865 Ma, and 1780–1400 Ma, reflecting the age characteristics of clastic zircons during sedimentation of the original rocks. The U-Pb ages of the rims are from 203 ± 2 Ma to 190 ± 1 Ma, which represent the age of metamorphism. The zircon U-Pb ages of one sample taken from the leucogranite veins that cut through granitic gneiss foliation range from 24 Ma to 22 Ma, interpreted as the age of the anatexis in the Demala Group complex. Biotite and muscovite separates were selected from the granitic gneiss, banded gneiss, and leucogranite veins for 40Ar/39Ar dating. The plateau ages of three muscovite samples are 16.56 ± 0.21 Ma, 16.90 ± 0.21 Ma, and 23.40 ± 0.31 Ma, and the plateau ages of four biotite samples are 16.70 ± 0.24 Ma, 16.14 ± 0.19 Ma, 15.88 ± 0.20 Ma, and 14.39 ± 0.20 Ma. The mica Ar-Ar ages can reveal the exhumation and cooling history of the Demala Group complex. Combined with the previous research results of the Demala Group complex, the authors refer that the Demala Group complex should be a set of metamorphic complex. The complex includes not only Precambrian basement metamorphic rock series, but also Paleozoic sedimentary rock and Mesozoic granitic rock. Based on the deformation characteristics, the authors concluded that two stages of the metamorphism and deformation can be revealed in the Demala Group complex since the Mesozoic, namely Late Triassic-Early Jurassic (203–190 Ma) and Oligocene–Miocene (24–14 Ma). The early stage of metamorphism (ranging from 203–190 Ma) was related to the Late Triassic tectono-magmatism in the area. The anatexis and uplifting-exhumation of the later stage (24–14 Ma) were related to the shearing of the Jiali strike-slip fault zone. The Miocene structures are response to the large-scale southeastward escape of crustal materials and block rotation in Southeast Tibet after India-Eurasia collision.
Leucogranite
Anatexis
Muscovite
Cite
Citations (0)
1. Introduction 2. Northern Victoria Land 3. Southern Victoria Land 4. Central Transantarctic Mountains 5. Queen Maud-Horlick Mountains 6. Thiel Mountains 7. Pensacola Mountains 8. Synthesis.
Cite
Citations (180)
Quartz monzonite
Geochronology
Hornblende
Basement
Cite
Citations (53)
Research Article| September 01, 2004 Provenance of Neoproterozoic and lower Paleozoic siliciclastic rocks of the central Ross orogen, Antarctica: Detrital record of rift-, passive-, and active-margin sedimentation John W. Goodge; John W. Goodge 1Department of Geological Sciences, University of Minnesota, Duluth, Minnesota 55812, USA Search for other works by this author on: GSW Google Scholar Ian S. Williams; Ian S. Williams 2Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia Search for other works by this author on: GSW Google Scholar Paul Myrow Paul Myrow 3Department of Geology, Colorado College, Colorado Springs, Colorado 80903, USA Search for other works by this author on: GSW Google Scholar Author and Article Information John W. Goodge 1Department of Geological Sciences, University of Minnesota, Duluth, Minnesota 55812, USA Ian S. Williams 2Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia Paul Myrow 3Department of Geology, Colorado College, Colorado Springs, Colorado 80903, USA Publisher: Geological Society of America Received: 26 Feb 2003 Revision Received: 17 Nov 2003 Accepted: 26 Nov 2003 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2004) 116 (9-10): 1253–1279. https://doi.org/10.1130/B25347.1 Article history Received: 26 Feb 2003 Revision Received: 17 Nov 2003 Accepted: 26 Nov 2003 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Tools Icon Tools Get Permissions Search Site Citation John W. Goodge, Ian S. Williams, Paul Myrow; Provenance of Neoproterozoic and lower Paleozoic siliciclastic rocks of the central Ross orogen, Antarctica: Detrital record of rift-, passive-, and active-margin sedimentation. GSA Bulletin 2004;; 116 (9-10): 1253–1279. doi: https://doi.org/10.1130/B25347.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Siliciclastic rocks in the Transantarctic Mountains record the tectonic transformation from a Neoproterozoic rift-margin setting to a passive-margin and ultimately to an active early Paleozoic orogenic setting along the paleo–Pacific margin of East Antarctica. New U-Pb detrital-zircon ages constrain both the depositional age and sedimentary provenance of these strata. In the central Trans-antarctic Mountains, mature quartz arenites of the late Neoproterozoic Beardmore Group contain Archean and Proterozoic zircons, reflecting distal input from the adjacent East Antarctic shield, Mesoproterozoic igneous provinces, and Grenville-age parts of East Gondwana. Similarly, basal sandstones of the Lower Cambrian Shackleton Limestone (lower Byrd Group) contain zircons reflecting a dominantly cratonic shield source; the autochthonous Shackleton was deposited during early Ross orogenesis, yet its basal sandstone indicates that the inner shelf was locally quiescent. Detrital zircons from the Koettlitz Group in southern Victoria Land show a similar age signature and constrain its depositional age to be ≤ 670 Ma. Significant populations (up to 22%) of ca. 1.4 Ga zircons in these Neoproterozoic and Lower Cambrian sandstone deposits suggest a unique source of Mesoproterozoic igneous material in the East Antarctic craton; comparison with the trans-Laurentian igneous province of this age suggests paleogeographic linkage between East Antarctica and Laurentia prior to ca. 1.0 Ga. In strong contrast, detrital zircons from upper Byrd Group sandstones are dominated by young components derived from proximal igneous and metamorphic rocks of the emerging Ross orogen. Zircon ages restrict deposition of this syn- to late-orogenic succession to ≤ 520 Ma (Early Cambrian or younger). Sandstone samples in the Pensacola Mountains are dominated by Grenville and Pan-African zircon ages, suggesting a source in western Dronning Maud Land equivalents of the East African orogen. When integrated with stratigraphic relationships, the detrital-zircon age patterns can be explained by a tectonic model involving Neoproterozoic rifting and development of a passive-margin platform, followed by a rapid transition in the late Early Cambrian (Botomian) to an active continental-margin arc and forearc setting. Large volumes of molassic sediment were shed to forearc marginal basins between Middle Cambrian and Ordovician time, primarily by erosion of volcanic rocks in the early Ross magmatic arc. The forearc deposits were themselves intruded by late-orogenic plutons as the locus of magmatism shifted trenchward during trench retreat. Profound syntectonic denudation, followed by Devonian peneplanation, removed the entire volcanic carapace and exposed the plutonic roots of the arc. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
Siliciclastic
Geological survey
Cite
Citations (222)
New zircon trace-element concentration data and U-Pb geochronology on gneisses from Colombia's Central Cordillera at 6°N allow for the recognition of the distinct Anacona suspect terrane separate from the known Tahamí terrane. These blocks underwent disparate Paleozoic and Mesozoic evolutions involving anatexis, S-type granite crystallization, and metamorphism. Orthogneisses from the Tahamí terrane basement have yielded a 244 ± 2 Ma mean age (n = 15), and associated migmatitic paragneisses yielded a 237 ± 2 Ma mean age (n = 11). Zircon geochemistry and textures show that the orthogneiss age represents the time of crystallization of early melts in the orogenic cycle, whereas the paragneiss age represents the time of metamorphic recrystallization of the suite. In contrast, orthogneisses from the small Anacona terrane have yielded U-Pb ages of 479+15/−11 Ma (median, n = 7) and 443 ± 8 Ma (mean, n = 8) in magmatic zircon rims. The main xenocrystic zircon populations are 1265–995 and 1510–1495 Ma (no Pan-African–Brasiliano signal). The above blocks experienced common histories with other known Paleozoic-Triassic peri-Gondwana terranes. The Tahamí terrane can be correlated with blocks now occupying southern Mexico (Chiapas Massif) and the northwestern Andes (Loja and Amotape) and perhaps the late Paleozoic-Triassic components of the Marañón complex in Peru. These areas underwent crustal reworking during Permo-Triassic transition from arc(?) magmatism to extension on the western margin of Pangea. In contrast, the Anacona terrane represents a portion of the Ordovician magmatic belt fringing Gondwana in the early Paleozoic. Potential correlatives include the Mixteca terrane in southern Mexico and the early Paleozoic component of the Marañón complex of Peru. The above correlations suggest that terranes in the Central Cordillera of Colombia, Central America, and southern Mexico may have occupied Gondwanan positions as far south as Ecuador and Peru. This southerly position constitutes a significant means in eliminating the problematic South America–Mexico overlap in Pangea reconstructions.
Geochronology
Yilgarn Craton
Continental arc
Cite
Citations (45)
Abstract We report U—Pb and 207 Pb/ 206 Pb zircon ages for a granulite facies gneiss assemblage exposed in a large quarry at Ihosy, southern Madagascar. The granulites are derived from pelitic to arkosic sediments and attained equilibrium conditions at 650–700°C and 4–5 kbar. Higher P—T conditions of 750–800°C and 6 kbar in the presence of low water activities have led to dehydration melting processes. The formation of granitic melts, which (partly) moved away from their source region, intruded into upper parts of the metapelitic gneisses as small granitic veins and left behind granulitic garnet-cordierite-quartz bearing rocks. Detrital zircons in a sample of metapelite and a sample of quartzofeldspathic gneiss yielded ages between ˜720 and ˜1855 Ma, suggesting a chronologically heterogeneous source region and a depositional age of less than ˜720 Ma for these rocks. High-grade metamorphism and anatexis are documented by zircon ages between 526 ±34 and 557 ±2 Ma with a mean age of about 550 Ma. The broad lithologies, metamorphic grades and ages recorded in the Ihosy rocks are similar to those in the Wanni Complex of northwestern Sri Lanka and in high-grade assemblages of southernmost India and support the contention that all these terrains were part of the Mozambique belt which formed as a result of collision of East and West Gondwana in latest Precambrian time.
Anatexis
Geochronology
Sillimanite
Pelite
Migmatite
Cite
Citations (89)