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1.
Protolith and metamorphic ages of the Haiyangsuo Complex, eastern China: a non-UHP exotic tectonic slab in the Sulu ultrahigh-pressure terrane 总被引:8,自引:0,他引:8
J. G. Liou T. Tsujimori W. Chu R. Y. Zhang J. L. Wooden 《Mineralogy and Petrology》2006,88(1-2):207-226
Summary The Haiyangsuo Complex in the NE Sulu ultrahigh-pressure (UHP) terrane has discontinuous, coastal exposures of Late Archean
gneiss with amphibolitized granulite, amphibolite, Paleoproterozoic metagabbroic intrusives, and Cretaceous granitic dikes
over an area of about 15 km2. The U–Pb SHRIMP dating of zircons indicates that theprotolith age of a garnet-biotite gneiss is >2500 Ma, whereas the granulite-facie
metamorphism occurred at around 1800 Ma. A gabbroic intrusion was dated at ∼1730 Ma, and the formation of amphibolite-facies
assemblages in both metagabbro and granulite occurred at ∼340–460 Ma. Petrologic and geochronological data indicate that these
various rocks show no evidence of Triassic eclogite-facies metamorphism and Neoproterozoic protolith ages that are characteristics
of Sulu-Dabie HP-UHP rocks, except Neoproterozoic inherited ages from post-collisional Jurassic granitic dikes. Haiyangsuo
retrograde granulites with amphibolite-facies assemblages within the gneiss preserve relict garnet formed during granulite-facies
metamorphism at ∼1.85 Ga. The Paleoproterozoic metamorphic events are almost coeval with gabbroic intrusions. The granulite-bearing
gneiss unit and gabbro-dominated unit of the Haiyangsuo Complex were intruded by thin granitic dikes at about 160 Ma, which
is coeval with post-collisional granitic intrusions in the Sulu terrane. We suggest that the Haiyangsuo Complex may represent
a fragment of the Jiao-Liao-Ji Paleoproterozoic terrane developed at the eastern margin of the Sino-Korean basement, which
was juxtaposed with the Sulu terrane prior to Jurassic granitic activity and regional deformation. 相似文献
2.
Summary The rocks of the crystalline basement of the East European Craton in southern Estonia show effects of partial melting under
granulite facies conditions. Zircons extracted from partial melting products (tonalite from the Tapa Zone – 1824 ± 26, tonalite
from the South Estonian Zone – 1788 ± 16 Ma and charnockite from the Tapa Zone – 1761 ± 11 Ma) yield U–Pb crystallisation
ages that span over approximately 80 Ma, suggesting a prolonged high-grade metamorphism or several separate events. U–Pb zircon
age of one sample of charnockite is concordant with the Nd model age of partial melting of its host mafic granulite facies
gneiss (intercept at 1.76 Ga). Linear geochemical trends and similar initial Nd isotopic compositions of mafic granulites
and charnockites suggest their possible genetic relationship. From our new and previously published data it follows that the
peak granulite metamorphic conditions and formation of tonalites and charnockites (850 °C and 6 kbar) in the Estonian basement
occurred at 1788–1778 Ma. Then, the rocks cooled down, passing through the garnet closure temperature of approximately 650–700 °C
at 1728 ± 24 Ma. The age of metamorphism of the Estonian granulites is lower than the metamorphic ages known from southern
Finland, but it is similar to the age of metamorphism reported from the Belarus-Baltic Granulite Belt in Latvia. 相似文献
3.
James L. Crowley Mark D. Schmitz Samuel A. Bowring Michael L. Williams Karl E. Karlstrom 《Contributions to Mineralogy and Petrology》2006,151(3):313-330
Zircon from lower crustal xenoliths erupted in the Navajo volcanic field was analyzed for U–Pb and Lu–Hf isotopic compositions
to characterize the lower crust beneath the Colorado Plateau and to determine whether it was affected by ∼1.4 Ga granitic
magmatism and metamorphism that profoundly affected the exposed middle crust of southwestern Laurentia. Igneous zircon in
felsic xenoliths crystallized at 1.73 and 1.65 Ga, and igneous zircon in mafic xenoliths crystallized at 1.43 Ga. Most igneous
zircon has unradiogenic initial Hf isotopic compositions (ɛHf=+4.1–+7.8) and 1.7–1.6 Ga depleted mantle model ages, consistent with 1.7–1.6 Ga felsic protoliths being derived from “juvenile”
Proterozoic crust and 1.4 Ga mafic protoliths having interacted with older crust. Metamorphic zircon grew in four pulses between
1.42 and 1.36 Ga, at least one of which was at granulite facies. Significant variability within and between xenoliths in
metamorphic zircon initial Hf isotopic compositions (ɛHf=−0.7 to +13.6) indicates growth from different aged sources with diverse time-integrated Lu/Hf ratios. These results show
a strong link between 1.4 Ga mafic magmatism and granulite facies metamorphism in the lower crust and granitic magmatism and
metamorphism in the exposed middle crust. 相似文献
4.
F. P. Florence R. S. Darling S. E. Orrell 《Contributions to Mineralogy and Petrology》1995,121(4):424-436
Garnet-sillimanite-biotite gneiss near Port Leyden, in the western Adirondack Highlands, New York, contains mineral assemblages
and textures that formed during high temperature metamorphism and anatexis at mid-crustal pressures. Evidence for melting
includes thin, plagioclase-rich veins, sieve textures in biotite, and the presence of small, euhedral garnet neoblasts. Hercynite-silicate
equilibria in combination with the solidus for biotite dehydration melting indicate metamorphic pressure was between 4 and
6.4 kbar at the temperature of melting (ca. 735° C). The gneiss is intruded by a small, discordant Fe-Ti oxide-apatite (nelsonite)
dike. Reported field occurrences of nelsonite demonstrate its common association with anorthosite plutons. Although no anorthosite
bodies are exposed in the Port Leyden region, the presence of nelsonite is evidence of anorthositic magmatism in the western
Adirondacks. Post-intrusion metamorphism has caused partial apatite recrystallization and produced a weak foliated texture
in the dike. U-Pb ages from zircon and monazite from both the gneiss and the nelsonite dike indicate that these rocks experienced
a complex, polymetamorphic history that we interpret to reflect two thermal episodes. An older event is recorded by discordant
zircons in the gneiss, which indicate a minimum age of 1129±6 Ma. A linear best fit to the data yields an upper intercept
at 1166±53 Ma. This range of ages coincides with anorthosite-suite magmatism in the Adirondacks. A minimum zircon age of 1104±3 Ma
was obtained from the nelsonite dike. Lead-loss or late zircon crystallization at about 1020 Ma affected the U-Pb systematics
of zircon in the dike. Monazite ages from both rocks also indicate high temperature metamorphism (>700° C) between 1040 and
960 Ma. The older zircon ages and textural relations in the metapelite are viewed as evidence for anatexis at ca. 1150 Ma,
and the presence of nelsonite suggests that the intrusion of anorthosite was coincident with partial melting in the gneiss.
P-T estimates of metamorphism, therefore, imply that anorthosite was emplaced to about 15 km depth in the western Adirondack
Highlands.
Received: 13 September 1994 / Accepted: 10 May 1995 相似文献
5.
Christina Wanhainen Kjell Billström Olof Martinsson Holly Stein Roger Nordin 《Mineralium Deposita》2005,40(4):435-447
Host rocks to the Aitik Cu–Au–Ag deposit in northern Sweden are strongly altered and deformed Early Proterozoic mica(-amphibole)
schists and gneisses. The deposit is characterised by numerous mineralisation styles, vein and alteration types. Four samples
were selected for Re–Os molybdenite dating and 12 samples for U–Pb titanite dating in order to elucidate the magmatic/hydrothermal
and metamorphic history following primary ore deposition in the Aitik Cu–Au–Ag deposit. Samples represent dyke, vein and alteration
assemblages from the ore zone, hanging wall and footwall to the deposit. Re–Os dating of molybdenite from deformed barite
and quartz veins yielded ages of 1,876±10 Ma and 1,848±8 Ma, respectively. A deformed pegmatite dyke yielded a Re–Os age of
1,848±6 Ma, and an undeformed pegmatite dyke an age of 1,728±7 Ma. U–Pb dating of titanite from a diversity of alteration
mineral associations defines a range in ages between 1,750 and 1,805 Ma with a peak at ca. 1,780 Ma. The ages obtained, together
with previous data, bracket a 160-Ma (1,890–1,730 Ma) time span encompassing several generations of magmatism, prograde to
peak metamorphism, and post-peak cooling; events resulting in the redistribution and addition of metals to the deposit. This
multi-stage evolution of the Aitik ore body suggests that the deposit was affected by several thermal events that ultimately
produced a complex ore body. The Re–Os and U–Pb ages correlate well with published regional Re–Os and U–Pb age clusters, which
have been tied to major magmatic, hydrothermal, and metamorphic events. Primary ore deposition at ca. 1,890 Ma in connection
with intrusion of Haparanda granitoids was followed by at least four subsequent episodes of metamorphism and magmatism. Early
metamorphism at 1,888–1,872 Ma overlapping with Haparanda (1,890–1,880 Ma) and Perthite-monzonite (1,880–1,870 Ma) magmatism
clearly affected the Aitik area, as well as late metamorphism and Lina magmatism at 1,810–1,774 Ma and TIB1 magmatism at 1,800 Ma.
The 1,848 Ma Re–Os ages obtained from molybdenite in a quartz vein and pegmatite dyke suggests that the 1,850 Ma magmatism
recorded in parts of northern Norrbotten also affected the Aitik area. 相似文献
6.
Petrological and geochronological constraints on high pressure, high temperature metamorphism in the Snowbird tectonic zone, Canada 总被引:7,自引:0,他引:7
The upper deck of the East Athabasca mylonite triangle (EAmt), northern Saskatchewan, Canada, contains mafic granulites that have undergone high P–T metamorphism at conditions ranging from 1.3 to 1.9 GPa, 890–960 °C. Coronitic textures in these mafic granulites indicate a near‐isothermal decompression path to 0.9 GPa, 800 °C. The Godfrey granite occurs to the north adjacent to the upper deck high P–T domain. Well‐preserved corona textures in the Godfrey granite constrain igneous crystallization and early metamorphism in the intermediate‐pressure granulite field (Opx + Pl) at 1.0 GPa, 775 °C followed by metamorphism in the high pressure granulite field (Grt + Cpx + Pl) at 1.2 GPa, 860 °C. U–Pb geochronology of zircon in upper deck mafic granulite yields evidence for events at both c. 2.5 Ga and c. 1.9 Ga. The oldest zircon dates are interpreted to constrain a minimum age for crystallization or early metamorphism of the protolith. A population of 1.9 Ga zircon in one mafic granulite is interpreted to constrain the timing of high P–T metamorphism. Titanite from the mafic granulites yields dates ranging from 1900 to 1894 Ma, and is interpreted to have grown along the decompression path, but still above its closure temperature, indicating cooling following the high P–T metamorphism from c. 960–650 °C in 4–10 Myr. Zircon dates from the Godfrey granite indicate a minimum crystallization age of 2.61 Ga, without any evidence for 1.9 Ga overgrowths. The data indicate that an early granulite facies event occurred at c. 2.55–2.52 Ga in the lower crust (c. 1.0 GPa), but at 1.9 Ga the upper deck underwent high P–T metamorphism, then decompressed to 0.9–1.0 GPa. Juxtaposition of the upper deck and Godfrey granite would have occurred after or been related to this decompression. In this model, the high P–T rocks are exhumed quickly following the high pressure metamorphism. This type of metamorphism is typically associated with collisional orogenesis, which has important implications for the Snowbird tectonic zone as a fundamental boundary in the Canadian Shield. 相似文献
7.
Rebecca M. Flowers Samuel A. Bowring Kevin H. Mahan Michael L. Williams Ian S. Williams 《Contributions to Mineralogy and Petrology》2008,156(4):529-549
New U–Pb geochronology for an extensive exposure of high-pressure granulites in the East Lake Athabasca region of the western
Canadian shield is consistent with a history characterized by 2.55 Ga stabilization of cratonic lithosphere, 650 million years
of lower crustal residence and cratonic stability, and 1.9 Ga reactivation of the craton during lithospheric attenuation and
asthenospheric upwelling. High precision single-grain and fragment zircon data define distinctive discordia arrays between
2.55 and 1.9 Ga. U–Pb ion microprobe spot analyses yield a similar range of U–Pb dates with no obvious correlation between
date and cathodoluminescence zonation. We attribute the complex U–Pb zircon systematics to growth of the primary populations
during a 2.55 Ga high-pressure granulite facies event (~1.3 GPa, 850°C) recorded by the dominant mineral assemblage of the
mafic granulite gneisses, with subsequent zircon recrystallization and minor secondary zircon growth during a second high-pressure
granulite facies event (1.0 GPa, ~800°C) at 1.9 Ga. The occurrence of two discrete granulite facies metamorphic events in
the lower crust, separated by an interval of 650 million years that included isobaric cooling for at least some of this time,
suggests that the rocks resided at lower crustal depths until 1.9 Ga. We infer that this phase of lower crustal residence
and little tectonic activity is coincident with an extended period of cratonic stability. Detailed structural and thermochronological
datasets indicate that multistage unroofing of the lower crustal rocks occurred in the following 200 million years. Extended
lower crustal residence would logically be the history inferred for lower crust in most cratonic regions, but the unusual
aspect of the history in the East Lake Athabasca region is the subsequent lithospheric reactivation that initiated transport
of the lower crust to the surface. We suggest that a weakened strength profile related to the 1.9 Ga heating left the lithosphere
susceptible to far-field tectonic stresses from bounding orogens that drove the lower crustal exhumation. An ultimate return
to cratonic stability is responsible for the preservation of this extensive lower crustal exposure since 1.7 Ga. 相似文献
8.
《International Geology Review》2012,54(13):1772-1790
The Quanji Massif (QM), in the northeast part of Tibet, consists of Palaeoproterozoic metamorphic rocks, granitoids, and mafic dikes. U–Pb dating of a diorite gneiss and a mafic dike in the QM yielded a crystallization age of 2272 ± 15 Ma and a metamorphic age of 1928 ± 11 Ma, respectively. Although some post-emplacement alteration has occurred, the mafic dikes display a sub-alkaline signature with slight light rare earth element-enrichment, depletion in Th, Nb, Ta, and Ti, and have a rare earth element pattern consistent with volcanic arc basalts. Based on the geochronology and field relationships, we conclude that the mafic dikes formed in an extensional setting within either a fore-arc or back-arc environment. We argue that the metamorphism that affected the dikes occurred shortly after intrusion. Our diorite gneiss and monzodiorite samples are characterized by relatively high Mg# (47–56) and Sr contents (367–1070 ppm), low-to-moderate Sr/Y (10–90), low Rb/Sr (0.03–0.28) and high K/Rb (179–775). These felsic melts likely originated from partial melting of a mafic source. Our new data, combined with results from previous studies, indicate that the QM formed between 2.50 and 2.30 Ga and underwent metamorphism around 1.95–1.75 Ga that may relate to the dispersal of Neoarchaean ‘Kenorland’ and the formation of the Columbia supercontinent. The similarity between the Palaeoproterozoic events in the Tiekelik, North Altyn–Dunhuang, Alashan blocks, and QM suggests that QM was part of either the Tarim or the North China Craton in the late Archaean and Palaeoproterozoic. If the model is correct, then there was a single ‘North China–Quanji–Tarim Craton’ that was later disrupted by Neoproterozoic to Phanerozoic tectonic events. 相似文献
9.
Geochronology and tectonic significance of Middle Proterozoic granitic orthogneiss, North Qaidam HP/UHP terrane, Western China 总被引:4,自引:0,他引:4
C. G. Mattinson J. L. Wooden J. G. Liou D. K. Bird C. L. Wu 《Mineralogy and Petrology》2006,88(1-2):227-241
Summary Amphibolite-facies para- and orthogneisses near Dulan, in the southeast part of the North Qaidam terrane, enclose minor ultra-high
pressure (UHP) eclogite and peridotite. Field relations and coesite inclusions in zircons from paragneiss suggest that felsic,
mafic, and ultramafic rocks all experienced UHP metamorphism and a common amphibolite-facies retrogression. Ion microprobe
U–Pb and REE analyses of zircons from two granitic orthogneisses indicate magmatic crystallization at 927 ± Ma and 921 ± 7 Ma.
Zircon rims in one of these samples yield younger ages (397–618 Ma) compatible with partial zircon recrystallization during
in-situ Ordovician-Silurian eclogite-facies metamorphism previously determined from eclogite and paragneiss in this area.
The similarity between a 2496 ± 18 Ma xenocrystic core and 2.4–2.5 Ga zircon cores in the surrounding paragneiss suggests
that the granites intruded the sediments or that the granite is a melt of the older basement which supplied detritus to the
sediments. The magmatic ages of the granitic orthogneisses are similar to 920–930 Ma ages of (meta)granitoids described further
northwest in the North Qaidam terrane and its correlative west of the Altyn Tagh fault, suggesting that these areas formed
a coherent block prior to widespread Mid Proterozoic granitic magmatism. 相似文献
10.
Geochemistry and geodynamic implications of the Triassic bimodal magmatism from Western Kunlun Orogen,northwest China 总被引:1,自引:0,他引:1
The Western Kunlun Orogen occupies a key tectonic position at the junction between the Tarim block and the Tethyan domain.
However, the late Paleozoic to early Mesozoic, especially the middle to late Triassic tectonic evolution history of the Western
Kunlun Orogen remains controversial. This study reports SHRIMP zircon U–Pb ages and geochemical as well as Sr–Nd–Hf isotopic
data for middle to late Triassic Taer pluton in Western Kunlun Orogen, Northwest China. The Taer pluton shows a strong bimodal
distribution of compositions, with the felsic rocks dominant and the mafic rocks subordinate. Zircon U–Pb dating reveals that
the coexisting mafic and felsic rocks are coeval, both emplacing in a period between 234 and 225 Ma. Most of the studied rocks
are potassium rich and can be classified into high-K calc-alkaline to shoshonitic series. They are also strongly enriched
in LREE, LILE and depleted in HFSE with strong negative Ti and Nb anomalies, and characterized by enriched Sr–Nd–Hf isotopic
signatures. Detailed geochemical and isotopic studies indicate that the Taer pluton was emplaced in a post-collisional extensional
setting, with the mafic rocks derived from partial melting of the enriched continental lithospheric mantle in the spinel facies
field, and the felsic rocks formed by anatexis of newly underplated basaltic rocks. The existence of middle to late Triassic
post-collisional magmas in Western Kunlun region suggests that the final closure of Paleo-Tethys and the initial collision
between the Western Kunlun and the Qiangtang terranes may have happened before ~234 Ma, most probably in late Permian, rather
than in late Triassic or early Jurassic. In assistance with other geological evidences, such as the presence of early Triassic
to late Triassic/early Jurassic S-type magmatism, terrestrial molasse depositions, regional unconformities, and strong deformation,
we propose that the Western Kunlun Orogen may have undergone a long post-collisional intracontinental process from early Triassic
to late Triassic/early Jurassic. 相似文献
11.
K. H. Mahan M. L. Williams R. M. Flowers M. J. Jercinovic J. A. Baldwin S. A. Bowring 《Contributions to Mineralogy and Petrology》2006,152(2):223-242
The Legs Lake shear zone marks the southeastern boundary of an extensive region (>20,000 km2) of high-pressure (0.8–1.5+ GPa) granulite-facies rocks in the western Churchill Province, Canada. The shear zone is one of the largest exhumation-related structures in the Canadian Shield and coincides with the central segment of the ∼2,800 km long Snowbird tectonic zone. The movement history of this shear zone is critical for the development of models for the exhumation history of the high-pressure region. We used electron microprobe U–Th–Pb dating of monazite with supplemental ID-TIMS U–Pb geochronology to place constraints on the timing of shear zone activity. Combining these and other data, we suggest that regional exhumation occurred during at least three distinct phases over an ∼150 million year period. The first phase involved high temperature decompression from ∼1.0 to 0.8–0.7 GPa shortly following 1.9 Ga peak metamorphism, possibly under an extensional regime. The second phase involved rock uplift and decompression of the hanging wall to 0.5–0.4 GPa during east-vergent thrusting across the Legs Lake shear zone at ca. 1.85 Ga. This phase was likely driven by early collision-related convergence in the Trans-Hudson orogen. The final phase of regional exhumation, involving the removal of 15–20 km of overburden from both footwall and hanging wall, likely occurred after ∼1.78 Ga and may have been related to regional extensional faulting.Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at . 相似文献
12.
To unravel the petrogenesis of a massif‐type anorthosite in terms of the crust‐mantle geodynamics, we dated zircons separated from six samples from the Sancheong‐Hadong (SH) complex, Korea, using a sensitive high‐resolution ion microprobe. The weighted mean 207Pb/206Pb age of two anorthosites is 1862 ± 2 Ma, whereas the ages of the hornblende gabbro and granitic gneiss are 1873 ± 4 Ma and 1875 ± 5 Ma respectively. Zircon rims from mafic granulite and migmatitic gneiss yielded ages of 1860 ± 5 Ma and 1858 ± 4 Ma, respectively, implying that the granulite facies metamorphism and anatexis are associated with anorthosite emplacement. Our results, together with available Re–Os data, are compatible with the ~1.9–1.86 Ga collisional orogeny prevalent in the North China Craton and the Korean Peninsula, and suggest that orogenesis was accompanied by mantle delamination beneath the craton. It is thus likely that the SH anorthositic rocks are a product of late‐orogenic magmatism during the post‐collisional extension‐dominated phase of orogeny. 相似文献
13.
V. A. Valencia J. Ruiz F. Barra G. Geherls M. Ducea S. R. Titley L. Ochoa-Landin 《Mineralium Deposita》2005,40(2):175-191
Uranium–lead zircon (laser ablation multi-collector ICP-MS spot analysis) ages from La Caridad porphyry copper deposit in
the Nacozari District, Northeastern Sonora, Mexico, suggest a short period of magmatism, between 55.5 and 52.6 Ma. Two U–Pb
ages from the mineralized quartz monzonite unit, showing different textural characteristics, yielded indistinguishable crystallization
ages (~54 Ma), and indicate that the intrusion responsible for the mineralization occurred as a single large complex unit,
instead of multiple pulses of magmatism. Some zircons analyzed also show inherited ages in cores recording dates of 112–124 Ma,
141–166 Ma and 1.4 Ga. The Re–Os molybdenite ages from the potassic and phyllic hydrothermal alteration veins yielded identical
ages within error, 53.6±0.3 Ma and 53.8±0.3 Ma, respectively (weighted average of 53.7±0.21 Ma), supporting a restricted period
for the mineralization. The geochronological data thus indicate a short-lived magmatic and hydrothermal system. The inherited
zircons of Precambrian and Late Jurassic-Mid Cretaceous age found in the intrusive rocks of La Caridad deposit, can be explained
considering two possible scenarios within the tectonic/magmatic evolution of the area. The first scenario considers the presence
of a Precambrian anorogenic granitic basement that is intruded by Mesozoic (Jurassic–Cretaceous) units present beneath the
La Caridad deposit. The second scenario suggests that the Mesozoic Glance Conglomerate Formation of Arizona underlies the
Paleocene volcanic-igneous pile in the La Caridad area. 相似文献
14.
Tectonic evolution of the South Tianshan orogen and adjacent regions,NW China: geochemical and age constraints of granitoid rocks 总被引:36,自引:0,他引:36
Jun Gao Lingli Long Reiner Klemd Qing Qian Dunyi Liu Xianming Xiong Wen Su Wei Liu Yitian Wang Fuqun Yang 《International Journal of Earth Sciences》2009,98(6):1221-1238
Geochemical and geochronological evidence was obtained from granitoids of the South Tianshan orogen and adjacent regions,
which consist of three individual tectonic domains, the Kazakhstan–Yili plate, the Central Tianshan Terrane and the Tarim
plate from north to south. The Central Tianshan Terrane is structurally bounded by the Early Paleozoic ‘Nikolaev Line–North
Nalati Fault’ and Late Paleozoic ‘Atbashy–Inyl’chek–South Nalati–Qawabulak Fault’ zones against the Kazakhstan–Yili and Tarim
plates, respectively. The meta-aluminous to weakly peraluminous granitic rocks, which are exposed along the Kekesu River and
the Bikai River across the Central Tianshan Terrane, have a tholeiitic, calc-alkaline or high-potassium calc-alkaline composition
(I-type). Geochemical trace element characteristics and the Y versus Rb–Nb or Y versus Nb discrimination diagrams favor a
continental arc setting for these granitoid rocks. SHRIMP U–Pb and LA-ICP-MS U–Pb zircon age data indicate that the magmatism
started at about 480 Ma, continued from 460 to 330 Ma and ended at about 275 Ma. The earlier magmatism (>470 Ma) is considered
to be the result of a simultaneous southward and northward subduction of the Terskey Ocean beneath the northern margin of
the Tarim plate and the Kazakhstan–Yili plate, respectively. The later magmatism (460–330 Ma) is related to the northward
subduction of the South Tianshan Ocean beneath the southern margin of the Kazakhstan–Yili–Central Tianshan plate. The dataset
presented here in conjunction with previously published data support a Late Paleozoic tectonic evolution of the South Tianshan
orogen, not a Triassic one, as recently suggested by SHRIMP U–Pb zircon dating for eclogites. 相似文献
15.
Geochronological Framework and Geodynamic Implications of Mafic Magmatism in the Liaodong Peninsula and Adjacent Regions, North China Craton 总被引:2,自引:0,他引:2
Mafic rocks are widespread on the Liaodong Peninsula and adjacent regions of the North China Craton. The majority of this magmatism was originally thought to have occurred during the Pre-Sinian, although the precise geochronological framework of this magmatism was unclear. Here, we present the results of more than 60 U–Pb analyses of samples performed over the past decade, with the aim of determining the spatial and temporal distribution of mafic magmatism in this area. These data indicate that Paleoproterozoic–Mesoproterozoic mafic rocks are not as widely distributed as previously thought. The combined geochronological data enabled the subdivision of the mafic magmatism into six episodes that occurred during the middle Paleoproterozoic, the late Paleoproterozoic, the Mesoproterozoic, the Late Triassic, the Middle Jurassic, and the Early Cretaceous. The middle Paleoproterozoic (2.1–2.2 Ga) mafic rocks formed in a subduction-related setting and were subsequently metamorphosed during a ca. 1.9 Ga arc–continent collision event. The late Paleoproterozoic (ca. 1.87–1.82 Ga) bimodal igneous rocks mark the end of a Paleoproterozoic tectono-thermal event, whereas Mesoproterozoic mafic dike swarms record global-scale Mesoproterozoic rifting associated with the final breakup of the Columbia supercontinent. The Late Triassic mafic magmatism is part of a Late Triassic magmatic belt that was generated by post-collisional extension. The Middle Jurassic mafic dikes formed in a compressive tectonic setting, and the Early Cretaceous bimodal igneous rocks formed in an extensional setting similar to a back-arc basin. These latter two periods of magmatism were possibly related to subduction of the Paleo-Pacific plate. 相似文献
16.
东南极Windmill群岛变质杂岩经历的变质和岩浆事件与西澳大利亚Albany-Fraser造山带在时间上相对应,并可能与罗迪尼亚超大陆的拼合有关。Windmill群岛Bailey半岛的镁铁质片麻岩(角闪石-单斜辉石-斜方辉石-黑云母-斜长石-石英-磁铁矿-锆石)被认为具有较早的形成年龄,其中还出露属于正片麻岩的淡色片麻岩(斜长石-钾长石-石英-黑云母-锆石)。对这两种片麻岩中的锆石分别进行了SHRIMP U-Pb年龄测定,首次获得该区镁铁质片麻岩锆石核部207Pb/206Pb加权平均年龄1403±28 Ma,该年龄记录了本区中元古代早期岩浆事件,这是Windmill群岛地区记录的最早一期岩浆事件,可能受到了东部莫森大陆(Mawson Continent)构造岩浆活动的影响。铁镁质片麻岩锆石增生边的年龄为1318±34 Ma,则记录了早期构造热事件。淡色片麻岩中锆石核部年龄为1257±51 Ma,与Bailey半岛的片麻状含石榴子石花岗岩侵位年龄一致,共同记录了该区的一期岩浆活动。淡色片麻岩中锆石增生边的年龄为1197±26 Ma,记录了晚期的变质事件。这些新的年龄数据强烈支持1375~1151 Ma期间东南极Windmill群岛与西澳大利亚Albany-Fraser造山带相连接的构造模型,同时也为罗迪尼亚超大陆拼合过程提供了重要的年代学约束。 相似文献
17.
K.A. Dokukina T.B. Bayanova T.V. Kaulina A.V. Travin M.V. Mints A.N. Konilov P.A. Serov 《Russian Geology and Geophysics》2012,53(10):1023-1054
Within the Belomorian eclogite province, near Gridino Village, rocks of different compositions (tonalite-trondhjemite-granodioritic gneisses, granites, mafic and ultramafic rocks) were metamorphosed. The metamorphism included subsidence with increasing pressure and temperature, an eclogite stage, decompression in the granulitic facies, and a retrograde stage in the amphibolitic facies. We attempted to characterize the succession and to date igneous and metamorphic events in the evolution of the Gridino eclogite association. For this purpose, we conducted the following studies: U–Pb isotope dating of zircon (conventional and SHRIMP II methods) from gneisses, a mafic dike, and a high-pressure granitic leucosome; U–Pb dating of rutile from mafic dikes; 40Ar/39Ar dating of amphibole and mica; and Sm–Nd studies of rocks and minerals. The Sm–Nd model ages of felsic (2.9–3.1 Ga) and mafic (3.0–3.4 Ga) rocks from the Gridino eclogite association and individual magmatic zircon grains with an age of ca. 3.0 Ga indicate the Mesoarchean age of the metamorphic-rock protoliths. The most reliable result is the upper age bound of eclogitic metamorphism (2.71 Ga), which reflects the time of the posteclogitic decompression melting of eclogitized rocks under high-pressure retrograde granulitic metamorphism. The mafic dikes formed from 2.82 Ga to 2.72 Ga, most probably, at 2.82 Ga, in accordance with the crystallization age of magmatic zircon from metagabbro. Superimposed amphibolitic metamorphism and the “final” exhumation of metamorphic complexes at 2.0–1.9 Ga are associated with the later Svecofennian tectonometamorphic stage. Successive cooling of the metamorphic associations to 300 °C at 1.9–1.7 Ga is shown by U–Pb rutile dating and 40Ar/39Ar mica dating. 相似文献
18.
Dmitry P. Gladkochub Sergei A. Pisarevsky Tatiana V. Donskaya Richard E. Ernst Michael T.D. Wingate Ulf Söderlund Anatoliy M. Mazukabzov Eugene V. Sklyarov Michael A. Hamilton John A. Hanes 《Precambrian Research》2010
We present a summary of late Paleoproterozoic to Neoproterozoic mafic magmatism in the Siberian craton, including recently published U–Pb and 40Ar–39Ar dates. These new precise ages suggest that at least some of the previously published K–Ar ages of Siberian mafic bodies should be ignored. The time–space geochronological chart, or the ‘barcode’ of mafic magmatic events shows significant differences between northern and southern Siberia. Both are characterized by ∼1900–1700 Ma magmatic events, but then there was an almost 1 Ga mafic magmatic ‘pause’ in south Siberia until ∼800 Ma. Meanwhile there are indications of multiple mafic magmatic events in North Siberia (Anabar shield and Olenek uplift) between ∼1600 and 1000 Ma. A series of magmatic events probably related to the breakup of Rodinia occurred in southern Siberia after ∼800 Ma. So far, there are no indications of late Neoproterozoic mafic magmatism in North Siberia. Ca. 1000–950 Ma mafic sills were reported from Meso- to Neo-Proterozoic sedimentary successions in the Sette-Daban area on the east side of the Siberian craton, but their tectonic setting is debated. Recent Ar–Ar dates of ∼1750 Ma for NW-trending dykes in the Aldan and Anabar shields, together with similar-age NNE-trending Baikal uplift dykes in south-eastern Siberia suggest the existence of a giant radial dyke swarm possibly related to a mantle plume centred in the Vilyui River area. 相似文献
19.
Eclogite occurs within the southern domain of the East Athabasca mylonite triangle in northern Saskatchewan. Situated at the boundary between the Archean Rae and Hearne Provinces of the western Canadian Shield, the East Athabasca mylonite triangle is a fundamental exposure of the ~3,000-km-long Snowbird tectonic zone. The eclogite occurs in association with a variety of lower crustal high-pressure granulites that record a complex metamorphic history from 2.6 to 1.9 Ga. Temperatures of the eclogite facies metamorphism are constrained by garnet-clinopyroxene exchange thermometry at 920–1,000 °C. Minimum pressure conditions are recorded by the jadeite+quartz=albite geobarometer at 1.8–2.0 GPa. A near-isothermal decompression path to granulite facies conditions is inferred from retrograde reaction textures involving the formation of granulite facies assemblages such as orthopyroxene-plagioclase and pargasite-plagioclase. U-Pb IDTIMS zircon geochronology of the eclogite yields a weighted mean 207Pb/206Pb date of 1,904.0±0.3 Ma, which we interpret as the time of peak eclogite facies metamorphism. SHRIMP in situ analyses of metamorphic zircons included within omphacitic clinopyroxene support this interpretation with a weighted mean 207Pb/206Pb date of 1,905±19 Ma. Inclusion suites of high-pressure phases and the petrographic setting of zircon are a direct link between zircon growth and eclogite facies metamorphism. Zircon from one eclogite sample has older cores that are 2.54 Ga, which is a minimum age for the emplacement or earliest metamorphism of the gabbroic protolith. U-Pb rutile data indicate slow cooling at ~1°C/Ma below ~500 °C from 1.88 to 1.85 Ga. The formation and exhumation of the eclogites at ca.1.9 Ga has important implications for the tectonic significance of the Snowbird tectonic zone during the Paleoproterozoic. The eclogites described here are consistent with transport of continental crust to mantle depths during the Paleoproterozoic, followed by rapid buoyancy-driven exhumation to normal lower crustal depths.Editorial responsibility: T.L. Grove 相似文献
20.
Jason E. French Larry M. Heaman Thomas Chacko Rajesh K. Srivastava 《Precambrian Research》2008,160(3-4):308-322
A newly recognized remnant of a Paleoproterozoic Large Igneous Province has been identified in the southern Bastar craton and nearby Cuddapah basin from the adjacent Dharwar craton, India. High precision U–Pb dates of 1891.1 ± 0.9 Ma (baddeleyite) and 1883.0 ± 1.4 Ma (baddeleyite and zircon) for two SE-trending mafic dykes from the BD2 dyke swarm, southern Bastar craton, and 1885.4 ± 3.1 Ma (baddeleyite) for a mafic sill from the Cuddapah basin, indicate the existence of 1891–1883 Ma mafic magmatism that spans an area of at least 90,000 km2 in the south Indian shield.This record of 1.9 Ga mafic/ultramafic magmatism associated with concomitant intracontinental rifting and basin development preserved along much of the south-eastern margin of the south Indian shield is a widespread geologic phenomenon on Earth. Similar periods of intraplate mafic/ultramafic magmatism occur along the margin of the Superior craton in North America (1.88 Ga Molson large igneous province) and in southern Africa along the northern margin of the Kaapvaal craton (1.88–1.87 Ga dolerite sills intruding the Waterberg Group). Existing paleomagnetic data for the Molson and Waterberg 1.88 Ga large igneous provinces indicate that the Superior and Kalahari cratons were at similar paleolatitudes at 1.88 Ga but a paleocontinental reconstruction at this time involving these cratons is impeded by the lack of a robust geological pin such as a Limpopo-like 2.0 Ga deformation zone in the Superior Province. The widespread occurrence of 1.88 Ga intraplate and plate margin mafic magmatism and basin development in numerous Archean cratons worldwide likely reflects a period of global-scale mantle upwelling or enhanced mantle plume activity at this time. 相似文献