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1.
Qing Qian Jun Gao Reiner Klemd Guoqi He Biao Song Dunyi Liu Ronghua Xu 《International Journal of Earth Sciences》2009,98(3):551-569
Traditionally the Chinese South Tianshan has been regarded as a late Paleozoic orogenic belt. However, little is known about
the early Paleozoic tectonic architecture of the region. This paper presents the first evidence of Cambrian–Ordovician MORB-type
basalts and adakitic diorites on the southern margin of the Yili plate in China. Basalts from Xiate in southwestern Tianshan
show a typical transitional (T-) MORB and ferrobasalt composition, which indicate a formation at a propagating spreading ridge.
The basalts give a weighted mean 206Pb/238U crystallization age of 516.3 ± 7.4 Ma by SHRIMP U–Pb zircon dating and have experienced contact metamorphism due to the
intrusion of a dioritic pluton. The dioritic pluton has a weighted mean 206Pb/238U crystallization age of 470 ± 12 Ma and geochemical characteristics resembling that of adakitic rocks. The pluton is considered
to have been formed by partial melting of garnet amphibolites from thickened lower crust in arc or continental collision settings.
The basalts and diorites are considered to outline the eastern extension of the early Paleozoic suture zone, the Nikolaev
Line, which stretches east–west for hundreds of kilometers between the Northern Tianshan and Central Tianshan terranes of
Kyrgyzstan. Our findings substantiate that the Yili and Central Tianshan plates were separated by the early Paleozoic Terskey
ocean. The Terskey ocean probably closed during the early stage of the late Ordovician (Lomize et al. in Geotectonics 31(6):463–482,
1997), resulting in the final amalgamation of the Yili and Central Tianshan plates. Consequently, an early Paleozoic suture zone
is documented in the Chinese Tianshan region, which is most likely represented by the North Nalati fault. 相似文献
2.
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
3.
Geochronological, isotopic, and geochemical data from Permo-Triassic granitic gneisses and granitoids of the Colombian Central Andes 总被引:1,自引:1,他引:1
C.J. Vinasco U.G. Cordani H. Gonzlez M. Weber C. Pelaez 《Journal of South American Earth Sciences》2006,21(4):355
New U–Pb SHRIMP ages in zircon, Ar–Ar ages in micas and amphiboles, Nd–Sr isotopes, and major and REE geochemical analyses in granitic gneisses and granitic stocks of the Central Cordillera of Colombia indicate the presence of a collisional orogeny in Permo-Triassic times in the Northern Andes related to the construction of the Pangea supercontinent. The collision is recorded by metamorphic U–Pb SHRIMP ages in inherited zircons around 280 Ma and magmatic U–Pb SHRIMP ages in neoformed zircons around 250 Ma within syntectonic crustal granitic gneisses. Magmatic U–Pb SHRIMP and Ar–Ar Triassic ages around 228 Ma in granitic stocks indicate the presence of late tectonic magmatism related to orogenic collapse and the beginning of the breakup of the supercontinent. During this period, the Central Cordillera of Colombia would have been located between the southern United States and northern Venezuela, in the leading edge of the Gondwana supercontinent. 相似文献
4.
Paolo D’Adda Andrea Zanchi Maria Bergomi Fabrizio Berra Marco G. Malusà Annalisa Tunesi Stefano Zanchetta 《International Journal of Earth Sciences》2011,100(5):1095-1113
The Triassic succession of the central Southern Alps (Italy) is stacked into several units bounded by south-verging low-angle
thrust faults, which are related to two successive steps of crustal shortening. The thrust surfaces are cut by high-angle
extensional and strike-slip faults, which controlled the emplacement of hypabissal magmatic intrusions that post-date thrusts
motions. Intrusion ages based on SHRIMP U–Pb zircon dating span between 42 ± 1 and 39 ± 1 Ma, suggesting close time relationships
with the earliest Adamello intrusion stages and, more in general, with the widespread calc-alkaline magmatism described in
the Southern Alps. Fission-track ages of magmatic apatites are indistinguishable from U–Pb crystallization ages of zircons,
suggesting that the intrusion occurred in country rocks already exhumed above the partial annealing zone of apatite (depth < 2–4 km).
These data indicate that the central Southern Alps were already structured and largely exhumed in the Middle Eocene. Although
we describe minor faults affecting magmatic bodies and local reactivations of older structures, no major internal deformations
have occurred in the area after the Bartonian. Neogene deformations were instead concentrated farther south, along the frontal
part of the belt. 相似文献
5.
HUO Hailong CHEN Zhengle ZHANG Qing HAN Fengbin ZHANG Wengao SUN Yue YANG Bin TANG Yanwen 《《地质学报》英文版》2019,93(5):1188-1204
The Baleigong granites, located in the western part of the southwestern Tianshan Orogen(Kokshanyan region, China), records late Paleozoic magmatism during the late stages of convergence between the Tarim Block and the Central Tianshan Arc Terrane. We performed a detailed geochronological and geochemical study of the Baleigong granites to better constrain the nature of collisional processes in the Southwest Tianshan Orogen. The LA-ICP-MS U-Pb zircon isotopic analyses indicate that magmatism commenced in the early Permian(~282 Ma). The granite samples, which are characterized by high contents of SiO_2(67.68–69.77 wt%) and Al_2O_3(13.93–14.76 wt%), are alkali-rich and Mg-poor, corresponding to the high-K calc-alkaline series. The aluminum saturation index(A/CNK) ranges from 0.93 to 1.02, indicating a metaluminous to slightly peraluminous composition. Trace element geochemistry shows depletions in Nb, Ta, and Ti, a moderately negative Eu anomaly(δEu=0.40–0.56), enrichment in LREE, and depletion in HREE((La/Yb)_N=7.46–11.78). These geochemical signatures are characteristic of an I-type granite generated from partial melting of a magmatic arc. The I-type nature of the Baleigong granites is also supported by the main mafic minerals being Fe-rich calcic hornblende and biotite. We suggest that the high-K, calc-alkaline I-type granitic magmatism was generated by partial melting of the continental crust, possibly triggered by underplating by basaltic magma. These conditions were likely achieved in a collisional tectonic setting, thus supporting the suggestion that closure of the South Tianshan Ocean was completed prior to the Permian and was followed(in the late Paleozoic) by collision between the Tarim Block and the Central Tianshan Arc Terrane. 相似文献
6.
Evolution of calc-alkaline to alkaline magmatism through Carboniferous convergence to Permian transcurrent tectonics,western Chinese Tianshan 总被引:7,自引:0,他引:7
Bo Wang Dominique Cluzel Liangshu Shu Michel Faure Jacques Charvet Yan Chen Sebastien Meffre Koen de Jong 《International Journal of Earth Sciences》2009,98(6):1275-1298
Continuous magmatic activity occurred in the western Chinese Tianshan, Central Asia, from the Carboniferous to the Permian,
i.e. before and after the Late Carboniferous amalgamation of Junggar and the Yili Blocks. Zircon U–Pb LA-ICPMS and Ar–Ar data
reveal a coincidence in time between regional wrench faulting and granitoid emplacement. Permian post-collisional granitoids
crop out within or at the margins of large-scale dextral strike-slip shear zones, some of them show synkinematic fabrics.
The whole rock geochemical features of the Early-Middle Permian granitoids indicate an evolution from high-K calc-alkaline
towards alkaline series. In other places of the North Tianshan, alkaline magmatism occurred together with deep marine sedimentation
within elongated troughs controlled by wrench faults. Therefore, in contrast with previous interpretations that forwarded
continental rift or mantle plume hypotheses, the coexistence of diverse magmatic sources during the same tectonic episode
suggests that post-collisional lithosphere-scale transcurrent shearing tightly controlled the magmatic activity during the
transition from convergent margin to intraplate anorogenic processes. 相似文献
7.
Liangshu Shu Bo Wang Wenbin Zhu Zhaojie Guo Jacques Charvet Yuan Zhang 《International Journal of Earth Sciences》2011,100(7):1647-1663
This paper describes an olistostrome formation and accompanied bimodal volcanic rocks occurring in the Baiyanggou area, south
of Bogda Shan. The main lithotectonic units consist of olistostrome, volcanic rocks and turbidite. The olistostrome is tectonically
underlain by Upper Carboniferous limestone and sandstone along a NEE-trending detachment fault. Paleo-growth fault is locally
observed. The olistostrome unit includes plenty of blocks of limestone, sandstone, rhyolite and volcaniclastic rocks, and
a matrix of graywacke. Limestone blocks are dated as Pennsylvanian-Bashkirian in age by the coral and brachiopod fossils that
are extensively recognized in the Upper Carboniferous strata. The volcanic unit consists of pillowed and massive basalt and
rhyolite, the latter occur as an 8- to 10-meter-thick layer above the olistostrome unit. The turbidite unit is mainly composed
of chert, siliceous mudstone and sandstone, within which the Bouma sequence can be locally recognized. Meter-wide gabbro and
diabase dykes intrude these three units. Geochemically, rhyolites are characterized by high ACNK value of >1.1, depletion
of Ba, Nb and Sm, and enrichment in Rb, Th and Zr. Basaltic rocks are rich in K2O, they show a LREE-enriched pattern and depletion in Ba, Nb and Zr, and enrichment in Ti, Ce and Hf, similar to continental
rift-type tholeiite series. A gabbro porphyrite intruding the olistostrome was dated at 288 ± 3 Ma by a sensitive high-resolution
ion microprobe (SHRIMP) zircon U–Pb method, and a rhyolite at 297 ± 2 Ma by a laser ablation inductively coupled plasma mass
spectrometer (LA-ICPMS) zircon U–Pb method. The Baiyanggou olistostrome and accompanying bimodal volcanic series are linked
to an extensional setting that developed in the south of the Bogda Shan. Several lines of evidence, e.g. occurrence of large-scale
strike-slip shear zones, large number of mantle-derived magmatic rocks and available geochronological data, demonstrate a
significant geodynamic change from convergence to extension in the Chinese Tianshan belt, even in the whole Central Asian
Orogenic Belt. The extension in the Chinese Tianshan belt is initiated at ca. 300 Ma, i.e. around Carboniferous–Permian boundary
times, and the peak period of intra-plate magmatism occurred in the interval of 300–250 Ma. 相似文献
8.
Two distinct Precambrian terranes in the Southern Prince Charles Mountains, East Antarctica: SHRIMP dating and geochemical constraints 总被引:1,自引:0,他引:1
The Southern Prince Charles Mountains (SPCM) are mostly occupied by the Archaean Ruker Terrane. The Lambert Terrane crops out in the northeastern part of the SPCM. New geochemical and zircon U–Pb SHRIMP ages for felsic orthogneisses and granitoids from both terranes are presented. Orthogneisses from the Ruker and Lambert terranes differ significantly in their major and trace-element compositions. Those from the Ruker Terrane comprise two distinct groups: rare Y-depleted and abundant Y-undepleted. U–Pb isotopic data provide evidence for tonalite−trondhjemite emplacement at 3392 ± 9 and 3377 ± 9 Ma, pre-tectonic granite emplacement at 3182 ± 9 Ma, metamorphism(?) at c. 3145 Ma, and thermal events at c. 1300(?) and 626 ± 51 Ma. The Lambert Terrane orthogneisses probably originated in a continental magmatic arc. Zircon dating shows a very different geological history: pre-tectonic granitoid emplacement at 2423 ± 18 Ma, metamorphism at 2065 ± 23 Ma, and syn-tectonic granitoid emplacement at 528 ± 6 Ma, syn-tectonic pegmatite emplacement at 495 ± 18 Ma. The Lambert Terrane can be correlated with neither the Meso- to Neoproterozoic Beaver Terrane in the Northern PCM, which differs in isotopic composition, nor with the Archaean Ruker Terrane, which differs in both granitoid chemical composition and the timing of major geological events. It represents a Palaeoproterozoic orogen which experienced strong tectonic re-activation in Pan-African times. The Lambert Terrane has some geochronological features in common with the Mawson Block, which comprises south Australia and some areas in East Antarctica. 相似文献
9.
10.
The Qinling–Dabie–Sulu orogenic belt is the junction between the North and South China blocks, which resulted from the final amalgamation of China continents during the Indosinian. Indosinian granitoids are widespread in the Qinling orogen, and their geneses can thus constrain the evolution of China continent. We carried out a combined U–Pb zircon dating and geochemical study for the Shuangpengxi granodiorite pluton and the Xiekeng diorite–granodiorite pluton in the middle part of the West Qinling orogen. U–Pb zircon dating shows that the magma crystallization ages of 242 ± 3 Ma for the Shuangpengxi pluton and ~244–242 Ma for the Xiekeng pluton. Geochemical and Sr–Nd–Hf isotopic compositions reveal that the magma of the Shuangpengxi granodiorite was derived from partial melting of crustal materials. The Xiekeng diorites can be divided into high-Al diorite and high-Mg diorite. Both of them resulted from partial melting of enriched lithospheric mantle, but their mantle source had been modified by previous slab-derived melt. The high-Al diorite was formed by fractional crystallization of olivine, pyroxene and/or preferential accumulation of plagioclase, and the high-Mg diorite was formed by fractional crystallization of olivine and/or preferential accumulation of pyroxene. The Xiekeng granodioritic porphyry was formed by mixing of crust-derived and mantle-derived melts. We propose that the Early Indosinian magmatism resulted from break-off of subducted oceanic slab after collision. The slab break-off model can well explain the linear distribution of the Early Indosinian plutons and rapid crustal uplift during the Middle Triassic in the West Qinling. 相似文献
11.
《International Geology Review》2012,54(11):1058-1066
The plate-tectonic evolution of the Tarim basin and nearby western Tianshan region during Paleozoic time is reconstructed in an effort to further constrain the tectonic evolution of Central Asia, providing insights into the formation and distribution of oil and gas resources. The Tarim plate developed from continental rifting that progressed during early Paleozoic time into a passive continental margin. The Yili terrane (central Tianshan) broke away from the present eastern part of Tarim and became a microcontinent located somewhere between the Junggar ocean and the southern Tianshan ocean. The southern Tianshan ocean, between the Tarim craton and the Yili terrane, was subducting beneath the Yili terrane from Silurian to Devonian time. During the Late Devonian-Early Carboniferous, the Tarim plate collided with the Yili terrane by sinistral accretional docking that resulted in a late Paleozoic deformational episode. Intracontinental shortening (A-type subduction) continued through the Permian with the creation of a magmatic belt. 相似文献
12.
Edson F. Mello Roberto P. Xavier Neal J. McNaughton Steffen G. Hagemann Ian Fletcher Larry Snee 《Mineralium Deposita》2006,40(8):849-866
U–Pb sensitive high resolution ion microprobe mass spectrometer (SHRIMP) ages of zircon, monazite and xenotime crystals from felsic intrusive rocks from the Rio Itapicuru greenstone belt show two development stages between 2,152 and 2,130 Ma, and between 2,130 and 2,080 Ma. The older intrusions yielded ages of 2,152±6 Ma in monazite crystals and 2,155±9 Ma in zircon crystals derived from the Trilhado granodiorite, and ages of 2,130±7 Ma and 2,128±8 Ma in zircon crystals derived from the Teofilândia tonalite. The emplacement age of the syntectonic Ambrósio dome as indicated by a 2,080±2-Ma xenotime age for a granite dyke probably marks the end of the felsic magmatism. This age shows good agreement with the Ar–Ar plateau age of 2,080±5 Ma obtained in hornblendes from an amphibolite and with a U–Pb SHRIMP age of 2,076±10 Ma in detrital zircon crystals from a quartzite, interpreted as the age of the peak of the metamorphism. The predominance of inherited zircons in the syntectonic Ambrósio dome suggests that the basement of the supracrustal rocks was composed of Archaean continental crust with components of 2,937±16, 3,111±13 and 3,162±13 Ma. Ar–Ar plateau ages of 2,050±4 Ma and 2,054±2 Ma on hydrothermal muscovite samples from the Fazenda Brasileiro gold deposit are interpreted as minimum ages for gold mineralisation and close to the true age of gold deposition. The Ar–Ar data indicate that the mineralisation must have occurred less than 30 million years after the peak of the metamorphism, or episodically between 2,080 Ma and 2,050 Ma, during uplift and exhumation of the orogen.Electronic supplementary material Supplementary material is available for this article at 相似文献
13.
Jiří Žák Zuzana Kratinová Jakub Trubač Vojtěch Janoušek Jiří Sláma Jan Mrlina 《International Journal of Earth Sciences》2011,100(7):1477-1495
The Štěnovice and Čistá granodiorite–tonalite plutons are small (~27 and ~38 km2, respectively) intrusions that are largely discordant to regional ductile structures in the center of the upper-crustal Teplá–Barrandian
unit, Bohemian Massif. Their whole-rock and trace-element compositions are consistent with medium-K calc-alkaline magma, generated
above a subducted slab in a continental margin arc setting. The U–Pb zircon age of the Štěnovice pluton, newly determined
at 375 ± 2 Ma using the laser ablation ICP-MS technique, is within the error of the previously published Pb–Pb age of 373 ± 1 Ma
for the Čistá pluton. The two plutons also share other characteristics that are typical of concentrically expanded plutons
(CEPs), such as elliptical cross-section in plan view, steep contacts, inferred downward-narrowing conical shape, faint normal
zoning, and margin-parallel magmatic foliation decoupled from the regional host-rock structures. We interpret the Štěnovice
and Čistá plutons as representing the initial Late Devonian stage of much more voluminous early Carboniferous arc-related
plutonism (represented most typically by the Central Bohemian Plutonic Complex) in the upper crust of the central Bohemian
Massif. These two plutons are important tectonic elements in that they indicate an overall shift of the arc-related plutonic
activity from the ~NW to the ~SE, accompanied with a general compositional trend of the magmas from medium-K calc-alkaline
to shoshonitic/ultrapotassic. Such a pattern is compatible with SE-directed subduction of the Saxothuringian Ocean beneath
the Teplá–Barrandian overriding plate as a cause of arc-related magmatism in this part of the Bohemian Massif. 相似文献
14.
Binyam W. Woldemichael Jun-Ichi Kimura Daniel J. Dunkley Kenichiro Tani Hiroto Ohira 《International Journal of Earth Sciences》2010,99(8):1773-1790
The reworked Pre-Neoproterozoic and juvenile Neoproterozoic terrane of the Western Ethiopian Shield (WES) consists of three
N–S trending terranes. These are the western migmatitic gneissic terrane, the central metavolcano sedimentary terrane (CVST)
and the eastern migmatitic gneissic terrane. The eastern part of the CVST mostly consists of suture-related ultramafic-metasedimentary
complexes, whereas metavolcanics predominate in the western part. Gabbroic to granitic intrusions frequently occur in the
CVST and in adjacent areas. New zircon SHRIMP U–Pb ages for two gabbros and three diorites in the Ghimbi-Nedjo region of the
WES indicate magmatic crystallization ages. Two pulses of magmatism, at 860–850 and 795–785 Ma, are documented with the former
for the first time. The tholeiitic Kemashi diorite and Bikilal-Ghimbi gabbros have oceanic affinities and yield U/Pb zircon
ages of 856.3 ± 9.8 and 846.0 ± 7.6 Ma, respectively. The calc-alkaline Gebeya Kemisa pyroxene diorite, and the Senbet Dura
hornblende diorite plus the tholeiitic Wayu Meni gabbro, which collectively have arc-back arc characteristics are indistinguishable
at ages of 794.3 ± 9.4, 787.7 ± 8.8 and 778.1 ± 6.3 Ma, respectively. Positive εNd (4.5–7.0) and low initial 87Sr/86Sr (0.7029 ± 0.0002) and a mean T
DM model age of 0.95 Ga for the Ghimbi-Nedjo region (mean T
DM model age of 0.95 Ga for the WES overall) indicate that the magmas were generated from juvenile Neoproterozoic depleted mantle
sources, with no discernable involvement of pre-Neoproterozoic continental crust. The occurrence of gabbros and diorites with
oceanic tholeiite affinities combined with the new ages suggests that the intrusions were emplaced in the earliest stages
of the rifting of Rodinia. This event in the WES led to the development of a passive margin and associated plume-type magmatism
at ~855 Ma. The two intrusive groups with differing magma chemistry and ages suggest that the earliest magmatism was tholeiitic
and associated with the passive margin system followed by continental breakup to form the Mozambique Ocean. The combination
of tholeiitic and calc-alkaline magmatism was related to arc and back-arc basin formation and later terrane accretion (~830–690 Ma). 相似文献
15.
In situ isotopic (U–Pb, Lu–Hf) and trace element analyses of zircon populations in six samples of the intrusive Mawson Charnockite,
east Antarctica, emphasise complex zircon behaviour during very high-grade metamorphism. The combination of geochemical data
sets is used to distinguish xenocrysts and identify a population of primary igneous zircon in situations where U–Pb data spread
close to concordia over a few hundred Myr. The population is filtered to exclude grains with: (1) U–Pb ages >2% discordant,
(2) anomalous trace element-content (Th, U, Y, REE) and (3) outlying Hf-isotopic values. Rare metamorphic-type grains were
also excluded. Upon filtering the population, minimum emplacement ages for each sample were determined using the oldest grain(s).
This approach improves upon age determinations in complex data sets that use weighted mean or isochron methods. Our results
suggest that the Mawson Charnockite was emplaced episodically at c. 1145–1140 Ma, c. 1080–1050 Ma and c. 985–960 Ma. Core-outer core-rim and core-rim textures were identified but are not correlated with U–Pb ages. We establish
that recrystallisation (mainly of zircon rims) must have occurred shortly following igneous crystallisation and that metamictisation/cracking
is a Paleozoic to Recent event. Therefore, intra-zircon diffusion in a high-T, high-strain environment during Meso-Neoproterozoic orogenesis is inferred to have caused the extensive U–Pb isotopic disturbance.
Charnockitic magmatism prior to c. 1,000 Ma has not previously been recorded in the Mawson region and indicates that orogenesis may have commenced c. 150 Myr earlier than previously thought. Correlations with similar aged rocks in adjacent regions have implications for supercontinent
reconstructions. 相似文献
16.
Age constraints on the evolution of the Austroalpine basement to the south of the Tauern Window 总被引:1,自引:0,他引:1
Siegfried Siegesmund Till Heinrichs Rolf L. Romer Daniel Doman 《International Journal of Earth Sciences》2007,96(3):415-432
The Austroalpine basement to the south of the Tauern Window once was part of the northern margin of Gondwana. It includes
the “Altkristallin” and the phyllitic Thurntaler Complex. In the Altkristallin (AMU, MPU), suites of arc-related metamafic
sequences occur together with calc-alkaline metagranite. SHRIMP U–Pb dating of zircon from calc-alkaline metagranite associated
with an eclogitic amphibolite give an age of 470 ± 3 Ma interpreted as the age of protolith emplacement. In the Thurntaler
Complex, metaporphyroids occur together with tholeiitic as well as alkaline within-plate basalt-type metabasite. The metaryholites
of this association give a crystallization SHRIMP age of 477 ± 4 Ma, which suggests contemporaneity of arc-related and extensional
settings in the Austroalpine basement units. The age data demonstrate widespread magmatic activity associated with the Early-Ordovician
amalgamation at the end of the 550–470 Ma subduction–accretion–collision cycle. The Pb–Pb and U–Pb systematics of step-wise
leached staurolite and kyanite from the peak-metamorphic assemblage of the Altkristallin indicate that (1) step-wise leaching
of staurolite and kyanite yields the age of inclusions rather than the host; (2) zircon inclusions in staurolite suggest an
Ordovician or older age for the precursor of the staurolite-schists; (3) the weighted average of the 206Pb/238U data of the various leaching steps yields a Variscan age for the inclusions (ilmenite, biotite, and andesine). Since these
inclusions are part of the metamorphic mineral assemblage, this age provides a minimum estimate for staurolite growth, i.e.,
metamorphism. Thus, the Pb–Pb and U–Pb systematics of staurolite provide evidence for a Variscan metamorphism of the Austroalpine
basement, e.g., MPU, AMU and Thurntaler Complex, to the south of the Tauern Window. 相似文献
17.
Hans-Jürgen F?rster Dieter Rhede Holly J. Stein Rolf L. Romer Gerhard Tischendorf 《International Journal of Earth Sciences》2012,101(1):57-67
We present geochronological data for late-Variscan magmatism in the Lausitz Block of the Saxo-Thuringian Zone, Germany. The
Th–U–total Pb age of uraninite and the Re–Os age of molybdenite from the composite biotite–monzogranite pluton of K?nigshain
overlap at the 2σ confidence limit: 328.6 ± 1.9 Ma (uraninite), and 327.0 ± 1.3 Ma and 327.6 ± 1.3 Ma (molybdenite), indicating
that crystallization of magmatic uraninite and deposition of molybdenite were nearly contemporaneous. These data imply that
magmatic processes in this part of the Variscan orogen already started in latest Visean time, about 10 Ma earlier than previously
assumed (315–320 Ma). The new ages correspond to ages for plutonic rocks in the Elbe Zone immediately west of the Lausitz
(around 335–325 Ma) and the bulk of late-Variscan igneous rocks in the Saxo-Thuringian Zone (335–320 Ma). 相似文献
18.
The Danish island of Bornholm is located at the southwestern margin of the Fennoscandian Shield, and features exposed Precambrian
basement in its northern and central parts. In this paper, we present new U–Pb zircon and titanite ages for granites and orthogneisses
from 13 different localities on Bornholm. The crystallization ages of the protolith rocks all fall within the range 1,475–1,445 Ma
(weighted average 207Pb/206Pb ages of zircon). Minor age differences, however, may imply a multi-phase emplacement history of the granitoid complex.
The presence of occasional inherited zircons (with ages of 1,700–1,800 Ma) indicates that the Bornholm granitoids were influenced
by older crustal material. The east–west fabric observed in most of the studied granites and gneisses, presumably originated
by deformation in close connection with the magmatism at 1,470–1,450 Ma. Most titanite U–Pb ages fall between 1,450 and 1,430 Ma,
reflecting post-magmatic or post-metamorphic cooling. Granitoid magmatism at ca. 1.45 Ga along the southwestern margin of
the East European Craton has previously been reported from southern Sweden and Lithuania. The ages obtained in this study
indicate that the Bornholm magmatism also was part of this Mesoproterozoic event. 相似文献
19.
Pedro Castiñeiras Carlos Villaseca Luis Barbero Cristina Martín Romera 《International Journal of Earth Sciences》2008,97(1):35-50
U–Pb SHRIMP ages obtained in zircons from the Sotosalbos and Toledo anatectic complexes in Central Spain give new constraints
to the evolution of the inner part of the Hercynian Iberian belt. Pre-Hercynian ages in zircons from the Sotosalbos complex
(∼464 Ma) are well preserved and reveal that an age diversity of the Lower Paleozoic magmatism in the area exists, as previous
data on westernmost orthogneisses yield significant older ages. Zircon ages in the pelite-derived granites from the Toledo
complex also show an important Neoproterozoic age component which points to a metasedimentary protolith deposited maximally
560 Ma ago. Younger zircon populations in both complexes at ∼330 Ma in the Sotosalbos region and ∼317 Ma in the Toledo complex
indicate an important diachronism between the anatectic processes in both areas but also that these processes are mainly unrelated
to the generation of the later Hercynian granite batholith of Central Spain, which could be of deeper crustal derivation.
In addition, as migmatization occurred late in the metamorphic cycle, after peak conditions were attained, the age of anatexis
is younger than the age of the main Hercynian metamorphic event, which still is not well constrained.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
20.
The South Tian Shan, which is located along the southwestern margin of the Central Asian Orogenic Belt, is widely accepted as a collisional orogen between the Kazakhstan-Yili Block in the north and the Tarim Craton in the south, and the collision is thought to have occurred in either Late Paleozoic or Triassic. Regardless of the timing of the collision, the major magmatic events in the South Tian Shan Orogen should be related to subduction, collision and post-collision. We investigate this problem through U–Pb age of detrital zircons from the eastward-flowing Tekes River and its southern branches flowing through the northern slope of the Chinese South Tian Shan. A total of 500 analyses on 494 zircon grains from five sand samples yield an age range of 2590 to 268 Ma, but they are dominated by Paleozoic magmatic zircon grains, with some Precambrian population, but no Mesozoic and Cenozoic grains were detected. One of the samples from the Tekes River contains zircon grains from the Chinese South Tian Shan and other areas because the river receives its discharge from multiple sources. The other four samples were collected from four branches originating from the Chinese South Tian Shan only. From west to east, the sample from the Kayintemuzhate River shows two peak ages of 475 and 345 Ma, sample from the Muzhaerte (also called Xiate) River has peak ages of 422 and 290 Ma, sample from the Akeyazi River is characterized by a single peak age of 421 Ma, and sample from the Kekesu River shows a more complicated spectra with peak ages of 426, 398, 362, 327, and 285 Ma. When pooled together, the four samples yield four distinct age populations of 500–460, 450–390, 360–320, and 300–270 Ma, indicating the major magmatic events in the Chinese South Tian Shan. These results, combined with regional data, show an absence of Mesozoic magmatic events in the drainage areas of the Tekes River, and thus the South Tian Shan does not seem to be a Triassic orogen because of the lack of syn-collisional and post-collisional magmatism. The 300–270 magmatic event is thought to post-date the closure of the South Tian Shan Ocean, while the 360–320 and 450–390 Ma events were closely related to the northward subduction of the South Tian Shan Ocean. Our results strongly suggest a Late Carboniferous (320–300 Ma) collision between the Kazakhstan-Yili Block and the Tarim Craton. Possibly, the 500–460 Ma magmatism was related to subduction and closure of the Early Paleozoic Terskey Ocean. 相似文献