共查询到20条相似文献，搜索用时 312 毫秒
1.
To better constrain the Early Paleozoic tectonic evolution of the western part of the Erguna–Xing’an Block, detrital zircon U–Pb dating was applied on the Ordovician to Devonian sedimentary strata along the southeast part of the China–Mongolia border. Most of the zircons from five sedimentary samples display fine-scale oscillatory growth zoning and Th/U ratios higher than 0.1, indicating a magmatic origin. All five Ordovician–Devonian samples display the similar age distribution patterns with age groups at ∼440 Ma, ∼510 Ma, ∼800 Ma, ∼950 Ma, and few Meso- to Paleo-Proterozoic and Neoarchean grains. This age distribution pattern is similar to those from adjacent blocks in the southeastern Central Asian Orogenic Belt. Considering previous tectonic studies, we propose bidirectional provenances from the Erguna–Xing’an Block and Baolidao Arc.Consequently, a new model was proposed to highlight the Early Paleozoic tectonic evolution of the western Erguna–Xing’an Block, which constrains two main Early Paleozoic tectonic events of the Xing-Meng Orogenic Belt: (a) pre-Late Cambrian collision between Erguna–Kerulen Block and Arigin Sum-Xilinhot-Xing’an Block; (b) the Early Paleozoic subduction of Paleo-Asian Ocean and pre-Late Devonian collision between Erguna–Xing’an Block and Songliao-Hunshandake Block. 相似文献
2.
The Inner Mongolia Highland (IMH), along the northern edge of the North China Craton, was considered to be a long-standing topographic highland, whose exhumation history remains elusive. The aim of this study is to reveal Late Paleozoic exhumation processes of the IMH based on an integrated analysis of stratigraphy, petrography of clastic rocks, and U–Pb ages and Hf isotopes of detrital zircons from Permian–Triassic succession in the middle Yanshan belt. The results of the study show that the Benxi Formation, which was originally regarded as a Late Carboniferous unit, proves to be Early Permian in age because it contains detrital zircons as young as ∼298 Ma. The Lower Shihezi Formation is demonstrated to be a unit whose age spans the boundary of the Middle and Upper Permian, constrained by a U–Pb age of 260 ± 2 Ma from a dacite layer. Clastic compositions of conglomerate and sandstone change markedly, characterised by the predominance of sedimentary components in the Benxi–Shanxi Formations, by large amounts of volcanic clastics in the Lower and Upper Shihezi Formations, and by the presence of both metamorphic and igneous clastics in the Sunjiagou–Ermaying Formations. Sedimentary clastics include chert, carbonate, sandstone and quartzite, which may have been derived from Proterozoic to Lower Paleozoic sedimentary covers. Volcanic clasts were directly related to volcanic eruptions, while granite and gneiss grains were sourced from exhumed Late Paleozoic intrusive rocks and basement rocks. Detrital zircon U–Pb ages can be divided into five populations: 2.6–2.4 Ga, 1.9–1.7 Ga, 400–360 Ma, 325–290 Ma and 270–250 Ma. Precambrian detrital zircons are typically subrounded to rounded in shape, implying a recycling origin. Late Paleozoic zircons show oscillatory zones and their Th/U ratios >0.4, suggesting a magmatic origin. Most Phanerozoic zircons have negative εHf(T) values of −3.2 to −25.5, which are compatible with those of Late Paleozoic plutons in the IMH. The results indicate that the IMH may have been covered with Proterozoic to Lower Paleozoic sedimentary strata, which then underwent subsequent erosion and served as provenances for adjacent Late Paleozoic basins. Vertical changes in both clastic compositions and detrital zircon ages in Permian–Triassic strata imply an unroofing process of the IMH. Three phases of the IMH uplift are distinguished. The first-phase uplift commenced 325–312 Ma and resulted from magmatic intrusion related to southward subduction of the Paleo-Asian Ocean. The second-phase uplift took place in the Middle Permian and may be attributed to crustal contraction related to the collision of the North China Craton and the Southern Mongolia terrane. The third-phase uplift happened at the end of the Permian, and may have been induced by upwelling of calc-alkali magma under an extensional setting. 相似文献
3.
Xiaoping Long Chao Yuan Min Sun Wenjiao Xiao Guochun Zhao Yujing Wang Keda Cai Xiaoping Xia Liewen Xie 《Tectonophysics》2010,480(1-4):213-231
Subduction–accretion complexes occur widely in the Central Asian Orogenic Belt (CAOB). Due to the scarcity of fossils, the depositional timing of the Habahe flysch sequence of the subduction–accretion complex in the Chinese Altai is poorly constrained, which gave rise to much controversy in understanding the time of the basement and the tectonic evolution of the Chinese Altai. U–Pb dating of detrital zircons from the Habahe sequence in the northwestern Chinese Altai reveals a young zircon population with a mean 206Pb/238U age around 438 Ma which, together with a mean 206Pb/238U age of 411 ± 5 Ma for the overlying rhyolite of the Dongxileke Formation, brackets the time of deposition of the sequence between early Silurian and early Devonian. The age of the Dongxileke rhyolite also indicates that the overlying Baihaba Formation possibly began to be deposited in the early Devonian, though U–Pb dating of detrital zircons from this formation gave a maximum depositional age of ～ 438 Ma. The youngest detrital zircons and metamorphic grains of the Habahe sequence reveal different provenance to the sequence in the east. The youngest and metamorphic zircon grains, with early Paleozoic, Neoproterozoic and pre-Neoproterozoic populations, suggest a multi-source for the Habahe sequence. The predominantly early Paleozoic zircons, characterized by concentric zoning, high Th/U ratios and euhedral shapes, imply that the sediments of the sequence were mostly derived from a proximal magmatic source. Based on the age patterns of the Neoproterozoic and pre-Neoproterozoic populations, the Tuva–Mongol Massif, along with adjacent island arcs and metamorphic belts, may be an alternative source region for the Habahe sequence. In view of new geochemical and chronological data for granitoids and advancement in the study of regional metamorphism in the Chinese Altai, we suggest a tectonic model of subduction beneath a huge subduction–accretion complex for the evolution of the Chinese Altai in the early Paleozoic. 相似文献
4.
Early Paleozoic evolution of the northern Gondwana margin is interpreted from integrated in situ U-Pb and Hf-isotope analyses on detrital zircons that constrain depositional ages and provenance of the Lancang Group, previously assigned to the Simao Block, and the Mengtong and Mengdingjie groups of the Baoshan Block. A meta-felsic volcanic rock from the Mengtong Group yields a weighted mean 206Pb/238U age of 462 ± 2 Ma. The depositional age for the previously inferred Neoproterozoic Lancang and Mengtong groups is re-interpreted as Early Paleozoic based on youngest detrital zircons and meta-volcanic age. Detrital U-Pb zircon analyses from the Baoshan Block define three distinctive age peaks at older Grenvillian (1200–1060 Ma), younger Grenvillian (~ 960 Ma) and Pan-African (650–500 Ma), with εHf(t) values for each group similar to coeval detrital zircons from western Australia and northern India. This suggests that the Baoshan Block was situated in the transitional zone between northeast Greater India and northwest Australia on the Gondwana margin and received detritus from both these cratons. The Lancang Group yields a very similar detrital zircon age spectrum to that of the Baoshan Block but contrasts with that for the Simao Block. This suggests that the Lancang Group is underlain by a separate Lancang Block. Similar detrital zircon age spectra suggest that the Baoshan Block and the Lancang Block share common sources and that they were situated close to one another along the northern margin of East Gondwana during the Early Paleozoic. The new detrital zircon data in combination with previously published data for East Gondwana margin blocks suggests the Early Paleozoic Proto-Tethys represents a narrow ocean basin separating an “Asian Hun superterrane” (North China, South China, Tarim, Indochina and North Qiangtang blocks) from the northern margin of Gondwana during the Late Neoproterozoic-Early Paleozoic. The Proto-Tethys closed in the Silurian at ca. 440–420 Ma when this “Asian Hun superterrane” collided with the northern Gondwana margin. Subsequently, the Lancang Block is interpreted to have separated from the Baoshan Block during the Early Devonian when the Paleo-Tethys opened as a back-arc basin. 相似文献
5.
N.S. Tychkov D.S. Yudin E.I. Nikolenko E.V. Malygina N.V. Sobolev 《Russian Geology and Geophysics》2018,59(10):1254-1270
Several thousand clinopyroxene, garnet, and phlogopite inclusions of mantle rocks from Jurassic and Triassic kimberlites in the northeastern Siberian craton have been analyzed and compared with their counterparts from Paleozoic kimberlites, including those rich in diamond. The new and published mineral chemistry data make a basis for an updated classification of kimberlite-hosted clinopyroxenes according to peridotitic and mafic (eclogite and pyroxenite) parageneses. The obtained results place constraints on the stability field of high-Na lherzolitic clinopyroxenes, which affect the coexisting garnet and decrease its Ca contents. As follows from analyses of the mantle minerals from Mesozoic kimberlites, the cratonic lithosphere contained more pyroxenite and eclogite in the Mesozoic than in the Paleozoic. It virtually lacked ultradepleted harzburgite-dunite lithologies and contained scarce eclogitic diamonds. On the other hand, both inclusions in diamond and individual eclogitic minerals from Mesozoic kimberlites differ from eclogitic inclusions in diamond from Triassic sediments in the northeastern Siberian craton. Xenocrystic phlogopites from the D’yanga pipe have 40Ar/39Ar ages of 384.6, 432.4, and 563.4 Ma, which record several stages of metasomatic impact on the lithosphere. These phlogopites are younger than most of Paleozoic phlogopites from the central part of the craton (Udachnaya kimberlite). Therefore, hydrous mantle metasomatism acted much later on the craton periphery than in the center. Monomineral clinopyroxene thermobarometry shows that Jurassic kimberlites from the northeastern craton part trapped lithospheric material from different maximum depths (170 km in the D’yanga pipe and mostly < 130 km in other pipes). The inferred thermal thickness of cratonic lithosphere decreased progressively from ~ 260 km in the Devonian-Carboniferous to ~ 225 km in the Triassic and to ~ 200 km in the Jurassic, while the heat flux (Hasterok-Chapman model) was 34.9, 36.7, and 39.0 mW/m2, respectively. Dissimilar PT patterns of samples from closely spaced coeval kimberlites suggest different emplacement scenarios, which influenced both the PT variations across the lithosphere and the diamond potential of kimberlites. 相似文献
6.
Rock magnetic and palaeomagnetic studies were performed on Mesozoic redbeds collected from the central and southern Laos, the northeastern and the eastern parts of the Khorat Plateau on the Indochina Block. Totally 606 samples from 56 sites were sampled and standard palaeomagnetic experiments were made on them. Positive fold tests are demonstrated for redbeds of Lower and Upper Cretaceous, while insignificant fold test is resulted for Lower Jurassic redbeds. The remanence carrying minerals defined from thermomagnetic measurement, AF and Thermal demagnetizations and back-field IRM measurements are both magnetite and hematite. The positive fold test argues that the remanent magnetization of magnetite or titanomagnetite and hematite in the redbeds is the primary and occurred before folding. The mean palaeomagnetic poles for Lower Jurassic, Lower Cretaceous, and Upper Cretaceous are defined at Plat./Plon. = 56.0°N/178.5°E (A95 = 2.6°), 63. 3°N/170.2°E (A95 = 6.9°), and 67.0°N/180.8°E (A95 = 4.9°), respectively. Our palaeomagnetic results indicate a latitudinal translations (clockwise rotations) of the Indochina Block with respect to the South China Block of −10.8 ± 8.8° (16.4 ± 9.0°); −11.1 ± 6.2° (17.8 ± 6.8°); and −5.3 ± 4.7° (13.3 ± 5.0°), for Lower Jurassic, Lower Cretaceous, and Upper Cretaceous, respectively. These results indicate a latitudinal movement of the Indochina Block of about 5–11° (translation of about 750–1700 km in the southeastward direction along the Red River Fault) and clockwise rotation of 13–18° with respect to the South China Block. The estimated palaeoposition of the Khorat Plateau at ca. 21–26°N during Jurassic to Cretaceous argues for a close relation to the Sichuan Basin in the southwest of South China Block. These results confirm that the central part of the Indochina Block has acted like a rigid plate since Jurassic time and the results also support an earlier extrusion model for Indochina. 相似文献
7.
We conducted paleomagnetic investigations on limestone from the Lower Carboniferous Huaitoutala Formation in the Qaidam Basin near Delingha City, Qinghai Province, China. The characteristic remanent magnetization (D = 5.8°, I = − 25.7°, k = 114.3, α95 = 4.8°) passes a fold test and indicates a paleopole position of − 39.2°N, 90.4°E and a paleolatitude of 13.5°N for the Qaidam Block for the early Carboniferous. Based on global tectonic reconstructions and paleontological evidence, we suggest that the Qaidam Block was adjacent to, but independent from, the North China, South China, Alashan–Hexi and Tarim blocks at this time. This result suggests that Pre-Carboniferous sutures reported around the Qaidam Basin represent collisional events within Gondwana, rather than the final sutures that gave rise to the present tectonic configuration. 相似文献
8.
U–Pb detrital zircon geochronology from Lower Devonian quartz arenites of the northwestern margin of the Yangtze block yields dominant early Neoproterozoic (0.85–1.0 Ga), Pan-African (0.5–0.65 Ga) and middle Neoproterozoic (0.68–0.8 Ga) age populations and minor Mesoproterozoic to middle Mesoarchean (1.0–3.0 Ga) ages. Middle Mesoarchean to Mesoproterozoic rocks, however, are widespread in the South China block. Although Hf isotopic compositions show both juvenile crustal growth and crustal reworking for all the age groupings, the crust growth, essentially mantle-derived, occurred mainly around 3.1 Ga, 1.9 Ga and 1.0 Ga, respectively. Zircon typology and youngest grain ages indicate that this suite of quartz arenites was the product of multiphase reworking. Abundant magmatic zircon detritus with concordant U–Pb Grenvillian and Pan-African ages, together with accompanying various εHf(t) values, indicate an exotic provenance for the quartz arenite external to the South China block. Qualitative comparisons of age spectra for the late Neoproterozoic sediments of the Cathaysian Block, early Paleozoic sediments of pre-rift Tethyan Himalaya sequence in North India and lower Paleozoic sandstone from the Perth Basin in West Australia, show that they all have two the largest age clusters representing Grenvillian and Pan-African orogenic episodes. The resemblance of these age spectra and zircon typology suggests that the most likely source for the Lower Devonian quartz arenites of the South China block was the East African Orogen and Kuunga Orogen for their early Grenvillian and Pan-African populations, whereas the Hannan–Panxi arc, Jiangnan orogen, and the Yangtze block basements might have contributed to the detrital zircon grains of the Neoproterozoic and Pre-Grenvillian ages. Hf isotopic data indicate that the crustal evolution of the drainage area matches well with the episodic crust generation of Gondwana. These results imply that the previously suggested position of the SCB in Gondwana should be re-evaluated, and the South China block should be linked with North India and West Australia as a part of East Gondwana during the assembly of Gondwana, rather than a discrete continent block in the paleo-Pacific. 相似文献
9.
The relationship of the Yangtze Block with other continental blocks of the Rodinia and Gondwana supercontinents is hotly debated. Here we report U–Pb and Lu–Hf isotopic data for zircons from the latest Neoproterozoic Yanjing Group and the overlying Silurian–Devonian rocks on the western margin of Yangtze Block, which provide critical constraints on the provenance of these sediments and further shed light on the crustal evolution and tectonic affinity of the western Yangtze Block in the context of Rodinia and the subsequent Gondwanaland. Mica schist from the middle part of the Yanjing Group contains dominant Neoproterozoic detrital zircons (0.72–0.80 Ga) with a pronounced age peak at 0.75 Ga. Based on the euhedral to subhedral shapes, high Th/U ratios and exclusively positive εHf(t) values (+ 6 to + 14) for the zircon crystals, and the lack of ancient zircons, we consider the sediments as products of proximal deposition near a Neoproterozoic subduction system in western Yangtze. Combined with the age of rhyolite from the lower part of the Yanjing Group, these strata were estimated to have been deposited in a period between 0.72 and 0.63 Ga. In contrast, the Silurian–Devonian sediments exhibit dominant Grenvillian ages (0.9–1.0 Ga), with middle Neoproterozoic (0.73–0.85 Ga), Pan-African (0.49–0.67 Ga) and Neoarchean (~ 2.5 Ga) age populations, suggesting a significant change of sedimentary provenance and thus a different tectonic setting. Although the shift occurred in the Silurian, the age spectra turn to be consistent along the western margin of the Yangtze Block until the Devonian, indicating persistence of the same sedimentary environment. However, the related provenance of these Paleozoic sediments cannot be found in South China. The presence of abundant Grenvillian, Pan-African and Neoarchean ages, along with their moderately to highly rounded shapes, indicates the possibility of exotic continental terrane(s) as a possible sedimentary provenance. Considering the potential source areas around the Yangtze Block when it was part of the Rodinia or Gondwana, we suggest that the source of these Paleozoic sediments had typical Gondwana affinities such as the Himalaya region, north India, which is also supported by their stratigraphic similarity, newly published paleomagnetic data and the tectono-thermal events of northwestern fragments of Gondwana. This implies that after a prolonged subduction in the Neoproterozoic, the western margin of the Yangtze Block began to incorporate into the assembly of the Gondwana supercontinent and was able to accept sediments from northwestern margin of Gondwanaland as a result of early Paleozoic orogeny. 相似文献
10.
Late Paleozoic peperites have been identified for the first time at the bottom of Tailegula Formation in West Junggar, China. This finding is significant for the reconstruction of Late Paleozoic evolution in the Junggar region. The peperites form successions up to 500 m thick interbedded with basaltic lava and sedimentary rocks. Four types of peperites are described and interpreted as resulting from basaltic lava bulldozed into wet, unconsolidated sediments at their basal contacts. Zircon LA-ICP-MS U–Pb dating of a tuff lens enclosed by lava showed that the peperites formed in the Late Devonian (ca. 364 Ma). The peperite-bearing units probably formed at a water depth of less than 3 km and are generally undeformed, occurring in continuous stratigraphic sections distributed regionally over a distance of 100 km on either side of the Darbut and Baijiantan ophiolitic belts, in contrast to the highly deformed slices of ophiolite. They demonstrate that the Darbut and Baijiantan ophiolitic belts should not be interpreted as significant plate boundaries and represent the underlying ocean crust uplifted along tectonic lineaments within a continuous shallow remnant ocean basin. The peperites formed during the spreading phase of the remnant ocean basin and represent the final stages of creation of oceanic crust. 相似文献
11.
The metamorphic belt in the Basongco area, the eastern segment of Lhasa terrane, south Tibet, occurs as the tectonic blocks in Paleozoic sedimentary rocks. The Basongco metamorphic rocks are mainly composed of paragneiss and schist, with minor marble and orthogneiss, and considered previously to be the Precambrian basement of the Lhasa terrane. This study shows that the Basongco metamorphic belt experienced medium-pressure amphibolite-facies metamorphism under the conditions of T = 640–705 °C and P = 6.0–8.0 kbar. The inherited detrital zircon of the metasedimentary rocks yielded widely variable 206Pb/238U ages ranging from 3105 Ma to 500 Ma, with two main age populations at 1150 Ma and 580 Ma. The magmatic cores of zircons from the orthogneiss constrain the protolith age as ca. 203 Ma. The metamorphic zircons from all rocks yielded the consistent metamorphic ages of 192–204 Ma. The magmatic cores of zircons in the orthogneiss yielded old Hf model ages (TDM2 = 1.5–2.1 Ga). The magmatic zircons from the mylonitized granite yielded a crystallization age of ca. 198 Ma. These results indicate that the high-grade metamorphic rocks from the Basongco area were formed at early Jurassic and associated with coeval magmatism derived from the thickening crust. The Basongco metamorphic belt, together with the western and coeval Sumdo and Nyainqentanglha metamorphic belts, formed a 400-km-long tectonic unit, indicating that the central segment of the Lhasa terrane experienced the late Paleozoic to early Mesozoic collisional orogeny. 相似文献
12.
We conducted field investigations, whole-rock geochemical, Sr-Nd and zircon U-Pb-Lu-Hf isotopic analyses on a suite of intrusive complex in the southern Nalati Range, SW Chinese Tianshan in order to better understand the Paleozoic tectonic and magmatic evolution of the belt. The intrusive complex comprises weakly foliated diorite, low-grade altered diabase, and deformed monzogranite; these plutonic rocks were in turn crosscut by undeformed coarse-grained diorite, granodiorite as well as granite stock. Foliated Late Silurian diorites (421 ± 4 Ma) show arc-type geochemical features, slightly negative whole-rock εNd(t) value (− 1.7; TDM-Nd = 1.52 Ga) and variably positive zircon εHf(t) values (2.34 to 7.27; TDM-Hf: 0.95– 1.26 Ga). Deformed Early Devonian porphyritic monzogranites (411 ± 4 Ma) show geochemical features similar to A-type granite, and their zircon εHf(t) values range from − 6.63 to 1.02, with TDM-Hf ages of 1.82 to 1.33 Ga. Metamorphosed Early Devonian diabases (ca. 410 Ma) have OIB-like REE patterns, εNd(t) values of − 2.0 ~ − 0.8 and TDM-Nd ages of 1.37– 1.25 Ga. The undeformed Early Carboniferous diorite and granodiorite (353– 344 Ma) exhibit arc-type geochemical features, positive εHf(t) values of 6.11– 7.91 with TDM-Hf ages of 0.97– 0.86 Ga, and positive εNd(t) value of 1.9 with TDM-Nd age of 1.04 Ga. The Early Permian granite stock (292 ± 5 Ma) has highly differentiated REE pattern, slightly negative εNd(t) value (− 4.4) and variable zircon εHf(t) values of − 9.73– 6.36. Combining with available data, Early Paleozoic (500– 410 Ma) arc-related magmatic rocks occurring on both sides of the suture zone along the southern Nalati Range, likely resulted from a bi-directional subduction of the Paleo-Tianshan Ocean beneath the Yili Block to the north and the Central Tianshan to the south. Occurrences of A-type granites and OIB-like diabases (ca. 410 Ma) along the Nalati Range likely indicate a hot extensional regime probably induced by the break off of the northward subducting slab of the Paleo-Tianshan Ocean. The closure of the Paleo-Tianshan Ocean and subsequent amalgamation during Early Carboniferous resulted in the regional deformation and metamorphism of the Early Paleozoic arc-related magmatic rocks. From Early to Late Carboniferous, a magmatic arc that corresponded to the well-developed Late Paleozoic Balkhash-Yili active continental margin, superimposed upon the southern Yili Block, most likely resulted from the southward subduction of the Junggar-North Tianshan Ocean. After the closure of the North Tianshan Ocean in Late Carboniferous, the study area was dominated by post-orogenic magmatism. 相似文献
13.
A new paleomagnetic pole position is obtained from the well-dated (636.3 ± 4.9 Ma) Nantuo Formation in the Guzhang section, western Hunan Province, and the correlative Long’e section in eastern Guizhou Province, South China. Remagnetization of the recent geomagnetic field was identified and removed for both sections. The hard dual-polarity, interpreted as primary, component of the Nantuo Formation, directs east–westward with medium inclinations, yielding an average pole of 9.3°N, 165°E, A95 = 4.3° that, for the first time, passed a strata-bound reversals test. The new data are consistent with previously published paleomagnetic data of the Nantuo Formation from Malong county, central Yunnan Province, which passed a positive syn-sedimentary fold test. Together, these sites represent shallow- to deep-water sections across a shelf-to-basin transect centered at ∼33° paleolatitude. The sedimentary basin may have faced an expansive ocean toward the paleo-East. In the ∼750 Ma and ∼635 Ma global reconstructions, the South China Block (SCB) was best fitted in the northern hemisphere close to northwestern Australia. However, a direct SCB-northwestern Australia connection, inferred to have existed during the Early Cambrian–Early Devonian, had not formed by the time of ∼635 Ma. 相似文献
14.
The Indochina–Simao and Yangtze blocks were separated by a branch of the Paleo-Tethys Ocean, commonly referred as the Ailaoshan Ocean in the Paleozoic. Remnants of this Ailaoshan Ocean have been variably suggested to locate along (from east to west) the Ailaoshan fault, Jiujia–Anding fault and Amojiang–Lixianjiang fault. In order to test these models, we have carried out comprehensive detrital zircon U–Pb dating and Hf isotope analyses on the Cambrian to Devonian sedimentary units in the Ailaoshan Belt and its adjacent western margin of the Yangtze Block. Our results indicate marked detrital zircon provenance variation on different sides of the Ailaoshan–Tengtiaohe fault: detrital zircons from east of the fault display a diagnostic age peak at 730–900 Ma, which is characterized by both positive and negative εHf(t) values with a Hf model age (TDMC) peak at ~ 1.8 Ga, whereas detrital zircons from west of the fault display two major age populations of 400–500 and 900–1000 Ma, both characterized by mainly negative εHf(t) values with a Hf model age (TDMC) peak at ~ 2.1 Ga. Our new data indicate that detritus from east and west of the Ailaoshan–Tengtiaohe fault may have been mainly derived from, respectively, the Yangtze Block and Indochina–Simao blocks, thus suggesting the fault may represent the actual suture between the two blocks. Our study also reveals that the Ailaoshan Ocean may have started its early continental rift in the Early Silurian. 相似文献
15.
We report field relationships, petrography and isotopic ages from two superposed basement units of the Kabul Block, the so called Lower Sherdarwaza and Upper Welayati formations. The Sherdarwaza Formation is represented mostly by migmatites and gneisses that are derived from pelitic and psammitic lithologies with lenses and layers of mafic and carbonate rocks. Several bodies of orthogneisses are also exposed in the Sherdarwaza Formation. The Upper Welayati Formation is characterized by micaschist, quartzite and amphibolites. SHRIMP U–Pb data on zircon from the orthogneiss in the Sherdarwaza Formation indicates a Neoarchean age of ca 2.5–2.8 Ga for their magmatic crystallization. The rocks exhibit granulite facies conditions of 5–7 kbar and 800 °C that are documented by the presence of orthopyroxene and Ti-rich biotite in the orthogneiss and by olivine and phlogopite in some calc-silicate rocks at contact with marble. A Paleoproterozoic age of ca. 1.85–1.80 Ga for this metamorphism was obtained using U-Pb SHRIMP dating on zircon and U-Th dating on monazite. Mineral textural relations also show a younger amphibolite facies metamorphism that is documented in both the Sherdarwaza and Welayati formations. This metamorphism occurred at relatively higher pressure conditions of up to 9 kbar at ca. 650 °C, compared to the granulite facies event. A Neoproterozoic age of ca 0.85–0.9 Ga, for this metamorphism is confirmed by Ar-Ar data on biotite and white mica as well as by U-Th data on monazite. By combining the presented results on the metamorphic petrology, geochronology and geochemistry, we conclude that: (1) The Kabul basement is a fragment of an Archean block (craton); (2) the ca. 1.85–1.8 and 0.9–0.85 Ga metamorphism marks an important orogenic events for the basement rocks of the Kabul Block which was stabilized during the early Precambrian; (3) the two metamorphic ages correlate well with global-scale orogenies related to the assembly of the Paleoproterozoic Columbia and Neoproterozoic Rodinia supercontinents; (4) based on metamorphic characteristics and ages, the Kabul basement rocks show an affinity to the Neoarchean rocks of the Tarim and/or South China cratons. 相似文献
16.
Carmen I. Martínez Dopico Mónica G. López de Luchi Augusto E. Rapalini Ilka C. Kleinhanns 《Journal of South American Earth Sciences》2011,31(2-3):324-341
New insights on the Paleozoic evolution of the continental crust in the North Patagonian Massif are presented based on the analysis of Sm–Nd systematics. New evidence is presented to constrain tectonic models for the origin of Patagonia and its relations with the South American crustal blocks. Geologic, isotopic and tectonic characterization of the North Patagonian Massif and comparison of the Nd parameters lead us to conclude that: (1) The North Patagonian Massif is a crustal block with bulk crustal average ages between 2.1 and 1.6 Ga TDM (Nd) and (2) At least three metamorphic episodes could be identified in the Paleozoic rocks of the North Patagonian Massif. In the northeastern corner, Famatinian metamorphism is widely identified. However field and petrographic evidence indicate a Middle to Late Cambrian metamorphism pre-dating the emplacement of the ca. 475 Ma granitoids. In the southwestern area, are apparent 425–420 Ma (?) and 380–360 Ma metamorphic peaks. The latter episode might have resulted from the collision of the Antonia terrane; and (3) Early Paleozoic magmatism in the northeastern area is coeval with the Famatinian arc. Nd isotopic compositions reveal that Ordovician magmatism was associated with attenuated crust. On the southwestern border, the first magmatic recycling record is Devonian. Nd data shows a step by step melting of different levels of the continental crust in the Late Palaeozoic. Between 330 and 295 Ma magmatism was likely the product of a crustal source with an average 1.5 Ga TDM (Nd). Widespread magmatism represented by the 295–260 Ma granitoids involved a lower crustal mafic source, and continued with massive shallower-acid plutono volcanic complexes which might have recycled an upper crustal segment of the Proterozoic continental basement, resulting in a more felsic crust until the Triassic. (4) Sm–Nd parameters and detrital zircon age patterns of Early Paleozoic (meta)-sedimentary rocks from the North Patagonian Massif and those from the neighboring blocks, suggest crustal continuity between Eastern Sierras Pampeanas, southern Arequipa-Antofalla and the northeastern sector of the North Patagonian Massif by the Early Paleozoic. This evidence suggests that, at least, this corner of the North Patagonian Massif is not allochthonous to Gondwana. A Late Paleozoic frontal collision with the southwestern margin of Gondwana can be reconcilied in a para-autochthonous model including a rifting event from a similar or neighbouring position to its post-collision location. Possible Proterozoic or Early Paleozoic connections of the NPM with the Kalahari craton or the western Antartic blocks should be investigated. 相似文献
17.
In this review, we describe the geological characteristics and metallogenic–tectonic origin of Fe deposits in the Altay orogenic belt within the Xinjiang region of northwestern China. The Fe deposits are found mainly within three regions (ordered from northwest to southeast): the Ashele, Kelan, and Maizi basins. The principal host rocks for the Fe deposits of the Altay orogenic belt are the Early Devonian Kangbutiebao Formation, the Middle to Late Devonian Altay Formation, with minor occurrences of Lower Carboniferous and Early Paleozoic metamorphosed volcano-sedimentary rocks. The principal mineral-forming element groups of the deposits are Fe, Fe–Cu, Fe–Mn, Fe–P, Fe–Pb–Zn, Fe–Au, and Fe–V–Ti. The Fe deposits are associated with distinct formations, such as volcanic rocks, skarn deposits, pegmatites, granite-related hydrothermal vein mineralization, and mafic pluton-related V–Ti-magnetite deposits. The Fe deposits are most commonly associated with volcanic rocks in the upper Kangbutiebao Formation, in the volcano-sedimentary Kelan Basin, and in skarn deposits at several localities, including the lower Kangbutiebao Formation in the volcano-sedimentary Maizi Basin, and the Altay Formation at Jiaerbasidao–Kekebulake region. Homogenization temperatures of fluid inclusions in the prograde, retrograde and sulfide stages of the skarn type deposit are mainly medium- to high-temperature (cluster between 200 and 500 °C), medium-temperature (cluster between 200 and 340 °C) and low- to medium temperature (cluster between 160 and 300 °C), respectively. Ore fluids in the sedimentation period in the volcano-sedimentary type deposit are characterized by low- to medium temperature (with a peak around 190 °C), low to moderate salinity (3.23 to 22.71 wt.% NaCl equiv). Ore fluids in the pegmatite type deposit are characterized by low- to medium temperature (with a peak at 240 °C), low salinity (with a peak around 9 wt.% NaCl equiv). An analysis of the isotopic data for Fe deposits from the Altay orogenic belt indicates that the sulfur was derived from several sources, including volcanic rocks and granite, as well as bacterial reduction of sulfate from seawater. The present results indicate that different deposit types were derived from various sources. The REE geochemistry of rocks and ores from the Fe deposits in the Altay orogenic belt suggests that the ore-forming materials were derived from mafic volcanic rocks. Based on isotopic age data, the timing of the mineralization can be divided into four broad intervals: Early Devonian (410–384 Ma), Middle Devonian (377 Ma), Early Permian (287–274 Ma), and Early Triassic (c. 244 Ma). The ore-forming processes of the Fe deposits are closely related to volcanic activity and the emplacement of intermediate and felsic intrusions. We conclude that Fe deposits within the Altay orogenic belt developed in a range of tectonic settings, including continental arc, post-collisional extensional settings, and intracontinental settings. 相似文献
18.
The high-grade metamorphic terrane in the Badu region along the northeastern Cathaysia Block in South China preserves retrograded eclogites and mafic granulites. Here we present the petrology, mineral phase equilibria and P-T conditions based on pseudosection computations, as well as zircon U-Pb ages of these rocks. Mineral textures and reaction relationships suggest four metamorphic stages for the retrograded eclogite as follows: (1) eclogite facies stage (M1), (2) clinopyroxene retrograde stage (M2), (3) amphibole retrograde stage (M3), and (4) chlorite retrograde stage (M4). For the mafic granulite, three stages are identified as: (1) plagioclase-absent stage (M1), (2) granulite facies stage (M2) and (3) amphibolite facies stage (M3). Metamorphic evolution of both of the rock types follows clockwise P-T path. Conventional geothermometers and geobarometers in combination with phase equilibria modelling yield metamorphic P-T conditions for each metamorphic stage for the eclogite as 500–560 °C, 23–24 kbar (M1), 640–660 °C, 14–16 kbar (M2), 730–750 °C, and 11–13 kbar (M3). The chlorite retrograde stage (M4) is inferred to have occurred at lower amphibolite to greenschist facies conditions. Phase equilibria modelling of the mafic granulite shows P-T conditions for each metamorphic stage as 600–720 °C, > 13 kbar (M1) and 860–890 °C, 5–6 kbar (M2) and M3 at amphibolite facies conditions. LA-ICPMS zircon U-Pb dating and trace element analysis show that the high pressure metamorphism occurred at 245–251 Ma. Protolith age of the mafic granulite is 997 Ma, similar to that of the mafic to ultramafic rocks widely distributed in the Cathaysia Block and also along the Jiangnan belt. Subduction of ancient oceanic lithospheric materials (or crustal thickening) during Mesozoic and formation of eclogites suggest that the Cathaysia Block was perhaps in the Tethyan oceanic domain at this time. The granulite formation might have been aided by Mesozoic mafic magma underplating associated with lithospheric delamination, heating and retrogression of the eclogite accompanied by rapid uplift. 相似文献
19.
Qinyan Wang Yuanming Pan Nengsong Chen Xiaoyan Li Haihong Chen 《Journal of Asian Earth Sciences》2009,34(5):686-698
The Quanji Block, situated close to the triple junction of three major Precambrian terranes in China (i.e., the North China Craton, the Yangtze Block and the Tarim Block), is composed of Precambrian metamorphic crystalline basement and an unmetamorphosed Mesozoic–Paleozoic sedimentary cover; it has been interpreted as a remnant continental fragment. Microtextural relationships, garnet trace element compositions, and monazite CHIME ages in paragneisses, schists and granitic leucosomes show two episodes of regional metamorphism in the Quanji Block basement. The first regional metamorphism and accompaning anatexis took place at ～1.93 Ga; the second regional metamorphism occurred between ～1.75 and ～1.71 Ga. Mineral compositions of the first metamorphism, including those of monazite, were significantly disturbed by the second event. These two regional metamorphic episodes were most likely linked to assembly and breakup of the supercontinent Columbia, respectively. 相似文献
20.
Different hypotheses have been proposed to account for the geologic evolution of the southwestern margin of Gondwana in the Early Paleozoic, involving accretion and displacement of different terranes in a protracted convergent margin. In order to constrain and understand the kinematic and paleogeographic evolution of the Pampia terrane a paleomagnetic study was carried out in different Cambrian to Devonian units of the Eastern Cordillera (Cordillera Oriental) and the Interandean Zone (Interandino) of NW Argentina. Paleomagnetic poles from the Campanario Formation (Middle to Upper Cambrian): 1.5°N 1.9°E A95 = 9.2° K = 37.46 N = 8; and Santa Rosita Formation (Lower Ordovician): 8.6°N 355.3°E A95 = 10.1° K = 26.78 n = 9, representative of the Pampia terrane, are interpreted to indicate a Late Cambrian significant displacement with respect to the Río de la Plata and other Gondwana cratons. A model, compatible with several geological evidences that explains this displacement in the framework of the final stages of Gondwana assembly is presented. We propose a simple dextral strike-slip kinematic model in which Pampia and Antofalla (? Arequipa?) blocks moved during Late Cambrian times from a position at the present southern border of the Kalahari craton into its final position next to the Rio de la Plata craton by the Early Ordovician. 相似文献