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1.
U–Pb dating and oxygen and Lu–Hf isotope analyses are applied to ~ 400 detrital zircon grains from the Neoproterozoic–Cambrian Kahar, Bayandor and Zaigun sandstones. The results reveal the evolutionary history of the Central Iranian continental crust in the northern margin of Gondwana during the Neoproterozoic–Cambrian. The U–Pb dating produces major peaks of crystallization ages at 0.5–0.7 Ga and minor peaks around the Tonian, Paleoproterozoic and Neoarchean. The zircon population in the Zaigun sandstone is dominated by long-transported grains and exhibits slightly different zircon distribution patterns than those from the older Kahar and Bayandor units. The zircon population ages and Hf isotopes of the Zaigun sample are very similar to the Neoproterozoic–Early Palaeozoic siliciclastic units in the Arabian Nubian shield (ANS) and Turkey, which suggests the late to post–Pan-African unroofing of the Afro–Arabia realm as the main process for detritus accumulation in Central Iran during the early Palaeozoic. A significant proportion of the Tonian-aged zircons (~ 64%) in the Kahar and Bayandor samples show positive εHf(t) values, whereas those with late Cryogenian–Ediacaran ages have high δ18O and variable εHf(t) values (~− 30‰ to + 17‰), suggesting that the crustal evolution of provenance of the Tonian-aged zircons commenced in an island arc setting and continued in an active continental margin. All the samples contain pre-Neoproterozoic zircons that are ca 1.9–2.3 Ga or 2.5–3.2 Ga, which are much older than the known Neoproterozoic igneous rocks in Iran and are more consistent with pre-Neoproterozoic igneous-metamorphic rocks in the eastern ANS and northern Africa. These ages support the eastern sector of the Afro–Arabia margin as a provenance for the detrital zircons in the oldest sedimentary sequences of Iran during the late Neoproterozoic–Cambrian. The Hf model ages of zircons with mantle-like δ18O values suggest that a significant amount of continental crust in the provenance of the detrital zircons was generated at around 1.0–2.0 and 3.0–3.5 Ga, likely by mantle-derived mafic magmas, and subsequently reworked during crustal differentiation into younger, more felsic crust with varying crustal residence times. 相似文献
2.
Chengli ZHANG 《《地质学报》英文版》2019,93(Z2):44-44
The Mianlue Belt is located in the central China and regarded as a tectonic mélange belt, representative of suture zone formed in the early Mesozoic between North and South China Blocks. However, its forming age has been controversial for a long time. This study provides the reliable LA‐ICPMS U‐Pb zircon dating and in‐situ Hf isotopes from the meta‐volcanics, gabbro and plagiogranite in this belt. Of which, two meta‐andesites yielded the ages of 934 Ma and 933 Ma, two meta‐dacites give the ages of 999 Ma and 873 Ma, and another plagiogranite define an age of 923 Ma, respectively, evidently older than those previously thoughted. Their Hf isotopes are quite coincident. The andesites have the εHf(t)= ‐0.03 ～ +11.76 with the TDMC of 1032‐1629 Ma, εHf(t) = +9.81～ +16.06 and the TDMC = 867‐1185 Ma for dacite and εHf(t) = +8.65 ～ +16.66 and the TDMC = 805～1123 Ma for plagiogranite, suggesting an important crustal growth in the early Neoproterozoic. In addition, the gabbro yielded younger ages of 224‐213 Ma and variable ages from 1225 Ma to 280 Ma in some inherited zircons, consistent with early Mesozoic mafic dykes in South Qinling belt. Their TDMC range from 1.2 to 2.7 Ga, indicating early‐middle Proterozoic crustal residence involved minor Neo‐Archean crustal materials. All new results lead us to propose that most of components in the Mianlue Belt were generated in the early Neoproterozoic and related to the subduction process in the northern margin of the Yangtze block, representative of an important juvenile crust growth in South Qinling during the Neoproterozoic. 相似文献
3.
《Gondwana Research》2013,24(4):1241-1260
An overview is presented for the formation and evolution of Precambrian continental lithosphere in South China. This is primarily based on an integrated study of zircon U–Pb ages and Lu–Hf isotopes in crustal rocks, with additional constraints from Re–Os isotopes in mantle-derived rocks. Available Re–Os isotope data on xenolith peridotites suggest that the oldest subcontinental lithospheric mantle beneath South China is primarily of Paleoproterozoic age. The zircon U–Pb ages and Lu–Hf isotope studies reveal growth and reworking of the juvenile crust at different ages. Both the Yangtze and Cathaysia terranes contain crustal materials of Archean U–Pb ages. Nevertheless, zircon U–Pb ages exhibit two peaks at 2.9–3.0 Ga and ~ 2.5 Ga in Yangtze but only one peak at ~ 2.5 Ga in Cathaysia. Both massive rocks and crustal remnants (i.e., zircon) of Archean U–Pb ages occur in Yangtze, but only crustal remnants of Archean U–Pb ages occur in Cathaysia. Zircon U–Pb and Lu–Hf isotopes in the Kongling complex of Yangtze suggest the earliest episode of crustal growth in the Paleoarchean and two episodes of crustal reworking at 3.1–3.3 Ga and 2.8–3.0 Ga. Both negative and positive εHf(t) values are associated with Archean U–Pb ages of zircon in South China, indicating both the growth of juvenile crust and the reworking of ancient crust in the Archean. Paleoproterozoic rocks in Yangtze exhibit four groups of U–Pb ages at 2.1 Ga, 1.9–2.0 Ga, ~ 1.85 Ga and ~ 1.7 Ga, respectively. They are associated not only with reworking of the ancient Archean crust in the interior of Yangtze, but also with the growth of the contemporaneous juvenile crust in the periphery of Yangtze. In contrast, Paleoproterozoic rocks in Cathaysia were primarily derived from reworking of Archean crust at 1.8–1.9 Ga. The exposure of Mesoproterozoic rocks are very limited in South China, but zircon Hf model ages suggest the growth of juvenile crust in this period due to island arc magmatism of the Grenvillian oceanic subduction. Magmatic rocks of middle Neoproterozoic U–Pb ages are widespread in South China, exhibiting two peaks at about 830–800 Ma and 780–740 Ma, respectively. Both negative and positive εHf(t) values are associated with the middle Neoproterozoic U–Pb ages of zircon, suggesting not only growth and reworking of the juvenile Mesoproterozoic crust but also reworking of the ancient Archean and Paleoproterozoic crust in the middle Neoproterozoic. The tectonic setting for this period of magmatism would be transformed from arc–continent collision to continental rifting with reference to the plate tectonic regime in South China. 相似文献
4.
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
5.
Detrital zircon provides a powerful archive of continental growth and recycling processes. We have tested this by a combined laser ablation ICP-MS U–Pb and Lu–Hf analysis of homogeneous growth domains in detrital zircon from late Paleozoic coastal accretionary systems in central Chile and the collisional Guarguaráz Complex in W Argentina. Because detritus from a large part of W Gondwana is present here, the data delineate the crustal evolution of southern South America at its Paleopacific margin, consistent with known data in the source regions.Zircon in the Guarguaráz Complex mainly displays an U–Pb age cluster at 0.93–1.46 Ga, similar to zircon in sediments of the adjacent allochthonous Cuyania Terrane. By contrast, zircon from the coastal accretionary systems shows a mixed provenance: Age clusters at 363–722 Ma are typical for zircon grown during the Braziliano, Pampean, Famatinian and post-Famatinian orogenic episodes east of Cuyania. An age spectrum at 1.00–1.39 Ga is interpreted as a mixture of zircon from Cuyania and several sources further east. Minor age clusters between 1.46 and 3.20 Ga suggest recycling of material from cratons within W Gondwana.The youngest age cluster (294–346 Ma) in the coastal accretionary prisms reflects a so far unknown local magmatic event, also represented by rhyolite and leucogranite pebbles. It sets time marks for the accretion history: Maximum depositional ages of most accreted metasediments are Middle to Upper Carboniferous. A change of the accretion mode occurred before 308 Ma, when also a concomitant retrowedge basin formed.Initial Hf-isotope compositions reveal at least three juvenile crust-forming periods in southern South America characterised by three major periods of juvenile magma production at 2.7–3.4 Ga, 1.9–2.3 Ga and 0.8–1.5 Ga. The 176Hf/177Hf of Mesoproterozoic zircon from the coastal accretionary systems is consistent with extensive crustal recycling and addition of some juvenile, mantle-derived magma, while that of zircon from the Guarguaráz Complex has a largely juvenile crustal signature. Zircon with Pampean, Famatinian and Braziliano ages (< 660 Ma) originated from recycled crust of variable age, which is, however, mainly Mesoproterozoic. By contrast, the Carboniferous magmatic event shows less variable and more radiogenic 176Hf/177Hf, pointing to a mean early Neoproterozoic crustal residence. This zircon is unlikely to have crystallized from melts of metasediments of the accretionary systems, but probably derived from a more juvenile crust in their backstop system. 相似文献
6.
We trace source variations of active margin granitoids which crystallised intermittently over ~300 Ma in varying kinematic regimes, by combining zircon Lu-Hf isotopic data from Early Palaeozoic to Early Jurassic igneous and metaigneous rocks in the Mérida Andes, Venezuela and the Santander Massif, Colombia, with new whole rock Rb/Sr and Sm-Nd isotopic data, and quartz O isotopic data. These new data are unique in South America because they were obtained from discrete magmatic and metamorphic zircon populations, providing a high temporal resolution dataset, and compare several isotopic systems on the same samples. Collectively, these data provide valuable insight into the evolution of the isotopic structure of the continental crust in long-lived active margins.Phanerozoic active margin-related granitoids in the Mérida Andes and the Santander Massif yield zircon Lu-Hf model ages ranging between 0.77 Ga and 1.57 Ga which clearly define temporal trends that can be correlated with changes in tectonic regimes. The oldest Lu-Hf model ages of >1.3 Ga are restricted to granitoids which formed during Barrovian metamorphism and crustal thickening between ~499 Ma and ~473 Ma. These granitoids yield high initial 87Sr/86Sr ratios, suggesting that evolved, Rb-rich middle to upper crust was the major source of melt. Granitoids and rhyolites which crystallised during subsequent extension between ~472 Ma and ~452 Ma yield younger Lu-Hf model ages of 0.80 Ga–1.3 Ga and low initial 87Sr/86Sr ratios, suggesting that they were derived from much more juvenile, Rb-poor sources such as mafic lower crust and mantle-derived melts. The rapid change in magmatic sources at ~472 Ma can be attributed either to reduced crustal assimilation during extension, or a short pulse of crustal growth by addition of juvenile material to the continental crust. Between ~472 Ma and ~196 Ma Lu-Hf model ages remain mostly constant between ~1.0 and ~1.2 Ga. The large scatter and the absence of definite trends in initial 87Sr/86Sr ratios suggest that both mafic, Rb-poor, and evolved Rb-rich sources were important precursors of active margin magmas in Colombia and Venezuela throughout the Palaeozoic to the Early Jurassic.Previous studies have shown that the genesis of arc magmas may be stimulated by heat advection to the crust during the underplating of mantle derived melt, but the absence of permanent younging trends in Lu-Hf model ages from ~472 Ma to ~196 Ma suggests that very little new crust was generated during this period in the studied region. An overwhelming majority of the analysed igneous rocks yield zircon Lu-Hf model ages of >1 Ga which may be accounted for by documented local crustal end members of 1 Ga–1.6 Ga, and do not require contributions from the depleted mantle. Therefore, recycling of ~1 Ga and older crust was a dominant process in the north-western corner of Gondwana between ~472 Ma and ~196 Ma.This study shows that whole rock Sm-Nd and zircon Lu-Hf data can be interpreted similarly regarding the age of the source regions, whereas Rb-Sr and O isotope data from the same rocks yield valuable information regarding the geochemical nature of the source. 相似文献
7.
鄂尔多斯盆地周缘地壳形成与演化历史:来自锆石U-Pb年龄与Hf同位素组成的证据 总被引：4，自引：0，他引：4
锆石U-Pb定年及Hf同位素测定结果表明,鄂尔多斯盆地周缘的华北板块北缘、兴蒙造山系及扬子板块-秦岭-大别-苏鲁造山带等构造单元系统具有明显不同的形成与演化历史。华北板块北缘锆石年龄平均值为1 837 Ma,最强烈的岩浆活动出现于2 200~1 800 Ma,该期锆石约占全部的40%;次为强烈的岩浆活动在2 800~2 200 Ma,其众数在全部锆石中约占30%;1 500~1 200 Ma、500~100 Ma这两个阶段形成的锆石在全区所占比例各约为15%。华北板块北缘最突出的特征是基本不含1 000~700 Ma期间形成的锆石,>3 000 Ma的锆石在全区分布极为有限。锆石Hf同位素亏损地幔模式年龄表明华北板块北缘平均值为2.55 Ga,较U-Pb平均年龄老,说明2 200~1 800 Ma期间形成的锆石含有较多的古老地壳再循环组分。Hf亏损地幔模式年龄最强峰值约为2.8 Ga,与全岩Nd亏损地幔模式年龄的峰值相一致,Hf模式年龄为3.0~2.25 Ga的颗粒占全部的近95%,证明华北板块北缘的地壳增生主要在太古宙至古元古代期间。Hf同位素亏损地幔模式年龄>3.0 Ga的锆石颗粒所占比例不到0.1%,另外近5%锆石的模式年龄分布于中元古代。晚古生代-中生代所形成的锆石均是先存地壳组分,尤其是中元古代增生地壳的熔融作用形成。兴蒙造山系中锆石U-Pb年龄平均值为497 Ma,最强峰分布于石炭纪(约320 Ma),石炭纪-二叠纪末(350~250 Ma)形成的锆石所占比例达30%以上。新元古代至早古生代(600~440 Ma)形成的锆石占全部锆石的55%以上,而中元古代末-新元古代期间(1 200~600 Ma)形成的锆石在全区仅占4%。中元古代以前形成的锆石非常有限,说明该区最早形成的地壳组分在兴蒙造山系的形成过程中较充分地参与到后期的岩浆作用过程中。兴蒙造山系中锆石相应的Hf同位素亏损地幔模式年龄平均为1.13 Ga,明显较相应的U-Pb年龄老,最强峰值出现于约0.6 Ga。Hf亏损地幔模式年龄为0.7~0.28 Ga的颗粒在兴蒙造山系所占比例达57%,证明该区最强烈的地壳增生发生于新元古代至古生代期间。Hf同位素亏损地幔模式年龄分布于1.5~0.7 Ga的锆石在全区约占38%,说明此期间也是该区地壳较强烈的增生期。Hf亏损地幔模式年龄大于1.5 Ga的锆石所占比例不到5%,古生代以后兴蒙造山系也基本没有明显的地壳增生。扬子与秦岭-大别-苏鲁造山带构造单元中的锆石U-Pb年龄平均为799 Ma,年龄为1 300~750 Ma的锆石在全部锆石中约占70%。晚古生代-燕山期形成的锆石约占20%。年龄在3 500~2 650 Ma、2 118~1 680 Ma的锆石在该区各约占5%。结合扬子与秦岭-大别-苏鲁造山带平均为1.56 Ga的Nd亏损地幔模式年龄特征,说明1 300~750 Ma期间该区较强烈的岩浆作用事件中有较多的古老地壳组分加入其中。锆石U-Pb年龄及Hf同位素组成均说明鄂尔多斯盆地周缘各构造单元具有不同的形成演化历史。地壳是幕式增长的,但各构造单元每幕发生的时间、强度存在明显差别。因此,由盆地中不同时代地层中碎屑锆石U-Pb年龄及Hf同位素组成及全岩Nd同位素特征的系统研究可反演盆地物源供给与周围构造单元之间的关系。 相似文献
8.
We provide new field observations and isotopic data for key areas of the Central Asian Orogenic Belt (CAOB), reiterating our previous assessment that no excessive crustal growth occurred during its ca. 800 Ma long orogenic evolution. Many Precambrian blocks (microcontinents) identified in the belt are exotic and are most likely derived from the northern margin of Gondwana, including the Tarim craton. Ocean opening in the Palaeo-Asian Ocean, arc formation and accretionary processes began in the latest Mesoproterozoic along the southern margin of the Siberian craton and continued into the Neoproterozoic, giving rise to tectono-metamorphic terranes distinct from the exotic microcontinents in that they include tectonically mixed ancient crust as well as juvenile, mantle-derived igneous rocks. Several previous assessments of crustal growth based on the distribution of oceanic and island arc complexes and on Nd isotopic data for post-accretion igneous rocks are questionable, and we show that such data, in combination with the occurrence of old zircon xenocrysts, frequently signify tectonic mixing of juvenile and ancient crustal components.The only truly juvenile terranes, including oceanic crust and intra-oceanic arcs, seem to occur in northeastern Kazakhstan, in the Altai-Sayan region of Siberia and in the Lake and Trans-Altai zones of Mongolia. The largest area of pre-CAOB continental crust forms a broad belt from northwestern Kazakhstan via the Kyrgyz North and Middle Tianshan to the Yili Block and Chinese Central Tianshan in NW China. Most arcs in the CAOB formed on older continental crust, or with substantial addition of old crustal material via sediment recycling, similar to the situation in the present Southwest Pacific in southern Indonesia, and we suspect that the volume of old material in the lower crust of the CAOB is considerable but largely unaccounted for because of lack of geophysical data. Comparing the lithospheric mantle domains as revealed by Os model ages, with ancient crust at least Mesoproterozoic in age and predating formation of the CAOB significantly reduces the volume of new juvenile crust generated during the orogeny. We conclude that the volume of truly juvenile crustal material in the CAOB is about 20%, similar to that in other accretionary orogens through Earth history, and considering the ca. 800 Ma history of the belt this is not anomalous. 相似文献
9.
A. Cambeses J. H. Scarrow P. Montero C. Lázaro F. Bea 《International Geology Review》2017,59(1):94-130
Cambro-Ordovician palaeogeography and fragmentation of the North Gondwana margin is still not very well understood. Here we address this question using isotopic data to consider the crustal evolution and palaeogeographic position of the, North Gondwana, Iberian Massif Ossa–Morena Zone (OMZ). The OMZ preserves a complex tectonomagmatic history: late Neoproterozoic Cadomian orogenesis (ca. 650–550 Ma); Cambro-Ordovician rifting (ca. 540–450 Ma); and Variscan orogenesis (ca. 390–305 Ma). We place this evolution in the context of recent North Gondwana Cambro-Ordovician palaeogeographic reconstructions that suggest more easterly positions, adjacent to the Sahara Metacraton, for other Iberian Massif zones. To do this we compiled an extensive new database of published late Proterozoic–Palaeozoic Nd model ages and detrital and magmatic zircon age data for (i) the Iberian Massif and (ii) North Gondwana Anti-Atlas West African Craton, Tuareg Shield, and Sahara Metacraton. The Nd model ages of OMZ Cambro-Ordovician crustal-derived magmatism and Ediacaran-Ordovician sedimentary rocks range from ca. 1.9 to 1.6 Ga, with a mode ca. 1.7 Ga. They show the greatest affinity with the Tuareg Shield, with limited contribution of more juvenile material from the Anti-Atlas West African Craton. This association is supported by detrital zircons that have Archaean, Palaeoproterozic, and Neoproterozoic radiometric ages similar to the aforementioned Iberian Massif zones. However, an OMZ Mesoproterozoic gap, with no ca. 1.0 Ga cluster, is different from other zones but, once more, similar to the westerly Tuareg Shield distribution. This places the OMZ in a more easterly position than previously thought but still further west than other Iberian zones. It has been proposed that in the Cambro-Ordovician the North Gondwana margin rifted as the Rheic Ocean opened diachronously from west to east. Thus, the more extensive rift-related magmatism in the westerly OMZ than in other, more easterly, Iberian Massif zones fits our new proposed palaeogeographic reconstruction. 相似文献
10.
《Gondwana Research》2002,5(1):197-203
Limited evidence from Sm-Nd TDM model ages, U-Pb ages of xenocrystic zircon, and Pb isotopic data indicates the presence of Paleoproterozoic and Mesoproterozoic crust (2.0-1.3 Ga) in the southern and central Appalachian orogen. This apparently unexposed older crust must underlie much of the Blue Ridge, and it was recycled to produce most of the rocks of the Blue Ridge with ages ≤1.3 Ga. In the eastern Blue Ridge and in blocks to the southeast, there also is a significant juvenile Neoproterozoic source component. Going toward the southeast, the central and eastern Piedmont (Carolina terrane) appears to be underlain by progressively less source component older than 1.0 Ga. Late Proterozoic rocks of the Carolina terrane are derived largely from a juvenile source with a Nd isotopic composition that approaches that of depleted mantle. 相似文献
11.
《Gondwana Research》2014,25(1):103-125
We argue that the production of mantle-derived or juvenile continental crust during the accretionary history of the Central Asian Orogenic Belt (CAOB) has been grossly overestimated. This is because previous assessments only considered the Palaeozoic evolution of the belt, whereas its accretionary history already began in the latest Mesoproterozoic. Furthermore, much of the juvenile growth in Central Asia occurred in late Permian and Mesozoic times, after completion of CAOB evolution, and perhaps related to major plume activity. We demonstrate from zircon ages and Nd–Hf isotopic systematics from selected terranes within the CAOB that many Neoproterozoic to Palaeozoic granitoids in the accreted terranes of the belt are derived from melting of heterogeneous Precambrian crust or through mixing of old continental crust with juvenile or short-lived material, most likely in continental arc settings. At the same time, juvenile growth in the CAOB occurred during the latest Neoproterozoic to Palaeozoic in oceanic island arc settings and during accretion of oceanic, island arc, and Precambrian terranes. However, taking together, our data do not support unusually high crust-production rates during evolution of the CAOB. Significant variations in zircon εHf values at a given magmatic age suggest that granitoid magmas were assembled from small batches of melt that seem to mirror the isotopic characteristics of compositionally and chronologically heterogeneous crustal sources. We reiterate that the chemical characteristics of crustally-derived granitoids are inherited from their source(s) and cannot be used to reconstruct tectonic settings, and thus many tectonic models solely based on chemical data may need re-evaluation. Crustal evolution in the CAOB involved both juvenile material and abundant reworking of older crust with varying proportions throughout its accretionary history, and we see many similarities with the evolution of the SW Pacific and the Tasmanides of eastern Australia. 相似文献
12.
In-situ hafnium and lead isotope analyses of detrital zircons from the Devonian sedimentary basin of NE Greenland: a record of repeated crustal reworking 总被引：14，自引：0，他引：14
T.-L. Knudsen W. Griffin E. Hartz A. Andresen S. Jackson 《Contributions to Mineralogy and Petrology》2001,141(1):83-94
An intramontane collapse basin developed within the hanging wall above the large-scale extensional Fjord Regional Detachment of NE Greenland in middle to late Devonian times. The continental clastic sediments within the basin are derived locally from Laurentian source rocks, which makes them well suited for a study of the crustal evolution of the source terrain. This is the first integrated in-situ Pb and Hf isotope study to be presented, and zircon data on a selected sandstone from the basin are combined with Sm-Nd whole-rock data on sand/siltstones. Nd whole-rock ages of two samples of sandstones and a siltstone are 2.0-2.1 Ga. Peak frequencies of zircon 207Pb/206Pb ages at 1,764-1,912 Ma, and 176Hf/177Hf values at 0.28142-0.28163 (tDM=2.47 to 2.06) for the sandstone suggest the generation of a considerable volume of juvenile continental crust in the ultimate zircon provenance at 1.9-2.0 Ga. The Hf isotopic compositions of Archaean zircons in the sandstone are distinct from those of the source materials of Proterozoic protocrust at 1.9-2.0 Ga, but zircons with elevated Hf-tDM ages of up to 2.47 Ga can be related to a component of Archaean crust or reworked Archaean material in the ultimate zircon source area. Zircon 207Pb/206Pb ages are also recorded at 1,480-1,572, 1,318 and 1,014 Ma (Grenvillian). The Hf isotope compositions of these zircons are consistent with reworking of the Proterozoic protocrust at these times, with little or no juvenile input. The Proterozoic zircons form two distinct groups defined by 176Yb/177Hf>0.05055 and 176Yb/177Hf<0.03301, and the latter group overlaps with Yb-Hf isotope data on the Archaean zircons. The two groups may represent zircons derived from evolved granites and intermediate to mildly felsic rocks, respectively. The repeated reworking of the continental crust also comprised erosion and deposition of sediments in the Proterozoic (the Krummedal sequence and the Eleonore Bay Supergroup, EBS) and intrusion of Caledonian anatectic granites in the EBS, which both represent provenance components to the Devonian sediments. No discrete Caledonian Pb-Pb zircon ages are recorded, but Caledonian magmatism may be represented by strongly discordant zircons which form arrays with a lower intercept age at ca. 400 Ma and an upper intercept at 1,600-2,000 Ma. One undated zircon records a 176Hf/177Hf ratio of 0.282218, higher than that of the Proterozoic protocrust in Caledonian/late-Caledonian times (380-450 Ma) which may represent a Caledonian mantle contribution. 相似文献
13.
We discuss the question whether the late Mesoproterozoic and early Neoproterozoic rocks of eastern, central and southern Africa, Madagascar, southern India, Sri Lanka and South America have played any role in the formation and dispersal of the supercontinent Rodinia, believed to have existed between about 1000 and 750 Ma ago. First, there is little evidence for the production of significant volumes of ˜1.4–1.0 Ga (Kibaran or Grenvillian age) continental crust in the Mozambique belt (MB) of East Africa, except, perhaps, in parts of northern Mozambique. This is also valid for most terranes related to West Gondwana, which are made up of basement rocks older than Mesoproterozoic, reworked in the Brasiliano/Pan-African orogenic cycle. This crust cannot be conclusively related to either magmatic accretion processes on the active margin of Rodinia or continental collision leading to amalgamation of the supercontinent. So far, no 1.4–1.0 Ga rocks have been identified in Madagascar. Secondly, there is no conclusive evidence for a ˜1.0 Ga high-grade metamorphic event in the MB, although such metamorphism has been recorded in the presumed continuation of the MB in East Antarctica. In South America, even the Sunsas mobile belt, which is correlated with the Grenville belt of North America, does not include high-grade metamorphic rocks. All terranes with Mesoproterozoic ages seem to have evolved within extensional, aulacogen-type structures, and their compressional deformation, where observed, is normally much younger and is related to amalgamation of Gondwana. This is also valid for the Trans-Saharan and West Congo belts of West Africa.Third, there is also no evidence for post-1000 Ma sedimentary sequences that were deposited on the passive margin(s) of Rodinia. In contrast, the MB of East Africa and Madagascar is characterized by extensive structural reworking and metamorphic overprinting of Archaean rocks, particularly in Tanzania and Madagascar, and these rocks either constitute marginal parts of cratonic domains or represent crustal blocks (terranes or microcontinents?) of unknown derivation. This is also the case for most terranes included in the Borborema/Trans-Saharan belt of northeastern Brazil and west-central Africa, as well as those of the Central Goíás Massif in central Brazil and the Mantiqueira province of eastern and southeastern Brazil.Furthermore, there is evidence for extensive granitoid magmatism in the period ˜840 to <600 Ma whose predominant calc-alkaline chemistry suggests subduction-related active margin processes during the assembly of the supercontinent Gondwana. The location of the main Neoproterozoic magmatic arcs suggests that a large oceanic domain separated the core of Rodinia, namely Laurentia plus Amazonia, Baltica and West Africa, from several continental masses and fragments now in the southern hemisphere, such as the São Francisco/Congo, Kalahari and Rio de La Plata cratons, as well as the Borborema/Trans-Saharan, Central Goiás Massif and Paraná blocks. Moreover, many extensional tectonic events detected in the southern hemisphere continental masses, but also many radiometric ages of granitois that are already associated with the process of amalgamation of Gondwana, are comprised within the 800–1000 age interval. This seems incompatible with current views on the time of disintegration of Rodinia, assumed to have occurred at around 750 Ma. 相似文献
14.
P. V. Crowhurst R. Maas K. C. Hill D. A. Foster C. M. Fanning 《Australian Journal of Earth Sciences》2013,60(1):107-122
New U–Pb zircon ages and Sr–Nd isotopic data for Triassic igneous and metamorphic rocks from northern New Guinea help constrain models of the evolution of Australia's northern and eastern margin. These data provide further evidence for an Early to Late Triassic volcanic arc in northern New Guinea, interpreted to have been part of a continuous magmatic belt along the Gondwana margin, through South America, Antarctica, New Zealand, the New England Fold Belt, New Guinea and into southeast Asia. The Early to Late Triassic volcanic arc in northern New Guinea intrudes high‐grade metamorphic rocks probably resulting from Late Permian to Early Triassic (ca 260–240 Ma) orogenesis, as recorded in the New England Fold Belt. Late Triassic magmatism in New Guinea (ca 220 Ma) is related to coeval extension and rifting as a precursor to Jurassic breakup of the Gondwana margin. In general, mantle‐like Sr–Nd isotopic compositions of mafic Palaeozoic to Tertiary granitoids appear to rule out the presence of a North Australian‐type Proterozoic basement under the New Guinea Mobile Belt. Parts of northern New Guinea may have a continental or transitional basement whereas adjacent areas are underlain by oceanic crust. It is proposed that the post‐breakup margin comprised promontories of extended Proterozoic‐Palaeozoic continental crust separated by embayments of oceanic crust, analogous to Australia's North West Shelf. Inferred movement to the south of an accretionary prism through the Triassic is consistent with subduction to the south‐southwest beneath northeast Australia generating arc‐related magmatism in New Guinea and the New England Fold Belt. 相似文献
15.
造山带内广泛发育的泥盆纪地层是揭示秦岭造山带古生代中期洋陆演化、地块构造属性和大地构造背景的良好载体.对南秦岭内部淅川地区泥盆系砂岩进行了岩石地球化学和锆石U-Pb定年,结果显示泥盆系碎屑岩具有中等的成分成熟度及一定程度的沉积再旋回特征,源区物质成分以上地壳长英质岩石为主;碎屑锆石的年龄区间主要集中在新元古代晚期-古生代（0.40~0.63 Ga）、新元古代（0.7~0.9 Ga）和中元古代（1.0~1.6 Ga）三个区间,并存在少量古元古代和中-晚太古代年龄.综合分析,淅川地区泥盆系主要形成于被动大陆边缘环境,其物源可能主要为南秦岭自身隆升的基底和构造高地,并未接受来自于北秦岭的物质,沿商丹洋的俯冲增生事件可能未影响到南秦岭内部. 相似文献
16.
Qiang Ma Yi‐Gang Xu Jian‐Ping Zheng Min Sun William L. Griffin Xiaoping Xia Shao‐Kui Pan 《地学学报》2017,29(4):211-217
Evidence for post‐Archaean crustal growth via magma underplating is largely based on U–Pb dating of zircons from granulite‐facies xenoliths. However, whether the young zircons from such xenoliths are genetically related to magma underplating or to anatexis remains controversial. The lower‐crustal xenoliths carried by igneous rocks in the Chifeng and Ningcheng (North China Craton) have low SiO2 and high MgO, indicating that parental melts of their protoliths were of unambiguous mantle origin. The xenoliths contain abundant magmatic zircons with late‐Palaeozoic ages, and have more radiogenic zircon Hf‐isotope compositions and hence younger model ages than ancient crustal magmas and the “reworking array” of the basement rocks. Our data suggest that the granulites represent episodic magmatic underplating to the lower crust of this craton in Phanerozoic time. Considering the observation that regional lowermost crust (~5 km) is mafic and characterized by Phanerozoic zircons, this work reports an example of post‐Archaean crustal growth via magma underplating. 相似文献
17.
秦岭岩群副变质岩碎屑锆石年龄谱及其地质意义探讨 总被引：17，自引：0，他引：17
报道了北秦岭地块中秦岭岩群夕线黑云石英片岩61个碎屑锆石测点的207Pb/206Pb年龄测试结果,其中15个测点在SHRIMPⅡ上进行,46个测点来自LA-ICPMS的测定结果。61个年龄值显示锆石主要来源为1·5~1·9Ga(共51个测点,占所有测点的83·6%)的古元古代末至中元古代早期的大陆地壳,1粒碎屑锆石来自新太古代岩石,5粒来自中元古代晚期的蚀源区,4个测点为0·9~1·0Ga。由于秦岭岩群被新元古代早期960~900Ma的花岗岩体侵入,新的碎屑锆石测年结果表明秦岭岩群副变质岩的沉积时代至少介于1500~960Ma之间,亦可能为中元古代末期。秦岭岩群在早古生代造山过程中受到强烈改造,但本次测定未从夕线黑云石英片岩中获得这次变质作用的年代学信息。 相似文献
18.
《Russian Geology and Geophysics》2007,48(1):61-70
We studied geology and main rock assemblages of the Precambrian Kan, Arzybei, and Derba terranes of the Central Asian Fold Belt which border the Siberian craton in the southwest. The Precambrian terranes include three isotopic provinces (Paleoproterozoic, Mesoproterozoic, and Neoproterozoic) distinguished from the Sm-Nd isotope compositions of granitoids, felsic metavolcanics, and metasediments. The terranes formed in three stages of crustal evolution: 2.3–2.5, 0.9–1.1, and 0.8–0.9 Ga. Proterozoic juvenile crust was produced by subduction-related magmatism; it was originally of transitional composition and transformed into continental crust by potassic plutonism as late as the Late Vendian-Cambrian. Terrigenous sediments in the Arzybei and Derba terranes vary in T(DM) Nd model ages from 1.0 to 2.0 Ga. The Nd ages of the underlying metavolcanics and lowest T(DM) of metasediments indicate that terrigenous sedimentation started in the Neoproterozoic. It was maintained by erosion of Mesoproterozoic-Neoproterozoic crust and, to a lesser extent, of Early Precambrian rocks on the craton margin or in Paleoproterozoic terranes. Ar-Ar dating of amphiboles and biotites from metamorphic rocks and U-Pb dating of zircons from granitoids yielded 600–555 and 500–440 Ma, respectively, corresponding to the Vendian and Early Paleozoic stages of nearly synchronous metamorphism and plutonism. Accretion and collision events caused amalgamation of the Paleoproterozoic, Mesoproterozoic, and Neoproterozoic terranes in the Vendian and their collision with the Siberian craton. The lateral growth of the paleocontinent completed in the Late Ordovician. 相似文献
19.
《地学前缘(英文版)》2019,10(6):2045-2061
The Southern Irumide Belt(SIB) is an orogenic belt consisting of a number of lithologically varied Mesoproterozoic and Neoproterozoic terranes that were thrust upon each other.The belt lies along the southwest margin of the Archaean to Proterozoic Congo Craton,and bears a Neoproterozoic tectonothermal overprint relating to the Neoproterozoic-Cambrian collision between the Congo and Kalahari cratons.It preserves a record of about 500 million years of plate interaction along this part of the Congo margin.Detrital zircon samples from the SIB were analysed for U-Pb and Lu-Hf isotopes,as well as trace element compositions.These data are used to constrain sediment-source relationships between SIB terranes and other Gondwanan terranes such as the local Congo Craton and Irumide belt and wider afield to Madagascar(Azania) and India.These correlations are then used to interpret the Mesoproterozoic to Neoproterozoic affinity of the rocks and evolution of the region.Detrital zircon samples from the Chewore-Rufunsa and Kacholola(previously referred to as Luangwa-Nyimba) terranes of the SIB yield zircon U-Pb age populations and evolved ε_(Hf)(t) values that are similar to the Muva Supergroup found throughout eastern Zambia,primarily correlating with Ubendian-Usagaran(ca.2.05-1.80 Ga) phase magmatism and a cryptic basement terrane that has been suggested to underlie the Bangweulu Block and Irumide Belt.These data suggest that the SIB was depositionally connected to the Congo Craton throughout the Mesoproterozoic.The more eastern Nyimba-Sinda terrane of the SIB(previously referred to as Petauke-Sinda terrane) records detrital zircon ages and ε_(Hf)(t) values that correlate with ca.1.1-1.0 Ga magmatism exposed elsewhere in the SIB and Irumide Belt.We ascribe this difference in age populations to the polyphase development of the province,where the sedimentary and volcanic rocks of the Nyimba-Sinda terrane accumulated in extensional basins that developed in the Neoproterozoic.Such deposition would have occurred following late-Mesoproterozoic magmatism that is widespread throughout both the Irumide and Southern Irumide Belts,presently considered to have occurred in response to collision between a possible microcontinental mass and the Irumide Belt.This interpretation implies a multi-staged evolution of the ocean south of the Congo Craton during the mid-Mesoproterozoic to late-Neoproterozoic,which ultimately closed during collision between the Congo and Kalahari cratons. 相似文献
20.
Sm—Nd and Zircon U—Pb Isotopic Constraints on the Age of Formation of the Precambrian Crust in Southeast China 总被引：1，自引：0，他引：1
Nd model ages(TDM) of the Pre-Mesozoic crustal rock samples from Southeast China range from 1.2 to 3.5Ga.Two age peaks of 1.4Ga and 1.8 Ga are observed in the histogram of TDM model ages.Available U-Pb zircon inheritance ages are concentrated around 1.2-1.4Ga,1.8Ga and 2.5Ga,respectively.The combined use of Sm-Nd and U-Pb zircon inheritance ages suggests that the formation of the Precambrian curst is of episodic character.The oldest crustal nucleus may have been formed during the Late Archean(2.5Ga or older?).A rapid production of the crust took place 1.8 Ga ago,consistent with the global crust formation event at 1.7-1.9Ga.Another important episode of the addition of juvenile crustal material from the mantle in Southeast China took place 1.2-1.4Ga ago,during which the pre-existing crust was strongly reworked and/or remelted. 相似文献