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Precise timing of granitoids and constraints of their magma sources are critical to understanding the subduction–collision tectonic evolution of the Altun orogenic belt (AOB), a vital part of the Qinghai-Tibet plateau in northwestern China. We provide in-situ zircon U–Pb age, Hf isotopic composition and whole-rock geochemistry of the Yusupualeke granitic pluton in the South Altun orogenic belt (SAOB), an integral unit of the AOB, to determine the tectono-magmatic evolution of the SAOB at early Palaeozoic. The Yusupualeke granitic pluton comprises the medium-coarse grained porphyritic monzogranite and medium-fine grained granodiorite. The monzogranite sample yielded a weighted mean 206Pb/238U age of 476.8 ± 3.6 Ma (MSWD = 0.59), while the granodiorite yielded a weighted mean 206Pb/238U age of 453.2 ± 4.7 Ma (MSWD = 0.013). Zircon U–Pb ages suggest that the subduction–collision process of the SAOB remained from the middle stage of the early Palaeozoic to the end. Both of the studied granitoids belong to metaluminous to weakly peraluminous series and show typical I-type granite characteristics with depletions in Ba, Nb, Sr, P, and Ti, and enrichments in light rare earth elements (LREEs), Rb, Th, K, and slightly negative Eu anomalies. Based on the geochronological data and regional geological background, we believe that the porphyritic monzogranites were formed during the northward subduction process of the South Altun ocean (SAO), while the granodiorites were formed during the tectonic regime transition stage. Besides, combing the previous research achievements with our newly obtained data, we put forward a new division and geodynamic model of the early Palaeozoic tectono-magmatic evolution for the South Altun orogenic belt. [ABSTRACT FROM AUTHOR]

The Altun orogenic belt, located on the northern margin of the Tibetan Plateau, records the assembly and breakup of the Rodinia supercontinent. In this paper, we report the petrography, zircon U–Pb ages and Hf isotope data, and bulk geochemistry of the Hongliugou alkali feldspar granites from the Altun orogenic belt to constrain their petrogenesis and tectonic implication. Zircon U–Pb dating yielded ages of 857–851 Ma, interpreted as the emplacement ages of the granites. The granites are metaluminous; have high SiO2, K2O, and rare‐earth element (REE) contents; low CaO and P2O5 contents; high FeOt/MgO ratios; and high 10,000 × Ga/Al values. They show marked depletion in heavy REEs, enrichment in light REEs, and pronounced negative Eu anomalies. These rocks are enriched in high‐field‐strength elements, depleted in Ba, Sr, P, and Ti, and lack Nb and Ta anomalies. These petrological and geochemical characteristics are consistent with those of A‐type granites. The samples plot in the A1‐type field in a discrimination diagram for A‐type granites. Zircon εHf(t) values vary from +1.76 to +7.40 with two‐stage Hf model ages of 1.27 to 1.63 Ga, implying that the granites were derived mainly from juvenile crust. On the basis of these and previous results, we propose that the Hongliugou alkali feldspar granites formed in an intraplate rift setting related to the initial breakup of Rodinia. [ABSTRACT FROM AUTHOR]

Abstract Numerous granitic intrusions crop out in the eastern segment of the North Qaidam block (NQ), NW China. To evaluate their ages, petrogenesis and genetic relationships to other granitoids in the NQ, we present geochemical and geochronologic data for six intrusive bodies and review regional data. Zircon U-Pb (SHRIMP) dating yielded ages of 413 ± 3 Ma for the Hadesengou granite; 254 ± 3 Ma for the Xugeigou granite; 251 ± 1 Ma for the Qiluoshan granite; 249 ± 1 and 248 ± 2 Ma for the Chahannuo hornblende diorite and granite, respectively; 240 ± 2 Ma for the Chahanhe granite; and 250 ± 1 and 244 ± 3 Ma for the Shailekegoulei granodiorite and granite, respectively. Consequently, the Wulan plutons can be divided into two petrologic groups: Early Devonian (D 1) quartz monzonite and syenogranite, and Late Permian to Early Triassic (P 3 -T 1) hornblende diorite, granodiorite, and granite. The D 1 granitic intrusions have geochemical affinities with A-type granites (A 2 -type) characterized by low Ca, Sr, Ba and Nb, and high Fe, Ga, Y and Rb, consistent with derivation by partial melting of metapelitic source rocks containing a small amount of metagraywacke. The P 3 -T 1 I-type granitic intrusions are geochemically typical of active continental margin rocks, consistent with derivation by partial melting of metabasalt and clay-poor metagraywacke. Combined with previous studies, we recognize five periods of granitic magmatism in the NQ: (1) 465–473 Ma; (2) 423–446 Ma; (3) 391–413 Ma; (4) 372–383 Ma; and (5) 240–271 Ma. Based on the temporal-spatial distribution of granitic intrusions in the NQ and the regional tectonic evolution, we interpret the first and second periods of granitic magmatism as related to normal plate subduction, and the third period to slab break-off and exhumation of the subducted plate. The fourth stage of granitic magmatism is attributed to large-scale lithospheric mantle delamination, involving the differential movement of orogenic blocks. The fifth period of granitic plutonism probably reflects northward subduction of the East Kunlun Paleotethys oceanic crust and southward subduction of Zongwulong oceanic crust beneath the Oulongbuluke continental block. Graphical abstract Unlabelled Image Highlights • Two periods of granitoids with ages of 413 Ma (D 1) and 254-240 Ma (P 3 -T 1) occurred in Wulan. • The D 1 granitoids have an affinity of A-type, and the P 3 -T 1 granitoids are of I-type. • The A-type granitoids derived from the partial melting of a clay-rich metapelitic source • The I-type granitoids derived from the partial melting of a metabasalt and metagreywacke • The granitoids in NQ is divided into five episodes, and the Wulan two stage granites belong to the third and fifth stages respectively. [ABSTRACT FROM AUTHOR]

We report new zircon U-Pb ages, Hf isotopic and geochemical results for the Tongling granitic plutons of Southeast China. SHRIMP U-Pb ages for the Miaojia quartz monzodiorite porphyrite，the Tianebaodan and Tongguanshan quartz monzodiorites, the Xinqiaotou granodiorite porphyry, and the Shatanjiao and Nanhongchong granodiorite are 143 ± 2, 141 ± 1 and 142 ± 1, 147 ± 1, and 145 ± 1 and 139 ± 1 Ma, respectively. Combined with previous geochronological data, our results indicate that the porphyritic rocks are older than rocks of the same type lacking porphyritic texture. Geochemically, these high-K calc-alkaline intrusive rocks are characterized by arc-like trace element distribution patterns, with significant enrichment in LILE and LREE but depletion in HFSE. Lu-Hf isotopic compositions of zircons from the high-K calc-alkaline (HKCA) rocks have εHf(t) values of magmatic 139-147 Ma zircons from −8.1 to −25.6, with two-stage model ages (tDM2) of 1.71-2.67 Ga, whereas εHf(t) values of inherited 582-844 Ma zircons range from 5.4 to −9.5, with tDM2 of 1.39-2.22 Ma, younger than tDM2 values of igneous zircon, indicating that newly formed mantle material was added to the continental crust of the Yangtze Block. Moreover, εHf(t) values of inherited zircon cores older than 1000 Ma are from −7.8 to −26, similar to magmatic zircons, and the tDM2 values are all greater than 3.0 Ga (3.16-3.75 Ga), reflecting partial melting of ancient sialic material. We conclude that the plutonic melts were derived from both the enriched mantle and the ancient crust. The HKCA Tongling intrusions coincide temporally with the J3-K1 magmatic event that was widespread in Southeast China. This igneous activity may have accompanied sinistral slip along the Tan-Lu fault due to oblique subduction of the Palaeo-Pacific plate. [ABSTRACT FROM AUTHOR]

Abstract: The South Altyn continental block is an important geological unit of the Altyn Tagh orogenic belt, in which numerous Neoproterozoic granitoids crop out. Granitoids are mainly located in the Paxialayidang–Yaganbuyang area and can provide indispensable information on the dynamics of Rodinia supercontinent aggregation during the Neoproterozoic. Therefore, the study of granitoids can help us understand the formation and evolutionary history of the Altyn Tagh orogenic belt. In this work, we investigated the Yaganbuyang granitic pluton through petrography, geochemistry, zircon U–Pb chronology, and Hf isotope approaches. We obtained the following conclusions: (1) Yaganbuyang granitoids mainly consist of two‐mica granite and granodiorite. Geochemical data suggested that these granitoids are peraluminous calc–alkaline or high‐K calc–alkaline granite types. Zircon U–Pb data yielded ages of 939±7.1 Ma for granodiorite and ∼954 Ma for granitoids, respectively. (2) The εHf(t) values of two–mica granite and granodiorite are in the range of –3.93 to +5.30 and –8.64 to +5.19, respectively. The Hf model ages (TDM2) of two‐mica granite and granodiorite range from 1.59–.05 Ga and 1.62–2.35 Ga, respectively, indicating that the parental magma of these materials is derived from ancient crust with a portion of juvenile crust. (3) Granitoids formed in a collisional orogen setting, which may be a response to Rodinia supercontinent convergence during the Neoproterozoic. [ABSTRACT FROM AUTHOR]

The South Altun orogenic belt (SAOB), consisting of the South Altun block (SAB) and the South Altun continental block (SACB), is one of several important orogenic belts in NW China. Numerous granite bodies are widely distributed in the SAB. However, the petrogenesis and tectonic environment of these granites, and their relationships to those of the SACB, Central Altun Continental block (CACB), North Altun block (NAB), Qilian block (QLB), and North Qaidam block (NQB) remain unclear. In this investigation, we selected the SAB granites for detailed study, and explore the petrogenesis employing bulk-rock geochemistry, zircon U-Pb dating, and Hf isotopic analysis. Zircon U–Pb LA-ICP-MS dating of the granites from the SAB identified seven spatially distinct Paleozoic plutonic suites: (a) Yigan—352–343 Ma; (b) Baiganhu—448–444 Ma; (c) west Mangya—444–435 Ma; (d) Aketishan—265 Ma; (e) Chaishuigou—406 Ma; (f) Changchungou—469 Ma; and (g) north Mangya—462 Ma. Based on previous research combined with our new U-Pb dating and bulk-rock geochemical investigations in the SAB, we identdified six distinct episodes of granitoid emplacement: episodes 1 and 2, quartz diorite + granodiorite + monzogranite with I-type affinities, and ages of 503–497 Ma and 483–458 Ma, respectively; episode 3, granodiorite + monzogranite + syenogranite with I- and S-type affinities, and an age of 456–432 Ma; episode 4, monzogranite + syenogranite + alkali feldspar granite with A-type affinities, and an age of 424–385 Ma; episode 5, granodiorite + monzogranite with S-type affinities, and an age of 352–338 Ma; and episode 6, quartz diorite + monzogranite + syenogranite with I-type affinities, and an age of 265–264 Ma. Zircon Lu-Hf isotope analyses from various episodes show that ε Hf ( t ) values are positive in most cases, but negative for a small number of inherited (xenocrystic) zircons. Source rocks were mainly juvenile crust, evidently mixed with minor ancient continental material. Based on our new results integrated with regional geological data, we conclude that episodes 1 and 2 granitic magma generations were related to the subduction of oceanic crust, episode 3 to post-collisional partial melting, episode 4 to the isostatic adjustment of orogenic blocks after plate suturing, episode 5 to petrotectonic thickening of the Altun crust, and episode 6 to Altun fault transcurrent slip attending Kunlun Paleo Tethys subduction. [ABSTRACT FROM AUTHOR]

The petrology, geochemistry, geochronology, and Sr–Nd–Hf isotopes of the backarc granitoids from the central part of the Qilian block are studied in the present work. Both S- and I-type granitoids are present. In petrographic classification, they are granite, alkali feldspar granite, felsic granite, diorite, quartz diorite, granodiorite, and albite syenite. The SHRIMP ages are 402–447 Ma for the S-type and 419–451 Ma for the I-type granitoids. They are mostly high-K calc-alkaline granitoids. The S-type granitoids are weakly to strongly peraluminous and are characterized by negative Eu anomalies (Eu/Eu* = 0.18–0.79). The I-type granitoids are metaluminous to weakly peraluminous and are characterized mostly by small negative to small positive Eu anomalies (Eu/Eu* = 0.71–1.16). The initial ( 87 Sr/ 86 Sr) values are 0.708848–0.713651 for the S-type and 0.704230–0.718108 for the I-type granitoids. The ε Nd (450 Ma) values are − 8.9–−4.1 and − 9.7–+ 1.9 for the S-type and I-type granitoids, respectively. The T DM values are 1.5–2.4 Ga for the S-type and 1.0–2.3 Ga for the I-type granitoids. For the Qilian block, the backarc granitoid magmatism took place approximately 60 million years after the onset of the southward subduction of the north Qilian oceanic lithosphere and lasted approximately 50 million years. Partial melting of the source rocks consisting of the Neoproterozoic metasedimentary rocks of the Huangyuan Group and the intruding lower Paleozoic basaltic rocks could produce the S-type granitoid magmas. Partial melting of basaltic rocks mixed with lower continental crustal materials could produce the I-type granitoid magmas. Major crustal growth occurred in the late Archean and Meso-Paleoproterozoic time for the Qilian block. The magma generation was primarily remelting of the crustal rocks with only little addition of the mantle materials after 1.0 Ga for the Qilian block. [ABSTRACT FROM AUTHOR]

We examined the petrography, litho-geochemistry, and geochronology of granite plutons in the Altyn orogenic belt, northern margin of the Qinghai–Tibet Plateau, to investigate the geodynamic history of the belt. The granites are peraluminous, with variable chondrite-normalized rare earth element patterns but generally similar trace element compositions; all are depleted in Ba, Nb, Sr, P, and Ti, and enriched in Rb, Th, Ta, Zr, and Hf. Their U–Pb zircon ages record multiple magmatic episodes between 500 and 404 Ma (north Altyn block (NAB)), 522 and 432 Ma (central Altyn block (CAB)), and 483 and 226 Ma (south Altyn block (SAB)). We propose a geodynamic model for the Altyn orogenic belt. Prior to 467 Ma, the north Altyn Ocean subducted southward below the NAB. The north Altyn region saw a change from subduction to collision between the Dunhuang block and the NAB during 467–450 Ma. The collision lasted until 430 Ma and was followed by post-collisional extension until 400 Ma. Farther south, the central Altyn Ocean subducted northwards beneath the CAB, resulting in 520–500 Ma granitic magmatism and leading to collision of the south Altyn micro-block (SAMB) with the CAB. Deep subduction of SAMB crust below the CAB resulted in granite intrusions during 490–455 Ma. The SAMB–CAB collision gave way to post-collisional extension, slab break-off, and delamination during 450–430 Ma. Bidirectional subduction of the south Altyn Ocean after ~485 Ma, dominated by southward subduction, continued until 456 Ma. Closure of the south Altyn Ocean led to continent–continent collision between the SAMB and the Qaidam block at 450–430 Ma, followed after ~410 Ma by repeated break-offs of slab segments until 337 Ma. Subsequent intrusions formed at 264–226 Ma in a setting of either post-collisional extension or sinistral strike-slip. [ABSTRACT FROM PUBLISHER]

Quantitative analyses of the spatial distribution of fault structures can provide a theoretical basis for forecasting prospective ore deposits. Characteristics and complexity of fault structure distribution in the Qitianling area, Southern Hunan Province, China, were quantitatively calculated and appraised by fractal and multifractal methods to evaluate the relation between fault structures and ore-prospecting potential. The results show that the lengths of faults can be modeled as multifractals. Multifractal spectra evidently reflect the characteristics of the scaling of fault structures. The box-counting dimension value (D) of fault structures is equal to 1.656, as indicates complexity of the spatial distribution of faults and favorable structural conditions for the formation of ore deposits. Moreover, the D values of sub-regions were calculated and isopleths of their fractal dimension values were plotted accordingly. Overlay analyses of isopleths of fractal dimension values and distributions of known ore deposits show that areas with the larger fractal dimension values of fault structures have more ore deposits. This spatial coupling relationship between D values and ore deposits can be used to forecast and explore other ore deposits. On the basis of complexity theory for ore-forming systems, three exploration targets with high D values were delineated as prospective ore deposits. [ABSTRACT FROM AUTHOR]

The Banshanping granitoid rocks distribute in the east of the North Qinling orogenic belt. It is a diorite-quartz diorite-granodiorite-granite series, spreading in a NW-SE direction, and intrudes into the Erlangping Group. The SiO2 content ranges from 57.04% to 76.56%, Na2O from 2.05% to 4.65%, K2O from 0.84% to 3.40%. Major element characteristics indicate that Banshanping granitoid rocks have properties of I type granotoids. SREE ranges from 36.51 ppm to 473.25 ppm, and LREE/HREE ratios lie between 3.95 and 22.18. Negative Eu anomalies are not obvious in most samples, though there are obvious Nb, P and Ti positive anomalies. The zircon LA-ICP-MS ages of Banshangping granitoid rocks are 496.0±8.1 Ma-486.9±9.3 Ma. Hf isotope shows that 176Hf/177Hf ratios range from 0.282721 to 0.282876, εHf( t) values from 8.5 to 14, all positive, and corresponding modal ages (TDM2) range from 559 Ma to 908 Ma. Based on Hf isotope characteristics and existing Sm-Nd and Rb-Sr isotope data, we consider that the Banshanping granitoid rocks originate from mantle-derived material, i.e. the igneous rocks that formed in Neoproterozoic, and there may be a certain amount of crust-derived material during the formation of Banshanping granitoid rocks. [ABSTRACT FROM AUTHOR]

The Boziguoer A-type granitoids in Baicheng County, Xinjiang, belong to the northern margin of the Tarim platform as well as the neighboring EW-oriented alkaline intrusive rocks. The rocks comprise an aegirine or arfvedsonite quartz alkali feldspar syenite, an aegirine or arfvedsonite alkali feldspar granite, and a biotite alkali feldspar syenite. The major rock-forming minerals are albite, K-feldspar, quartz, arfvedsonite, aegirine, and siderophyllite. The accessory minerals are mainly zircon, pyrochlore, thorite, fluorite, monazite, bastnaesite, xenotime, and astrophyllite. The chemical composition of the alkaline granitoids show that SiO2 varies from 64.55% to 72.29% with a mean value of 67.32%, Na2O+K2O is high (9.85%-11.87%) with a mean of 11.14%, K2O is 2.39%-5.47% (mean = 4.73%), the K2O/Na2O ratios are 0.31-0.96, Al2O3 ranges from 12.58% to 15.44%, and total FeOT is between 2.35% and 5.65%. CaO, MgO, MnO, and TiO2 are low. The REE content is high and the total SREE is (263-1219) ppm (mean = 776 ppm), showing LREE enrichment and HREE depletion with strong negative Eu anomalies. In addition, the chondrite-normalized REE patterns of the alkaline granitoids belong to the 'seagull' pattern of the right-type. The Zr content is (113-1246) ppm (mean = 594 ppm), Zr+Nb+Ce+Y is between (478-2203) ppm with a mean of 1362 ppm. Furthermore, the alkaline granitoids have high HFSE (Ga, Nb, Ta, Zr, and Hf) content and low LILE (Ba, K, and Sr) content. The Nb/Ta ratio varies from 7.23 to 32.59 (mean = 16.59) and the Zr/Hf ratio is 16.69-58.04 (mean = 36.80). The zircons are depleted in LREE and enriched in HREE. The chondrite-normalized REE patterns of the zircons are of the 'seagull' pattern of the left-inclined type with strong negative Eu anomaly and without a Ce anomaly. The Boziguoer A-type granitoids share similar features with A1-type granites. The average temperature of the granitic magma was estimated at 832-839°C. The Boziguoer A-type granitoids show crust-mantle mixing and may have formed in an anorogenic intraplate tectonic setting under high-temperature, anhydrous, and low oxygen fugacity conditions. [ABSTRACT FROM AUTHOR]

The Gonghe geothermal basin is situated in the westernmost part of the western Qinling orogen and possesses the supreme potentials to explore and develop hot dry rock (HDR) geothermal resources in China. The basal rock of HDR reservoir in Gonghe basin is composed of granitoids. In this contribution, in order to constrain the formation mechanism of the Gonghe HDR, granitic samples from outcropping have been collected and drilling core samples data from the archives also been compiled. The studied results show that the obtained zircon U–Pb ages of 255.1 ± 1.9 Ma and 253.9 ± 2.6 Ma for granodiorite and monzogranite, respectively. All granitoids from both outcropping and drilling core have the similar rock associations and their major and trace elements possess the consistent evolved patterns, such as relative enrichment of LILEs (e.g., K, Rb), depletion of HFSEs (e.g., Nb, Ti), and negative Eu anomalies (0.32–0.66), indicating that they share the same magma sources and evolutional processes. And they have the affinity of I-type granites. They were derived from the mixture of partial melting of metabasaltic rocks in the lower crust and a small amount of mantle-derived magma and formed in a subduction-related setting relative to the southward subduction of the Zongwulong oceanic crust beneath the west Qinling terrane. The heat production values of rocks around the Gonghe basin were calculated and all basal granitic rocks ranges from 0.35 to 8.51 μW/m3, yielding an arithmetic mean value of 1.97 μW/m3, indicating that the radioactive heat generation capacity of granitoids in the Gonghe basin is slightly lower. The HDR reservoir in the Gonghe basin was probably due to an allied thermal effect of the radiogenic heat production in the thickening continental crust and the heat contributed by a deep magma chamber below the basin. The early Triassic granitoids with a higher thermal conductivity serve as the conductive medium of the geothermal heat; whilst the sedimentary rocks marked by lower thermal conductivity above the granitic batholiths act as the reservoir cap. This contribution provides a relatively rational understanding for the mechanism of the HDR reservoir in Gonghe geothermal basin from the petrological and geochemical perspectives, which is conducive to the geothermal potential assessment and estimation, and to-be implementation of the Enhanced Geothermal System demonstration project in China. • Granitoids formed between 236 and 255 Ma have same geochemical features, suggesting a prolonged magmatism. • Gonghe basin area has a lower heat production value, 1.97 μW/m3 on average. • HDR reservoir in Gonghe basin was an allied result of the radiogenic heat production and a deep magma chamber. [ABSTRACT FROM AUTHOR]

The North Qilian Orogenic Belt (NQOB), which consists of ophiolitic melange and island-arc assemblages containing many granites, blueschists, and eclogites, lies between the Alax and Qilian terranes in northwestern China. The Minleyaogou and Niuxinshan granitoids occur at the northern and southern margins, respectively, in the middle segment of the NQOB. The Minleyaogou pluton is granodiorite in composition, whereas the Niuxinshan pluton consists mainly of red granite with minor grey quartz diorite. Geochemically, the Minleyaogou granite differs from the Niuxinshan granite in that it contains a smaller range in SiO2, has lower total alkalis, and is more peraluminous. Both granitoids are magnesian but the Niuxinshan granite is alkali-calcic, whereas the Minleyaogou granodiorite is calcic. Both granitoids have similar chondrite-normalized rare earth element patterns with light rare earth element enrichment and negative Eu anomalies. They have pronounced negative Ba, Nb, Sr, P, and Ti anomalies indicating that they have an affinity to island-arc or active continental margin magmatism. SHRIMP U-Pb dating of zircons from the granitoids yields a formation age of 477 Ma for the Niuxinshan granite and 463 Ma for the Minleyaogou granodiorite. These ages, combined with the geochemistry and locations of the plutons, suggest that they formed by the double subduction of the North Qilian oceanic plate during early Palaeozoic time. Formation of the Niuxinshan granite may be related to southward subduction under the Qilian terrane at 477 Ma, whereas the Minleyaogou granodiorite was formed by northward subduction at 463 Ma under the Alax terrane. [ABSTRACT FROM AUTHOR]

Abstract: Granitic rocks in the Altun terrane, NW China crop out in a 50-km-long, E–W-trending belt along the southern margin of the Bashikaogong Basin, north Altun. They intrude the north Altun subduction complex and are hosted in Precambrian sandstones, schists, mudstones and tuffs. Four lithologic types are recognized; (I) gray, very coarsely phyric granite, (II) red, fine- to medium-grained, aphyric granite, (III) gray, medium- to coarse-grained, moderately phyric granite and (IV) pink, medium- to coarse-grained, moderately phyric granite. All of the granites are peraluminous with normative corundum ranging from 0.8 to 3.9 wt.%. Silica contents vary between 65.1% and 75.7%, and total alkalis (Na2O+K2O) range from 7.5 to 9.0 wt.%, giving K2O/Na2O ratios of 1.1 to 2.7. Rittman indices vary from 1.8 to 2.8, with an average of 2.3. Total rare earth elements (∑REE) are between 89 and 335 ppm, and all samples show significant but variable negative Eu anomalies on chondrite-normalized REE patterns. On mantle-normalized trace element patterns all the granites have pronounced negative Ba, Nb, Sr, P and Ti anomalies. Zircons from the granites show slightly different SHRIMP U–Pb ages for the different lithologies; 474.3±6.8 Ma for type I granites, 446.6±5.2 Ma for type II, 434.5±3.8 Ma for type III, and 431.1±3.8 Ma for type IV. The geochemical and geological data indicate that these are S-type granites formed by partial melting of crustal materials during or shortly after collision of the Altun and Tarim continental blocks in the Paleozoic. The age and geochemistry of the north Altun granites suggest that they can be correlated with similar rocks in north Qilian on the opposite side of the Altun strike-slip fault. [Copyright &y& Elsevier]

Abstract: Adakitic intrusive rocks of ∼430–450 Ma were discovered in the North Qilian orogenic belt, the western section of the Central Orogenic System (COS) in China. These adakitic rocks were lower crust melts rather than slab melts as indicated by their crustal Ce/Pb, Nb/U, Ti/Eu, and Nd/Sm ratios and radiogenically enriched (87Sr/86Sr)i of 0.7053–0.7066 and ε Nd(t) of −0.9 to −1.7. While they are all characterized by low Yb (<1.1 ppm) and Y (<11.5 ppm) abundances with high Sr/Y (>65) and (La/Yb)N (>13.7) ratios, these adakitic rocks are classified into the low-MgO–Ni–Cr and high-MgO–Ni–Cr groups. The low-MgO samples were derived from partial melting of thickened lower crust, whereas the high-MgO samples were melts from delaminated lower crust, which subsequently interacted with mantle peridotite upon ascent. Adakitic rocks from the adjacent North Qinling orogenic belt also originated from thickened lower crust at ∼430 Ma. In addition, the North Qilian and North Qinling orogenic belts both consist of lithological assemblages varying from subduction-accretionary complexes at south to central arc assemblages, which include adakitic rocks, then to backarc phases at north. Such a sequence reflects northward subduction of the Qilian and Qinling oceans. In these two orogenic belts, the occurrence of adakitic rocks of common origin and ages together with the similarities in tectonic configurations and lithological assemblages are considered to be the evidence for the continuity between eastern Qilian and western Qinling, forming a >1000 km Early Paleozoic orogenic belt. In such a tectonic configuration, the Qilian and Qinling oceans that subducted from south possibly represent parts of the large “Proto-Tethyan Ocean”. This inference is supported by the coexistence of Early Paleozoic coral and trilobite specimens from Asia, America and Australia in the North Qilian orogenic belt. Post-400 Ma volcanic rocks occur in the North Qinling orogenic belt but are absent in the North Qilian orogenic belt, indicating that these two orogenic belts underwent distinct evolution history after the closure of the Proto-Tethyan Ocean (∼420 Ma). [Copyright &y& Elsevier]

The article present the research that the Dunhuang Block, Western China represents a Paleozoic orogenic belt. Topic include the zircons were imaged using cathodoluminescence (CL) at the Chinese Academy of Geological Sciences to examine internal structures; and the Yulinhe granodiorite is an I-type granite, and the residual rock is mainly amphibolite facies, comprising amphibole and plagioclase, which may have links with the coeval amphibolite in the Dunhuang Block.

Discusses the determination of the Altyn Tagh strike-slip fault basin and its relationship with mountains in China. Ratio of length to width; Influence of the straight normal faults with strike-slip component on the long boundaries at the sides of the basin; Formation of the reverse thrust structures at the two sides of the center of the basin.

Abstract: The main hole (MH), and pre-pilot holes PP1, and PP3 of the Chinese Continental Scientific Drilling Project (CCSD) penetrated three different garnet peridotite bodies in the Sulu ultrahigh pressure (UHP) metamorphic belt, which are 80 m, 120 m, and 430 m thick, respectively. The bodies occur as tectonic blocks hosted in eclogite (MH peridotite) and gneisses (PP1 and PP3 peridotites). The peridotites in the MH are garnet wehrlites, whose protoliths were ultramafic cumulates based on olivine compositions (Fo79–89) and other geochemical features. Zoned garnet and omphacite (with 4–5 wt.% Na2O) are typical metamorphic minerals in these rocks, and, along with P–T estimates based on mineral pairs, suggest that the rocks have undergone UHP metamorphism. SHRIMP U–Pb isotope dating of zircon from the garnet wehrlite yielded a Paleozoic protolith age (ca. 346–461 Ma), and a Mesozoic UHP metamorphic age (ca. 220–240 Ma). The peridotites in PP1 consist of interlayered garnet (Grt)-bearing and garnet-free (GF) peridotite. Both types of peridotite have depleted mantle compositions (Mg#=90–92) and they display transitional geochemical features. The intercalated layers probably reflect variations in partial melting rather than pressure variations during metamorphism, and the garnets may have been formed by exsolution from orthopyroxene during exhumation. These peridotites were probably part of the mantle wedge above the subduction zone that produced the UHP metamorphism and thus belonged to the North China Block before its tectonic emplacement. The exhumation of the subducted Yangtze Block brought these mantle fragments to shallow crustal levels. The ultramafic rocks in PP3 are dominantly dunite with minor garnet dunite. Their high Mg# (92–93) and relatively uniform chemical compositions indicate that they are part of a depleted mantle sequence. The presence of garnet replacing spinel and enclosing pre-metamorphic minerals such as olivine, clinopyroxene and spinel suggests that these rocks have undergone progressive metamorphism. SHRIMP U–Pb isotope dating of zircon from these rocks yielded two age groups: 726±56 Ma for relic magmatic zircon grains and 240±2.7 Ma for the newly formed metamorphic zircon. The older group is similar in age to granitic intrusions within the Dabie–Sulu belt, suggesting that the PP3 garnet peridotite may record the early emplacement of the peridotite into the crust. The younger dates coincide with the age of UHP metamorphism during continent–continent collision between the Yangtze and North China Blocks, suggesting that these peridotites were subducted to depths equivalent to the coesite facies and later exhumed. Thus, the garnet peridotites in the CCSD cores include both ultramafic rocks that existed originally in the subducted plate and rocks from the mantle wedge above the subducted plate, i.e., part of the North China Block. [Copyright &y& Elsevier]