Mesozoic Igneous Rocks Research Articles

Mid-Triassic felsic igneous rocks from the southern Lancangjiang Zone, SW China: Petrogenesis and implications for the evolution of Paleo-Tethys

The southern Lancangjiang magmatic belt is an important component of the Triassic San-Jiang igneous zone in Southwestern China and is mainly composed of the Lincang (LC) batholith and a Mesozoic volcanic belt that contains abundant rhyolites. Our new LA-ICP-MS zircon U–Pb results, together with previous SHRIMP and LA-ICP-MS ages, define two emplacement ages for the Lincang batholith: at ~230Ma and ~220Ma, corresponding to the eruption times of volcanic rocks of the Manghuai and Xiaodingxi formations, respectively. Most of the ~230Ma LC granites possess high A/CNK values (>1.1) and display strongly peraluminous characteristics, similar to S-type granite, whereas the Manghuai Formation (MHF) rhyolites show an affinity to A-type granite, especially their elevated FeOt/(FeOt+MgO) and Ga/Al ratios. Both of the granitic and volcanic rocks have strongly fractionated REE patterns ((La/Yb)N=2.66–33.2 and 13.1–19.7, respectively) and have conspicuous negative Eu anomalies (Eu*/Eu=0.06–0.65 and 0.52–0.74, respectively) with a similar depletion in HFSE (Nb, Zr, Hf), P, Ba and Sr. The Sr–Nd isotopic data and TDM2 model ages suggest that the LC granitic magma had a dominantly crustal source, whereas the MHF rhyolites were derived from mixing between middle/upper crustal rocks similar to the source of the LC granitic magma, with a small volume of mantle-derived melt.In combination with regional studies, our new geochemical data and geochronological results show that the mid-Triassic magmatism was generated in a post-collisional tectonic setting. The spatial distribution pattern of the Mesozoic igneous rocks along the Lancangjiang zone favors a slab breakoff model, which resulted in post-collisional extension and asthenospheric upwelling that induced large-scale partial melting of the middle-lower crust to produce voluminous amounts of felsic magma. Therefore, the occurrence of the mid-Triassic post-collisional magmatism clearly indicates that the final continent–continent/arc collision between the Gondwana-derived Sibumasu and Indochina blocks of Paleo-Tethys was completed by the early mid-Triassic.

Origins of ultramafic rocks in the Sulu Ultrahigh-pressure Terrane, Eastern China

Ultramafic rocks in the Sulu belt are associated with high-pressure (HP) and ultra-high-pressure (UHP) rocks, a metamorphic product of the northern margin of the Yangtze Craton (YZC). These ultramafic rocks are important because they provide information relevant to the nature and evolution of the Mesozoic collisional belt. We selected ultramafic rocks from Yangkou Bay (YKB), Suoluoshu (SLS) and Hujialin (HJL) in the central region of Sulu belt. The ultramafic rocks in YKB and SLS are hydrated to form serpentinites and they contain low concentrations of moderately incompatible elements (Al, Ti, and V), high contents of Ir-group platinum-group elements (IPGE; Ir, Os, and Ru; 12.8–21.7ppb in total), and high ratios (1.2–5.5) of IPGE to Pd-group PGE (PPGE) in bulk rocks. Spinel contains high Cr (Cr#=atomic ratio of Cr/[Cr+Al], 0.57–0.79). The data suggest that they likely represent hydrated forearc mantle peridotites underlying the margin of the North China Craton (NCC). Dunite samples from HJL are not fully hydrated with loss on ignition (LOI) values ranging from 6.6 to 13.2wt.%, and contain olivine grains with high forsterite components (Fo=100*Mg/[Mg+Fe], 91.7–92.4) and NiO contents (0.36–0.41wt.%). Spinel grains show high Cr# (0.68–0.76). The bulk rock contains high IPGE (5.0–22.7ppb total) and show high ratios (up to 8.8) of IPGE to PPGE. The data suggest that they are also residual mantle peridotites after high degrees of influx partial melting in the subduction setting. The geochemical features of our serpentinite and dunite samples are different from peridotites of young Cenozoic subcontinental lithospheric mantle (SCLM) that have been brought to the surface as xenoliths of young volcanic rocks. Instead, our samples are similar but even more refractory than peridotites of relict Archean SCLM below the NCC that were enclosed as xenoliths in Paleozoic–Mesozoic igneous rocks. Thus, the studied ultramafic rocks likely represent the relic of old refractory lithospheric mantle peridotites that underwent partial melting in the margin of the NCC during the subduction of oceanic lithosphere before the collision with the YZC. The peridotites in the forearc mantle were dragged into the subduction channel during the Mesozoic subduction of the YZC below the NCC, and exhumed together with the buoyant granitic metamorphic rocks in the Sulu belt.

A comparison for a multiscale study of structural lineaments in southern Brazil: LANDSAT-7 ETM+ and shaded relief images from SRTM3-DEM

This paper presents a comparison of descriptive statistics obtained for brittle structural lineaments extracted manually from LANDSAT images and shaded relief images from SRTM 3 DEM at 1:100, 000 and 1:500, 000 scales. The selected area is located in the southern of Brazil and comprises Precambrian rocks and stratigraphic units of the Paraná Basin. The application of this methodology shows that the visual interpretation depends on the kind of remote sensing image. The resulting descriptive statistics obtained for lineaments extracted from the images do not follow the same pattern according to the scale adopted. The main direction obtained for Proterozoic rocks using both image types at a 1:500, 000 scale are close to NS±10, whereas at a 1:100, 000 scale N45E was obtained for shaded relief images from SRTM 3 DEM and N10W for LANDSAT images. The Paleozoic sediments yielded the best results for the different images and scales (N50W). On the other hand, the Mesozoic igneous rocks showed greatest differences, the shaded relief images from SRTM 3 DEM images highlighting NE structures and the LANDSAT images highlighting NW structures. The accumulated frequency demonstrated high similarity between products for each image type no matter the scale, indicating that they can be used in multiscale studies. Conversely, major differences were found when comparing data obtained using shaded relief images from SRTM 3 DEM and Landsat images at a 1:100, 000 scale.

Links between Mesozoic intermediate–felsic igneous rocks and lower crustal granulite xenoliths, North China Craton: O and Pb isotopic evidence

We present and compare whole-rock and zircon O and Pb isotopic compositions for the Hannuoba granulite xenoliths and Mesozoic intermediate-to-felsic igneous rocks from the Zhangjiakou region, northern margin of the North China Craton, northeast China. The xenoliths have an overall Pb isotopic range similar to rocks from the regionally exposed Neoarchaean granulite terrain. Mesozoic zircons from different types of granulite xenoliths have a narrow range of δ18O values (6.0–7.7‰) higher than normal mantle δ18O values (∼5.7‰). Mesozoic intermediate–felsic igneous rocks have O and Pb isotopic compositions indistinguishable from the Hannuoba intermediate–mafic granulite xenoliths. Our new data suggest that the Mesozoic igneous rocks and granulite xenoliths are genetically linked and that both were derived from the late Neoarchaean lower crust. This argues against previous proposals that the granulite xenoliths are either products of Mesozoic basaltic underplating or formed by mixing between mantle-derived and pre-existing crustal magmas.

Zircon U–Pb geochronology and Hf isotopic compositions of the Mesozoic granites in southern Anhui Province, China

Mesozoic magmatism is extensively developed in eastern China along the eastern Asian continental margin, but the geochronological framework is not well understood for each area. In this study, seventy-eight samples were collected from the Mesozoic igneous rocks in south Anhui Province, east-central China, in order to precisely constrain their formation ages and contributions to crustal growth. Zircon U–Pb age determination using ion probe and laser ablation techniques indicate that magmatism in the area can be divided into two separate stages: at 150–136 and 136–120Ma, respectively. The first stage of granitic rocks, not documented in other areas of eastern China, is mostly composed of hornblende-bearing I-type granodiorite and monzogranite, and is considered to be formed by slab-tearing during Pacific subduction. The second stage of magmatism, coeval to that in other areas of eastern China, is characterized by the occurrence of A-type granite and syenite, and their volcanic counterparts, although I-type granitic rocks are also developed locally. These rocks are mostly distributed around and within the fault-controlled volcanic basins, and some are closely related to detachment shearing, indicating their formation in an extensional setting. Zircon Hf isotopic analyses indicate that Archean material might be present in the area, but that the main episode of crustal growth took place during the Mesoproterozoic, with very little juvenile material in the Mesozoic.

The volcanic margins of the northern Labrador Sea: Insights to the rifting process

A new interpretation of seismic reflection data on the continental margin of northern Labrador shows basement structures similar to those observed on other volcanic rifted margins. Seaward dipping reflections, inner flows, volcanic plateaus, and lava deltas are observed on these data. Magnetic chron 27n (∼61 Ma) is coincident with the volcanic plateaus, connecting these features to the Paleocene volcanism farther north in Davis Strait. Therefore, we are able to extend the region of volcanism about 500 km south along the margin. Similar structures are also observed on the conjugate west Greenland margin. Below the volcanic plateaus, gravity and wide‐angle seismic data show thick igneous crust, which is fairly symmetrically distributed across the conjugate margins. However, the geometry of the thinned continental crust is not symmetrical: a narrower zone of thinning is observed off northern Labrador. The thick igneous crust lies seaward of thinned continental crust, which exhibits little or no underplating by the magmatic event. This observation is compatible with recent models for the formation of nonvolcanic margins, followed by a magmatic event late in the rift evolution. In Mesozoic time rifting of the cold, thick cratonic lithosphere occurred between Greenland and North America with minimal volcanic activity. Then in Late Cretaceous time, the zone of rifting narrowed and localized seaward of the shelf, creating a relatively narrow zone of lower lithospheric thinning and mantle upwelling into which the Paleocene magmas were eventually channeled. This scenario is supported by studies of Mesozoic igneous rocks on land in coastal west Greenland and Labrador.

Geochronological and geochemical results from Mesozoic basalts in southern South China Block support the flat-slab subduction model

The debate on the Mesozoic tectonics of the South China Block (SCB), featuring a broad orogenic belt and a large continental magmatic province, has been rejuvenated in the past years. There are a number of competing tectonic models, each predicting different time, space, and compositional evolutional trends for the Mesozoic igneous rocks, including sporadic basalts. In this paper, we report high precision 40Ar/ 39Ar ages and geochemical and Sr–Nd isotopic data for basaltic rocks in central–eastern SCB. These results, together with a data compilation, indicate three evolutionary stages for the basalts. Stage 1 (195–160 Ma) basalts occur only in inland SCB. They exhibit low initial 87Sr/ 86Sr ratios (0.7038 to 0.7078), high ε Nd(t) values (− 1.5 to 6.0) and ocean island basalt (OIB)-like geochemical characteristics such as low La/Nb ratios (0.6 to 1.4), implying negligible to minor lithosphere contamination. Stage 2 (160–110 Ma) basalts, mostly from the same inland region with minor occurrence closer to the coast, are characterized by variable initial 87Sr/ 86Sr ratios (0.7053 to 0.7102), εNd(t) values (− 6.0 to 5.0) and low La/Nb ratios (0.9 to 1.8), indicating an enhanced asthenosphere–lithosphere interaction. Stage 3 (110 to ≤ 80 Ma) basalts can be further divided into two sub-groups based on their geographic and geochemical variations. Basalts in the coastal regions are characterized by low εNd(t) values (− 8.1 to 3.7) and variably high La/Nb ratios (up to 4.8) indicating a strong arc signature. On the other hand, basalts in the inland regions have high ε Nd(t) values (− 1.9 to 6.8) and low La/Nb ratios (0.6 to 1.2) that are similar to the stage 1 basalts. We interpret these features as results of geodynamics processes related to the break-up, foundering and retreating of an early Mesozoic flat-subducted oceanic slab.

Petrology, geochemistry, and tectonic significance of Mesozoic shoshonitic volcanic rocks, Luzong volcanic basin, eastern China

We studied the geochemical characteristics of three types of Mesozoic igneous rocks from the Luzong volcanic basin: basaltic trachyandesite at Shuangmiao, pyroxene monzonite at Bajiatan, and quartz-syenite (A-type granite) at Huangmeijian. Based on analyses of whole-rock major elements, all investigated rocks are enriched in K, Na, Ti, Al, but depleted in Ca, representing a shoshonitic series. Trace element analyses show that these rocks are characterized by enrichments of large-ion lithophile elements and high field strength elements. Positive Nb and Ta anomalies in the chondrite-normalized spider diagram indicate that the shoshonitic volcanic rocks share similar features with Nb-enriched basalts, which are different from normal island-arc volcanical rocks (they are typically strongly depleted in Nb and Ta). Bulk-rock chemical compositions and Sr–Nd isotopes indicate that the three types of igneous rocks are geochemically comagmatic, suggesting that the melts were derived from an enriched mantle reservoir. We postulate an extensional tectonic setting for the formation of Luzong volcanic basin, possibly related to subduction of a palaeo-Pacific plate beneath the east Chinese continent during the Yanshanian period (Cretaceous). Therefore, the petrogenetic features of those volcanic rocks as well as A-type granites in the Luzong basin indicate that the regional large-scale Fe–Cu–Au mineralization was associated with oceanic slab melting, but not delamination or recycling of the ancient lower continental crust, as previously proposed.

Source of Mesozoic intermediate-felsic igneous rocks in the North China craton: Granulite xenolith evidence

Four intermediate to felsic igneous rocks from the Zhangjiakou region, along the northern margin of the North China craton, have magmatic zircon U–Pb ages from 122 to 144Ma. Two of these samples have inherited zircon U–Pb ages of ~2.5Ga, similar to the zircon ages of rocks from the surrounding granulite terrain. Zircons from two intermediate composition granulite xenoliths (JN0811 and JN0919) in the nearby Cenozoic Hannuoba basalts yield two groups of ages. The rims have concordant Mesozoic ages mostly between 120 and 145Ma, coeval with the Mesozoic intermediate-felsic magmatism in the region, while the cores have discordant U–Pb ages with upper-intercepts of ~2.5Ga, overlapping the zircon ages of granulite terrain rocks, and lower-intercept ages of ~130Ma, approximating the ages of the Mesozoic intermediate-felsic magmatism. The Sr–Nd isotopic compositions of the Mesozoic intermediate-felsic igneous rocks are completely different from those expected for basaltic melts from either the lithospheric mantle or the asthenospheric mantle, precluding a derivation by extensive fractional crystallization of mantle-derived magmas. The lack of correlation between (86Sr/87Sr)i, εNd(t) and SiO2 for the Mesozoic igneous rocks, the very narrow range of zircon εHf(t) for individual intermediate-felsic igneous rocks, and simple binary mixing calculations argue against them being formed by mixing between mantle-derived magma and preexisting crust that has extremely evolved Sr–Nd isotopic compositions like granulite xenoliths JN0811 and JN0919. Hf isotopic compositions of the Mesozoic zircons and whole-rock geochemistry show that the granulite xenoliths with extremely evolved Sr–Nd isotopic compositions have not undergone partial melting during the Mesozoic and thus do not contribute to the Mesozoic intermediate-felsic magmas. Further comparisons show that the source rocks for the Mesozoic intermediate-felsic magmas likely were late Archean lower crustal rocks similar in chemical and isotopic compositions to rocks with SiO2<62wt.% from the granulite terrain. If so, pyroxene-rich mafic granulite xenoliths found in the Hannuoba basalts could be restites left behind after the partial melting of the late Archean lower crust. The results shed new light on the origin for Mesozoic zircons in granulite xenoliths from Nushan, at the southern margin of the North China craton. We suggest that the widespread Mesozoic intermediate-felsic igneous rocks in the eastern North China craton are most likely derived from partial melting of the intermediate-mafic rocks of the late Archean lower crust.

Review of the stable isotope geochemistry of Mesozoic igneous rocks and Cu–Au deposits along the middle–lower Yangtze Metallogenic Belt, China

Ore deposition took place in the Yangtze Valley episodically during the Jurassic and Cretaceous periods, generating approximately 200 polymetallic Cu–Fe–Au, Mo, Zn, Pb, and Ag deposits. We analysed the stable isotopes of sulphur, oxygen, and hydrogen from the Cu–Au deposits and correlated our new data with published stable isotope for associated Yanshanian (Mesozoic) igneous rocks. The latter bears a close relationship to Cu–Au mineralization in the area. Cu–Au deposits in the middle–lower Yangtze Valley can be divided into three types: skarn, porphyry, and volcanic. The S–O–H isotopic values allow constraints to be placed on the conditions of origin of these famous Cu–Au ores and their related igneous rocks. Sulphur from the sulphide ores mostly was derived from a magmatic source; however, a few deposits reflect a sedimentary source of sulphur. Oxygen isotope values in quartz from the Shaxi porphyry Cu–Au deposit and from the Tongling skarn Cu–Au deposits range from 2.6‰ to 12.5‰ and from −1.3‰ to 24.5‰, respectively; these values represent larger variations compared with those from other Cu–Au deposits in this metallogenic belt. Hydrogen versus oxygen isotope plots of the Cu–Au ore-forming fluids demonstrate that the fluids came from different sources: the most important involved the mixing of magmatic and meteoric water; the second most important was strictly magmatic water; and the third most important may have been a mixture of formation water or meteoric water that had reacted with carbonate wall rocks.

Diagenesis of early Permian high-latitude limestones, Lower Parmeener Supergroup, Tasmania

The Darlington (Sakmarian) and Berriedale (Artinskian) Limestones are neritic deposits that accumulated in high-latitude environments along the south-eastern margin of Pangea in what is now Tasmania. These rocks underwent a series of diagenetic processes that began in the marine palaeoenvironment, continued during rapid burial and were profoundly modified by alteration associated with the intrusion of Mesozoic igneous rocks. Marine diagenesis was important but contradictory; although dissolution took place, there was also coeval precipitation of fibrous calcite cement, phosphate and glauconite, as well as calcitization of aragonite shells. These processes are interpreted as having been promoted by mixing of shelf and upwelling deep ocean waters and enabled by microbial degradation of organic matter. In contrast to warm-water carbonates where meteoric diagenesis is important, the Darlington and Berriedale Limestones were largely unaffected by meteoric diagenesis. Only minor dissolution and local cementation took place in this diagenetic environment, although mechanical compaction was ubiquitous. Correlation with burial history curves indicates that chemical compaction became important as burial depths exceeded 150 m, promoting precipitation of extensive ferroan calcite. This effect resulted from burial by rapidly deposited, overlying, thick, late Permian and Triassic terrestrial sediments. This diagenetic pathway was, however, complicated by the subsequent intrusion of massive Mesozoic diabases and associated silicifying diagenetic fluids. Finally, fractures most probably connected with Cretaceous uplift were filled with late-stage non-ferroan calcite cement. This study suggests that both carbonate dissolution and precipitation occur in high-latitude marine palaeoenvironments and, therefore, the cold-water diagenetic realm is not always destructive in terms of diagenesis. Furthermore, it appears that for the early Permian of southern Pangea at least, there was no real difference in the diagenetic pathways taken by cool-water and cold-water carbonates.

Sr–Nd–Pb isotope mapping of Mesozoic igneous rocks in NE China: Constraints on tectonic framework and Phanerozoic crustal growth

New Sr–Nd–Pb isotope dataset of Mesozoic igneous rocks shows that the NE China can be subdivided into four Sr–Nd–Pb isotope provinces: (1) the northern Hinggan Mountains (NHM) region; (2) the southern Hinggan Mountain (SHM)–Yanji-Liaoyuan (YL) region; (3) the Zhangguangcai Range–Jiamusi (ZGJ) Block; and (4) the exotic Wandashan massif (WDM). The Wandashan massif contains Mesozoic (high-μ)-type oceanic island basalts (HIMU-OIBs) with highly radiogenic Pb isotopic compositions (e.g., 206Pb/ 204Pb(i) = 18.9–22.7), quite different from other regions that have moderately radiogenic Pb (i.e., 206Pb/ 204Pb(i)) is generally less than 18.6. These HIMU-OIBs also show negative Δ7/4 and Δ8/4 values, signatures of Southern Gondwanaland Continent. By contrast, the majority of Mesozoic igneous rocks in other areas of NE China have positive Δ7/4 and Δ8/4 values, akin to the Northern Laurasian Continent. Such isotopic variations were probably due to the enrichment processes mainly caused by Paleozoic Paleo-Asian ocean subduction and to some extent by subduction of the Paleo-Pacific Ocean since early Mesozoic. The mantle-derived rocks in the NHM region is characterized by moderately radiogenic Nd and Pb isotopic compositions (ε Nd(t) = −0.2 to + 3.6 and 206Pb/ 204Pb(i) = 18.3–18.6). Compared with the NHM region, the mantle-derived magmas in the SHM–YL region show wider Nd isotopic variation (ε Nd(t) = −1.1 to + 6.6) and less radiogenic Pb ( 206Pb/ 204Pb(i) = 18.1–18.4). Along the Hegenshan-Solonker suture distributes an early Cretaceous felsic magmatic belt with highly positive-ε Nd (ε Nd(t) = + 4.0 to + 5.9) and radiogenic Pb compositions ( 206Pb/ 204Pb(i) = 18.4–18.6), suggesting that it was not only an important Phanerozoic crustal growth belt but also a zone containing significant volume of pelagic sediments or their metamorphosed derivates. Adjacent to the Hengenshan ophiolite occurs a suite of andesites showing nonradiogenic Nd (ε Nd(t) = −10.5 to −6.3) and Pb ( 206Pb/ 204Pb(i) = 17.22–17.26), as well as DUPAL Pb isotopic signatures. These features indicate the existence of “old” lower continental crust beneath the area. Compared with the majority of crust-derived rocks in the NHM and SHM–YL regions (ε Nd(t) = −2.9 to + 6.8 and 206Pb/ 204Pb(i) = 17.4 to 18.6), the Mesozoic granitoids in the ZGJ block have relatively less radiogenic Nd (ε Nd(t) = −2.9 to + 2.1) and more radiogenic Pb composition ( 206Pb/ 204Pb(i) = 18.2 to 18.9). Considering that the Paleozoic granitoids have nonradiogenic Nd (ε Nd(t) < −6), we suggest that pelagic sediments or their metamorphosed derivates were an important crustal component in the region. The new isotope mapping results suggest that during Mesozoic time the crustal growth mainly occurred around the collisional sutures (e.g., the Hegenshan-Solonker suture) and/or along the major lithosphere-scale faults (e.g., the Tan-Lu fault), in which highly positive-ε Nd rocks are distributed. However, the extent of Mesozoic crustal growth was subordinate relative to the Paleozoic time in terms of Nd isotopic evolution. Generation of Mesozoic voluminous felsic magmas in NE China was mainly ascribed to remelting, recycling and redistribution of the preexistent crustal components (juvenile and “old” crustal components), which had been juxtaposed during the tectonic evolution of the Paleo-Asian Ocean.

Origin of the volcanic complexes of La Désirade, Lesser Antilles: Implications for tectonic reconstruction of the Late Jurassic to Cretaceous Pacific-proto Caribbean margin

La Désirade Island is located on the hanging wall of the present-day Lesser Antilles subduction zone and consists of a suite of Mesozoic igneous rocks capped by Neogene limestone. The basement suite contains Kimmeridgian to Tithonian (~ 153–145 Ma) mafic lava flows and pillow basalts overlain by felsic flows and breccias and intruded by a Mid-Berriasian (~ 144 Ma) trondhjemite pluton and intermediate to felsic dykes. The mafic rocks form a ~ 300 m thick sequence which trace element geochemistry reveals to contain, in stratigraphic order: (1) tholeiites with a very weak subduction signature; (2) calc-alkaline and tholeiitic arc rocks containing pelagic and terrigenous sediment slab-related components and (3) arc tholeiites with a minor subduction signature. The mantle wedge source was depleted and did not contain a significant plume-related component. The overlying felsic rocks show similar trace element patterns and incompatible trace element ratios to the mafic units. Factors such as pelagic sedimentary deposition and re-working, low eruption rates and the presence of MORB-like and felsic rocks are best explained by an origin at a back-arc spreading ridge. This back-arc was most likely in the proto-Caribbean (Colombian Marginal) seaway and was related to east-dipping Andean/Cordilleran subduction. Other sites in the Greater Antilles and Central America older than the ~ 135 Ma westward acceleration of North America appear to corroborate a latest Jurassic–Early Cretaceous east-dipping arc system. The preservation of La Désirade in the fore-arc of the present Antilles arc is consistent with Mid-to-Late Cretaceous inception of west-dipping subduction along the former back-arc axis which had previously given rise to La Désirade.

Upper mantle structure and dynamics beneath Southeast China

We applied teleseismic tomography to 5671 relative travel-time residuals from 257 teleseismic events recorded by 69 seismic stations to determine the 3D P-wave velocity structure of the upper mantle under Southeast (SE) China. Our results show prominent low P-wave velocity (low-Vp) anomalies under SE China which may reflect the remnant magma chambers and channels of the Late Mesozoic igneous rocks, which may be reheated by the upwelling mantle flow from the lower mantle driven by the deep subduction in East Asia during the Cenozoic. High-Vp anomalies are revealed in the upper mantle to the east of Taiwan, which represent the subducted Eurasian plate. Our result also suggests the break-off of the subducted Eurasian plate caused by its interaction with the Philippine Sea plate under Central and North Taiwan. The slab break-off may have created a mantle window through which the asthenospheric flow arises, causing the high heat flow and rapid uplift in the Taiwan orogen.

Neoproterozoic zircon inheritance in eastern North China craton (China) Mesozoic igneous rocks: derivation from the Yangtze craton and tectonic implications

We propose that inherited Neoproterozoic zircons in Mesozoic igneous rocks from the eastern portion of the North China craton (NCC) were initially derived from the Yangtze/South China block, rather than from the NCC itself. The mechanism that introduced these zircons into the NCC was likely tectonic underplating during Triassic continental subduction/collision of the Yangtze block beneath the NCC. The addition of abundant crustal materials represented by the exotic zircons, probably along the Moho or weak interfaces within the NCC crust, led to the crustal thickening of the NCC. These sialic materials contributed significantly to the Mesozoic igneous rocks, either as source rocks or as contaminants of magmas generated during an extensional environment following crustal thickening. Crustal thickening was spatially linked to lithospheric thinning, with both occurring mainly in the eastern segment of the NCC, suggestive of an intrinsic relationship between thickening and thinning events during Mesozoic evolution of the NCC.

SHRIMP zircon U-Pb ages for the Paleoproterozoic metamorphic-magmatic events in the southeast margin of the North China Craton

A garnet-pyroxene bearing amphibolite as a xenolith hosted by the Mesozoic igneous rocks from Xuzhou-Suzhou area was dated by zircon SHRIMP U-Pb method, which yields a metamorphic age of 1918 ± 56 Ma. In addition, the zircons from a garnet amphibolite as a lens interbedded with marble in the Archean metamorphic complex named Wuhe group in the Bengbu uplift give a metamorphic U-Pb age of 1857 ± 19 Ma, and the zircons from Shimenshan deformed granite in the eastern margin of the Bengbu uplift give a magma crystallization U-Pb age of 2054 ± 22 Ma. Both the Xuzhou-Suzhou area and Bengbu uplift are located in the southeastern margin of the North China Craton. Therefore, these ages indicate that there is a Paleoproterozoic tectonic zone in the southeastern margin of the North China Craton, and its metamorphic and magmatic ages are consistent with those of the other three Paleoproterozoic tectonic zones in the North China Craton. In view of the large scale sinistral strike-slip movement occurred at the Mesozoic along the Tan-Lu fault zone, the position of the eastern Shandong area, which is a south section of the Paleoproterozoic Jiao-Liao-Ji Belt, was correlated to Xuzhou-Suzhou-Bengbu area prior to movement of the Tan-Lu fault zone. This suggests that the Xuzhou-Suzhou-Bengbu Paleoproterozoic tectonic zone might be a southwest extension of the Paleoproterozoic Jiao-Liao-Ji Belt.

Geochemical and zircon U–Pb and Hf isotopic study of the Baijuhuajian metaluminous A-type granite: Extension at 125–100 Ma and its tectonic significance for South China

The Early Cretaceous Baijuhuajian pluton is an A-type granitic intrusion, emplaced along the Jiangshan-Shaoxing (JSSX) fault zone in western Zhejiang Province, SE South China. It intruded into a Late Jurassic volcanic basin bounded by Proterozoic sandstone and siltstone. The granite has a coarse-grained, porphyritic texture and is composed of alkali feldspar phenocrysts in a matrix of K-feldspar, quartz, plagioclase and biotite. The pluton has a clear A-type geochemical signature, e.g. it is metaluminous (A/CNK ~ 1.0) and has high SiO 2 (75 to 78 wt.%), total alkalis (Na 2O + K 2O = 4.8 to 8.5 wt.%), rare earth elements (total REE = 228 to 438 ppm), HFSE and Fe⁎ [FeO t/(FeO t + MgO) = 0.87 to 0.97]. On the other hand, it is characterized by low CaO (0.51 to 1.01 wt.%), TiO 2 (0.06 to 0.13 wt.%), P 2O 5 (below detection) and Sr (7.0 to 9.5 ppm). The hypersolvus texture and fine-grained groundmass indicate emplacement at a shallow-depth. SHRIMP U–Pb zircon dating yielded a weighted mean 206Pb/ 238U age of 126 ± 3 Ma and zircons from this pluton give εHf( T) values between − 0.52 and + 4.24, suggesting the importance of juvenile material in the magma source. Most of the plutonic rocks in southeast China are calc-alkaline, subduction-related intrusions of Jurassic and Cretaceous age. Previous studies suggested that the sparse A-type granites in South China were emplaced in two episodes: 190–155 Ma in the inland area and ~ 100 Ma along the coastal area in SE South China. Our study of the Baijuhuajian granite, together with the coeval Suzhou A-type granite (123 Ma) in Jiangsu Province, defines an important extensional event between 125 and 100 Ma. Considering the available data for the Mesozoic igneous rocks in South China, we suggest that subduction of the Pacific plate in the Mesozoic produced voluminous calc-alkaline granitoids and volcanic rocks with a younging trend from west to east. The A-type granites were generated during periods of local extension at 190–155 Ma and 125–100 Ma, perhaps corresponding to localized rollback of the Pacific plate.

Mesozoic decratonization of the North China block

Research Article| June 01, 2008 Mesozoic decratonization of the North China block Jin-Hui Yang; Jin-Hui Yang * 1State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, P.O. Box 9825, Beijing 100029, China *E-mail: jinhui@mail.igcas.ac.cn. Search for other works by this author on: GSW Google Scholar Fu-Yuan Wu; Fu-Yuan Wu 1State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, P.O. Box 9825, Beijing 100029, China Search for other works by this author on: GSW Google Scholar Simon A. Wilde; Simon A. Wilde 2Department of Applied Geology, Curtin University of Technology, P.O. Box U1987, Perth, Western Australia 6845, Australia Search for other works by this author on: GSW Google Scholar Elena Belousova; Elena Belousova 3Australian Research Council's National Key Centre for Geochemical Evolution and Metallogeny of Continents (GEMOC), Department of Earth and Planetary Sciences, Macquarie University, New South Wales 2109, Australia Search for other works by this author on: GSW Google Scholar William L. Griffin William L. Griffin 3Australian Research Council's National Key Centre for Geochemical Evolution and Metallogeny of Continents (GEMOC), Department of Earth and Planetary Sciences, Macquarie University, New South Wales 2109, Australia Search for other works by this author on: GSW Google Scholar Geology (2008) 36 (6): 467–470. https://doi.org/10.1130/G24518A.1 Article history received: 17 Oct 2007 rev-recd: 13 Feb 2008 accepted: 15 Feb 2008 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Jin-Hui Yang, Fu-Yuan Wu, Simon A. Wilde, Elena Belousova, William L. Griffin; Mesozoic decratonization of the North China block. Geology 2008;; 36 (6): 467–470. doi: https://doi.org/10.1130/G24518A.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Cratons are old, stable parts of the continental crust that have survived at least since Proterozoic time and have not undergone strong magmatism or tectonism since their stabilization. Traditionally, the growth of continental crust in the North China craton is considered to have been complete by Paleoproterozoic time, Phanerozoic events being largely restricted to surrounding orogenic belts. However, the eastern part of the North China craton contains large volumes of Mesozoic igneous rocks, with widespread metamorphic core complexes and pull-apart basins. Hf isotope compositions of magmatic zircon grains from igneous rocks in the Liaodong Peninsula indicate that widespread late Mesozoic granitoids formed by partial melting of ancient crust, but with significant input of a mantle component via magma mixing and crustal assimilation. This magmatism has resulted from removal and modification of lithospheric mantle, accompanied by asthenospheric upwelling. The Hf isotopic signatures thus record the addition of juvenile crust beneath the eastern part of the North China craton, which appears related to major extension and possibly slab rollback of the Pacific plate. Whatever the mechanism, it is apparent that since ca. 200 Ma, ancient lithosphere beneath the eastern North China craton has been progressively reactivated and replaced, resulting in “decratonization.” Tertiary to Holocene volcanism in the area and major subsidence around the Gulf of Bohai suggest that the effects of the process are continuing. Similar processes probably operated in the geological past, leading to significant modification of continental crust and requiring reconsideration of mechanisms for continental breakup and dispersal and of continental growth rates. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Geochemical studies on REE and trace elements from several Cu-Au deposits along the lower Yangtze metallogenic valley, central-southern Anhui Province

The Yangtze Valley was one of the most important metallogenic regions during the Jurassic-Cretaceous period in East China, where more than 200 polymetallic Cu-Fe-Au, Mo, Zn, Pb, Ag deposits have been found. Trace elements were chemically analyzed and the relevant data were collected from literature for the Yanshanian (Mesozoic) igneous rocks which have close relationship with Cu-Au mineralization. Copper mineralization in the lower Yangtze Valley can be divided into three major types: skarn type, porphyry type and volcanic type. The porphyry type is of rare occurrence, such as the Shaxi porphyry copper deposit in the northern part of the lower Yangtze metallogenic valley. This paper focuses on the REE and trace element geochemistry of several Cu-Au deposits along the lower part of Yangtze metallogenic valley in Anhui. The results showed that there are differences in REE distribution for these four types of Cu-Au mineralization, which confine the sources of REE and trace elements as well as other mantle and transitional compatible elements. The results of both REE and trace element geochemical studies showed that these elements with different characteristics have different origins, probably representing different sources of Cu-Au deposits in the deep crust and upper mantle environments. The 40Ar/39Ar dating of one biotite sample gave an age of 131 Ma with a high level of confidence, which represents the age of formation of the Shaxi porphyrite intrusive with porphrytic Cu-Au mineralization, which is consistent with that of the majority of the adjacent acid intrusives with mass Cu-Au mineralization along the Yangtze metallogenic belt in the Yanshanian period (Mesozoic). This is the first attempt to use the high precision method to date the Shaxi porphyrite intrusive.

Diagenesis of diatomite from the Kolubara Coal Basin, Baroševac, Serbia

Diatomite associated with the Kolubara Coal Basin was studied to better understand early stage silica diagenesis of shallow water deposits. The Kolubara Basin consists of Neogene siliciclastic rocks, diatomite, marlstone and rare carbonates. Palaeozoic metamorphic and Mesozoic sedimentary and igneous basement rocks are transgressively overlain by Upper Miocene sandstone, siltstone, shale and mudstone. This Upper Miocene section is transgressively overlain by the Pontian section, which contains diatomite and coal beds. White and grey diatomite forms beds 0.7-2.2 m thick that are continuous over an area of about 2 km2. Siliceous rocks vary in composition from diatomite (81-89 per cent SiO2) to diatom-bearing shale (58-60 per cent SiO2). Siliceous deposits are laminated in places, with the laminae defined by variations in clay minerals, organic matter and diatoms. Diatomite shows only incipient diagenesis characterized by the fragmentation of diatom frustules, the minor to moderate corrosion of frustules and the formation of minor amounts of opal-A' (X-ray amorphous inorganic opal) cement. The low degree of diagenesis results from the young age of the deposits, low burial temperatures and possibly also from the presence of abundant organic matter and the dissolution of kaolinite. The presence of only weak diagenesis is also reflected by the characteristically poor consolidation of the rocks and low rank of the associated coal.