Tarim Large Igneous Province Research Articles

Petrogenesis of Early Permian basalts in the Turpan-Hami basin, NW China: Implications for the spatial limits of the Tarim mantle plume

Controversies remain as to the area of the Tarim Large Igneous Province (TLIP), in particular, the relationship between extensive Permian magmatism in the Central Asian Orogenic Belt (CAOB) and the activity of Tarim plume. Here we report the geochronological, mineralogical and geochemical characteristics of the Permian basalts from the Turpan-Hami (Tu-Ha) basin, located in southwestern CAOB. LA-ICP-MS zircon U-Pb dating yielded an age of 298.4 ± 2.6 Ma, temporally close to that of the Tarim plume. The basalts could be classified into lower porphyritic basalt with phenocrysts of plagioclase, olivine, minor clinopyroxene, and upper aphyric basalts. Geochemically, the former is characterized by relatively higher Na2O + K2O (3.97–5.13 wt%), low (La/Yb)N (∼2) and depleted Sr-Nd values [εNd(t)= +8.2 to +8.7; (87Sr/86Sr)i = 0.7032–0.7034], whereas the latter have lower Na2O + K2O (4.19–4.43 wt%) content, higher (La/Yb)N (∼4–6) and more enriched Sr-Nd values [εNd(t)= +4.6 to +6.2; (87Sr/86Sr)i = 0.7033–0.7048]. The compositional variation of plagioclase phenocrysts and pressure estimation (∼7kbar) indicate that Tu-Ha magmas were stored and evolved in a lower crustal magma chamber which experienced at least one-time magma replenishment. The estimated mantle potential temperature (1270–1480 °C) in Tu-Ha basin is similar to MOR, with no obvious thermal anomaly. Furthermore, higher Na/Ti ratio of quartz-normative Tu-Ha basalts suggest a shallower melting depth for Tu-Ha basin than central area of TLIP, which against a typical plume model. These characteristics alongside regional geologic records collectively suggest that the formation of Permian Tu-Ha basalts is more closely linked post-orogenic extension, implying that the extensive Permian magmatism in the CAOB is unrelated to the Tarim plume.

New Estimates on the Basalt Volume of the Tarim (Not So Large) Igneous Province, NW China

AbstractThe early Permian basalts of the Tarim Basin of NW China are geographically widespread, covering over 200,000 km2 and are in places up to 1‐km thick and hence frequently referred to represent a Large Igneous Province (LIP). Available volume estimates are based on average lava thickness multiplied by area, using these values results in volumes exceeding 100,000 km3, and is commonly cited as being evidence of LIP status. Using a database of 58 boreholes, field sections, and seismic data we calculate a range of basalt isopach maps, and use these to estimate new, more refined overall eruption volumes. These volumes are significantly smaller than previously reported estimates. We demonstrate that the thickness distribution of erupted basalts is nonuniform and strongly skewed, indicating that volume estimates using an arithmetically averaged thickness of input data will result in overestimation of total volumes. We find that even with the addition of an estimated nonerupted volume component, representing cumulates and intrusions, that the total volume of the Tarim volcanics is significantly below the minimum threshold of a LIP. Using a simple Monte Carlo model we demonstrate that even while accounting for uncertainty and error in the input data, the probability of the total volume exceeding 100,000 km3 is very low. The new volume estimates imply a revision of the climate and environmental impact of the Tarim volcanism. We therefore suggest that the term Tarim Igneous Province should be used instead of Tarim Large Igneous Province.

Phonotephrite and phonolite in the Tarim Large Igneous Province, northwestern China: Petrological, geochemical and isotopic evidence for contrasting mantle sources and deep carbon recycling

The igneous units of Permian Tarim Large Igneous Province (TLIP) is typically characterized by alkaline affinity. Here we report for the first time the petrological, geochemical and isotopic characteristics of phonotephrite and phonolite dykes from the Wajilitag complex in the northwestern margin of the TLIP. Our data, especially Sr-Nd-Mg isotopes, suggest that the dykes have different mantle sources. Phonotephrite with mantle-like Mg isotope values (−0.295 to −0.382 ‰), relatively enriched Sr isotopes (0.70487 to 0.70574) and slightly lower εNd(t) values (−0.23 to +2.06), were possibly derived from a lithospheric mantle source that was metasomatized by calcitic carbonate melt. The phonotephrites are highly evolved rocks formed through fractional crystallization from a parental magma which is similar to that of the mafic–ultramafic intrusions. Phonolites show relatively depleted Sr isotopes (0.70362 to 0.70409), higher εNd(t) values (+1.27 to +3.45), markedly lighter Mg isotopes (−0.851 to −0.906‰) than the normal mantle indicating a mantle plume source with the involvement of carbonated eclogite. The parental magma of phonolites may be related to the liquid immiscibility with calciocarbonatites present in the Wajilitag complex due to their similar extremely light Mg isotopic compositions. The distinct geochemical features between two series of dykes in the Wajilitag complex reflect the diversity of mantle source of the TLIP, and their Sr-Nd-Mg isotopic characteristics indicate the role of subducted recycled sedimentary carbonates at different depths in the mantle.

Petrology and geochemistry of early Permian mafic–ultramafic rocks in the Wajilitag area of the southwestern Tarim Large Igneous Province: Insights into Fe-rich magma of mantle plume activity

The majority of global Fe–Ti-oxide deposits hosted in mafic–ultramafic layered intrusions are closely related to mantle plume activity. The metallogenesis of these Fe–Ti-oxide deposits is still debated, especially with regard to their mantle source and relationship to magmatism. Here we report detailed petrology and geochemistry for early Permian (ca. 280 Ma) mafic–ultramafic igneous rocks in the Wajilitag area of the western Tarim Large Igneous Province (TLIP) to establish the relationships among mantle source, magmatism, and metallogenesis in mantle plume activity. The mafic rocks (i.e., gabbro and diabase) show alkaline affinities and OIB-like trace-element patterns. Clinopyroxenites closely related to Fe–Ti-oxide deposits were derived from the same magmatic system as that of the mafic rocks. The primary magma of the Wajilitag mafic rocks was enriched in FeOT and TiO2 and depleted in SiO2, and has high FC3MS (FeOT/CaO − 3MgO/SiO2) and Fe/Mn, indicating the involvement of Si-poor pyroxenite/eclogite in the mantle source. Primary olivines from the Wajilitag gabbro have consistently high NiO and Fe/Mn. Wajilitag mafic rocks have variable Sr–Nd–Hf isotopes owing to their derivation from a hybrid mantle source with the involvement of subducted oceanic crust and sediments. Subducted slabs within the upper mantle are inferred to have been entrained by the upwelling mantle plume and preferentially melted to produce mainly Fe-rich magma. The occurrence of an adjacent oceanic subduction event just prior to the operation of a mantle plume played a crucial role in the formation of large-scale Fe–Ti-oxide deposits in LIPs.

Mantle source of tephritic porphyry in the Tarim Large Igneous Province constrained from Mg, Zn, Sr, and Nd isotope systematics: Implications for deep carbon cycling

AbstractThe nature and source of magmatism associated with large igneous provinces (LIPs) remain disputed. Here we investigate the role of recycled materials that contributed to mantle heterogeneity in the Tarim Large Igneous Province (TLIP) in China through integrated Zn–Mg–Sr–Nd isotopes of a rare tephritic rock suite. The Sr–Nd isotopes [(87Sr/86Sr)i = 0.70368–0.70629; εNd(t) = −0.25–4.64] and δ26Mg values (−0.23‰ to −0.34‰) of the tephritic porphyries are consistent with a normal mantle origin. In contrast, the whole rock and pyroxene phenocrysts yield δ66Zn values of +0.28‰ to +0.46‰ and +0.30‰ to +0.39‰, which are slightly heavier than those of the terrestrial mantle (+0.16 ± 0.06‰) and mid-oceanic-ridge basalts (MORBs) (+0.27 ± 0.05‰). We exclude the possibility that the heavy Zn isotopes of the Wajilitag tephritic porphyries are caused by magmatic processes such as fractional crystallization and partial melting and correlate the isotopic features to the role of altered oceanic crust along with magnesite in the mantle source. The Wajilitag tephritic porphyry displays trace-element patterns similar to those of the melts from natural hornblendite, especially those of hornblendite + peridotite. Additionally, the geochemical characteristics such as enrichment in Nb and Ta, depletion in K, high TiO2, and constant Na2O/K2O ratios also suggest that the tephritic porphyries were derived from an amphibole-bearing source contributed by altered oceanic crust along with sedimentary carbonates. Our study provides insight into the contribution of subducted materials to the mantle heterogeneity beneath the TLIP and highlights the role of subduction in the deep carbon cycle and subducted slab-lithosphere-plume interaction in the generation of LIPs.

Constraining the duration of the Tarim flood basalts (northwestern China): CA-TIMS zircon U-Pb dating of tuffs

Abstract The Early Permian Tarim large igneous province (LIP) in northwestern China comprises voluminous basaltic lava flows, as well as ultramafic and silicic intrusions. The age and duration of the Tarim LIP remains unclear, and thus the rate of magma production and models of potential environmental effects are uncertain. Here we present high-precision chemical abrasion–isotope dilution–thermal ionization mass spectrometry zircon U-Pb ages for three newly discovered tuff layers interlayered with lava flows in the Kupukuziman and Kaipaizileike formations in the Keping area (Xinjiang, northwest China). The volcanism of the Kupukuziman Formation is constrained to a short duration from 289.77 ± 0.95 to 289.41 ± 0.52 Ma. An age for the overlying Kaipaizileike Formation is 284.27 ± 0.39 Ma, bracketing the duration of the entire eruptive phase of the Tarim flood basalts at ~5.5 m.y. The low eruption rate and relatively long duration of magmatism is consistent with a plume incubation model for the Tarim LIP.

A Thermal Pulse Induced by a Permian Mantle Plume in the Tarim Basin, Northwest China: Constraints From Clumped Isotope Thermometry and In Situ Calcite U‐Pb Dating

AbstractHigh burial temperature and a lack of material for traditional thermal proxies significantly impede the understanding of the thermal history of carbonate stratigraphic sequences in deep time. Carbonate clumped isotope thermometry interpreted through models of solid‐state isotopic reordering and in situ U‐Pb dating provides a new methodology for reconstructing thermal histories of such successions. Calcite fabrics (micrite cements and veins) from deeply buried (5,000–8,000 m) Ordovician carbonate intervals in the Tarim Basin were analyzed for their carbonate clumped isotope compositions and U‐Pb ages, and the results were used to estimate maximum peak burial temperatures. Reconstructed burial temperatures reveal a previously ignored thermal pulse in the range of 160°C–190°C during the Permian period. Maximum geothermal gradients at the time of peak burial temperature varied from 26.8°C/km to 69.3°C/km, with higher values in the northern Tarim Basin. We show that the spatial patterns of peak burial temperature and geothermal gradients closely correspond to the distribution of the Tarim Large Igneous Province, which emplaced during the Permian following the emplacement of a mantle plume beneath the Tarim Basin. We thus propose that the thermal pulse recorded in Tarim Ordovician limestones resulted from Permian mantle plume activity. The reconstructed thermal history has important implications for our understanding of source‐rock hydrocarbon generating history, hydrocarbon accumulation, and fluid flow history in the Tarim Basin. This study also demonstrates the potential of the integration of Δ47, U‐Pb dating of carbonates and solid‐state reordering models as an integrated thermochronological method for reconstructing thermal histories of deeply buried carbonate intervals.

Granitoids of the Kalba batholith, Eastern Kazakhstan: U–Pb zircon age, petrogenesis and tectonic implications

This is a synthesis of published and new data on the Kalba batholith in Eastern Kazakhstan, the large granitic body in the western part of the Central Asian Orogenic Belt. The batholith consists of granodiorite-granite and leucogranite rocks discriminated on the basis of major- and trace-element chemistry and isotope systematics. The granodiorite-granite rocks, which form the bulk of the batholith, are compositionally variable and can be classified as mixed S-I-type granites. The leucogranites occurring as a few large intrusions in the northwestern part of the batholith have more stable compositions, with high contents of REE, HFSE, F, Li, and B, typical of A-granites. Judging by the isotope systematics of the Kalba granites, compared with that of their potential parent rocks from the Kalba-Narym zone and its surroundings, the two groups originated by different mechanisms in two magmatic events. The granodiorite-granites were produced by large-scale melting of crustal material, including the metabasaltic basement and overlying metavolcanic and metasedimentary rocks. The origin of leucogranites was associated with low-degree partial melting of the deepest Kalba-Narym sediments under the effect of fluoride fluids. The batholith formation spanned about 21 myr: granodiorites and granites formed in the 297–286 Ma interval and leucogranites between 288 and 276 Ma. The ages of the two events bracket the intraplate postorogenic stage of the CAOB history that was coeval to the formation of the Tarim large igneous province.

Geochemical and O–C–Sr–Nd Isotopic Constraints on the Petrogenetic Link between Aillikites and Carbonatites in the Tarim Large Igneous Province

Abstract Aillikites are carbonate-rich ultramafic lamprophyres often associated with carbonatites. Despite their common field relationships, the petrogenetic links, if any, between aillikites and carbonatites remain controversial. To address this question, this study reports the results of a detailed geochemical and isotopic examination of the Permian Wajilitag aillikites in the northwestern Tarim large igneous province, including bulk-rock major- and trace-element and Sr–Nd isotope compositions, olivine major- and trace-element and (in situ secondary ion mass spectrometry) oxygen isotope compositions, oxygen isotope data for clinopyroxene separates, and bulk-carbonate C–O isotopic analyses. Olivine in the aillikites occurs in two textural types: (1) microcrysts, 0·3–5 mm; (2) macrocrysts, 0·5–2·5 cm. The microcrysts exhibit well-defined linear correlations between Fo (79–89) and minor and trace elements (e.g. Ni = 1304–3764 μg g–1 and Mn = 1363–3042 μg g–1). In contrast, the olivine macrocrysts show low Fo (79–81), Ni (5·3–442 μg g–1) and Ca (477–1018 μg g–1) and very high Mn (3418–5123 μg g–1) contents, and are displaced from the compositional trend of the microcrysts. The microcrysts are phenocrysts crystallized from the host aillikite magmas. Conversely, the lack of mantle-derived xenoliths in these aillikites suggests that the macrocrysts probably represent cognate crystals (i.e. antecrysts) that formed from earlier, evolved aillikite melts. Olivine phenocrysts in the more primitive aillikite dykes (Dyke 1) have relatively higher Fo (Fo82–89) and mantle-like oxygen isotope values, whereas those in the more evolved dykes (Dykes 2 and 3) exhibit lower Fo (Fo79–86) and oxygen isotope values that trend toward lower than mantle δ18O values. The decreasing δ13C values of carbonate from Dyke 1 to Dykes 2 and 3, coupled with the indistinguishable Sr–Nd isotopes of these dykes, suggest that the low δ18O values of olivine phenocrysts in Dykes 2 and 3 resulted from carbonate melt/fluid exsolution from a common progenitor melt. These lines of evidence combined with the overlapping emplacement ages and Sr–Nd isotope compositions of the aillikites and carbonatites in this area suggest that these exsolved carbonate melts probably contributed to the formation of the Tarim carbonatites, thus supporting a close petrogenetic relationship between aillikites and carbonatites.

Discovery of Permian crustal carbonatite in the northwestern margin of Tarim Basin and its geological significance

碳酸岩是自然界较为特殊的一类火成岩，由于其在上侵过程中不易受到地壳物质的混染，可以很好地保留源区原始特征，因而在揭示岩浆源区属性和地球深部碳循环等方面具有重要的研究价值。塔里木盆地西北缘阿克苏-乌什南部地区发育多条侵位到新元古界南华系中的火成碳酸岩岩墙或岩脉。这些岩脉的锆石U-Pb测年结果显示出多个年龄峰值，其中最年轻一组（3颗）岩浆锆石的谐和加权年龄为272±4Ma，另外还有400Ma、450Ma、790Ma、850Ma等年龄峰，而这些锆石可能均为碳酸岩岩浆捕获成因。结合区域上发育大量早二叠世辉绿岩岩床及岩墙等侵入事件，推测这些碳酸岩很可能形成于早二叠世（~270Ma）。碳酸岩主要由方解石（90%以上）构成，并含少量的白云石、重晶石、天青石、赤铁矿等其它矿物，可见方解石与白云石之间明显的出溶结构以及野外宏观上碳酸岩包裹围岩等现象。元素地球化学分析显示，碳酸岩CaO含量高（44.40%~50.40%），SiO₂含量低（1.83%~7.97%）；稀土元素总量很低（ΣREE=21.67×10^-6~91.32×10^-6），轻重稀土分异明显（LREE/HREE=3.90~8.40），具有中等负铕异常（δEu=0.61~0.68）和中等至弱负铈异常（δCe=0.59~0.98）；大离子亲石元素Sr、Rb、Ba等相对富集，Nb、Ta、Ti等高场强元素相对亏损；稳定同位素δ¹³C_V-PDB值高（-2.69‰~-2.93‰）、δ¹⁸O_V-SMOW值高（17.33‰~17.86‰）。这些特征与壳源碳酸岩特征相似，而与幔源碳酸岩差别较大。Sr-Nd同位素结果显示高的（⁸⁷Sr/⁸⁶Sr）_i值（0.710106~0.710558），低的ε_Nd（t）值（-8.46~-12.80），也进一步证实碳酸岩为地壳来源。综合分析认为这些碳酸岩很可能是塔里木二叠纪大火成岩省晚期岩浆事件的组成部分，系由塔里木西北缘地幔柱减压熔融后形成高温的基性岩浆向上侵位运移时，导致下地壳的碳酸盐储库部分熔融形成碳酸岩岩浆，并沿着断裂快速向上侵位形成。本文研究不仅丰富了塔里木大火成岩省的岩石组成认识，而且有助于增进对二叠纪深部复杂壳幔作用过程的理解。;Igneous carbonatites is a kind of special igneous rock in nature. Because they are not easily contaminated by crustal materials in the process of upwelling, they can well retain the original characteristics of the magma source. Therefore, they have important research value in revealing the properties of the magma source and the carbon cycle of the deep earth. Several carbonatite dikes or dykes are found intruded into the Neoproterozoic Nanhua System in the southern Aksu-Wushi area, the northwestern margin of Tarim Basin. Zircon U-Pb geochronology dating of these carbonatites yield multiple peak ages, including a youngest one at 272±4Ma obtained by three zircons, and other ones at 400Ma, 450Ma, 790Ma, 850Ma, respectively. However, all these zircons were probably captured by carbonate magma. Considering the intrusive events of massive Early Permian diabase sills and dikes in the region, we speculate that these carbonatite dikes were probably formed in the Early Permian (~270Ma). The carbonatites are mainly composed of calcite (over 90%) and a small amount of dolomite, barite, celestite, hematite and other minerals. In addition, the carbonatites have obvious exsolution structures between calcite and dolomite, and the country rock breccias are found wrapped by the carbonatites in the field. The element geochemistry analysis results show that carbonatites have high CaO content (44.40%~50.40%), low SiO₂ content (1.83%~7.97%), extremely low total rare earth elements content (21.67×10^-6~91.32×10^-6) with obvious differentiation of LREE and HREE (LREE/HREE=3.90~8.40) and weak negative Eu and Ce anomalies (δEu=0.61~0.68; δCe=0.59~0.98). And the large ion lithophile elements like Sr, Rb, Ba are relatively enriched, and high field-strength elements such as Nb, Ta, Ti are relatively depleted. The stable isotope of δ¹³C_V-PDB and δ¹⁸O_V-SMOW are high (-2.69~-2.93‰ and 17.33~17.86‰, respectively). All these characteristics are similar to the crustal carbonatite, but quite different from the mantle carbonatite. The Sr-Nd isotopic results of high (⁸⁷Sr/⁸⁶Sr)_i values (0.710106~0.710558) and low ε_Nd(t) values (-8.46~-12.80) also confirm that the Aksu carbonatites are derived from the crust. After comprehensive analysis, we propose that these carbonatites are probably the components of the late magmatic event in the Permian Tarim Large Igneous Province. When the mantle plume in the northwestern margin of Tarim was decompressed, it would form high-temperature basic magma and emplaced upward. These basic magma would heated the carbonate reservoir in the lower crust and partially melted it to form carbonatites magma, which was rapidly emplaced upward along the extension fault. This study not only enriched the petrological compositions of the Permian Tarim Large Igneous Province, but also promoted the understanding of the complex crust-mantle interaction processes in the deep area of Permian Tarim Basin.

Possible Use of Satellite Geomagnetic Observations in Geological and Tectonic Studies of Lithosphere Structure

Features that reflect parameters of the geological and tectonic structure in lithospheric magnetic anomalies obtained using measurements by the CHAMP Earth satellite. A database on full vector module Ta and vertical component Za of the lithosphere’s magnetic field at satellite altitudes is created using a original technology for separating an anomaly magnetic field from measurements made by the CHAMP satellite. The positions of large-scale anomalies over the territories of the eastern Carpathians, the Tarim large igneous province, the Khatanga trap plume and the Kolyma–Omolon microcontinent was determined. Data analysis on the magnetization of the lower crust structures in conjunction with other geophysical means allows us to identify conditions of the origin and evolution of the mantle and the mantle–crust ore-forming systems that result in the formation of large and unique ore deposits. It is shown that quantitative geological information can be derived from magnetic data by clarification of the boundaries position of Precambrian provinces covered by Phanerozoic sediments. As a parameter reflecting the actual positions of structures of the lower crust and their physical properties, the lithospheric magnetic field can be used to distinguish, contour and correct them in addition to other geological and geophysical means.

Ultramafic xenoliths from aillikites in the Tarim large igneous province: Implications for Alaskan-type affinity and role of subduction

The Tarim large igneous province (TLIP) located in northwestern China is characterized by a relatively long duration of magmatism and complex lithology as compared to other global LIPs. Previous studies correlated these features to the interaction between mantle plume and subducted slab. However, no direct subduction-related magmatic records were so far recognized to support this interpretation. Here we report the petrological, mineralogical, and geochemical characteristics of a suite of ultramafic xenoliths occurring within aillikites from the northwestern margin of the TLIP. The xenoliths include dunite, wehrlite, olivine clinopyroxenite, clinopyroxenite, amphibole clinopyroxenite, clinopyroxene hornblendite, and hornblendite. These rocks show broadly similar mineralogy and are mainly composed of olivine, clinopyroxene and amphibole with rare phlogopite, chromite, and magnetite, in the absence of orthopyroxene and plagioclase. We evaluate the petrogenesis of these rocks based on whole-rock major and trace element compositions and mineral chemistry. The rocks exhibit enrichment of large ion lithophile elements (LILEs) relative to high field strength elements (HFSE) with negative Nb, Ta, and Ti anomalies, similar to the features of arc-like lavas. Their (87Sr/86Sr)t (0.7035–0.7041) and εNd(t) (1.17–5.67) values are consistent with depleted mantle source. The Mg# [molar Mg/(Mg + Fe2+)] and Fe3+# [molar Fe3+/(Fe3++Al + Cr)] values of spinel in the ultramafic xenoliths are consistent with those of the Alaskan-type mafic-ultramafic intrusions. The Al2O3 contents in clinopyroxene increase with decreasing Mg#, which is comparable with the Al2O3 variation trend of clinopyroxene in Alaskan-type and arc-related magma, in contrast to those of the LIPs. Our data establish that the ultramafic xenoliths in the aillikites are comparable to Alaskan-type ultramafic complexes, and correspond to magmatism associated with the southward subduction of oceanic plate beneath the Tarim craton during Neoproterozoic or Early Paleozoic. Our study provides direct evidence for the interaction between mantle plume and subducted slab in generating the TLIP.

Olivine from aillikites in the Tarim large igneous province as a window into mantle metasomatism and multi-stage magma evolution

Abstract Aillikites are carbonate-rich ultramafic lamprophyres, and although they are volumetrically minor components of large igneous province (LIP), these rocks provide important clues to melting and meta-somatism in the deep mantle domain during the initial stages of LIPs. In this study, we investigate the Wajilitag “kimberlites” in the northwestern part of the Tarim LIP that we redefine as hypabyssal aillikites based on the following features: (1) micro-phenocrystic clinopyroxene and Ti-rich andradite garnet occurring in abundance in the carbonate-rich matrix; (2) Cr-spinel exhibiting typical Fe-Ti enrichment trend also known as titanomagnetite trend; and (3) olivine showing dominantly low Mg values (Fo < 90). To constrain the magma source and evolution, the major, minor, and trace element abundance in olivine grains from these rocks were analyzed using electron microprobe and laser ablation-inductively coupled plasma-mass spectrometry. Olivine in the aillikites occurs as two textural types: (1) groundmass olivines, as sub-rounded grains in matrix, and (2) macrocrysts, as euhedral-anhedral crystals in nodules. The groundmass olivines show varying Mg (Fo89–80) with high-Ni (1606–3418 ppm) and Mn (1424–2860 ppm) and low-Ca (571–896 ppm) contents. In contrast, the macrocrysts exhibit a restricted Fo range but a wide range in Ni and Mn. The former occurs as phenocrysts, whereas the latter are cognate cumulates that formed from earlier, evolved aillikite melt. The two olivine populations can be further divided into sub-groups, indicating a multi-stage crystallization history of the aillikite melt. The crystallization temperatures of groundmass olivines and macrocrysts in dunite nodules as computed from the spinel-olivine thermometers are 1005–1136 and 906–1041 °C, respectively. The coupled enrichment of Ca and Ti and lack of correlation between Ni and Sc and Co in the olivine grains suggest a carbonate-silicate metasomatized mantle source. Moreover, the high 100·Mn/Fe (average 1.67) at high Ni (up to 3418 ppm), overlapping with OIB olivine, and the 100·Ni/Mg (~1) of primitive Mg-Ni-rich groundmass olivines suggest a mixed source that involved phlogopite- and carbonate-rich metasomatic veins within mantle peridotite.

Hisingerite in Trachydacite from Tarim: Implications for Voluminous Felsic Rocks in Transitional Large Igneous Province

Unlike the typical large igneous provinces (LIPs) that are dominated by mafic-ultramafic rocks, the Tarim large igneous province (TLIP) is characterized by a high proportion of felsic rocks, based on which the TLIP is classified as a transitional LIP. In this study, we focus on the trachydacite from the TLIP in which we report the characteristics of hisingerite employing a variety of techniques such as EMPA, LA-ICPMS, CCD single crystal diffraction, and bulk-rock oxygen isotopes. The hisingerite in this rock is associated with plagioclase, amphibole, apatite and ilmenite. These minerals occur as aggregates of fine curled fibers in micron-scale and display heavy rare earth elements (HREE) enriched signature with significant negative Eu anomalies. In the primitive mantle-normalized trace element spider diagrams, they show pronounced Th and U spikes and Nb, Zr, Hf troughs. Petrological observation and mineralogical study reveal a closely genetic relationship between hisingerite and amphibole, indicating that the hisingerite might have been derived from the breakdown of amphibole during the magma ascent. The formation of hisingerite requires excess water from the surrounding melts, suggesting a hydrous parental magma. The hisingerite and amphibole assign a hydrous crustal source for the rock, and extensive crustal melting accounts for the voluminous felsic rocks in the TLIP.

The Character and Petrogenetic Model of the Permian Tarim Large Igneous Province

AbstractTarim Large Igneous Province (TLIP) is the second Late Paleozoic LIPs in China after the recognition of the Emeishan LIP. The residual distribution range of TLIP is up to 250000 km2, and the largest residual thickness is 780 m. The eruption of basalt happened during 290–288 Ma and belongs to LIPs magmatic event with fast eruption of magma. The lithological units of the TLIP include basalt, diabase, layered intrusive rock, breccia pipe mica‐olivine pyroxenite, olivine pyroxenite, gabbro, ultramafic dyke, quartz syenite, quartz syenite porphyry and bimodal dyke. The basalt and diabase of TLIP exhibit OIB‐like trace element patterns and enrichment of LILE and HFSE, and mainly belong to high TiO2 series. There is an obvious difference in isotope among the basalt from Keping and the basalt and dibase from the northern Tarim Basin. The basalt from Keping with negative Nd and high REE value derives from enriched mantle, and the diabase and basalt from the northern Tarim Basin with positive Nd and low REE value are related to depleted mantle. The crust uplifting in the Early Permian and the development of picrite and large scale dyke and formation of large scale V‐Ti‐magnetite deposit in Wajilitag area support the view that the TLIP is related to mantle plume. The TLIP has a temporal‐spatial relationship with Permian basic‐ultrabasic igneous rock, which is distributed widely in Central Asia, and they represent a tectono‐magmatic event with very important geodynamic setting. This study also systematically demonstrates the two‐stage melting model for the TLIP based on our previous research work and predecessor achievements, and highlights the two types of magmatic rocks within the TLIP. The two‐stage melting model suggests that the formation of the TLIP is mantle plume related. The early hot mantle plume caused the low‐degree partial melting of the lithosphere mantle, while in the later stage, the plume partially melted due to adiabatic uplift and decompression. Therefore, this model carries signatures of both the “Parana” and “Deccan” models in terms of mantle plume activity. During the early stage, the mantle plume provided the heat required for partial melting of sub‐continental lithosphere mantle (SCLM), similar to the “Parana Model”, while later the plume acted as the main avenue for melting, as in the “Deccan Model”. Basalts that erupted in the first stage have higher 87Sr/86Sr, lower 143Nd/144Nd ratios, and are enriched in large ion lithophile elements and high field strength elements, indicating a possible origin from the enriched continental lithosphere mantle, similar to the Parana type geochemical features. The basic‐ultrabasic intrusive rocks in the second stage exhibit lower 87Sr/86Sr, higher 143Nd/144Nd ratios relative to the basalts, consistent with the involvement of a more depleted asthenospheric material, such as a mantle plume, similar to the Deccan type geochemical features. The first stage basalts can be further subdivided into two categories. Developing this petrogenetic model for the TLIP aids in comprehensively understanding its magmatism and deep geological and geodynamic processes. Furthermore, this work enriches the theories describing the origin of large igneous province and mantle plume activity.

Orogenic Volcanism in Eastern Kazakhstan: Composition, Age, and Geodynamic Position

Studies of volcanic rocks in orogenic troughs of Eastern Kazakhstan were carried out. The troughs were formed at late-orogenic stages of evolution of Hercynian Altai collision system. Volcanic rocks are represented by basalts, andesites, dacites and rhyolites. Based on geochemical and isotopic data, the basalts and andesites derived from mafic magmas that formed as a result of partial melting of garnet peridotites in the upper mantle under the orogen. U–Pb zircon data prove two volcanic stages: more-scaled Middle Carboniferous (~311 Ma) and less-scaled Early Permian (297–290 Ma). Basalts and andesites in lower parts of the orogenic troughs and independent dacite-rhyolite structures were formed at the Middle Carboniferous stage. Parental mafic magmas were formed as a result of partial melting of mantle substrates in local transtensional zones along large shear faults. The formation of dacites and rhyolites could have been caused by partial melting of crustal substrates under effect of mafic magmas. Transtensional movements in the lithosphere of orogenic belts may indicate the beginning of collapse of orogens. A smaller volume of basalts and andesites formed at the Early Permian stage. Geochemical data prove the independent episode of partial melting in upper mantle. Synchronous basalts and andesites also appeared at wide territory in Tian Shan, Central Kazakhstan, and Central and Southern Mongolia. Early Permian volcanism indicates general extension of the lithosphere at the postorogenic stages. Large-scaled Early Permian mafic and granitoid magmatism in Central Asia has been interpreted in recent years as the Tarim Large Igneous Province caused by Tarim mantle plume activity. Thus, the extension of the lithosphere and associated volcanism in the Early Permian can be an indicator of the onset of the plume–lithosphere interaction process.

Petrogenesis of Transitional Large Igneous Province: Insights From Bimodal Volcanic Suite in the Tarim Large Igneous Province

AbstractThe Tarim large igneous province (TLIP) corresponds to a transitional large igneous province based on the high proportion of felsic rocks, classifying between mafic and silicic large igneous provinces. Here we investigate a bimodal suite including trachydacite, rhyolite, and basanite from the Northern Tarim Uplift using petrological, geochemical, stable, and radiogenic isotopic techniques with a view to understand the formation of the TLIP. Our study reveals a multistage origin involving multiple components, although the various rock suites are genetically linked and formed under a rift incubation setting related to mantle plume. The low δ26 Mg values (−0.48‰ to −0.71‰), Fe/Mn > 60, FC3MS (FeOT/CaO‐3*MgO/SiO2) > 0.65, and high TiO2 contents (4.45–4.93 wt.%) of basanite from this suite suggest formation through partial melting of carbonated eclogite formed by recycled oceanic crust. The thick lithosphere beneath the Tarim Craton promoted extensive interaction between the underplated basaltic magmas and crust‐derived magmas leading to the formation of multistage magma chambers. Geochemical and mineralogical studies suggest that the trachydacite experienced a mixing, assimilation, storage, and hybridization process, whereas the rhyolite was produced by fractional crystallization from the associated mantle‐derived magma with significant crustal contamination. The abundance of amphibole in the trachydacite suggests a hydrous parental magma with H2O content in the range of 2.75 to 4.05 wt.%. Our results suggest that hydrous crustal components contributed significantly in the formation of voluminous felsic rocks of the TLIP.

Tarim Large Igneous Province Caused by a Wide and Wet Mantle Plume

AbstractLarge igneous provinces (LIPs) can form by interactions between a hot mantle plume and the lithosphere. The Tarim LIP between ~300 and 280 Ma, located in Northwest China, has been investigated by geochemistry and sedimentology studies. However, the factors controlling Tarim LIP formation and the ancient Tarim plume characteristics remain unclear. Here, a series of 3‐D geodynamic models are combined with geological observations to constrain the Tarim LIP evolution and the features of the related Tarim plume. Our results show that (1) an ancient plume produced abundant melts attributed to decompression melting, excess temperature, high water contents, and slow plate motion velocities to form the banded Tarim LIP. (2) The simulated pre‐eruption topography coincides with the stratigraphic records from the late Carboniferous to early Permian. Specifically, the swell area of pre‐eruption topography is sensitive only to the plume radius and enables us to constrain the ancient mantle plume size well. (3) Based on the volcanic activity and pre‐eruption topography, we infer that the ancient Tarim plume had a very large radius of ~200 km, a high excess temperature of ~250 K, and a high water content of ~5 wt.%. (4) Our parameter tests and global plate reconstruction results show that high water contents and slow plate motion velocities facilitate continental flood basalts to form with thick lithosphere. Our geodynamic modeling not only provides new constraints for the Tarim LIP evolution but also first quantificationally demonstrates that water in the mantle plays a key role in continental flood basalt formation.

An Absolute Paleogeographic Positioning of the Early Permian Tarim Large Igneous Province

AbstractThis paper presents a quantitative characterization of the early Permian latitude and longitude of the Tarim block and its relationship to the supercontinent Pangea using a combination of newly acquired paleomagnetic data and inferences drawn from the plume generation zone reconstruction method. Early Permian magmatic rocks from Tarim have previously been interpreted as constituents of a large igneous province (LIP) and were therefore possibly derived from a mantle plume originating at the core‐mantle boundary. Here, we present the results of a paleomagnetic investigation of early Permian rocks (~288 Ma) in the Keping area of northwestern Tarim. A stable high‐temperature component (HTC) was isolated from 413 samples from 51 sites. The directions of this HTC pass the fold test and are of exclusively reversed polarity, which is consistent with their acquisition during the late Carboniferous to mid‐Permian Kiaman Reverse Polarity Superchron, suggesting that the HTC is likely primary. From these results, we compute a new early Permian pole for Tarim: 50.1°N, 170.5°E, A95 = 3.6°. Taking the estimated eruption center of the Tarim LIP (41°N, 80°E) as a reference point, this pole restores the LIP to a paleolatitude of ~30° at 288 Ma. Given this paleolatitude estimate, we attempt to fit the LIP to the edge of one of the large low shear velocity provinces in the lowermost mantle. It is not feasible to reconstruct the Tarim LIP directly above the margins of either the African or Pacific large low shear velocity provinces, but its reconstructed position could potentially be associated with the “Perm” anomaly.

Petrogenesis of the early Permian A-type granites in the Halajun region, southwest Tianshan, western Xinjiang, NW China: implications for geodynamics of Tarim large igneous province

ABSTRACT Formation of a large igneous province, an explosive magmatic event in earth, is intimately related to geodynamic processes. The Tarim large igneous province, a famous representative in China, contains A-type granites. However, the petrogenesis of the A-type granites is debated. Some researchers think that the A-type granites are developed through extensive fractionation of magma derived from partial melting of newly underplated or gabbroic rocks. Others insist that the A-type granites are developed through intensive fractional crystallization of plume-derived mafic magma. Here, we present zircon U–Pb ages and whole-rock geochemical and Sr–Nd isotopic data for the Kezilekezitage, Keziertuo, Tamu, and Halajun II intrusions in northwest Tarim to elucidate their petrogenesis and geodynamic implications. Zircon U–Pb dating yielded crystallization ages of the Kezilekezitage, Keziertuo, and Halajun II intrusions of 275.1 ± 3.1 Ma (MSWD = 1.14), 274.8 ± 1.8 (MSWD = 0.46) and 275.6 ± 0.7 (MSWD = 1.04), respectively. The whole-rock geochemistry of the four intrusions is characterized by REE and HFSE enrichment, Ba, Sr, P, Ti, and Eu depletion, εNd (t) values of – 1.2 to +0.3, two-stage Nd model ages (T2DM) of 1.14–1.02 Ga, and an A1-type granite affinity. Whole-rock zircon geothermometry indicates a high formation temperature of 721–924°C. It is concluded that these A-type granites were generated by partial melting of Neoproterozoic OIB-like rocks, coupled with extensive fractional crystallization and minor crustal contamination. The production of the A-type granites at ca. 275 Ma represented the termination and greatest degree of lithospheric thinning during large igneous province formation.