A mantle plume origin for the Siberian traps: uplift and extension in the West Siberian Basin, Russia

The West Siberian Basin (WSB) records a detailed history of Permo-Triassic rifting, extension and volcanism, followed by Mesozoic and Cenozoic sedimentation in a thermally subsiding basin. Sedimentary deposits of Permian age are absent from much of the basin, suggesting that large areas of the nascent basin were elevated and exposed at that time. Industrial seismic and well log data from the basin have enabled extension and subsidence modelling of parts of the basin. Crustal extension (β) factors are calculated to be in excess of 1.6 in the northern part of the basin across the deep Urengoy graben. 1-D backstripping of the Triassic to Cenozoic sedimentary sequences in this region indicates a period of delayed subsidence during the early Mesozoic. The combination of elevation, rifting and volcanism is consistent with sublithospheric support, such as a hot mantle plume.

This interpretation accords with the geochemical data for basalts from the Siberian Traps and the West Siberian Basin, which are considered to be part of the same large igneous province. Whilst early suites from Noril'sk indicate moderate pressures of melting (mostly within the garnet stability field), later suites (and those from the West Siberian Basin) indicate shallow average depths of melting. The main region of magma production was therefore beneath the relatively thin (ca. 50–100 km) lithosphere of the basin, and not the craton on which the present-day exposure of the Traps occurs. The indicated uplift, widespread occurrence of basalts, and short duration of the volcanic province as a whole are entirely consistent with published models involving a mantle plume. The main argument against the plume model, namely lack of any associated uplift, appears to be untenable.     

亚洲3个大火成岩省(峨眉山、西伯利亚、德干)对比研究

峨眉山(～260Ma)、西伯利亚(～250Ma)和德干(～66Ma)大陆溢流玄武岩是世界上3个重要的大火成岩省。大火成岩省至少具有4个通常被用于识别古地幔柱的标志:(1)先于岩浆作用的地表隆升;(2)与大陆裂谷化和裂解事件相伴;(3)与生物灭绝事件联系密切;(4)地幔柱源玄武岩的化学特征。虽然这3个大火成岩省都是来源于原始地幔柱,但是它们的地球化学特征有本质上的差异,反映其地幔柱曾与不同的上地幔库相互作用。(1)峨眉山和西伯利亚大陆溢流玄武岩的母岩浆,在上升过程中经受了与地球化学上和古老克拉通岩石圈地幔相同的上地幔库(EM1型幔源)的相互作用;(2)而德干大火成岩省没有受到地壳(或岩石圈)混染的原生玄武岩则显示地幔柱和EM2之间的Sr-Nd同位素变化。这种差异有可能制约了3个大火成岩省的成矿潜力。峨眉山和西伯利亚大火成岩省含有世界级岩浆矿床,而德干大火成岩省则不含矿。     

四川宝兴大石包组高钛玄武岩地球化学特征及其岩石成因

分布于龙门山推覆构造带以西、松潘-甘孜地块上的宝兴二叠纪高钛玄武岩具有高的TiO2含量(＞3%)、Ti/Y比值(平均658)和∑REE(平均237μg/g),具有LREE富集的右倾型稀土元素分布模式((La/Yb)N=5.39～13.5),富含大离子亲石元素,不相容元素比值Zr/Nb为9.18～10.1,La/Nb比值为1.19～1.34,Ba/Nb比值为6.11～20.4,8Nd(t)=0.82～2.35,(87Sr/86Sr)i=0.704837～0.706157,具有洋岛玄武岩(OIB)的地球化学特征,形成于板内环境.与典型峨眉山玄武岩对比显示,其岩相学、主元素、微量元素地球化学特征和同位素组成均类似于峨眉山大火成岩省(ELIP)上部的高钛玄武岩系列(HT),表明它们可能同时或在类似的环境下形成.基于上述认识,同时结合最新的年代学研究结果,认为宝兴大石包组高钛玄武岩是峨眉山地幔柱活动的产物,属于峨眉山大火成岩省的一部分.这为峨眉山大火成岩省分布范围从扬子克拉通向西北拓展提供了重要的地球化学证据,为更好地理解该火成岩省事件及其时空分布提供了新的直接资料.     

Evolution of Mesozoic fluvial systems along the SE flank of the West Siberian Basin, Russia

The Mesozoic stratigraphy in the subsurface of the West Siberian Basin contains prolific hydrocarbon accumulations, and thus the depositional environments of marine and marginal marine Jurassic and Cretaceous age sediments are well-established. However, no information is currently available on strata of equivalent age that crop out along the SE basin margin in the Mariinsk–Krasnoyarsk region, despite the potential of these exposures to supply important information on the sediment supply routes into the main basin. Detailed sedimentological analysis of Jurassic–Cretaceous clastic sediments, in conjunction with palaeo-botanical data, reveals five facies associations that reflect deposition in a range of continental environments. These include sediments that were deposited in braided river systems, which were best developed in the Early Jurassic. These early river systems infilled the relics of a topography that was possibly inherited from earlier Triassic rifting. More mature fluvial land systems evolved in the Mid to Late Jurassic. By the Mid Jurassic, well-defined overbank areas had become established, channel abandonment was commonplace, and mudrocks were deposited on floodplains. Coal deposition occurred in mires, which were subject to periodic incursions by crevasse splay processes. Cretaceous sedimentation saw a renewed influx of sand-grade sediment into the region. It is proposed that landscape evolution throughout the Jurassic was driven simply by peneplanation rather than tectonic processes. By contrast, the influx of sandstones in the Cretaceous is tentatively linked to hinterland rejuvenation/ tectonic uplift, possibly coeval with the growth of large deltaic clinoform complexes of the Neocomian in the basin subsurface.     

Permian basaltic rocks in the Tarim basin, NW China: Implications for plume–lithosphere interaction

There are large areas of Permian basaltic rocks in the Tarim basin (PBRT) in northwestern China. Precise Ar–Ar dating of these rocks revealed an eruption age span of 262 to 285 Ma. Most of the PBRT is composed of alkaline basaltic rocks with high TiO₂ (2.43%–4.59%, weight percent), high Fe₂O₃ + FeO (12.63%–17.83%) and P₂O₅ (0.32%–1.38%) contents. Trace elements of these rocks have affinities with oceanic island basalts (OIB), as shown in chondrite normalized rare earth elements (REE) diagrams and primitive mantle normalized incompatible elements diagrams. The rocks show complex Sr–Nd isotopic character based on which they can be subdivided into two distinct groups: group 1 has relatively small initial (t = 280 Ma)⁸⁷Sr/⁸⁶Sr ratio ( 0.7048) and positive εNd(t) (3.42–4.66) values. Group 2 has relatively large initial ⁸⁷Sr/⁸⁶Sr ratio (0.7060–0.7083) and negative εNd(t) (from − 2.79 to − 2.16) values. Lead isotopes are even more complex with variations of (²⁰⁶Pb/²⁰⁴Pb)t, (²⁰⁷Pb/²⁰⁴Pb)t and (²⁰⁸Pb/²⁰⁴Pb)t ranging from 17.9265 to 18.5778, 15.4789 to 15.6067 and 37.2922 to 38.1437, respectively. Moreover, these two groups have different trace elements ratios such as Nb/La, Ba/Nb, Zr/Nb, Nb/Ta and Zr/Hf, implying different magmatic processes. Based on the geochemistry of basaltic rocks and an evaluation of the tectonics, deformation, and the compositions of crust and lithospheric mantle in Tarim, we conclude that these basaltic rocks resulted from plume–lithosphere interaction. Permian mantle plume caused an upwelling of the Tarim lithosphere leading to melting of the asthenospheric mantle by decompression. The magma ascended rapidly to the base of lower crust, where different degrees of assimilation of OIB-like materials and fractionation occurred. Group 1 rocks formed where the upwelling is most pronounced and the assimilation was negligible. In other places, different degrees of assimilation and fractionation account for the geochemical traits of group 2.     

Geology and geochemistry of Pachmarhi dykes and sills,Satpura Gondwana Basin,central India: problems of dyke-sill-flow correlations in the Deccan Traps

Many tholeiitic dyke-sill intrusions of the Late Cretaceous Deccan Traps continental flood basalt province are exposed in the Satpura Gondwana Basin around Pachmarhi, central India. We present field, petrographic, major and trace element, and Sr–Nd–Pb isotope data on these intrusions and identify individual dykes and sills that chemically closely match several stratigraphically defined formations in the southwestern Deccan (Western Ghats). Some of these formations have also been identified more recently in the northern and northeastern Deccan. However, the Pachmarhi intrusions are significantly more evolved (lower Mg numbers and higher TiO₂ contents) than many Deccan basalts, with isotopic signatures generally different from those of the chemically similar lava formations, indicating that most are not feeders to previously characterized flows. They appear to be products of mixing between Deccan basalt magmas and partial melts of Precambrian Indian amphibolites, as proposed previously for several Deccan basalt lavas of the lower Western Ghats stratigraphy. Broad chemical and isotopic similarities of several Pachmarhi intrusions to the northern and northeastern Deccan lavas indicate petrogenetic relationships. Distances these lava flows would have had to cover, if they originated in the Pachmarhi area, range from 150 to 350 km. The Pachmarhi data enlarge the hitherto known chemical and isotopic range of the Deccan flood basalt magmas. This study highlights the problems and ambiguities in dyke-sill-flow correlations even with extensive geochemical fingerprinting.     

Melting of the subcontinental lithospheric mantle by the Emeishan mantle plume; evidence from the basal alkaline basalts in Dongchuan, Yunnan, Southwestern China

The Emeishan continental flood basalt (ECFB) sequence in Dongchuan, SW China comprises a basal tephrite unit overlain by an upper tholeiitic basalt unit. The upper basalts have high TiO₂ contents (3.2–5.2 wt.%), relatively high rare-earth element (REE) concentrations (40 to 60 ppm La, 12.5 to 16.5 ppm Sm, and 3 to 4 ppm Yb), moderate Zr/Nb and Nb/La ratios (9.3–10.2 and 0.6–0.9, respectively) and relatively high _{Nd (t)} values, ranging from − 0.94 to 2.3, and are comparable to the high-Ti ECFB elsewhere. The tephrites have relatively high P₂O₅ (1.3–2.0 wt.%), low REE concentrations (e.g., 17 to 23 ppm La, 4 to 5.3 ppm Sm, and 2 to 3 ppm Yb), high Nb/La (2.0–3.9) ratios, low Zr/Nb ratios (2.3–4.2), and extremely low _{Nd (t)} values (mostly ranging from − 10.6 to − 11.1). The distinct compositional differences between the tephrites and the overlying tholeiitic basalts cannot be explained by either fractional crystallization or crustal contamination of a common parental magma. The tholeiitic basalts formed by partial melting of the Emeishan plume head at a depth where garnet was stable, perhaps > 80 km. We propose that the tephrites were derived from magmas formed when the base of the previously metasomatized, volatile-mineral bearing subcontinental lithospheric mantle was heated by the upwelling mantle plume.     

Origin of early Triassic rift-related alkaline basalts from Southwest China: age,isotope, and trace-element constraints

We report new analytical data regarding major and trace element geochemistry, Sr-Nd isotopic composition, and zircon LA-ICP-MS U-Pb analysis from the Kaiyuan alkaline basalts of Yunnan Province, along the southern margin of the Emeishan Large Igneous Province (ELIP). Zircon U-Pb ages and bulk-rock geochemistry indicate that the mafic lavas erupted at 248 ± 6 Ma with OIB-like trace element and isotope ratios similar to the Emeishan high-Ti basalts. These characters suggest that the Kaiyuan alkaline basalts are the products of the post-ELIP magmatism, involving remelting of the plume head after the main ELIP phase. By analogy with the Neogene Red Sea rift system, the Kaiyuan alkaline basalts may have been caused by a Red Sea-like extension along the southwestern margin of the Yangzte during the Early Triassic, during which the hypothesized rift system experienced plate–boundary forces that vanished quickly in the Late Triassic period.     

峨眉山大火成岩省西部苦橄岩及其共生玄武岩的地球化学：地幔柱头部熔融的证据

丽江地区的苦橄岩位于峨眉山大火成岩省的西部,其与辉斑玄武岩、无斑玄武岩和玄武质火山碎屑岩共生。苦橄岩中的斑晶主要为富镁橄榄石,其F0含量最高达91．6％,CaO含量最高达0．42％,其内含有少量玻璃包裹体,指示了橄榄石是在熔体中结晶形成的。苦橄岩中的铬尖晶石具有高的Cr#值（73-75）。计算的初始岩浆的MgO含量大约为22wt％,初始熔融的温度为1630-1680℃。研究结果表明,玄武质岩石是苦橄质岩浆通过橄榄石和单斜辉石分离结晶形成的。苦橄岩和玄武岩的Nd-Sr-Pb同位素比值差别不大,只落在一个很小的范围内（如εNd（t）=-1．3 to＋4．0）。高的εNd（t）值以及抗蚀变不相容元素的原始地幔标准化图解与洋岛玄武岩相似,并且其重稀土元素特征指示了源区有石榴子石的残余,而且是低部分熔融的产物。同位素比值与抗蚀变不相容元素比值（如Nb／La）的相关性表明,岩浆形成过程中有少量的大陆地壳物质或者相对低εNd（t）组分的大陆岩石圈地幔的混染。因此,总体上,苦橄岩的地球化学特征的研究结果支持了峨眉山大火成岩省是地幔柱头部熔融的成因模型。     

西准噶尔玛依勒地区枕状玄武岩年代学、地球化学及岩石成因

通过对造山带内洋岛玄武岩的时代及地球化学性质研究,不仅可以进行古海山/大洋高原的识别,而且还可以进行古洋盆演化及古构造格局恢复。笔者等最新在西准噶尔玛依勒山北侧识别出一套枕状玄武岩,其与火山碎屑岩、硅质岩共生。枕状玄武岩斜长石微晶普遍发育中空骸晶结构,是在水下熔岩急剧萃冷条件下迅速结晶的产物。通过LA-ICP-MS锆石U-Pb测年,获得枕状玄武岩206Pb/238U加权平均年龄为437.2±2.2Ma,该年龄的获得填补了志留纪碱性玄武岩的空白。岩石地球化学分析结果显示,玛依勒枕状玄武岩为碱性玄武岩系列,岩石具有中等Si O2(44.89%~47.81%),高Ti O2(3.28%~4.12%)及P2O5(0.50%~0.70%),低Mg O(3.49%~6.79%),轻、重稀土元素分异较为明显((La/Yb)N=5.5~7.3),无明显Eu异常(Eu/Eu*=0.96~1.06),相对富集Rb、Th、U,亏损Ba、K、Sr,没有明显Nb、Ta负异常,这些地球化学特征与洋岛玄武岩(OIB)极其相似。微量元素含量及反映源区性质的比值表明,枕状玄武岩来源于富集地幔源区,主要组成为尖晶石和石榴石二辉橄榄岩,并发生了5%±的部分熔融,其形成于大洋板内与地幔柱有关的海山/大洋岛屿环境。结合前人研究,认为西准噶尔乃至古亚洲洋在中古生代洋内俯冲的同时,大洋板内可能存在地幔柱活动。     

峨眉山大火成岩省岩石成因与空间差异性研究——基于全区高Ti玄武岩地球化学数据分析与模拟

高Ti玄武岩成因是峨眉山大火成岩省(ELIP)研究的热点问题.由于高Ti玄武岩地球化学特征在空间上存在差异,其岩石成因尚未达成共识.本文系统收集了峨眉山大火成岩省中高Ti玄武岩地球化学数据以及锆石ID-TIMS U-Pb测年结果,并进行统一处理分析与模拟.研究结果显示,峨眉山大火成岩省形成于约259～258 Ma,高T...     

Modelling of thermochemical plumes and implications for the origin of the Siberian traps

Thermochemical plumes form at the base of the lower mantle as a consequence of heat flow from the outer core and the presence of local chemical doping that decreases the melting temperature. Theoretical and experimental modelling of thermochemical plumes show that the diameter of a plume conduit remains practically constant during plume ascent. However, when the top of a plume reaches a refractory layer, whose melting temperature is higher than the melt temperature in the plume conduit, a mushroom-shaped plume head develops. Main parameters (melt viscosity, ascent time, ascent velocity, temperature differences in the plume conduit, and thermal power) are presented for a thermochemical plume ascending from the core–mantle boundary. In addition, the following relationships are developed: the pressure distribution in the plume conduit during the ascent of a plume, conditions for eruption-conduit formation, the effect of the P–T conditions and controls on the shape and size of a plume top, heat transfer between a thermochemical plume and the lithosphere (when the plume reaches the bottom of a refractory layer in the lithosphere), and eruption volume versus the time interval t₁ between plume formation and eruption. These relationships are used to determine thermal power and time t₁ for the Tunguska syneclise and the Siberian traps as a whole.

The Siberian and other trap provinces are characterized by giant volumes of lavas and sills formed a very short time period. Data permit a model for superplumes with three stages of formation: early (variable picrites and alkali basalts), main (tholeiite plateau basalts), and final (ultrabasic and alkaline lavas and intrusions). These stages reflect the evolution of a superplume from the ascent of one or several independent plumes, through the formation of thick lenses of mantle melts underplating the lithosphere and, finally, intrusion and extrusion of differentiated mantle melts. Synchronous syenite–granite intrusions and bimodal volcanism abundant in the margins of the Siberian traps are the result of melting of the lower crust at depths of 65–70 km under the effect of plume melts.     

塔里木柯坪地区库普库兹曼组玄武岩锆石LA-ICPMS年代学、Hf同位素特征及其意义

塔里木盆地广泛发育有二叠纪玄武岩,产于库普库兹曼组和开派兹雷克组中。本文对库普库兹曼组玄武岩进行锆石LA-ICPMSU-Pb精确定年,并首次进行该区玄武岩锆石的铪(Hf)同位素分析。库普库兹曼组底部玄武岩的锆石LA-ICPMSU-Pb加权平均年龄为291.9±2.2Ma(MSWD=0.30,n=17),说明玄武岩为早二叠世岩浆活动产物,该年龄值指示了塔里木大火成岩省二叠纪基性岩浆活动的下限年龄;库普库兹曼组顶部玄武岩获得了293.9±4.6Ma的锆石年龄,与底部锆石年龄在误差范围内基本一致,指示了库普库兹曼组玄武质岩浆活动的时间较为短暂,291.9±2.2Ma可以代表塔里木盆地二叠纪普库兹曼组玄武岩的成岩时代。库普库兹曼组玄武岩中存在大量继承性或捕获的老年龄锆石,指示玄武岩浆在上升过程中与地壳物质发生了混染作用。锆石原位微量、稀土元素分析显示,库普库兹曼组玄武岩锆石具有典型岩浆结晶的基性岩锆石特征,且没有发生明显的后期改造作用。库普库兹曼组玄武岩锆石εHf(t)同位素值在-4.84～-0.65之间,具富集岩石圈地幔源区特征,指示了塔里木大火成岩省二叠纪基性岩浆岩源于富集岩石圈地幔,其地幔源区性质明显不同于新疆北部准噶尔地区同时代A型花岗岩的地幔源区。     

藏南马扎拉地区玄武岩地球化学特征、成因及其地质意义

西藏东南部特提斯喜马拉雅带东段的遮拉组(J₂z)中出露有大量的玄武岩,其地球化学特征对了解该地区中侏罗世的构造背景具有重要意义。本文在详细的野外工作基础上,对发现于马扎拉地区遮拉组的玄武岩进行了地球化学研究。全岩主量元素及微量元素地球化学特征显示,玄武岩属钙碱性系列,SiO₂含量为47.50%~50.61%,具有高钾(K₂O平均为0.61%)、高钛(TiO₂平均为4.02%)、高磷(P₂O₅平均为0.52%)等特点;轻、重稀土元素分馏较为明显(∑LREE/∑HREE=7.30~7.58),(La/Yb)_N比值平均为7.94,富集大离子亲石元素(LILE)如Ba、Th和高场强元素(HFSE)如Nb、Ta、Zr、Hf,呈现出典型洋岛玄武岩(OIB)的地球化学特性。岩浆源于主要由石榴石橄榄岩组成的富集地幔发生10%左右部分熔融的产物,岩浆上升过程中未受到明显的地壳混染。结合区域地质资料,初步认为马扎拉玄武岩应为被动大陆边缘地幔柱或热点的产物。     

峨眉山大火成岩省东区普安玄武岩系年代学、地球化学及成因研究

广泛分布于中国西南川、滇、黔三省的峨眉山玄武岩是我国最早被国际认可的大火成岩省,受到了国内外学者的广泛关注.前人对大火成岩省西区玄武岩已达成多项共识,而对东区玄武岩的岩石组合、火山活动时限、岩石成因等方面还存在诸多争议.本文以峨眉山大火成岩省东区贵州普安玄武岩系为研究对象,通过解析典型剖面,明确该区玄武岩系岩石类型从底...     

藏南浪卡子地区卡龙辉长岩的时代、成因及其大地构造意义

早白垩世OIB（洋岛玄武岩）型基性岩在特提斯喜马拉雅带广泛分布,但对其形成构造背景的认识仍存在争议。本文基于浪卡子地区东北部卡龙辉长岩的锆石LA-ICP-MS U-Pb年代学、微量元素与同位素地球化学的新证据显示,该基性岩体年龄为136.6±1.4 Ma,形成于早白垩世的早期。地球化学显示出高的TiO₂和Nb含量,低的MgO含量,弱的Nb、Ta正异常,以及轻稀土相对富集而重稀土亏损的特点。这些特征与OIB型基性岩的地球化学特征完全一致。而且卡龙辉长岩具有较低的Sr同位素初始值I_Sr以及较高的ε_Nd（t）值,也与特提斯喜马拉雅带上典型的OIB型基性岩的同位素组成一致。综合分析后认为,卡龙辉长岩应与措美大火成岩省中的OIB型基性岩成因一致,均代表了Kerguelen地幔柱作用下的产物。     

西南天山托云地区白垩纪-早第三纪玄武岩地球化学及其成因机制

托云玄武岩主要分布于托云盆地东侧，按形成时代可分为白垩纪玄武岩和早第三纪玄武岩。白垩纪玄武岩包括早白垩世玄武岩和晚白垩世玄武岩，以碱玄岩和碱性橄榄玄武岩为主，碱性程度高；早第三纪玄武岩包括早第三纪玄武岩及脉岩，以碱性橄榄玄武岩、碱性橄榄辉绿岩为主，碱性程度低。所有岩石稀土元素(REE)、微量元素分布模式相似，REE均为向右陡倾型，富集不相容元素。白垩纪玄武岩的∑REE、Rb、Ba、Th、K、Sr、Nb和Ta等元素富集程度均高于早第三纪玄武岩，相容元素富集程度大体较低。微量元素和同位素特征显示，玄武岩起源于与洋岛玄武岩源区相似的富集地幔源。玄武岩中赋存有交代地幔捕虏体，这表明玄武岩浆可能是交代地幔经不同程度部分熔融的产物。微量元素的特征同时显示，早白垩世玄武岩部分熔融程度较低，早第三纪玄武岩部分熔融程度较高，且在不断的部分熔融过程中，形成的岩浆又有结晶分异作用发生。托云玄武岩形成于大陆板内拉伸环境，在形成过程中经历了较弱的壳幔相互作用。     

鹤壁新生代玄武岩源区及成因: 地球化学和Sr-Nd-Hf同位素证据

大陆碱性玄武岩是研究大陆地幔、软流圈和岩石圈、壳幔相互作用的窗口。鹤壁碱性玄武岩为华北中部新生代玄武岩重要组成部分,其源区和成因对了解新生代期间华北克拉通中部岩石圈地幔改造提供了重要依据。鹤壁新生代玄武岩主要为碱性玄武岩,贫硅(SiO₂=45.0%~47.8%)富镁(MgO=7.3%~8.5%)和全碱(Na₂O+K₂O=4.6%~6.3%),富集轻稀土元素,轻、重稀土元素强烈分馏,无明显Eu异常。富集大离子亲石元素(LILEs)和高场强元素(HFSEs)。在原始地幔标准化蛛网图上,具有明显的Nb、Ta正异常,其中Nb/U=35~48、La/Nb=0.4~0.7、Ba/Nb=3.6~11。 全岩的Sr、Nd、Hf同位素比值分别为⁸⁷Sr/⁸⁶Sr_i=0.7036~0.7044,ε_Nd(t)=+0.4~+5.4, ε_Hf(t)=+5.0~+9.7,显示鹤壁新生代玄武岩具有洋岛玄武岩(OIB)的地球化学特征和同位素组成。岩相学特征和地球化学特征表明鹤壁新生代玄武岩是软流圈地幔(>80km)小程度部分熔融形成的熔体与富集的岩石圈地幔相互作用后的结果,地壳物质混染和结晶分离作用不显著。     

Relative contributions of crust and mantle to the generation of the Tianshan Carboniferous rift-related basic lavas, northwestern China

The Tianshan Carboniferous–Permian rift-related volcanism in northwestern China represents a newly recognized large igneous province extending over at least 1.5 × 10⁶ km². The volcanic successions comprise thick piles of basaltic lavas and subordinate intermediate and silicic lavas and pyroclastics, and are interpreted to result from a mantle plume head with component of ε_Nd(t) ≈ +5, ⁸⁷Sr/⁸⁶Sr(t) ≈ 0.704 and La/Nb ≈ 0.9. On the basis of petrogeochemical data, the Carboniferous basic lavas can be generally incorporated into low-Ti/Y (LT, Ti/Y < 500) magma type that can be further divided into three subtypes: LT1, LT2 and LT3. The chemical evolution of the LT1, LT2 (in central Tianshan) and LT3 (in western Tianshan and Jungar) lavas is controlled by an olivine (ol) + clinopyroxene (cpx) fractionation, but gabbroic fractionation accounts for the chemical variation of the LT3 lavas from eastern Tianshan. Elemental and isotopic data suggest that the chemical variation of Tianshan Carboniferous basic lavas cannot be explained by crystallization from a common parental magma.The Sr–Nd isotopic variation of the crustally contaminated LT3 lavas is related to the nature of lithosphere through which the plume-derived melts have erupted. The involvement of an older (Precambrian) lithosphere led the LT3 lavas in western Tianshan to have lower to negative ε_Nd(t) (−1.2 to +6.1) and variable ⁸⁷Sr/⁸⁶Sr(t) (0.7036–0.7061), whereas the LT3 lavas from eastern Tianshan and Jungar are characterized by high ε_Nd(t) (+4.2 to +9.7) and low ⁸⁷Sr/⁸⁶Sr(t) (0.7035–0.7044), that are related to the contamination of upper crust containing early Paleozoic and Devonian arc-basin volcanic rocks and/or to a pre-Carboniferous subduction enrichment of the lithospheric mantle source region. The observed geochemical variations in the Tianshan data are consistent with an AFC process.The Tianshan Carboniferous rift-related volcanic rocks display a spatial petrogeochemical variation in which predominantly uncontaminated LT1 and less-contaminated LT2 tholeiitic lavas erupted in central Tianshan rift and predominantly the strongly contaminated LT3 tholeiites erupted in the circumjacent regions of the central Tianshan rift. The LT1 and LT2 lavas were generated by a higher degree (10–30%) of partial melting in the garnet stability field of the mantle plume compared to the LT3 lavas. The lower degree (<10%) of partial melting in the spinel–garnet transition zone of the mantle plume, as is characteristic of the LT3 lavas, may be the result of a relatively lower geotherm.