河北阳原新生代玄武岩中橄榄岩捕虏体矿物化学:华北岩石圈地幔演化

橄榄岩及其中矿物的组成, 特别是单斜辉石的微量元素, 可以很好的揭示岩石圈地幔性质.在对河北阳原新生代玄武岩中橄榄岩捕虏体详细岩相学和矿物化学研究基础上, 重点分析了单斜辉石的激光原位微量元素, 讨论了新生代华北内部山带岩石圈地幔特征及其演化机制.阳原地区陆下岩石圈, 除个别样品的部分熔融程度为15%~20%外, 多数样品<5%, 显示该区的地幔演化是不均一的, 并表现为饱满与难熔-过渡型地幔的交叉并存.这种共存现象可以用软流圈物质对古老地幔进行不均匀侵蚀、改造和置换作用来解释.      

华北东部橄榄岩岩石化学特征及其岩石圈地幔演化意义

华北东部古生代以来火山岩中捕虏体橄榄岩和苏鲁早中生代构造侵位橄榄岩的岩石化学结果表明: 古生代金伯利岩侵位时仍然存在的难熔、漂浮克拉通地幔在中、新生代时其大部被新生饱满的岩石圈地幔物质取代置换.在100 Ma前(但不早于178 Ma), 新生软流圈物质就已开始沿古老岩石圈内的地幔薄弱带和岩石圈深断裂带对克拉通地幔进行侵蚀、交代和混合作用, 引起岩石圈大幅减薄.这一减薄存在时间、空间的不均匀性, 但在老第三纪达最大.新第三纪以来, 上涌的软流圈物质由于温度下降回落(岩石圈小幅增厚)并转化为新生岩石圈地幔, 实现地幔置换过程.分析的苏鲁造山带橄榄岩是早中生代构造侵位改造过的古老岩石圈地幔物质.      

华北克拉通中部新生代岩石圈地幔的特征与长期演化:来自地幔橄榄岩捕虏体的岩石学和地球化学制约

岩石圈-软流圈的相互作用可以通过向古老、难熔的岩石圈地幔中输入主量元素饱满的物质、从而将其改造成为主量元素相对饱满的岩石圈.     

长白山新生代玄武岩中橄榄岩包体所揭示的岩石圈地幔特征

长白山地区位于华北克拉通东北部,广泛出露富含地幔橄榄岩包体的新生代玄武岩,为研究岩石圈地幔的性质和演化提供了优越条件。本文对长白山地区天池和龙岗新生代火山岩群中尖晶石相橄榄岩包体进行了岩石学、全岩主微量元素、矿物主量元素、单斜辉石微量元素和Sr-Nd-Hf同位素分析。研究结果表明,尖晶石相橄榄岩包体由二辉橄榄岩和少量的方辉橄榄岩组成,Mg#值为87.4~91.2,表现出新生饱满的特征,平衡温度为900~1100℃。橄榄石的Mg#值（% Fo）为85.6~91.3。单斜辉石包括四种类型：（1）轻稀土元素严重亏损型;（2）轻稀土元素亏损型;（3）向右微倾型和（4）"勺型"。单斜辉石表现出Sr同位素（87Sr/86Sr=0.702749~0.707276）整体亏损,部分样品富集的特征,单斜辉石的Nd-Hf同位素呈现出亏损特征（143Nd/144Nd=0.512886~0.51333、εHf=+17.7~+49.8）。长白山地区二辉和方辉橄榄岩分别经历了小于10%和略大于10%的部分熔融作用,并受到富水硅酸盐熔体的地幔交代作用。太平洋板块向西俯冲作用使得软流圈上涌并携带大量壳源物质进入地幔深部,与岩石圈地幔发生橄榄岩-熔体反应,形成了长白山地区不均一的岩石圈地幔,以新增生饱满地幔为主,夹有少量古老难熔岩石圈地幔碎片。     

华北克拉通西北部显生宙岩石圈地幔属性与演化特征: 橄榄岩捕虏体证据

众所周知,华北克拉通东部岩石圈地幔的组成和性质在显生宙发生了显著变化,但由于西部出露含有捕虏体的火山岩较少,这在一定程度上限制了人们对该区岩石圈地幔属性与演化特征的认识。本文将华北克拉通西北部晚白垩世-新生代玄武岩中橄榄岩捕虏体的研究成果归纳总结,旨在进一步揭示该区岩石圈地幔的属性与演化特征。研究表明,华北克拉通西北部岩石圈地幔主要由低Mg^#的二辉橄榄岩和少量高Mg^#的方辉橄榄岩组成。高Mg^#橄榄岩代表该区受轻微再富集作用影响的古老岩石圈地幔残余,低Mg^#橄榄岩是软流圈来源熔体与高Mg^#橄榄岩反应的产物,代表地幔再富集作用对古老岩石圈地幔改造的结果。该区岩石圈地幔经历了多期地幔交代作用的改造,早期交代事件与古亚洲洋俯冲有关,近期与软流圈来源的玄武质熔体有关。这种广泛的地幔再富集作用对华北克拉通古老岩石圈地幔的转变做出了重要贡献。

     

华北地台东部古生代与新生代岩石圈地幔特征及其演化

古生代含金刚石及捕虏体的金伯利岩和新生代含捕虏体的玄武岩先后共同侵位于华北地台东部,提供了研究自古生代以来板内岩石圈地幔特征及其演化的深源岩石探针。通过对古生代与新生代,新生代时郯庐断裂带内与带外岩石圈地幔物质之间岩相学,岩石和矿物的主元素,微量元素,地幔热状态的对比研究,结合现代地球物理资料,建立了以新生地幔物质对古老岩石圈置换作用为主的华北地台东部地幔减薄模型。该模型强调,古老岩石圈地幔业已成     

中国东部岩石圈地幔的演化——地幔岩捕虏体微量元素的证据

对中国东部赋存于新生代玄武岩中的地幔岩捕虏体的全岩和单斜辉石等作了主元素和微量元素分析，证实了二辉橄榄岩及其单斜辉石在主元素有连续变化的趋势，反映了具部分熔融后残留相的性质。方辉橄榄岩及其中的单斜辉石的主元素，Ｎｄ／Ｙｂ，Ｔｉ／Ｚｒ和Ｓｒ／Ｚｒ值与二辉橄榄岩的同类矿物是不连续过渡。     

宽甸橄榄岩包体微区地球化学特征及其岩石圈地幔演化

华北克拉通东部宽甸新生代碱性玄武岩中携带的地幔橄榄岩包体为我们认识该地区岩石圈地幔性质和演化过程提供了约束。根据橄榄石的Mg^#可将宽甸橄榄岩包体分成两类: 第1类为低Mg^#二辉橄榄岩包体(橄榄石Mg^#相对较低: 89.8～90.3),其单斜辉石具有高TiO₂(0.38%～0.57%)、Al₂O₃(4.41%～6.87%)、FeO_T(2.46%～3.73%)、MnO(0.08%～0.11%)含量和低Cr^#(7.42～14.2)的特征,它们所经历的部分熔融程度较低,这些特征类似于中国东部晚白垩世和新生代玄武岩中低Mg^#橄榄岩,代表了新生饱满的岩石圈地幔;第2类为高Mg^#方辉橄榄岩包体(橄榄石Mg^#相对较高:91.0～92.3),其单斜辉石具有低TiO₂(0.03%～0.33%)、Al₂O₃(2.27%～5.49%)、FeO_T(2.04%～2.40%)、MnO(0.07%～0.08%)含量和高Cr^#(15.3～25.8)的特征,它们经历了较高程度的部分熔融作用,其难熔的地球化学特征完全不同于低Mg^#二辉橄榄岩,却与克拉通内部太古宙和元古宙地幔包体类似,代表了古老难熔岩石圈地幔的残留。两类橄榄岩包体的平衡温度没有显著差异说明宽甸岩石圈地幔不存在明显的分层现象,而是新老岩石圈地幔混杂出现。宽甸橄榄岩包体的微量元素特征表明了它们受到过多期复杂的地幔交代作用,交代介质类型不仅有硅酸盐熔/流体还有碳酸盐熔体,其来源既有太平洋板块俯冲释放的熔/流体,又有因受太平洋板块俯冲扰动而上涌的软流圈熔体,因此太平洋板块俯冲可能对华北克拉通的破坏起到了重要作用。     

辽西中生代晚期岩石圈地幔的性质:来自玄武岩和地幔捕虏体的证据

辽西中生代玄武岩中幔源气榄岩捕虏体的岩石学、矿物学和地球化学研究表明，中生代岩石圈地幔是由古老富集型的岩石圈地幔和新增生的岩石圈地幔所组成。前者以角闪尖晶二辉橄榄岩为代表，它经历了富钠质的地幔交代作用。橄榄岩类捕虏体富含轻稀土元素，并具有较高的ω(^87Sr)/ω(^86Sr)比值；后者以二辉石岩为代表，具典型堆积结构，与本区尖晶石二辉橄榄岩相比，具有较高的稀土元素丰度。在矿物成分和稀土元素丰度上，本区辉石岩捕虏体类似于中国东部新生代玄武岩中幔源辉石岩捕虏体，这意味着辉石岩捕虏体可能是上地幔中更早期的岩浆堆积体。     

吉林东部汪清新生代玄武岩中地幔包体的矿物化学：对该地区岩石圈地幔形成过程的启示

在对吉林汪清新生代玄武岩中橄榄岩包体进行全岩主、微量元素分析的基础上,重点分析了矿物的主、微量元素含量,讨论了华北克拉通东北缘与兴蒙造山带结合部位陆下岩石圈地幔所经历的部分熔融作用和地幔交代作用。橄榄石的Fo、单斜辉石以及尖晶石的Mg#和Cr#均表明该地区陆下岩石圈地幔相对饱满。对地幔橄榄岩透辉石微量元素模拟计算证实,汪清陆下岩石圈地幔经历了1%~3%的部分熔融作用,并遭受后期硅酸盐熔体交代作用。这些地幔特征与中国东部其他地区新生代主体岩石圈相似。研究结果证明,吉林汪清中、新生代以来岩石圈性质的转变是在汇聚板块构造体制下通过“拆沉作用”实现的。     

内蒙古集宁新生代玄武岩中橄榄岩包体矿物化学特征及其地幔演化意义

在无水"干"体系的四矿物相橄榄岩中,单斜辉石由于熔点低而通常记录着丰富的部分熔融作用和地幔交代作用信息。在详细岩相学特征和组成矿物主元素分析基础上,重点对内蒙古集宁玄武岩中橄榄岩包体的单斜辉石进行了激光原位微量元素研究。通过与新生代时华北具古老克拉通地幔特征(如鹤壁)和具新生岩石圈地幔特征(如山旺)的橄榄岩对比,讨论了新生代时集宁地区陆下岩石圈地幔性质及其形成和演化机制。集宁地区岩石圈地幔是相当于原始地幔经过较低程度的部分熔融抽取形成的,除个别样品的部分熔融程度5%外,多数样品为5%～10%。橄榄岩的平衡温度与橄榄石Mg#关系表明新生代时集宁地区的陆下岩石圈地幔是不均一的,无明显分层现象,表现为饱满与过渡型地幔的共存。这种主体饱满并兼有过渡型地幔的不均一现象,可能是软流圈物质对古老地幔进行不均匀侵蚀、改造和置换作用的结果。     

华北中、新生代岩石圈地幔的交代作用：含金云母地幔岩提供的证据

本文对华北克拉通三个不同地区（河北汉诺坝、内蒙古集宁三义堂、河南鹤壁）新发现的含金云母尖晶石二辉橄榄岩和尖晶石橄榄单斜辉石岩捕虏体进行了详细的矿物组成、单斜辉石的微量元素和Sr-Nd同位素研究.通过与相同地区不含金云母尖晶石二辉橄榄岩捕虏体的系统对比发现通常含金云母的地幔橄榄岩比不含金云母的地幔橄榄岩岩富Al2O3、CaO、NaO、K2O、TiO2,但相对贫镁;其单斜辉石的LREE更为富集,但Sr、Nd同位素组成则相对亏损.这说明地幔交代作用不仅能够造成地幔橄榄岩的玄武质组分和稀土元素的富集,而且亦能够造成全岩和橄榄石Mg#的降低和同位素组成的相对亏损.捕虏体的Rb-Sr等时线年龄暗示地幔交代作用发生在中、新生代;其交代熔体来源于软流圈.同时说明华北新生代岩石圈地幔普遍存在的主、微量元素和同位素组成类似于“大洋型”岩石圈地幔的特征很可能是岩石圈地幔橄榄岩与软流圈来源的熔体的大规模反应的结果,而非真正意义上的新增生的岩石圈地幔.     

Refertilization of ancient lithospheric mantle beneath the central North China Craton: Evidence from petrology and geochemistry of peridotite xenoliths

The petrology and geochemistry of peridotite xenoliths in the Cenozoic basalts from Fanshi, the central North China Craton (NCC), provide constraints on the evolution of sub-continental lithospheric mantle. These peridotite xenoliths are mainly spinel-facies lherzolites with minor harzburgites. The lherzolites are characterized by low forsterite contents in olivines (Fo < 91) and light rare earth element (LREE) enrichments in clinopyroxenes. In contrast, the harzburgites are typified by high-Fo olivines (> 91), high-Cr# spinels and clinopyroxenes with low abundances of heavy REE (HREE). These features are similar to those from old refractory lithospheric mantle around the world, and thus interpreted to be relics of old lithospheric mantle. The old lithospheric mantle has been chemically modified by the influx of melts, as evidenced by the Sr–Nd isotopic compositions of clinopyroxenes and relatively lower Fo contents than typical Archean lithospheric mantle (Fo > 92.5). The Sr–Nd isotopic compositions of harzburgites are close to EM1-type mantle, and of the lherzolites are similar to bulk silicate earth. The latter could be the result of recent modification of old harzburgites by asthenospheric melt, which is strengthened by fertile compositions of minerals in the lherzolites. Therefore, the isotopic and chemical heterogeneities of the Fanshi peridotite xenoliths reflect the refertilization of ancient refractory lithospheric mantle by massive addition of asthenospheric melts. This may be an important mechanism for the lithospheric evolution beneath the Central NCC.     

华北东部中、新生代岩石圈地幔的不均一性：来自橄榄石的组成填图结果

华北中、新生代玄武质火山岩和基性脉岩携带的地慢橄榄岩捕虏体中橄榄石和／或橄榄石捕虏晶系统的组成填图显示华北东部中、新生代岩石圈地幔存在明显的时空分布规律和不均一性。这与通过岩石圈地幔源基性岩石的地球化学反演获得的华北中生代岩石圈地幔的时空不均一性及其块体特征完全一致。太行山和鲁皖地区新生代岩石圈地慢的差异演化主要反映古老地幔橄榄岩与熔体相互作用时熔体性质和来源的不同。同时,橄榄石Fo填图还揭示了郯庐断裂对华北东部中、新生代基性岩浆活动及其岩石圈地幔演化的重要制约作用。而且,华北东部中生代岩石圈减薄后尚存古老岩石圈地幔残留。因此,华北东部岩石圈减薄的整体拆沉模式很难成立。     

Petrochemistry of peridotites from North China: Significance for lithospheric mantle evolution

A petrochemical analysis was undertaken of peridotitic xenoliths in volcanic rocks that erupted from the Paleozoic to the Cenozoic within the eastern part of the North China craton, and the peridotites as tectonic intrusion in the Early Mesozoic from the Sulu orogen. The results show that the cratonic mantle, which was refractory and existed when the kimberlites intruded in the Paleozoic, had almost been replaced by the newly accreted fertile lithospheric mantle during the Mesozoic-Cenozoic. The erosion, metasomatism, and intermingling caused by the accreted asthenospheric material acting on the craton mantle along the weak zone and deep fault (such as the Tanlu fault) in the existing lithosphere resulted in the lithospheric thinning at a larger scale 100 Ma ago (but later than 178 Ma). The largest thinning would be in the Eogene. The upwelling asthenospheric material transformed into accreted lithospheric mantle due to the asthenospheric temperature falling in the Neogene (leading to relatively slight lithospheric incrassation), and finally accomplished mantle replacement. The peridotitic body in the Sulu orogen represents the products spreading from the modified cratonic lithospheric mantle. Translated from Earth Science—Journal of China University of Geosciences, 2006, 31(1): 49–56 [译自: 地球科学—中国地质大学学报]     

华北克拉通西部陆块北缘新生代岩石圈地幔特征的初步研究

凉城、四子王旗、三义堂和大同的地幔包体的岩石学和矿物的主、微量元素成分显示华北克拉通中、西部北缘总体为过渡型岩石圈地幔,为原始地幔经过不同程度的熔体抽取和后期交代富集作用的残留.凉城岩石圈地幔经历的熔体抽取程度最低,后期交代富集作用比较强烈,这与其橄榄岩中尖晶石的Cr#较低,并且共存的单斜辉石的Mg#较低一致.三义堂岩石圈地幔经历的熔体抽取程度最高,后期交代富集作用最强烈,不同样品甚至同一样品中不同单斜辉石颗粒的La/Yb和LREE配分模式变化范围非常大,且矿物边部比核部更富集微量元素.大同、四子王旗岩石圈地幔经历的熔体抽取程度介于凉城和三义堂之间,但后期的交代富集作用明显不如凉城和三义堂强烈.研究区的岩石圈地幔主要受硅酸盐熔体交代作用的影响,只有三义堂岩石圈地幔还可能也受到了碳酸盐交代作用的影响.     

Ultra-depleted peridotite xenoliths in the Northern Taihang Mountains: Implications for the nature of the lithospheric mantle beneath the North China Craton

We report the finding of peridotite xenoliths in the Early Cretaceous Longmengou olivine-bearing diabase (138 Ma) in the Northern Taihang Mountains in the central North China Craton. Based on the modal proportions of olivine, clinopyroxene, amphibole and anorthite, these peridotite xenoliths can be divided into three zones: clinopyroxene-bearing olivine zone (COZ), olivine-clinopyroxene zone (OCZ), and amphibole-bearing anorthite-clinopyroxene zone (AACZ). The core of olivine grains in clinopyroxene-bearing olivine zone have higher Mg^# (> 95), SiO₂ (41.80–42.53 wt%) and lower CaO (< 0.07 wt%), FeO (3.91–4.54 wt%) than the rim (Mg^# = 92.5–93.4, SiO₂ = 41.27–41.98 wt%, CaO = 0.20–0.34 wt%, and FeO = 7.02–8.87 wt%), suggesting that rim is reaction product. The core of olivine grains with higher Mg^# (> 95) and lower NiO content (< 0.04 wt%) in the clinopyroxene-bearing olivine zone was derived from ultra-depleted mantle subsequently altered by high Mg^# melts/magma with low Ni. Two generations of olivine grains occur in the OCZ where the first generation shows exsolution of ilmenite and magnetite rods containing up to 0.35 wt% TiO₂, and was likely derived from garnet peridotite hydrated by water. The second generation shows high Mg^# (96.2–97.1) and cataclastic texture, and was possibly formed by decomposition of the COZ. The occurrence of aluminous spinel suggests the role of melts with extremely high Al and Mg. Clinopyroxene in the AACZ shows systematic core-rim compositional variation with CaO and SiO₂ contents increasing towards the rim, and MgO and Fe₂O₃ concentrations decreasing from the core to the rim, indicating that the amphibole-bearing anorthite-clinopyroxene zone is a product of the reaction between mantle xenoliths and mafic magma. Plagioclase with high An value (92.0–99.95, average 97.79) indicates that the metasomatic melts have high Ca/Na and Al/Si ratios, possibly produced by the partial melting of ultra-depleted mantle under “wet” conditions. Combined with the data on other mantle xenoliths discovered in the NCC, our results suggest that the Mesozoic lithospheric mantle beneath the North Taihang Mountains within the central NCC is composed of ultra-depleted Archean and Paleoproterozoic peridotites and dunites modified by complex melts. We also propose that the destruction of eastern part of the NCC mainly occurred during Early Cretaceous, and that the boundary of the lithospheric destruction coincides with the Taihang Mountains.     

Lithospheric mantle beneath the south-eastern Siberian craton: petrology of peridotite xenoliths in basalts from the Tokinsky Stanovik

We provide petrographic, major and trace element data for over 30 spinel peridotite xenoliths from the Tokinsky Stanovik (Tok) volcanic field on the Aldan shield to characterize the lithospheric mantle beneath the south-eastern margin of the Siberian craton, which formed in the Mesoproterozoic. High equilibration temperatures (870–1,010°C) of the xenoliths and the absence of garnet-bearing peridotites indicate a much thinner lithosphere than in the central craton. Most common among the xenoliths are clinopyroxene-poor lherzolites and harzburgites with Al₂O₃ and CaO contents nearly as low as in refractory xenoliths from kimberlite pipes (Mir, Udachnaya) in the central and northern Siberian craton. By contrast, the Tok peridotites have higher FeO, lower Mg-numbers and lower modal orthopyroxene and are apparently formed by shallow partial melting (3 GPa). Nearly all Tok xenoliths yield petrographic and chemical evidence for metasomatism: accessory phlogopite, amphibole, phosphates, feldspar and Ti-rich oxides, very high Na₂O (2–3.1%) in clinopyroxene, LREE enrichments in whole-rocks.Electronic Supplementary Material Supplementary material is available for this article at