黑龙江省东部饶河杂岩的就位时代与东北东部中生代构造演化

黑龙江省东部饶河杂岩由含放射虫深海沉积岩以及镁铁质的熔岩和侵入岩组成,并被视为大洋壳的残片。该杂岩被晚期蛤蚂河和太平村花岗岩侵入。锆石U-Pb年龄结果表明,上述两花岗岩岩体均形成于早白垩世,其中蛤蚂河岩体形成于131、124和～115Ma三个阶段,太平村岩体形成于111～114Ma左右。饶河杂岩中辉长岩的锆石U-Pb年龄为166±1Ma,深海沉积岩中最晚出现的放射虫的时代为160～150Ma,显示饶河杂岩的就位应发生在150～131Ma的晚侏罗世—早白垩世,古地磁资料显示本区自晚三叠世—侏罗纪有明显的从低纬度向高纬度的北移现象：从而表明在晚侏罗世—早白垩世及以前该区存在太平洋板块的俯冲-走滑作用。岩石学研究显示,两花岗岩岩体中均存在岩浆结晶成因的堇青石,并具有过铝质花岗岩的特点,为典型的来源于沉积岩部分熔融形成的S型花岗岩。Hf同位素测定发现,这些花岗岩中的锆石具有较高的~(176) Hf/~(177)Hf同位素比值和较正的ε_(Hf)(t)值,以长英质地壳为源岩的Hf同位素模式年龄为500～780Ma,说明其源岩应为新元古代—显生宙新增生的地壳物质,从而反映在晚侏罗世—早白垩世以前本区曾发生过显著的地壳抬升与风化剥蚀。     

Geochemical Charactristics and Genesis of Topaz—Bearing Porphyries in Yangbin Area of Taishun County,Zhejiang Province

The host rocks of the porphyry tin deposits in the Yangbin area are principally topaz-bearing porphyry dikes about 2 km long and 2–20m wide. Three lithologie types are identified for the dikes: topaz-bearing potassium feldspar granitic porphyry, topaz-bearing monzonitic granitic porphyry and topaz-bearing quartz porphyry. The content of topaz in the rocks ranges from 10 to 20 vol.%. Porphyritic texture is characteristic, with quartz, potassium feldspar and albite as main phenocryst minerals. The phenocryst occupies 10–20 vol% of the rocks. The rock groundmass consists of subhedral topaz, quartz and protolithionite. Topaz has a unit-cell parameter b=8.797 (Å), and F:OH=1.92:0.18, indicating a F-rich variety formed at high temperature. The topaz-bearing porphyries occurring in this area are strongly peraluminous (A/NKC=1.574–12.94), with high ratios of F/Cl (146–303) and Rb/Sr (5–122). They are rich in incompatible elements (Sn, 313 × 10^?6–1042 × 10^?6; W, 6 × 10^?6–218 × 10^?6; Nb, 27 × 10^?6–54 × 10^?6), but poor in compatible elements (Sr, 10 × 10^?6–28 × 10^?6; Ba, 58 × 10^?6–73 × 10^?6; V, 3 × 10^?6–12 × 10^?6, Cl, 150 × 10^?6–226 × 10^?6). The rocks are also characterized by high total REE amount (281.69 × 10^?6–319.76 × 10^?6), with strong Eu depletion (δEu=0.01–0.03) and low ratio of LREE/HREE (0.78–0.84). In summary, the authors propose an idea of S-type genesis for the topaz-bearing porphyries with tin mineralization, instead of I-type.     

Pan-African Magmatism, and Sedimentation in the NW Himalaya

Correlation of early Palaeozoic, Pan-African (500 ± 50 Ma) granites that intruded the Chail, Salkhala, Haimanta Formations in the Lesser Himalaya, Zanskar crystallines, and Lower Taglang La of Tso-Morari crystallines in the northwestern Himalaya, is based on the field relationship, tectonic setting, mineralogical, and geochemical characteristics, and isotope dating of the granites. These granite plutons exhibit identical petrographical, and geochemical character. The mineralogical composition of the granites is quite similar, consisting of quartz, K-feldspar, plagioclase feldspar, biotite, muscovite, garnet, tourmaline, ± cordierite, andalusite, and sillimanite fibrolite. The granite which are massive, and inequigranular in the core of the plutons, show strongly foliated character indicating development of ductile shear zone at the margins. These are peraluminous S-type granites having high A/CNK value (> 1). Presence of normative corundum, rounded shape of zircon, and high initial Sr ratio suggest crustal source of the granites. Mantle normalized spider-diagram exhibits similar characters for all these granitoids. The intrusion of the Pan-African granites mark an abrupt end of the sedimentation that continued virtually uninterrupted from Palaeoproterozoic. The sudden break in sedimentation towards the terminal phases of the Lower Cambrian has been observed in almost all parts in Lesser as well as the Tethys Himalaya. Occurrences of large number of plutons along different tectonic belts of northwestern Himalaya are indicative of widespread tectono-thermal event during early Palaeozoic (500 ± 50 Ma). The bracketing of the two features like, the break in sedimentation during post-Late Cambrian, and the intrusion of granites around 500 ± 50 Ma, is considered to be the result of a strong diastrophic orogenic event correlatable to the late phases of the Pan-African Orogeny in Africa.     

Petrology, geochemistry and zircon age for redwitzite at Abertamy, NW Bohemian Massif (Czech Republic): tracing the mantle component in Late Variscan intrusions

A small body of mafic texturally and compositionally varied igneous intrusive rocks corresponding to redwitzites occurs at Abertamy in the Western pluton of the Krušné hory/Erzgebirge granite batholith (Czech Republic). It is enclosed by porphyritic biotite granite of the older intrusive suite in the southern contact zone of the Nejdek-Eibenstock granite massif. We examined the petrology and geochemistry of the rocks and compared the data with those on redwitzites described from NE Bavaria and Western Bohemia.The redwitzites from Abertamy are coarse- to medium-grained rocks with massive textures and abundant up to 2 cm large randomly oriented biotite phenocrysts overgrowing the groundmass. They are high in MgO, Cr and Ni but have lower Rb and Li contents than the redwitzites in NE Bavaria. Compositional linear trends from redwitzites to granites at Abertamy indicate crystal fractionation and magma mixing in a magma chamber as possible mechanisms of magma differentiation. Plots of MgO versus SiO₂, TiO₂, Al₂O₃, FeO, CaO, Na₂O, and K₂O indicate mainly plagioclase and orthopyroxene fractionation as viable mechanisms for in situ differentiation of the redwitzites.The porphyritic biotite monzogranite enclosing the redwitzite is the typical member of the early granitic suite (Older Intrusive Complex, OIC ) with strongly developed transitional I/S-type features. The ages of zircons obtained by the single zircon Pb-evaporation method suggest that the redwitzites and granites at Abertamy originated during the same magmatic period of the Variscan plutonism at about 322 Ma.The granitic melts have been so far mainly interpreted to be formed by heat supply from a thickened crust or decompression melting accompanying exhumation and uplift of overthickened crust in the Krušné hory/Erzgebirge due to a previous collisional event at ca. 340 Ma. The presence of mafic bodies in the Western pluton of the Krušné hory/Erzgebirge batholith confirms a more significant role of mantle-derived mafic magmas in heating of the sources of granitic melts than previously considered.     

赣东北朱溪矿集区构造控岩-控矿特征

赣东北朱溪为钦杭成矿带新发现的重要钨铜多金属矿集区,位于钦杭结合带萍（乡）乐（平）坳陷带东部逆冲推覆抬升地段。朱溪矿集区燕山期受逆冲推覆构造影响,形成由新元古界变质基底与上古生界-中生界沉积盖层组成的构造岩片堆叠构造;具有逆冲推覆深断裂带控岩-控矿、碳酸盐岩构造岩片赋矿、燕山晚期浅层对冲构造破矿的构造背景;发育有燕山早期I型花岗闪长（斑）岩钼铜和S型花岗岩钨铜两个岩浆岩成矿系列,在空间上形成张家坞—月形与塔前—朱溪两个矿田、张家坞—毛家园和塔前—朱溪上下两个成岩台阶,下成矿台阶朱溪巨大钨铜矿床的发现打开了钦杭成矿带坳陷区“深地”找矿的一扇窗户。     

中亚造山带东段古元古代结晶基底:来自中蒙边境花岗岩和沉积地层的证据

中亚造山带东段多个地块内鲜有古老结晶基底物质报道,严重制约了我们对其早期属性的认识。本研究在内蒙古北部与蒙古国接壤的乌力吉特敖包地区,发现了被中下泥盆统泥鳅河组不整合覆盖的古元古代细粒二长花岗岩和沉积地层(乌兰敖包组)。对二长花岗岩开展的LA-ICM-MS锆石U-Pb定年显示其结晶年龄为(1686±10) Ma,说明形成于古元古代。乌力吉特敖包二长花岗岩高钾钙碱性,过铝质(A/CNK=1.08～1.11),且含有大量白云母,属S-型花岗岩。不同于常见的显生宙以来的S-型花岗岩,乌力吉特敖包古元古代花岗岩具有正的εHf(t)值(+2.9～+6.7),但εHf(t)值远低于1.7 Ga地壳演化趋势线,且锆石原位Hf同位素二阶段模式年龄为2.0～2.3 Ga,因此其应该来源于古老变泥质岩部分熔融。乌力吉特敖包古元古代花岗岩形成于陆陆同碰撞的构造环境。在古元古代乌兰敖包组变质泥岩获得了一个显著的碎屑锆石峰值年龄(1698 Ma),且该地层被元古宙花岗岩侵入。本研究发现的乌力吉特敖包古元古代末期花岗岩和乌兰敖包组沉积地层说明:中亚造山带东缘各地块内存在古老的结晶基底物质。这为我们认识这些地块早期演化历史提供了重要地质证据。     

赣南大埠加里东期花岗岩岩石地球化学特征及其成因

大埠加里东期花岗岩富硅(SiO2平均含量为74.68%)、富钾(K2O/Na2O平均值为1.53),属髙钾钙碱性过铝质花岗岩(A/CNK=1.00~1.22,平均值1.10);稀土总量较低(平均值为145.98×10-6),配分模式为轻稀土相对富集的右倾型,轻稀土分异较明显,重稀土无明显分异,具强烈的铕负异常(δEu平均值为0.24);以相对富集大离子元素Rb、Th、U、Zr、Hf和稀土元素Ce、Nd、Sm、Y,明显亏损Ba、Sr、P、Ti为特征。研究表明:大埠加里东期花岗岩为上地壳以泥质岩为主、含少量砂质组分的物源区在后碰撞伸展构造环境下经部分熔融而形成的S型花岗质岩浆,在伸展构造体制下上升侵位而成。     

河北省S型与I型花岗岩体上的航磁异常特征及找矿作用

S型与I型花岗岩体在河北省境内广泛分布,前者含矿性不好,后者与成矿关系密切,普遍矿化。通过分析河北省高精度航磁资料,总结对比了S型与I型花岗岩体的航磁异常特征,并分析了它们磁性差异的原因,以便于在航磁资料的研究中圈定这两类花岗质岩体,区分矿与非矿异常,间接圈定找矿靶区。     

麻粒岩相变质作用与花岗岩成因-Ⅱ:变质泥质岩高温-超高温变质相平衡与S型花岗岩成因的定量模拟

高温-超高温变质岩石的矿物组合及组构特点取决于不同的进变熔融反应,不同程度的熔体丢失以及不同程度的退变反应三种过程的综合效应。利用相平衡定量研究方法可以很好地模拟进变熔融反应的类型、P-T条件、熔体含量及其丢失行为、以及熔融过程中熔体与残余物的化学成分变化等,这对探讨高温-超高温变质作用过程以及花岗岩的成因非常重要。对平均泥质岩(APR)进行相平衡模拟表明变质泥质岩在等压(0.8GPa)升温熔融过程中可发生5种熔融反应:饱和流体固相线、白云母脱水熔融、黑云母熔融、钾长石-石榴石熔融和铝铁镁矿物熔融,后两种熔融反应主要发生在超高温条件下。减压过程中发生怎样的熔融反应受减压温度控制:在麻粒岩相(如850℃)减压可发生钾长石熔融、黑云母熔融和钾长石-石榴石熔融反应;在高角闪岩相(如750℃)减压主要发生白云母脱水熔融和钾长石熔融;在超高温麻粒岩相(如950~1000℃)减压主要发生钾长石-石榴石熔融和铝铁镁矿物熔融。熔体成分受熔融反应和P-T条件控制,如在高角闪岩相发生的饱和流体固相线和白云母脱水熔融可形成弱过铝的奥长花岗质和二长花岗质熔体;在麻粒岩相发生的黑云母熔融和钾长石熔融形成的熔体具有强过铝的二长花岗岩成分;在中压超高温发生的钾长石-石榴石熔融和铝铁镁矿物熔融形成强过铝的二长(钾长)花岗岩质熔体,可形成石榴石花岗岩;在低压超高温下发生的铝铁镁矿物熔融可形成堇青石花岗岩。除了极端超高温下的铝铁镁矿物熔融外,其它熔融反应都会使残余物的成分更贫硅,贫Na_2O和K_2O,富FeO和MgO,但Al_2O_3和Mg#基本不变。高温-超高温下发生深熔的岩石只记录降温过程形成的固相线组合,但固相线的类型与温度条件取决于熔体的丢失行为。在不丢失熔体或者获得熔体的岩石中,岩石最后只记录流体饱和固相线组合;发生熔体部分丢失的岩石会记录缺流体固相线组合,并且熔体丢失越多,缺流体固相线的温度越高;发生全部流体丢失的岩石可记录岩石所达到的最高温度。因此,在一个麻粒岩相区,甚至一个野外露头上不同部位的岩石记录不同的P-T条件。熔体丢失是导致使麻粒岩相组合在升温过程中发生超高温变质,在降温过程中得以部分保存的重要条件。发生部分熔融的高级变质岩中随着温度升高,熔体含量增加,会发生锆石分解,只有在降温过程中发生锆石结晶,因此,麻粒岩中新生锆石只记录降温过程到固相线及以后的年龄,一般不会记录麻粒岩相峰期时代。对泥质高压麻粒岩来说,如果经历ITD型变质演化,会发生递进减压熔融,变质反应易于达到平衡,但如果减压速度快并使岩石直接抬升到地壳浅部,会出现一些ITD型结构标志,如残留金红石、蓝晶石,或在石榴石周围出现堇青石的反应冠状体等,此时锆石记录的退变质年龄会与峰期变质年龄相差不大(如10~30Myr);但如果泥质高压麻粒岩减压至中、深地壳,受其中有滞留熔体影响易于发育IBC型结构特征,表现为麻粒岩组合被(中压)角闪岩相组合叠加,在泥质岩中出现黑云母+夕线石构成的暗色条带,或者出现退变白云母和含白云母的浅色体。在中、深地壳经历IBC过程的麻粒岩锆石记录的退变质年龄会与峰期年龄相差很大(如~100Myr)。高级变质岩中由于出现熔体使水流体活度降低,麻粒岩作为排除部分熔体的残余物,其水活度更低。从这一角度来说,水活度低是麻粒岩相变质作用的结果,而不是条件。某些麻粒岩区之所以出现多期麻粒岩相变质叠加受流体行为控制。在亚固相线下流体饱和岩石变质熔融作用从饱和水固相线开始,然后依次发生含水矿物的脱水熔融和无水矿物熔融,这一过程中流体是内部缓冲的,在麻粒岩相温度峰期形成一组平衡矿物组合,难以保留峰期之前的信息。而流体不饱和岩石(如已形成的麻粒岩或岩浆侵入体)变质作用受外部注入流体控制,与构造变形密切相关。如果发生两期麻粒岩相变质叠加变质,在强应变域会形成晚期麻粒岩组合;在弱应变域,会出现两期麻粒岩组合,其中晚期矿物表现为反应冠状体或细粒交生体;而在一些应变非常弱的区域,可能只保留早期矿物组合。     

青海南山地区加里东期强过铝质花岗岩锆石U-Pb年龄、地球化学特征及其地质意义

青海南山地区位于南祁连构造带和西秦岭造山带的交接部位,在该地区元古宇变质地层中新厘定出一套含石榴子石白云母二长花岗岩,并对其进行了详细的岩石学、岩石地球化学和LA-ICP-MS锆石U-Pb定年研究。结果表明,浪日娘含石榴子石白云母二长花岗岩结晶年龄为438.7±4.2Ma,形成于早志留世早期。岩石含石榴子石、白云母、电气石等高铝矿物,同时具高SiO_2、富Al_2O_3特征,高铝饱和指数A/CNK=1.09～1.28,属高钾钙碱性强过铝质S型花岗岩;微量元素富集大离子亲石元素Cs、Rb、U、K和Pb,亏损高场强元素Nb、Ti、Zr、P和Ba、Sr;稀土元素总量低,配分曲线为轻稀土元素富集的右倾模式,具有弱-中等负Eu异常。高Rb/Sr值(1.83～3.95)、低CaO/Na_2O值(0.11～0.19),伴随有Pb正异常和Ba负异常,暗示源区物质成分为泥质岩并经历了缺水熔融条件下的白云母脱水熔融。结合岩体年龄及区域地质资料,推断其可能形成于原特提斯洋闭合碰撞造山过程。