粤北扶溪岩体成因及时代:来自矿物化学、岩石地球化学及LA-ICP-MS锆石U-Pb年龄证据

分析了粤北扶溪地区花岗闪长岩角闪石、黑云母矿物化学组成,全岩岩石地球化学及LA-ICP-MS锆石U-Pb年龄。结果显示,花岗闪长岩中角闪石属镁角闪石,黑云母属镁质黑云母。岩石硅含量较高,w(SiO_2)为63.86%~66.19%;富碱,w(K_2O)为4.07%~4.71%,w(Na_2O)在2.42%~2.76%;铝质量分数中等,w(Al_2O_3)为14.27%~15.02%。稀土元素总量w(ΣREE)为183.22×10~(-6)~283.31×10~(-6),稀土元素配分模式右倾,中等强度负Eu异常(0.62~0.80),富集Rb、K、Th、Sr、Pb、Nd等大离子亲石元素,亏损Th、U、Zr、Hf、Nb、Ta、Ti等高场强元素。LA-ICP-MS锆石U-Pb年龄为(440.7±3.3)Ma(MSWD=2.4,n=18)。上述分析结果表明花岗闪长岩为I型花岗岩,是早志留世岩浆活动产物,岩浆主要来源于地壳物质的部分熔融,在温度777~802℃、压力316~442 MPa和氧逸度约lgf(O_2)=-14条件下侵位结晶。     

北淮阳古碑花岗闪长岩侵位时代及地球化学特征：对大别山中生代构造体制转换的启示

SHRIMP 锆石 U-Ph 定年表明大别山北淮阳带古碑花岗闪长岩形成于125±3Ma,而不是以前所认为的属晚侏罗世岩体。古碑花岗闪长岩的 SiO_2为61%～63%,K_2O 为3%～3.7t%,Al_2O_3>15%,Mg~#[100×Mg~(2 )/(Mg~(2 ) Fe~T)]为45～49,具有准铝质(A/CNK=0.84～0.88)和高钾钙碱性特征。岩石富集大离子亲石元素(Sr 500×10~(-6)～650×10~(-6),Ba 1640×10~(-6)～2053×10~(-6))和轻稀土元素[(La/Yb)_N 比值为13～20],亏损高场强元素(Nh、Ta、Ti),具有富集且均一的锶和钕同位素组成[(~(87)Sr/~(86)Sr)_i=0.709240～0.709315,ε_(Nd)(t)=-17.96～-18.05]。这些地球化学特征及同位素组成与早白垩世毛坦厂组幔源火山岩及镁铁-超镁铁侵入岩很相似,表明古碑花岗闪长岩起源于富集地幔的部分熔融。该岩体的侵位可能代表了大别山强烈伸展活动的开始。大别山地区晚中生代的岩浆活动可能是古太平洋板块俯冲引起的中国东部早白垩世岩浆活动的一部分,而与三叠纪造山旋回无关。     

桂北新寨强过铝质花岗岩的岩石成因及其构造意义——来自年代学、地球化学及Sr-Nd-Hf同位素的制约

LA-ICP-MS锆石U-Pb定年结果显示,桂北新寨花岗岩形成于中奥陶世(465±2Ma)。该花岗岩的地球化学特征表现为化学成分较均一,具有高硅(SiO_2=68.54%~74.57%)、富碱(K_2O+Na_2O=7.61%~8.31%)、更富钾(K_2O/Na_2O=1.77~2.35)、强过铝质(A/CNK=1.09~2.39)和富集大离子亲石元素而亏损高场强元素等特征,属于S型花岗岩。新寨花岗岩具有比较均一的Sr、Nd同位素组成(I_(Sr)=0.71137~0.71328,ε_(Nd)(t)=-7.89~-7.26)。锆石Hf同位素组成为:(~(176)Hf/~(177)Hf)_i=0.28232~0.28252,ε_(Hf)(t)=-6.18~+0.61,Hf同位素两阶段模式年龄TDM2变化于1.67~2.11Ga之间。元素及Nd-Sr-Hf同位素分析结果显示,新寨花岗岩可能源自古元古代地壳变质泥岩的部分熔融,在成岩过程中有少量幔源组分的参与。新寨S型花岗岩可能是广西运动第二幕在桂北地区的岩石学响应,为早古生代构造-岩浆群事件的建立提供了新证据。     

湘东地区板杉铺加里东期埃达克质花岗闪长岩的成因及地质意义

湘东地区板杉铺加里东期岩体是一套具埃达克岩性质的花岗闪长岩。该岩石具有高的SiO2(~70%)和Al2O3(~16.5%)、中等高的Na2O/K2O比值(普遍大于1.0,可达1.4)和低但可变的Mg质指数(Mg#= 37-59)。相对高的Sr(均值: 520 ppm)和Ba(1052~1502 ppm)以及低的Y(<12 ppm)和Yb(<1 ppm)丰度,导致该岩石具有低的Rb/Sr(0.17~0.42)、高的Sr/Y(34~64)比值,以及LREE强烈富集[(La/Yb)N= 27 ~ 71]而铕弱负异常(Eu/Eu*= 0.76 ~ 0.91)的稀土配分模式。因此,板杉铺岩体源区岩可能为石榴角闪岩或石榴角闪岩-角闪榴辉岩过渡相。但低Nd和高Sr同位素组成[?Nd(t)= -6.7 ~ -8.4],(87Sr/86Sr)i= 0.7078 ~ 0.7140]说明它们并不来源于俯冲的玄武质洋壳或亏损地幔;而高放射性成因Pb[(206Pb/204Pb)i=18.22~18.78]、高微量元素比值(如Ba/La=~15-28、Th/Ce=0.29-0.36)暗示深海沉积物及再循环的陆源沉积物可能已卷入这些岩石的成因。结合区域地质、地层和构造事件,我们认为,早古生代可能的陆-弧-陆碰撞是导致研究区埃达克质花岗闪长岩产生的重要机制,而源于先前富集地幔的玄武质岩浆底侵则诱导了加厚的中酸性弧下地壳岩石部分熔融。部分熔融产生的岩浆可能经同化混染和分离结晶作用过程最终形成了板杉铺埃达克质花岗闪长岩。华南埃达克质花岗闪长岩的厘定不仅揭示早古生代时期华南地区经历了地壳增生事件,对正确理解华南、特别是扬子板块东南缘Au-Sb-W-Cu等多金属成矿作用还具有重要的意义。     

甘肃省南祁连化石沟地区发现中二叠世埃达克质岩:大地构造及成矿意义

南祁连地区化石沟花岗闪长岩位于化石沟铜矿附近,东距阿克塞县城约120 km。花岗闪长岩LA-ICP-MS锆石U-Pb年龄为261.1±3.8 Ma,形成于中二叠世晚期。岩石属钙碱性系列,具有埃达克岩的地球化学特征,SiO_2含量在68.35%~69.14%之间,高铝(Al_2O_3=15.83%~16.06%)、Sr(367×10~(–6)~381×10~(–6))、低Y(15.12×10~(–6)~19×10~(–6))和Yb(1.34×10~(–6)~1.85×10~(–6)),富Na贫K(Na_2O=4.3%~4.47%,K_2O=2.22%~2.46%,Na_2O/K2O=1.75~2.01),MgO介于0.79%~0.89%之间,Mg~#为0.35左右。岩石富集强不相容元素Ba、Rb、Sr、Th、U和LREE,强烈亏损高场强元素Nb、Ta、Ti以及HREE,(La/Yb)_N=8.3~11.77,具轻微的Eu负异常(δEu=0.76~0.86),高Rb/Sr(≈0.2)值。化石沟花岗闪长岩的(~(87)Sr/~(86)Sr)i、ε_(Nd)(t)、(~(176)Hf/~(177)Hf)_i、δ~(18)O_(V-SMOW)分别为0.7065~0.7068、–1.45~–0.78、0.282765、12.1‰~12.5‰。综合以上特征,认为化石沟花岗闪长岩源于新生地壳物质在玄武岩浆底侵作用下发生的部分熔融,在岩浆作用过程中可能发生过轻微的分离结晶作用,形成于板内背景,处于造山挤压向后造山伸展的构造体制转变阶段。花岗闪长岩的Nd和Hf模式年龄(分别为1.1 Ga和0.9 Ga)指示玄武质岩浆上侵的时间应为中元古代晚期。化石沟埃达克质岩显示了良好的斑岩型Cu、Au成矿潜力,寻找与埃达克岩有关的斑岩型Cu、Au矿应是下一步找矿的重点方向。     

新疆西天山备战基性-超基性岩年代学和岩石地球化学研究及其对铁成矿背景的制约

对新疆西天山备战铁矿区附近的基性-超基性岩体———金云母辉石橄榄岩与侵入其中的闪长岩脉进行了年代学和岩石地球化学研究。金云母辉石橄榄岩中金云母~(40)Ar/~(39)Ar坪年龄为298.1±1.9 Ma,该岩石的锆石U-Pb年龄为302.5±1.3 Ma,与备战铁矿的成矿年龄相近。备战金云母辉石橄榄岩具有低Si O_2(42.51%~50.82%)、Al_2O_3(4.87%~7.38%)、Ti O_2(0.25%~0.77%)和全碱(Na_2O+K_2O=0.87%~1.87%)含量,而高Mg O(26.36%~30.17%)、TFe O(12.33%~15.99%)含量的特征,过渡元素丰度(Cr=523×10~(-6)~7 026×10~(-6),Ni=906×10~(-6)~1 088×10~(-6),Co=109×10~(-6)~132×10~(-6))和Mg~#值(0.76~0.79)均较高,表明岩浆经历了橄榄石堆晶作用。由橄榄石最高Fo值(0.79)和岩石的TFe O含量计算得其母岩浆为玄武质岩浆。所有的岩石具有相似的稀土、微量元素配分模式,均呈轻稀土元素富集的右倾型,且重稀土元素较平坦[(Gd/Lu)_N=0.70~2.00],明显富集大离子亲石元素Rb、Ba、U、K,亏损高场强元素Nb、Ta、Zr、Hf和Ti。总体上Sr、Nd同位素较均一,金云母辉石橄榄岩的(~(87)Sr/~(86)Sr)_i=0.704 4~0.704 7,εNd(t)=2.23~3.90,闪长岩(~(87)Sr/~(86)Sr)_i=0.704 4,εNd(t)=3.79~4.07,表明金云母辉石橄榄岩和闪长岩为同源演化的岩石。微量元素特征表明金云母辉石橄榄岩起源于尖晶石相,源区为受俯冲流体或熔体交代的软流圈地幔。结合区域构造背景,推测金云母辉石橄榄岩的形成与西天山造山带在晚古生代的山根拆沉引起的软流圈上涌有关,而备战铁矿晚期成矿事件很可能形成于相同的深部动力学背景下。     

胶东地区郭家岭花岗闪长岩的地球化学特征及成因

本文系统地报道了郭家岭花岗闪长岩的主量元素、微量元素和Sr-Nd同位素组成,重点讨论了郭家岭花岗闪长岩的岩石成因、成岩物质来源及其地质意义.研究结果表明,郭家岭花岗闪长岩的SiO2含量从62%至72%,Na2O/K2O=0.64-1.79,多数样品大于1.0;K2O+Na2O值为7.34-8.49%,铝指数A/CNK=0.82～1.1,属于准铝质或过铝质Ⅰ型花岗岩;高Sr含量(Sr＞800μg/g)、低Y和Yb含量(Y＜10μg/g;Yb＜1.0μg/g)、轻重稀土分馏强烈(LaN/YbN=17.4～47.8);这些地球化学特征类似于adakite、太古代TTG岩系、Na质花岗岩及HiSrBa花岗岩而不同于岛弧环境的英安岩.高的初始87Sr/86Sr比值(0.7094～0.7114),负的δNd(t)值(-11.2～-17.5),表明花岗闪长岩与adakite、HiSrBa花岗岩的成因不同而类似于Na质花岗岩和TTG岩系,即郭家岭花岗闪长岩是由下部地壳镁铁质岩石脱水部分熔融作用形成的.Nd同位素与胶东地区基性脉岩的Nd同位素组成相近,表明二者有可能具有相似或相同的源区.但基性脉岩出露面积明显小于花岗岩,二者之间存在着SiO2成分间隔,并且基性脉岩的不相容元素明显高于花岗闪长岩,从而表明花岗闪长岩不是基性脉岩结晶分异的产物,这与由幔源岩浆直接分异形成的高Sr、Ba花岗岩(HiSrBa)的成因不同.因此,花岗闪长岩有可能来源于早先与脉岩源区相似的基性岩浆底侵作用而形成的下地壳镁铁质岩石.其地球化学特征表明母岩浆在岩浆演化过程中经历了少量地壳混染作用.Mg#＞50的岩石具有高Sr、Sr/Y、La/Yb等地球化学特征,表明岩浆形成时源区残留相中含有密度较大的石榴石,从而可能引起下地壳物质及岩石圈地幔的拆沉.这对研究胶东地区地区乃至中国东部在中生代期间岩石圈强烈减薄作用的机制和过程具有重要的地质意义.     

甘肃北山南带沙枣园复式岩体年代学、地球化学特征及其构造意义

北山南带沙枣园复式岩体由中细粒黑云母花岗闪长岩、细粒黑云母石英闪长岩、中粒黑云母二长花岗岩和中粗粒黑云母正长花岗岩4个岩相单元组成。LA-ICP-MS锆石U-Pb定年结果表明,中细粒黑云母花岗闪长岩、细粒黑云母石英闪长岩和中粒黑云母二长花岗岩侵位于晚二叠世(252.1±1.9Ma、252.2±2.1Ma和248.8±3.5Ma),为海西晚期的产物;而中粗粒黑云母正长花岗岩侵位于早三叠世(246.4±2.0Ma),为印支早期的产物。该花岗质岩石均具有稀土元素的球粒陨石标准化配分曲线呈右倾型,轻重稀土分馏大,轻稀土富集且分异明显,而重稀土亏损且分异不显著特征。中细粒黑云母花岗闪长岩和细粒黑云母石英闪长岩具有较高的SiO_2、Al_2O_3和Na_2O含量,以及较低的MgO含量,强烈富集Sr而亏损Yb和Y,具轻微的铕异常(δEu=0.75～1.16),表现出典型的埃达克岩特征;中粒黑云母二长花岗岩和中粗粒黑云母正长花岗岩总体富硅(SiO_2)、富钾(K_2O)、富碱(K_2O+Na_2O),Al_2O_3含量中等,铕分别呈现负异常(δEu=0.45～0.73)和强负异常(δEu=0.02～0.08)。年代学及地球化学特征研究表明:①中细粒黑云母花岗闪长岩和细粒黑云母石英闪长岩属准铝质-弱过铝质的钙碱性Ⅰ型花岗岩,并具有典型的埃达克岩特征,中粒黑云母二长花岗岩属弱过铝质的高钾钙碱性Ⅰ型花岗岩,中粗粒黑云母正长花岗岩属弱过铝质的高钾钙碱性A2型花岗岩;②中细粒黑云母花岗闪长岩、细粒黑云母石英闪长岩和中粒黑云母二长花岗岩的岩浆来源于下地壳玄武质岩石部分熔融源区,并在上升过程中混染了下地壳物质,而中粗粒黑云母正长花岗岩的岩浆来源于年轻地壳中富含黑云母的变质泥岩部分熔融源区;③中细粒黑云母花岗闪长岩、细粒黑云母石英闪长岩和中粒黑云母二长花岗岩是俯冲-碰撞构造背景条件下的岩浆产物,而中粗粒黑云母正长花岗岩是同碰撞-碰撞后构造背景条件下的岩浆产物。     

胶东西北部北截岩体岩石成因:锆石U-Pb年龄、岩石地球化学与Sr-Nd-Pb同位素制约

胶东半岛西北部是我国最重要的金矿集区,95%以上的金资源储量赋存于晚侏罗世玲珑型和早白垩世郭家岭型花岗岩中。然而,对郭家岭型花岗岩形成的大地构造背景及其与金成矿的关系,尤其是岩石成因仍存有争议。本文通过对归属于郭家岭型花岗岩的北截岩体开展详细的岩相学、岩石地球化学、锆石U-Pb年代学和Sr-Nd-Pb地球化学研究,识别出细粒花岗闪长岩、含斑细粒花岗闪长岩、斑状中粒花岗闪长岩、斑状粗粒花岗闪长岩和花岗伟晶岩脉5种侵入岩类型,它们具有相似的地球化学特征和同位素组成,呈连续演化关系,为同一期岩浆活动的产物。电子探针分析显示,样品中的黑云母具有富FeO~T、MgO、高Al_2O3低TiO_2的特点,为岩浆成因的富铁黑云母,Mg和Al元素的负相关性表明结晶过程中二者可能发生了置换。岩石地球化学研究表明,花岗闪长岩具有高的全碱(K_2O+Na_20=6.92%～9.31%)、Ba(518×10~(-6)～3330×10~(-6))、Sr(305×10~(-6)～1371×10~(-6)),低的Al_2O_3(14.41%～15.82%)、MgO(0.19%～0.77%)、Rb(39.3×10~(-6)～105×10~(-6))、Y(1.2×10~(-6)～6.05×10~(-6))、Yb(0.08×10~(-6)～0.40×10~(-6))含量特征,轻稀土(LREE)富集、重稀土(HREE)相对亏损(LREE/HREE=13.13-21.40),轻、重稀土元素分馏明显[(La/Yb) N=18.39～45.76],Rb、Sr、Ba、Pb等大离子亲石元素(LILE)富集,Nd、Ta、Zr、Hf等高场强元素(HFSE)明显亏损,具有高Ba-Sr花岗岩的地球化学特征。锆石LA-ICP-MS定年结果表明,斑状粗粒花岗闪长岩形成于131.53±0.86Ma,花岗伟晶岩脉形成于127.4±1.3Ma,说明其形成于早白垩世早期,伟晶岩脉应该是本次岩浆活动后期的产物。Sr-Nd同位素分析表明,初始~(87)Sr/~(86)Sr(I_(Sr))和ε_(Nd)(t)分别为0.710658-0.711568和-18.53～-11.17,二阶段亏损地幔模式年龄(t_(DM2))为2107-2425Ma,与胶东群变质岩年龄一致,指示了其原始岩浆有部分熔融的胶东群参与;Pb同位素分析表明,初始~(206)Pb/~(204)Pb和初始~(208)Pb/~(204)Pb分别为17.047～17.945和37.744～38.389,说明有大量的下地壳物质参与成岩。上述数据分析表明,北截岩体是基底岩石胶东群变质岩部分熔融形成的下地壳酸性岩浆与幔源基性岩浆混合作用的结果,太平洋板块向欧亚板块俯冲构造背景下的软流圈物质上涌和下地壳的部分熔融可能是形成这套花岗岩的机制,是板块俯冲产生的欧亚板块边缘火山弧的组成部分;在区域金成矿方面,其为金成矿提供了有利的赋存空间,而应该不是成矿流体来源或热动力条件。     

滇西梁河勐养花岗闪长岩LA-ICP-MS锆石U-Pb年龄、地球化学特征及其构造意义

勐养花岗闪长岩体位于滇西腾冲地块梁河县南勐养镇一带。用LA-ICP-MS技术测得花岗闪长岩锆石U-Pb年龄为115.2±1.0Ma,该年龄被解释为花岗闪长岩的形成年龄,表明该区花岗闪长岩体的形成时代为早白垩世。岩石地球化学特征表明,花岗闪长岩中SiO_2含量为62.39%~67.97%,Na_2O+K_2O为6.26%~7.80%,K_2O为1.98%~4.11%,具有贫钾(K_2O/Na_2O值为0.45~1.11)、低P2O5(0.09%~0.38%)的特征;MgO为1.78%~1.98%,Mg~#为34.90~48.40,属于准铝质-弱过铝质钙碱性系列。微量元素具有相对富集大离子亲石元素(U、Th、Rb、Ba)、亏损高场强元素(Tb、Nb、Zr、Hf)的特点。该花岗闪长岩具有I型花岗岩的特征,同时兼有S型花岗岩之特点,具有明显的岩浆混合作用特征。岩石具有岛弧或活动陆缘岩系的微量元素分布特征。地球化学特征和微量元素构造判别图解揭示,勐养早白垩世花岗闪长岩形成于碰撞后岩浆弧环境。花岗闪长岩为幔源岩浆与高黎贡山群古老地壳部分熔融的岩浆混合的产物。该区早白垩世花岗闪长岩是腾冲地块早白垩世侵入岩与班公湖-怒江-泸水-瑞丽洋盆的闭合、洋壳向南西俯冲及板块间的碰撞造山作用的产物。     

Roles of xenomelts,xenoliths, xenocrysts,xenovolatiles, residues,and skarns in the genesis,transport, and localization of magmatic Fe-Ni-Cu-PGE sulfides and chromite

Most sulfide-rich magmatic Ni-Cu-(PGE) deposits form in dynamic magmatic systems by partial melting S-bearing wall rocks with variable degrees of assimilation of miscible silicate and volatile components, and generation of barren to weakly-mineralized immiscible Fe sulfide xenomelts into which Ni-Cu-Co-PGE partition from the magma. Some exceptionally-thick magmatic Cr deposits may form by partial melting oxide-bearing wall rocks with variable degrees of assimilation of the miscible silicate and volatile components, and generation of barren Fe ± Ti oxide xenocrysts into which Cr-Mg-V ± Ti partition from the magma. The products of these processes are variably preserved as skarns, residues, xenoliths, xenocrysts, xenomelts, and xenovolatiles, which play important to critical roles in ore genesis, transport, localization, and/or modification. Incorporation of barren xenoliths/autoliths may induce small amounts of sulfide/chromite to segregate, but incorporation of sulfide xenomelts or oxide xenocrysts with dynamic upgrading of metal tenors (PGE > Cu > Ni > Co and Cr > V > Ti, respectively) is required to make significant ore deposits. Silicate xenomelts are only rarely preserved, but will be variably depleted in chalcophile and ferrous metals. Less dense felsic xenoliths may aid upward sulfide transport by increasing the effective viscosity and decreasing the bulk density of the magma. Denser mafic or metamorphosed xenoliths may also increase the effective viscosity of the magma, but may aid downward sulfide transport by increasing the bulk density of the magma. Sulfide wets olivine, so olivine xenocrysts may act as filter beds to collect advected finely dispersed sulfide droplets, but other silicates and xenoliths may not be wetted by sulfides. Xenovolatiles may retard settling of – or in some cases float – dense sulfide droplets. Reactions of sulfide melts with felsic country rocks may generate Fe-rich skarns that may allow sulfide melts to fractionate to more extreme Cu-Ni-rich compositions. Xenoliths, xenocrysts, xenomelts, and xenovolatiles are more likely to be preserved in cooler basaltic magmas than in hotter komatiitic magmas, and are more likely to be preserved in less dynamic (less turbulent) systems/domain/phases than in more dynamic (more turbulent) systems/domains/phases. Massive to semi-massive Ni-Cu-PGE and Cr mineralization and xenoliths are often localized within footwall embayments, dilations/jogs in dikes, throats of magma conduits, and the horizontal segments of dike-chonolith and dike-sill complexes, which represent fluid dynamic traps for both ascending and descending sulfides/oxides. If skarns, residues, xenoliths, xenocrysts, xenomelts, and/or xenovolatiles are present, they provide important constraints on ore genesis and they are valuable exploration indicators, but they must be included in elemental and isotopic mass balance calculations.     

Mountains,nations, parks,and conservation

Between 1985 and 1991, two new mountain protected areas (MTNPA) covering more than 35,000 km² and based on participatory management models — the Makalu-Barun National Park and Conservation Area, Nepal, and Qomolangma Nature Preserve, Tibet Autonomous Region — were successfully established through the collaborative efforts of Woodlands Mountain Institute and conservationists in China and Nepal. Characteristics common to both projects include the importance of establishing (1) effective rationales, (2) local support constituencies, (3) a senior advisory group, (4) a task force, (5) linkages between conservation and development, and (6) fund raising mechanisms. The lessons derived from the experiences of Woodlands Mountain Institute are of significant value to others in preserving MTNPA. Increased collaboration and communication between all interested in conservation, however, will remain a critical component for expanding mountain protected area coverage to throughout the world.     

Parents,permission, and possibility: Young women,college, and imagined futures in Gujarat,India

This article advances critical geographies of youth through examining the spatiality implicit in the imagined futures of young women in rural India. Geographers and other scholars of youth have begun to pay more attention to the interplay between young people’s past, present, and imagined futures. Within this emerging body of scholarship the role of the family and peer group in influencing young people’s orientations toward the future remain underexamined. Drawing on eleven months of ethnographic fieldwork, my research focuses on a first generation of college-going young women from socioeconomically marginalized backgrounds in India’s westernmost state of Gujarat. I draw on the “possible selves” theoretical construct in order to deploy a flexible conceptual framework that links imagined post-educational trajectories with motivation to act in the present. In tracing the physical movement of these young women as they navigate and complete college, my analysis highlights the ways in which particular kinds of spaces and spatial arrangements facilitate and limit intra- and inter-generational contact, and the extent to which this affects young women’s conceptions of the future. I conclude by considering the wider implications of my research for ongoing debates surrounding youth transitions, relational geographies of age, and education in the Global South.     

Comparative study of As,Cd, Cu,Cr, Mg,Mn, Ni,Pb and Zn concentrations between sediment and water from estuary and port

The contents of As, Cd, Cu, Cr, Mg, Mn, Ni, Pb and Zn have been determined in sediment and water samples from Valle de las Garzas estuary and Port Manzanillo (Colima, Mexico) using ICP-AES. The concentrations of these elements were used for a comparative study to determine the distribution of heavy metals and to evaluate which elements reflect natural or anthropogenic backgrounds. For this purpose, seven sampling points were selected: Four of them correspond to the lagoon, and three were situated in the port. Statistical analysis of the mineral content was assessed. Initially, data comparison was assessed by statistical tests for each variable. Principal component analysis was then applied considering the influence of all variables at the same time by obtaining the distribution of samples according to their scores in the principal component space. In this way, four studies were carried out: (1) study of sediments collected during the dry season; (2) study of sediments collected during the rainy season; (3) comparative study between sediments from rainy and dry season; and (4) study of water composition collected during rainy season. From the results of the performed analyses, it can be concluded that metals distribution pattern reflected natural and anthropogenic backgrounds (e.g., sediments from the lagoon, situated at the beginning of the rain channel, presented high contents of Zn and Cu, perhaps related to anthropogenic activities or the influence of igneous sediments).     

Partition coefficients of Hf,Zr, and REE between zircon,apatite, and liquid

Concentration ratios of Hf, Zr, and REE between zircon, apatite, and liquid were determined for three igneous compositions: two andesites and a diorite. The concentration ratios of these elements between zircon and corresponding liquid can approximate the partition coefficient. Although the concentration ratios between apatite and andesite groundmass can be considered as partition coefficients, those for the apatite in the diorite may deviate from the partition coefficients. The HREE partition coefficients between zircon and liquid are very large (100 for Er to 500 for Lu), and the Hf partition coefficient is even larger. The REE partition coefficients between apatite and liquid are convex upward, and large (D=10–100), whereas the Hf and Zr partition coefficients are less than 1. The large differences between partition coefficients of Lu and Hf for zircon-liquid and for apatite-liquid are confirmed. These partition coefficients are useful for petrogenetic models involving zircon and apatite.     

Coprecipitation of Ti,Mo, Sn and Sb with fluorides and application to determination of B,Ti, Zr,Nb, Mo,Sn, Sb,Hf and Ta by ICP-MS

We examined the coprecipitation behavior of Ti, Mo, Sn and Sb in Ca–Al–Mg fluorides under two different fluoride forming conditions: at < 70 °C in an ultrasonic bath (denoted as the ultrasonic method) and at 245 °C using a Teflon bomb (denoted as the bomb method). In the ultrasonic method, small amounts of Ti, Mo and Sn coprecipitation were observed with 100% Ca and 100% Mg fluorides. No coprecipitation of Ti, Mo, Sn and Sb in Ca–Al–Mg fluorides occurred when the sample was decomposed by the bomb method except for 100% Ca fluoride. Based on our coprecipitation observations, we have developed a simultaneous determination method for B, Ti, Zr, Nb, Mo, Sn, Sb, Hf and Ta by Q-pole type ICP-MS (ICP-QMS) and sector field type ICP-MS (ICP-SFMS). 9–50 mg of samples with Zr–Mo–Sn–Sb–Hf spikes were decomposed by HF using the bomb method and the ultrasonic method with B spike. The sample was then evaporated and re-dissolved into 0.5 mol l^− 1 HF, followed by the removal of fluorides by centrifuging. B, Zr, Mo, Sn, Sb and Hf were measured by ID method. Nb and Ta were measured by the ID-internal standardization method, based on Nb/Mo and Ta/Mo ratios using ICP-QMS, for which pseudo-FI was developed and applied. When 100% recovery yields of Zr and Hf are expected, Nb/Zr and Ta/Hf ratios may also be used. Ti was determined by the ID-internal standardization method, based on the Ti/Nb ratio from ICP-SFMS. Only 0.053 ml sample solution was required for measurement of all 9 elements. Dilution factors of ≤ 340 were aspirated without matrix effects. To demonstrate the applicability of our method, 4 carbonaceous chondrites (Ivuna, Orgueil, Cold Bokkeveld and Allende) as well as GSJ and USGS silicate reference materials of basalts, andesites and peridotites were analyzed. Our analytical results are consistent with previous studies, and the mean reproducibility of each element is 1.0–4.6% for basalts and andesites, and 6.7–11% for peridotites except for TiO₂.     

Models,validation, and applied geochemistry: Issues in science,communication, and philosophy

Models have become so fashionable that many scientists and engineers cannot imagine working without them. The predominant use of computer codes to execute model calculations has blurred the distinction between code and model. The recent controversy regarding model validation has brought into question what we mean by a ‘model’ and by ‘validation.’ It has become apparent that the usual meaning of validation may be common in engineering practice and seems useful in legal practice but it is contrary to scientific practice and brings into question our understanding of science and how it can best be applied to such problems as hazardous waste characterization, remediation, and aqueous geochemistry in general. This review summarizes arguments against using the phrase model validation and examines efforts to validate models for high-level radioactive waste management and for permitting and monitoring open-pit mines. Part of the controversy comes from a misunderstanding of ‘prediction’ and the need to distinguish logical from temporal prediction. Another problem stems from the difference in the engineering approach contrasted with the scientific approach. The reductionist influence on the way we approach environmental investigations also limits our ability to model the interconnected nature of reality. Guidelines are proposed to improve our perceptions and proper utilization of models. Use of the word ‘validation’ is strongly discouraged when discussing model reliability.     

Pools,riffles, and channelization

The addition of regularly spaced deeps (pools) and shallows (riffles) that provide a variety of flow conditions, areal sorting of stream-bed material, cover for wildlife, and a positive aesthetic experience, may be desirable in many channel projects. Such designs will reduce adverse environmental impacts of stream channel modifications. Analysis of variance for pool-to-pool spacing data suggests that there is no significant difference with respect to channel width between pools that form in natural streams and those in streams affected by a variety of human uses. Short of channelization, which changes the channel width, pools and riffles, within limits, are not particularly sensitive to environmental stress. Experiments in Gum Branch near Charlotte, North Carolina, support the hypothesis that channel form and process evolve in harmony and that manipulation of cross-channel morphology can influence the development of desired channel processes. Planned manipulation of its channel form induced Gum Branch to develop as desired. Morphologic stability consisting of incipient point bars, pools, and riffles was maintained over a period of high magnitude flood events, only to be degraded later by a wave of sediment derived from upstream construction and stream-bank failures. Thus, environmentally desirable channel morphology in urban streams cannot remain stable if changes in the sediment load or storm-water runoff exceed the limits of the stream's ability to make internal adjustments while maintaining morphologic stability.     

Entropy,materials, and posterity

Materials and energy are the interdependent feedstocks of economic systems, and thermodynamics is their moderator. It costs energy to transform the dispersed minerals of Earth's crust into ordered materials and structures. And it costs materials to collect and focus the energy to perform work — be it from solar, fossil fuel, nuclear, or other sources. The greater the dispersal of minerals sought, the more energy is required to collect them into ordered states.But available energy can be used once only. And the ordered materials of industrial economies become disordered with time. They may be partially reordered and recycled, but only at further costs in energy. Available energy everywhere degrades to bound states and order to disorder — for though entropy may be juggled it always increases. Yet industry is utterly dependent on low entropy states of matter and energy, while decreasing grades of ore require ever higher inputs of energy to convert them to metals, with ever increasing growth both of entropy and environmental hazard.Except as we may prize a thing for its intrinsic qualities — beauty, leisure, love, or gold — low-entropy is the only thing of real value. It is worth whatever the market will bear, and it becomes more valuable as entropy increases. It would be foolish of suppliers to sell it more cheaply or in larger amounts than their own enjoyment of life requires, whatever form it may take. For this reason, and because of physical constraints on the availability of all low-entropy states, the recent energy crises is only the first of a sequence of crises to be expected in energy and materials as long as current trends continue.The apportioning of low-entropy states in a modern industrial society is achieved more or less according to the theory of competitive markets. But the rational powers of this theory suffer as the world grows increasingly polarized into rich, over-industrialized nations with diminishing resource bases and poor, supplier nations with little industry. The theory also discounts posterity, the more so as population density and percapita rates of consumption continue to grow. A new social, economic, and ecologic norm that leads to population control, conservation, and an apportionment of low-entropy states across the generations is needed to assure to posterity the options that properly belong to it as an important but voiceless constituency of the collectivity we call mankind.

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Zusammenfassung Rohstoffe und Energie sind die Grundlagen unseres ökonomischen Systems, das von den Gesetzen der Thermodynamik bestimmt wird. Es kostet Energie, um die auf der Erde verteilten Rohstoffe diesem System zuzuführen. Andererseits braucht man Rohstoffe, um die Energie nutzbar zu machen.Die verfügbare Energie kann nur einmal genutzt werden und das Material verbraucht sich. Verbrauchtes Material kann teilweise zur weiteren Nutzung zurückgeführt werden, das kostet wiederum Energie. Die verfügbare Energie nimmt überall ab, und einmal geschaffene Ordnung gerät wieder in Unordnung — das heißt, die Entropie des Systems nimmt ständig zu. Die Industrie ist jedoch abhängig von einem niedrigen Entropiezustand sowohl der Materie als auch der Energie.Je ärmer die Erze sind, um so höher wird die Energie sein, um sie in Metalle umzuwandeln, wobei die Entropie und die Belastung der Umwelt ständig zunimmt.Außer den Dingen, die wir wegen höherer ideeller Werte schätzen, ist eine niedrige Entropie der einzige realistische Wertmaßstab, und der wirkliche Wertzuwachs ist nur an einer höheren Entropie zu messen. Es ist unverantwortlich, Dinge, die eine höhere Entropie bedingen, billiger zu verkaufen oder in größerer Menge zu erzeugen, als unbedingt notwendig ist. Da wir dies heute in unserem Handeln nicht berücksichtigen, ist die derzeitige Energiekrise nur der Anfang einer Folge von Krisen, die Energie und Rohstoffe betreffen, solange wir nicht umdenken.Die Verteilung von niedriger Entropie in einer modernen Industriegesellschaft wird mehr oder weniger nach dem Prinzip der konkurrierenden Märkte erreicht. Das selbstregulierende System gerät jedoch mit zunehmender Polarisierung in reiche Industrienationen mit abnehmenden Ressourcen und armen Nationen mit geringer Industrialisierung in Unordnung. Dieses Prinzip berücksichtigt auch nicht die Nachwelt, vor allem wenn die Bevölkerungsdichte stetig zunimmt und die Konsumbedürfnisse anwachsen. Es sind neue soziale, ökonomische und ökologische Normen notwendig, die zur Populationskontrolle, zur Erhaltung der Umwelt und zu einem Zustand niedriger Entropie für zukünftige Generationen führen. Die nach uns kommenden Menschen haben ein Anrecht darauf.

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Résumé Matériaux et énergie sont les sources des systèmes économiques et sont régis par les lois de la thermodynamique. Il faut de l'énergie pour transformer les ressources minérales dispersées dans la croûte terrestre en matériaux et structures ordonnancées. Et il faut des matériaux pour receuillir et concentrer l'énergie, qu'elle soit solaire ou atomique, ou provienne de combustibles fossiles ou d'autres sources. Plus les minéraux recherchés sont dispersés et plus est côuteuse l'énergie pour leur donner une ordonnance.Or l'énergie disponsible ne peut être utilisée qu'une seule fois. Et les matériaux ordonnancés des économies industrielles se dégradent avec le temps. Ils peuvent être remis partiellement en état et recyclés, mais pour cela il faut de nouveau de l'énergie. Partout l'énergie disponible se dégrade et l'ordre devient désordre; -malgré toutes les jongleries possibles l'entropie augmente toujours.L'industrie dépend clairement d'états de basse entropie tant en ce qui concerne les matériaux que l'énergie, tandis que plus pauvres sont les minerais, plus; élevée est l'énergie à mettre en jeu pour en extraire les métaux, avec toujours augmentation à la fois de l'entropie et de la degradation des milieux.A l'exception de ce que nous apprécions pour leur valeur intrinsèque — la beauté, le loisir, l'amour ou l'or — la basse entropie est la seule chose de réelle valeur. Son prix est réglé par le marché, et sa valeur augmente au fur et à mesure que l'entropie s'accroît. Ceux qui en disposent seraient insensés de la vendre à bas prix ou en quantité supérieure à ce qu'exige leur propre niveau de vie. Pour cette raison, et à cause des contraintes physiques liées à la disponibilité en états de basse entropie, la récente crise d'énergie n'est, en ce qui concerne les matières premières et l'énergie, que la première d'une série de crises auxquelles il faut s'attendre aussi longtemps que se poursoit la marche actuelle des étènements.Dans les sociétés industrielles modernes, les approvisionnement en basse entropie s'effectuent plus ou moins conformément à la théorie de la concurrence des marchés. Cependant la rationalité de cette théorie se ressent de l'accentuation croissante de la polarisation, à l'échelle du monde, en nations riches, surindustrialisées, à ressources de base décroissantes, et en nations pauvres, sous-industrialisées, mais fournisseurs de resources-naturelles. De plus cette théorie ne tient pas compte de notre postérité, et ce, en face d'une densité de population et d'un taux de la consommation par tête d'habitant en augmentation continue.Nous avons donc besoin de nouvelles normes sociales, économiques et écologiques qui conduisent au contrôle de la population, à la conservation et à la répartition des états de basse entropie à travers les générations pour assurer à notre postérité les options qui leur riviennent de droit comme une constituante importante, mais encore muette, de la collectivité que nous appelons l'Humanité.

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Dedicated with appreciation to Nicholas Georgescu-Roegen, distinguished economist, realist among cornucopians