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常量、微量及Sr、Nd同位素研究表明,藏北赤布张错地区分布的一套始新世(35～4 0Ma)高钾钙碱性火山岩具有C型埃达克岩的地球化学特征。火山岩SiO2 含量为5 8%～6 9% ,K2 O、Al2 O3 、Sr的含量相对偏高,而Y、Yb的含量和Mg# 值相对较低,Nb明显亏损,Zr、Ti、P弱亏损,LREE富集,无明显Eu负异常,ISr(0 .70 72 3～0 .70 777)值偏高,而INd(0 .5 12 32 0～0 .5 12 35 2 )值偏低,指示其为一套壳源中酸性火山岩系,源自加厚陆壳下部的一个榴辉岩质源区的部分熔融。这套新生代埃达克质火山岩的厘定,指示藏北羌塘地区或更大范围的大陆地壳在4 0Ma左右已经加厚到超过4 0km ,且青藏高原的隆升开始于4 0Ma以前。 相似文献
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内蒙古图林凯蛇绿岩中,新发现了埃达克岩,岩性包括石英闪长岩、奥长花岗岩、斜长岩和英安岩。它们是温都尔庙—图林凯早古生代消减带的一种岩浆岩标志。精确的SHRIMP U-Pb测年表明:①石英闪长岩侵位于约467±13Ma,说明温都尔庙古洋壳的消减可能始于约467±13Ma或更早。随后不久,这一岩石经历了约451±18Ma的高级变质和部分熔融事件。②英安岩喷发于约459±8Ma,奥长花岗岩形成略晚,约451±7Ma,最后形成了斜长岩的岩墙,其时代约为429±7Ma。据此认为,温都尔庙—图林凯古洋壳在早古生代时期,经历了愈38Ma的消减事件。 相似文献
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Geochemical and mineralogical characteristics of the Eocene volcanic succession in Tafresh area of the Urumieh–Dokhtar Magmatic Assemblage (UDMA) are unique in the 2000‐km‐length assemblage. Demonstrating rather steep rare earth element (REE) patterns and the widespread presence of amphibole (+biotite) phenocrysts are two distinct characters that dominate the Eocene volcanic succession of mainly andesitic composition. Coincidence of the geochemical and mineralogical characteristics of the whole volcanic succession with adakites, rather amphibole‐ (+biotite) rich dacitic (with 61–64 wt% SiO2) stocks and dykes, is considered as the key in unraveling the role of ‘slab‐derived melt contribution’ in petrogenesis of the volcanic succession. Slab‐derived melting has been an ongoing process that metasomatized some parts of the mantle wedge from which hybrid rocks (andesites) are derived. Basalts with distinct signatures of slab melt metasomatism are yet another support for the occurrence of slab melting. Interlayering of normal, island‐arc‐type calc‐alkaline volcanic rocks with the slab‐melt metasomatized basalts and hybrid andesites suggests that the slab melting has been motivated by the subduction. Formation of the Tafresh Caldera, the likely consequence of an explosive eruption, is compatible with the volatile‐bearing nature of the adakitic volcanism in the study area. It is indicated by the ubiquitous presence of the hydrous minerals. Beneath the Tafresh area, in Eocene time, the subducting slab seems to have reached a critical high depth that is enough for the development of amphibolite–eclogite. The slab deformation, motivated by the geometry of subduction and/or the underlying mantle's steeper geotherms, is suggested to have resulted in the slab melting that helped develop a rock assemblage unique to the UDMA. 相似文献
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皖南及邻区燕山期两个类型花岗岩地球化学对比与岩石成因 总被引：9，自引：0，他引：9
皖南周边分布着40余处大小不等的燕山期花岗岩体,依据岩石年龄可划分出2个幕次:一是130～170Ma,平均145Ma,为晚侏罗世-早白垩世早期(J3-K11),以花岗闪长(斑)岩为主;二是109～132.2Ma,平均123.5Ma,为早白垩世中、晚期(K12),岩性为花岗岩。研究表明,J3-K11花岗闪长岩为C型、高钾钙碱性埃达克岩,发育于造山后构造,应力由挤压转变为伸展的转折期,源自印支期加厚地壳部分熔融。而K21幕花岗岩为A2型花岗岩,产生于造山后的构造伸展环境,源自正常安山质地壳在印支期加厚地壳熔融结束之后继续受地幔物质底侵部分熔融。埃达克岩与斑岩铜矿及金、银等矿床成因上密切相关,A型花岗岩富集稀土元素及W、Zr、Nb、Ta、U等。因此加强皖南及邻区埃达克岩和A型花岗岩的研究,可为该地区寻找斑岩铜矿床及稀土、稀有金属等矿床提供一个新的思路和方向。 相似文献
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The research of the petrology and the geochemistry of the Mosozoic intrusive rocks in Xu-Huai area indicated that they are mainly composition of dioritic porphyry and monzodioritic porphyry, and the features of the petrology and geochemistry of the Mosozoic intrusive rocks are extremely similar to those with the typical adakites. Combined with the petrography and the testimated results of the deep-seated xenoliths in the intrusive rocks, it indicates that the petrogenesis of the Mosozoic intrusive rocks could be resulted from the partial melting of amphibole-bearing garnet pyroxenite and garnet amphibolite in lower continental crust in this area. 相似文献
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内蒙古乌兰沟埃达克岩锆石U-Pb年龄及构造环境 总被引：2，自引：1，他引：1
内蒙古中部贺根山缝合带的梅劳特乌拉蛇绿岩中,新发现乌兰沟埃达克岩,岩性为花岗闪长岩。LA-ICP-MS锆石UPb测年结果表明,乌兰沟埃达克岩的侵位年龄为279.3±1.4Ma,其形成时代为早二叠世。乌兰沟埃达克岩SiO_2含量为65.92%~69.65%,MgO为1.34%~2.16%,Al_2O_3为15.30%~17.33%,Na_2O/K_2O值为3.95~14.09,Sr=359.60×10~(-6)~734.00×10~(-6),Yb=0.83×10~(-6)~2.02×10~(-6),Y=6.65×10~(-6)~12.84×10~(-6);富集K、Rb、Sr等大离子亲石元素,亏损Nb、Ta、Ti、P等高场强元素;稀土元素总量为32.18×10~(-6)~65.41×10~(-6),明显较低,轻、重稀土元素分馏明显,(La/Yb)N值为2.84~7.56,无明显Eu异常,显示出高硅埃达克岩(HSA)的地球化学特征。该埃达克岩具有岛弧型岩浆岩特征,形成于俯冲带岛弧环境,可能为洋内俯冲洋壳+俯冲深积物部分熔融并与上覆地幔楔橄榄岩反应成因。根据乌兰沟埃达克岩与梅劳特乌拉蛇绿岩的时空分布与演化特征,贺根山缝合带在早二叠世可能存在洋内俯冲作用。 相似文献
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西秦岭天水地区晚三叠世柴家庄二长花岗岩及其暗色包体地球化学——岩石成因及岩浆混合作用 总被引：1，自引：0，他引：1
晚三叠世花岗岩类在秦岭-大别造山带西端广泛分布,其成因机制及地球动力学背景的研究对于反演华北、扬子两大板块沿秦岭-大别造山带在三叠纪时期的拼合历史具有重要意义.本文选择西秦岭天水地区柴家庄晚三叠世二长花岗岩及其中的暗色包体进行精细的岩石学和地球化学研究.暗色包体中普遍发育针状磷灰石及斜长石捕掳晶,暗示岩浆混合作用;暗色包体具有较低的SiO2（60.27%~60.38%）、高的Mg#（54~55）和Nb/Ta比值（14.8~16.6）,表明其来源于富集岩石圈地幔的部分熔融作用;寄主二长花岗岩表现出典型埃达克岩的地球化学特征,其富集Sr、Ba,亏损Y和HREE,岩石的Sr/Y比值介于88~98之间,Y/Yb比值介于13~15之间,暗示源区有石榴石残余.结合前人的研究结果,提出柴家庄二长花岗岩可能为增厚的造山带下地壳在碰撞后伸展环境下发生部分熔融作用的产物,可能与晚三叠世时期秦岭造山带的板片断离作用有关 相似文献
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