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地幔柱研究中几个问题的探讨及其找矿意义 总被引：10，自引：1，他引：10
本文在简要回顾地幔柱研究历史的基础上,针对近年来研究中提出的一些科学问题进行初步的探讨,提出了识别古老地幔柱的地质一环境一地球化学综合判别原则,提出了存在地幔柱的第3种类型,而埃达克岩很可能是第3类地幔柱的典型产物之一,指出了地幔柱对于成矿作用影响的双重性,也指出了地幔柱研究将对成矿学研究产生深刻的影响及其对于地质找矿的意义。中国西南部地区以二叠纪峨眉山玄武岩为标志的峨眉地幔柱最终喷发于海陆过渡相环境,具有与俄罗斯西伯利亚地幔柱类似的成矿条件和含矿性,有着良好的找矿前景。 相似文献
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《International Geology Review》2012,54(5):562-583
ABSTRACTThe results of zircon U–Pb age dating and whole-rock geochemistry for the Late Cretaceous Nize granodiorite porphyries, combined with analysis of near-coeval structural deformation of the Lower Cretaceous Langshan Formation, provide new data to better understand the tectonic evolution of the northern Lhasa subterrane, central Tibet. Zircon U–Pb ages of 89.2 ± 0.3 Ma to 87.8 ± 0.3 Ma indicate emplacement during the Late Cretaceous. Granodiorite porphyry intrusions were contemporaneous with the development of a regional angular unconformity, overlain by the Upper Cretaceous Jingzhushan (or Abushan) Formation, within the collision zone between the South Qiangtang and Lhasa terranes. Geochemical data for Nize granodiorite porphyries indicate that they have a calc-alkaline composition enriched in large-ion lithophile elements and light rare earth elements and depleted in high-field-strength elements and heavy rare earth elements. High Al2O3 and Sr contents, low Yb and Y contents, and high Sr/Y ratios are similar to adakitic magmas.Structural analysis indicates two stages of deformation (D1 and D2), with D1 forming the focus of the present study. The D1 deformation is represented by large-scale faults and records two periods of faulting. These periods are recognized as early compressional thrust faulting and a dominant late stage characterized by normal faulting and extension, with the latter stages of D1 being near-coeval with the emplacement of the Nize granodiorite porphyries. The combination of zircon ages, geochemical data, and structural analysis indicates that the Nize granodiorite porphyries formed after collision of the South Qiangtang and Lhasa terranes. Adakitic magma derived from partial melting of the thickened lower or middle crust resulted from lithospheric delamination that may have been promoted by the convective removal of deeper lithospheric mantle. 相似文献
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内蒙古敖仑花斑岩铜钼矿床花岗岩类地质地球化学特征 总被引：5，自引：0，他引：5
敖仑花斑岩铜钼矿床位于大兴安岭南段西拉木伦河断裂北侧,矿床赋存于花岗闪长斑岩岩体及长英质角岩中.矿区脉岩发育,多形成于花岗闪长斑岩体及成矿之后.岩石地球化学表明,赋矿斑岩具有高Si、富Al、Na,低Ca、Mg和Fe2OT3,A/CNK值小于1.1等特征,为偏钠质的高钾钙碱性Ⅰ型花岗岩;稀土元素具微弱负Eu异常,轻重稀土分异比较明显,LREE/HREE值在11.43～18.33,LaN/YbN值在14.64～37.55;岩石具高Sr(＞400×10-6),低Y(≤18×10-6)和Yb(≤1.9×10-6),显示出典型的埃达克岩特征.矿区后期的脉岩中,流纹斑岩与赋矿斑岩的地球化学特征差别较大,具有低Sr,高Y和Yb,明显的负Eu异常等特征,反映其构造背景为张性环境;英安斑岩具有弱的负Eu异常,轻重稀土分异度高于流纹斑岩,但略低于花岗闪长斑岩.通过分析矿区花岗岩岩类的地球化学特征及形成构造环境,认为敖仑花铜钼矿床具有有利的成矿条件和很大的找矿潜力. 相似文献
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近年来,蒙古戈壁天山和中国北山一天山地区均发现重要斑岩型铜(金钼)矿床,但这些斑岩型矿床是否属于同一条斑岩成矿带一直没有明确的结论。本文通过对戈壁天山、北山、天山典型斑岩矿床地质特征和成岩成矿年龄学资料的分析和总结,发现这些地区的斑岩型矿床均主要形成于泥盆-石炭纪岛弧背景之下,并且大多数矿床与埃达克岩有关。因此,提出它们应属于同一斑岩成矿带,与世界新生代巨型斑岩成矿带形成背景相似,暗示中亚造山带具有重大的资源潜力。 相似文献
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Geochemistry and Zircon U-Pb Dating of Changshagou Adakite from the South Altyn UHPM Terrane: Evidence of the Partial Melting of the Lower Crust 总被引：3，自引：0，他引：3
KANG Lei LIU Liang WANG Chao CAO Yuting YANG Wenqiang WANG Yawei LIAO Xiaoying 《《地质学报》英文版》2014,88(5):1454-1465
Changshagou adakite, an outcrop in the middle segment of the South Altyn Tagh ultra-high pressure metamorphism （UHPM） terrane, contains medium-K cal-alkaline and weakly peraluminous compositions （SiO2 = 66.79% to 68.65%, Al2O3 = 17.48% to 18.31%, K20 ＋ Na20 = 6.32% to 6.88%, K2O/Na2O = 0.25 to 0.33, A/CNK = 1.01 to 1.06）. This outcrop is also enriched with large ion lithophile elements but with depleted high-field strength elements （HFSE） showing clearly negative Nb, Ta, and Ti anomalies. REE distribution patterns show a positive anomaly of Eu （6Eu = 1.15 to 1.31） and weakly enriched with LREE compared with HREE （LREE/HREE = 1.02 to 4.20）. Experimental results and several characteristics, including relatively low Nb/Ta ratios （6.03 to 8.45） and high Sr, Sr/Y, （La/Yb）N and low Y and Yb, which indicate the presence of residual garnet and the absence of plagioclase in the source region, show that adakite may form at a pressure ranging from 1.2 GPa to 1.5 GPa and at a temperature of approximately 900~C. Low Cr, Ni, and Mg# values, trace element patterns, and SiO2- Mg# and SiO2-MgO diagrams indicate that rocks are formed by the partial melting of a thickened lower continental crust. LA-ICP-MS in situ U-Pb dating yields two group ages： 503.1±1.7 Ma （core） and 453.1±3.0 Ma （rim）. The Th/U ratios of the core and the rim are 0.11 to 0.40 and 0.03 to 0.07, respectively. Considering the zircon CL image characteristics, Th/U ratios, and previous studies on regional UHPM rocks, adakite formed at 503.1 ± 1.7 Ma and underwent a tectothermal event as a result of the break-off of the Altyn deep subducted continental crust at 453.1 ± 3.0 Ma. 相似文献
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Petrogenesis of Adakitic Porphyries in an Extensional Tectonic Setting, Dexing, South China: Implications for the Genesis of Porphyry Copper Mineralization 总被引：71，自引：0，他引：71
WANG QIANG; XU JI-FENG; JIAN PING; BAO ZHI-WEI; ZHAO ZHEN-HUAN; LI CHAO-FENG; XIONG XIAO-LIN; MA JIN-LONG 《Journal of Petrology》2006,47(1):119-144
The Dexing adakitic porphyries (quartz diorite–granodioriteporphyries), associated with giant porphyry Cu deposits, arelocated in the interior of a continent (South China). They exhibitrelatively high MgO, Cr, Ni and Sr contents, high La/Yb andSr/Y ratios, but low Yb and Y contents, similar to adakitesproduced by slab melting associated with subduction. However,they are characterized by bulk Earth-like Nd–Sr isotopecompositions (Nd(t) = –1·14 to +1·80 and(87Sr/86Sr)i = 0·7044 – 0·7047), and highTh (12·6–27·2 ppm) contents and Th/Ce (0·19–0·94)ratios, which are different from those of Cenozoic slab-derivedadakites. Sensitive High-Resolution Ion Microprobe (SHRIMP)geochronology studies of zircons reveal that the Dexing adakiticporphyries have a crystallization age of 171 ± 3 Ma.This age is contemporaneous with Middle Jurassic extension withinthe Shi-Han rift zone, and within-plate magmatism elsewherein South China, indicating that the Dexing adakitic porphyrieswere probably formed in an extensional tectonic regime in theinterior of the continent rather than in an arc setting. Theirhigh Th contents and Th/Ce ratios, and Middle Jurassic age,argue against an origin from a Neoproterozoic (1000 Ma) stalledslab in the mantle. Taking into account available data for theregional metamorphic–magmatic rocks, and the present-daycrustal thickness (31 km) in the area, we suggest that the Dexingadakitic porphyries were most probably generated by partialmelting of delaminated lower crust, which was possibly triggeredby upwelling of the asthenospheric mantle due to the activityof the Shi-Hang rift zone. Moreover, the Dexing adakitic magmasmust have interacted with the surrounding mantle peridotiteduring their ascent, which elevated not only their MgO, Cr andNi contents, but also the oxygen fugacity (fO2) of the mantle.The high fO2 could have induced oxidation of metallic sulfidesin the mantle and mobilization of chalcophile elements, whichare required to produce associated Cu mineralization. Therefore,the Cu metallogenesis associated with the Dexing adakitic porphyriesis probably related to partial melting of delaminated lowercrust, similar to the metallogenesis accompanying slab melting. KEY WORDS: adakite; lower crust; delamination; porphyry copper deposit, South China 相似文献
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云南马厂箐富碱斑岩埃达克岩性质的厘定及其成矿意义 总被引：9，自引：0，他引：9
马厂箐复式岩体SiO2含量变化于61.56%～71.63%,平均67.30%(≥56%);Al2O3含量变化于13.38%～17.18%,平均15.44%(≥15%);K2O含量变化于3.36%～8.92%,平均5.35%;K2O+Na2O变化于7.75%～11.55%,平均9.08%;K2O/Na2O变化于0.65～4.00,平均1.49,明显具有高钾钙碱性或钾玄岩系列特征;MgO含量变化于0.40%～4.59%,平均1.11%,在R1-R2图解中处于造山晚期和同碰撞期岩浆岩的范围内.地球化学特征显示高场强元素HFSE(Nb、Ta、Ti)相对亏损,Sr含量高(337×10-6～718×10-6),Y主要集中在6.2×10-6～15.8×10-6之间(≤18×10-6),Yb含量变化于0.20×10-6～1.63×10-6之间(≤1.9×10-6),轻重稀土元素强烈分异,且具有明显的轻稀土元素富集的特点,LREE/HREE变化于8.02～24.01,Sr/Y变化于40.5～57.4之间,平均48.2(＞40),La/Yb变化于17.5～105.8之间,平均43.4(＞20),Sc含量变化于2.5×10-6～7.9×10-6之间(＜10×10-6);δEu 变化于0.81～1.38之间,显示出埃达克岩的地球化学特征.马厂箐岩体属于C型埃达克岩中的钾质埃达克岩.马厂箐岩体埃达克岩性质的厘定及其与同一成矿带上的玉龙斑岩体具有相似地球化学特征和形成环境的认识,对于该区地质找矿具有一定的意义. 相似文献