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1.
孙吴-嘉荫地区早中生代花岗岩的年代学、地球化学与成因 总被引：3，自引：0，他引：3
对小兴安岭北部孙吴-嘉荫地区早中生代花岗岩进行了年代学和地球化学研究,据此探讨其成因及形成的构造背景。锆石U-Pb同位素定年结果表明,研究区早中生代花岗岩分为晚三叠世和早侏罗世两期,形成时代分别为210 Ma和187~181 Ma。晚三叠世碱长花岗岩属铝质A型花岗岩,岩浆源区为新元古代从亏损地幔中增生的基性火成岩地壳。早侏罗世英云闪长岩-花岗闪长岩和二长花岗岩属埃达克岩,是由加厚下地壳物质部分熔融形成的;正长花岗岩-碱长花岗岩与同期埃达克岩具明显不同的地球化学特征,岩浆源区为中元古代从亏损地幔中增生的基性地壳物质。结合区域地质构造演化特征,认为晚三叠世花岗岩是华北板块和西伯利亚板块碰撞造山后伸展构造环境下的产物,早侏罗世花岗岩的形成与古太平洋板块俯冲产生的挤压构造环境有关。 相似文献
2.
通过对太行－五台山区太古宙、元古宙和中生代等不同时代的花岗岩类岩石学和地球化学特征的对比，并将晚太古时期花岗岩类同国内外同时期花岗岩类进行对比，确定了本区晚太古时期花岗岩类岩石组合为英云闪长岩－奥长花岗岩－花岗闪长岩或英云闪长岩－奥长花岗岩－花岗闪长岩－花岗岩，并以奥长花岗岩演化趋势为主，叠加了部分钙碱性演化；而元古宙、中生代花岗岩类岩石组合则主要为花岗闪长岩－花岗岩或花岗岩，以钙碱性演化趋势为特 相似文献
3.
通过对太行－五台山区太古宙、元古宙和中生代等不同时代的花岗岩类岩石学和地球化学特征的对比，并将晚太古时期花岗岩类同国内外同时期花岗岩类进行对比，确定了本区晚太古时期花岗岩类岩石组合为英云闪长岩－奥长花岗岩－花岗闪长岩或英云闪长岩－奥长花岗岩－花岗闪长岩－花岗岩，并以奥长花岗岩演化趋势为主，叠加了部分钙碱性演化；而元古宙、中生代花岗岩类岩石组合则主要为花岗闪长岩－花岗岩或花岗岩，以钙碱性演化趋势为特征。可以认为晚太古时期的太行－五台山区正处于陆壳演化的初始阶段和成熟阶段之间的过渡性阶段。 相似文献
4.
华北地块南缘熊耳山早中生代正长花岗岩——SHRIMP锆石U-Pb年龄、地球化学及意义 总被引：1，自引：0，他引：1
报道了华北地块南缘河南熊耳山寨凹正长花岗岩的SHRIMP锆石U-Pb年龄为217.7±3.6 Ma,为早中生代。该正长花岗岩在岩石化学上高碱和Al,贫Mg、Fe;在微量元素上明显亏损Ba、Sr、P、Ti,相对富集高场强元素U、Th、Zr、Hf;在稀土元素上具有明显的四组分效应。研究结果表明,寨凹正长花岗岩与东秦岭北部富碱侵入岩、北秦岭褶皱带和南秦岭褶皱带早中生代花岗岩的地球化学特征有明显差异,为高分异的Ⅰ型花岗岩。其形成的构造环境与东秦岭地区其他早中生代侵入体相似,为后碰撞或后造山。 相似文献
5.
蒙古西部呼伦陶勒盖地区花岗岩类的初步研究 总被引：5，自引：1，他引：4
靠近中蒙边界的内蒙古西部呼伦陶勒盖地区的中元古界和石炭系中产出数个花岗岩体,其中以英格特-巴格毛道岩体的出露面积最大,岩性变化显著,包括石英闪长岩、花岗闪长岩和花岗岩,含有围岩的残留体,并被年轻的花岗岩和伟晶岩等侵入.以前的资料显示该岩体是晚古生代形成的,而其他红色的花岗岩和钾长花岗岩小岩体(如库楚乌拉和一连)是中生代形成的.SHRIMP锆石UPb定年结果显示,英格特-巴格毛德岩体的年龄为313±5 Ma,相当于晚石炭世.原定为中生代的库楚乌拉和一连两个红色花岗岩体的年龄分别为277±2 Ma和278±4 Ma,相当于早二叠世,而侵入于英格特巴格毛道岩体中的石英二长岩的年龄为130±2 Ma,相当于早白垩世.晚石炭世花岗岩具有IA型过渡的元素地球化学特征,而早二叠世花岗岩具有A型花岗岩的特征,属于铝质A型花岗岩.晚古生代花岗岩的共同特征是均以具正的εNd(t)值(0.90～3.43)为特征,具有新生地壳的性质,是内蒙古西部地区陆壳生长的标志.而早白垩世石英二长岩的εNd(t)值为-8.71,指示岩浆起源可能以壳源物质为主,有地幔物质参与. 相似文献
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7.
江西武功山穹隆花岗岩岩石地球化学特征与成因 总被引：15，自引：1，他引：15
江西武功山地区发育典型的穹隆花岗岩（变质核杂岩），该区中心部位出露中生代花岗岩类和花岗质片麻岩，近EW向展布的晚古生代－中生代萍乡、安福盆地分别位于其北、南两侧。武功山中生代花岗岩类以富SiO2、K2O，Rb、Th、LREE，贫Ba、Nb，且具明显Eu负异常为特点，同时花岗岩中含有夕线石、石榴子石等富铝矿物，表明属于S型花岗岩，反映陆内构造环境。与中生代花岗岩相比，山庄加里东期花岗闪长岩具有不同的岩石地球化学特点，ISr为0．7066，接近于I型，其构造背景与大陆边缘岩浆弧环境较为相似。中生代花岗岩类具有3个不同的岩相分带，岩石学与地球化学研究表明，不同岩相带具有相似的岩石学和地球化学特征，说明武功山穹隆状花岗岩经历了从三叠纪到早白垩世的演化过程，武功山变质核杂岩伸展构造发育在一个古老的加里东期变质基底之上。通过对该区花岗岩类及花岗质片麻岩的岩石学、地球化学特征分析，为揭示穹隆花岗岩构造的形成机制和地球动力学背景提供了依据。 相似文献
8.
长江中下游贵池矿集区燕山期岩浆作用及其地质意义:年代学、地球化学及Sr-Nd-Hf同位素证据 总被引：17，自引：10，他引：7
长江中下游贵池地区燕山期侵入岩发育,与成矿关系密切.本文对该区侵入岩开展了详细的锆石U-Pb年代学、地球化学及Sr-Nd-Hf同位素研究.结果表明,马头花岗闪长斑岩形成于147±2Ma,而花园巩石英二长岩形成于127±1Ma,比花岗闪长斑岩晚约20Ma.早期的花岗闪长斑岩(147 ～ 145Ma)为高钾钙碱性系列,具有高Al2O3、Sr含量和Sr/Y、La/Yb比值,以及低的Y、Yb含量,与埃达克质岩的地球化学特征一致;而晚期石英二长岩(127Ma)和石英正长岩为钾玄岩系列,具有高的(Na2O+ K2O)、Zr、Nb、Y含量和Y/Nb、Yb/Ta比值,与造山带A2型花岗岩地球化学特征相似;碱长花岗岩(125～124Ma)同样具有A型花岗岩的地球化学特征,但与石英二长岩、石英正长岩相比,碱长花岗岩的Y/Nb、Yb/Ta比值相对较低,具板内环境A1型花岗岩的地球化学特征.因此,贵池地区岩浆岩从早期的埃达克质岩变为晚期的A型花岗岩,反应了晚中生代时期长江中下游地区的构造环境由大陆边缘环境向伸展环境的转变. 相似文献
9.
在俄罗斯远东地区晚中生代花岗岩类年龄和相关地球化学数据的基础上,初步建立了该区晚中生代花岗岩类的年代学格架：大致以145Ma为界,分为侏罗纪(178~151Ma)和早白垩世(142~122Ma)2期。侏罗纪的花岗岩类主要为花岗岩－花岗闪长岩－石英二长岩组合,总体上为准铝质—强过铝质高钾钙碱性系列;早白垩世的花岗岩类主要为花岗岩－石英闪长岩－石英二长岩组合,主要为过铝质钙碱性—高钾钙碱性系列—钾玄岩系列。2期花岗岩稀土元素配分曲线均呈右倾型,重稀土元素曲线较平坦,都富集大离子亲石元素(如U、K)和轻稀土元素。与中国东北地区晚中生代花岗岩类对比,中国东北地区总体以兴安岭为中心,中间为早白垩世的花岗岩类,两侧为侏罗纪花岗岩类对称分布。境内外的侏罗纪花岗岩类构造背景不同,其分布与鄂霍次克洋和太平洋板块的俯冲有关,早白垩世花岗岩类可能形成于鄂霍次克带挤压造山后的伸展垮塌和太平洋板块的俯冲弧后伸展阶段。 相似文献
10.
浙西余杭、临安和富阳交界区中生代岩浆侵入活动频繁,发育有闲林、千家花岗闪长岩,拔山、长乐桥二长花岗(斑)岩,鹤山坞和朱村花岗岩,与成矿作用关系密切。SHRIMP锆石U-Pb定年结果表明,中生代岩浆侵入活动分为晚侏罗世(152~147 Ma)、早白垩世早期(139~137 Ma)和早白垩世晚期(104~103 Ma)3个期次,分别对应于花岗闪长岩、二长花岗(斑)岩、花岗岩的成岩时段,即由早期至晚期,岩性具花岗闪长岩→二长花岗(斑)岩→花岗岩的演变规律,与岩石HREE和LREE/HREE分异程度逐渐减弱的地球化学特征一致。余临富交界区中生代中酸性侵入岩具有低TFeO/MgO(1.72~5.28)特征,且P_2O_5与SiO_2呈明显负相关关系,属"Ⅰ"型花岗岩,为地壳深熔和壳幔混合作用的产物。研究表明,晚侏罗世花岗闪长岩形成于太平洋板块俯冲的挤压环境,早白垩世早期二长花岗(斑)岩形成于后碰撞挤压背景向伸展背景的转换阶段,而晚期花岗岩则形成于持续伸展扩张的构造环境。余临富交界区成岩时代与区域晚侏罗世(164~145 Ma)、早白垩世早期(139~135 Ma)和早白垩世晚期(109Ma左右)的3期成矿时代具有较好的一致性,显示了良好的找矿前景。 相似文献
11.
Early Cretaceous adakitic granites in the Northern Dabie Complex, central China: Implications for partial melting and delamination of thickened lower crust 总被引：21，自引：0，他引：21
Qiang Wang Derek A. Wyman Ping Jian Chaofeng Li Jinlong Ma 《Geochimica et cosmochimica acta》2007,71(10):2609-2636
To date, few adakitic rocks have been reported in direct association with contemporary intra-continental extensional structures, which has cast doubt on genetic models involving partial melting of the lower crust. This study presents Early Cretaceous (143-129 Ma, new Sensitive high-resolution ion microprobe (SHRIMP) zircon U-Pb ages) adakitic granites, which are directly associated with a contemporary metamorphic core complex (i.e., the Northern Dabie Complex in the Dabie area). These granites exhibit relatively high Sr contents, negligible to positive Eu and Sr anomalies, high La/Yb and Sr/Y ratios, but very low Yb and Y contents, similar to subducted oceanic crust-derived adakites. They are also characterized, however, by very low MgO or Mg# and Ni values, and Nd-Sr isotope compositions (εNd(t) = −14.6 to −19.4 and (87Sr/86Sr)i = 0.7067-0.7087) similar to Triassic continent-derived eclogites subducted in the Dabie-Sulu Orogen. Additionally, late granitic dikes in the adakitic intrusions exhibit low Sr contents, clearly negative Eu and Sr anomalies, low La/Yb and Sr/Y ratios, but relatively high Yb and Y contents, similar to 118-105 Ma granites in the Northern Dabie Complex. Based on composition and geochronology data of Neoproterozoic amphibolites and orthogneisses, Triassic high- to ultra-high pressure metamorphic rocks, and Early Cretaceous mafic-ultramafic intrusive rocks, and the constraints provided by experimental melt data for tonalites, metabasaltic rocks and eclogites, we suggest that the adakitic granites were most probably generated by partial melting of thickened amphibole or rutile-bearing eclogitic lower crust as a consequence of Triassic-Middle Jurassic subduction and thrusting. The late dikes probably originated from plagioclase-bearing intermediate granulites. Moreover, we suggest that late Mesozoic delamination or foundering of thickened eclogitic lower crust is also a more plausible mechanism for the petrogenesis of Early Cretaceous mafic-ultramafic intrusive rocks in the Dabie area, and probably involved partial melting of a mixed source comprising eclogitic lower crust that had delaminated or foundered into upper lithospheric or asthenospheric mantle peridotite. Asthenospheric upwelling in response to post-collisional delamination of lithospheric mantle was likely to have provided the heat source for the Cretaceous magmatism. 相似文献
12.
Geochemistry and Genesis of the Late Jurassic Granitoids at Northern Great Hinggan Range: Implications for Exploration 总被引：2，自引：1，他引：1
<正>The Longgouhe and Ershiyizhan intrusions of the Late Jurassic,located in the Upper Heilongjiang Basin of the northern Great Hinggan Range,are closely related to porphyry Cu-Au mineralizations.In lithology the intrusions are quartz diorite,quartz monzodiorite and granodiorite of high-K calc-alkaline series,with minor aspects of shoshonite series.Their SiO_2 and Al_2O_3 contents range from 61.37%to 66.59%and 15.35%to 17.06%,respectively.The MgO content ranges from 2.02%to 3.47%,with Mg~# indices of 44-59.The(La/Yb)_N and Eu/Eu~* values range from 16.85 to 81.73 and 0.68 to 0.93,respectively,showing strong differentiation rare earth element(REE) patterns similar to those of adakites.The rocks are enriched in Ba,Sr and light REE(LREE),obviously depleted in Nb and Ta,slightly depleted in Rb and Ti,and poor in Yb and Y,with Yb and Y contents of 0.31-1.32 ppm and 4.32-12.07 ppm,respectively.As indicated by Sr/Y ratios of 67.74-220.60,the rocks are characterized by low-Y and high-Sr contents,which characterize the adakites in the world.Holistically, geochemical tracers suggest that the interested intrusions are adakitic rocks.Given that the Paleo-Asian Ocean and Mongol-Okhotsk Ocean were closed in the Late Paleozoic and Permian-Middle Jurassic,respectively,the interested intrusions should be formed by partial melting of delaminated crust,which had been thickened during collisional orogeny between the Siberian and Mongolian-Sinokorean continents. 相似文献
13.
为深化对华北克拉通破坏机制的认识,选取山西黄榆沟岩体中较新鲜的石英二长斑岩开展年代学和地球化学研究。研究结果表明,黄榆沟岩体由石英二长斑岩组成,LA-ICP-MS锆石U-Pb谐和年龄为(149.3±0.9)Ma,是晚侏罗世岩浆活动的产物。石英二长斑岩富碱,为钙碱性钾玄岩系列,属于准铝质花岗岩类。相对富集K、Sr、Eu等大离子亲石元素,相对亏损Nb、Ce、Zr、Ti等高场强元素;轻稀土元素相对富集,重稀土元素相对亏损,Eu具弱正异常,为I型花岗岩成因。具高Al2O3、Sr、Ba、高Sr/Y比值和低Yb、MgO等特征,具埃达克岩性质。岩石地球化学特征表明,黄榆沟岩体总体为下地壳物质的部分熔融成因,并有幔源物质成分的加入和遭受岩浆混合作用,推测其形成于碰撞造山后的伸展构造环境。 相似文献
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Orhan Karsli Abdurrahman Dokuz İbrahim Uysal Faruk Aydin Raif Kandemir Jan Wijbrans 《Lithos》2010,114(1-2):109-120
Early Cenozoic (48–50 Ma) adakitic volcanic rocks from the Eastern Pontides, NE Turkey, consist of calc-alkaline and high-K calc-alkaline andesite and dacite, with SiO2 contents ranging from 56.01 to 65.44 wt.%. This is the first time that Early Eocene volcanism and adakites have been reported from the region. The rocks are composed of plagioclase, amphibole, quartz, and Mg-rich biotite. They have high and low-Mg# values ranging from 55 to 62 and 13 to 42, respectively. High-Mg# rocks have higher Ni and Co contents than low-Mg# samples. The rocks exhibit enrichments in large ion lithophile elements including the light rare earth elements, depletions in Nb, Ta and Ti and have high La/Yb and Sr/Y ratios. Their relative high ISr (0.70474–0.70640) and low εNd (50 Ma) values (? 2.3 to 0.8) are inconsistent with an origin as partial melts of a subducted oceanic slab. Combined major- and trace element and Sr–Nd isotope data suggest that the adakitic magmas are related to the unique tectonic setting of this region, where a transition from a collision to an extension stage has created thickening and delamination of the Pontide mafic lower crust at 50 Ma. The high-Mg adakitic magmas resulted from partial melting of the delaminated eclogitic mafic lower crust that sank into the relatively hot subcrustal mantle, and its subsequent interaction with the mantle peridotite during upward transport, leaving garnet as the residual phase, elevates the MgO content and Mg# of the magmas, whereas low-Mg# magmas formed by the melting of newly exposed lower crustal rocks caused by asthenospheric upwelling, which supplies heat flux to the lower crust. The data also suggest that the mafic lower continental crust beneath the region was thickened between the Late Cretaceous and the Late Paleocene and delaminated during Late Paleocene to Early Eocene time, which coincides with the initial stage of crustal thinning caused by crustal extensional events in the Eastern Pontides and rules out the possibility of an extensional regime before ~ 50 Ma in the region during the Late Mesozoic to Early Cenozoic. 相似文献
15.
Jinyang Zhang Changqian Ma Jianwei Li Zhenbing She Chao Zhang 《International Journal of Earth Sciences》2013,102(4):1045-1067
The Jigongshan and Qijianfeng batholiths in the Tongbai orogen consist mainly of porphyritic hornblende-biotite monzogranite, biotite monzogranite, and biotite syenogranite, which are variably intruded by lamprophyre, diorite, and syenogranite dykes. Mafic microgranular enclaves commonly occur in the hornblende-biotite monzogranite, whereas surmicaceous enclaves are found in the biotite monzogranite. Both batholiths have zircon U–Pb ages ranging from ca. 139 to 120 Ma, indicating their emplacement in the Early Cretaceous. The hornblende-biotite monzogranite has an adakitic affinity marked by relatively high Sr/Y and (La/Yb) N ratios, lack of Eu anomalies, low MgO and Ni contents, and Na2O > K2O. Its chemical compositions, combined with enriched Sr–Nd isotopic signatures, suggest formation by dehydration melting of mafic rocks in a thickened lower crust. This thickened crust resulted from the Permo-Triassic subduction-collision between the North China and South China blocks and persisted until the Early Cretaceous. The biotite monzogranite and biotite syenogranite have low Al2O3, CaO, and Sr contents, low Rb/Sr, FeOt/MgO, and (Na2O + K2O)/CaO ratios, and flat HREE patterns with moderate to weak Eu anomalies. They were produced by partial melting of crustal materials under relatively low pressure. Partial melting at different crustal levels could have significantly contributed to mechanical weakening of the crust. The diorite and lamprophyre dykes show linear trends between SiO2 and major or trace elements on Harker diagrams, with two lamprophyre samples containing normative nepheline and olivine. These rocks have high La/Yb and Dy/Yb ratios, both displaying co-variation with contents of Yb. They were originated from relatively deep lithospheric mantle followed by fractionation of olivine + clinopyroxene + apatite + Fe–Ti oxides. Extensive partial melting in the lithospheric mantle indicates relatively high temperatures at this level. We suggest that the presence of adakitic magmas, thickened but weakened crust and high temperatures in the lithosphere mantle point to lower crustal delamination in the Early Cretaceous in the Tongbai orogen. 相似文献
16.
《International Geology Review》2012,54(13):1755-1771
The tectonic setting of the West Qinling orogenic belt (QOB) during the Middle–Late Triassic remains a subject of debate. Petrogenesis of adakitic granodiorite plays a critical role in determining the nature of the lower continental crust and mantle dynamics during orogenic processes in the region. The Tadong adakitic granodiorite pluton in the western part of the West QOB is an important element of this system. Its petrogenesis can place severe constraints on the nature of the lower continental crust and mantle dynamics during the formation of the orogenic belt. U–Pb dates obtained through zircon laser-ablation inductively coupled mass spectrometry indicate that the Tadong pluton was emplaced at 220.2 ± 2.5 Ma, coeval with abundant magmatic rocks in the region. This indicates a prominent magmatic event in the western part of West Qinling during the Late Triassic. Geochemically the granodiorites are metaluminous to peraluminous high-K calc-alkalic and characterized by relatively high SiO2 (63.84–67.91 wt.%), Al2O3 (15.39–16.54 wt.%), and Sr (435.08–521.64 ppm), and low MgO (1.16–1.88 wt.%; Mg# = 38–46), Y (5.49–8.84 ppm) and Yb (0.34–0.91 ppm) contents, variable Eu anomalies (Eu/Eu* = 0.87–1.1), and high Sr/Y (51.72–84.45) ratios. These are compositional features of adakites that are commonly assumed to have been produced through partial melting of subducted oceanic basalt. In addition, the adakitic rocks are relatively enriched in light rare earth elements, large ion lithophile elements (Rb, Ba, Sr, Th, and K), and depleted in high field strength elements. However, petrological, geochronological, and geochemical characteristics indicate that the adakitic rocks were most likely formed by partial melting of a thickened mafic lower crust. Therefore, we suggest that the Tadong adakitic granodiorites were produced in a syn-collisional regime and associated with asthenospheric upwelling triggered by slab break-off or gravitational instability. This mechanism was responsible for generating the Late Triassic magmatism of West Qinling. 相似文献
17.
ABSTRACTThe adakitic dikes with zircon ages of ~120–118 Ma are identified in the Xiejiagou gold deposit, Jiaobei terrain. The Early Cretaceous intermediate-acidic dikes include monzonite, quartz monzonite, and monzogranite, which have SiO2, Al2O3, K2O, Na2O contents ranging from 61.01 to 74.72 wt. %, 14.42 to 17.28 wt.%, 2.55 to 4.45 wt.%, and 3.09 to 4.64 wt.%, respectively. The dikes are enriched in large ion lithophile elements (LILEs) (e.g., Rb, Sr, and Ba) and light rare earth elements (LREEs), but are depleted in high field strength elements (HFSEs) (e.g., Nb, Ta) and heavy rare earth elements (HREEs). They are also characterized by continental crust-like isotopic compositions: whole-rock δ18O = 7.6–9.9‰, (87Sr/86Sr)i = 0.70893–0.71036, and εNd(t) = ?13.16 to ?17.06. Assimilation and fractional crystallization are limited, and partial melting of source rock is the main mechanism in controlling the compositional variation. The high Sr/Y (41.51–93.25) and (La/Yb)N (22.9–44.7) ratios imply that the dikes have affinities similar to adakitic rocks. The regional geological setting, coupled with the geochemical and isotopic data, indicate that the adakitic dikes were unlikely produced by partial melting of a subducted oceanic slab or a thickened/delaminated lower crust, or AFC processes of mantle-derived magmas. We conclude that the adakitic dikes are generated by partial melting of lower crust which was triggered and modified by underplating of the lithospheric mantle. We also propose that the eastern part of the North China Craton experienced severe thinning in the Early Cretaceous (~135–120 Ma), and the lithospheric thinning is related to delamination of the lower crust. 相似文献
18.
内蒙古科尔沁右翼中旗敖兰三队侵入体的同位素年代学及岩石地球化学研究表明,敖兰三队侵入体巨晶正长花岗岩具有低Sr、高Yb型花岗岩特征,其LA-ICP-MS锆石~(206)Pb/~(238)U年龄加权平均值为220±1Ma,表明该侵入体是晚三叠世早期侵位形成的。岩石高硅、富碱、高铁镁比、贫钙、贫镁和低钛;稀土元素配分曲线呈现"海鸥式"分布特征,显示强烈的Eu负异常。微量元素特征显示较低的Sr、Ba含量,较高的Yb、Zr和Y含量,在微量元素原始地幔标准化蛛网图上显示明显的Sr、Ba和Ti的负异常。岩石具有高的Rb/Sr和Rb/Nb,显示出壳源岩浆的成分特征。综合分析表明,本区巨晶正长花岗岩为低压下地壳部分熔融的产物。根据(Y+Nb)-Rb、(Yb+Ta)-Rb、Nb-Y-Ce三角图解,并结合区域构造演化,认为巨晶正长花岗岩形成于造山后伸展的构造环境。在中—晚三叠世,内蒙古科尔沁右翼中旗地区构造体制经历了重要的转变,由挤压体制转变为造山后软流圈上涌、岩石圈减薄。 相似文献
19.
Qiang Wang Zhen-Hua Zhao Zhi-Wei Bao Ji-Feng Xu Wei Liu Chao-Feng Li Zheng-Hua Bai Xiao-Lin Xiong 《Resource Geology》2004,54(2):137-152
Abstract. The late Jurassic Tongshankou and Yinzu plutons in southeast Hubei have been investigated for their contrasting metal mineralization features. The former is closely associated with porphyry Cu‐Mo mineralization, while the latter is barren of metal mineralization, althouth both are located very close to each other. The Tongshankou granodiorite porphyries and the Yinzu granodiorites are geochemically similar to adakites, e.g., high Al2O3 and Sr contents and La/Yb and Sr/Y ratios, enriched in Na2O, depleted in Y and Yb, very weak Eu anomalies and positive Sr anomalies. However, different geochemi‐cal characteristics exist between the two plutons: the Tongshankou adakitic rocks (1) are relatively enriched in SiO2, K2O, MgO, Cr, Ni, and Sr and depleted in Y and Yb; (2) have higher degree REE differentiation; (3) have positive Eu anomalies in contrast with very weak negative or unclear Eu anomalies in the Yinzu rocks; and (4) isotopically have relatively higher ePNd(t) values (‐5.19 to ‐5.38) and lower initial 87Sr/86Sr ratios (0.7060 to 0.7062), while the Yinzu adakitic rocks have relatively lower ePNd(t) values (‐7.22 to ‐8.67) and higher initial 87Sr/86Sr ratios (0.7065 to 0.7074). The trace element and isotopic data demonstrate that the Tongshankou adakitic rocks were most probably originated from partial melting of delaminated lower crust with garnet being the main residual mineral whereas little or no plagioclase in the source. On the contrary, the Yinzu adakitic rocks were likely derived from partial melting of thickened lower crust, with residual garnet and a small quantity of plagioclase and hornblende in the source. Interactions between the adakitic magmas and mantle peridotites possibly took place during the ascent of the Tongshankou adakitic magmas through the mantle, considering that MgO, Cr, and Ni contents and ePNd(t) values of the adakitic magmas were possibly elevated and initial 87Sr/86Sr ratios were possibly lowered due to the contamination of mantle peridotites. In addition, the Fe2O3 of the adakitic magmas was likely released into the mantle and the oxygen fugacities (?o2) of the latter were obviously possibly raised, which made metallic sulfide in the mantle oxidized and the chalcophile elements such as Cu were incorporated into the adakitic magmas. The ascent of the adakitic magmas enriched in Cu and Mo will lead to the formation of porphyry Cu‐Mo deposit. Nevertheless, the Yinzu adakitic magmas were possibly lack of metallogenetic materials due to not interacting with mantle peridotite, and thus unfavorable to metal mineralization. 相似文献
20.
新疆东天山白山钼矿深部岩体地球化学特征及成因意义 总被引：2，自引：2，他引：0
白山钼矿深部钻探表明矿体下部存在着矿化花岗斑岩体,所获岩芯显示其岩性主要为似斑状钾长花岗岩、黑云母斜长花岗岩和花岗斑岩.该岩体具有高Al、Na和Sr,低Mg、Y和Yb,以及高Sr/Y和La/Yb比值等特点,类似于埃达克质岩的地球化学特征,暗示来源于较深的含石榴子石的源区;岩石形成时代和地球化学构造判别图解表明,岩体形成于造山后的构造环境.因此,白山钼矿岩体可能为加厚下地壳熔融的产物.白山钼矿床的成矿作用可能与埃达克质岩浆活动有关,其成矿过程得益于高Mo丰度的地壳源区、成岩过程中提供流体和岩浆高氧逸度环境等. 相似文献