【作者】 郭春丽；

【导师】 吴福元；

【作者基本信息】 吉林大学 ， 矿床学、岩石学、矿物学， 2004， 硕士

【摘要】 近几年来，我国东部中生代地质研究的重要进展是揭示出早白垩世岩浆活动极为发育，与此同时相伴的还有大规模金属成矿作用，但对这些现象产出的地球动力学机制目前还缺乏应有的研究。尽管多数学者认为上述早白垩世岩浆活动与我国东部的岩石圈减薄或构造转折关系密切，应暗示其形成于伸展构造背景，但一直缺乏应有的地质证据。针对上述问题，本文选择辽东半岛南部的中生代饮马湾山花岗岩进行研究。该岩体是辽东半岛南部众多中生代花岗岩体中的一个，它出露面积大（约1120km2），岩性多样，具有代表性。同时，该花岗岩的侵位与辽南变质核杂岩密切相关，这为我们研究早白垩世岩浆活动的构造体制提供了难得的机会。本文对饮马湾山岩体进行了详细的野外地质调查，并开展了高精度的同位素年代学测定与地球化学分析。取得了如下研究成果：1、定年结果运用西北大学地质系的LA-ICP-MS仪器对不同组成岩相的岩石进行了锆石U-Pb同位素测定，其分析结果显示：饮马湾山不同岩相岩石的锆石U-Pb年龄为120(4 ~129(2 Ma，表明不同岩相岩石是基本同时形成的；该结果同时还表明，以前认定的饮马湾山岩体形成于三叠纪的观点是不正确的。 <WP=46>2、饮马湾山岩体成岩机制根据岩石化学，饮马湾山花岗岩可分为闪长岩和二长花岗岩。通过对Harker图解、εNd（t）—MgO之间相关关系图解、以及饮马湾山岩体中广泛发育的镁铁质细粒包体的讨论分析，可知饮马湾山花岗岩和闪长岩是经过至少两种成分的岩浆混合形成的。二长花岗岩具有高的SiO2（71-74%），低Mg#，(87Sr86Sr)i>0.705，εNd（t）<0，表明二长花岗岩主要来源于下地壳。闪长岩SiO2含量为54－66％，但Mg#为47-53，富集大离子亲石元素（LILE）和轻稀土元素（LREE）、亏损高场强元素（HFSE），可知闪长岩母岩浆可能来源于富集岩石圈地幔。古道岭岩体位于饮马湾山岩体的北面，它与饮马湾山岩体在形成时代、地球化学特征上一致。古道岭花岗岩及其闪长质包体的地球化学研究表明研究辽东地区早白垩世花岗岩来源于三个端元，即新生下地壳，岩石圈地幔以及古老下地壳。在Sr－Nd同位素相关图上，采自饮马湾山花岗岩体的样品具有较大范围的Sr、Nd同位素组成，即87Sr/86Sri=0.7092-0.7111, (Nd(t) =-14.90－-19.32，明显位于三个端元组分之间。综合上述结果，我们认为饮马湾山花岗岩是来自富集岩石圈地幔、下地壳的岩浆经过岩浆混合、分离结晶、地壳混染作用形成的。3、岩体形成与伸展作用的时间关系本文对出露于辽东半岛南部饮马湾山岩体的野外观察和岩相学研究已经明显显示，该岩体就位于辽南变质核杂岩形成时期，属于同变形就位的花岗岩体，从而为我国东部早白垩世岩浆活动形成于伸展构造背景这一认识提供了直接的地质证据。 <WP=47>另外，Yang et al (2004) 对辽南变质核杂岩的金洲拆离断层带中韧性变形岩的Ar-Ar年代学系统测定发现，其角闪石年龄为112.6(0.5Ma，白云母的年龄为111.9(0.1Ma，黑云母的年龄为114－111Ma，钾长石的年龄为112－105Ma，上述年龄均比饮马湾山岩体就位年龄略显年轻，很显然，它们应该是变质核杂岩的冷却抬升年龄，而不能视为变质核杂岩形成年龄。还有一个证据来自对A型花岗岩的研究。A型花岗岩的年代学研究结果显示在东北的大兴安岭地区、张广才岭地区、本文研究区的辽东半岛，几乎所有的上述A型花岗岩都是在120-130 Ma期间形成的，与本文研究的饮马湾山I型花岗岩同时。地球化学资料还显示，这些花岗岩基本具有A1型非造山花岗岩的特点，充分反映了我国东部早白垩世的地质演化与伸展体制有关。根据上述资料我们推测，辽东半岛南部饮马湾山岩体形成时的我国东部由于受岩石圈减薄作用影响而使全区处于伸展构造体制。岩石圈减薄而导致的软流圈上涌和幔源岩浆的底侵作用，促使地壳发生大规模熔融而形成壳源花岗岩，并导致地壳深部岩石上隆而形成变质核杂岩，而幔源岩浆本身与壳源岩浆的混合即随后的结晶演化便形成了现今所见的饮马湾山岩体。更多还原

【Abstract】 In the last years, the important development of Mesozoic geological study in the eastern China showed that the early Cretaceous magmatism were very prosperous, at the same time, accompanying with large-scaled metallization, but nowadays, the dynamics of this phenomena lacks some studies. Majority of scholars thought that the early Cretaceous magmatism was closely related to the lithosperic thinning or the tectonic transition, indicating that it formed in the extensional setting, but there are no enough evidences. According to this problem mentioned above, we studied the Mesozoic Yinmawanshan batholith of the southern part of the Liaonan peninsula. Yinmawanshan batholith is one of the Mesozoic granitic batholiths, and has large area (about 1120km2) and various lithologic characters. Meanwhile, its emplacement is closely related to the Liaonan metamorphic core complex, so this point provides an uncommon opportunity to studying the tectonic mechanism of the early Cretaceous magmatism. This paper takes field surveys to the Yinmawanshan batholith in detail, and takes precise isotopic dating and the geochemical analyses. The achievements are listed as <WP=49>follows. 1、the results of dating We took zircon U-Pb isotopic dating by using LA-ICP-MS of the college of geology in Xibei university, and the analyzing results showed that the zircon U-Pb age is 120(4 ~129(2 Ma, showing that the rocks with different petrofacies formed nearly at the same time, and this viewpoint that the Yinmawanshan batholith formed in Triassic is wrong. 2、the forming mechanism of the Yinmawanshan batholithAccording to the geochemistry, the Yinmawanshan batholith can be divided into the diorite and the monzogranite. The Harker diagram, εNd（t）—MgO diagram and the mafic fine-grained enclaves show that the Yinmawanshan batholith is mixed by at least two kinds of magmas. The monzogranite has high SiO2（71-74%）content, low Mg#, (87Sr86Sr)i>0.705，εNd（t）<0, which all indicate the monzogranite came from the low crust. The SiO2 content of the diorite is 54－66％, Mg# is 47-53, and the large ion lithophile element ( LILE ) and the light rare earth element ( LREE ) are rich, but the high field strength element（HFSE）is deficited, so it can be known that dioritic original magma may comes from the enriching lithospheric mantle. The Gudaoling batholith is located in the north of the Yinmawanshan batholith, and has coincident forming age and the geochemical characteristics with the Yinmawanshan batholith. The geochemical characteristics of the Gudaoling granite and its dioritic enclaves <WP=50>show that the early Cretaceous granite came from three end members, that is, the new low crust, the lithospheric mantle and the old low crust. In the isotopic Sr－Nd diagram, the Yinmawanshan batholith has pretty large-scaled composition of the Sr、Nd isotope ( 87Sr/86Sri=0.7092-0.7111, (Nd(t) =-14.90－-19.32 ), which is evidently located among above three end members.Summing up these results, we think that the Yinmawanshan batholith came from the mixing, the fractional crystallization and the crust contamination of the enriched lithospheric mantle and the low crust magma.3、the time relationship between the Yinmawanshan batholith’ formation and the tectonic extension The field observation and petrology have clearly showed that the Yinmawanshan batholith intruded in the forming period of the Liaonan metamorphic core complex, so this provided direct geological evidence to the viewpoint that the early Cretaceous magamatism of the eastern China developed in the extensionally tectonic setting. Besides, through the Ar-Ar dating to the ductile deformed rock in the Jinzhou detachment fault of Liaonan metamorphic core complex, Yang et al (2004) found that the age of the hornblende is 112.6(0.5Ma, the age of the muscovite is 111.9(0.1Ma, the age of the biotite is 114－111Ma, the age of the feldspar is 112－105Ma, above ages are all little younger than the emplacement age of the Yinmawanshan batholith, therefore, it is evident that they are the co更多还原