古生代中国中西部三大陆块古地理位置重建与演变

针对古生代中国中西部华北、华南和塔里木三大陆块在全球洋-陆格局中的古地理位置还存在的争议问题,本论文以国际最新的古地理位置重建研究方法和思路,在对中国三大陆块盆地(鄂尔多斯、四川和塔里木盆地)古生界钻井岩心的古地磁实测研究、全球古生代古地磁数据收集与有效性筛选处理、全球主要地质事件约束等多参数融合分析的基础上,采用最新的 GPlates 板块重建方法,对中国华北、华南和塔里木三大陆块在全球洋-陆格局中的古地理位置进行了重建和定位。研究结果表明:古生代三大陆块主要在全球 ±30° 之间的南北中低纬度之间迁移;三大陆块在古生代至少发生了 3 次不同的顺时针旋转和方位角转换;三大陆块运移速率至少经历了 3 次以上不同高、低速度间的转换与变化过程;响应于古生代全球洋-陆形成与演化,中国三大陆块古构造格局总体上经历了洋盆扩张下的“多岛洋”离散、俯冲碰撞下的离散-汇聚并存、俯冲消减下的差异汇聚隆升、新旧洋盆转换下的差异汇聚-离散、拼合与地幔柱控制下的差异汇聚-离散内部拉张的差异性演变过程。古生代中国三大陆块在全球洋-陆格局中的位置与差异性演变,奠定了中国三大陆块古生代不同性质盆地的形成与演化、不同层系油气烃源、储集原始物质差异性发育的基础。     

Origin and tectonic significance of a Mesozoic multi-layer over-thrust system within the Yangtze Block (South China)

In the Yangtze Block (South China), a well-developed Mesozoic thrust system extends through the Xuefeng and Wuling mountains in the southeast to the Sichuan basin in the northwest. The system comprises both thin- and thick-skinned thrust units separated by a boundary detachment fault, the Dayin fault. To the northwest, the thin-skinned belt is characterized by either chevron anticlines and box synclines to the northwest or chevron synclines to the southeast. The former structural style displays narrow exposures for the cores of anticlines and wider exposures for the cores of synclines. Thrust detachments occur along Silurian (Fs) and Lower Cambrian (Fc) strata and are dominantly associated with the anticlines. To the southeast, this style of deformation passes gradually into one characterized by chevron synclines with associated principal detachment faults along Silurian (Fs), Cambrian (Fc) and Lower Sinian (Fz) strata. There are, however, numerous secondary back thrusts. Therefore, the thin-skinned belt is like the Valley and Ridge Province of the North American Applachian Mountains. The thick-skinned belt structurally overlies the thin-skinned belt and is characterized by a number of klippen including the Xuefeng and Wuling nappes. It is thus comparable to the Blue Ridge Province of Appalachia.The structural pattern of this thrust system in South China can be explained by a model involving detachment faulting along various stratigraphic layers at different stages of its evolution. The system was developed through a northwest stepwise progression of deformation with the earliest delamination along Lower Sinian strata (Fz). Analyses of balanced geological cross-sections yield about 18.1–21% (total 88 km) shortening for the thin-skinned unit and at least this amount of shortening for the thick-skinned unit. The compressional deformation from southeast to northwest during Late Jurassic to Cretaceous time occurred after the westward progressive collision of the Yangtze Block with the North China Block and suggests that the orogenic event was intracontinental in nature.     

基于择优的块体模型解算南北地震带中南段主要断层滑动速率

利用1999 ～2007期GPS速度场数据,通过块体模型择优得到了南北地震带中南段主要块体边界带变形的适用模型,并给出了块体边界主要断层的滑动速率.结果表明,龙门山断裂带宝兴-汶川段张压速率较小,为0.5 ～ 1.8mm·a-1;汶川-茂县压性相对显著,速率达1.8～3.8mm·a-1;鲜水河断裂带张压及走滑速率存在一定的空间差异性特征,即炉霍以北张性滑动速率(8.1mm·a-1)比左旋走滑速率(4.8mm·a-1)大,炉霍-道孚段张压速率与走滑速率基本相同,道孚-康定段呈现出左旋走滑速率减小、张性速率增大的变化趋势,康定-石棉段表现出较明显的左旋走滑性质;小江断裂带走滑速率明显大于张压速率;红河断裂带空间分段性较为明显,北西段滑动量较小,但存在一定的张压分量(景东段速率4.7 mm·a-1),南东段(个旧以西)以走滑为主(速率4.5mm·a-1).     

"三江"北段昌都陆块晚三叠世钾质-超钾质火山岩成因及地质意义

昌都微陆块内部发育一套晚三叠世粗安岩.本文基于系统的野外踏勘,对具有代表性的火山岩进行岩石学、地球化学等研究.结果显示该区火山岩的SiO₂含量为51.36%~58.04%,全碱含量(Na₂O+K₂O)为5.03%~7.84%,根据岩石K₂O,MgO及K₂O/Na₂O比值判断,属钾质-超钾质火山岩,具高K、高Al、低Ti的特征.本区岩石强烈富集大离子亲石元素(LILE)和轻稀土元素(LREE),Nb、Ta、Ti的负异常明显,整体特征类似于弧火山岩.其稀土总量较高(270×10^-6~960×10^-6),轻重稀土分馏明显,重稀土分布形态较平缓.岩石具有较高的初始锶同位素比值(⁸⁷Sr/⁸⁶Sr)_i=0.7150~0.7176和较低的初始钕同位素比值(¹⁴³Nd/¹⁴⁴Nd)_i=0.51180~0.51184,ε_Nd(t)=-10.9~-10.2,二段Nd模式年龄为t_2DM=1.82~1.88Ga.本区岩石的地球化学特征显示其源区是由俯冲板片所产生的流体/熔体交代的岩石圈地幔,源区矿物组成分析结果显示,其源区以尖晶石二辉橄榄岩为主,含少量石榴石二辉橄榄岩及金云母.本区钾质-超钾质岩石虽然与西藏南部的钾质-超钾质岩石有相似的地球化学特征,但却产于碰撞后的构造背景之下.结合其所具有的弧火山岩特征及时代构造背景判断其为一种"滞后型"弧火山岩,其形成过程可以概括为三个阶段.     

阿拉善右旗地区晚石炭世埃达克岩的发现及其大地构造意义

阿拉善地块西南缘沙枣泉石英闪长岩LA-ICP-MS锆石U-Pb年龄302 ± 9.2 Ma,SiO2含量在60.66%~61.37%之间,MgO 含量在2.13%~2.51%(Mg#= 0.48~0.51)之间,具高Al(Al2O3=17.98%~ 18.44%),富Ca(CaO= 6.08%~6.59%)、富Na贫K(Na2O= 4.20%~4.46%,K2O= 0.67% ~0.92%,K2O/Na2O= 0.16~0.22), 以及高Sr(582×10 - 6~620×10 - 6), 低Y(11.4×10-6~13.7×10–6)、Yb(1.02×10- 6 ~1.51×10–6),高的Sr/Y(35.15~53.25),Y/Yb(11.00~11.23)和La/Yb(7.28~15.10)比值;岩石富集不相容元素（Rb,Th, K, U, Pb等） 及LREE,强烈亏损高场强元素Nb,Ta,Ti以及HREE,轻微的正Eu异常（δEu为0.97~1.18,平均值为 1.1）。岩体总体特征类似于环太平洋新生代埃达克岩。结合霍尔森-查干楚鲁蛇绿岩年代学及区域内其他花岗岩类地球化学 特征认为,沙枣泉埃达克岩是晚石炭世晚期霍尔森-查干楚鲁弧后盆地向南初始俯冲于阿拉善微陆块之下,玄武质洋壳 发生部分熔融且与地幔发生一定程度的交代作用、快速上升形成的,指示雅布赖-巴音诺尔公“陆缘弧”建造始于晚石 炭世-早二叠世, 古亚洲大洋最南端的南蒙古大洋闭合时限应介于275~250 Ma之间,为中-晚二叠世。     

澜沧江河流沉积物碎屑锆石U-Pb年龄、Hf同位素组成及其地质意义

为研究澜沧江沉积物的物质来源及相邻地块的地壳生长和演化规律,利用LA-MC-ICP-MS分析技术,对澜沧江河流沉积物碎屑锆石进行了U-Pb年龄和Hf同位素研究。结果表明：锆石U-Pb年龄主要有5个年龄段,分别是＜177 Ma、201~418 Ma、428~544 Ma、581~1189 Ma和1406~2533 Ma,主要峰值为260 Ma、788 Ma、1 827 Ma和2 474 Ma。其年龄分布特征与北羌塘地块的年龄分布非常一致,说明澜沧江沉积物主要来源于北羌塘地块;结合Hf同位素分析结果,能够反映源区北羌塘地块的形成与演化历史。新太古代-中元古代是北羌塘地块从亏损地幔物质增生的地壳持续生长阶段,它们构成现今北羌塘地块全部地壳物质的78%以上,此后直到0.64 Ga,北羌塘地块的地壳增生作用基本结束。     

武夷地块中古元古代镁铁质-超镁铁质岩石的发现——剖面介绍及岩石学、岩相学、年代学特征

通过1:250 000衢州区域地质调查,在武夷地块浙西南地区发现古元古代镁铁质-超镁铁质岩石。该套岩石在金华、龙游-带呈面状分布,金华张村出露最为完整,主要由辉石角闪石岩、角闪石岩、斜长阳起石岩、斜长辉石岩和斜长角闪岩等组成。对辉石角闪石岩与阳起石岩开展了LA-ICP-MS锆石U-Pb测年分析,分别获得其成岩年龄为1 834±14 Ma(MSWD=0.23,N=16)、1 839±17 Ma(MSWD=0.22,N=11),暗示这套镁铁质-超镁铁质岩石为古元古代岩浆活动的产物。这一发现表明,约1 830 Ma武夷地块处于板内伸展构造环境,同时该时期武夷地块已经具备足够的刚性,以致产生大规模的脆性破裂以及可能由地幔对流作用引发的基性岩浆活动,推测在约1.83 Ga武夷地块已经具有克拉通的性质。     

滇东北下田坝花岗岩年代学、地球化学及其构造意义

滇东北下田坝花岗岩的SiO2质量分数在71.1%～78.15%之间,Al2O3值在11.55%～14.90%之间,A/CNK=0.94～1.25,属于弱过铝质花岗岩。稀土元素总量(∑REE)为259.71×10-6～804.60×10-6,∑LREE/∑HREE为4.12～10.28,说明轻稀土较重稀土富集。岩石具有明显的负Eu异常(δEu=0.04～0.07),大离子亲石元素Rb、Ba、Pb、U等相对富集,高场强元素Nb、Ta、Zr、Ti等明显亏损,这些特征说明下田坝花岗岩是由壳源物质部分熔融形成的,具有A型花岗岩的特征。对下田坝花岗岩进行的激光探针等离子体质谱(LA-ICP-MS)锆石U-Pb同位素年代学研究获得了206Pb/238 U加权年龄年龄769±4.4Ma(MSWD=0.45),可代表花岗岩的形成年龄,下田坝花岗岩并非原来认为的早古生代花岗岩。结合对区域地质资料的分析认为,下田坝花岗岩的形成年龄与扬子地块西部Rodinia超大陆裂解事件在时间上一致,该花岗岩是在Rodinia超大陆裂解过程中由地幔柱活动引起的大陆裂谷环境中形成的,这也证实了扬子地块西南缘新元古代的裂谷环境已影响到滇东北的东川地区。     

湘东北文家市蛇绿混杂岩带的发现及意义

在湘东北文家市首次识别出蛇绿岩套残片 ,它由变沉积岩、变玄武岩、变辉绿岩、变辉长岩、变辉石岩类及变硅质岩组成。综合其地质学、岩石学、地球化学和同位素年代学的资料 ,提出文家市蛇绿岩可能形成于有限小洋盆的构造环境。文家市蛇绿混杂岩带、前陆盆地、磨拉石建造和“S”型花岗岩等构造岩石组合记录了碰撞造山的全过程 ,证实了江南雪峰古陆属元古宙造山带。这一发现为华南前寒武纪的大地构造格架和地壳演化提供了依据 ,同时该地区也将成为研究早期华南大陆地壳演化———武陵运动的关键地带。     

Episodic crustal growth in the Tanzania Craton: evidence from Nd isotope compositions

The analysis of available Nd isotope data from the Tanzania Craton places important constraints on the crust-mantle separation ages, and events marking juvenile crustal addition and crustal recycling. Nd model ages date the oldest crust extraction to 3.16 Ga in the Tanzania Craton, although a rock record of such antiquity is yet to be found there. The most significant period of juvenile crustal addition as well as crustal recycling is 2.7–2.6 Ga. The Nd isotopes of mafic samples show that chemical heterogeneity existed in the mantle beneath the Tanzania Craton, with some samples originating from significantly depleted mantle, and most samples originating from the mixture of primitive mantle and depleted mantle. The Nd isotope section reveals significant differences in Nd isotopes between the north craton and central craton; compared to the north craton, the central craton yields a Nd model age that is approximately 100 Ma older, and its ε_Nd(t) values are more negative, indicating that the two parts of the craton have different mantle source regions. Different types of granitoids are distributed in the Tanzania Craton, such as high-K and low-Al granite, calc-alkaline granite, peraluminous granite and transitional types of tonalite-trondhjemite-granodiorites (TTGs). Most of the granitoids formed later than the mafic rocks in syn-collision and post-collision events.