A Paleoproterozoic orogeny recorded in a long-lived cratonic remnant (Wuyishan terrane), eastern Cathaysia Block, China

The Precambrian basement of northern Wuyishan (southern Zhejiang Province, eastern Cathaysia Block, South China), consists mainly of Paleoproterozoic granites and metamorphic rocks of the Badu Complex, which are the oldest rocks found in the Cathaysia Block. LA-ICPMS zircon U–Pb ages for a gneiss and five gneissic granites from the Tianhou, Danzhu, Xiaji and Lizhuang plutons indicate that magmatism and metamorphism took place between 1888 and 1855 Ma. The Xiaji (1888 ± 7 Ma) and Lizhuang (1875 ± 9 Ma) granites have high SiO₂, K₂O and Rb contents, high A/CNK (1.09–1.40) and Rb/Sr, and low contents of Sr, REE and mafic components (Mg, Fe, Ti, Mn and other transition metals). They have the geochemical signature of S-type granites, and a sedimentary protolith is confirmed by the presence of abundant inherited zircons with a range of ages and Hf-isotope compositions. The Tianhou and Danzhu granites are metaluminous to weakly peraluminous (A/CNK = 0.80–1.07), and have low SiO₂ contents, high Ga/Al and FeO/(FeO + MgO) ratios, and Zn and HFSE concentrations typical of A-type granites. They also record high crystallization temperatures (885–920 °C), consistent with A-type granites. High Y/Nb ratios (>1.4) indicate that they belong to the A₂ subgroup, suggesting that they probably formed in a post-orogenic tectonic setting. Their ages range from 1867 to 1855 Ma, slightly later than the syn-collisional Lizhuang and Xiaji S-type granites. These granitic rocks and the metamorphic rocks of the Badu Complex define a late Paleoproterozoic orogenic cycle in the area. All the 1.86–1.90 Ga zircons, whether derived from S- or A-type granites, show similar Hf-isotopic compositions, with Hf model ages clustering at 2.8 Ga. These model ages, and inherited zircons (ca. 2.5–2.7 Ga) found in some rocks, indicate that the late Paleoproterozoic magmatism and tectonism of the eastern Cathaysia Block represent an overprint on an Archaean basement. This Paleoproterozoic orogeny in the Wuyishan terrane coincides with the assembly of the supercontinent Columbia, suggesting that the Wuyishan terrane was the part of this supercontinent.Zircon ages also record an early Mesozoic (Triassic) tectonothermal overprint that was very intensive in the northern Wuyishan area, leading to high-grade metamorphism of Paleoproterozoic basement, Pb loss from Paleoproterozoic zircons and overgrowth of new zircon. The central and southern parts of Wuyishan and the Chencai area (northern Zhejiang Province) also experienced strong reworking in Neoproterozoic and early Paleozoic times. The Wuyishan terrane (especially in the north) represents a long-lived remnant of the old craton, which has survived for at least one billion years. The compositions of the basement rocks, the Paleoproterozoic orogeny and the Triassic tectonothermal imprint in the Wuyishan terrane are similar to those recognized in the Yeongnam massif of South Korea, suggesting that the two terranes may have been connected from Paleoproterozoic to Triassic time.     

岩石边坡裂隙渗流的流形元模拟

为了能够更好地考虑裂隙渗流在岩石边坡破坏中的作用,在考虑裂纹扩展的数值流形方法程序基础上,从最小势能原理出发,阐述了渗流与变形的耦合作用机理并推导了相应的耦合方程,在程序中实现了对渗流与断裂的模拟。最后利用该程序对含初始裂隙的岩石边坡在渗流作用下的破坏过程进行了模拟。模拟结果很好地再现了边坡在渗流作用下的实际破坏过程。同时通过对裂纹扩展过程中应力强度因子的计算发现,第一应力强度因子始终大于第二应力强度因子,且随着计算时间增加,二者的差值逐渐增大,裂纹扩展以Ⅰ型为主。     

利用分形参数进行地貌定量分区研究——以鄂尔多斯块体及周边为例

地貌分区是地学研究的基础内容之一.传统的地貌分区大多是定性的划分,随着数字地形技术以及分形分析方法的成熟,利用分形参数进行定量化的地貌分区成为可能.本文利用水平分辨率为90m的SRTM数据,采用元分维模型,通过变差函数法计算了鄂尔多斯块体及周边地形的分形参数.在65×65,129×129以及257×257等3种尺度滑动...     

扬子板块西缘新元古代典型中酸性岩浆事件及其深部动力学机制:研究进展与展望

华南板块发育有巨量新元古代岩浆岩,因而是研究罗迪尼亚（Rodinia）超大陆演化期间华南板块地幔属性、地壳演化和壳幔相互作用最理想的场所。虽然在扬子西缘新元古代镁铁质和酸性岩浆作用方面已有大量的研究,但是在系统研究中酸性花岗岩类所代表的不同深部动力学意义的方面还较为薄弱。文章基于团队近期对于扬子板块西缘新元古代典型花岗岩类的研究成果,系统揭示不同深度层次的岩浆作用。最新研究支持扬子西缘新元古代受控于俯冲构造背景,除发生俯冲流体和板片熔体交代地幔作用外,最新识别的ca.850~835 Ma高Mg#闪长岩指示俯冲沉积物熔体也参与了地幔交代作用。Ca.840~835 Ma过铝质花岗岩的发现说明扬子西缘新元古代时期不仅存在新生镁铁质下地壳的熔融,也发生了俯冲背景下成熟大陆地壳物质的重熔。Ca.780 Ma Ⅰ型花岗闪长岩-花岗岩组合揭示了俯冲阶段后期板片回撤断离后软流圈地幔瞬时上涌引发的不同地壳层次的岩浆响应。从ca.800 Ma的增厚下地壳来源的埃达克质花岗岩到ca.750 Ma的酸性地壳来源的A型花岗岩的出现,表明扬子西缘新元古代时期经历了俯冲有关的地壳增厚到俯冲后期弧后扩张背景下的区域性地壳减薄。      

华南中生代玄武岩地球化学特征及其地球动力学意义北大核心CSCD

华南板块是中国东部岩石圈的重要组成部分,广泛发育中生代玄武岩,这些玄武岩为研究华南岩石圈演化提供了重要的窗口。前人对华南中生代玄武岩开展了大量的研究,但是对于玄武岩的源区性质以及构造环境等认识仍存在较大争议。本文系统性分析了华南宁远、道县、长城岭、白面山、汝城等地区中生代玄武岩的主微量元素及Sr-Nd-Pb同位素组成,获得如下主要认识:(1)华南中生代玄武岩主要由碱性和亚碱性玄武岩组成,其SiO_(2)和全碱(Na_(2)O+K_(2)O)含量分别为42.81 wt%~55.54 wt%和1.6 wt%~5.97 wt%;(2)除了宁远玄武岩具有OIB微量元素特征,华南中生代玄武岩具有岛弧玄武岩相似的微量元素配分型式;(3)主量和微量元素特征表明华南中生代玄武岩的形成主要受控于部分熔融,且在岩浆演化过程中经历不同程度的分离结晶作用,未遭受明显的地壳混染作用。Ni-MgO正相关、CaO/Al_(2)O_(3)-CaO正相关和Eu无明显异常表明华南中生代玄武质岩浆经历了橄榄石和单斜辉石结晶,但无明显的斜长石结晶;(4)Sr-Nd-Pb同位素特征表明华南中生代玄武岩为EMⅡ地幔源区,其源区可能有洋壳沉积物的参与;(5)华南中生代玄武岩可能形成于与古太平洋板块俯冲相关的大陆板内环境;(6)华南岩石圈改造可能与中生代古太平洋俯冲板块的交代作用有关,后者所释放的酸性熔体/流体与地幔橄榄岩相互作用,最终造成了华南岩石圈物理化学性质的强烈改变;(7)古太平洋俯冲板块可能对华南有色金属、稀有金属等多金属成矿发挥着重要作用,其释放的熔体或流体为矿石活化和迁移提供了重要的驱动力。     

华北地区晚中生代镁铁质岩浆作用及其地球动力学背景

华北陆块及周缘地区晚中生代镁铁质岩浆岩的元素-同位素地球化学特征显示岩石圈地幔的区域不均一性。华北内部为古老而富集的EM1型岩石圈地幔,主要岩性为弥散状金云母相橄榄岩;华北北缘的岩石圈地幔相对华北内部在化学成分上饱满,在微量元素特征上高度富集LILE、LREE和亏损Nb-Ta和U-Th,在同位素组成上相对高87Sr/86Sr(i)和εNd(t),为受到再循环古老陆壳组分改造的富集型地幔;华北陆块南缘的岩石圈地幔以高87Sr/86Sr(i)和低εNd(t)为特征,与深俯冲大陆地壳改造作用 (残留陆壳板片和熔体 -地幔反应等多种形式 )密切相关。发育在华北陆块及周缘地区的晚中生代镁铁质岩浆作用形成于岩石圈伸展 -减薄的统一动力学背景。考虑到晚中生代华北陆块受到了来自周缘陆块相互作用,如西南特提斯域构造演化、印支陆块和西伯利亚板块的侧向挤压作用和古太平洋板块迅速向北运动引起的走滑拉分作用的共同影响, 我们倾向认为这些板块边界作用引起的板内效应可能是导致华北岩石圈地幔晚中生代广泛熔融和岩石圈减薄的重要动力来源.     

U–Pb geochronology,Sr–Nd isotopic compositions,geochemistry and petrogenesis of Shah Soltan Ali granitoids,Birjand, Eastern Iran

The Shah Soltan Ali area (SSA) is located in the eastern part of the Lut Block metallogenic province. In this area different types of sub-volcanic intrusions including diorite porphyry, monzonite porphyry and monzodiorite porphyry have intruded into basaltic and andesitic rocks. Zircon U–Pb dating and field observations indicate that intermediate to mafic volcanic rocks (38.9 Ma) are older than subvolcanic units (38.3 Ma). The subvolcanic intrusions show high-K calc-alkaline to shoshonitic affinity and are metaluminous. Based on mineralogy, high values of magnetic susceptibility [(634 to 3208) × 10^?5 SI], and low initial ⁸⁷Sr/⁸⁶Sr ratios, they are classified as belonging to the magnetite-series of oxidant I-type granitoids and are characterized by an enrichment in LREEs relative to HREEs, with negative Nb, Ti, Zr and Eu anomalies. These granitoids are related to volcanic arc (VAG) and were generated in an active continental margin. Low initial ⁸⁷Sr/⁸⁶Sr ratios (0.7043 to 0.7052) and positive εNd values (+1.48 to +3.82) indicate that the parental magma was derived from mantle wedge. Parental magma was probably formed by low degree of partial melting and metasomatized by slab derived fluids. Then assimilation and fractional crystallization processes (AFC) produced the SSA rocks. This magma during the ascent was contaminated with the crustal material.All data suggest that Middle-Late Eocene epoch magmatism in the SSA area, occurred during subduction of Neo-Tethys Ocean in east of Iran (between Afghan and Lut Blocks).     

Metamorphism in the Olary Block, South Australia: compression with cooling in a Proterozoic fold belt

Abstract The sedimentary and igneous rocks comprising the lower Proterozoic Olary Block, South Australia, were deformed and metamorphosed during the mid-Proterozoic 'Olarian'Orogeny. The area is divided into three zones on the basis of assemblages in metapelitic rocks, higher grade conditions occurring in the south-east. Mineral assemblages developed during peak metamorphism, which accompanied recumbent folding, include andalusite in Zones I and II and sillimanite in Zone III. Upright folding and overprinting of mineral assemblages occurred during further compression, the new mineral assemblages including kyanite in Zone II and kyanite and sillimanite in Zone III. The timing relationships of the aluminosilicate polymorphs, together with the peak metamorphic and overprinting parageneses, imply an anticlockwise P–T path for the 'Olarian'Orogeny, pressure increasing with cooling from the metamorphic peak.     

新疆西南天山霍什布拉克碱长花岗岩体岩石学及地球化学特征——岩石成因及其构造与成矿意义

位于中国西南天山南缘的霍什布拉克岩体,由碱长花岗岩和碱长花岗斑岩组成。岩石化学成分比较均一,具有富SiO2、Al2O3,贫Fe2O3T、MgO、TiO2、P2O5等特点。AR-SiO2图解中,样品均落入碱性区间,在A/CNK-A/NK图解中,样品主要为准铝质。微量元素总体表现为高场强元素(HFSE)相对于大离子亲石元素的富集以及高场强元素P、Ti和大离子亲石元素Sr、Ba的明显亏损。稀土元素中轻稀土元素相对于重稀土元素富集,Eu的负异常十分明显。岩体含副矿物萤石,并具有高FeOT/MgO、低CaO等特征,10000Ga/Al的比值和Zr+Ni+Sr+Y的含量亦较高,岩石学和地球化学特征表明它为典型的A1型花岗岩,是铁镁质下地壳在低压条件下部分熔融的产物。岩体具有极低的Ti含量是由于源区部分熔融过程中大量磁铁矿的残留所致,而较高的Nb-Ta含量则与岩浆中富含F有关。岩体产出于板内环境,在构造岩体的形成上受到塔里木板块内部裂谷体系的影响。岩体对霍什布拉克铅锌矿成矿意义不大,但具有Sn元素的成矿潜力。     

华夏地块龙泉地区发现亚洲最古老的锆石

锆石这一矿物是迄今为止所发现的地球最初500个百万年间(地质学界通常称为"冥古代")的唯一地壳物质残留,对于了解地球早期地壳演化过程至关重要。近年来,随着高精度SHRIMP测年技术的广泛运用,笔者最近在华夏地块龙泉地区发现了2颗约4100 Ma的碎屑锆石。其中一颗为目前发现亚洲最古老的锆石,其内部结构简单,具有正常的震荡环带,207Pb/206Pb年龄为(4127±4)Ma;其δ18O与地幔岩浆的氧同位素类似,可能来自于早期的幔源岩浆或者未经历地表过程的深部地壳物质的熔融。另外一颗锆石具有明显的核边结构,其核部结晶年龄约为4100 Ma,变质边年龄约为4070 Ma,外围还有2层岩浆增生边年龄介于3800~3600 Ma,代表了该4100 Ma的锆石核部在后期经历了复杂的地壳演化过程,4070 Ma的变质边是目前已获得最为可靠的全球变质年龄。上述发现表明冥古宙时地壳性质和构造环境存在多样性,为认识地球早期大陆演化过程提供了重要新信息。