The Araçuaí-West-Congo Orogen in Brazil: an overview of a confined orogen formed during Gondwanaland assembly

The Neoproterozoic Adamastor-Brazilide Ocean was generated during the breakup of the Rodinia supercontinent, and remnants of its oceanic lithosphere have been found in the Brasiliano-Pan African orogenic system that includes the Araçuaí, West-Congo, Brasília, Ribeira, Kaoko, Dom Feliciano, Damara and Gariep belts. The Araçuaí and the West-Congo belts are counterparts of the same Neoproterozoic orogen. The first belt comprises two thirds of the Araçuaí-West-Congo Orogen. This orogen is rather unique owing to its confined nature within the embayment outlined by the São Francisco and Congo cratons. In spite of this, the presence of ophiolitic remnants, and a calc-alkaline magmatic arc, indicate that the basin/orogen evolution comprise both oceanic spreading and consumption. It is assumed that coeval Paramirim and Sangha aulacogens played a key role by making room for the Araçuaí-West-Congo Basin. Sedimentary successions record all major stages of a basin that evolved from continental rift, when glaciation-related sedimentation was very significant, to passive margin. Rifting started around 1.0–0.9 Ga. The oceanic stage is constrained by an ophiolitic remnant dated at 0.8 Ga. If the cratonic bridge that once linked the São Francisco and Congo palaeocontinental regions did not hinder the opening of an ocean basin, it certainly limited its width. As a consequence, only a narrow oceanic lithosphere was generated, and it was subducted afterwards. This is also suggested by orogenic calc-alkaline granitoids occuping a small area of the orogen. Geochronological data for pre-, syn- and late-collisional granitoids indicate that the orogenic stage lasted from 625 Ma to 570 Ma. A period of magmatic quiescence was followed by intrusion of postcollisional plutons at 535–500 Ma. The features of the Araçuaí-West-Congo Orogen suggest the development of a complete Wilson Cycle in a branch of the Adamastor Ocean, which can be interpreted as a gulf with limited generation of oceanic lithosphere.     

Metamorphic record of collision and collapse in the Ediacaran‐Cambrian Araçuaí orogen,SE‐Brazil: Insights from P–T pseudosections and monazite dating

The Araçuaí orogen is the Brazilian counterpart of the Araçuaí‐West Congo orogenic system (AWCO), a component of the Ediacaran‐Cambrian orogenic network formed during the amalgamation of West Gondwana. The northwestern portion of the Araçuaí orogen is dominated by a succession of metasedimentary rocks made up of Meso‐ to Neoproterozoic rift, passive margin and syn‐orogenic sequences, locally intruded by post‐collisional granites. These sequences are involved in three distinct tectonic units, which from west to east are: the southern Espinhaço fold‐thrust system (SE‐thrust system), the normal‐sense Chapada Acauã shear zone (CASZ) and the Salinas synclinorium. Three deformation phases were documented in the region. The first two phases (D₁ and D₂) are characterized by contractional structures and represent the collisional development stage of the orogen. The third phase (D₃) is extensional and currently viewed as a manifestation of orogenic collapse of the system. The distribution of the metamorphic mineral assemblages in the region characterizes two metamorphic domains. The M‐Domain I on the west, encompassing the SE‐thrust system and the CASZ, is marked by a syn‐collisional (syn‐D₁) Barrovian‐type metamorphism with P–T conditions increasing eastwards and reaching ~8.5 kbar at ~650°C between 575 and 565 Ma. The M‐Domain II comprises the Salinas synclinorium in the hangingwall of the CASZ, and besides the greenschist facies syn‐collisional metamorphism, records mainly a Buchan‐type metamorphic event, which took place under 3–5.5 kbar and up to 640°C at c. 530 Ma. The northwestern Araçuaí orogen exhibits, thus, a paired metamorphic pattern, in which the Barrovian and Buchan‐type metamorphic domains are juxtaposed by a normal‐sense shear zone. Lithospheric thinning during the extensional collapse of the orogen promoted ascent of the geotherms and melt generation. A large volume of granites was emplaced in the high grade and anatectic core of the orogen during this stage, and heat advected from these intrusions caused the development of Buchan facies series over a relatively large area. Renewed granite plutonism, hydrothermal activities followed by progressive cooling affected the system between 530 and 490 Ma.     

西昆仑甜水海地体早寒武世花岗岩浆作用及其构造意义

瓦仍孜拉甫岩体和阿依里西岩体出露于西昆仑造山带的甜水海地体中。LA-ICP-MS锆石U-Pb定年表明,阿依里西岩体的花岗质斑岩的侵位年龄为（530±6）Ma,瓦仍孜拉甫岩体的黑云母二长花岗质片麻岩的侵位年龄为（515±2）Ma,都形成于早寒武世。岩石地球化学特征表明,阿依里西岩体中花岗质斑岩的SiO2含量为67.7%~69.4%,具有较高的Mg#值（44~46）,A/CNK值为0.81~0.93;K2O含量为2.15%~3.02%,呈钙碱性至高钾钙碱性特征;其εHf（t）值为-3.3~-0.8;以轻重稀土分异较为明显,富集Cs、Rb、K、Th、Zr、Hf、Y等元素,而亏损Ba、Nb、Ta、Sr、P和Ti等元素为特点,是由幔源岩浆与壳源岩浆发生混合作用而成。瓦仍孜拉甫岩体黑云母二长花岗质片麻岩的SiO2含量高其变化范围为75.0%~76.3%,Mg#值比较低,为18~26;A/CNK值为1.01~1.30,K2O含量为4.31~4.98,表现为高钾钙碱性、过铝质特征,其εHf（t） 值为+2.5~+4.3;属于高分异I型花岗岩,源于高钾钙碱性的安山岩和玄武质安山岩的部分熔融。根据这些地球化学特征,结合西昆仑不同地质单元中早古生代花岗岩体的分布特征、地质年代学和岩石成因特征,研究认为这2个花岗质岩体形成于岛弧环境,其为进一步深入研究西昆仑造山带早古生代的构造演化过程提供了新的地质资料。     

羌塘中西部红脊山地区蓝片岩Sr-Nd同位素与锆石U-Pb年龄特征及其构造意义

红脊山构造混杂岩带位于羌塘地块的中西部,为古特提斯洋在该地区俯冲、碰撞形成的高压变质带,是羌塘中部低温高压变质带的重要组成部分。本文对红脊山混杂岩带内蓝片岩进行了系统的地球化学、锆石U-Pb定年及Sr-Nd同位素研究。结果显示,红脊山地区蓝片岩的原岩为碱性、亚碱性玄武岩,其中碱性玄武岩具有高TiO2(2.86%~4.84%),属高Ti玄武岩,富集轻稀土元素[(La/Yb)N=11.42~20.05]和高场强元素,地球化学特征类似于OIB;而亚碱性玄武岩,具有低TiO2(1.74%~1.81%),稀土总量较低(67.27×10-6~68.59×10-6)和轻稀土略微富集的特征[(La/Yb)N=2.49~2.81],与典型的E-MORB特征一致。Sr、Nd同位素组成:εNd(t)=-0.1~3.9,(~(87)Sr/~(86)Sr)i=0.704812~0.708365,表明该地区基性岩浆来自亏损型地幔。锆石的Th/U比值为0.33~1.33,并具有典型岩浆振荡环带结构;获得两组206 Pb/238 U年龄数据:其年龄加权平均值分别为288.3±1.9 Ma(n=15,MSWD=0.39)和304.2±2.3 Ma(n=14,MSWD=0.54),因此该两组年龄应代表蓝片岩原岩形成年龄,红脊山蓝片岩原岩形成时间相当于晚石炭世—早二叠世。结合区域地质事实和前人研究成果,红脊山基性原岩形成于大陆裂谷环境,其成因可能与地幔柱有关,与南羌塘二叠纪基性岩墙具有相同的构造背景及动力学机制。蓝片岩基性原岩年龄在红脊山乃至整个羌塘地区都鲜有报道,红脊山地区晚石炭世—早二叠世岩浆活动的厘定为精细刻画羌塘地区古特提斯构造演化过程提供了重要依据。     

Guandishan Granitoids of the Paleoproterozoic Lüliang Metamorphic Complex in the Trans-North China Orogen: SHRIMP Zircon Ages, Petrogenesis and Tectonic Implications

Abstract: The Paleoproterozoic Lüliang Metamorphic Complex (PLMC) is situated in the middle segment of the western margin of the Trans-North China Orogen (TNCO), North China Craton (NCC). As the most important lithological assemblages in the southern part of the PLMC, Guandishan granitoids consist of early gneissic tonalities, granodiorites and gneissic monzogranites, and younger gneissic to massive monzogranites. Petrochemical features reveal that the early gneissic tonalities and granodiorites belong to the medium-K calc-alkaline series; the early gneissic monzogranites are transitional from high-K calc-alkaline to the shoshonite series; the younger gneissic to massive monzogranites belong to the high-k calc-alkaline series, and all rocks are characterized by right-declined REE patterns and negative Nb, Ta, Sr, P, and Ti anomalies in the primitive mantle normalized spidergrams. SHRIMP zircon U–Pb isotopic dating reveals that the early gneissic tonalities and granodiorites formed at ~2.17 Ga, the early gneissic monzogranites at ~2.06 Ga, and the younger gneissic to massive monzogranites at ~1.84 Ga. Sm–Nd isotopic data show that the early gneissic tonalities and granodiorites have εNd(t) values of +0.48 to ?3.19 with Nd-depleted mantle model ages (TDM) of 2.76–2.47 Ga, and early gneissic monzogranites have εNd(t) values of ?0.53 to ?2.51 with TDM of 2.61–2.43 Ga, and the younger gneissic monzogranites have εNd(t) values of ?6.41 to ?2.78 with a TDM of 2.69–2.52 Ga.These geochemical and isotopic data indicate that the early gneissic tonalities, granodiorites, and monzogranites were derived from the partial melting of metamorphosed basaltic and pelitic rocks, respectively, in a continental arc setting. The younger gneissic to massive monzogranites were derived by partial melting of metamorphosed greywackes within the continental crust. Combined with previously regional data, we suggest that the Paleoproterozoic granitoid magmatism in the Guandishan granitoids of the PLMC may provide the best geological signature for the complete spectrum of Paleoproterozoic geodynamic processes in the Trans-North China Orogen from oceanic subduction, through collisional orogenesis, to post-orogenic extension and uplift.     

Alkaline Intrusives at the East Foot of the Taihang-Da Hinggan Mountains: Chronology, Sr, Nd and Pb Isotopic Characteristics and Their Implications

Based on the Rb-Sr isochron dating results, this paper suggests that the alkaline intrusive belt at the east foot of the Taihang-Da Hinggan Mountains were formed between 135 and 122 Ma. And the alkaline intrusives in the north and south sections of this belt have entirely different Sr, Nd and Pb isotopic characteristics, i.e., all the rocks in the south section have positive εSr(t) and negative εNd(t) values and all those in the north have the opposite values. On the εSr(t) versus εNd(t) correlation diagram, the samples from the south are concentrated along the enriched mantle evolution trend lines and nearby, while those from the north fall along the depleted mantle trend lines and nearby. On the Pb isotope composition diagram, most of the samples from the south section fall on the mantle Pb evolution line and nearby, while those from the north lie between the Pb evolution lines of the mantle and the erogenic belt. The above-stated isotopic characteristics not only indicate that the source rocks of     

东蒙地区燕山期花岗岩Nd、Sr、Pb同位素及其岩石成因

由于缺乏系统的同位素分析研究工作，过去对东蒙地区燕山期岩浆岩的成因探讨，主要集中在大量岩石地球化学方面的分析研究，因此，其成因观点和岩浆起源的认识也各持己见，主要有3种认识：1)本区中生代壳源和幔源共生的“双模式”观点，认为锡多金属成矿与这种“双模式”的岩浆岩有成因联系；2)中生代花岗岩属于引张环境下，地幔上隆所引发的亚碱性一碱性非造山岩浆作用的产物；3)中生代岩浆岩是中生代大陆内部伸展造山环境下底侵作用形成的一套壳幔混熔岩浆的产物。总之，研究者多认为燕山期岩浆岩具有壳幔混合起源的特征。笔者对燕山期花岗质岩石的钕、锶、铅同位素进行了分析研究。其εNd(t)全为正值，变化范围为 0．75～ 8．12，平均值为 3．07，说明该区燕山期花岗岩的物质来源与亏损地幔有成因联系。其初始锶比值比较集中，变化于0．7028～0.7096，平均为0．7063，介于现代大洋玄武岩(0．702～0．706)和大陆地壳(0．706～0．718)之间，更接近大洋玄武岩。该区燕山期花岗岩的初始铅同位素的3个比值^206Pb/^204Pb、^207Pb／^204Pb、^308b／^204Pb都较高，平均值分别为18．3742，15．5500，38．1810。由钾长石的铅同位素比值计算出来的μ值介于9．51～8．91之间，低于μ=9．74的陆壳演化线。结合邻区兴蒙—北疆一带的岩浆岩同位素研究成果，笔者认为东蒙地区的燕山期花岗岩岩浆起源于亏损地幔的部分熔融作用和亏损地幔起源的晚华力西期古蒙古洋壳的部分熔融作用，即燕山期花岗岩浆最终起源于亏损地幔。并且提出了亏损地幔—古蒙古洋壳—边缘陆块活化的演化模式。     

Pegmatite Emplacement in the Seridó Belt, Northeastern Brazil: Late Stage Kinematics of the Brasiliano Orogen

Geometric and kinematic analysis was performed in an area located in the central part of the Seridó Belt (NE Brazil), where supracrustal rocks affected by polyphase deformation are well exposed. The first event recognized in this area (and regionally known as the D₂ deformation) is characterized by top to the south thrust tectonics while a second one (D₃ deformation) is marked by upright folds, strike-slip or transpressive shear zones and the development of flower structures. Major pegmatite swarms were emplaced during and late as regards the second event (dated ca. 580 Ma), being part of the Brasiliano orogeny; similar dyke swarms are known from the Nigerian Shield. These pegmatite swarms provide reliable kinematic markers of the late evolutionary stage of the Neoproterozoic Trans-Sahara-Borborema collisional belt. Mineralogical, geometric and kinematic features support two stages of pegmatite emplacement during the strike-slip event: (i) older, syn-D₃ homogeneous pegmatites intruded mostly along lithological and structural discontinuities, such as foliation surfaces; (ii) late, D₃ heterogeneous pegmatites were emplaced along tension gashes and other dilation structures. The heterogeneous pegmatites are economically more important, being exploited for precious metals and stones, as well as industrial minerals.     

Tectonic significance of Late Neoproterozoic granites from the Tibesti massif in southern Libya inferred from Sr and Nd isotopes and U–Pb zircon data

The Neoproterozoic crust of the Tibesti massif was stabilized by magmatism that included subduction-generated batholithic suites and post-orogenic granite plutons. All of the magmatism occurred in a period of about 20 million years centered around 550 Ma, and nearly all of the granites have initial ⁸⁷Sr/⁸⁶Sr ratios of about 0.706. The Wadi Yebigue pluton has U–Pb zircon ages of 563 Ma and 558 Ma on two different phases and ε_Nd at 550 Ma from −0.5 to −2.2. These isotopic data and the geologic history of the massif suggest that granites in the Tibesti massif developed during and shortly after closure of a short-lived ocean basin that developed by fragmentation of pre-existing continental crust of the Saharan region.     

Nd and Sr isotopic compositions of sediments from the Yellow and Yangtze Rivers: Implications for partitioning tectonic terranes and crust weathering of the Central and Southeast China

New Nd and Sr isotope data are presented in this paper for sediments from the Yellow and Yangtze River drainage basins. The average ¹⁴³Nd/¹⁴⁴Nd isotope compositions of fine-grained sediments from two drainage basins seem similar. The T _DM^Nd ages of sediments from the two drainage basins are relatively uniform but exhibit subtle differences. This reflects the different underlying bedrocks, in association with the unique tectonic terranes that comprise central and southeastern China, including the North China Block, the Yangtze Block, the South China Block, the Tibet Plateau and the Qinling-Dabie Orogenic Belt. In contrast, there is an obvious difference in the ⁸⁷Sr/⁸⁶Sr ratios between fine-grained sediments of the Yellow and Yangtze Rivers, which actually reflects an increase in chemical weathering intensity from northwestern to southeastern China.     

距今7Ma以来甘肃灵台剖面 Nd和 Sr同位素特征

测定了 7 Ma B.P.以来灵台剖面红粘土和黄土-古土壤序列的酸不溶物 Sr和 Nd同位素组成.样品酸不溶物 87Sr/86Sr变化可明显分为两个阶段.第一个阶段,从 7 Ma B.P.到 2.5 Ma B.P.,为红粘土层,酸不溶物 87Sr/86Sr稳定位于高值,反映了东亚冬季风处于相对平稳的弱势.第二个阶段,从 2.5 Ma B.P.到现在,酸不溶物 87Sr/86Sr呈下降趋势,波动加强,反映了东亚冬季风不断增强,并且冬季风和夏季风交替变化加强. 7 Ma B.P.以来灵台剖面红粘土和上覆的黄土-古土壤的 Nd同位素组成一致,并揭示 7 Ma B.P.以来,北太平洋中部沉积物与黄土高原黄土都来自相同的物源区.     

峨眉山玄武岩Sr、Nd、Pb同位素特征及其物源探讨

选择峨眉山玄武岩区2个出露最全的云南永胜大迪里剖面和宾川上仓剖面进行了Sr、Nd、Pb同位素地球化学研究.结果表明, 少数样品的Pb同位素与Hanan和Graham定义的C组分相似, 而大多数样品则不在C组分范围之内, 说明除地幔柱物质外, 有岩石圈物质的加入.在多元同位素图解上, 峨眉山玄武岩位于EMⅠ、EMⅡ和DMM三端元之间, 表明其源区可以由地幔柱、富集的岩石圈地幔和地壳不同程度的混合来解释.结合已有的微量元素资料分析, 其中的地壳组分主要为下地壳, 而早期玄武质岩浆在上升过程中由于通道不畅通, 有较多的上地壳组分的混染.岩石圈地幔的富集作用可能与地幔柱释放出的小体积富Na、P而贫K的流体交代作用有关.粗面岩的同位素组成和玄武岩接近, 说明粗面岩是玄武质岩浆分离结晶作用形成的.      

Tonian rift-related, A-type continental plutonism in the Araçuaí Orogen, eastern Brazil: New evidence for the breakup stage of the São Francisco–Congo Paleocontinent

Zircon U–Pb SHRIMP, petrographical and geochemical data lead to the first characterization of the Tonian plutonism (Salto da Divisa Granite Suite), ascribed to the continental rift stage of the precursor basin of the Araçuaí Orogen (Eastern Brazil). The suite includes batholitic plutons and comprises mainly fluorite-bearing, dominantly mesoperthitic hornblende–biotite leucogranites. The presence of mafic (tholeiitic) gabbroic enclaves and syn-plutonic dykes confers to the suite a bimodal character. The plutons were locally deformed and foliated under amphibolite facies conditions, in response to the Neoproterozoic collage of the Araçuaí Orogen against the São Francisco Cratonic margin. However, undeformed magmatic facies are well preserved at inner portions of the plutons. The granitoids are metaluminous, with high SiO₂ and HFSE: Nb, Zr, Y, Ta and REE (except Eu); low CaO, Al₂O₃, Sc, Ba, Sr; high FeOt/MgO ratios, characterizing a chemical signature akin to the subalkaline, A-2 type granites. U–Pb SHRIMP data obtained on zircons from the main pluton yielded a magmatic crystallization age of 875 ± 9 Ma. Some inherited xenocrysts revealed ages of ca. 2080 Ma, corresponding to ages of the host rocks, a Paleoproterozoic basement. Nd isotopic evolution studies confirm the Paleoproterozoic influence on magma genesis with a T_DM model age of ca. 1.6 Ga and ε_Nd of − 5.58 at 880 Ma. The African counterpart, the West Congo Belt, encompasses thick rift-related alkaline volcanic-sedimentary basin (Zadinian and Mayumbian groups, and associated anorogenic granites), dated in the interval of ca. 1000–900 Ma. The age differences between the Salto da Divisa Suite intrusion and the anorogenic magmatic episode at the West Congo Belt suggests a westward migration (i.e. to the Brazilian side) of the thermal axis of the rift, ca. 30 Ma after the ending of the extensional process in Africa.     

河北矾山钾质碱性超镁铁岩—正长岩杂岩体Sm—Nd年龄和Sr、Nd同位素特征

河北矾山侵入杂岩,由层状钾质超镁铁岩--正长岩组成,已知它含有大型磁铁矿磷灰石矿床.现在已测定了岩体的岩石和矿物的Sm-Nd同位素资料,并获得了杂岩体的Sm-Nd同位素年龄.4个矿物样品和2个全岩样品Sm-Nd等时线年龄为243.4±9.7Ma,INd=0.512045,εNd(t)=-5.4;4个矿物样品和7个全岩样品等时线年龄为239±19Ma,INd=0.512055,εNd(t)=-5.3.这些年龄资料表明,矾山岩体可能侵位于早三叠.而矾山岩体的Rb-Sr等时线年龄为218±8Ma,Isr=0.70554,εsr=18.4的事实可能暗示矾山岩体在中三叠才完全固结并达到Rb-Sr体系封闭的温度.上述矾山岩体的Sr、Nd同位素特征表明,矾山岩体的物质源自富集的上地幔.     

Sr and Nd isotope data from the fluorspar district of Asturias, northern Spain

The origin and age of the hydrothermal fluids related to the precipitation of fluorite, barite and calcite in the Villabona, La Collada and Berbes localities (Asturias fluorspar district, N Spain) have been evaluated from Sr and Nd radiogenic isotopes. Sr isotope data (⁸⁷Sr / ⁸⁶Sr = 0.7081 to 0.7096) are compatible with mixing between seawater and a more evolved groundwater that interacted with the basement. From Nd isotopes in fluorite, an isochron age of 185 ± 29 Ma (Lower Jurassic) was obtained, consistent with other hydrothermal events in the Iberian Peninsula and Europe. These constraints are essential to proceed with a quantitative model for the genesis of the mineralization that includes fluid and heat flow together with reactive transport of solutes.     

Trace Elements and Sr, Nd Isotope Geochemistry of the Lajimiao Norite-Gabbro from the North Qinling Belt

The Lajimiao norite-gabbro complex, as a part of the ophiolites on the southern side of the North Qinling belt, consists of gabbro and norite-gabbro. They were derived from different magma series: the gabbro was derived from tholeiitic magma series with higher TiO2, REE abundance and Fe3+/Fe2+ ratio ; norite-gabbro was derived from calc-alkali magma series with lower TiO2, Fe3+/Fe2+ ratio and REE abundance and much lower HREE abundance, which suggests that the source of the norite-gabbro magma was deeper and controlled by eclogite facies. Geochemical characteristics of both plutonic rocks are similar to those of island-arc basalts, such as relatively high contents of Ba, Pb and Sr and relatively low contents of Nb, Zr and N j.The Sr, Nd isotopic characteristics of the Lajimiao norite-gabbro complex are similar to those of ophiolites. Its εNd values are constant, about+2; whereas εst values have wide variation from - 6.4 to +31.2 and positively correlate with Na2O, H2O+ and CO2 contents and the Fe3+/Fe     

Geochronology,Geochemistry, Whole Rock Sr‐Nd and Zircon Hf‐O Isotopes of the Early Neoproterozoic Volcanic Rocks in Jiangshan,Eastern Part of the Jiangnan Orogen: Constraints on Petrogenesis and Tectonic Implications

This paper presents the results of combined studies of geochronology, geochemistry, whole rock Sr-Nd and zircon Hf-O isotopes carried out upon the rhyodacite and ignimbrite of Shangshu village, Shangyu town and Shanghupeng village of Jiangshan City in Zhejiang Province, along the northwestern side of the Jiangshan–Shaoxing suture. SHRIMP zircon U-Pb dating of samples in the three areas yielded weighted mean 206 Pb/238 U ages of 842.8 ± 6.9 Ma and 850.0 ± 7.3 Ma, 839 ± 9 Ma and 832.2 ± 8.1 Ma, 82...     

张家口水泉沟正长岩杂岩体成因的REE和Sr、Nd、Pb同位素证据

水泉沟杂岩体位于尚义 赤城断裂的南侧,侵位于太古宙桑干群变质岩中。岩体形成于晚加里东至早海两期。其稀土元素含量为8.543×10~(-6)～211.6×10~(-6),随着岩石的CaO、MgO、FeO、Fe_2O_3含量降低,SiO_2、K_2O、Na_2O含量增大,稀土含量减小,稀土分布模式由右倾直线型变为近平直的“～”型。在铅同位素构造模式图上杂岩体落在地幔铅同位素演化线附近。在ε_(Nd)-ε-(Sr)图解上处于地幔演化线的下方。杂岩体的钕模式年龄低于围岩桑干群的形成年龄。岩体可能来源干上地幔与下地壳太古宙变质杂岩混熔作用所形成的正长岩岩浆。     

Mantle diversity beneath the Colombian Andes, Northern Volcanic Zone: Constraints from Sr and Nd isotopes

In order to provide mantle and crustal constraints during the evolution of the Colombian Andes, Sr and Nd isotopic studies were performed in xenoliths from the Mercaderes region, Northern Volcanic Zone, Colombia. Xenoliths are found in the Granatifera Tuff, a deposit of Cenozoic age, in which mantle- and crustal-derived xenoliths are present in bombs and fragments of andesites and lamprophyres compositions. Garnet-bearing xenoliths are the most abundant mantle-derived rocks, but websterites (garnet-free xenoliths) and spinel-bearing peridotites are also present in minor amounts. Amphibolites, pyroxenites, granulites, and gneisses represent the lower crustal xenolith assemblage. Isotopic signatures for the mantle xenoliths, together with field, petrographic, mineral, and whole-rock chemistry and pressure–temperature estimates, suggest three main sources for these mantle xenoliths: garnet-free websterite xenoliths derived from a source region with low P and T (16 kbar, 1065 °C) and MORB isotopic signature, ⁸⁷Sr/⁸⁶Sr ratio of 0.7030, and ¹⁴³Nd/¹⁴⁴Nd ratio of 0.5129. Garnet-bearing peridotite and websterite xenoliths derived from two different sources in the mantle: i) a source with intermediate P and T (29–35 kbar, 1250–1295 °C) conditions, similar to that of sub-oceanic geotherm, with an OIB isotopic signature (⁸⁷Sr/⁸⁶Sr ratio of 0.7043 and ¹⁴³Nd/¹⁴⁴Nd ratio of 0.5129); and ii) another source with P and T conditions similar to those of a sub-continental geotherm (>38 kbar, 1140–1175 °C) and OIB isotopic characteristics (⁸⁷Sr/⁸⁶Sr ratio=0.7041 and ¹⁴³Nd/¹⁴⁴Nd ratio=0.5135).     

Metallogenic Province Derived from Mantle Sources: Nd, Sr, S and Pb Isotope Evidence from the Central Asian Orogenic Belt

The Central Asian Orogenic Belt (CAOB) is one of the most important regions for Cu, Au and polymetallic and rare metallic (Li, Be, Nb, Ta) mineralization over the world. Most of the ore deposits in the CAOB are closely associated with granitoids. Available Sr, Nd, S and Pb isotopic data indicate that the metallogenic epoch and sources of the mineral deposits in the CAOB are consistent with that of the regional granites. Available data suggest that mantle sources could have played an important role in the Paleozoic to Mesozoic mineralization in the CAOB.