Genesis of LCT Pegmatites during Early Paleozoic Orogeny of the North Qinling Orogenic Belt,China:Emplacement Conditions and Structural Control

The Guanpo pegmatite field in the North Qinling orogenic belt(NQB),China,hosts the most abundant LCT pegmatites.However,their emplacement conditions and structural control remain unexplored.In this contribution,we investigated it combining pegmatite orientation measurement with oxygen isotope geothermometry and fluid inclusion study.The orientations of type A1 pegmatites(P_(f)<σ_(2))are predominantly influenced by P-and T-fractures due to simple shearing in Shiziping dextral thrust shear zone during D_(2)deformation,whereas type A2 pegmatites(contemporaneous with D_(4))are governed by hydraulic fractures aligned with S_(0)and S_(0+1)stemming from fluid pressure(P_(f)<σ_(2)).Additionally,type B pegmatites(P_(f)≤σ_(2))exhibit orientations shaped by en echelon extensional fractures in local ductile shear zones(contemporaneous with D_(3)).The albite-quartz oxygen isotope geothermometry and microthermometric analysis of fluid inclusions in elbaites from the latest pegmatites(including types B and A2)suggest that the crystallization P-T for late magmatic and hydrothermal stages are 527.5-559.2℃,320℃,3.1-3.6 kbar and 2.0 kbar,respectively.Our observations along with previous studies suggest that the genesis of the LCT pegmatites was a long-term,multi-stage event during early Paleozoic orogeny(including the collision stage)of the NQB,and was facilitated by various local fractures.

Geochronology,Petrogenesis and Tectonic Setting of the Late Jurassic I-type Granites in the North Qinling Orogenic Belt,Central China

The North Qinling Orogenic Belt(NQOB)is a composite orogenic belt in central China.It started evolving during the Meso-Neoproterozoic period and underwent multiple stages of plate subduction and collision before entering intra-continental orogeny in the Late Triassic.The Meso-Cenozoic intra-continental orogeny and tectonic evolution had different responses in various terranes of the belt,with the tectonic evolution of the middle part of the belt being particularly controversial.The granites distributed in the Dayu and Kuyu areas in the middle part of the NQOB can provide an important window for revealing the geodynamic mechanisms of the NQOB.The main lithology of Dayu and Kuyu granites is biotite monzogranite,and the zircon U-Pb dating yielded intrusive ages of 151.3±3.4 Ma and 147.7±1.5 Ma,respectively.The dates suggest that the biotite monzogranite were formed at the end of the Late Jurassic.The whole-rock geochemistry analysis shows that the granites in the study areas are characterized by slightly high SiO_(2)(64.50-68.88 wt%)and high Al_(2)O_(3)(15.12-16.24 wt%)and Na_(2)O(3.55-3.80 wt%)contents.They are also enriched in light rare earth elements,large ion lithophile elements(e.g.,Ba,K,La,Pb and Sr),and depleted in high field strength elements(HFSEs)(e.g.,Ta,Nb,P and Ti).Additionally,the granites have weakly negative-slightly positive Eu anomalies(δEu=0.91-1.19).Zircon Lu-Hf isotopic analysis showedε_(Hf)(t)=-6.1--3.8,and the two-stage model age is T_(2DM(crust))=1.5-1.6 Ga.The granites in the study areas are analyzed as weak peraluminous high-K calc-alkaline I-type granites.They formed by partial melting of the thickened ancient lower crust,accompanied by the addition of minor mantle-derived materials.During magma ascent,they experienced fractional crystallization,with residual garnet and amphibole for a certain proportion in the magma source region.Comprehensive the geotectonic data suggest that the end of the Late Jurassic granite magmatism in the Dayu and Kuyu areas represents a compression-extension transition regime.It may have been a response to multiple tectonic mechanisms,such as the late Mesozoic intra-continental southward subduction of the North China Craton and the remote effect of the Paleo-Pacific Plate subduction.

Metamorphism of the East Sector of the Southern Qinling Orogenic Belt and Its Geological Significance

The east sector of the southern Qinling belt is, lithologically, composed mainly of metapelites, ***qüartzites, marbles and small amount of metabasites and gneisses, whose protoliths are the Silurian, Devonian and less commonly the Sinian and Upper Palaeozoic. They have been subjected at least to two epochs of metamorphism. The early epoch belongs to progressive metamorphism which is centered on high amphibolite-granulite fades in the Fuping area and changed outwards into low amphibolite facies (staurolite-kyanite zone), epidote amphibolite facies (garnet zone) and greenschist facies (chlorite and biotite zones), the metamorphic age of which is about 220–260 Ma. This early-epoch metamorphism belongs to different pressure types: the rocks from greenschist to low amphibolite facies belong to the typical medium-pressure type which shows geothermal gradients of about 17–20 ***C/km and was probably produced by a crustal thickening process related to continental collision, and the high amphibolite-granulite facies belongs to the low-pressure type which shows geothermal gradients of about 25–38 ***C/km and was probably affected by some magmatic heats. Based on the basic characteristics of the P-T paths of the different facies calculated from the garnet zonations, it can be deduced that the metamorphism of medium-pressure facies series took place during an imbricated thickening process, rather than during the uplifting process after thickening. The late-epoch metamorphism belongs to dynamic metamorphism of greenschist facies which is overprinted on the early-epoch metamorphic rocks and is Yanshanian or Himalayan in age, probably related to intracontinental orogeny.

Structural Geology and Chronology of Shear Zones along the Shangdan Suture in Qinling Orogenic Belt,China:Implications for Late Mesozoic Intra-Continental Deformation of East Asia

The Shangdan suture zone(SDZ)in the Qinling orogenic belt(QOB)is a key to understanding the East Asia tectonic evolution.The SDZ gives information about convergent processes between the North China Block(NCB)and South China Block(SCB).In the Late Mesozoic,several shear zones evolved along the SDZ boundary that helps us comprehend the collisional deformation between the NCB and SCB,which was neglected in previous studies.These shear zones play an essential role in the tectonic evolution of the East Asia continents.This study focuses on the deformation and geochronology of two shear zones distributed along the SDZ,identified in the Shaliangzi and Maanqiao areas.The shear sense indicators and kinematic vorticity numbers(0.54–0.90)suggest these shear zones have sinistral shear and sub-simple shear deformation kinematics.The quartz’s dynamic recrystallization and c-axis fabric analysis in the Maanqiao shear zone(MSZ)revealed that the MSZ experienced deformation under green-schist facies conditions at∼400–500℃.The Shaliangzi shear zone deformed under amphibolite facies at∼500–700℃.The^(40)Ar/^(39)Ar(muscovite-biotite)dating of samples provided a plateau age of 121–123 Ma.Together with previously published data,our results concluded that QOB was dominated by compressional tectonics during the Late Early Cretaceous.Moreover,we suggested that the Siberian Block moved back to the south and Lhasa-Qiantang-Indochina Block to the north,which promoted intra-continental compressional tectonics.

Zircon U-Pb ages and Hf isotopic characteristics of the Dehe biotite monzonitic gneiss pluton in the North Qinling orogen and their geological significance

The Dehe granitic pluton intruded the Xiahe Group which is in the core complex of the North Qinling Orogenic Belt(NQOB).It shows gneissic bedding and possesses typical S-type granite minerals such as muscovite and garnet.LA-ICP-MS U-Pb isotopic dating of the Dehe granite yielded a weighted average age of 925±23 Ma which represents the emplacement age of the pluton.Most of the εHf(t) values are negative,and the two-stage model ages are consistent with the age of the Qinling Group.The isotope data show that the Dehe granite was formed in the following geological setting:in the syn-collision setting of the NQOB in the Neoproterozoic,crustal thickening induced partial melting of materials derived from the Qinling complex,and then the maga upwelled and intruded into the Xiahe Group.The formation of the Dehe S-type granite implied the occurrence of a convergent event in the QOB during the Neoproterozoic.

New Zircon U-Pb Ages of the Shirenshan Gneiss, North Qinling and Their Geological Implications

The Qinling Orogenic Belt(QOB)is a composite continental orogenic belt that has experienced many tectonic events.The QOB is subdivided into the following three litho-tectonic units:the North Qinling terrane,the Middle Qinling microplate and the South Qinling terrane.The North Qinling Terrane(NQT)underwent destruction and lithospheric thinning during the late Mesozoic,accompanied by extensive magmatic activity and increased surface heat flux,led to large-scale tectonic extension(e.g.,Ren Shenglian et al.,2016).The Shirenshan gneiss is located along the contact between the NQT and the North China Block(Fig.1).Previous studies suggested that it was produced as a result of the northward subduction of the NQT beneath the North China Block(e.g.,Wang Jingya et al.,2017).Therefore,it is significant to study its structural geology,petrology,geochemistry and chronology in order to understand the tectonic settings and the interaction between the Middle Qinling microplate and the North China Block.

中条山地区二叠系含煤岩系碎屑锆石年龄及其对区域构造活动的沉积学制约

【目的】沉积盆地中碎屑沉积物的物质组成变化与源区的隆升剥蚀过程紧密相关。华北克拉通南缘作为中国大陆的主要构造单元,拥有二叠纪较为完整的地质记录,中条山地区位于华北克拉通南部汾渭地堑系核心部位,物源主要指向华北克拉通南缘及相邻的秦岭造山带,是研究二叠纪时期秦岭造山带及相邻地区构造演化过程的理想场所。【方法】通过对华北克拉通南缘中条山地区米汤沟剖面二叠系山西组潮坪-潟湖相含煤岩系及其上覆下石盒子组冲积扇-河流相沉积碎屑锆石U-Pb年代学分析,系统开展沉积物源对比示踪,综合讨论了沉积物源与源区构造作用的相互耦合关系。【结果和结论】结果表明:二叠系山西组潮坪-潟湖相含煤岩系碎屑锆石年龄序列具有297、327、443、921、969、1 826、1 990、2 272、2 443 Ma 9个主要峰值;下石盒子组冲积扇-河流相沉积碎屑锆石年龄序列具有305、1 755、1 882、2 284、2 490 Ma 5个峰值,缺少新元古代和早古生代的碎屑锆石年代记录。分析认为二叠系山西组含煤岩系物源主要来自于北秦岭-华北克拉通南缘构造带,下石盒子组沉积物源仅来自于华北克拉通南缘构造带。二者的沉积物源差异响应了早中二叠世华北板块与秦岭-大别板块的相互作用过程,显示构造活动自南向北逐渐迁移。早二叠世早中期,华北南缘整体隆升幅度较低,北秦岭构造带的物源能够进入中条山地区;早二叠世晚期至中二叠世早期,由于华北克拉通南缘的快速抬升,隆升幅度较大,阻隔了南部的北秦岭物源,导致中条山地区不再接受北秦岭的物源供给。研究成果从沉积学角度为华北克拉通南缘及相邻秦岭造山带在二叠纪时期的构造活动过程提供了新的佐证。

北秦岭东段二郎坪单元辉长岩成因及其构造意义:来自锆石U-Pb年代学、地球化学和Sr-Nd-Hf同位素的制约

北秦岭造山带二郎坪单元的形成时代与构造属性一直是争论的焦点,解决此问题的关键在于精确约束与俯冲相关的岩浆作用的时限和性质。本文对北秦岭东段二郎坪单元辉长岩开展了岩相学、锆石U-Pb年代学、全岩主微量元素地球化学和Sr-Nd-Hf同位素分析研究。地球化学特征表明,二郎坪单元辉长岩具有较低的w(SiO_(2))(49.61%~50.58%),表现出富Na贫K的特征(Na_(2)O/K 2O=8.44~14.09);稀土配分型式呈右倾型,相对富集大离子亲石元素(LILEs)、亏损高场强元素(HFSEs),具有Nb、Ta、Zr、Hf的负异常,Sr-Nd同位素组成略微富集,显示出岛弧岩浆岩的特征,具有CAB的性质,其原始岩浆来源于含角闪石的石榴子石相地幔源区的部分熔融,形成于岛弧环境,岩浆源区经历了俯冲流体的交代。利用锆石SIMS U-Pb定年手段获得二郎坪单元辉长岩加权平均年龄为(464±2.9)Ma,限定其成岩时代属中奥陶世。结合区域地质资料和前人研究成果,认为二郎坪单元辉长岩是宽坪洋向北秦岭微陆块下南向俯冲的产物,但不排除商丹洋向北秦岭微陆块下北向俯冲带来的影响。

华北板块南缘洛南地区二叠系石盒子组沉积物源特征及其隆升过程

华北板块南缘的隆升过程对认识秦岭造山带与华北盆地盆山相互作用具有重要意义。文中以华北板块南缘洛南地区二叠系石盒子组为研究对象,在沉积相及其演化分析的基础上,开展碎屑锆石U-Pb年代学及裂变径迹年代学研究,探讨华北板块南缘二叠系石盒子组沉积物源特征及其隆升过程,期望为勉略洋盆的俯冲时限提供沉积学约束,为华北盆地南部三叠系再旋回沉积物提供可能的物源区。研究结果显示,华北板块南缘二叠系石盒子组经历了冲积扇→辫状河→三角洲的沉积演化过程。石盒子组下部碎屑锆石样品形成了3组U-Pb年龄,分别为353—280 Ma、1139—400 Ma和2620—1306 Ma,裂变径迹年龄分解为199 Ma、255 Ma和408 Ma共3个峰值;而上部样品主要形成2组U-Pb年龄,分别为339—259 Ma和2655—1700 Ma,裂变径迹年龄分解为205 Ma、268 Ma和656 Ma共3个峰值。上述测试结果表明华北板块南缘在石盒子组沉积早期还接受来自秦岭造山带的碎屑物,但在石盒子组沉积后期沉积物主要来自于华北板块北缘,完成了由“南高北低”向“北高南低”的构造转换。推测华北板块南缘的初始隆升发生在中—晚二叠世,这次隆升与勉略洋盆的初始俯冲作用相关,并成为华北盆地南部三叠系的一个潜在物源区。

～4.1 Ga xenocrystal zircon from Ordovician volcanic rocks in western part of North Qinling Orogenic Belt

High-precision U-Pb dating by in situ LA-ICP-MS yields an age of 4079±5 Ma for a xenocrystal zircon from Ordovician volcanics of the Caotangou Group in western part of the North Qinling Orogenic Belt. As a result, the North Qinling Orogenic Belt becomes one of a few localities in the world that contain Hadean age records (4276±6 Ma and 4404±8 Ma detrital zircons from Jack Hill of the Yilgarn craton, 4016 Ma Acasta gneisses of the Wopmay Orogeny and Burang quartzite with detrital zircon of 4103 Ma in Tibet). It is also the first report of the Hadean age in Phanerozoic volcanics. The finding of the 4.1 Ga xenocrystal zircon provides not only the geochronological record of the oldest crustal materials in China, but also the condition for further search for rocks forming in the region during the early time of the Earth’s evolution. Thirty-six zircon U-Pb dates from the Ordovician volcanic rocks are subgrouped into seven generations that represent different tectono-magmatic events in the North Qinling Orogenic Belt. Among them, two periods of 0.9-1.5 Ga and 0.4-0.5 Ga are consistent with Mesoproterozoic and Early Paleozoic orogenies, respectively.

北秦岭饭铺闪长岩的岩石成因及其构造意义

饭铺闪长岩的岩石成因模型可为深入认识北秦岭古生代中性岩浆作用的活动规律及深部过程提供进一步的限定。饭铺岩体两件样品的锆石U-Pb同位素年龄值分别为422.1±5.5 Ma和424.2±5.2 Ma,表明其形成于晚志留世。其锆石的^(176)Hf/^(177)Hf比值介于0.282560~0.282676,ε_(Hf)(t)值介于-8.48~14.45,T_(DM2)为1938~488 Ma。地球化学分析结果显示,饭铺岩体属钙碱性系列,均具有富硅、碱、钙和镁,Mg^(#)值介于41.7~57.4。在微量元素蛛网图中,饭铺岩体具有Nb、Ta、Ti异常。饭铺岩体的稀土总量为117×10^(-6)~171×10^(-6),(La/Yb)_(N)比值范围是6.71~18.1,δEu值介于0.82~0.95,表现为轻稀土元素富集、重稀土元素亏损的配分特征,未显示明显的负Eu异常。饭铺岩体形成于岛弧构造环境,岩浆起源于下地壳,可能受到少量幔源物质的混合,推测是商丹洋向北深俯冲作用的产物。

北秦岭东段晶质石墨矿床地质特征及成因探讨

北秦岭东段石墨矿是近年来陕西省新发现的大中型优质大鳞片晶质石墨矿床矿产地。矿体赋存于秦岭岩群雁岭沟岩组地层中,具有明显的层位特征。含矿岩石以石墨大理岩、石墨片麻岩、石墨石英片岩为主,石墨矿物呈浸染状集合体产出,鳞片片径大多大于0.147 mm,以正目石墨为主。本文通过变质岩原岩恢复、石墨碳质来源、成岩成矿环境等角度,对研究区晶质石墨矿矿床成因进行探讨,认为研究区δ^(13)C具有中间碳同位素特征,为有机物在还原环境下分解不彻底造成,其碳质来源于元古代沉积的含碳有机质。石墨矿品位及其分布主要与沉积相有关,推测晶质石墨由浅海相沉积的碎屑岩-钙泥质岩-碳酸盐岩中的有机碳在区域变质作用下变质形成。北秦岭东段晶质石墨矿为沉积变质成因。

The Paleozoic Huoshenmiao iron skarn deposit in the Tongbai area of North Qinling Orogen,China:Insights from garnet U-Pb dating and geological constraints

The Qinling Orogen is a composite orogenic belt that can be subdivided into the North and South Qinling,broadly separated by the Shangdan suture zone.These two orogenic belts were generated by subduction-collisional processes in the Early Paleozoic and Late Triassic,respectively.During the Late Jurassic to Early Cretaceous,the eastern portion of the Qinling Orogen was tectonically reactivated due to westerly subduction of the Izanagi plate underneath the East China continental margin.The Qinling Orogen is well-endowed with numerous Au,Mo,Ag-Pb-Zn deposits that predominantly formed in the Late Triassic to Early Cretaceous,with rare Paleozoic varieties documented.In this study,we present garnet and zircon U-Pb dating results to show that the Huoshenmiao iron skarn deposit in the Tongbai area of North Qinling orogenic belt formed in the Early Silurian and is genetically related to subduction-related magmatism.The Huoshenmiao deposit consists of lenticular and stratiform orebodies that contain massive or densely disseminated magnetite variably associated with garnet,diopside,epidote,hornblende,and actinolite.Garnets from iron ores are andradite and grossular in composition(Ad_(83.1)Gr_(13.3)-Ad_(86.5)Gr_(10.2))and characterized by enrichment in light rare earth elements(ΣLREE=57.85-103.82 ppm)and depletion in heavy rare earth elements(ΣHREE=5.50-11.34 ppm),with significantly positive Eu and Ce anomalies(δEu of 1.09-1.89 andδCe of 1.39-1.69).These compositional signatures are distinctly different from those of garnets in the ore-hosting metamorphic rocks that are typically dominated by almandine,spessartine and grossular(Al_(47.4)Sp_(30.4)Gr_(13.8)-Al_(51.9)Sp_(24.8)Gr_(17.6)),depleted in LREE(0.14-0.69 ppm),enriched in HREE(95.68-841.60 ppm)and have pronounced negative Eu anomalies(δEu=0.24-0.51).In addition,garnets from iron ores of the Huoshenmiao deposit contain abundant daughter mineral-bearing,multiphase fluid inclusions,further confirming their hydrothermal origin.Two samples of those hydrothermal garnets yield U-Pb dates of 437±9 Ma and 437±10 Ma(2σ),revealing a Paleozoic mineralization event that has long been ignored and rarely documented.These garnet dates agree well with zircon U-Pb dates of 438±4 Ma to 436±3 Ma for a gabbroic diorite and 430±4 Ma for a granite intrusion in close proximity of the mine,supporting a possible genetic link between the iron mineralization and Early Silurian magmatism.The Paleozoic intrusions are enriched in large ion lithophile elements(LILEs:Ba,K,Sr)and LREEs,depleted in high field strength elements(HFSEs:Nb,Ta,P,Ti),have whole-rock(^(87)Sr/^(86)Sr)i,ε_(Nd)(t),and zirconεHf(t)values of 0.7039-0.7042,3.32-4.33,and 13.0-14.9,respectively.These geochemical and isotopic characteristics suggest that the Paleozoic intrusions were affiliated with arc magmatism triggered by subduction of the Shangdan oceanic plate in the Early Paleozoic.Recognition of the Silurian Huoshenmiao iron skarn deposit opens a new window for exploration of Paleozoic mineral resources in the Tongbai area and other portions of the North Qinling Orogen.

柴北缘-东昆仑地区的造山型金矿床

柴北缘－东昆仑是中国西部秦祁昆褶皱山系的一部分，它的显生宙造山经历了加里东和晚华力西－印支两个旋回，并以多岛洋／裂陷槽、软碰撞和多旋回造山为特点。该区已发现多个造山型金矿床，它们具有相似的地质、地球化学特征。有两组成矿年龄：一是晚加里东期（相当于加里东造山晚期）；二是晚华力西—印支期（处于该造山族回晚期）。前期为发生于中地壳顶部一上地壳底部的金矿化，后期则是形成于较浅层次（１．２～５．７ｋｍ）的金矿体侵位。自区域北部向南部，矿床元素组合由Ａu－Ａｓ向Ａu－Ｓｂ转化，金成矿年龄由老变新，成矿深度相应变浅。研究认为，与碰撞有关的热事件以及逐步升高的地热增温率，驱动被加热的建造水和大气降水流体沿碰撞带和大型剪切带长距离地迁移、活动，并淋取围岩的成矿元素，形成含金流体。在进人到矿床或矿体构造后，由于构造性质转换，物理化学条件亦随之改变，含金流体沉淀，形成金矿体。这些金矿床形成于造山晚期，是造山作用的产物，后者为前者提供了空间、热一动力条件。

北秦岭宽坪岩群的解体及新元古代N-MORB

本文通过LA-ICPMS单颗粒锆石微区U-Pb测年方法研究,确定宽坪岩群中的变基性火山岩形成年龄为943Ma,宽坪岩群中的变质沉积岩原岩形成于小于600Ma。因此,本文提出宽坪岩群从地层学意义上应予废除或解体。即宽坪岩群中变沉积岩与变基性火山岩不属于一个延续的沉积层序,是晚期构造运动将这些形成于不同时代、不同构造环境的岩石单元混杂叠置在一起。宽坪岩群中绿片岩类具有典型N-MORB的特征,属于新元古代一套蛇绿岩残片,代表格林威尔造山期的地质记录。

中央碰撞造山带中两期超高压变质作用来自含柯石英锆石的定年证据

沿中央造山带存在一条巨大的超高压变质带,其西起阿尔金—祁连,往东经秦岭,延至大别—苏鲁,全长超过4000 km。柴北缘片麻岩中含柯石英锫石的SIMS离子探针原位微区U-Pb定年获得超高压变质年龄452±13.8 Ma。锆石的退变质年龄419±6.7 Ma。SHRIMP U-Pb定年获得秦岭含金刚石片麻岩中锆石的下交点年龄502±45 Ma,上交点年龄1545±100 Ma,认为前者代表超高压变质年龄,后者为原岩岩浆锆石年龄;获得榴辉岩锆石的上交点年龄1381±82 Ma和下交点493±170 Ma,认为上交点代表榴辉岩原岩年龄,下交点代表超高压变质年龄;获得江苏东海县青龙山榴辉岩含柯石英等超高压矿物锆石的年龄为441±9 Ma,449±9 Ma,和442±9Ma,平均444±9 Ma,核部含斜长石+磷灰石锆石年龄为761±13 Ma,认为前者代表超高压变质年龄,后者代表榴辉岩原岩结晶年龄。认为中国中部沿中央造山带中存在两期超高压变质作用,第一期为加里东期,第二期为印支期,两期超高压变质事件在时空分布方面是不同的,加里东期超高压变质事件由西部阿尔金—柴北缘延至东部大别—苏鲁,印支期超高压变质事件没有在大别以西发现。认为中央造山带应是一个多期活动的造山带,较早形成罗德尼亚大陆的格林威尔造山运动可能留下了10亿年左右的构造岩浆事件记录。

华北和扬子陆块及秦岭—大别造山带地表和深部太古宙基底的新信息

本文根据华北和扬子陆块及秦岭-大别造山带地表和深部出露的各种岩石中发现的继承性锆石的测年数据,报道了太古宙基底和岩浆事件的新信息,并简要地论述其地质意义。华北陆块东北缘、东南缘、北缘、西北缘共6个地区的深部都存在新太古代和中、古太古代岩浆事件的新信息;南缘深部也存在古太古代岩浆事件的新信息。在华北陆块早前寒武纪同位素年龄直方图(以太古宙岩浆事件为主)上,最高峰值位于2.45-2.6 Ga区间,而以2.5-2.55 Ga最为突出,显示该区间岩浆事件最为强烈,可能代表一次重要的碰撞事件。此外还见有2.7 Ga,2.8 -2.85 Ga,2.95-3.0 Ga,3.1-3.15 Ga,3.3-3.4 Ga,3.45-3.5 Ga,3.6 Ga和3.8 Ga等较高峰值,反映了岩浆事件不同活动阶段的演化趋势。扬子陆块北缘地表和深部有与华北陆块相似的太古宙古老基底信息。扬子陆块中部的长江中下游地区、东南缘相当于江南古陆的地区以及扬子陆块西南缘地区在地壳深部均保留有新太古代和/或古太古代岩浆锆石的年龄信息。秦岭-大别造山带从东到西,多处(主要是深部)也发现有新-中太古代残余岩浆锆石的年龄信息。

华北克拉通及相邻造山带古生代—侏罗纪早期大地构造演化

华北克拉通古生代的大地构造演化始于大约520 Ma,此时冈瓦纳古陆的聚合正处于峰期。中寒武世华北克拉通古生代最早的沉积记录始于其边缘的更老地层或者变质基底之上。随后,海相环境扩展,广泛的海侵导致中寒武世晚期馒头组及其上的地层广泛分布于华北克拉通。华北克拉通北部以北的白乃庙岛弧带新的研究结果显示这一岛弧始于520 Ma,并延续到420 Ma,其可以向东延伸到我国东北的四平以东。沿着华北克拉通南部边缘,商丹洋在514~420 Ma期间发生向北的俯冲。华北克拉通的大部分地区在中奥陶世马家沟期发生海退。近10年来在华北克拉通北缘识别出一个又一个泥盆纪深成岩体和火山岩。石炭纪晚期开始的新的沉积层序以"G层"铝土矿为底,其平行不整合,或假整合在中奥陶世马家沟组灰岩之上。铝土矿很可能是从内蒙古古隆起,一个深位剥蚀的岩浆弧,曾经发育的火山喷发活动形成的广布的火山灰转变而来。这进一步说明晚古生代华北克拉通北缘曾经是一个安第斯型活动大陆边缘。这一沉积序列以碎屑岩为主,下部夹海相灰岩和火山灰层,表明其形成于海陆过渡的火山弧环境。二叠纪早期之后华北克拉通的沉积环境转变为陆相。华南地块与南秦岭地块和华北克拉通之间的勉略洋在晚古生代持续向北俯冲增生,三叠纪晚期发生碰撞,导致大别—苏鲁超高压变质带的形成。与此同时,在华北克拉通北部显著的构造变形和岩浆作用发生在三叠纪晚期。燕山地区盘山等地三叠纪晚期的强烈褶皱、冲断发生在约210 Ma,与华北克拉通周缘的强烈构造变形同期。这也暗示华北克拉通此时已经开始失去克拉通的稳定构造性质。

东秦岭早古生代两条不同构造-岩浆杂岩带的形成构造环境

东秦岭造山带早古生代（５００Ｍａ～４００Ｍａ）分别在北秦岭和南秦岭发育两条构造－岩浆杂岩带。北秦岭带由洋盆消减的火山杂岩和深成侵入杂岩组成，是活动陆缘挤压构造背景的产物；南秦岭带由辉长、辉绿岩体、岩脉，超浅成隐爆的碱基性－超基性火山岩和粗面岩组成，是被动陆缘拉张裂陷环境的产物。它们平行造山带走向分布，南、北对峙，构成时空有序的构造－岩浆杂岩带。其形成的构造机制整体上受旱古生代古秦岭洋盆沿商丹一线的俯冲和消减作用的控制，造成北部俯冲挤压，南部拉张裂陷，同时南部的拉张裂陷也受陆壳之下地幔热柱上涌的影响。

东秦岭-大别造山带北缘逆冲推覆构造特征及油气前景

东秦岭-大别山北缘逆冲推覆构造由南、北两支逆冲断裂组成,是联系东秦岭-大别造山带和南华北盆地的构造纽带。该逆冲推覆构造在走向上具有分段性,在倾向上具有分带性;即沿倾向分为前锋带、逆冲岩席带和根带;在走向上分为豫西逆冲推覆区段、周口南缘逆冲推覆区段和淮南-合肥逆冲推覆区段。构造演化分为3个阶段:印支期碰撞造山阶段、燕山晚期陆内造山阶段和燕山末期-喜马拉雅早期走滑拉张阶段。北缘逆冲推覆构造各区带烃源岩保存条件差异较大,油气显示集中分布在前锋带附近。评价前锋逆断带及前渊区(盆地/凹陷)为油气勘探最有利区带,南、北两支逆断带之间的逆冲岩席区(盆地/凹陷)为较有利区带。