华北陆块北缘尚义地区下井-厂汉营韧性剪切带变形特征及年代学研究

华北陆块北缘晚古生代经历了多期构造事件,构造活动复杂多样,位于其中段的下井-厂汉营韧性剪切带构造变形强烈,研究其变形特征以及形成时代,对进一步探讨华北陆块北缘晚古生代构造演化特别是古亚洲洋晚阶段洋壳俯冲的时间和机制有重要意义.鉴于此,对该韧性剪切带进行了运动学和几何学实测剖面、显微构造解析及锆石LA-ICP-MS U-...     

早古生代阿拉善地块与华北地块之间的关系:来自阿拉善东缘中奥陶统碎屑锆石的信息

阿拉善东缘奥陶纪地层位于鄂尔多斯(华北地块)与北祁连早古生代造山带之间的过渡地区,该区的构造背景一直是长期争论的问题,它涉及到阿拉善地块是否与华北地块相连、奥陶系的物源以及"贺兰拗拉槽"是否存在等问题。分布于阿拉善地块东缘的中奥陶统米钵山组的碎屑锆石LA-ICP-MSU-Pb年龄测试表明,样品中数量最多的锆石年龄为900～950Ma,Alxa-1的峰值年龄为916Ma,Alxa-2的峰值年龄为953Ma,次者在494～623Ma之间,这个区间内存在多个峰值,如Alxa-1存在505Ma和588Ma两个主要峰值,Alxa-2则存在494Ma、517Ma、623Ma等几个峰值。在2.5Ga左右两个样品都存在一个弱的峰值,Alxa-1峰值为2517Ma,而Alxa-2峰值为2552Ma和2670Ma。除此之外,两个样品都有个别大于3.0Ga的成分,Alxa-1样品中最年轻的锆石为451±8Ma,Alxa-2样品则为483±4Ma。这些年龄以及沉积特征表明:(1)传统认为的奥陶纪"贺兰拗拉槽"并不存在,鄂尔多斯西南缘地区以及阿拉善东部地区当时属于北祁连早古生代周缘前陆盆地系统;(2)早古生代主要物源来自北祁连造山带,新元古代物源来自阿拉善地块;(3)鄂尔多斯西缘整个米钵山组的锆石年龄分布及其变化,指示出北祁连造山带(岛弧)逐渐靠近阿拉善地块,其间洋盆逐渐消失的过程;(4)阿拉善地块基底与华北有明显差别,阿拉善地块明显受到新元古代和古生代构造热事件的影响,两者可能是在中奥陶世或之后才拼贴在一起。     

华北克拉通东部地块中生代变形的关键时限及其对构造的制约——以胶辽地区为例

胶辽地块是华北克拉通东部地块的重要组成,处于北倾的大别-苏鲁构造带的上盘。过去近十年来提出的几个关于东北亚构造演化的重要构造模型涉及到了胶辽地块。本文主要利用我们在辽东半岛南部地区获得的SHRIMP U-Pb锆石定年结果,结合华北克拉通东部野外地质调查的野外第一手资料、我们获得的渤海湾盆地中的中生代构造资料以及其它研究人员的SHRIMP定年资料,系统建立华北克拉通东部地块中生代的构造变形过程,并讨论相关构造模型或构造问题。最近SHRIMP定年研究发现,胶辽地块中古元古代地质体经历了～160 Ma的重熔事件。CL和BSE图象显示,在辽南新太古宙地块附近丹东花岗岩体的两个样品LJ023和LJ030中发现一些167～157Ma的自形岩浆锆石和围绕年龄大约为2100 Ma核部锆石的岩浆型锆石环带。这次重熔事件很可能为华北克拉通的下地壳原地重熔。丹东岩体呈NE走向排列,经历了强烈的近水平韧性剪切变形和随后NNE走向的褶皱变形。本文以丹东地区为例,准确确定了这些变形的年龄。根据辽东半岛东西向剪切带中白云母K-Ar和~(40)Ar/~(39)Ar年龄,第一幕变形界定在195～193 Ma之间。根据野外侵入体与变形叶理之间的关系,丹东花岗岩遭受的第二幕变形发生于153～145Ma之间。第三幕变形,也即为NNE向走滑作用,约束在135Ma～95Ma     

Petrogenesis and tectonic significance of the Early Devonian lamprophyres and diorites in the Alxa Block,NW China

The North Qilian orogenic belt (NQOB) has been defined as a subduction-collision zone between the Alxa Block and the Qilian Block during the Early Paleozoic. To constrain the post-collisional tectonic evolution of the NQOB, analyses of zircon U-Pb-Hf isotopes, whole-rock major, trace element and Sr-Nd-Pb isotope compositions of the newly discovered Early Devonian lamprophyres and diorites dikes from the Longshoushan area in southwestern margin of the Alxa Block were conducted. Zircon U-Pb dating yields emplacement ages of 400 ± 4 Ma and 403 ± 6 Ma for two lamprophyre dikes and 391 ± 3 Ma for two diorite dikes. The lamprophyres dikes are shoshonitic-high-K (calc-alkaline) in nature, and are characterized by SiO₂ contents of 53.6–56.3 wt %, (⁸⁷Sr/⁸⁶Sr)_i ratios of 0.7064 to 0.7072, εNd(t) values of 0.1–1.0, and zircon εHf(t) values of −8.0 to −2.9. The diorite dikes are high-K (calc-alkaline), and are characterized by MgO contents of 6.32–6.98 wt %, (⁸⁷Sr/⁸⁶Sr)_i ratios of 0.7089–0.7137, εNd(t) values of −3.8 to −3.5, and zircon εHf(t) values of −9.9–0.4. Both the lamprophyre and diorite dikes show parallel enrichments in LREEs and LILEs and depletions in HREEs and HFSEs and have similar ratios of (²⁰⁶Pb/²⁰⁴Pb)_i (17.587–18.133), (²⁰⁷Pb/²⁰⁴Pb)_i (15.518–15.584) and (²⁰⁸Pb/²⁰⁴Pb)_i (37.676–38.058). Geochemical and isotopic data suggest that the lamprophyre and diorite dikes were derived from low-degrees melts of amphibole- and phlogopite-bearing lherzolite and phlogopite-bearing lherzolite, respectively, in the spinel-garnet transition facies. Their parental magmas both experienced extensive fractional crystallization in a deep magma chamber and negligible crustal contamination during their ascent. Regarding the Palaeozoic tectonic development of the North Qilian orogenic belt, we propose that the Early Devonian lamprophyres and diorites possibly are related to North Qilian orogen unrooting and collapse and marking the end of the North Qilian orogenic events.     

华北与阿拉善两个古陆在早古生代晚期拼合——来自宁夏牛首山沉积岩系的证据

华北与阿拉善两个古陆块是何时拼合在一起的,一直是地质界激烈争论的问题.本文报道了宁夏牛首山西南麓出露的泥盆纪与石炭纪地层波痕及斜层理等沉积构造和构造变形方面的新资料,结合前人近年来获得的区域上奥陶纪砂岩碎屑锆石年龄资料,推测华北与阿拉善两个古陆拼合发生在晚奥陶世至泥盆纪早期之间的某一地质时期.     

Structures,kinematic analysis,rheological parameters and temperature-pressure estimate of the Mesozoic Xingcheng-Taili ductile shear zone in the North China Craton

The NE to ENE trending Mesozoic Xingcheng-Taili ductile shear zone of the northeastern North China Craton was shaped by three phases of deformation. Deformation phase D₁ is characterized by a steep, generally E–W striking gneissosity. It was then overprinted by deformation phase D₂ with NE-sinistral shear with K-feldspar porphyroclasts forming a subhorizontal low-angle stretching lineation on a steep foliation. During deformation phase D₃, lateral motion accommodated by ENE sinistral strike-slip shear zones dominated. Associated fabrics developed at upper greenschist metamorphic facies conditions and show the deformation characteristics of middle- to shallow crustal levels. In some parts, the older structures have been in turn overprinted by late-stage sinistral D₃ shearing. Finite strain and kinematic vorticity in all deformed granitic rocks indicate a prolate ellipsoid (L-S tectonites) near plane strain. Simple shear-dominated general shear during D₃ deformation is probably of general significance. The quartz c-axis textures indicate prism-gliding with a dominant rhomb <a> slip and basal <a> slip system formed mainly at low-middle temperatures. Mineral deformation behavior, quartz c-axis textures, quartz grain size and the Kruhl thermometer demonstrate that the ductile shear zone developed under greenschist facies metamorphic conditions at deformation temperatures ranging from 400 to 500 °C. Dislocation creep is the main deformation mechanism at a shallow crustal level. Fractal analysis showed that the boundaries of recrystallized quartz grains had statistically self-similarities. Differential stresses deduced from dynamically recrystallized quartz grain size are at around 20–39 MPa, and strain rates in the order of 10⁻¹² to 10⁻¹⁴ s⁻¹. This indicates deformation of granitic rocks in the Xingcheng-Taili ductile shear zone at low strain rates, which is consistent with most other ductile shear zones. Hornblende-plagioclase thermometer and white mica barometer indicate metamorphic conditions of medium pressures at around ca. 3–5 kbar and temperatures of 400–500 °C within greenschist facies conditions. The main D₃ deformation of the ENE-trending sinistral strike-slip ductile shearing is related to the roll-back of the subducting Pacific plate beneath the North China Craton.     

Amalgamation of North China Craton with Alxa Block in the Late of Early Paleozoic: Evidengce from Sedmentary Sequences in the Niushou Mountain, Ningxia Hui Autonomous Region, NW China

华北与阿拉善两个古陆块是何时拼合在一起的,一直是地质界激烈争论的问题.本文报道了宁夏牛首山西南麓出露的泥盆纪与石炭纪地层波痕及斜层理等沉积构造和构造变形方面的新资料,结合前人近年来获得的区域上奥陶纪砂岩碎屑锆石年龄资料,推测华北与阿拉善两个古陆拼合发生在晚奥陶世至泥盆纪早期之间的某一地质时期.     

New Paleomagnetic Study on Early Triassic Liujiagou Formation of North China Block *

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胶北地体中的深层次拆离构造:扬子板片折返的板上响应

通过对胶北地体基底中的韧性变形构造的研究,厘定了位于太古宙胶东群和古元古界粉子山群之间及粉子山群与晚元古界蓬莱群之间的2条深层次韧性拆离断层。显微构造和石英组构研究表明它们的剪切指向自SE向NW,并经历了高温(>650℃)到低温(350℃)的组构演化过程。对剪切带中的长英质糜棱岩进行SHRIMP U-Pb测年,获得153±2Ma和128.5±1.5Ma两组重结晶变形年龄,代表韧性拆离断裂形成及活化的时限。结合地体中岩浆作用、莱阳白垩纪盆地沉积以及制约盆地的韧性拆离断裂(148Ma)等相关伸展构造特征,认为胶北深层次拆离构造是扬子深俯冲板块折返后期的板上伸展的响应。     

A New SHRIMP Age of the Xiamaling Formation in the North China Plate and Its Geological Significance

Setting up the hypostratotype of late Precambrian is the main aim of the research on the Meso- and Neoproterozoic in North China. The chronostratigraphic position is the key in this study. However, many key horizons have not been calibrated with the high-quality isotopic ages. Using the reported new U-Pb age with the Sensitive High-Resolution Ion Microprobe (SHRIMP II), a zircon U-Pb age was obtained of the ash bed in the Xiamaling Formation in North China Plate, yielding a weighted mean 206Pb/238U age of 1368±12 Ma. It is the first SHRIMP U-Pb age from the Xiamaling Formation in the North China Plate, and represents the depositing time of the middle part of the Xiamaling Formation. The zircon age plays an important role to understanding geological evolution of the North China Plate during Meso- and Neoproterozoic.     

内蒙古阿拉善北部杭乌拉地区圆包山组时代、沉积特征及大地构造意义

通过阿拉善北部杭乌拉地区圆包山组碎屑锆石峰值年龄(420±3 Ma和419.6±3.6 Ma)以及圆包山组底部层位发育的笔石、头足类化石,认为圆包山组形成时代并非早志留世,而是泥盆纪.圆包山组中发育的大量沉积构造及其岩性特征,表明了圆包山组为典型的半深海-深海浊积岩沉积,但鲍马序列发育不完整,主要有AE、ABE、ADE和ABDE等序列组合,并划分了内扇、中扇和外扇三个沉积亚相.研究区位于阿拉善地区北部,属于西伯利亚板块南缘部分,是研究古亚洲洋闭合时间的关键部位.早古生代硅质岩岩石特征表明,研究区在早古生代处于一个被动大陆边缘的稳定大地构造背景.自晚古生代开始,研究区的大地构造活动性开始增强,逐渐由被动大陆边缘转变为活动大陆边缘,并形成了巨厚的浊积岩.根据浊积岩中槽模、沟模等沉积构造确定了物源区为研究区北部的西伯利亚板块,并根据浊积岩岩性、沉积特征以及砂岩地球化学特征的研究,认为研究区晚古生代早期的浊积岩形成于西伯利亚板块南缘的活动大陆边缘,并同时受岛弧作用的影响,导致浊积岩具有岛弧物源区属性.结合圆包山组中碎屑锆石特征及其年龄可以进一步确定圆包山组物源区位于研究区北部Gobi-Altai构造带.     

华北板块北缘东段二叠纪的构造属性:来自火山岩锆石U-Pb年代学与地球化学的制约

本文对华北板块北缘东段大河深组、关门咀子组火山岩进行了锆石LA-ICP-MSU-Pb定年和岩石地球化学研究以便制约该区的区域构造演化。大河深组和关门咀子组火山岩中的锆石均呈自形-半自形晶,具有清晰的岩浆振荡生长环带和条痕状吸收(玄武安山岩)的特点,其Th/U比值高达0.31～1.56,表明其岩浆成因。测年结果表明,桦甸大河深组流纹岩形成于早二叠世(279±3Ma～293±2Ma),珲春和图们关门咀子组玄武安山岩和玄武岩分别形成于早二叠世(275±7Ma)和晚二叠世(250±5Ma)。大河深组火山岩SiO2含量介于64.9%～75.4%,Mg#值介于0.21～0.57,属于中钾-高钾钙碱性系列,明显富集轻稀土元素(LREEs)和大离子亲石元素(LILEs)、亏损高场强元素(HFSEs,如Nb、Ta、Ti)以及P元素,类似活动大陆边缘火山岩;其锆石的εHf(t)值为+0.9～+10.37,Hf同位素二阶段模式年龄值为785～1240Ma,表明它们均起源于中-新元古代新增生玄武质下地壳的部分熔融。珲春早二叠世关门咀子组属于中钾钙碱性系列;贫硅(53.4%～53.7%)和HFSEs,富铝(16.4%～16.8%)和LILEs,具有较低的稀土元素总量,以及较平坦的稀土配分型式,显示出岛弧火山岩的地球化学属性;该组火山岩的原始岩浆应起源于受俯冲板片脱水熔融交代的亏损地幔楔。图们晚二叠世关门咀子组玄武岩SiO2含量为48.7%～49.6%,Mg#值高达0.64～0.72,相对富集LREEs和LILEs,亏损HREEs和HFSEs,具有火山弧玄武岩的地球化学属性,同时其εNd(t)=+6.01,暗示其原始岩浆起源于亏损的岩石圈地幔。综上所述,我们认为早二叠世至晚二叠世期间,华北板块北缘东段(吉林中部地区)和兴凯地块西南缘均处于古亚洲洋的俯冲作用下。     

中国东部华北克拉通南缘和华南地块地幔岩中的钼含量及其意义

对中国东部华北克拉通南缘(山东临朐、昌乐、胶州和安徽明光)和华南地块(福建牛头山、广东英峰岭、海南定安和海南蓬莱)80件地幔岩包体及其寄主玄武岩石中的钼含量进行了分析。中国东部华北克拉通南缘和华南地块新生代地幔岩包体钼含量在0.10～0.41μg/g之间,平均含钼0.19μg/g;这些包体的寄主玄武岩中的钼含量明显高于其地幔岩包体中的钼含量。寄主玄武岩中钼含量在0.75～7.21μg/g之间,平均含钼3.17μg/g。其中安徽明光寄主玄武岩中钼含量最高,平均6.8μg/g;山东临朐、昌乐寄主玄武岩中钼含量平均为3.6μg/g;福建牛头山、海南定安和海南蓬莱寄主玄武岩中钼含量低,这三地平均为1.4μg/g,与世界基性岩钼的丰度1.4μg/g一致。中国东部华北克拉通南缘和华南地块地幔岩包体的寄主玄武岩中的钼含量在空间分布上明显表现为华北克拉通南缘高而华南地块低。结合我国大型钼矿集中于华北克拉通南缘以及成矿元素来源于下地壳的事实,说明寄主玄武岩中钼含量的高低对地壳中钼矿床和钼矿集中区的分布有指示意义。     

Geochemical and isotopic constraints on the age and origin of mafic dikes from eastern Shandong Province,eastern North China Craton

Post-orogenic mafic dikes are widespread across eastern Shandong Province, North China Craton, eastern China. We here report new U–Pb zircon ages and bulk-rock geochemical and Sr–Nd–Pb isotopic data for representative samples of these rocks. LA-ICP-MS U–Pb zircon analysis of two mafic dike samples yields consistent ages of 118.7 ± 0.25 million years and 122.4 ± 0.21 million years. These Mesozoic mafic dikes are characterized by high (⁸⁷Sr/⁸⁶Sr) _i ranging from 0.7082 to 0.7087, low ?_Nd(t) values from??17.0 to??17.5, ²⁰⁶Pb/²⁰⁴Pb from 17.14 to 17.18, ²⁰⁷Pb/²⁰⁴Pb from 15.44 to 15.55, and ²⁰⁸Pb/²⁰⁴Pb from 37.47 to 38.20. Our results suggest that the parental magmas of these dikes were derived from an ancient, enriched lithospheric mantle source that was metasomatized by foundered lower crustal eclogitic materials prior to magma generation. The mafic dikes underwent minor fractionation during ascent and negligible crustal contamination. Combined with previous studies, these findings provide additional evidence that intense lithospheric thinning beneath eastern Shandong occurred at ～120 Ma, and that this condition was caused by the removal/foundering of the lithospheric mantle and lower crust.     

New Ar–Ar age constraints on the deformation along the Machaoying fault zone: Implications for Early Cambrian tectonism in the North China Craton

The Machaoying fault zone extends along the southern margin of the North China Craton (NCC) and controlled the regional structures and hydrothermal mineral systems in this area. The fault underwent at least two major deformational phases, as revealed by macro- and micro-structural observations from a well-developed segment of the fault in the Hongzhuang–Baitu area, located south of the Xiong'er Mountains. Early ductile deformation is characterized by thrusting from north to south, which was subsequently overprinted by late brittle faulting. Syntectonic strain shadows of biotite are preserved around rotated porphyroclasts of quartz amygdales in mylonite. The biotite yields a ⁴⁰Ar–³⁹Ar plateau age of 524.9 ± 1.9 Ma, which is interpreted as the time of regional thrusting along the Machaoying fault zone. The thrusting may be temporally correlated with an Early Cambrian discontinuity in sedimentation observed in the rocks sequences of the NCC, suggesting a compressional regime in this area and a craton-wide tectonic event. Many 540–500 Ma tectonic events have been previously identified in the Qinling–Qilian–Kunlun Orogenic Belt of central China and in massifs in northeastern China, both of which surround the NCC, and some of these were interpreted to be associated with assembly of Gondwana. However, paleomagnetic data indicate that the NCC was unlikely to have been connected with Gondwana in the Early Cambrian and thus our new biotite date cannot record deformation along the Gondwanan margin. Dating of K-feldspar from a quartz–K-feldspar vein formed along one of the brittle faults of the Machaoying fault zone yields a much younger ⁴⁰Ar–³⁹Ar plateau age of 119.5 ± 0.7 Ma. This is a minimum age for the brittle deformation along the southern margin of the NCC, which also overlaps the age of widespread gold and molybdenum mineralization in the region.     

华北板块南缘中段中上三叠统软沉积变形构造的发现及其地质意义

豫西地区中上三叠统主要出露在济源、义马、伊川和南召一带。印支期秦岭造山运动控制和影响着邻区中上三叠统盆地属性和沉积地层展布。通过观察研究区野外露头剖面,发现中上三叠统发育一系列典型的软沉积变形构造,包括液化底辟、枕状构造、液化柱、液化卷曲变形、负载、球-枕、火焰状构造、液化角砾岩。这些软沉积变形在垂向上表现出明显的复现性,在侧向上表现为沿地层连续展布,表明该时期研究区内地层受到频繁强烈的地震影响。通过对这些软沉积现象的识别和形成机制解释,判定其触发因素为秦岭造山过程中伴生的地震。区内地层中震积岩的存在即是对秦岭造山过程中构造活动的响应。     

华北克拉通东部中生代高Mg闪长岩——对岩石圈减薄机制的制约

在华北克拉通东部鲁西—徐淮地区,存在一套辉石闪长岩-二长闪长岩-花岗闪长岩组成的adakitic岩石。锆石SHRI MP和LA-ICP-MS U-Pb定年结果表明它们形成于早白垩世(130~132Ma)。该类岩石具有较高的MgO含量(质量分数为1·46%~9·76%)、高的Mg#值(0·46~0·68)和高的Sr/Y值(主体介于30~52之间,个别高达410)。这些特征类似于由俯冲大洋板片部分熔融形成的adakitic岩石。然而,它们所表现出来的相对较高的87Sr/86Sr初始比值(0·7051~0·7077)和较低的εNd(t)值(-4·43~-15·92)则反映岩浆形成或演化过程中应有陆壳物质的参与。徐淮地区该类岩石中榴辉岩类捕虏体和石榴石捕虏晶的存在和鲁西辉石闪长岩中众多地幔橄榄岩捕虏体的发现,以及这些捕虏体中普遍发育富硅质交代作用,由此可以判定该类岩浆应起源于拆沉下部大陆地壳的部分熔融及其在上升过程中与地幔橄榄岩的反应,石榴石作为残留相。华北克拉通东部早白垩世adakitic岩石的存在以及榴辉岩类捕虏体的年代学表明,中生代早期曾存在一次重要的陆壳加厚过程,之后相继出现的加厚岩石圈的拆沉应是中生代岩石圈减薄的主导机制。     

京北云蒙山地区四合堂韧性逆冲型剪切带的变形特征及早期变形时限约束

云蒙山杂岩是华北克拉通内记载了晚中生代构造演化的重要构造单元之一。云蒙山地区区域构造格架主要由四合堂背斜推覆体、四合堂逆冲型韧性剪切带、云蒙山背形、河防口正断层及水峪伸展型韧性剪切带等组成。对于四合堂逆冲型剪切带的活动时限及其与水峪剪切带之间的关系,是长期争论的课题之一。在四合堂韧性剪切带中广泛发育有剪切演化各个阶段就位的花岗质岩脉。本文研究云蒙山四合堂地区剪切变形特征及广泛发育的岩脉与构造变形之间关系,将岩脉厘定为构造期前(剪切前)岩脉、同构造期(同剪切)岩脉和构造期后(剪切后)岩脉等6期。不同类型的同构造岩脉锆石U-Pb定年获得了岩脉结晶年龄为170~150Ma。从构造-岩浆关系分析角度考虑,本文认为四合堂剪切带韧性逆冲作用早期的活动始于约170Ma,并持续到约150Ma。     

北秦岭二郎坪岩群两侧韧性剪切带的构造变形及其意义

北秦岭二郎坪岩群南、北两侧分别被朱夏韧性剪切带和瓦乔韧性剪切带与秦岭岩群和宽坪岩群分开,这两条韧性剪切带对二郎坪弧后盆地的演化起着十分重要的作用。本文对这两条剪切带进行了详细的几何学、运动学和⁴⁰Ar-³⁹Ar年代学研究。几何学和运动学分析结果指示瓦乔剪切带具有由北向南逆冲剪切的运动学特征,而朱夏剪切带早期具有由南向北逆冲的运动学特征,而后期又发生右行走滑活动。对瓦乔剪切带和朱夏剪切带内的糜棱岩中白云母进行了⁴⁰Ar-³⁹Ar法定年,结果指示瓦乔剪切带逆冲活动发生在387±1.7 Ma,朱夏韧性剪切早期逆冲发生在晚古生代,后期右行走滑的年龄为146±2.8 Ma。综合两条剪切带的构造变形特征和年代学数据,结合前人的地质资料,本文认为二郎坪弧后盆地曾沿着瓦乔剪切带和朱夏剪切带发生双向式俯冲。     

华北板块南缘栾川群研究

栾川群出露于东秦岭北部。在栾川群分布区域，古华北板块不同时代的地层往南逆冲，构成北秦岭的太华推覆体。栾川群存在于该推覆体内部的特定逆冲岩席之中，沿这一逆冲岩席追索，确定古华北板块南缘的栾川群是连续沉积的，而受后期推覆构造的改造，栾川群在推覆体前缘的分布是断续相连的。根据地层之间的接触关系、岩浆活动、沉积作用的研究，对栾川群的划分提出了新的看法，认为栾川群由三川组、南泥湖组、煤窑沟组及大红口组构成。栾川群形成于震旦纪晚期，由湖坪及潮下斜坡等滨浅海沉积物构成。栾川群的岩浆岩为具双众数特征的岩套，具典型的大陆裂谷岩浆岩特征。并认为中元古代以来，古华北板块南缘处于裂陷拉张环境。早期的裂陷形成了熊耳群、汝阳群、官道口群及竞坪群，晚期裂陷的过程形成了栾川群、陶湾群，其进一步发育导致以二郎坪群为代表的洋壳生成。