Strontium isotopic compositions of Mesozoic granitic rocks in the Hida belt, central Japan: diversities of magma sources and of processes of magma evolution in a continental margin area

The Sr isotopic compositions of Late Triassic to Early Jurassic Funatsu granitic rocks in the Hida belt, Japan, were determined and variations of the compositions within single intrusions and on a regional scale were compared with previously reported data.

Relatively low and constant (or narrow range of) initial ⁸⁷Sr/⁸⁶Sr ratios of granitic rocks within an intrusion (0.7044-0.7055) are found mostly in the outer part of the belt, while intrusions with high and wide ranges of initial ratios (0.7056-0.7105) are situated in the inner part. This difference in initial ratios within an intrusion is due to the different degrees of mixing between the parental mafic magma from the lower crust or upper mantle and the middle to upper crustal (or crust-derived) materials. On a regional scale, a smooth and regular increase of the ratios from 0.7044 to 0.7057, from outer to inner part, is outlined by the lowest ratio in each intrusion and this almost coincides with a trend given by the ratios of mafic rocks (or mafic enclaves) in the intrusion. This suggests a gradual change of source materials in the lower crust or upper mantle. The degree of crustal contributions to the parental magma, lesser in the outer part and larger in the inner part of the Hida belt, shows close relationships to some geophysical factors, such as the emplacement depth and uplift rate of mafic magma from deeper levels and stress state (extensional or compressional) in the middle to upper crustal levels. These factors are probably due to the plate tectonic configuration in the continental margin area where the Hida belt was included.     

Qualitative analysis of mafic dyke swarms and kimberlites from morphological and geophysical signatures,NW of Proterozoic Cuddapah basin,Eastern Dharwar craton

Widespread distribution of mafic dykes and scanty occurrence of ultrabasic intrusives of kimberlitic affinity around Proterozoic Cuddapah basin, parts of Eastern Dharwar craton of south India has been the focus of attention since their discovery, to understand the structural fabric in relation to their emplacement in geological time. Satellite Imagery, geomorphological, geophysical and radiometric age data of Narayanpet area, northwest of Cuddappah basin, have clearly displayed the alignments and structures of geological significance, such as deep seated fault / fracture / shear zones, stratigraphic / lithological contacts, basic / ultrabasic intrusives and younger granites etc,. Based on the field observations such as emplacement of mafic dykes, their cross cutting relationship, study of morphological and geophysical signatures, inferred linears drawn from satellite imagery, aeromagnetic and gravity maps are arranged in a chronological order. A system of long, narrow and widely spaced dykes trending NW-SE direction conformable to gneissic foliation, typically associated with migmatites in the southwestern part of the study area are the oldest. Followed by E-W dykes, cut across by the sparsely distributed dykes associated with NW-SE and N-S features and in turn off set by dykes of NE-SW trends are the youngest. Kimberlites of Narayanpet area, belongs to hypabysal facies, which are essentially controlled by E-W to ENE-WSW deep seated fault / fracture zone, their intersection with NW-SE, NE-SW to N-S trends, which may have been reactivated during Proterozoic period as indicated by the intrusion of mafic dykes (～2270 to 1701 Ma) and emplacement of kimberlitic magmatism (～1300 to 1100 Ma) suggesting different intrusive episodes. Kimberlite pipes of Narayanpet field, falls in an ellipsoid form trending WNW-ESE direction in the northern part of the area, associated with radial drainage / topographic high and a gravity low. In addition, physical properties such as density and magnetic susceptibilities of mafic dykes and kimberlites, their geophysical signatures, emplacement of kimberlites at the close vicinity of mafic dykes or at their intersections have also been discussed.     

前寒武纪的超大陆旋回及其板块构造演化意义

太古代末早古生代存在４次超大陆或大陆聚合时期,超大陆的聚合与裂解造成全球性的重大构造热事件,成为全球板块构造演化的主线,威尔逊旋回在早前寒武纪已明显起作用。超大陆的聚合表现为克拉通的增生与陆块的碰撞造山作用;超大型的裂解表现为非造山岩浆活动、大规模基性岩墙群侵位及大陆裂谷的爆发等。超大陆的裂解可能与地幔柱上涌或超大陆下放射性物质积聚造成的热能积累有关,或地外物质冲击的触发有关。华北克拉通与世界古陆块的前寒武纪构造演化对比,及其在超大陆中的拼合模式成为我国大陆地质学研究面临的挑战性重大科学问题。     

关于南海北部特提斯的讨论

南海及邻区处于欧亚大陆与冈瓦纳古陆拼合带的东南端,是特提斯构造域和濒太平洋构造域交汇的重要地区.特提斯缝合带沿金沙江-哀牢山构造带进入南海,人们从而认为南海可能存在特提斯洋遗迹,并认为缝合带存在于磁静区中.本文通过对南海北部陆坡地球物理资料的解释结果,包括重力、磁力、海底地震和深反射地震数据,以及区域地质特征分析,研究...     

Changing mantle sources in a suture zone in the heart of Pangea: implications for collisional tectonics during the waning stages of ocean closure

The formation and emplacement of syn-collisional mafic dykes that intrude suture zones and their association with orogenic processes are enigmatic. Southern Iberia records the Late Paleozoic amalgamation of Pangea and exposes today a fragment of Laurussia (South Portuguese Zone), which is spatially juxtaposed with autochthonous Gondwana. Fault-bounded oceanic metasedimentary rocks, mélanges and ophiolite complexes characterize the suture zone and are in turn crosscut by intrusive granitoid rocks and mafic dykes. The generation and emplacement of these mafic dykes and their relationship to the suture zone are undetermined. Field evidence shows the dykes were emplaced at high angles to pre-existing orogenic fabrics in the mélange, granitoid and metasedimentary rocks. Geochemical analyses (major, trace, rare earth elements) indicate the dykes exhibit a mid-ocean ridge basalt signature. U/Pb zircon geochronology reveals the crystallization age of the dykes is ca. 316 Ma and Sm–Nd isotopic analysis suggests a deep mantle source. Taken together, these data support existing temporal constraints on events leading up to the amalgamation of Pangea, and suggest progressive lower crustal delamination during the waning stages of continent–continent collision.     

Timing of collision initiation and location of the Scandian orogenic suture in the Scandinavian Caledonides

The Scandinavian Caledonides represent a classical example of a deeply eroded Himalayan‐style orogen formed during Baltica–Laurentia continent collision. We propose that initial contact along continental‐margin promontories led to a drop in convergence rate, resulting in increased slab rollback along parts of the margin still undergoing oceanic subduction. Slab rollback caused extension of the overlying lithosphere with orogen‐wide emplacement of mafic layered intrusions, ophiolite formation and bimodal magmatism at 438–434 Ma, in what immediately thereafter became the upper plate (Laurentia) in the Scandian continent–continent collision. A compilation of magmatic ages provides evidence of long‐lived, Ordovician arc magmatism in units above the suture, which is essentially absent below the suture. This model provides a tight constraint on the timing of collision initiation, and provides a framework by which tectonic units comprising the Scandinavian Caledonides can be assigned a Baltican or more exotic heritage.     

Two- and three-dimensional gravity modeling along western continental margin and intraplate Narmada-Tapti rifts: Its relevance to Deccan flood basalt volcanism

The western continental margin and the intraplate Narmada-Tapti rifts are primarily covered by Deccan flood basalts. Three-dimensional gravity modeling of +70mgal Bouguer gravity highs extending in the north-south direction along the western continental margin rift indicates the presence of a subsurface high density, mafic-ultramafic type, elongated, roughly ellipsoidal body. It is approximately 12.0 ±1.2 km thick with its upper surface at an approximate depth of 6.0 ±0.6 km, and its average density is {dy2935} kg/m³. Calculated dimension of the high density body in the upper crust is 300 ±30 km in length and 25 ±2.5 to 40 ±4 km in width. Three-dimensional gravity modeling of +10mgal to -30mgal Bouguer gravity highs along the intraplate Narmada-Tapti rift indicates the presence of eight small isolated high density mafic bodies with an average density of {dy2961} kg/m³. These mafic bodies are convex upward and their top surface is estimated at an average depth of 6.5 ±0.6 (between 6 and 8km). These isolated mafic bodies have an average length of 23.8 ±2.4km and width of 15.9 ±1.5km. Estimated average thickness of these mafic bodies is 12.4±1.2km. The difference in shape, length and width of these high density mafic bodies along the western continental margin and the intraplate Narmada-Tapti rifts suggests that the migration and concentration of high density magma in the upper lithosphere was much more dominant along the western continental margin rift. Based on the three-dimensional gravity modeling, it is conjectured that the emplacement of large, ellipsoidal high density mafic bodies along the western continental margin and small, isolated mafic bodies along the Narmada-Tapti rift are related to lineament-reactivation and subsequent rifting due to interaction of hot mantle plume with the lithospheric weaknesses (lineaments) along the path of Indian plate motion over the Réunion hotspot. Mafic bodies formed in the upper lithosphere as magma chambers along the western continental margin and the intraplate Narmada-Tapti rifts at estimated depths between 6 and 8 km from the surface (consistent with geological, petrological and geochemical models) appear to be the major reservoirs for Deccan flood basalt volcanism at approximately 65 Ma.     

Re-interpreting the Devonian ophiolites involved in the Variscan suture: U–Pb and Lu–Hf zircon data of the Moeche Ophiolite (Cabo Ortegal Complex,NW Iberia)

New U–Pb zircon data of a mylonitic greenschist from the Moeche Ophiolite, one of the mafic units involved in the Variscan suture in the Cabo Ortegal Complex (NW of the Iberian Massif), yielded an age of 400 ± 3 Ma. Consequently, this unit can be considered one of the Devonian ophiolites, the most extended group of oceanic units in the Variscan belt. The mafic rocks show transitional compositions between N-MORB and island-arc tholeiites, although Lu–Hf isotope signatures of its zircons clearly indicate contribution from an old continental source. εHf values in the analysed zircons are negative (generally below εHf = ?5), and thence, they are not compatible with their generation from a juvenile mantle source. Accordingly, the igneous protoliths were generated in a setting where juvenile mafic magmas interacted with an old continental crust. The Devonian ophiolites from the Variscan suture have been repeatedly interpreted as remnants of the Rheic Ocean. However, the presence of a continental source in the origin of the mafic rocks of the Moeche Ophiolite allows discarding an intraoceanic setting for their generation, at least for the NW Iberian counterparts. The tectonic setting for the Devonian ophiolites of NW Iberia is very likely represented by an ephemeral oceanic basin opened within a continental realm. Herein, the real Rheic Ocean suture could only be located west of the terrane represented by the upper units of the allochthonous complexes. Apparently that suture is not represented in NW Iberia.     

Early Mesoproterozoic bimodal plutonism in the southeastern Gawler Craton,South Australia

The Curramulka Gabbronorite on Yorke Peninsula, southeastern Gawler Craton has an emplacement age of 1589 ± 5 Ma. This is similar to previously determined ages for Arthurton Granite (1582 ± 7 Ma), Tickera Granite (ca 1600 – 1575 Ma), regional alteration, the Moonta – Wallaroo mineralisation (ca 1585 Ma) and localised deformation (Tiparra Deformation). Mesoproterozoic bimodal plutonism is interpreted to have resulted from mafic underplating, emplacement of mafic magmas during lithospheric attenuation and enhanced high heat flow assisting in melting of the lower crust to form the broadly A-type Arthurton and Tickera Granites. Plutonism either directly or indirectly created advective fluid-flow to form Cu – Au mineralisation in the Moonta – Wallaroo area. The nature and characteristics of Mesoproterozoic mafic bodies on the Gawler Craton are poorly known. The Curramulka Gabbronorite has a continental tholeiitic composition and igneous layering that is partly of cumulus origin but also contains magmatic segregations formed by fractionation. Some of these segregations have provided zircons for dating. This igneous layering is overprinted by two foliations of tectonic origin: the first is interpreted to be coeval with magma emplacement and the second with conjugate shearing accompanied by retrogression.     

Continuity between eastern and western Bushveld Complex, South Africa, confirmed by xenoliths from kimberlite

The three-dimensional shapes of mafic layered intrusions have to be inferred from surface outcrops, in some cases aided by drilling and/or geophysical data. However, geophysical models are often equivocal. For the 2.06?Ga Bushveld Complex of South Africa, early geological models proposed a shape of a single, gently inward dipping lopolith. Subsequent resistivity and gravity data were interpreted to suggest that the eastern and western limbs were discrete, dipping wedge-shaped intrusions separated by ~150?km. A more recent gravity model that takes crustal flexure into account allows continuity and the reversal to the original model. Distinguishing between these possibilities is difficult from surface-based studies because the central regions of the Complex are obscured by large volumes of younger granites and sedimentary/volcanic cover rocks. Here, we describe xenoliths from the Cretaceous Palmietgat kimberlite pipe, located mid-way between the exposed western and eastern lobes of the Complex. They are chromite-bearing feldspathic pyroxenites considered equivalent to those of the typical outcropping Critical Zone of the Bushveld Complex. This result provides strong support for a regionally interconnected Bushveld Complex, implying its emplacement as a single sill-like body. Confirming the continuity of the Bushveld Complex greatly expands exploration opportunities and implies that other layered mafic intrusions could have similar geometry.     

Metamorphism and Anatexis in the Mafic Complex Contact Aureole, Ivrea Zone, Northern Italy

Emplacement of mantle-derived magma (magmatic accretion) isoften presumed or inferred to be an important cause of regionalgranulite facies metamorphism and crustal anatexis. The juxtapositionof mafic cumulates and regionally distributed granulite faciesrocks has led some to consider the Ivrea zone (northern Italy,Southern Alps) as an important exposure that demonstrates thiscausal relationship. However, regional PTt paths indicated bymetamorphic reaction textures and PT conditions inferred fromgeothermobarometry indicate that the emplacement of mafic plutonicrocks (Mafic Complex) at the Ivrea zone occurred during decompressionfrom ambient pressures at the regional thermal maximum. Fieldand petrographic observations, supported by PT estimates, indicatethat regional retrograde decompression and emplacement of theupper parts of the Mafic Complex probably accompanied extensionduring the Late Carboniferous–Early Permian. A spatiallyrestricted decompression-melting event accompanied final emplacement,depleting supracrustal rocks enclosed by an     

Post-orogenic shoshonitic magmas of the Yzerfontein pluton,South Africa: the ‘smoking gun’ of mantle melting and crustal growth during Cape granite genesis?

The post-orogenic Yzerfontein pluton, in the Saldania Belt of South Africa was constructed through numerous injections of shoshonitic magmas. Most magma compositions are adequately modelled as products of fractionation, but the monzogranites and syenogranites may have a separate origin. A separate high-Mg mafic series has a less radiogenic mantle source. Fine-grained magmatic enclaves in the intermediate shoshonitic rocks are autoliths. The pluton was emplaced between 533 ± 3 and 537 ± 3 Ma (LA-SF-ICP-MS U–Pb zircon), essentially synchronously with many granitic magmas of the Cape Granite Suite (CGS). Yzerfontein may represent a high-level expression of the mantle heat source that initiated partial melting of the local crust and produced the CGS granitic magmas, late in the Saldanian Orogeny. However, magma mixing is not evident at emplacement level and there are no magmatic kinships with the I-type granitic rocks of the CGS. The mantle wedge is inferred to have been enriched during subduction along the active continental margin. In the late- to post-orogenic phase, the enriched mantle partially melted to produce heterogeneous magma batches, exemplified by those that formed the Yzerfontein pluton, which was further hybridised through minor assimilation of crustal materials. Like Yzerfontein, the small volumes of mafic rocks associated with many batholiths, worldwide, are probably also low-volume, high-level expressions of crustal growth through the emplacement of major amounts of mafic magma into the deep crust.     

Reworking of intra-oceanic rocks in a deep sea basin: example from the Bou-Maiza complex (Edough massif,eastern Algeria)

Metagabbros and amphibolites exposed in the Bou-Maïza area of the Edough massif (northeast Algeria) are described in detail. Field and petro-structural observations point to the syn-sedimentary emplacement of gabbros as clasts, blocks and lenses of polymictic gabbroic breccias. Associated amphibolites display fine-scale parallel sedimentary bedding and represent mafic epiclastites, litharenites and mafic greywackes. The mafic beds and lenses are intercalated with aluminous pelitic schists of continental origin, quartzite and marble. It is concluded that all mafic rocks from this locality derive from the erosion of an oceanic plutono-volcanic complex of MORB affinity that was reworked in a block matrix mélange and emplaced as turbidites and debris flows during the Mesozoic. We propose a convergent plate margin setting for these formations connected with the subducted Calabrian branch of the Tethyan slab.     

The role of extensional tectonics at different crustal levels on granite ascent and emplacement: an example from Tuscany (Italy)

The role of regional extension on the rise and emplacement of granites in the crust is still debated. Pluton ascent and emplacement widely occurred in Tuscany (Italy) since late Miocene during the post-orogenic collapse of the inner Apennines, and are presently occurring in the geothermal areas of Amiata and Larderello. Tuscany offers a preferred test site to study the role of regional extension on pluton ascent and emplacement at different crustal levels. Ductile extension enhanced the segregation and ascent of granitic melts in the lower crust, controlling pluton emplacement in correspondence with the brittle–ductile transition. In the brittle crust, magma ascent occurred through subvertical faults and fractures compatible with the regional extension direction; pluton emplacement mainly occurred by means of roof lifting. The case of Tuscany suggests that the extensional structures enhance melt segregation and ascent in the ductile crust, but are not efficient alone to provide a pathway for the ascent of granitic magmas in the brittle-extending crust. The estimated magmatic strain rates due to pluton emplacement in the geothermal areas are much larger than the regional tectonic strain rates. This suggests that regional tectonics did not control magma emplacement in the brittle crust and explains why nontectonic processes (roof lifting) accommodated the space required for pluton emplacement.     

The role of discontinuous magma inputs in felsic magma and ore generation

For a long time, granites have been considered as passive bodies ascending under intrinsic negative density and viscosity contrasts with their host rocks. Chemical variations within a granitic body resulted from in situ differentiation and crystal fractionation. Since the mid 1980s, this global view has been significantly modified by (i) shifting melting from water-saturated conditions to fluid-absent reactions, (ii) increasing the role played by the mantle during granite generation, (iii) reassessing the rheology of partially molten rocks, (iv) demonstrating stepwise segregation and ascent of magmas by analogue and numerical models, (v) combining structural, geophysical and geochemical studies to reveal the internal structures in granitic plutons. It results that a granitic body is built up by a discontinuous accumulation of successive magma intrusions. The discontinuous nature of magma emplacement has also significant consequences for its ability to generate ore. The processes that lead to ore deposits are examined, with a brief review of the magmatic and fluid phases that concentrate ore forming elements. Examples are taken from crustal-derived granites and porphyry-type deposits. Those are considered as the two end-members of magmatic and hydrothermal ore deposits. The source characteristics of the magma, the emplacement mechanisms and magma mixing processes are the frame that controls the potential to carry base metals with the magma. The distribution of elements is controlled by diffusion, partition between minerals and melt, solubility and redox conditions. Variations of those parameters are examined by considering their activation energy which controls the exponential dependence with temperature. A characteristic length depending on the activation energy, temperature variation and time is estimated for a characteristic time lag of 30 ka. The intrusion of a magma into a magma chamber of similar composition, hence temperature, has few effects on diffusion, partition coefficient and redox conditions, because of a too low temperature contrast. The intrusion of a mafic magma into a felsic one induces a variation of 300 °C in both magmas. The characteristic length of diffusion may vary by up to two orders of magnitude, whereas the variation of partition coefficients is only one order of magnitude. The redox conditions are about 2.5 log unit in the mafic magma, but they can vary by 7 log units in the felsic magma. Hence, a strong decrease in δD values is observed in porphyry-type deposits. The effect is a removal of the elements with higher activation energy (W, Sn, Zr) from the mafic to the felsic magma. Deformation during the late stages of emplacement also controls ore formation.     

吉林中部晚三叠世和早侏罗世两期铝质A型花岗岩的厘定及对吉黑东部构造格局的制约

高精度同位素年代学和岩石学、元素地球化学研究结果表明,吉林省中部地区存在晚三叠世和早侏罗世两期铝质A型花岗岩。其中三道河正长花岗岩的锆石LA ICPMS年龄为(216±3) Ma,形成于晚三叠世,受控于华北板块和其北侧板块在晚二叠世—早三叠世沿西拉木伦河—长春—延吉缝合带碰撞拼合后的岩石圈伸展作用,标志古亚洲洋构造域的演化结束。天桥岗碱长花岗岩的锆石SHRIMP和TIMS年龄分别为(182±3) Ma和(188±4) Ma,全岩Rb Sr等时线年龄为(185±4) Ma,形成于早侏罗世,可能是与佳木斯板块和松嫩—张广才岭板块在早侏罗世早期沿嘉荫—牡丹江缝合带碰撞拼合有关的伸展作用的产物。这次板块碰撞作用很有可能标志着东北地区东部此时已经开始进入滨太平洋构造域的演化阶段。更详细的研究显示,两期A型花岗岩岩浆都来源于年轻的基性玄武质下地壳的部分熔融,岩浆经历了分离结晶作用。     

Magmatism evolution and carbonatite-granite association in the neoproterozoic active continental margin of the Siberian craton: Thermochronological reconstructions

Neoproterozoic carbonatites and related igneous rocks, including A-type granites in the Tatarka-Ishimba suture zone of the Yenisey Ridge are confined to a horst-anticlinal structure that was formed in a transpression setting during the oblique collision between the Central Angara terrane and the Siberian craton. The carbonatites, associating mafic (including alkaline) dikes as well as the Srednetatarka nepheline syenites are the oldest igneous formations of the Tatarka active continental margin complex. Geochronological data indicate that magmatic evolution continued in the studied anticline for nearly 100 m.y. On the earliest stage carbonatites were formed and on the last stage — the emplacement of mantle-crustal A-type Tatarka granites took place. According to new U/Pb zircon studies, the earliest rocks in the Tatarka pluton are A-type leucogranites aged 646 ± 8 Ma. The younger ⁴⁰Ar/³⁹Ar ages of carbonatites obtained for phlogopites (647 ± 7 and 629 ± 6 Ma) are related to the last tectonic events in the studied region of the Tatarka-Ishimba suture zone, which are coeval with the formation of the A-type granitoids (646–629 Ma).     

Emplacement History of Pasupugallu Gabbro Pluton, Eastern Ghats Belt, India: a Structural Study

Structural mapping of the Pasupugallu pluton, an elliptical intrusive gabbro-anorthosite body, emplaced into the western contact zone between the Eastern Ghats Mobile Belt and the Archaean East Dharwar Craton, along the east coast of India, reveals concentric, helicoidal and inward dipping magmatic and/or tectonic foliations. We identify a <1 km-wide structural aureole characterized by pronounced deflection of regional structures into margin parallel direction, mylonitic foliations with S-C fabrics, sigmoidal clasts, moderately plunging stretching lineations, non-cylindrical intrafolial folds, and stretched elliptical mafic enclaves in the aureole rocks. Our results suggest that the pluton emplacement is syn-tectonic with respect to the regional ductile deformation associated with the terrane boundary shear zone at the western margin of the Eastern Ghats. We present a tectonic model for the emplacement of the pluton invoking shear-related ductile deformation, rotation and a minor component of lateral expansion of magma. The intrusive activity (1450-800 Ma) along the western margin of the Eastern Ghats can be correlated with the significant event of recurring mafic, alkaline and granitic magmatism throughout the global Grenvillian orogens associated with the continent-continent collision tectonics possibly related to the amalgamation and the breakup of the supercontinent Rodinia.     

内蒙古贺根山蛇绿岩形成时代及构造启示

贺根山蛇绿岩位于兴蒙造山带北缘,发育完整的地幔橄榄岩、堆晶岩和基性熔岩组合,伴生有放射虫硅质岩,但贺根山蛇绿岩的形成时代一直存在争议,给兴蒙造山带北部构造演化阶段划分造成了很大障碍。锆石U-Pb年代学研究表明,贺根山蛇绿岩中辉长闪长岩(341±3Ma)和玄武岩(359±5Ma)结晶年龄为早石炭世早期,同时玄武岩继承锆石峰值年龄为晚泥盆世早期(375±2Ma),这些继承锆石呈短柱状、棱角状,生长环带宽缓,多为补丁状、平坦状,为典型的基性岩浆锆石,表明最迟在晚泥盆世早期洋壳物质已经开始形成。上石炭统格根敖包组火山岩与蛇绿岩局部呈喷发不整合接触,该组的晶屑凝灰岩夹层时代为晚石炭世(323±3Ma),提供了蛇绿岩构造侵位年龄的上限。因此,将贺根山蛇绿岩形成时代定为晚泥盆世-早石炭世,侵位时代为晚石炭世。侵入地幔橄榄岩中的部分基性岩脉时代为早白垩世(132±1Ma、139±3Ma和120±1Ma),它们含有大量继承锆石(144±1Ma~2698±25Ma),继承锆石峰值年龄密切响应了兴蒙造山带北部早白垩世之前复杂的岩浆及构造事件,这些基性岩脉是燕山期伸展环境下的岩浆产物,并非早白垩世蛇绿岩。结合前人的工作成果和区域岩浆岩、地层时空分布特征,建立了兴蒙造山带北部晚古生代构造演化历程:二连贺根山一线早泥盆世处于剥蚀阶段,中泥盆世陆壳拉张出现新生洋盆,晚泥盆世早期洋盆持续扩张形成新生洋壳,早石炭世晚期洋壳开始向北俯冲消减,并持续增生至西伯利亚活动陆缘,晚石炭世洋盆陆续闭合,部分已经构造侵位的蛇绿岩被晚石炭世火山岩不整合覆盖,贺根山蛇绿岩正是该洋盆的残余产物。