Accretion and post-accretion metamorphism in subduction complex terranes of the New England Fold Belt, eastern Australia

Abstract Regional metamorphic rocks that form Late Palaeozoic subduction complexes in central Queensland, Australia, are products of two metamorphic episodes. Synaccretion metamorphism (M1) gave rise to prehnite-pumpellyite and greenschist facies rocks, whereas a subsequent episode (M2) at about 250 Ma formed upper greenschist to upper amphibolite facies rocks of both intermediate- and low-pressure type, probably in a compressive arc or back-arc setting. A similar pattern can be recognized for 1000 km along the New England Fold Belt, although at several localities, where higher grade rocks are exposed, metamorphism was essentially continuous over the M1-M2 interval, with a rapid rise in geothermal gradient at the end of accretion. Where out-stepping of tectonic elements has occurred at long-lived convergent margins elsewhere, similar overprinting of high- by lower-pressure facies series is anticipated, complicating the tectonic interpretation of metamorphism. The discrete character of metamorphic events may be blurred where conditions giving rise to a major episode of accretion and out-stepping are followed by the subduction of a major heat source.     

The geochemistry, mineralogy and maturity of gossans derived from volcanogenic Zn–Pb–Cu deposits of the eastern Lachlan Fold Belt, NSW, Australia

The Eastern Highlands of Australia have probably been in existence since the Late Cretaceous or earlier and so there has been ample time for mature gossan profiles to form over outcropping volcanogenic Zn–Pb–Cu mineralisation in the eastern Lachlan Fold Belt. The mature gossan profiles are characterised by the upward progression from supergene sulfides to secondary sulfates, carbonates and phosphates into a Fe-oxide dominated surficial capping which may contain boxwork textures after the original sulfides (as at the Woodlawn massive sulfide deposit). However, the region has locally been subjected to severe erosion and the weathering profile over many deposits is incomplete (immature) with carbonate and phosphate minerals, especially malachite, being found in surficial material. These immature gossans contain more Cu, Pb and Zn but lower As, Sn (and probably Au) than the mature gossans. Although Pb is probably the best single pathfinder for Zn–Pb–Cu VHMS deposits of the eastern Lachlan Fold Belt, Ag, As, Au, Bi, Mo, Sb and Sn are also useful, with most of these elements able to be concentrated in substantial amounts in Fe oxides and alunite–jarosite minerals.     

Petrogenesis of peraluminous magmas from the Akum-Bamenda Massif,Pan-African Fold Belt,Cameroon

Peraluminous intrusives of the Akum-Bamenda Massif, Pan-African Belt, Central Cameroon, were synkinematically emplaced in a Pan-African sinistral strike-slip shear zone. The rock sequences consist of medium-grained leucogranites, fine-grained leucogranites, and orthogneisses of biotite granite composition; in aggregate, they cover a range from about 65 to 74 wt.% SiO₂, defining a continuous chemical evolutionary trend and displaying characteristics of the high-K and medium calc-alkaline series. Leucogranites are strongly peraluminous (A/CNK > 1.1) and plot in the field of S-type granites, whereas orthogneisses are metaluminous and plot in the field of I-type granitoids. Major and trace element compositions and the Rb/Sr isotopes of the leucogranites indicate crustal derivation by remelting of a composite metapelite?+?metagreywacke protolith similar to the metasedimentary rocks of the central domain of the Cameroon Pan-African North-Equatorial fold belt.     

羌塘东部治多县直根尕卡一带二叠纪栖霞期火山岩地球化学特征及其构造意义

羌塘东部治多县直根尕卡一带二叠纪栖霞期火山岩主要由中基性火山碎屑岩及熔岩组成,火山岩地球化学研究表明,其主元素表现为高TiO_2和低TiO_2两种特征,球粒陨石标准化稀土配分模式为LREE富集型.MORB标准化的微量元素配分型式为大洋隆起型,显示岩浆形成于板内裂谷构造环境.Sr、Nd、Pb同位素地球化学研究表明火山岩显示明显的亏损地幔源区特征.综合研究表明直根尕卡一带二叠纪栖霞期火山岩形成于大陆边缘拉张构造(或陆缘始裂谷)环境,岩浆起源于地幔,属地幔柱作用的产物.     

Early Mesoproterozoic metamorphism in the Barossa Complex,South Australia: links with the eastern margin of Proterozoic Australia

LA-ICP-MS U–Pb geochronological data from metamorphic monazite in granulite-facies metapelites in the Barossa Complex, southern Australia, yield ages in the range 1580–1550 Ma. Metapelitic rocks from the Myponga and Houghton Inliers contain early biotite–sillimanite-bearing assemblages that underwent partial melting to produce peak metamorphic garnet–sillimanite-bearing anatectic assemblages. Phase equilibrium modelling suggests a clockwise P–T evolution with peak temperatures between 800 and 870°C and peak pressures of 8–9 kbar, followed by decompression to pressures of ～6 kbar. In combination with existing age data, the monazite U–Pb ages indicate that the early Mesoproterozoic evolution of the Barossa Complex is contemporaneous with other high geothermal gradient metamorphic terranes in eastern Proterozoic Australia. The areal extent of early Mesoproterozoic metamorphism in eastern Australia suggests that any proposed continental reconstructions involving eastern Proterozoic Australia should share a similar tectonothermal history.     

Stratigraphic and structural synthesis of the New England Orogen

The Spring Well volcanic complex in the Eastern Goldfields Province of Western Australia, is a relatively fresh and well exposed Archaean felsic volcanic centre that is preserved in a synclinal structure at the top of the local greenstone succession. Subaerial acid pyroclastic deposits and subordinate lava flows, intruded by anastomosing intermediate‐acid dykes and sills, comprise the near‐vent facies. In the distal regions of the centre, subaqueous crystal tuff and other tuff units are intercalated with epiclastic sediments.

Geochemical modelling indicates that the acid rocks are unlikely to have been derived by batch partial melting of probable crustal sources. However, differentiation from intermediate parents is compatible with the available geochemical data. The intermediate rocks, in turn, have critical geochemical characteristics comparable with all other studied intermediate calc‐alkaline rocks in the Yilgarn Block. Since it can be demonstrated that many of these rocks have an ultimate mantle source (through differentiation of LIL element enriched mafic primary magmas) it follows that such an origin is applicable in the Spring Well rocks. Therefore, it is concluded that the Spring Well volcanic complex represents a mantle‐derived, calc‐alkaline differentiation series, in which the more silicic members of the suite predominate. Apart from the diagnostic geochemical characteristics of these acid volcanic rocks, their spatial association with intermediate rocks distinguishes them from anatectic acid volcanic rocks that also occur in the greenstone sequences of the Yilgarn Block.     

小兴安岭东部早古生代花岗岩的发现及其构造意义

通过全岩-单矿物的Rb-Sr法和锆石激光剥蚀等离子体U-Pb法定年研究,确定小兴安岭东部地区存在508～471Ma的早古生代花岗岩.根据岩石学和年代学的特征.进一步将小兴安岭东部地区的早古生代花岗岩划分为与高级变质岩伴生的片麻状花岗冈长岩-二长花岗岩(508Ma+15Ma)、块状花岗闪长岩-二长花岗岩(499Ma+1Ma)和碱长-碱性花岗岩(471 Ma±3Ma)3种岩石组合类型.上述3类花岗岩组合的依次出现反映了同碰撞-碰撞后伸展的构造演化特点,表明小兴安岭东部早古生代存在碰撞造山事件.     

东天山觉罗塔格构造带晚三叠世镁安山岩的厘定及其构造意义

新疆东天山地区印支期岩浆活动的岩石成因、源区性质及相关动力学背景一直是区域地质问题争论的焦点。对东天山构造带阿奇山安山岩开展岩石学、地球化学及锆石U-Pb-Hf系统研究,结果表明安山岩具斑状结构和气孔状构造,斑晶矿物主要为单斜辉石和斜长石,基质以针状斜长石微晶为主。锆石U-Pb定年结果表明镁安山岩喷发于235 Ma(晚三叠世),并含有石炭纪年龄的继承锆石。锆石Hf同位素分析显示岩浆期锆石具有低的ε_Hf(t)值(-31.7~-7.6)和古老的亏损地幔模式年龄(T_DM=2.2~0.7 Ga)。岩石地球化学特征显示样品为高MgO含量(3.7%~4.7%)和K₂O/Na₂O比值(0.6~1.1)及低TFeO/MgO比值(1.6~1.8)的高钾钙碱性镁安山岩。岩石地球化学特征结合区域构造-岩浆-成矿作用揭示阿奇山镁安山岩为板内伸展背景下含金云母的富集岩石圈地幔在较浅深度(<80 km)部分熔融的产物,且母岩浆混有古老地壳物质。晚三叠世阿奇山镁安山岩的厘定反映了该时期东天山地区处于岩石圈伸展-减薄阶段。     

藏东八宿地区朱村组火山岩地球化学、同位素年代学及其构造意义

藏东八宿县城西南出露一套由中酸性火山碎屑岩及熔岩组成的火山岩地层体,研究程度不高,报道较少,时代争论较大,构造意义不明确,称之为朱村组。在朱村组获得角闪英安岩锆石SHRIMP U－Pb年龄为128Ma±2Ma,将朱村组的时代厘定为早白垩世。地球化学特征反映朱村组火山岩形成于怒江洋壳向冈底斯－念青唐古拉板块俯冲、消减的火山弧环境,是伯舒拉岭火山岩浆弧的组成部分,与伯舒拉岭早白垩世花岗闪长岩应为同源不同相的产物,并认为藏东地区班公湖－怒江缝合带的闭合在早白垩世晚期已经完成。     

Structure and metamorphism of the Calliope Volcanic Assemblage: Implications for middle to Late Devonian orogeny in the northern New England Fold Belt

The Late Silurian to Middle Devonian Calliope Volcanic Assemblage in the Rockhampton region is deformed into a set of northwest‐trending gently plunging folds with steep axial plane cleavage. Folds become tighter and cleavage intensifies towards the bounding Yarrol Fault to the east. These folds and associated cleavage also deformed Carboniferous and Permian rocks, and the age of this deformation is Middle to Late Permian (Hunter‐Bowen Orogeny). In the Stanage Bay area, both the Calliope Volcanic Assemblage and younger strata generally have one cleavage, although here it strikes north to northeast. This cleavage is also considered to be of Hunter‐Bowen age. Metamorphic grade in the Calliope Volcanic Assemblage ranges from prehnite‐pumpellyite to greenschist facies, with higher grades in the more strongly cleaved rocks. In the Rockhampton region the Calliope Volcanic Assemblage is part of a west‐vergent fold and thrust belt, the Yarrol Fault representing a major thrust within this system.

A Late Devonian unconformity followed minor folding of the Calliope Volcanic Assemblage, but no cleavage was formed. The unconformity does not represent a collision between an exotic island arc and continental Australia as previously suggested.     

Evidence for hybridisation in the Tynong Province granitoids,Lachlan Fold Belt,eastern Australia

The role of mafic–felsic magma mixing in the formation of granites is controversial. Field evidence in many granite plutons undoubtedly implies interaction of mafic (basaltic–intermediate) magma with (usually) much more abundant granitic magma, but the extent of such mixing and its effect on overall chemical features of the host intrusion are unclear. Late Devonian I-type granitoids of the Tynong Province in the western Lachlan Fold Belt, southeast Australia, show typical evidence for magma mingling and mixing, such as small dioritic stocks, hybrid zones with local host granite and ubiquitous microgranitoid enclaves. The latter commonly have irregular boundaries and show textural features characteristic of hybridisation, e.g. xenocrysts of granitic quartz and K-feldspars, rapakivi and antirapakivi textures, quartz and feldspar ocelli, and acicular apatite. Linear (well defined to diffuse) compositional trends for granites, hybrid zones and enclaves have been attributed to magma mixing but could also be explained by other mechanisms. Magmatic zircons of the Tynong and Toorongo granodiorites yield U–Pb zircon ages consistent with the known ca 370 Ma age of the province and preserve relatively unevolved ?_Hf (averages for three samples are +6.9, +4.3 and +3.9). The range in zircon ?_Hf in two of the three analysed samples (8.8 and 10.1 ?_Hf units) exceeds that expected from a single homogeneous population (～4 units) and suggests considerable Hf isotopic heterogeneity in the melt from which the zircon formed, consistent with syn-intrusion magma mixing. Correlated whole-rock Sr–Nd isotope data for the Tynong Province granitoids show a considerable range (0.7049–0.7074, ?_Nd +1.2 to –4.7), which may map the hybridisation between a mafic magma and possibly multiple crustal magmas. Major-element variations for host granite, hybrid zones and enclaves in the large Tynong granodiorite show correlations with major-element compositions of the type expected from mixing of contrasting mafic and felsic magmas. However, chemical–isotopic correlations are poorly developed for the province as a whole, especially for ⁸⁷Sr/⁸⁶Sr. In a magma mixing model, such complexities could be explained in terms of a dynamic mixing/mingling environment, with multiple mixing events and subsequent interactions between hybrids and superimposed fractional crystallisation. The results indicate that features plausibly attributed to mafic–felsic magma mixing exist at all scales within this granite province and suggest a major role for magma mixing/mingling in the formation of I-type granites.     

大兴安岭南段早二叠世两类火山岩岩石地球化学特征及其构造意义

大兴安岭南段二叠系大石寨组发育两套火山岩，即林西地区拉斑玄武岩系列的细碧－角斑岩类和大石寨地区钙碱性岩石系列玄武岩和玄武安山岩类。细碧岩的主元素以富铁为特征，成分类似于N－MORB，微量元素表现为岛弧拉斑玄武岩的地球化学特征。细碧岩类形成于大石寨裂陷槽强烈拉张的中心位置，是地幔源区较高程度部分熔融的产生。大石寨地区玄武岩和玄武安山岩类的化学成分表现为大陆缘弧火山岩的地球化学特点，形成于大石寨裂隙槽拉张中心以外的环境，是地幔物质较低程度部分熔融和地壳物质严重混染的产物。大石寨裂隙槽中火山岩的这种独特的成分和组合特点可能反映了裂隙槽的形成是一个快速而短暂的强烈拉张过程。     

Carboniferous palaeogeography of the Yarrol and New England Orogens,eastern Australia

During the Carboniferous Period the Yarrol and New England Orogens comprised an active depositional margin east of cratonised parts of Australia. Patterns of deposition within the orogens were probably controlled by dextral shear systems believed responsible for tectonism and the positions of the various depositional elements (volcanic chain, shelf, slope and basin, pull‐apart troughs and graben), and global changes in sea level. These patterns are illustrated by a series of non‐palin‐spastic palaeogeographic reconstructions.

In the Early Carboniferous, similar patterns of deposition existed within the western volcanic chain, marine shelf, and eastern slope and basin provinces of both orogens. Sediments were deposited in two cycles. They range from volcanic fluvial and marine sandstone to siltstone, mudstone and turbidites. Complex depositional patterns within shelfal regions are shown in detailed palaeogeographic reconstructions.

This uniform pattern changed during the latest Visean and Namurian, with the uplift of the New England Arch, subsidence of a non‐marine graben (Werrie Trough) to the west, and development of a new shelf in the east. The Werrie Trough received volcanics as well as fluvial and glacigene sediments, and the shelf marine sandstone and siltstone. The Yarrol Orogen was unaffected by tectonism but there was a change in provenance.

Late in the Carboniferous the Yarrol Orogen was restructured by the intrusion of granitoids into the former volcanic chain, and development of the Yarrol and North D'Aguilar Troughs as probable pull‐apart basins. In the New England Arch, deformation and metamorphism were followed by intrusion of S‐type granitoids. A comparable episode of deformation and metamorphism affected the southeastern part of the Yarrol Orogen at the end of the Carboniferous Period. This partial cratonisation of the mobile zone was a prelude to widespread basin formation during the Permian Period.     

东天山卡拉塔格泥盆纪岩浆岩地球化学特征及成因

文中对卡拉塔格地区泥盆纪岩浆岩进行了系统的岩相学、岩石地球化学研究,探讨其成因及形成构造背景。卡拉塔格地区泥盆纪火山岩主要为安山岩,并被同期一套成分连续的侵入体,包括辉长岩、闪长岩、石英闪长岩、二长岩等侵入。其中,辉长岩为钙碱性低钾系列准铝质岩石,具有较高的Al2O3含量(18.76%~19.06%)和Mg#(57.28~69.37),具有正Eu异常;闪长岩、石英闪长岩、二长岩和安山岩为钙碱性高钾钙碱性系列的准铝质弱过铝质岩石,也具有较高的Al2O3含量(15.02%~17.43%)和Mg#(53.67~72.91),具有较弱的Eu负异常或无Eu异常。这些岩浆岩都具有较低的初始Sr值(0.703 11~0.705 18)以及较高的εNd(t)值(5.36~7.72),均富集轻稀土和大离子亲石元素Rb、Ba、K等,亏损重稀土和高场强元素Ta、Nb、Ti等,都具有岛弧岩浆岩的特征。相似的岩石地球化学特征显示它们可能为同源岩浆活动的产物,可能是由俯冲洋壳形成的流体交代地幔楔岩石发生部分熔融而形成。泥盆纪岩浆岩形成于康古尔洋向卡拉麦里洋俯冲的岛弧背景。     

Granite provinces and basement terranes in the Lachlan Fold Belt,southeastern Australia

Many granites have compositional features that directly reflect the composition of their source rocks. Since most granites come from the deeper parts of the Earth's crust, their study provides information about the nature of parts of that deep crust. Granites and related volcanic rocks are abundant and widely distributed in the Palaeozoic Lachlan Fold Belt of southeastern Australia. These granites show patterns of regional variation in which sharp discontinuities occur between provinces which internally are of a rather constant character. Such a discontinuity has long been recognized at the I‐S line and the extent of that line can now be defined more fully. Breaks of this type are thought to correspond to sharp changes in the composition of the deep crust that correspond to unexposed or basement terranes. Nine such basement terranes can be recognized in the Lachlan Fold Belt. The character of these basement terranes appears to be different from that of the terranes recognized in the Mesozoic‐Cainozoic Cordilleran fold belt, in which the plates accreted during the period of tectonism reflected in the exposed surface rocks. In the Lachlan Fold Belt, it is postulated that fragments of continental crust, or microplates, were assembled in the Late Proterozoic or Early Palaeozoic to form the substrate of the presently exposed Palaeozoic sedimentary rocks; the compositional features of these fragments were later redistributed vertically by magmatic processes. The identification of basement terranes of this type shows that models which involve the lateral growth of the Lachlan Fold Belt during the Palaeozoic, in a manner analogous to the accretion of younger belts, are untenable. These basement terranes have implications for mineral exploration because the content of heavy metals can vary from one to another and this would ultimately affect the probability of concentrating these metals to form a mineral deposit.     

云南思茅大平掌矿区火山岩的地球化学特征及构造意义

大平掌矿区细碧岩-石英角斑岩建造为典型的双峰式火山岩组合,缺失SiO_2为52％～61％之间的中性火山岩。火山岩的TiO_2含量低及其它岩石化学特征、稀土元素地球化学特征均表明这套火山岩很可能形成于岛弧环境。不相容元素N-MORB标准化型式以Ba、Nd、Sm相对富集和Nb、Sr、Ti的相对亏损为特征,其中Ba 富集和Nb亏损更是岛弧火山作用的主要特征之一。大平掌矿区细碧岩具非常低的 Nb/Y(<0.15)和Zr/TiO_2(<0.01)比值,石英角斑岩的低Zr/TiO_2和Nb/Y特征以及Zr/Y比值(3.34～4.23)、(La/Yb)_N比值(0.47～2.50)变化范围都可以反映出火山岩形成于岛弧环境。大平掌火山岩的Sr、Nd同位素特征与世界上典型岛弧火山岩的Sr、Nd特征相似,其岩浆来源于亏损地幔,且经受地壳混染和(或)海水热液蚀变的影响。岩石中富含的放射成因铅也与岛弧环境密切相关。因此,大平掌铜多金属矿床的形成很可能受岛弧环境下的双峰式火山作用控制。     

中国东部及近海磁异常特征及大地构造意义

根据全球磁异常数据和中国近海高精度、高分辨率的海洋船磁资料,通过频率域的迭代下延方法,将两种不同分辨率的数据进行融合,得到了覆盖我国东部及近海的大面积地磁异常数据。对磁异常进行大范围变倾角化极,并进行了小波分解和频谱分析,计算、分析磁源重力异常、磁异常解析信号及倾斜角等转换场。结果显示中国东部及近海主要地质构造单元的磁异常特征,揭示了华北地块古陆块分布和扬子地块的南北边界走向,并指出浙闽火山岩带向西南可能和东沙隆起相连,都是中生代古俯冲的火山弧,南海北部NW向断裂可能是古特提斯构造域向太平洋构造域转换边界断裂,对中生代古俯冲及由主动陆缘向被动陆缘转化过程都有控制作用。     

Refining accretionary orogen models for the Tasmanides of eastern Australia

The well-known southwest-to-northeast younging of stratigraphy over a present-day cross strike distance of >1500 km in the southern Tasmanides of eastern Australia has been used to argue for models of accretionary orogenesis behind a continually eastwards-rolling paleo-Pacific plate. However, these accretionary models need modification, since the oldest (ca 530 Ma) outcrops of Cambrian supra-subduction zone rocks occur in the outboard New England Orogen, now ～900 km east of the next oldest (520–510 Ma) supra-subduction zone rocks. This is not consistent with simple, continuous easterly rollback. Instead, the southern Tasmanides contain an early history characterised by a westwards-migrating margin between ca 530 and ca 520 Ma, followed by rapid eastwards rollback of the paleo-Pacific plate from 520 to 502 Ma that opened a vast backarc basin ～2000 km across that has never been closed. From the Ordovician through to the end of the Carboniferous, the almost vertical stacking of continental margin arcs (within a hundred kilometres of each other) in the New England Orogen indicates a constant west-dipping plate boundary in a Gondwana reference frame. Although the actual position of the boundary is inferred to have undergone contraction-related advances and extension-related retreats, these movements are estimated to be ～250 km or less. Rollback in the early Permian was never completely reversed, so that late Permian–Triassic to Cretaceous arcs lie farther east, in the very eastern part of eastern Australia, with rifted fragments occurring in the Lord Howe Rise and in New Zealand. The northern Tasmanides are even more anomalous, since they missed out on the middle Cambrian plate boundary retreat seen in the south. As a result, their Cambrian-to-Devonian history is concentrated in a ～300 km wide strip immediately west of Precambrian cratonic Australia and above Precambrian basement. The presence in this narrow region of Ordovician to Carboniferous continental margin arcs and backarc basins also implies a virtually stationary plate boundary in a Gondwana frame of reference. This bipolar character of the Tasmanides suggests the presence of a segmented paleo-Pacific Plate, with major transform faults propagating into the Tasmanides as tear faults that were favourably oriented for the formation of local supra-subduction zone systems and for subsequent intraplate north–south shortening. In this interpretation of the Tasmanides, Lower–Middle Ordovician quartz-rich turbidites accumulated as submarine fan sequences, and do not represent multiple subduction complexes developed above subduction zones lying behind the plate boundary. Indeed, the Tasmanides are characterised by the general absence of material accreted from the paleo-Pacific plate and by the dominance of craton-derived, recycled sedimentary rocks.     

东昆仑祁漫塔格伊涅克阿干花岗岩特征及构造意义

伊涅克阿干花岗岩是含白云母过铝质花岗岩，由二长花岗岩一钾长花岗岩分3次侵入组成的复式岩体。岩石呈灰白色，富含钾长石和钠一更长石，普遍含原生白云母，富含浅源捕虏体和残留体；A/CNK=0．99～1．34；ISr=0．71199，Rb—Sr全岩等时线年龄为435.7Ma，是早古生代柴达木板块与塔里木板块碰撞导致地壳加厚，并在地幔热流注入参与作用下，地壳深部发生熔融作用形成花岗岩浆侵位形成的同碰撞花岗岩。     

北羌塘坳陷东缘石炭纪砂岩地球化学特征及构造背景

为了探讨羌塘盆地石炭纪的演化特征,于羌塘盆地北坳陷东部刻莫地区采集了一批早石炭世早期杂多群砂岩样品,对其进行了全岩地球化学测试。地球化学研究结果表明,岩石矿物成分主要在方解石-石英到含镁黑云母组分端元之间,部分样品接近钾长石组分端元;化学风化作用指标（CIW）、化学蚀变作用指标（CIA）和A-CN-K图解,反映该组砂岩的碎屑成分受到了中等的风化作用,并在风化过程中发生微弱钾交代,长石发生伊利石化。化学组分指标（ICV）表明岩石碎屑为第一次旋回沉积物,受沉积分选和再循环作用影响不大;A-CN-K图解还反映出砂岩碎屑源岩中斜长石含量高于钾长石含量,主要在花岗岩和花岗闪长岩之间变化。主量、微量和稀土元素特征指示,该组砂岩的沉积构造背景为活动大陆边缘和大陆岛弧的性质,说明在早石炭世早期古特提斯大洋已经开始进入俯冲消亡和萎缩阶段。