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首页> 外文OA文献 >Geology of the Dundas-Mt Youngbuck area, Western Tasmania : the stratigraphy and structure of the regional geology, and the petrology, chemistry and petrogenesis of the ultramafic-mafic complexes in the Dundas-Mt Youngbuck area of Western Tasmania
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Geology of the Dundas-Mt Youngbuck area, Western Tasmania : the stratigraphy and structure of the regional geology, and the petrology, chemistry and petrogenesis of the ultramafic-mafic complexes in the Dundas-Mt Youngbuck area of Western Tasmania

机译：塔斯马尼亚州西部Dundas-Mt Youngbuck地区的地质：塔斯马尼亚州西部Dundas-Mt Youngbuck地区的地层学和构造以及超镁铁质-镁铁质复合物的岩石学，化学和岩石成因

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摘要

An onlap landscape unconformity has been proved between the PrecambrianudOonah Formation and Eocambrian Success Creek Group. This unconformityudrepresents a hiatus in sedimentation as well as a structural and lowudgrade metamorphic break.udThe areal distribution of the Oonah Formation has been extended fromudthe type area to as far north as Mt Livingstone and west to WhalebackudRidge, where rocks of the Oonah Formation are gradational with rockudsequences of the Arthur Lineament. The Oonah Formation consists ofudtwo parts: a lower succession of fine-grained, siliceous, induratedudquartz sandstone and wacke interbedded with phyllitic mudstone andudsiltstone, typical of the sequence at Oonah Hill; and an upper successionudof interbedded carbonate, mudstone and conglomerate with volcanic rockudhorizons and minor sandstone.udStructurally the Oonah Formation is characterised by the presence ofudoutcrop-scale refolded isoclinal folds. Up to five cleavages can beudfound in rocks of the Oonah Formation, the last two being the northerlyudand northwesterly cleavages associated with Devonian deformation.udThe Success Creek Group has been redefined, after Taylor (1954), toudconsist of four mappable formations. All formations crop out in Taylor'sudtype section along the Pieman River, where they have a total measuredudminimum thickness of 950 m. The basal formation is a mixtite. Theudsecond formation, the Dalcoath Formation, is a sequence of interbedded,udclean, shallow-water quartz sandstone with minor siltstone, pebblyudsandstone and conglomerate. The Dalcoath Formation grades into theudthird formation which is dominated by laminated mudstone and siltstoneudwith minor sandstone and conglomerate units. This formation isudcharacterised by pervasive intraformational soft sediment deformationudand slump structures indicative of an unstable basin of deposition.udThe top formation is the Renison Bell Formation whose dominant units areudclassic siliceous siltstone with mudstone partings. The upper memberudof this formation is the 'red rock' of Conder (1918).udOverlying the Success Creek Group with transitional conformity isudthe Crimson Creek Formation. This formation consists of a turbiditicudsequence of volcaniclastic lithic wacke with laminated siltstone andudmudstone interbedded with tholeiitic basalt. The proportion ofudvolcaniclastic lithic wacke and basalt in the succession increasesudnorthwards from the type area along the Pieman River towards Cleveland. Following an implied hiatus in sedimentation, during which theudtectonic regime changed from tensional to compressional emplacinguddismembered ultramafic bodies into basins of deposition, the DundasudGroup (Elliston, 1954) was deposited. Remapping of Elliston's type area of the Dundas Group has shown thatudit consists of two distinct successions which are now faultudjuxtaposed, but may originally have been separated by a break inudsedimentation or period of shallow water deposition. The lower partudis sparsely fossiliferous and of Middle Cambrian age. Using theudterminology of Elliston, the lower part consists of all rock unitsudfrom the Judith Formation up to and including the lower part of theudBrewery Junction Formation. The upper succession is a fossiliferousudturbidite sequence, extending from the middle of Elliston's BreweryudJunction Formation, up to and including at least the MiseryudConglomerate and possibly including a white friable sandstoneudsequence on the western slope of Misery Hill.udThe Huskisson Group of Taylor (1954) is a biostratigraphic correlateudof part of the Dundas Group. The group'is composed of a successionudof clastic sedimentary rocks whose background sedimentation consistsudof laminated and thinly bedded siltstone and mudstone with minorudsandstone and lithic wacke units into which numerous horizons ofudmass-flow conglomerate and turbidite units were deposited. Theudconglomeratic units in the lower 1000 m of the sequence were derivedudfrom a mixed metasedimentary and active acid to intermediateudvolcanic terrain, whereas those in the upper 200 m are from auddominantly metasedimentary terrain. The dominance in most of theudsequence of acid to intermediate volcanic detritus is the mainuddifference between the Huskisson and Dundas Group sequences.udStructurally, all folds and cleavage surfaces found within theudSuccess Creek Group, Crimson Creek Formation, Dundas and HuskissonudGroups and correlates are consistent with having been formed during'udDevonian deformation.udLitho- and biostratigraphic correlates of part of the GordonudSub-Group Limestone succession occur around the outer edges of theudHuskisson Syncline. On the southern nose of the Huskisson Synclineudthe limestone sequence is in faulted contact with the HuskissonudGroup, but a hiatus in sedimentation from the middle of the LateudCambrian to the middle Middle Ordovician is indicated. Along the easternudside of the Huskisson Syncline the transition between the limestoneudsequence and basal Eldon Group correlate successions appears to beudconformable. udWithin the study area there exists an area of Tertiary basalt,udDevonian granite and numerous gabbroic phases. Volcanic activityudassociated with the Eocambrian-Cambrian successions was dominantlyudtholeiitic to andesitic in character. Three separate phases ofudvolcanism were differentiated. The first is the tholeiiticudvolcanism associated with the Crimson Creek Formation, the second isuda succession of high-magnesian andesite lavas considered to be theudsecond stage melting of the same source as the Crimson CreekudFormation tholeiitic basalts. The third phase is a low-titaniumudtholeiite suite which interdigitates with the basal conglomerateudunits of the Dundas Group. The ultramafic rocks of western Tasmania fall into three groups.udA succession of Layered Pyroxenite-Dunite (LPD); a succession ofudLayered Dunite-Harzburgite (LDH); and a succession of LayeredudPyroxenite-Peridotite and associated Gabbro (LPG). These threeudultramafic rock successions can be recognised both by fieldudcharacteristics and mineral chemistry. Comparison of mineralogy andudmineral chemistry with experimental work indicates that theudultramafic rocks formed at high temperatures and low pressures, theudparental melt having low oxygen fugacity and a low water content.udAll three of the ultramafic successions are consistent with beingudcumulate bodies formed as crustal magma chamber products, each fromudone of the three different magma events found within theudEocambrian-Cambrian successions within the Dundas Trough.udThe LPD succession is a monotonous, finely layered sequenceudcontaining orthopyroxene of En89_89; olivine of F087-89; minorudchrome diopside (Ca:Mg:Fe = 47:49:4), and chrome spinel with anudaverage 100 x Cr/(Cr + Al) ratio of 65 and a variableud100 x Mg/(Mg + Fe 2+) ratio with an average of 43.udThe LDH succession is well layered, contains a tectonic foliationudparallel to layering, the result of flattening of the mineraludgrains, and contains olivine of F098-94; orthopyroxene of En93 - 94udwith very low to undetectable Al 20 3and CaO contents. Chrome spineludgrains have a 100 x Cr/(Cr + Al) ratio of 87-93 and a variableud100 x Mg/(Mg + Fe 2+) ratio with an average of 49.udThe LPG succession consists of multiple intrusions which formed an -udorthopyroxene-rich layered sequence, an olivine-rich sequence and audgabbroic unit. Locally the ultramafic sequences are plagioclaseudbearing, and the orthopyroxene-rich sequence contains numerousudprimary structural features. The orthopyroxene-rich sequence isudintruded by the olivine-rich sequence which locally containsudchromite-rich zones. No relic olivine cores were encountered;udorthopyroxene is En89-37, chrome diopside (Ca:Mg:Fe = 48:48:4), andudthere are two compositions of chrome spinel. Within the ultramaficudrocks chrome spinel has a 100 x Cr/(Cr + Al) ratio with an averageudof 60, and an 100 x Mg/(Mg + Fe 2+) average ratio of 48. In theudchrome-rich zones within the olivine-rich sequence spinel grainsudhave an average 100 x Cr/(Cr + Al) of 69 and an averageud100 x Mg/(Mg + Fe 2 +) ratio of 40. The gabbroic phase is audtwo-pyroxene gabbro with a variable grainsize and texture. The shallow water nature of the original sediments which infilledudthe proto-Dundas Trough; a gradual deepening of an elongate basin,udprobably less than 70 km wide, into which tholeiitic lavas andudassociated turbiditic sedimentary rocks formed; the low pressureudmelting required to form the ultramafic rocks; high-magnesianudandesite lavas associated with terrigenous rocks; and the presenceudof areas of Precambrian rocks in the Ramsay River and Dundas areas,udadded to previous data, reinforces the implication that the DundasudTrough represents part of a failed continental rift zone.
机译：在前寒武纪 udOonah组和Eucambrian Success Creek组之间已经证明了重叠的景观不整合。这种不整合面表示沉积的中断以及结构性的和低级的变质破裂。 udOonah组的面积分布已经从 udthe类型区域扩展到了北部的利文斯通山和西至Whaleback udRidge，欧纳（Oonah）组的岩石是由亚瑟（Arthur）阵线的岩阶组成的。欧纳（Oonah）地层由两个部分组成：一系层的细粒，硅质，硬化二石英石英砂岩和厚粉岩，中间夹有发育性泥岩和 udsiltstone，这是乌纳山的典型特征。夹层碳酸盐岩，泥岩和砾岩的上部演替 ud与火山岩 udhorizo​​ns和小砂岩。 ud结构上，Oonah组的特征是存在 udoutcrop规模的重折叠的等时线褶皱。在Oonah组的岩石中最多可以发现5条乳沟，最后2条是与泥盆纪形变有关的北向 udw和西北向乳沟。 ud泰勒（1954）之后，成功克里克群已被重新定义为由四个可映射的编队。所有地层都在皮曼河沿泰勒的 udtype段中切出，在那里测得的总 udminimum厚度为950 m。基础形成是一个混合。第二层，即Dalcoath层，是层状，二层净水的浅层石英砂岩层，其中有少量粉砂岩，卵石 udsandstone和砾岩。 Dalcoath地层划分为 ud第三地层，以层状泥岩和粉砂岩 ud和少量砂岩和砾岩单元为主。该岩层的特征是普遍的构造内软沉积物变形表明沉积盆地不稳定的岩浆塌陷结构。 ud顶部岩层是雷尼森钟形岩层，其主要单元是具有泥岩分型的超经典硅质粉砂岩。该地层的上部成员是康德（1918）的“红色岩石”。具有过渡一致性的成功河群的上方是克里姆森河地层。该地层由带叠层粉砂岩和 udmudstone夹杂有厚生玄武岩的火山岩碎屑奇石构成的湍流/后序。从沿彼得曼河的典型地区向克利夫兰， u火山岩碎屑岩块和玄武岩的比例逐渐增加。在隐含的沉积裂隙之后，在构造过程中，构造由拉性转变为压缩，将超支性超镁铁质体转变为沉积盆地，Dundas udGroup（Elliston，1954）被沉积。对Dundas集团Elliston类型区域的重新映射表明， udit由两个截然不同的演替组成，这些演替现在已经错断并置，但最初可能是由于淤积中断或浅水沉积而分开的。下部稀疏化石和中寒武纪。使用Elliston的 udterminology，下半部分包括从Judith地层直到 udBrewery交汇处的下半部分的所有岩石单元。上层演替是化石/灰浊岩层序，从Elliston的Brewery udJunction组的中部延伸，直至并至少包括Misery ud砾岩，并可能在Misery Hill的西坡上包括白色的易碎砂岩 udsequence。泰勒的赫斯基森小组（1954）是邓达斯小组的一部分。该组由一系列 udof碎屑沉积岩组成，其背景沉积包括 udof层状和薄层粉砂岩和泥岩，以及次要的 udsandstone和lithic wacke单元，在其中沉积了许多水平的 udmass-flow砾岩和浊石单元。序列下部1000 m中的砾岩单元是从混合的沉积和活性酸到中部火山岩地带的，而上部200 m中的单元则来自主要的沉积岩地带。大部分的酸对中等火山碎屑的支配作用是赫斯基森和邓达斯群序列之间的主要差异。 ud群和相关性与在 udDevonian变形过程中形成的一致。 udGordon udSub-Group石灰岩演替的一部分的岩石和生物地层学相关性发生在 udHuskisson向斜的外缘附近。在赫斯基森向斜线 ud的南鼻上，石灰岩层序与赫斯基森 udGroup断层接触，但显示了晚寒武纪中期至中奥陶纪中期沉积的中断。沿着赫斯基森向斜的东部外侧，在石灰岩超序层序与基底埃尔登群相关的演替之间的过渡似乎是超整合的。在研究区域内，存在着第三纪玄武岩，德凡尼花岗岩和大量辉长岩相。火山活动与欧肯布-寒武纪演替相关联，主要表现为安第斯山脉到安第斯山脉。区分了 udvolcanism的三个独立阶段。第一个是与Crimson Creek地层有关的生统火山作用，第二个是高镁质安山岩熔岩的 uda演替，被认为是与Crimson Creek ud形成型玄武岩相同来源的第二阶段融化。第三阶段是低钛盾构石套件，与Dundas集团的基础集团 udunits相互交叉。塔斯马尼亚州西部的超镁铁质岩石分为三类。 ud分层的Dunite-Harzburgite（LDH）的继承；以及一系列的 ud辉绿岩-橄榄岩和相关的Gabbro（LPG）。这三个 udramdafafic岩序可以通过现场 udcharacteristics和矿物化学来识别。矿物学和矿物化学与实验结果的比较表明，在高温和低压下形成的超金铁矿岩，表观熔体的氧逸度低，含水量低。 LPD演替是单调的，层状细密的层序 udud包含En89_89的邻二甲苯； Dudas槽内的 udEucambrian-Cambrian演替过程中发现了三种不同的岩浆事件。 F087-89的橄榄石；次要 udchrome透辉石（Ca：Mg：Fe = 47：49：4）和铬尖晶石，其平均100 x Cr /（Cr + Al）比为65， ud100 x Mg /（Mg + Fe 2 +）平均比率为43。 udLDH演替是分层良好的，包含构造叶面平行于分层，是矿物 udgrains变平的结果，并且包含F098-94的橄榄石； En93-94 ud的邻二甲苯，Al 20 3和CaO含量极低至无法检测。铬尖晶石 udgrains的100 x Cr /（Cr + Al）比为87-93，可变的 ud100 x Mg /（Mg + Fe 2+）比平均为49. udLPG序列由多次侵入组成它形成了一个富含的邻位富勒索的层状序列，一个橄榄石型的序列和一个 udbbbric单元。局部地，超镁铁质序列是斜长石承重的，富含邻苯二酚的序列包含许多主要的结构特征。富含邻苯二酚的序列由富含橄榄石的序列（其局部包含富含铬铁矿的区域）表示。没有遇到遗迹的橄榄石核； upythopyroxene是En89-37，是透辉石的铬（Ca：Mg：Fe = 48：48：4），并且有铬尖晶石的两种成分。在超镁铁矿铬铁矿中，铬尖晶石的比率为100 x Cr /（Cr + Al），平均 udof为60，而100 x Mg /（Mg + Fe 2+）的平均比率为48。富含橄榄石的层状尖晶石晶粒中的区域平均具有100 x Cr /（Cr + Al）为69，平均 ud100 x Mg /（Mg + Fe 2 +）比为40。辉长相为a udtwo -辉石辉长岩具有可变的粒度和质地。原始Dundas海槽中填充的原始沉积物的浅水性质；拉长的盆地逐渐加深，大约不到70公里宽，形成了熔岩熔岩和超混浊的浊积沉积岩；形成超镁铁质岩石所需的低压溶融作用；与陆源岩有关的高镁质棕铁矿熔岩；和拉姆齐河和邓达斯地区前寒武纪岩石的存在 udof区域，再加上以前的数据，进一步说明了Dundas udTrough代表了一个大陆大陆裂陷带的一部分。

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    Brown AV;

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  • 年度 1986
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