Characterization of Galena and Vein Paragenesis in the Penjom Gold Mine, Malaysia: Trace Elements, Lead Isotope Study and Relationship to Gold Mineralization Episodes

The Penjom Gold Mine is located 30 km from the Bentong-Raub Suture at the western boundary of the Central Belt in Peninsular Malaysia. Gold mineralization hosted within the vein system is associated with pyrite, arsenopyrite, and minor base metals including galena. Trace element and lead isotope analysis was undertaken on nine samples that represent two stages of galena formed during two tectonic events. Both the Pb isotopes and the trace elements show that the first stage galena within the mineralized areas at the footwall has different geochemical characteristics compared with galena in non mineralized areas in the hanging wall, suggesting that galena crystallized from two different ore fluids and probably at two different times. Higher Te, Se and Bi in the galena from the mineralized area may indicate hydrothermal fluids that migrate through the structural conduit and leached out the metal along the pathway that consist of dominant carbonaceous unit. The Pb isotopic ratio composition are transitional between the bulk crustal growth and an upper crustal growth curve, indicating that derivation was from arc rocks associated with continental crust or a crustal source that includes arc volcanic and old continental sedimentary rocks.     

Seismic evidence of Caledonian deformed crust and uppermost mantle structures in the northern part of the Trans-European Suture Zone, SW Baltic Sea

Collisional structures from the closure of the Tornquist Ocean and subsequent amalgamation of Avalonia and Baltica during the Caledonian Orogeny in the northern part of the Trans-European Suture Zone (TESZ) in the SW Baltic Sea are investigated. A grid of marine reflection seismic lines was gathered in 1996 during the DEKORP-BASIN '96 campaign, shooting with an airgun array of 52 l total volume and recording with a digital streamer of up to 2.1 km length. The detailed reflection seismic analysis is mainly based on post-stack migrated sections of this survey, but one profile has also been processed by a pre-stack depth migration algorithm. The data provides well-constrained images of upper crustal reflectivity and lower crustal/uppermost mantle reflections. In the area of the Caledonian suture, a reflection pattern is observed with opposing dips in the upper crust and the uppermost mantle. Detailed analysis of dipping reflections in the upper crust provides evidence for two different sets of reflections, which are separated by the O-horizon, the main decollement of the Caledonian deformation complex. S-dipping reflections beneath the sub-Permian discontinuity and above the O-horizon are interpreted as Caledonian thrust structures. Beneath the O-horizon, SW-dipping reflections in the upper crust are interpreted as ductile shear zones and crustal deformation features that evolved during the Sveconorwegian Orogeny. The Caledonian deformation complex is subdivided into (1) S-dipping foreland thrusts in the north, (2) the S-dipping suture itself that shows increased reflectivity, and (3) apparently NE-dipping downfaulted sedimentary horizons south of the Avalonia–Baltica suture, which may have been reactivated during Mesozoic normal faulting. The reflection Moho at 28–35 km depth appears to truncate a N-dipping mantle structure, which may represent remnant structures from Tornquist Ocean closure or late-collisional compressional shear planes in the upper mantle. A contour map of these mantle reflections indicates a consistent northward dip, which is steepest where there is strong bending of the Caledonian deformation front. The thin-skinned character of the Caledonian deformation complex and the fact that N-dipping mantle reflections do not truncate the Moho indicate that the Baltica crust was not mechanically involved in the Caledonian collision and, therefore, escaped deformation in this area.     

Crustal architecture beneath Madurai Block,southern India deduced from magnetotelluric studies: Implications for subduction–accretion tectonics associated with Gondwana assembly

The Madurai Block in southern India is considered to represent the eroded roots of an arc-accretionary complex that developed during the subduction–collision tectonics associated with the closure of the Mozambique Ocean and final suturing of the crustal fragments within the Gondwana supercontinent in the Late Neoproterozoic–Cambrian. Here we present a magnetotelluric (MT) model covering the main collisional suture (Palghat–Cauvery Suture Zone) in the north into the central part of the Madurai Block in the south comprising data from 11 stations. Together with a synthesis of the available seismic reflection data along a N–S transect further south within the Madurai Block, we evaluate the crustal architecture and its implications on the tectonic development of this region. According to our model, the predominantly south dipping seismic reflectors beneath the Madurai Block define a prominent south-dipping lithological layering with northward vergence resembling a thrust sequence. We interpret these stacked layers as imbricate structures or mega duplexes developed during subduction–accretion tectonics. The layered nature and stacking of contrasting velocity domains as imaged from the seismic profile, and the presence of thick (>20 km) low resistivity layers ‘floating’ within high resistivity domains as seen from MT model, suggest the subduction of a moderately thick oceanic crust. We identify several low resistivity domains beneath the Madurai Block from the MT model which probably represent eclogitised remnants of oceanic lithosphere. Their metamorphosed and exhumed equivalents in association with ultrahigh-temperature metamorphic orogens have been identified from surface geological studies. Both seismic reflections and MT model confirm a southward subduction polarity with a progressive accretion history during the northward migration of the trench prior to the final collisional assembly of the crustal blocks along the Palghat–Cauvery Suture Zone, the trace of the Gondwana suture in southern India.     

CENOZOIC TECTONIC EVOLUTION AND GEODYNAMICS OF KEKEXILI BASIN IN NORTHERN QINGHAI—XIZANG PLATEAU

CENOZOIC TECTONIC EVOLUTION AND GEODYNAMICS OF KEKEXILI BASIN IN NORTHERN QINGHAI—XIZANG PLATEAU     

Oblique crustal detachment in the Variscan Schwarzwald,southwestern Germany

The Schwarzwald is part of the central polymetamorphic crystalline belt of the Variscan Orogen (»Moldanubian Belt«). From north to south it consists of four terranes: the metasedimentary Zone of Baden-Baden, the polymetamorphic Central Schwarzwald Gneiss Complex, the sedimentary — metamorphic Zone of Badenweiler-Lenzkirch, and the Hotzenwald Complex. The largest of these terranes is the Central Schwarzwald Gneiss Complex (CSGC) whose rocks record a history of protracted regional metamorphism and anatectic melt generation. During Variscan convergence between 350 and 325 Ma the CSGC became detached from a high-temperature lower crustal substratum and was emplaced southeastward over Paleozoic clastics, volcanic rocks and crystalline slivers of the Zone of Badenweiler-Lenzkirch and the Hotzenwald Complex. Kinematic indicators suggest that these early convergent movements on retrograde shear zones and the concomitant crustal thickening were superseded by movements on divergent shear zones. The ascent of voluminous granitic plutons from a mid-crustal zone of melt generation into the upper crust was probably triggered by a change in the crustal kinematics from overall convergence to overall divergence at about 325 Ma. In detail this process was probably diachronous. Detachment of upper crust and large scale melt generation in the middle crust of the Schwarzwald was probably facilitated by the tectonic stacking of water-rich pelitic clastics and gneiss slivers, with relatively even proportions of crystalline and pelitic materials.     

利用接收函数方法研究青藏高原东南部地壳结构

青藏高原东南部作为板块碰撞的前缘地带一直是地球科学研究的热点,为了揭示碰撞前缘地带地壳结构特征,作者 利用布设在中国青藏高原东南部的38个宽频带流动台站记录的2487条远震P波接收函数,采用接收函数CCP叠加（共转换点 叠加）和H-κ叠加两种方法获得了研究区域详细的地壳厚度图像和泊松比值。研究结果显示：两种方法获得的地壳厚度特征 具有较好的一致性;青藏高原东南部地壳厚度存在明显的东西差异和南北差异;喜马拉雅构造区内莫霍面深度变化较大, 介于65~80 km之间;拉萨地体内莫霍面深度介于72~80 km之间;雅鲁藏布缝合带两侧地壳厚度突变,缝合带北侧和南侧地 壳厚度相差约8 km。研究区域平均泊松比值较小,为0.24,和大多数造山带泊松比偏低的特征类似。研究区域中下地壳广 泛存在强转换界面,该界面可能对应中下地壳高速层的上界面,埋深40~70 km,表明壳内发生深熔或部分熔融作用,导致 壳内发生重力分异,在中下地壳形成了高速薄层。     

Seismological Evidences for the Multiple Incomplete Crustal Subductions in Himalaya and Southern Tibet

SEISMOLOGICAL EVIDENCES FOR THE MULTIPLE INCOMPLETE CRUSTAL SUBDUCTIONS IN HIMALAYA AND SOUTHERN TIBET     

Seismic imaging and crustal architecture across the Lachlan Transverse Zone,a possible early cross‐cutting feature of eastern Australia

A 2‐D crustal velocity model has been derived from a 1997 364 km north‐south wide‐angle seismic profile that passed from Ordovician volcanic and volcaniclastic rocks (Molong Volcanic Belt of the Macquarie Arc) in the north, across the Lachlan Transverse Zone into Ordovician turbidites and Early Devonian intrusive granitoids in the south. The Lachlan Transverse Zone is a proposed west‐northwest to east‐southeast structural feature in the Eastern Lachlan Orogen and is considered to be a possible early lithospheric feature controlling structural evolution in eastern Australia; its true nature, however, is still contentious. The velocity model highlights significant north to south lateral variations in subsurface crustal architecture in the upper and middle crust. In particular, a higher P‐wave velocity (6.24–6.32 km/s) layer identified as metamorphosed arc rocks (sensu lato) in the upper crust under the arc at 5–15 km depth is juxtaposed against Ordovician craton‐derived turbidites by an inferred south‐dipping fault that marks the southern boundary of the Lachlan Transverse Zone. Near‐surface P‐wave velocities in the Lachlan Transverse Zone are markedly less than those along other parts of the profile and some of these may be attributed to mid‐Miocene volcanic centres. In the middle and lower crust there are poorly defined velocity features that we infer to be related to the Lachlan Transverse Zone. The Moho depth increases from 37 km in the north to 47 km in the south, above an underlying upper mantle with a P‐wave velocity of 8.19 km/s. Comparison with velocity layers in the Proterozoic Broken Hill Block supports the inferred presence of Cambrian oceanic mafic volcanics (or an accreted mafic volcanic terrane) as substrate to this part of the Eastern Lachlan Orogen. Overall, the seismic data indicate significant differences in crustal architecture between the northern and southern parts of the profile. The crustal‐scale P‐wave velocity differences are attributed to the different early crustal evolution processes north and south of the Lachlan Transverse Zone.     

Research of the Conductive Structure of Crust and the Upper Mantle beneath the South-Central Tibetan Plateau

With the super-wide band magnetotelluric sounding data of the Jilong (吉隆)-Cuoqin (措勤) profile (named line 800) which was completed in 2001 and the Dingri (定日)-Cuomai (措迈) profile (named line 900) which was completed in 2004,we obtained the strike direction of each MT station by strike analysis,then traced profiles that were perpendicular to the main strike direction,and finally obtained the resistivity model of each profile by nonlinear conjugate gradients (NLCG) inversion. With these two models,we described the resistivity structure features of the crust and the upper mantle of the center-southern Tibetan plateau and its relationship with Yalung Tsangpo suture: the upper crust of the research area is a resistive layer with resistivity value range of 200-3 000 ?·m. The depth of its bottom surface is about 15-20 km generally,but the bottom surface of resistive layer is deeper in the middle of these two profiles. At line 900,it is about 30 km deep,and even at line 800,it is about 38 km deep. There is a gradient belt of resistivity at the depth of 15-45 km,and a conductive layer is beneath it with resistivity even less than 5 ?·m. This conductive layer is composed of individual conductive bodies,and at the south of the Yalung Tsangpo suture,the conductive bodies are smaller with thickness about 10 km and lean to the north slightly. However,at the north of the Yalung Tsangpo suture,the conductive bodies are larger with thickness about 30 km and also lean to the north slightly. Relatively,the conductive bodies of line 900 are thinner than those of line 800,and the depth of the bottom surface of line 900 is also shallower. At last,after analyzing the effect factors to the resistivity of rocks,it was concluded that the very conductive layer was caused by partial melt or connective water in rocks. It suggests that the middle and lower crust of the center-southern Tibetan plateau is very thick,hot,flabby,and waxy.     

http://www.sciencedirect.com/science/article/pii/S1674987111000582

The Central India Tectonic Zone(CITZ) marks the trace of a major suture zone along which the south Indian and the north Indian continental blocks were assembled through subduction-accretioncollision tectonics in the Mesoproterozoic.The CITZ also witnessed the major,plume-related,late Cretaceous Deccan volcanic activity,covering substantial parts of the region with continental flood basalts and associated magmatic provinces.A number of major fault zones dissect the region,some of which are seismically active.Here we present results from gravity modeling along five regional profiles in the CITZ, and combine these results with magnetotelluric(MT) modeling results to explain the crustal architecture. The models show a resistive(more than 2000Ω·m) and a normal density(2.70 g/cm~3) upper crust suggesting\ dominant tonalite-trondhjemite-granodiorite(TTG) composition.There is a marked correlation between both high-density(2.95 g/cm~3) and low-density(2.65 g/cm~3) regions with high conductive zones (<80Ω·m) in the deep crust.We infer the presence of an interconnected grain boundary network of fluids or fluid-hosted structures,where the conductors are associated with gravity lows.Based on the conductive nature,we propose that the lower crustal rocks are fluid reservoirs,where the fluids occur as trapped phase within minerals,fluid-filled porosity,or as fluid-rich structural conduits.We envisage that substantial volume of fluids were transferred from mantle into the lower crust through the younger plume-related Deccan volcanism,as well as the reactivation,fracturing and expulsion of fluids transported to depth during the Mesoproterozoic subduction tectonics.Migration of the fluids into brittle fault zones such as the Narmada North Fault and the Narmada South Fault resulted in generating high pore pressures and weakening of the faults,as reflected in the seismicity.This inference is also supported by the presence of broad gravity lows near these faults,as well as the low velocity in the lower crust beneath regions of recent major earthquakes within the CITZ.     

http://www.sciencedirect.com/science/article/pii/S1674987113001382

The area from the Greater Caucasus to the southeast Turkey is characteri：;.ed and shaped by several major continental blocks. These are Scythian Platform, Pontian-Transcaucasu.,; Continent-Arc System （PTCAS）, the Anatolian-lranian and the Arabian Platforms. The aim of this paper is to define these continental blocks and describe and also compare their boundary relationships along the suture zones. The Scythian Platform displays the evidence of the Hercynian and Alpine orogens. This platform is separated from the PTCAS by the Greater Caucasus Suture Zone. The incipient collision began along this suture zone before middle-late Carboniferous whereas the final collision occurred before Oligocene. The PTCAS can be divided into four structural units： （1） the Georgian Block - northern part of the Pontian-Transcaucasian island-arc, （2） the southern and eastern Black Sea Coast-Adjara-Trialeti Unit, （3） the Artvin-Bolnisi Unit, comprising the northern part of the southern Transcaucasus, and （4） the Imbricated Bayburt-Garabagh Unit. The PTCAS could be separated from the Anatolian Iranian Platform by the North Anatolian-Lesser Caucasus Suture （NALCS） zone. The initial collision was developed in this suture zone during Senonian-early Eocene and final collision before middle Eocene or Oligocene-Miocene. The Anatolian-lranian Platform （AIP） is made up of the Tauride Platform and its metamorphic equivalents together with Iranian Platform. It could be separated from the Arabian Platform by the Southeastern Anatolian Suture （SEAS） zone. The collision ended before late Miocene along this suture zone. The southernmost continental block of the geotraverse is the Arabian Platform, which constitutes the northern part of the Arabian-African Plate. This platform includes a sequence from the Precambrian felsic volcanic and clastic rocks to the Campanian-early Maastrichtian fiyschoidal clastics. All the suture zones include MORB and SSZ-types ophiolites in different ages. However, the ages of the suture     

The Nature of the Crustal Structure of the Eastern Anatolian Plateau,Turkey

The Eastern Anatolian Plateau (EAP) of Turkey, with an elevation ranging from 1700 to 2000 m, is located between the Eastern Pontide Arc to the north and the Arabian Platform to the south. In this region, pre-Maastrichtian tectonic units representing the crust crop out in only a few localities. As they are covered by Maastrichtian-Quaternary rock units, it is difficult to study the nature and mutual relationships of these pre-Maastrichtian tectonic units.

The palaeotectonic units of the EAP comprise two different levels in the present study: (1) The lower level consists of platform-type carbonates and their metamorphic equivalents. These units may represent the Taurus Platform and its metamorphic equivalents. (2) The upper level consists of an ophiolitic-mélange prism which is made up mainly of oceanic crust; the prism comprises a complex of ophiolite, ophiolitic mélange, and fore-arc deposits. This upper unit represents a subduction-accretion prism and may have originated partly from the North Anatolian Suture to the north, and partly from the South-eastern Anatolian Suture to the south.

Continental crustal rocks were thrust over by the ophiolitic mélange prism; thus outcrops of them are scarce in the region as they are exposed in tectonic windows through the ophiolitic thrust sheets. The pre-Maastrichtian tectonic units of the EAP are blanketed by Maastrichtian to Quaternary volcanic and sedimentary rock units; these sequences include successive transgressive and regressive intervals and overlie the palaeotectonic units along a pronounced unconformity. Olistostromal units are abundant in the Eocene sedimentary units and were derived from the ophiolites and ophiolitic mélange. The Maastrichtian-Quaternary cover is made up of collisional and post-collisional deposits across the whole region.

Although the EAP has been experiencing considerable N-S compression, it has not been affected by significant crustal thickening because of the strike-slip tectonic regime that is dominant in the region.     

Electrical Structure and Fault Features of Crust and Upper Mantle beneath the Western Margin of the Qinghai-Tibet Plateau： Evidence from the Magnetotelluric Survey along Zhada-Quanshui Lake Profile

The magnetotelluric (MT) survey along the Zhada (札达)-Quanshui (泉水) Lake profile on the western margin of the Qinghai (青海)-Tibet plateau shows that the study area is divided into three tectonic provinces by the Yalung Tsangpo and Bangong (班公)-Nujiang (怒江) sutures. From south to north these are the Himalayan terrane, Gangdise terrane, and Qiangtang (羌塘) terrane. For the study area, there are widespread high-conductivity layers in the mid and lower crust, the top layers of which fluctuate intensively. The high-conductivity layer within the Gangdise terrane is deeper than those within the Qiangtang terrane and the Himalaya terrane, and the deepest high-conductivity layer is to the south of the Bangong-Nujiang suture. The top surface of the high-conductivity layer in the south of the Bangong-Nujiang suture is about 20 km lower than that in the north of it. The high-conductivity layer within the Gangdise terrane dips toward north and there are two high-conductivity layers within the crust of the southern Qiangtang terrane. In the upper crust along the profile, there are groups of lateral electrical gradient zones or distortion zones of different scales and occurrence indicating the distribution of faults and sutures along the profile. According to the electrical structure, the structural characteristics and space distribution of the Yalung Tsangpo suture,Bangong-Nujiang suture, and the major faults of Longmucuo (龙木错) and Geerzangbu are inferred.     

Seismic investigations along the European Geotraverse and its surroundings in Central Europe

Since 1975 several high-resolution seismic-refraction and reflection surveys have been carried out in western Germany to investigate the structure of the Earth's crust and uppermost mantle. The investigation culminated in the seismic-refraction survey along the 825 km long central part of the European Geotraverse (EGT) in 1986. This contribution summarizes the main results of the more recent crustal investigations along and around the EGT. The internal crustal structure throughout the area of the Variscides is very complex and changes laterally considerably. Distinct crustal blocks differing in their internal structure can be assigned to geologically defined units of the Variscan and Caledonian orogeny. In spite of local deviations, in general a more or less transparent and low-velocity upper crust contrasts with a highly reflective lower crust. A subdivision of upper and lower crust by a well-defined boundary (Conrad discontinuity) is not always seen. Towards the Alps the average velocity of the lower crust is as low as 6.2 km s^?1, in contrast to the area north of the Swabian Jura where the velocities above Moho vary between 6.8 and 7.2 km s^?1. In Northern Germany, the Elbe line separates the lower crust into two regions with 6.4 km s^?1 average velocity in the south and 6.9 km s^?1 in the north. The total crustal thickness under the Variscan part of Germany is fairly constant between 28 and 30 km, except under the Rhine Graben area with 25–26 km and beneath the central part of the Rhenish Massif where an anomalous crustal thickening to 37 km is observed. Under northern Germany the Moho rises to about 26 km depth and the data indicate at least one fault-like step of 1 km before the crust thickens toward the Ringkobing-Fyn basement high. The synthesis of seismic velocity structure and petrological information from xenolith studies allows us to propose a mafic composition for the deeper levels of the crust and uppermost mantle which may be valid at least for the central part of the Variscan crust along the European Geotraverse in Central Europe.     

冀北坝上地区深部地质构造特征及其对火山活动和铀成矿的控制作用

冀北坝上地区位于华北地台北缘。其深部地质构造有两个显著特征：一是全区性的莫霍面下拗，地壳增厚；二是软流圈部分伸入到下岩石图上部，造成局部地区地幔上隆，地壳减薄。火山喷发形成的沽源火山盆地和大滩火山盆地与两个地幔上隆，地壳减薄区，上下相互对应。铀矿床（点）沿地幔隆起周边构造活动带规律性分布。上述两事实有力地证明了深部地质构造对中新生代火山活动和铀成矿的控制作用。沿地幔隆起周边构造活动带是今后寻找铀及多金属矿产的有利地段。     

华北克拉通早前寒武纪基性火山作用与地壳增生

大量的年代学资料表明,华北克拉通在早前寒武纪阶段有两个主要的基性火山活动时期,一期发生在2.7Ga左右,另一期发生在2.5Ga左右,代表了两期强烈的地壳增生事件。太古宙末期基性火山岩的分布、地球化学特征、基性火山岩与其他岩石的关系和组合特征表明,华北克拉通在新太古代时期,在陆块之间基性火山岩的喷溢使地壳面积增大并把原本分离的小陆块拼合到一起,造成地壳的增生。在陆块内部,地壳的增生主要通过地幔柱的方式进行,在较均匀的地壳部分主要通过基性岩浆的垫托方式使地壳增厚,部分岩浆侵位到地壳较浅部位,甚至溢出地表。这两种地壳增生方式是相辅相成的,它们的联合作用形成了太古宙末的华北古大陆。     

中上扬子北缘二叠纪碎屑岩组分和地球化学特征

对中上扬子北缘二叠纪碎屑岩成分和地球化学特征进行了分析.结果表明,本次研究的碎屑岩物源主要来自上部大陆壳,沉积旋回不高,大部分样品来自基性岩和长英质火山源区.主元素受到风化作用和沉积后作用的影响,对区分构造环境意义不大;几种非迁移性微量元素,如Cr、Co、Th、Sc、La和Zr,较主元素有区分构造环境意义.本次研究的碎...     

安徽庐枞盆地何家小岭黄铁矿床特征和成因研究

何家小岭黄铁矿床受控于砖桥组下段第一韵律层(J_3zh)的火山碎屑岩中,热液蚀变作用明显。矿床成因分四类:1、火山沉积型;2、次火山岩型;3、叠加改造型;4、火山热液型。硫主要来源于上地幔或深部地壳。矿床通过火山岩浆内生成矿和盆地环境外部因素综合作用形成。该黄铁矿床确定为典型中低温火山沉积—热液叠加改造型层控矿床。     

DISCUSSION ABOUT THE PETROGENESIS OF THE CENOZOIC VOLCANIC ROCKS FROM YUMEN AND HOH XIL AREA, QINGHAI-TIBET PLATEAU

DISCUSSION ABOUT THE PETROGENESIS OF THE CENOZOIC VOLCANIC ROCKS FROM YUMEN AND HOH XIL AREA, QINGHAI-TIBET PLATEAU     

The geochemical and Sr–Nd isotopic characteristics of Eocene to Miocene NW Anatolian granitoids: Implications for magma evolution in a post-collisional setting

Early Eocene to Early Miocene magmatic activity in northwestern Anatolia led to the emplacement of a number of granitoid plutons with convergent margin geochemical signatures. Granitoid plutons in the area are mainly distributed within and north of the suture zone formed after the collision of the Anatolide-Tauride platform with the Pontide belt. We present geochemical characteristics of three intrusive bodies in the region in order to identify their source characteristics and geodynamic significance. Among these, the Çataldağ and Ilıca-Şamlı plutons are located to the north and the Orhaneli pluton is located to the south of the IAESZ (Izmir-Ankara-Erzincan Suture Zone). The plutons are calc-alkaline, metaluminous, and I-type with compositions from granite to monzonite. They display clear enrichments in LILE and LREE and depletions in HFSE relative to N-MORB compositions and have high ⁸⁷Sr/⁸⁶Sr and low ¹⁴³Nd/¹⁴⁴Nd ratios.The results of theoretical Fractional Crystallization (FC) model show that the samples are affected by fractionation of K-feldspar, plagioclase, biotite and amphibole. Assimilation and Fractional Crystallization (AFC) modeling indicates that the r value, the proportion of variable contamination to fraction, is high, indicating significant crustal contamination in the genesis of granitoid magmas. Combined evaluation of isotopic and trace element data indicates that the granitoids are the products of mantle-derived mafic magmas variably differentiated by simultaneous crustal contamination and fractional crystallization in lower to middle crustal magma chambers in a post-collisional setting.