SHRIMP Age and Geochemistry of the Bikou Volcanic Terrane:Implications for Neoproterozoic Tectonics on the Northern Margin of the Yangtze Craton

The Bikou volcanic terrane is predominated by subalkaline tholeiitic lavas. Rock samples display lower initial ratios of Sr and Nd, 0.701248-0.704413 and 0.511080-0.512341 respectively. 207Pb and 208Pb are significantly enriched in the lavas. Most samples have positive εNd, which indicates that the magma was derived from EM-type mantle source, while a few samples with negative εNd indicate that there was contamination in the magma evolution. Magma differentiation is demonstrated by variations of LREE and LILE from depletion to enrichment. Additionally, normalized REE patterns and trace elements showed that lavas from the Bikou volcanic terrane have similar characteristics to those of basalts in arc settings caused by subduction and collision. Analyses showed that the Bikou volcanic terrane is a volcanic arc. New evidence proved that the Hengdan Group, north of the Bikou arc, is a turbidite terrane filling a forearc basin. Consequently, the Bikou volcanic terrane and the Hengdan turbidite terrane construct an arc-basin system. New SHRIMP ages showed that this arc-basin system developed on the northern margin of the Yangtze craton in the Neoproterozoic (846-776 Ma), and this arc-basin system is in agreement with the tectonic processes of Rodinia in the Neoproterzoic.

Further Study on Geochemical Characteristics and Genesis of the Boninitic Rocks from Bikou Group, Northern Yangtze Plate

Compared with the major and trace elements of typical boninite, the metabasalts collected from the Nanfanba （南范坝）-Miaowanli （庙湾里） region in the Bikou （碧口） block could be treated as boninite characterized by low-Si, low-Ti, low-P, high-Mg^2 and high Al2O3/TiO2, consistent with geochemical features of boninite. The normal mid-ocean ridge basalt （N-MORB） normalized spider diagram displays fairly depleted high field strong elements （HFSE） （Zr, Y, Ti）. Enriched refractory elements （Cr, Co, Ni） as well as light rare earth elements （LREE）-depleted chondrite-normalized REE distribution patterns suggest the boninitic magmas are derived from an extremely depleted mantle wedge in the presence of a hydrous fluid, meanwhile signifying the source region had previously undergone a high degree partial melting process yielding primary magmas with enriched large ion lithophile elements （LILE）. In addition, almost all the samples in the Nb-Zr-Y and Ti-Zr-Y discrimination diagrams were plotted in the island arc basalt （IAB） field. Coupled with the island arc tholeiitic （IAT） basalt in the study region, therefore, the geochemical characteristics of the studied rocks indicate the meta-basalts probably occurred in a fore-arc subduction setting. This conclusion may be of great significance for the further study of the tectonic background of the Bikou volcanism.

Metamorphism of the Bikou Group in the Shanxi-Gausu-Sichuan Border Region

The Blkou Group on the Shaanxi-Gansu-Sichuan border is composed of Mid-Late Proterozoic metamorphosed bimodal volcanic rocks and flysch sediments. Its metamorphism may be divided into the blueschist and greenschist facies. Three metamorphlc zones, i.e. zones A, B, and C, may be distinguished on the basis of the field distribution of metamorphlc rocks and the variation of b0 values of muscovite. Blueschists are characterized by coexistence of sodic amphiboles and epidote and occur as stripes or relict patches in extensive greenschists of zone A. Studies of metamorphic minerals such as amphiboles, chlorite, epidote and muscovite and their textural relationships indicate that blueschists and greenschists were not formed under the same metamorphic physico-chemical conditions. The blueschist facies was formed at temperatures of 300-400℃ and pressures of 0.5-0.6 GPa. The greenschist facies in zones A and B has similar temperatures but its pressure is only 0.4 GPa or so. The transition from the blueschist to greenschist facies is a nearly isothermal uplift process. The rock and mineral assemblages of the Bikou Group indicate that the blueschist facies metamorphism of the group might be related to crustal thickening or A-subduction accompanying the closure of an intracontinental small ocean basin.

Post-collisional plutonism with adakitic signatures:The Triassic Yangba granodiorite (Bikou terrane,northern Yangtze Block)

The post-collisional Yangba granodiorite intruded into the Bikou metasedimentary-volcanic group, southern Mianlue Suture, central China. The host granodiorites contain many mafic microgranular enclaves which have acicular apatite, phenocrysts of host granodiorites, implying that the enclaves have been incorporated as magma globules into host granodioritic magma and undergone rapid cooling. The variation trends of major and trace ele- ments between enclaves and host rocks suggest a mixing and mingling process with respect to their petrogenesis. The mafic microgranular enclaves are characterized by shoshonite with SiO2≤63%, σ (4.54–6.18)>3.3, high K2O content (4.22%–6.04%), K2O/Na2O>1; in the K2O-SiO2 diagram, all the samples plot in the shoshonite field, which are enriched in LILE and LREE, with obvious Nb, Ta negative anomalies, indicating a subducting fluid-metasomatised mantle source. Zircon LA-ICP-MS dating of the granodiorites yielded an age of 215.4±8.3 Ma, indicating they were formed during the late-orogenic or post-collisional stage (≤242±21 Ma) of the South Qinling Mountain Belt. The host granodiorites have many close compositional similarities to high-silica adakites from su- pra-subduction zone setting, but tend to have a higher concentration of K2O (3.22%–3.84%) and Mg#. Chon- drite-normalized rare-earth element patterns are characterized by high ratios of (La/Yb)N, the extreme HREE deple- tion and a lack of significant Eu anomalies. In conjunction with the high abundances of Ba and Sr as well as the low abundances of Y and HREE, these patterns suggest a feldspar-poor, garnet ± amphibole-rich fractionation mineral assemblage. High Mg# values demonstrate that the host granodiorites were contaminated by enclave magma. On a whole, integrated geological and geochemical studies suggested the Yangba granodiorites and their mafic micro- granular enclaves resulted from mixing of enriched mantle-derived shoshonitic magma and thickened lower crust-derived felsic magma. In combination with previous studies we consider that the Yangba granodiorites were likely to represent underplating activities and delamination of the lower crust during the late orogenic stage in west- ern Qinling Orogenic Belt.

Geochemical and Pb-Sr-Nd isotopic compositions of Indosinian granitoids from the Bikou block,northwest of the Yangtze plate:Constraints on petrogenesis,nature of deep crust and geodynamics

This paper reports geochemical and Pb-Sr-Nd isotopic compositions of the Indosinian Yangba (215 Ma),Nanyili (225 Ma) and Mopi granitoids from the Bikou block of the northwestern margin of the Yangtze plate. These granitoids are enriched in Al (Al2O3:14.56%―16.48%) and Sr (352 μg/g―1047 μg/g),and depleted in Y (<16 μg/g) and HREE (e.g. Yb<1.61 μg/g),resulting in high Sr/Y (36.3―150) and (La/Yb)N (7.8―36.3) ratios and strongly fractionationed REE patterns. The Indosinian granotoids show initial Sr isotopic ratios (ISr) from 0.70419 to 70752,εNd(t) values from-3.1 to -8.5,and initial Pb isotopic ratios 206Pb/204Pb=17.891-18.250,207Pb/204Pb=15.494-15.575,and 208Pb/204Pb=37.788-38.335. Their geochemi-cal signatures indicate that the granitoids are adakitic. However,they are distinct from some adakites,generated by partial melting of subducted oceanic slab and/or underplated basaltic lower crust,be-cause they have high K (K2O: 1.49%―3.84%) and evolved Nd isotopic compositions,with older Nd iso-topic model ages (TDM=1.06―1.83 Ga). Geochemical and Sr-Nd isotopic compositions suggest that the magmas of the Insoninian adakitic rocks in the Bikou block were derived from partial melting of thick-ened basaltic lower crust. Combined with regional analyses,a lithospheric delamination model after collision between the North China and South China plates can account for the Indosinian adakitic magma generation. On the other hand,based on the Pb-Sr-Nd isotopic probing to the magma sources of the adakitic rocks,it is suggested that there is an unexposed continent-type basement under the exposed Bikou Group volcanic rocks. This can constrain on the Bikou Group volcanic rocks not to be MORB-or OIB-type.

Geochemical characteristics of Bikou volcanic group and Sr-Nd-Pb isotopic composition: Evidence for breakup event in the north margin of Yangtze plate, Jining era

The geodynamic setting of the Bikou volcanic group is a critical question to trace the Precambrain tectonic framework and evolution for the Yangtze plate. This study has suggested that the Bikou volcanic group is composed of several residual oceanic crust units: MORB (mid-ocean ridge basalt), Alk-OIB (alkaline ocean island basalt) and Th-OIB (tholeiitic ocean island basalt) as well as subduction-related volcanic rocks. According to field observation, those distinct rocks occurred collectively in form of tectonic contact, implying that the Bikou volcanic group was an ophiolitic mélange. Coupled with geochronological data, a perished oceanic basin at the northern margin of the Yangtze block during Neoproterozoic was tested by this ophiolitic mélange. Meanwhile, the isogeochemical data suggest that the ocean occurred in the Southern Hemisphere identical to Indian, South Atlantic and South Pacific oceans in terms of their Dupal anomalies, and the original source of the rocks could be probably mixing by EMⅠand EMⅡ component caused by dehydration melting of subducting oceanic crust during subduction process. On the basis of geochemical characteristics of the studied rocks, the Bikou volcanic group could imply that a partial breakup event occurred in the northern margin of Yangtze plate during the Neoproterozoic era.

Sr and Pb isotopic constraints on ore formation of the copper deposits in Bikou-Group rocks, Qinling area, China

BIKOU Group comprises spilite and keratophyre, which are lower-grade (greenschist facies) metamorphosed and interbedded by main basic rocks at the bottom and acid rocks on the top. Some copper deposits and ore spots such as Damaoping, Faziba and Yangba have been found in spilite stratum. Becauseresearches have not been well carried out on geology of these ore deposits, some basic problems concerning ore source, characteristics of ore-forming fluid and mineralization age, etc. remain unsolved. Thispaper mainly discusses the mineralization mechanism and mineralization age.

Trace elements in volcanic rocks from Yangba Formation, Bikou Group, Qinling area, China——Implications for tectonics

YANGBA Formation of Bikou Group is located in south Qinling, a famous orogenic belt separating Chinesecontinent into two parts: North China plate and Yangzi plate. The Yangba Formation comprises the maficand felsic volcanic rocks formed in an ancient seafloor environment during the Proterozoic era. The suitesof mafic and felsic volcanic rocks are petrochemically divided into tholeiite and calc-alkaline dacite, respectively, showing characteristics of bimodal volcanic rock mainly by lithology and major element content, and a lack of typical intermediate rocks. These signatures indicate that the volcanic rocks of YangbaFormation were generated in rift tectonics setting. The tholeiites of Yangba Formation are similar in trace element content to mid-ridge basalt, displaying a slight depletion to enrichment in light rare earth elements (LREE’s) (La/Yb_n = 0.6-1.4), slightfractionation between LREE (La/Sm_n =0.55-1.14) and HREE (Gd/Lu_n = 1.09-1.50), and relative flat patterns in whole. The decoupling of Eu to its neighboring elements in two samples likely indicates an effect of fractional crystallization in magma evolution. The La-La/Sm, Ni-La, Ni-Th, Ni-Ta,and Ni-Hf diagrams all support a conclusion that the mafic rocks are generated by partial melting pro-

四川平武地区碧口群碎屑锆石U-Pb年龄及其地质意义

本文对四川平武县碧口群中原岩沉积构造特征保存仍然完整的二云石英岩碎屑锆石,通过LA-(MC-)ICP-MS-激光原位分析方法开展平武碧口群最大沉积年龄的研究,同时对源岩属性、沉积环境以及沉积盆地构造演化等展开讨论。四川平武地区碧口群的碎屑锆石测点Th/U比值多介于0.27~2.6之间,具岩浆锆石特征,应为岩浆成因。最年轻碎屑锆石年龄为207 Ma,最老锆石年龄为2819 Ma。碎屑锆石年龄多集中于617~941Ma,说明该区沉积岩主体形成于新元古代地壳物质,在之后的古生界-中生界历经多次地质沉积事件。最老锆石年龄2819Ma推测其有太古宙残留物质信息,大致可以指明碧口群桂花桥岩组地层物质应该来源于古元古代—太古代及以前的岩石、地层。

碧口群火山岩岩石成因研究

新元古代（846-776Ma）碧口群火山岩喷发于大陆板内裂谷环境。该火山岩系以基性火山岩为主，酸性火山岩次之，中性火山岩少见。根据岩石地球化学数据，碧口群裂谷基性熔岩总体上属于低Ti／Y（〈500）岩浆类型。元素和同位素数据表明，碧口群基性熔岩的化学变化不是由一个共同的母岩浆的结晶分异作用所产生。它们极有可能是源于地幔柱源（εNd（t）≈＋3，^87Sr／^86Sr（t）≈0．704，La／Nb≈0．7）。地壳混染作用对于碧口群裂谷基性熔岩的形成有重要贡献。我们的研究揭示，碧口群火山岩存在空间上的岩石地球化学变化。东部红岩沟和辛田坝-黑木林地区的碧口群基性熔岩以拉斑玄武岩为主，产生于幔源石榴子石稳定区的高度部分熔融。相反，西部白杨-碧口地区的碧口群基性熔岩的母岩浆则是形成于幔源的尖晶石-石榴子石过渡带：碱性熔岩是产生于部分熔融程度较低的条件下，拉斑玄武质熔岩则是产生于部分熔融条件较高的条件下。它们经受了浅层位辉长岩质（cpx＋plag±01）分离作用，化学变异较大。

扬子板块北缘碧口群火山岩的地球化学特征及其构造环境

碧口群火山岩系中部的基性熔岩以拉斑系列为主 ,基性火山岩的Sr同位素初始比值和Nd同位素初始比值较低 ,分别为 0 .70 12 4 8～ 0 .70 4 4 13和 0 .5 110 80～ 0 .5 12 341,大部分样品的εNd(t) >0 ,表明母岩浆主要来自地幔源区。岩石显示明显的富2 0 7Pb及2 0 8Pb特征。在以部分熔融作用为主的演化过程中岩浆发生了一定程度的分异 ,LREE、大离子亲石元素等表现了从亏损到富集的变化特点。基性熔岩的稀土与微量元素表现出与俯冲碰撞型的弧区玄武岩相同的特点。分析表明 :碧口群火山岩系形成于岛弧环境 ,它与横丹群浊积岩系在扬子板块西北缘构筑了一个弧盆系统 ,其时代为新元古代。

川西北碧口地块老河沟岩体和筛子岩岩体地球化学特征及其构造环境

老河沟岩体和筛子岩岩体位于碧口地块西南部。岩体的SiO2(69.89%～71.69%)和Al2O3(15.01%～16.25%)含量均很高,A/CNK在1.04～1.12之间,为硅和铝过饱和类型,属典型的强过铝质花岗岩。稀土元素总量(∑REE)为33.13×10-6～150.42×10-6,稀土元素配分曲线呈右倾型,具有弱的负铕异常。高场强元素(Ta、Nb、Ti等)具有明显的负异常,大离子亲石元素(Rb、Ba、Sr等)具有明显的正异常。岩体可能是以杂砂岩成分为主的沉积岩部分熔融形成的花岗质岩浆上升侵位过程中形成的,是一种典型的壳源成因类型。老河沟岩体和筛子岩岩体具有后碰撞岩浆活动的特征,是印支期华北和扬子地块碰撞导致地壳加厚环境下下地壳部分熔融的产物,形成于同碰撞(挤压环境)向碰撞后(伸展环境)转化阶段,为后造山花岗岩类。

扬子板块北缘碧口地区阳坝花岗闪长岩体成因研究及其地质意义

本文对出露于勉略缝合带南侧碧口地区的阳坝岩体进行了系统的岩石学、锆石U-Pb年代学和地球化学研究研究,重点讨论了阳坝岩体的岩石成因、成岩物质来源及其地质意义。岩体的主体岩性为花岗闪长岩,其中广泛发育代表岩浆混合作用的暗色微粒包体。锆石LA-ICP-MS定年结果表明阳坝花岗闪长岩的成岩年龄为215．4±8．3Ma,晚于秦岭造山带的主造山期。地球化学特征上,寄主花岗闪长岩显示部分埃达克岩的地球化学特征,具体表现为SiO2≥56％,Al2O3>15％, Na2O>K2O,Mg#(50．8-54．5)>47,富集LILE和LREE,Sr>900μg/g,Sr／Y比值(65-95)>65,负Eu异常不明显(δEu=0．84 -0．89),亏损HREE、Y(Y=9．51-14．5μg／g,Yb=0．74-1．20μg／g,Y／Yb=11．12-15．10),REE强烈分异((La／Yb)N= 22．18-29．51),但是,花岗闪长岩相对高的K2O含量和HREE相对平坦的特征更类似于中国东部中生代C型埃达克岩,暗示其可能是由加厚基性下地壳脱水部分熔融形成的,岩石的高Mg#暗示其受到地幔物质混染。暗色微粒包体显示钾玄岩的地球化学特征,具体表现为SiO2≤63％,σ(4．54-6．18)>3．3,K2O含量(4．22％-6．04％)高,大多数样品K2O／Na2O>1;在K2O -SiO2图中,所有样品均落入钾玄岩区域,暗色微粒包体强烈富集LILE和LREE及明显的Nb、Ta和Ti负异常暗示其可能起源于曾经受到俯冲流体交代的富集地幔。Harker图解上,寄主花岗闪长岩和暗色微粒包体的主量和微量元素表现出混合成因的演化趋势,表明岩体可能是富集的岩石圈地幔发生部分熔融产生的基性岩浆和其所诱发的加厚下地壳酸性岩浆混合的产物。结合秦岭地区已有研究成果,本文的研究认为阳坝岩体的形成可能代表了西秦岭地区在秦岭主造山晚期或造山期后发生的下地壳的拆沉作用和幔源岩浆的底侵作用。

碧口群火山旋回及其地质构造意义

通过详细的野外剖面观察和室内岩石地球化学研究,将碧口群火山岩划分为3个火山旋回,每个旋回下部为基性火山岩(细碧岩及细碧质凝灰岩),上部为酸性火山岩(石英角斑岩或石英角斑质凝灰岩)。基性火山岩富集LREE及LIL。第一旋回基性火山岩属碱性系列,第二、三旋回基性火山岩属拉斑玄武岩系列。基性火山岩浆形成于与洋岛玄武岩类似的地幔柱源,其中第三旋回基性火山岩浆晚期受岩石圈地幔混染;酸性火山岩为地壳重熔作用的产物。碧口群火山岩属大陆裂谷双峰式火山岩系,是中—新元古代扬子地块北缘大陆拉张作用的产物。这种拉张作用是秦岭造山带从震旦纪开始的大规模扩张作用的先兆。

扬子西北缘碧口块体花岗质岩体锆石U-Pb年龄、Hf同位素特征及其地质意义

对扬子西北缘碧口块体中白雀寺和大安花岗质岩体进行了锆石 U-Pb 定年及 Hf 同位素研究。结果表明，白雀寺岩体的年龄分2组：（855±6）Ma（n＝23）和（917±14）Ma（n＝3）。前者εHf （t）为3．8～10．4，一阶段 Hf 模式年龄为1．00～1．27 Ga；后者εHf （t）为2．0～8．1，一阶段 Hf 模式年龄为1．14～1．40 Ga。而大安岩体给出了6组不同的年龄：（854±10）Ma（n＝3）、（801±7）Ma（n＝3）、（702±10）Ma（n＝3）、（565±6）Ma（n＝1）、（246±7）Ma（n＝1）和（207±2）Ma（n＝1）。其εHf （t）为-12．6～11．4（t ＝854 Ma），一阶段和二阶段 Hf 模式年龄分别为0．95～1．90 Ga 和1．02～2．55 Ga。白雀寺和大安岩体的侵位年龄分别为（855±6）Ma 和（854±10）Ma，代表了扬子西北缘碧口块体内的一次重要岩浆事件，前者主体来源于中元古代新生陆壳源区，而后者主要来源于中元古代新生陆壳与晚太古代地壳物质的混合源区。此外，白雀寺岩体中（917±14）Ma 的年龄代表新元古代早期的岩浆活动，而大安岩体中年轻的年龄可能记录着岩体后期所经历的复杂热改造事件。

碧口地块麻山、木皮岩体岩石地球化学与地质年代学:对构造属性的指示意义

对侵位于康县断层南侧青川-平武断层北侧碧口地块中的麻山和木皮岩体进行了系统的锆石U-Pb年代学、岩石地球化学和Sr-Nd同位素研究。锆石LA-ICP-MSU-Pb年龄分析表明木皮岩体的形成时代为226±2Ma。麻山和木皮岩体分别由二长花岗岩和花岗闪长岩组成,岩石为过铝质,主量元素特征为SiO2≥56%,Al2O3≥15%和MgO<3%。岩石具有较高的Sr(578×10-6～1146×10-6)和较低的Yb(0.4×10-6～0.9×10-6)含量,Sr/Y比值介于69～139之间。岩石显示右倾的REE配分型式和弱的负Eu异常,(La/Yb)N比值为12～36。这些地球化学特征表明麻山和木皮岩体可能主要是由埃达克质岩石组成。岩石较高的ISr(0.706～0.705)和较低的εNd值(-6.5～-9.4)表明这些埃达克质岩石可能是加厚下地壳物质部分熔融的结果。麻山和木皮岩体的地球化学特征及年龄与勉-略缝合带北侧光头山等岩体一致,表明这些岩体可能代表了秦岭造山带南部晚三叠世造山加厚地壳条件下的产物,因此碧口地块可能属于南秦岭造山带,并推测麻山和木皮岩体及所在的碧口地块可能是印支期加厚的下地壳韧性流壳层向SW方向斜向挤出的结果。

碧口地体中元古代构造属性

有关中元古界碧口岩群的成岩构造环境及中元古代碧口地体构造属性长期存在争议。本文综合火山岩、硅质岩所反映的构造信息，认为碧口地体中元古代曾发育过裂谷-有限洋盆构造环境，是在扬子陆缘基础上伴随元古代仰展构造作用发展和演化的。

扬子克拉通北西缘碧口群的解体与地层划分

碧口群组成十分复杂．论述了对其解体的必要性；解体出了包括鱼洞子花岗绿岩地体周缘的稳定陆缘沉积建造、扬子地台北西缘古元古代陆间裂谷型火山－沉积建造、中元古代洋壳残片及深海沉积物和新元古代的火山弧前盆地堆积、新元古代的残留地中海式堆积以及造山后的山间盆地堆积等众多不同性质的构造地层单元；

碧口群火山岩性质及形成环境

中元古代—新元古代碧口群火山岩系分布在扬子地块北缘、秦岭造山带南侧。碧口群火山岩系具大陆裂谷火山岩特点,形成于大陆裂谷作用构造环境。火山岩系特征为:①具双峰式火山岩组合,火山岩系由基性火山岩(细碧岩及细碧质凝灰岩)及酸性火山岩(石英角斑岩及石英角斑质凝灰岩)组成。②基性火山岩包括两个岩浆系列的岩石,即碱性玄武岩浆系列及拉斑玄武岩浆系列。③火山岩富集LREE及LIL。微量元素及同位素(Sm-Nd,Rb-Sr)研究表明,基性火山岩形成于相似于洋岛玄武岩源的地幔柱源,酸性火山岩为地壳重熔的产物。扬子地块北缘分布有碧口群、西乡群等中元古代—新元古代大陆火山岩系,表明在这一时期大陆裂谷拉张火山作用发育,成为秦岭地壳的主要增生成壳期。

甘肃阳山金矿床花岗岩成因:来自地球化学、Sr-Nd-Pb同位素和年代学的证据

甘肃文县阳山金矿为西秦岭近十年来发现的超大型卡林–类卡林型金矿床,地处扬子板块西北部碧口地体北缘。本文选取阳山矿区与矿体在空间上密切相关的花岗岩样品,进行系统的元素地球化学特征分析,结合前人的年代学和Sr-Nd-Pb同位素数据来探讨其成因。阳山花岗岩SiO_2含量为60.64%~80.77%、Al_2O_3为13.68%~23.71%,K_2O为0.74%~4.32%,A/CNK为1.34~6.02,富集Cs、U、K、Pb等元素,亏损Ba、Nb、La、Ce、Sr、Ti等元素,ΣREE=14.45×10–6~143.14×10–6,平均70.31×10–6,LREE/HREE=1.39~19.52,平均10.12,具有轻稀土富集,重稀土亏损的特征,（La/Yb）N=1.48~37.26,平均17.08,球粒陨石标准化配分模式显示弱负Eu异常（δEu=0.50~1.21,平均0.77）,为过铝质钙碱性花岗岩。结合前人对花岗岩、碧口群和泥盆系三河口组的元素地球化学、年代学和Sr-Nd-Pb同位素等测试数据以及区域构造演化历史,认为阳山花岗岩来源于碰撞增厚的地壳物质——碧口群的部分熔融,在上升的过程中与泥盆系发生混染。