邓阜仙花岗岩的构造环境、岩浆来源与演化

本文利用An-Ab-Or-Q-H_2O体系相图等对邓阜仙复式岩体的分析研究表明。四期花岗岩为同一深部岩浆房岩浆结晶分异演化的产物,岩浆房深度约为12km,并且该岩体的主体第一期岩浆也经历了部分就地结晶分异作用。邓阜仙岩体不仅仅具有S型花岗岩特征,而且还显示出某些Ⅰ型花岗岩的特征,其源岩可能为前寒武纪的正、副变质岩混杂的岩石。该岩体总体上形成于同碰撞构造环境,且从第一期到第四期有着同碰撞向板内花岗岩变化的趋势,反映了本区从印支到燕山晚期陆壳成熟度不断增强的过程。     

吉林钾长花岗岩构造背景及铀对大型金矿床的控制

Ｕ的放射能和特性构成吉林夹皮沟金矿和海沟金铀矿主要成矿条件之一,它从另一侧面为大型、超大型金矿的形成探求一条新途径：（１）成矿背景效应：板块俯冲使幔源物质发生分熔形成含铀钾长花岗岩,随构造活动的进行Ｕ进一步富集,由Ｕ、Ｋ蜕变出α粒子组成一个巨大放射能量场;（２）加热释放效应：幔源基性脉、Ｃ－Ｈ－Ｏ流体和壳源中酸性脉、岩浆热液同时脉动性上侵;（３）富硅低钙效应：石英正长斑岩脉控矿;（４）辐射致色效应;（５）易溶稳定效应：Ｕ６＋易溶呈络离子;（６）有利载金效应：ＵＯ２２＋加入易形成黄铁矿;（７）选择沉淀效应：沥青铀矿沉淀同时易促使Ａｕ和多金属硫化物沉淀;（８）产状控制效应：因钾长花岗岩体形态、大小与金矿规模、产状具对应关系,所以探矿靶区应重点选定在钾长花岗岩体之内或之上的变质及沉积地质体中,石英正长斑岩脉可直接作为找矿标志。     

东昆仑—柴达木盆地北缘岩浆活动、构造演化、深部过程与成矿

利用岩石大地构造学方法 ,研究了东昆仑—柴达木盆地北缘地区的火成岩构造组合 ,对区内重要边界进行了重新分析研究 ;对本区的构造演化和深部过程得出了新的认识 ;重点分析了早古生代和晚古生代—早中生代两个构造岩浆旋回 ;初步对区内构造分区进行了重新厘定 ;在分析火成岩分布与矿产关系的基础上 ,重新总结了区域成矿规律 ,明确提出了找矿方向。研究成果主要为以下几个方面。(1)昆南断裂作为东昆仑—柴北缘与巴颜喀拉地块的分界断裂 ,事实上是中国南北两大坂块的边界。昆中断裂带是区内一条重要的地质界线 ,早古生代 (可能包括晚前寒武纪…     

非洲中部基巴拉带的地质及构造演化特征

基巴拉带（Kibara Belt）是位于非洲中部的一条中元古代构造带,该带对于重建哥伦比亚和罗迪尼亚超大陆具有重要的地质意义。以古元古代的Ubendian—Rusizi带为界,基巴拉带可分为两部分：北部Karagwe—Ankole带（KAB）和南部Kibaride带（KIB）。其中Karagwe—Ankole带又被Kabanga—Musongati（KM）基性—超基性线性杂岩体分为东部区域（ED）和西部区域（WD）,其内分别沉积有Kagera超群和Akanyaru超群,而南部Kibaride带内沉积有Kibaran超群。所有地层开始沉积于乌本迪造山作用之后,且碎屑物主要来源于坦桑尼亚克拉通及周边古元古代的活动带。基巴拉带内发育有不同成因的基性—超基性岩浆作用,年龄为1375~1400 Ma左右,早于或近同期于最早期的花岗质岩浆作用。带内发育的花岗质岩浆从早到晚分为4期：D1期、A型、D2期及含锡花岗岩浆作用,除A型花岗质岩浆作用可能来源于亏损地幔外,其他3期都为变质沉积岩局部熔融的产物。根据地层序列及岩浆活动期次,可以将整个基巴拉带的构造演化划分为：① 俯冲作用前沉积阶段：1780 Ma左右的东部区域沉积和1420 Ma左右的西部区域和/或Kibaride带内沉积作用;② 俯冲作用阶段：1400~1375 Ma左右的基性—超基性岩浆作用、1375 Ma左右的D1期花岗质岩浆作用和1200 Ma左右的A型花岗质岩浆作用;③ 陆陆碰撞阶段：1100 Ma左右的D2期岩浆作用;④ 碰撞晚期和碰撞后阶段：980 Ma左右的含锡花岗质岩浆作用和之后的Itombwe超群沉积。     

华北燕山带:构造、埃达克质岩浆活动与地壳演化(英文)

埃达克质火成岩在中国东部,包括燕山带是很常见的,一般认为它们是下地壳不均匀的镁铁质岩石及/或富集的上地幔岩石在高压(≥1.5 GPa)下部分熔融的结果。在燕山带内埃达克岩浆的形成有一个很长的时间(约190～80 Ma),然而岩浆活动的峰期却与约170～130 Ma间有基底岩石卷入的陆壳收缩期相一致。尽管埃达克质岩浆活动的历史很长,但那种把岩浆活动与岩石圈的拆沉效应相联系的模式似乎是不适当的。在该带内,埃达克质与非埃达克质岩浆活动有一部分是同时的,而且在地理分布上也是相间的,这说明了在下地壳和上地幔岩石的部分熔融中成分是相当不均匀的。侏罗纪及白垩纪熔融作用的热源应当是与古太平洋板块俯冲相关的中生代板底垫托的玄武岩浆。除了局部例外,在燕山带,埃达克质岩浆活动的终结和碱性岩浆活动的开始约在130～120 Ma,在此时期收缩作用使东亚大达200万km~2以上的地区发生了NW—SE向的区域性伸展作用。强烈的地壳伸展仅局限于华北克拉通北缘分布的少数几个变质核杂岩中。陆壳的伸展减薄合理地解释了130～120 Ma间发生高压埃达克质熔融条件的终结,尽管还有局部年轻的埃达克火山活动(约120～80Ma)可以在伸展规模有限而厚的地壳依然存在的地区继续出现。燕山区早白垩世的碱性侵入体中的锆石不存在前寒武纪?     

浙江普陀山黑云母钾长花岗岩及其岩石包体的地球化学与岩浆混合作用

浙江普陀山岩体是我国东南沿海产出的由多阶段岩浆作用形成的典型I_A型复合花岗质杂岩体。锆石U_Pb定年结果显示该杂岩体主要由 3期岩浆侵入活动形成 ,自早至晚分别为石英闪长玢岩 (约 170Ma)、黑云母钾长花岗岩 (约 110Ma)和晶洞钾长花岗岩 (约 90Ma) ,其中黑云母钾长花岗岩是该杂岩体的主体岩性 ,在该类岩石中常发育有丰富的深色闪长质包体。本文重点研究了该杂岩体中的黑云母钾长花岗岩 (寄主岩 )及其中的深色闪长质包体。寄主花岗岩为高演化的I型花岗岩 ,地球化学特征表现为高硅、富碱、准铝或弱过铝质 ,富大离子亲石元素 (如Rb、Th等 )和轻稀土元素 (LREE/HREE =8.5 8～ 13.83) ,具有中强的铕负异常 (δEu =0 .2 9～ 0 .4 3) ,并显著亏损Sr、Ba、P和Ti等。闪长质包体与寄主岩之间主、微量元素表现出混合成因的演化趋势 ,二者具有相似的Nd同位素组成〔εNd(t)值分别为 - 6 .30～ - 6 .6 0和 - 6 .95～ - 7.12〕 ,均表现出壳幔混源花岗岩类岩石的特点。对包体与寄主岩产出构造背景和地球化学特征的综合分析表明 ,该杂岩体中的深色闪长质包体是在伸展引张构造背景下 ,上涌的幔源基性岩浆与其诱发的长英质岩浆混合作用的产物     

碱质A型花岗岩的判别、成因与构造环境

碱质A型花岗岩（简称AAG）是A型花岗岩的亚类之一。近年来,随着研究的深入,对AAG有了新的认识。本文总结了AAG独特的岩相学、地球化学特征及产出构造环境,讨论了其判别标志和判别方法,指出对AAG的成因和地球动力学机制的认识目前还存在明显分歧,亟待进一步的深入研究。     

印度南部安得拉邦部分地区富含Zr、Hf、U、Th和稀土元素的古元古代钾质花岗岩

印度南部安得拉邦 Karim nagar地区 Dharmawaram的中、粗粒斑状花岗岩是一种黑云角闪花岗岩 ,含有大量的富稀有金属 ( Zr、Hf、Th)和稀土元素 (包括 Y)的矿物 ,如锆石、钍石、褐帘石、独居石、磷钇矿。从化学成分看 ,它是偏铝质 (平均 A/C N K=0 .95 )钾质 (平均K2 O 5 % )花岗岩 ,具明显的亚碱性特征。与正常的未分异花岗岩相比 ,其稀有元素 ( Zr、Hf、U、Th)和稀土元素的含量高达 8倍 ,因而 ,这些元素的含量甚丰。钾质花岗岩的野外、岩石学、地球化学和同位素资料表明 ,在其形成过程中有富硅变质沉积 -基性地壳岩 (角闪石英岩、角…     

秦岭—祁连造山带印支-燕山期构造与大型-超大型矿床的形成关系

印支－燕山期构造－岩浆热液活动，对秦岭－祁连造山带的区域成矿控制与影响作用十分显著，主要表现在该期北东向构造－岩浆活动不仅控制了金等矿产的形成，而且使先期形成的铜，铅锌等矿产发生了较强烈的改造和富集作用，该期北东向构造带与先期的北西、近东西向构造或含矿层交汇叠加部位，是形成大型－超大型矿床的重要条件。文章对秦岭－祁连造山带印支－燕山期构造－岩浆活动带的发育特征及其对大型－超大型矿床的控制与影响等进行了初步分析与探讨，提出了本区新一轮矿产勘查研究对策与思路。     

天然火山作用探测华北下地壳组成、结构及其形成过程

与中上地壳相比，对下地壳组成、结构的认识受限于样品的获取，然而天然火山作用携带的下地壳捕虏体可以为了解下地壳提供关键样品。华北克拉通是世界上最古老的克拉通之一，显生宙以来的火山作用携带有丰富的下地壳捕虏体，为探测华北下地壳组成、结构及其形成过程提供了可能。通过对这些捕虏体定深、定性及定年的综合研究，构建了以信阳，莒南，汉诺坝和女山等典型地区为代表的下地壳组成、结构剖面模型。这些剖面表明，华北克拉通下地壳具有分层的特点，且上老下新，暗示可能与底侵作用有关。其中捕虏体的锆石U- Pb年龄和Hf同位素的研究，揭示了该克拉通下地壳复杂的形成与演化过程：最古老的组成部分可能老至~4. 0 Ga冥古宙，此后经历了3. 80~3. 65 Ga古太古代的再造作用，2. 8~2. 5 Ga 新太古代和2. 3~1. 8 Ga 古元古代的增生与再造共存，同时还经历了显生宙以来包括462~220 Ma，140~90 Ma和47~45 Ma的增生与再造事件。     

冈底斯新近纪钾质火山作用:消减沉积物折返的地球化学与Sr-Nd-Pb同位素证据

在冈底斯岩浆岩带的羊八井地区,林子宗火山岩系上部出现小规模的粗面质火山岩.岩石学与地球化学研究表明粗面岩与时空密切相关的大体积安山质-英安质-流纹质火山岩属于不同的火山岩系:碱性钾质系列与钙碱性系列.详细的地球化学研究证明林子宗晚期小体积钾质岩具有独立的岩浆源区,而非早期钙碱性系统低压岩浆过程演化的产物.粗面质熔岩SiO2含量为62.91%～64.63%,具有高K2O(7.52%～8.05%)、Al2O3(16.64%-17.35%)、低TiO2(0.59%～0.68%)与MsO(0.15%～0.77%).钾质熔岩富集LILE与LREE,亏损HFSE,具有高Rb/Sr(1.1～2.3)、Th/La(0.59～0.80)、Th/U(6.3～10.9)和低Ce/Pb(4.1～6.2)与Ba/Th(4.3～14.5)比值,其同位素组成变化范围分别是87Sr/86Sr(I)=0.7068～0.7075、143Nd/144Nd(I)=0.51241～0.51252、206Pb/204Pb=18.87～18.95、207Pb/204Pb=15.63～15.70和208Pb/204Pb=39.24～39.68.粗面岩的地球化学与同位素特征表明冈底斯新近纪钾质火山岩来源于角闪岩相的消减沉积物熔融.因此,羊八井新近纪钾质火山熔岩提供了印度-亚洲大陆碰撞早期消减沉积物折返的证据.     

Mineralization,geochronology, and Pb isotope studies of the shoshonitic lava-hosted Nariniya Pb deposit,central Tibet: linking ore formation to post-collisional potassic magmatism

Abstract

A newly discovered, shoshonitic lava-hosted Pb deposit at Nariniya in central Tibet provides an excellent example to help improve our understanding of the linkage between post-collisional potassic magmatism and ore formation in Tibet. The Pb ores exist as veins or veinlets in NWW-striking fracture zones within the potassic lava (trachyte). The veins contain quartz, galena, pyrite, and sericite (muscovite) as well as minor chalcopyrite, sphalerite, calcite, and dolomite with sericitization, pyritization, and minor silicification. The ⁴⁰Ar–³⁹Ar plateau age of the hydrothermal muscovite is 37.95 ± 0.30 Ma, which represents the Pb mineralization age. This obtained age is indistinguishable, within analytical error, from the zircon U–Pb age of 37.88 ± 0.22 Ma for potassic lava. Therefore, the ore formation can be genetically linked to potassic magmatism. Galena has similar Pb isotopic composition to magmatic feldspar from the host lava, suggesting the derivation of Pb from the magmatic system. Previous studies have suggested that S- and ore-forming fluids are of magmatic origin. Published data show that the Nariniya volcanic rocks are acidic, shoshonitic, akakitic, peraluminous, and enriched in Sr–Nd–Pb isotopes. Thus, they are geochemically different from other potassic volcanic rocks (no adakitic affinity) in the North Qiangtang terrane, but similar to the 46–38 Ma high-K calc-alkaline peraluminous adakitic rocks in this terrane and the late Eocene Cu-generating potassic porphyries from the Sanjiang region of eastern Tibet. As such, the Nariniya potassic magma likely originated from melting of subducted continental crust, with or without interaction with the overlying enriched mantle. Such post-collisional potassic rocks in Tibet are thought to be potential targets for prospecting of both Pb–Zn and porphyry Cu ores. Note that other ore styles (in addition to the Nariniya ore style) may exist in the potassic volcanic districts of Tibet.     

Sediment geochemistry as a provenance indicator: Unravelling the cryptic signatures of polycyclic sources,climate change,tectonism and volcanism

Interpretation of bulk‐sediment geochemistry is one of several approaches for determining sediment provenance. This study investigates the value added by bulk‐sediment geochemical analysis in interpreting provenance in a passive margin clastic basin, the Upper Jurassic–Lower Cretaceous deltaic sediments of the Scotian Basin. Provenance studies in this basin are challenging because source tectonic terranes are parallel to the basin margin and polycyclic sediment sources are abundant. More than 400 samples of mudstone and sandstone representing the geographical and stratigraphic range of interest were analysed for 57 elements. Diagenetic processes added calcium to many samples and removed potassium in rocks buried below 3 km, thus impacting principal component analysis and published weathering indices. However, multiple geochemical approaches to assessing the degree of weathering showed climatically controlled changes in weathering in the Tithonian and Barremian, and changes in supply from major tectonic events, such as the top‐Aptian uplift in the Labrador rift. Covariance of elements in heavy minerals demonstrates the varying magnitude of polycyclic supply and stratigraphic changes in sources. Geochemical analyses revealed a previously unsuspected Tithonian alkali volcanic sediment source, characterized by high niobium and tantalum. The lack of highly contrasting sources means that geochemistry alone is inadequate to determine sediment provenance. Published discrimination diagrams are of limited value. Statistical analysis of geochemical data is strongly influenced by diagenetic processes, episodic volcanic inputs and polycyclic concentration of resistant heavy minerals in sandstones. Single indicator elements for particular sources are generally lacking. Nevertheless, careful consideration of geochemical variability on a case by case basis, integrated with detrital mineral studies, provides new insights into palaeoclimate, sediment provenance and, hence, regional tectonics. Although there is no simple template for such analysis, this study demonstrates an approach that can be used for other basins.     

山西地堑系甸子梁期低起伏高海拔地貌面成因及新构造演化

在山西地堑系的山地顶部广泛发育着一级低起伏高海拔地貌面,即甸子梁面。认识甸子梁面的形成模式,是能否以其作为地貌标志进行区域地貌演化和构造变形研究的关键。文章在阐述低起伏高海拔地貌面形成模式的基础上,以蔚县-广灵盆地南缘山地上发育的甸子梁面为例,探索该级低起伏高海拔地貌面的成因机制。结果表明,甸子梁面是残留的准平原,其被准平原化后分别经历了新近纪早期构造抬升、新近纪晚期断裂形成、唐县期山麓剥蚀以及第四纪断陷等4个时期。蔚县-广灵盆地南缘断裂自开始正断运动以来,该断裂总的水平断错量约902±71 m,总的垂直断错量约1567±5 m,其中在唐县期之前（>3 Ma）的垂直断错量约276±16 m,在唐县期之后（< 3 Ma）的垂直断错量约1291±15 m。蔚县-广灵盆地南缘断裂在距今3 Ma以来的活动性稳定,不同时间尺度的垂直断错速率均约0.4~0.5 mm/a。

     

Sand,hearths, lithics and a bit of bioturbation: Site formation processes at Umhlatuzana rockshelter,South Africa

Umhlatuzana rockshelter is known for its continuous record of Middle and Later Stone Age lithic assemblages. This study presents multiproxy geoarchaeological data (micromorphology, X-ray diffraction and scanning electron microscopy with energy-dispersive spectroscopy) to reconstruct the depositional and post-depositional history of the site. Although the Stone Age deposits macroscopically appear homogeneous, micromorphological analysis reveals the existence of primary, unaltered depositional microlayering throughout the sequence. Sediments related to combustion activities on-site are observed in both the Holocene and Pleistocene deposits. Post-depositional geochemical alterations result in the formation of several phosphatic minerals that significantly affect the site's preservation conditions. One of those is vashegyite, a rare magnesium phosphate mineral related to acidic and moist sedimentary environments. Bioturbation features are prominent at the microscale, but sediment mixing does not seem to affect the vertical distribution of the artifacts. The observation of horizontal microlayering in both the Pleistocene and Holocene illuminates the dominant mechanism of sedimentation throughout the site's 70,000-year occupational history. It moreover shows that the lithics can be analysed as coherent assemblages.     

Petrochemistry of granulite xenoliths from the Cenozoic Qiangtang volcanic field,northern Tibetan Plateau: implications for lower crust composition and genesis of the volcanism

High-K calc-alkaline magmas from the Cenozoic Qiangtang volcanic field, northern Tibetan Plateau, contain lower crustal two-pyroxene and clinopyroxene granulite xenoliths. The petrology and geochemistry of six mafic and three felsic xenoliths from the Hol Xil area south of Ulan Ul Lake are discussed. Mafic granulites (Pl, Opx, Cpx, Ksp, and Bt) contain 48.76–58.61% SiO₂, 18.34–24.50% Al₂O₃, 3.16–5.41% Na₂O, 1.58–3.01% K₂O, low Mg# (30–67), LREE and LILE enrichment, high Rb/Sr (0.09–0.21), (La/Yb)_N (17.32–49.35), low Nb/Ta (9.76–14.92), and variable Eu anomalies (Eu?=?0.19?0.89). They also have more evolved Sr-Nd-Pb isotopic compositions in comparison with the host dacites ⁸⁷Sr/⁸⁶Sr (0.710812 vs. 0.713241), ?_Sr (+169.13 vs.?+203.88), ¹⁴³Nd/¹⁴⁴Nd (0.512113 vs. 0.512397), ?_Nd (?4.70 to??10.05), ²⁰⁶Pb/²⁰⁴Pb (18.7000 vs. 18.9565), ²⁰⁷Pb/²⁰⁴Pb (15.7135 vs. 15.7662), and ²⁰⁸Pb/²⁰⁴Pb (39.1090 vs. 39.4733). Felsic granulites (Qtz, Pl, Ksp, Bt, and Cpx) show enrichment of LREE and LILE and have evolved Sr-Nd-Pb isotopic compositions with (La/Yb)_N (2.04–10.82), ⁸⁷Sr/⁸⁶Sr (0.712041–0.729088), ?_Sr (+180.71–+430.59), ¹⁴³Nd/¹⁴⁴Nd (0.512230–0.512388); ?_Nd (?4.74 to??7.96), ²⁰⁶Pb/²⁰⁴Pb (18.9250–19.1717), ²⁰⁷Pb/²⁰⁴Pb (15.7662–15.7720), and ²⁰⁸Pb/²⁰⁴Pb (39.2109–39.6467). These geochemical data suggest that the protolith of the mafic granulites could have been a hybrid mafic magma (e.g. enriched mantle type II) or metasomatized restite derived from the partial melting of metamafic-intermediate rocks rather than basaltic cumulates, whereas the felsic granulite protolith was a quartzofeldspathic S-type granitic rock. We argue that the lower crust of the northern Tibetan Plateau is hot and heterogeneous rather than wholly gabbroic. Interaction between the mantle-derived magma and the metasedimentary/granitic lower crust of the Tibetan Plateau may have played an important role in the generation of shoshonitic and high-K calc-alkaline andesite-dacite rocks.     

Textural and chemical evolution of a fractionated granitic system: the Podlesí stock, Czech Republic

The Podlesí granite stock (Czech Republic) is a fractionated, peraluminous, F-, Li- and P-rich, and Sn, W, Nb, Ta-bearing rare-metal granite system. Its magmatic evolution involved processes typical of intrusions related to porphyry type deposits (explosive breccia, comb layers), rare-metal granites (stockscheider), and rare metal pegmatites (extreme F–P–Li enrichment, Nb–Ta–Sn minerals, layering). Geological, textural and mineralogical data suggest that the Podlesí granites evolved from fractionated granitic melt progressively enriched in H₂O, F, P, Li, etc. Quartz, K-feldspar, Fe–Li mica and topaz bear evidence of multistage crystallization that alternated with episodes of resorption. Changes in chemical composition between individual crystal zones and/or populations provide evidence of chemical evolution of the melt. Variations in rock textures mirror changes in the pressure and temperature conditions of crystallization. Equilibrium crystallization was interrupted several times by opening of the system and the consequent adiabatic decrease of pressure and temperature resulted in episodes of nonequilibrium crystallization. The Podlesí granites demonstrate that adiabatic fluctuation of pressure (“swinging eutectic”) and boundary-layer crystallization of undercooled melt can explain magmatic layering and unidirectional solidification textures (USTs) in highly fractionated granites.     

Crustal anatexis and formation of two types of granitic magmas in the Kontum massif, central Vietnam: Implications for magma processes in collision zones

Asia grew in the Late Permian by the collision of a number of micro-continents. Syn- to post-collisional magmatism occurred along the continental collision zones . In this study, we report two types of granitic rocks, garnet granite (Grt granite) and orthopyroxene granite (Opx granite), from the Kontum massif, central Vietnam, which is situated on the continental collision zone between the South China and Indochina cratons. These granitic rocks were formed at ca. 250 Ma when high-temperature (HT) and ultrahigh-temperature (UHT) metamorphism took place in the same zone. Based on the petrological and geochemical features compared with previously reported experimental results, garnet-bearing granite is derived from pelitic gneisses by partial melting, whereas orthopyroxene-bearing granite is produced by the partial melting of garnet-bearing mafic granulites. We inferred that a significantly high-geothermal gradient is required to produce Vietnamese granitic magmatism and related HT to UHT metamorphism. This geotherm may be attributed to upwelling mantle plume beneath the Kontum massif during the Late Permian.     

Growth, linkage, and termination processes of a 10-km-long strike-slip fault in jointed granite: the Gemini fault zone, Sierra Nevada, California

Field-based structural analysis of an exhumed, 10-km-long strike-slip fault zone elucidates processes of growth, linkage, and termination along moderately sized strike-slip fault zones in granitic rocks. The Gemini fault zone is a 9.3-km-long, left-lateral fault system that was active at depths of 8–11 km within the transpressive Late-Cretaceous Sierran magmatic arc. The fault zone cuts four granitic plutons and is composed of three steeply dipping northeast- and southwest-striking noncoplanar segments that nucleated and grew along preexisting cooling joints. The fault core is bounded by subparallel fault planes that separate highly fractured epidote-, chlorite-, and quartz-breccias from undeformed protolith. The slip profile along the Gemini fault zone shows that the fault zone consists of three 2–3-km-long segments separated by two ‘zones’ of local slip minima. Slip is highest (131 m) on the western third of the fault zone and tapers to zero at the eastern termination. Slip vectors plunge shallowly west-southwest and show significant variability along strike and across segment boundaries. Four types of microstructures reflect compositional changes in protolith along strike and show that deformation was concentrated on narrow slip surfaces at, or below, greenschist facies conditions. Taken together, we interpret the fault zone to be a segmented, linked fault zone in which geometrical complexities of the faults and compositional variations of protolith and fault rock resulted in nonuniform slip orientations, complex fault-segment interactions, and asymmetric slip-distance profiles.