Evidence for the Jurassic arc volcanism of the Lolotoi complex,Timor: Tectonic implications

We report the first sensitive high-resolution ion microprobe (SHRIMP) U–Pb zircon ages with geochemical data from metavolcanic rocks in the Lolotoi complex, Timor. The zircon U–Pb ages of two andesitic metavolcanic rocks yield a permissible range of the Middle Jurassic extrusion from 177 Ma to 174 Ma. The geochemical data indicate that the origins of the basaltic and andesitic metavolcanic rocks are products of prolonged oceanic crust and arc magmatism, respectively. They are originated from partial melting of lherzolites, providing an insight into the tectonic evolution of the forearc basements of the Banda volcanic arc. Thus, parts of the Banda forearc basement are pieces of allochthonous oceanic basalts and Jurassic arc-related andesites accreted to the Sundaland during the closure of Mesotethys, and are incorporated later into the Great Indonesian Volcanic Arc system along the southeastern margin of the Sundaland.     

东昆仑灶火沟早志留世花岗岩岩石学、地球化学特征及地质意义

灶火沟早志留世(436.8~433.7 Ma)花岗岩发育于东昆中蛇绿构造混杂岩带中,主要岩石类型为花岗闪长岩和二长花岗岩,其围岩分别为中元古代万宝沟群和奥陶—志留纪纳赤台群。花岗闪长岩和二长花岗岩w(Si O2)分别为56.12%~63.49%和70.62%~76.54%,均为钙碱性系列。二长花岗岩显示向富碱质过渡的特征,铝饱和指数A/CNK为0.79~1.02,属准铝质—弱过铝质系列,为I型花岗岩。花岗闪长岩∑REE低于二长花岗岩∑REE,两者均具有LREE相对富集而HREE相对亏损的相似的右倾球粒陨石标准化配分曲线特征,花岗闪长岩具弱负Eu异常,二长花岗岩具强负Eu异常;两者均具有相对富集LILE而相对亏损HFS的微量元素特征。地球化学特征显示灶火沟花岗岩为岛弧型花岗岩,是原特提斯洋壳向北俯冲引起地幔楔物质底侵东昆仑岛弧下地壳部分熔融的产物,表明东昆仑造山带在早志留世仍处于原特提斯洋壳俯冲消减阶段。     

New U–Pb ages and lithochemical attributes of the Ediacaran Rio Doce magmatic arc,Araçuaí confined orogen,southeastern Brazil

The Araçuaí orogen of southeastern Brazil, together with its counterpart located in Africa, the West Congo belt, formed through closure of a gulf connected to the Adamastor Ocean by the end of the Ediacaran and beginning of the Cambrian. Convergence of the margins of the gulf led to the development of the Rio Doce magmatic arc between 630 Ma and 580 Ma on a continental basement mostly composed of Rhyacian orthogneisses. The Rio Doce arc mainly consists of tonalite-granodiorite batholiths, generally crowded with mafic to dioritic enclaves, and minor gabbronorite-enderbite-charnockite plutons, suggesting mixing processes involving crustal and mantle sources. We investigate the basement, magma sources and emplacement ages of the Rio Doce arc. Our data suggest the arc comprises three main granitic rock groups: i) Opx-bearing rocks mostly of enderbite to charnockite composition; ii) enclave-rich tonalite-granodiorite (ETG); and iii) enclave-poor granite-granodiorite with minor tonalite (GT). The Opx-bearing rocks are magnesian, calc-alkalic to alkali-calcic and metaluminous. Together, the ETG and GT rock groups range in composition from tonalite to granite, are metaluminous to slightly peraluminous, show a predominantly medium- to high-K, expanded calc-alkaline signature, and other geochemical and isotopic attributes typical of a pre-collisional volcanic arc formed on a continental margin setting. Mineralogical, chemical, and geochronological data suggest the involvement of HT-melting of granulitic (H₂O-depleted) sources of Rhyacian age for the generation of Opx-bearing granitic rocks, additionally to magma mixing and fractional crystallization processes. In conclusion, the studied rock groups of the Rio Doce arc were likely formed by interactions of mantle and crustal processes, in an active continental margin setting. These processes involved ascent of mantle magmas that induced partial melting on the continental basement represented by the Rhyacian gneisses.     

Zircon U–Pb geochronology of granitic rocks of the Cordón de Lila and Sierra de Almeida ranges,northern Chile: 30 m.y. of Ordovician plutonism on the western border of Gondwana

In this paper we determined the chronology of Lower Paleozoic arc-related granitic rocks in the Cordón de Lila and Sierra de Almeida ranges, northern Chile, based on new U–Pb ages obtained by Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) on single zircons. Plutonism lasted ∼30 m.y., spanning from 490 to 460 Ma (Lower to Mid Ordovician). The obtained ages correspond to the plutonic units' crystallization ages and fit well with the observed contact relationships with their country rocks and mutual intrusion relationships, and also with biostratigraphical data from the sedimentary country rocks. Our geochronological results on the granitic rocks of Cordón de Lila and Sierra de Almeida ranges broadly agree with the known ages of the plutonic rocks in the Argentinian Puna, strengthening the idea that they formed part of the same magmatic arc in the western border of west Gondwana during the Early to Middle Ordovician.     

内蒙古阿巴嘎旗阿德拉嘎碱长花岗岩锆石LA- ICP- MS U- Pb年龄、地球化学特征及构造意义

阿巴嘎旗阿德拉嘎碱长花岗岩位于贺根山蛇绿岩带北侧。为了确定该碱长花岗岩体的岩石成因类型,探讨其构造环境,对该岩体进行了野外地质、岩石学、地球化学和LA- ICP- MS锆石U- Pb年代学研究。锆石LA- ICP- MS U- Pb测年表明,阿德拉嘎碱长花岗岩体的侵位年龄为310. 7±2. 6Ma,形成时代为晚石炭世。岩石地球化学研究表明,阿德拉嘎碱长花岗岩具有较高的SiO2、Na2O+K2O含量和较高的Ga/Al、（Na2O+K2O）/CaO值,相对贫CaO、MgO、Sr、Ba、Eu、Ti和P。稀土元素总量较低,轻重稀土分馏不明显,稀土配分曲线呈海鸥性,负铕异常明显（δEu=0. 15~0. 37）。岩石学和岩石地球化学特征表明,该碱长花岗岩为A型花岗岩,形成于弧后伸展构造环境,为晚石炭世古亚洲洋向西伯利亚俯冲作用的产物。     

西藏唐加地区卓隆普斜长角闪岩锆石U-Pb年代学、地球化学及地质意义北大核心CSCD

本文以西藏唐加地区卓隆普斜长角闪岩为研究对象,通过岩相学、锆石U-Pb年代学和全岩地球化学组成分析,探讨了其岩石成因以及对松多古特提斯洋演化的地质意义。结果显示,卓隆普斜长角闪岩原岩形成于264.7±1.3 Ma(n=28,MSWD=0.88),属中二叠世。全岩地球化学特征显示该套岩石呈钙碱性,富集轻稀土元素(LREE/HREE=4.69~4.88),弱铕异常(δEu=0.81);样品富集大离子亲石元素(LILEs),具有强烈的Nb-Ta负异常,表现出岛弧玄武岩亲缘性。多种判别图解显示斜长角闪岩原岩形成于俯冲相关的岛弧环境,原岩岩浆由俯冲大洋板片和洋壳物质融熔体以及其脱水过程中形成的俯冲流体交代上覆地幔楔形成,岩浆上升过程中可能受到轻微的地壳物质混染。结合区域资料,本次研究认为唐加-松多古特提斯洋在265 Ma(中二叠世)之前已经发生俯冲。     

内蒙古东乌珠穆沁旗海勒斯台岩体的年代学和地球化学特征及其地质意义

本文报道了分布于兴蒙造山带东北部东乌珠穆沁旗海勒斯台岩体的岩石学、地球化学和年代学特征,以讨论该岩体的形成时代、岩石成因及其构造环境。岩石学研究表明,海勒斯台岩体岩性较为单一,主要为花岗斑岩。LA-ICP-MS锆石U-Pb定年结果显示,海勒斯台花岗斑岩的年龄为463.5±2.0 Ma,表明其形成时代为中奥陶世。花岗斑岩具有富硅(75.14%～77.88%)、富碱(6.15%～7.92%)、低钛(0.15%～0.17%)和铝(11.25%～12.61%)、贫钙(0.18%～1.25%)和镁(0.14%～0.31%),富集大离子亲石元素Rb、Th、K及高场强元素Zr、Hf,强烈亏损Sr、Eu、P、Ti,中等亏损Ba、Nb、Ta等元素,10000Ga/Al值和Zr+Nb+Ce+Y含量较高,属于A2型花岗岩。花岗斑岩的锆石饱和温度介于878～899℃之间,同时具有非常低的Sr和高Yb特征,指示岩石形成于低压高温的伸展构造背景,可能为减薄地壳的部分熔融。结合区域地质资料,认为该花岗斑岩可能形成于古亚洲洋沿着苏尼特左旗—锡林浩特一线向西伯利亚板块俯冲引起的陆缘弧后拉张环境。     

中非铜钴成矿带地质特征及铜钴矿床资源量分析

中非铜钴成矿带是世界最大的沉积型铜钴成矿带、全球最大钴矿、第三大铜矿发现区。因铜钴价格持续走高和中资企业持续关注的迫切性,本文对中非铜钴成矿带地质特征、铜钴矿床资源分布规律、权益资源量情况进行分析研究。同时,系统收集研究区学术研究成果、商业数据库、企业年报等数据,分析认为Lufilian弧形构造带是中非铜钴成矿带构造背景,从北向南依次为弧外部褶皱推覆带、穹窿地区、复式向斜带、加丹加高原。地层分为孔德龙古、恩古巴、罗安三个群,地层年龄自<573±5 Ma至879±16 Ma。含矿层位主要是罗安群矿床组,下分R2.1、R2.2、R2.3三个含矿层。矿床类型主要为碳酸盐质巨型角砾岩型、含矿页岩型、含矿砂岩型、含矿基底型铜矿,构成6个铜钴矿集区,具有等间距分布特征,间距为±20 km。截至2021年,研究区探获铜资源量1.91亿t,钴资源量1404万t。以当量铜资源量排序,>100万t的矿床33个,>1000万t级别的矿床7个。共有14个国家55家矿业企业参与铜钴成矿带勘探及开发。我国权益铜钴资源量分别为6467万t、648万t。大于50万t权益铜资源量的企业有洛阳钼业、紫金...     

Unwrapping reworked crust at the Columbia supercontinent margin within central southern Amazon Craton using multi-source geophysics and geochronology data synergy

The geometry and evolution of pre-existing basement in accretionary belts bordering supercontinents are often unclear. Integrative interpretation of long-wavelength potential field satellite data can image deep crust structure, improving our understanding of lithospheric processes that formed these margins bottom-up. Here, we present a multidisciplinary interpretation of the lithospheric architecture of the central southern Amazon Craton, a fragment of an accretionary belt at the southwestern Columbia supercontinent margin. Satellite-borne gravity and magnetic data, airborne magnetic data, passive seismic (V_p/V_s ratio, crustal thickness) and seismic tomography data reveals that basement terranes from the interior of the craton extend into the accretionary margin of Columbia. We demonstrate a vertically heterogeneous structure with an underlying strongly reworked pre-Columbia tectonic wedge that sustained prolonged modification during the supercontinent assembly as corroborated by Nd isotope and geochronology data. Nd isotope data suggest that the protracted orogenic wedge was influenced by subduction angle shifts over time, including addition of substantial juvenile material during slab retreat events. This interplay promoted Craton growth at the supercontinent margin while keeping a subtle record of the pre-existing framework. Our findings point to the possible misrepresentation of basement extension and geometry of supercontinent margins elsewhere.     

Geology and mineralization of the Pulang supergiant porphyry copper deposit (5.11 Mt) in Shangri-la,Yunnan Province,China: A review

The porphyry copper belt in the Geza island arc in southwestern China is the only Indosinian porphyry copper metallogenic belt that has been discovered and evaluated so far. The Pulang porphyry copper deposit (also referred to as the Pulang deposit) in this area has proven copper reserves of 5.11×10⁶ t. This deposit has been exploited on a large scale using advanced mining methods, exhibiting substantial economic benefit. Based on many research results of previous researchers and the authors’ team, this study proposed the following key insights. (1) The Geza island arc was once regarded as an immature island arc with only andesites and quartz diorite porphyrites occurring. This understanding was overturned in this study. Acidic endmember components such as quartz monzonite porphyries and quartz monzonite porphyries have been identified in the Geza island arc, and the mineralization is mainly related to the magmatism of quartz monzonite porphyries. (2) Complete porphyry orebodies and large vein orebodies have developed in the Pulang deposit. Main orebody KT1 occurs in the transition area between the potassium silicate alteration zone of quartz monzonite porphyries and the sericite-quartz alteration zone. Most of them have developed in the potassium silicate alteration zone. The main orebody occurs as large lenses at the top of the hanging wall of rock bodies, with an engineering-controlled length of 1920 m and thickness of 32.5‒630.29 m (average: 187.07 m). It has a copper grade of 0.21%‒1.56% (average: 0.42%) and proven copper resources of 5.11×10⁶ t, which are associated with 113 t of gold, 1459 t of silver, and 170×10³ t of molybdenum. (3) Many studies on diagenetic and metallogenic chronology, isotopes, and fluid inclusions have been carried out for the Pulang deposit, including K-Ar/Ar-Ar dating of monominerals (e.g., potassium feldspars, biotites, and amphiboles), zircon U-Pb dating, and molybdenite Re-Os dating. The results show that the porphyries in the Pulang deposit are composite plutons and can be classified into pre-mineralization quartz diorite porphyrites, quartz monzonite porphyries formed during the mineralization, and post-mineralization granite porphyries, which were formed at 223±3.7 Ma, 218±4 Ma, and 207±3.9 Ma, respectively. The metallogenic age of the Pulang deposit is 213‒216 Ma. (4) The petrogeochemical characteristics show that the Pulang deposit has the characteristics of volcanic arc granites. The calculation results of trace element contents in zircons show that quartz monzonite porphyries and granite porphyries have higher oxygen fugacity. The isotopic tracing results show that the diagenetic and metallogenic materials were derived from mixed crust- and mantle-derived magmas.©2022 China Geology Editorial Office.