Palaeomagnetic assessment of plutons from the southern Peninsular Ranges batholith and the Jurassic Vizcaíno igneous suites,Baja California,México     

《International Geology Review》2012,54(4):489-509

ABSTRACT

We report geological and palaeomagnetic data from five discrete plutons in the southern part of the Peninsular Ranges batholith (PRB) and one pluton that is part of the Jurassic plutonic suite in the Vizcaíno peninsula. The PRB plutons are Cretaceous and belong to the Alisitos island arc. The Jurassic pluton intrudes a Triassic-Jurassic ophiolite.

Our study was designed to evaluate the palaeomagnetic homogeneity of the batholith from the Sierra San Pedro Mártir, at ~31°N, to about ~28.3°N. The Punta Prieta, Nuevo Rosarito, San Jerónimo, and La Rinconada plutons in the western zone of the PRB are characterized by magnetizations residing in magnetite. The Compostela pluton is emplaced in a transition zone and has a magnetization that resides in haematite. The five Cretaceous plutons yield a combined palaeopole at 80.3°N, 162.1°E, A₉₅ = 9.8°, N = 5 that after correcting for the opening of the Gulf of California rotates to 77.6°N, 173.6°E, the rotated pole being in angular distance of only 4.4° from the North America reference pole. The Jurassic San Roque pluton yields a mean 0.6°N, 306.1°E, A₉₅ = 9.2°, N = 10, which is discordant, showing a clockwise rotation of about 131° ± 16° and flattening of 9.5° ± 12.9° with respect to the 150 Ma cratonic reference palaeopole. The results suggest that the intrusion of the undeformed Cretaceous Punta Prieta to Compostela plutons (128.1 ± 1.4 and 100.5 ± 2.7 Ma, respectively) restricts tectonic accretion of the Jurassic-Early Cretaceous sequences to the North America margin to the time before mid-Cretaceous magmatism (~100 Ma) in the PRB near present latitude 28°N. Mesozoic and Cenozoic strike-slip faulting along the Vizcaíno margin can account for the 131° clockwise rotation of the San Roque pluton. Our results do not support significant latitudinal movement between Vizcaíno, the PRB, and mainland Mexico with the exception of the Neogene San Andreas Fault-related right lateral movement.  相似文献   

山东半岛城市群高新技术产业空间布局协调研究     

任建兰  史会剑  张淑敏 《世界地理研究》2009,18(3):75-82

本文在对山东半岛城市群高新技术产业空间布局的类型、特点和存在问题分析的基础上．提出了山东半岛城市群高新技术产业空间协调布局的战略,为推动山东半岛城市群高新技术产业的发展．提升山东半岛城市群竞争力以及为其他区域高新技术产业带的研究提供理论依据。  相似文献   

Mountain building across a lithospheric boundary during arc construction: The Cretaceous Peninsular Ranges batholith in the Sierra San Pedro Martir of Baja California, Mexico     

K.L. Schmidt  S.R. Paterson  A.E. Blythe  C. Kopf 《Tectonophysics》2009,477(3-4):292

The Jura-Cretaceous Peninsular Ranges batholith (PRB) of Southern and Baja California contains a remarkable example of variation in crustal composition and structure across a batholith-parallel lithospheric-scale discontinuity. This lithospheric boundary between western oceanic-floored and eastern continental-floored crust influenced contractional deformation, arc magmatism, and differential exhumation of western and eastern zones in the batholith during its evolution.In the Sierra San Pedro Martir of Baja California, Mexico, a ca. 20 km wide, doubly vergent fan structure occurs across the PRB basement transition that consists of inward-dipping mylonite thrust sheets on the sides of the fan that gradually transition to a steeply-dipping tectonized zone in the center. A dramatic inverted metamorphic gradient occurs on the western side of this structure where mid-crustal amphibolite metamorphic grade rocks with peak pressures of 5–6 kbar in the center of the fan were thrust over upper-crustal sub-greenschist grade rocks (peak pressures < 2 kbar) in the western zone footwall. An inverted but smaller gradient occurs on the eastern side of the structure where rocks of the fan interior have been thrust eastwards over amphibolite to upper greenschist grade rocks (peak pressures 4–5 kbar).Gradients in cooling ages determined by ⁴⁰Ar/³⁹Ar biotite and K-feldspar and apatite fission track methods coupled with U–Pb zircon ages and Al in hornblende thermobarometry studies on plutons across this zone indicate that structures focused along the transition zone between contrasting lithosphere in the PRB accommodated nearly 15 km of the differential exhumation of western and eastern basement in the orogen. The western zone of the batholith was a major forearc depo-center for thick clastic sequences derived from the uplifting eastern PRB and remained at low average elevation during the Late Cretaceous and Paleogene. In contrast the eastern zone experienced dramatic uplift subsequent to achieving a crustal thickness in excess of 55 km by mid-Cretaceous time. This region had the isostatic potential for 4–5 km surface elevations, and likely formed a topographically high orogenic plateau. Exhumation of the fan structure initiated after 100 Ma and was largely complete by 85 Ma. Eastward-migrating unroofing of the rest of the eastern PRB continued into the Paleogene.A variety of factors were responsible for exhumation in this region. Structural thickening of the eastern zone of the orogen resulted from more than 30 million years of episodic contractional deformation in the fan structure, much of which followed island arc accretion of the western zone along this segment of the batholith. An episode of voluminous magmatism involving the intrusion of the 99–92 Ma La Posta-type magmatic suite across the eastern zone of the PRB triggered exhumation in the fan structure. Denudation in this region appears to have been solely by erosion; no evidence has been found for extensional tectonics during this time. This arc orogen demonstrates the important influence of inherited tectonic boundaries in controlling the spatial distribution of structural thickening and magmatism. It also displays the complex interrelationships among structural thickening, exhumation, and the role of magmatism in triggering exhumation episodes within orogens.  相似文献   

Geochemistry,zircon U–PB ages and HF isotopes of the Muong Luan granitoid pluton,Northwest Vietnam and its petrogenetic significance     

Pham T. Hieu  Nong T. Q. Anh  Pham Minh  Nguyen T. B. Thuy 《Island Arc》2020,29(1)

The Indosinian Orogeny plays a significant role in tectonic background and magmatic evolution in Indochina and surrounding regions. Being a part product of the Indosinian magmatism in northwest Vietnam during late Permian–middle Triassic period, Muong Luan granitoid pluton dominantly consists of granodiorite, less diorite and granite. This pluton is located in the Song Ma suture and assigned to the Dien Bien complex. Geochemically, the Muong Luan granitoid rocks are characterized by a wide range of SiO₂ contents (59.9–75.1 wt%) and high K₂O contents. They display typical features of I‐type granites. The presence of hornblende and no muscovite and cordierite in the rocks further supports for I‐type character of granitoids. The emplacement age of the Muong Luan pluton obtained by LA–ICP–MS U–Pb zircon is at 242–235 Ma, corresponding to Indosinian time. Zircon ε_Hf values of –5.6 to –10.4, in combination with moderate Mg values of 34–45 suggested that the Muong Luan granitoid was derived from partial melting of mafic crustal source rocks, which are probably Paleoproterozoic in age as revealed by Hf model ages (T_DM2 = 1624–1923 Ma).  相似文献   

东南亚生物质燃烧对我国霾和降水的影响     

王继康  江琪  尤媛  饶晓琴  盛黎  桂海林  花丛  张碧辉 《气象》2021,(3):348-358

基于生物质燃烧排放源清单、地面观测和数值模式对东南亚中南半岛生物质燃烧气溶胶的排放特征,以及其在2020年春季对我国云南地区霾天气和南方前汛期降水过程的影响进行了分析。结果表明:中南半岛生物质燃烧气溶胶排放主要集中于每年3—4月,排放峰值时段集中于3月下旬至4月上旬,主要排放区域为缅甸东部和老挝北部。中南半岛生物质燃烧气溶胶在地面主要影响我国云南南部城市的霾天气,缅甸的生物质燃烧气溶胶是最主要的贡献源。中南半岛生物质燃烧气溶胶在低空西南急流作用下,可以在800~600 hPa高度传输至我国华南和江南南部大部分区域上空。传输至我国南方上空的生物质燃烧气溶胶通过抑制对流性降水、增强非对流性降水,可以改变南方前汛期降水过程的空间分布,使降水更集中于切变线附近。  相似文献   

印支地块思茅地区早白垩世古地磁结果及其构造意义   总被引：2，自引：0，他引：2  

张海峰  仝亚博  王恒  杨振宇 《地质学报》2012,86(6):923-939

对印支地块思茅地区的早白垩世红层开展详细的岩石磁学和古地磁学研究,获得镇沅剖面特征剩磁方向Ds=52.4°,Is=45.5°,κ=77.9,α95=6.3°;普洱剖面特征剩磁方向Ds=46.2°,Is=46.6°,κ=50.9,α95=5.6°;江城剖面特征剩磁方向Ds=8.6°,Is=42.2°,κ=117.1,α95=4.0°。对普洱和江城剖面进行E-I磁倾角偏低检验,结果显示江城剖面不存在磁倾角偏低,普洱剖面由于偏角较分散,导致其伸展方向出现假象,推测的磁倾角偏大,出现实测磁倾角偏低的假象。思茅地区各采样剖面之间的磁偏角差异表明,块体内部发生过差异性旋转变形,其变形的过程不仅受控于边界深大断裂,也与内部小断裂的活动有密切关系。若进一步考虑华南地块白垩纪可能存在的磁倾角偏低现象,则该结果说明印度支那地块思茅地区白垩纪以来相对于华南地块向南滑移量为570±310km,接近构造地质研究推测的红河大断裂左行滑移量。  相似文献   

滇西印支地块东北缘新元古代侵入岩形成时代的厘定及其构造意义:锆石LA-ICP-MS U-Pb定年及地球化学证据   总被引：9，自引：8，他引：1  

戚学祥  王秀华  朱路华  胡兆初  李志群 《岩石学报》2010,26(7):2141-2154

印支地块北东缘姚家寨复式岩体位于哀牢山构造带西南翼的浅变质带中,主要由角闪辉长岩和花岗闪长岩组成。角闪辉长岩以含有大量含水矿物——角闪石为特征,出露面积达70km2的规模表明岩浆侵位于挤压的区域构造条件。岩石的高铝基性岩性质(Al2O3≥16%)及在微量元素蛛网图上展示出的大离子亲石元素(Rb、Sr、K和Ba)和轻稀土元素(La、Ce)相对原始地幔强烈富集,尤其是Nb和Ta的负异常,以及Mg#(52.14～65.35)与原始的幔源岛弧岩浆相近及在Ta/Yb-Th/Yb图解上所有的角闪辉长岩样品均投在洋内岛弧玄武岩区,揭示其岛弧的岩浆岩性质及其形成于与板块俯冲有关的岛弧环境。花岗闪长岩的埃达克岩性质及K、La和Tb正异常,Nb、Ta、P和Ti强烈负异常的特征,表现出明显的岛弧型岩浆岩属性揭示其形成于与角闪辉长岩一样的与板块俯冲有关的岛弧环境。锆石LA-ICP-MSU-Pb定年结果显示代表角闪辉长岩和花岗闪长岩形成时代的锆石生长边结晶年龄分别为763±10Ma(MSWD=4.1)和761±11Ma(MSWD=5.9)。花岗闪长岩穿插于角闪辉长岩之中,展现出前者的侵位时间要晚于后者,但两个样品锆石生长边结晶年龄的相似,说明它们是同一期岩浆活动过程中不同阶段的产物。印支地块东北缘姚家寨复式岩体与扬子地块西缘岩浆岩带一样都具有明显岛弧性质,形成时代基本一致,两地块中早古生代沉积岩演变特点及晚古生代沉积岩、古生物和δ18O/δ13C比值和古地磁的相似性,以及印支地块中缺失扬子地块广泛出露的震旦纪地层,表明印支地块与扬子地块之间的古洋壳是在新元古代开始双向俯冲碰撞,于新元古代晚期拼贴在一起,并在扬子地块西缘和印支地块东北缘各形成一条规模不等的岛弧型岩浆岩带。  相似文献   

U/Th dating of the travertine deposited at transfer zone between two normal faults and their neotectonic significance: Cambazli fissure ridge travertines (the Gediz Graben-Turkey)     

《Geodinamica Acta》2013,26(2):95-105

Abstract

The neotectonic characteristics of the travertines that outcrop near Cambazli Village to the west of the Gediz Graben in the Western Anatolia and the age determination of the travertine were carried out using the ²³⁰Th/^234,238U disequilibrium method. The Cambazli fissure ridge travertines represent the travertine depositions that develop at a transfer zone. The extent of these travertines is at NW-SE and NE-SW orientations and the ridge crest-trend of these travertines range between approximately 55° and 82° and they are located at an intersecting position. The evaluation of the fissure ridge travertine directions indicated that the compression stress that was responsible for the deposition of the Cambazli travertine was determined to be in the N-S orientation and the extensional stress was determined to be in the E-W orientation. The orientation of the dominant extension in Western Anatolia during the neotectonic period was N-S and this orientation is not in accordance with the directions of stress for the travertines. This situation indicates that the travertines were deposited along a transfer zone in N10W orientation between two normal faults. The travertines were determined to be active since the Upper Pleistocene as indicated by the age determination conducted using the ²³⁰Th/^234,238U disequilibrium method. The dilation rate of the travertines during dilation and the post-dilation period and the average dilation rate of the Cambazli travertines to the north of the Gediz Graben were calculated as 0.01–0.02 mm yr^?1 during deposition and as 0.05 mm yr^?1 during the post-dilation period. These dilation rates indicate lower tectonic activity along the northern ridge of the Gediz Graben than along the southern ridge.

© 2011 Lavoisier SAS. All rights reserved  相似文献   

Temperature variability caused by internal tides in the coastal waters of east coast of Peninsular Malaysia     

ROSELI Nur Hidayah  AKHIR Mohd Fadzil 《海洋学报(英文版)》2019,38(1):22-31

The effects of tidal currents (i.e., barotropic and internal tides) are important in the biogeochemistry of a coastal shelf sea. The high-frequency of currents and near-bottom temperatures collected in three consecutive southwest monsoon seasons (May, June, July and August of 2013 until 2015) is presented to reveal the role of the tidal currents to the temperature variability in the coastal shelf sea of the east coast of Peninsular Malaysia (ECPM), south of the South China Sea (SCS). The results of a spectral density and harmonic analysis demonstrate that the near-bottom temperature variability and the tidal currents are influenced by diurnal (O₁ and K₁) and semidiurnal (M₂) tidal currents. The spectral density of residual currents (detided data) at 5, 10 and 16 m depth also shows significant peaks at the diurnal tidal frequency (K₁) and small peaks at the semidiurnal tidal frequency (M₂) indicating the existence of internal tides. The result of the horizontal kinetic energy (HKE) shows a strong intermittent energy of internal tides in the ECPM with the strongest energy is found at 16 m depth during a sporadic cooling event in June and July. A high horizontal cross-shore heat flux (16 m) also indicates strong intrusions of cooler water into the ECPM in June and July. During the short duration of cold pulse water observed in June and July, a cross-wavelet analysis also reveals the strong relationship between the near-bottom temperatures and the internal tidal currents at the diurnal tidal frequency. The intrusion of this cooler water is probably related to the monsoon-induced upwelling in June. It is loosely interpreted that the interaction between the strong barotropic tides and the steep slope in the central basin of the SCS under the stratified condition in southwest monsoon has generated these internal tides. The dissipation of internal tides from the slope area probably has driven the cold-upwelled water into the ECPM coastal shelf sea when the upwelling intensity is the highest in June and July.  相似文献   

山东半岛城市群高新技术产业发展定位研究     

任建兰  史会剑  张淑敏 《世界地理研究》2008,17(1):60-66

本文在对山东半岛城市群高新技术产业发展特点和存在问题深入分析的基础上,提出了山东半岛城市群高新技术产业的发展战略和发展定位,将为提升山东半岛城市群区域竞争力及其打造半岛他区高新技术产业带提供依据。  相似文献