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81.
《International Geology Review》2012,54(6):734-755
We used illite Ar/Ar dating to obtain absolute ages of folds and shear zones formed within the Mexican Fold–Thrust Belt (MFTB). The methodology takes advantage of illite dating in folded, clay-bearing layers and the ability to obtain accurate ages from small-size fractions of illite using encapsulated Ar analysis. We applied our approach to a cross-section that involves folded Aptian–Cenomanian shale-bentonitic layers interbedded with carbonates of the Zimapán (ZB) and Tampico–Misantla (TMB) Cretaceous basins in central-eastern Mexico. Basinal carbonates were buried by syn-tectonic turbidites and inverted during the formation of the MFTB in the Late Cretaceous. Results from folds and shear zones record different pulses of deformation within this thin-skinned orogenic wedge.Mineralogical compositions, variations in illite polytypes, illite crystallite size (CS), and Ar/Ar ages were obtained from several size fractions in limbs and hinges of the folds and in the shear zones. 1Md-illite polytype (with CS of 6–9 nm) dominates in two folds in the TMB while 2M1-illlite (with CS of 14–30 nm) dominates in the third fold, in the ZB, and in the fold/shear zone. From west (higher grade) to east (lower grade): Ar retention ages indicate shearing occurred at ~84 Ma in the westernmost shear zone, folding at ~82 Ma in the ZB with subsequent localized shearing at ~77 Ma, and Ar total gas ages constrain the time of folding at ~64 Ma on the west side of the TMB and ~44 Ma on the eastern edge. These results are consistent with the age and distribution of syn-tectonic turbidites and indicate episodic progression of deformation from west to east. 相似文献
82.
《International Geology Review》2012,54(5):539-561
ABSTRACTThere are voluminous ultrahigh pressure-related orthogneisses and minor metamorphic supracrustal rocks in the northeastern Sulu UHP terrane (NSL), East China. The tectonic affinities of the supracrustal rocks are crucial for unravelling the deep continental subduction processes and locating the tectonic suture between the South China (SCB) and North China (NCB) blocks. In this contribution, we report new zircon U–Pb ages and Hf isotope data for the supracrustal rocks and metagabbros in the Zeku region of the NSL. In the Zeku region, the supracrustal rocks are spatially associated with granitic gneisses, metagabbros, and eclogites. Detrital zircon U–Pb analyses yield ages between 3.39 and 0.65 Ga that cluster as three major age populations including (1) 2.15–1.68 Ga with two subpeaks at ~1.83 Ga and~1.97 Ga, (2) 2.45–2.15 Ga with a peak at ~2.37 Ga, and (3) 0.79–0.65 Ga. In addition, there is a small age population between 3.39 and 2.61 Ga. The youngest age population of 0.79–0.65 Ga indicates that the Zeku supracrustal rocks must have been deposited after 650 Ma rather than during the Palaeoproterozoic as previously thought. The 210–190 Ma metamorphic ages suggest that the Zeku rocks were affected by Triassic collision–subduction and exhumation. Most of the Archaean-Palaeoproterozoic zircons have negative εHf(t) values and two-stage Hf model ages concentrating at 2.4–3.4 Ga (peak at ~2.9 Ga), indicating that source rocks of these zircons were mainly derived from recycling of ancient crustal material. These ages, together with the Hf isotopic compositions and rock assemblages, indicate that the Zeku supracrustal rocks were mainly derived from the Precambrian basement rocks of the northern Yangzte Block and have a tectonic affinity to the SCB, rather than the NCB. Our results, together with previously published data, suggest that there are two types of supracrustal rocks with different zircon U–Pb ages and tectonic affinities in the NSL. On the basis of new data, we suggest that the surface boundary between the SCB and NCB in the Jiaodong Peninsula is a complicated tectonic mélange zone rather than a single fault. 相似文献
83.
84.
85.
北山成矿构造背景概论 总被引:26,自引:0,他引:26
北山地区可划分为星星峡-明水-旱山微板块和敦煌微板块,二者以红柳河-牛圈子-洗肠井缝合带为界。古陆裂解初期的寒武纪浅海具有形成磷钒铀锰沉积矿产的有利背景;奥陶纪洋盆和弧后盆地具备形成海相火山-沉积岩系有关铜锌矿的有利背景,被动陆缘裂谷具备形成海相沉积岩系有关铅锌银矿的有利背景;志留—泥盆纪岛弧火山建造具备形成斑岩铜矿的有利背景;石炭—二叠纪陆内裂谷具备形成火山沉积铁矿、斑岩铜矿、基性-超基性岩有关铜镍矿的有利背景;各单元古陆壳活化重熔型花岗岩具形成钨锡稀有金属矿的有利背景。 相似文献
86.
H. Zöllner K. Reicherter P. Schikowsky 《International Journal of Earth Sciences》2008,97(5):1013-1027
The pre-Alpine structural and geological evolution in the northern part of the North German Basin have been revealed on the
basis of a very dense reflection seismic profile grid. The study area is situated in the coastal Mecklenburg Bay (Germany),
part of the southwestern Baltic Sea. From the central part of the North German Basin to the northern basin margin in the Grimmen
High area a series of high-resolution maps show the evolution from the base Zechstein to the Lower Jurassic. We present a
map of basement faults affecting the pre-Zechstein. The pre-Alpine structural evolution of the region has been determined
from digital mapping of post-Permian key horizons traced on the processed seismic time sections. The geological evolution
of the North German Basin can be separated into four distinct periods in the Rerik study area. During Late Permian and Early
Triassic evaporites and clastics were deposited. Salt movement was initiated after the deposition of the Middle Triassic Muschelkalk.
Salt pillows, which were previously unmapped in the study area, are responsible for the creation of smaller subsidence centers
and angular unconformities in the Late Triassic Keuper, especially in the vicinity of the fault-bounded Grimmen High. In this
area, partly Lower Jurassic sediments overlie the Keuper unconformably. The change from extension to compression in the regional
stress field remobilized the salt, leading to a major unconformity marked at the base of the Late Cretaceous. 相似文献
87.
本文选择博格达-哈尔里克一带作为研究区,从区域成矿地质背景入手,鉴于该地区已知成型铜矿床较少,成矿规律研究薄弱,故作者采用ArcGIS平台下的证据权模型(WofE),以数据驱动方式为主,从断裂构造、沉积岩相与建造、火山岩建造、侵入岩岩性等方面,以学生化反差S(C)作为有利因子衡量指标,对各控矿因素进行影响程度分类,利用加权逻辑斯回归模型计算成矿后验概率,根据后验概率值的大小进行成矿远景区的圈定和分级,在博格达-哈尔里克成矿带内共圈定7个成矿远景区。最后结合区域化探资料进行了验证,结果显示所圈定的铜矿成矿远景区内化探异常明显,与Cu元素异常套合较好,说明ArcGIS证据权模型能很好地为区域矿产预测提供良好的技术支撑,为研究区铜矿找矿方向提供理论依据,文中所总结的基于ArcGIS平台的证据权计算方法流程也为区域矿产预测提供了方法借鉴。 相似文献
88.
Fikret Koçbulut 《Geodinamica Acta》2013,26(1-2):26-37
A palaeomagnetic study is reported from the lavas of Eocene, Miocene and Pliocene age cropping out immediately to the north of the North Anatolian Fault Zone (NAFZ) in the Re?adiye–Mesudiye region of central-eastern Anatolia. Rock magnetic investigations identify a high percentage of multi-domained magnetite as the dominant ferromagnet in these rocks and this probably accounts for a relatively poor response to alternating field and thermal demagnetisation. Thirty of 37 units yielded acceptable groupings of characteristic magnetisation directions. An earlier study indicated small anticlockwise crustal block rotation in this region since Upper Cretaceous times (D/I?=?347/50°), and our study indicates that this was overtaken by clockwise rotation in Eocene times (D/I?=?40/47°), although sample size control from the Palaeogene is poor. Results from later Miocene (D/I?=?2/62°) and Pliocene (D/I?=?0/53°) volcanic rocks indicate that no significant tectonic rotation has occurred in the north of the NAFZ in Neogene times. This contrasts with rotations in the weaker crust comprising the Anatolian collage south of the NAFZ, where differential and sometimes large anticlockwise rotations occurred during the latter part of the Neogene. 相似文献
89.
为解释横向载荷作用下刚性桩的失稳机理,针对桩头自由的刚性桩做了一系列横向加载试验。基础土为粉质粘土,含水量介于9.85 %~13.85 %之间。由载荷-位移全过程曲线发现,刚性桩在横向载荷达到一定值时会失稳;由试验录像及土体剖面发现,由于土体的软化破坏,在桩后土体内会出现贯穿的局部破坏并形成一楔体,同时在土面伴随一不完全的椭圆形鼓包及一条平行于加载方向的拉伸裂缝,而在桩前土中,由于桩的挤压会形成一条侵彻沟。分析认为,对大位移刚性桩桩后土体的破坏是桩失稳的根本原因。 相似文献
90.
新疆东天山南缘富钾硝酸盐盐湖成矿带地质特征及资源潜力 总被引:3,自引:0,他引:3
新疆东部是中国主要的盐类矿床聚集区,在东天山南缘形成了巨大的富钾硝酸盐盐湖成矿带。文章在系统总结东天山南缘富钾硝酸盐成矿带地质特征、成矿条件特征和晶间卤水特征的基础上,分析了富钾硝酸盐矿床成矿的地质条件、物质来源和气候因素,以及已有矿床的资源状况和资源潜力,指出富钾硝酸盐矿床是一种特殊类型的盐类矿床,特殊的构造条件是该类矿床物质来源和成矿作用发生的重要因素,晶间卤水和层间、裂隙卤水具有较大的资源潜力。加强该区富钾硝酸盐矿床的研究和勘查评价工作,不仅可以丰富中国陆相盐类矿床成盐理论,而且可以为罗布泊钾盐基地提供后续资源保障,同时也有利于新疆新型钾、氮肥工业基地的建立。 相似文献