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Penelitian Gayaberat Dan Geomagnit Kepulauan Aru, Cekungan Wokam

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Penelitian Gayaberat Dan Geomagnit Kepulauan Aru, Cekungan Wokam PENELITIAN GAYABERAT DAN GEOMAGNIT KEPULAUAN ARU, CEKUNGAN WOKAM GRAVITY AND GEOMAGNETIC STUDIES OF ARU ISLANDS, WOKAM BASIN Tatang Patmawidjaya dan Subagyo Pusat Survei Geologi, Badan Geologi, Jln Diponegoro No 57, Bandung Diterima : 16-6-2013, Disetujui : 18-02-2014 ABSTRAK Paparan Arafura di bagian selatan Kepulauan Aru merupakan depresi Lempeng Indo-Australia yang ditunjukkan oleh anomali gayaberat dan geomagnet tinggi. Sedangkan depresi di bagian utara yang tertahan Palung Aru diperlihatkan oleh anomali gayaberat tinggi dan anomali geomagnet rendah. Anomali ini diduga sebagai penebalan batuan metamorf yang mengalami pangangkatan sebagai alas cekungan Wokam. Analisis data gayaberat dan geomagnet mengindikasikan penurunan cekungan ini ke arah utara. Penurunan anomali gayaberat ke arah Pulau Wokam yang berarah baratdaya-timurlaut di selatan dan baratlaut-tenggara di daerah utara ditafsirkan sebagai struktur sesar. Hal ini dicirikan oleh arah sungai atau selat sebagai pemisah pulau-pulau di Kepulauan Aru. Anomali gayaberat residual mengindikasikan cekungan dan punggungan berarah baratdaya-timurlaut yang membentuk antiklin dan sinklin. Sesar dan lipatan ini menerus sebagai struktur geologi dangkal bawah permukaan. Berdasarkan pemodelan gayaberat dan geomagnet dapat dikatakan bahwa Cekungan Wokam cenderung menurun ke arah utara akibat sesar normal. Kata Kunci : gayaberat, geomagnet, pemodelan geologi, Cekungan Wokam ABSTRACT Arafura Shelf in the southern part of the Aru Islands is a depression of the Indo-Australian crust at the south that indicated by high gravity and geomagnetic anomalies. While the northern depression blocked by the Aru Trough indicated by high gravity anomaly and low geomagnetic anomaly. These anomalies presumed as a thickening of the metamorphic rocks due to uplifting and acting as the basement of Wokam Basin. Gravity and geomagnetic analyses indicate a northward subsidence of the basin. The decreasing of the southwest–northeast gravity anomaly in the south and the northwest-southeast in the north, interpreted as a fault. It this characterized by the river direction or strait as islands separation in Aru Archipilagoes. Residual gravity anomaly indicates a southwest-northeast basin and ridge form anticline and syncline. These faults and folds are continuous as the shallow subsurface geological structures. On the base gravity and geomagnetic models, it can be concluded that Wokam Basin tends to subside northward as the result of a normal fault. Keywords: gravity, geomagnetic, geological models, Wokam Basin PENDAHULUAN menghasilkan batas Cekungan Wokam (Chartlon, Peta cekungan sedimen Indonesia 1999). berdasarkan data gayaberat dan geologi (Badan Penelitian gayaberat dan geomagnet Geologi, 2009) yang menunjukkan sumber daya Cekungan Wokam terletak di Kepulauan Aru, energi belum sepenuhnya dianalisis prospeknya mencakup wilayah pulau-pulau besar dan kecil oleh karena keterbatasan data kebumian. Salah seperti Pulau Kola, Pulau Wokam, Pulau Kobroor satu cekungan yang menjadi fokus pembahasan dan Pulau Trangan. Secara administrasi lokasi adalah Cekungan Wokam. Pembahasan didasarkan penelitian masuk dalam Kabupaten Aru, Provinsi atas analisis data gayaberat dan geomagnet. Maluku dengan batas koordinat antara 7 °10'00" - Penelitian sebelumnya adalah kajian tektonik 5°32'00" LS dan 134 °00'00" - 135°00'00" BT regional Indonesia bagian timur yang (Gambar 1). Untuk mencapai titik ukur gayaberat JURNAL GEOLOGI KELAUTAN 1 Volume 12, No. 1, April 2014 5°15'LS(S) P. Ngo ba Tg . Watuleijuring Utara u t wa p K EP. JEDAN P. Jelan l i P. Tob a P. WARILAUp li K P. Lut . S P . Latusa S. KOLA WA TU P. Belading P . Tiga P. Tapusu r Marjina A N P. Kulur JI t R P. Buwar A M a . S Marlessi r Wak alamaar a 30' B P .WAS IR P. KO L A Masidan Timur Tg. Ritfane Tg. Leitin Wa sir Selmana S. S IS Waitua l P. Binaar P. Konan WUTUL ieteng Maha Wo dawoda Ujir Nganhonlau S . M P. UJIR A L Be leting W F ila A Gobeltien T U P. Koo tboai T g. Tutupa n Berdatan Selatan Komfane Tg . Komfane Tg . Samang Sa man g Faiwakwaka Wukatultulak P. Wodinhun P. Lewakai P. Wa halau lau S. Wal iramai Lualaut P. W OK A M K EPULAUAN WATUTOI T g. Malakafani Wok am P. Manien P. Rewan Kabalasiang S. Benjuting J Houtingerr a Tg . Ular r a P. Aduar Kora n DO B O ga Keterangan 45' y i n P. MANGAN P. Ilmamui Kobamari Wan gil u at Jabulenga Toan gawatu w P. Kumul P. WARMAR u Kelamar gg Kumul Jurjela Tg . Fa tujuring un T Ma ngan . Kartufuie n S P. Tugu r Faturei P. Watulai Tg . Kar K eli Tun gu P. Taba r Watulai P . Elef Kota Tg . Ba tudu a P . Ramye P. Korle P . Menlau P. Meiran g P. Waria Karau m P. Lamar K E P U L A U A N A R U Matutu P . Ngawab Sewer Jursian Kampung Kula im Tg . Lalau Silmar P. Jursian Namalau n au t u r P . Jursian a e Waiguai lama . F w S u a P. Maria Tg. Tao rdefe te D . S P. Kutu Wa igu ai Dosi Sungai S ilmar P. Maar P. Karaweira Besar P. Derwaria s i I o Karwai A L umlum D Karwai Kobrau B S. M r Tg . Lingajuring U a N a A m r M e P. Karaweira Ma riri I g A n Titik Pengukuran G a 6°00'LS(S) N M P. Dorlau U . Tg. Meijuring S S Manumba i S. Gairwatu M a Bed ing Warlai ri Kongan rr em B ejina a r a ji n r a M . S Tg. Belata njuring P. M AIKO OR Kejabi P. Lak Lakar P. Mimin Indek Peta Ma ikoo r P. Nyamuk S Jarau kin . To rfi ra n S UN P. KO B ROO R P. Leliling G Workau A P. Mariri I W Tg . Walai Tg . Ngo ni O 4°S RK I Taberfane A R LO I WA KEP ULAUAN MARIRI Wongali S. P . Wadijili A D I P. Seja P. Leer P. Urea P. Lola 15' Bedidi Kobroo r P. MAIKOOR Tg. Molmotajuring P. Kokwana Tg. Loorjuring t L A U T A R U i i d P. Kuling ed . B 5°S S P. Waria P. Bu i P. Koolmimien Tg. Uafutenjuring P. Tengah P. Kaim eer i Lutu ra B osada u P . Mimien M . S Tg. Watanjuring P. KO B A S. Wo rk ai P. W a sir R abal P. M anggar Tual P. PEN AMBULAI P. R o e P. H aniar P. N um ai P. Nusreen P. NU H U YU T D ob o P .Wo lvat W O K A M P. Lelamtuti P. T a a m P. W a m a r Tg. Faturel P. N ihutoa u r Tg . Ujirje P. K aitanimb ar P. K a i K e cil A 6°S Tg. Derehi n K O BR O O R Alarjir Gunung Jirjirtur Jambuai a M A +50 T P. Warja Kobaselfara Pe naibula f u K a O Tg . Medar l O R K O BA P. Mocam B arokan u p 30' P . BAU N e B a un Lerdera TR A N G AN P. B a ra k a n P. BAROKAN K Wa rde ro P. Tu r tu r jur ing S . P. TRANGAN S A P. K ultubai U tara R W Feruni A T U P. Ketombe P. Jeh P. Karang Bergain 7°S P. Trang an P. Koolmiri P. E n u P . Bambu P . Bab i Naiguli P. Tu furjuring Masian 132°E 133°E 134°E 135°E Fa turai Gomogomo P. WORKA I ng P. Kultboi Utara o b re i a Tg. Waidaier . W S Ngaiber Krai baru P. Re ngeri P . Ban gori 45' Krei lama P. Pen juring Tg. Juring Baimun Le ngar Afara Tg . Lelar P. Karwoi P. Penjering Gunun g Bain Wajin +89 P. Wofil KEP ULAUAN JIN S. Tafermaar Tg. Bain Tafermaar P. Wadidin P. Jeud in P . Kultbai Selatan Jamman P. M arjinjin P . Mer Tg . Masian Tg . Nga bardamlu P. Jeh P. Batu Goy ang 7°00'LS(S) P. Karang P . Enu L A U T A R A F U R A 7°15'LS(S) 134°00'BT(E) 15' 30' 45' 135°00'BT(E) Gambar 1. Lokasi penelitian dan titik pengamatan gayaberat dan geomagnet 2 JURNAL GEOLOGI KELAUTAN Volume 12, No. 1, April 2014 dan geomagnet di sepanjang pantai dan sungai dan napalan dan batupasir. Sebagian sungai digunakan sarana transportasi berupa perahu. terbentuk oleh kekar berarah timurlaut-baratdaya, Cekungan Wokam merupakan cekungan sebagian lagi terbentuk oleh sesar. Di daerah sedimen yang terletak di Wilayah Indonesia berbatu gamping kapuran, retakan dan kekar Bagian Timur (Gambar 2) dan berpotensi membentuk topografi kars lorong. Seluruh kekar mengandung sumber daya energi. Geometri tersebut tergenang air laut sehingga tampak Cekungan Wokam dianalisis berdasarkan data sebagai sungai dan selat. gayaberat dan geomagnet, dikontrol oleh struktur Tektonika daerah penelitian membentuk geologi permukaan (Hartono dan Ratman, 1992). Tinggian Arafura ( Arafura High ) dari bongkah- Pendekatan geometri dilakukan melalui bongkah tegar dan stabil berasal dari Benua interpretasi pola anomali gayaberat dan geomagnet Australia (Gambar 3). Batuan ini mendasari Laut sehingga dihasilkan model geologinya. Arafura yang dangkal dan bagian tenggara Irian Secara tektonika Cekungan Wokam terletak Jaya. Di tepi barat terdapat Palung Aru yang di bagian utara Tinggian Arafura ( Arafura High ) berbatasan dengan Busur Banda (Bemmelen, dan bagian timur Palung Aru ( Aru Trough ). 1949). Pola struktur dasar laut sebelah utara Tinggian dan palung tersebut merupakan depresi Kepulauan Aru berarah utara-selatan dan utara dari sistem penujaman Lempeng Indo-Australia timurlaut-selatan baratdaya. dari arah selatan dan dikenal sebagai Depresi Struktur geologi yang dijumpai di Kepulauan Arafura (Charlton, 1999). Depresi tersebut Aru berupa sesar turun dan kelurusan (Gambar 4).
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